Design of Modern Highrise Reinforced Concrete Structures (Series on Innovation in Structures and Construction)

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Series on Innovation in Structures and Construction —Vol. 3 Series Editors: A . S. Elnashai & P. J. Dowling

DESIGN OF MODERN HIGHRISE REINFORCED CONCRETE STRUCTURES Editor: Hiroyuki Aoyama

irfk

Imperial College Press

DESIGN OF MODERN HIGHRISE REINFORCED CONCRETE STRUCTURES

SERIES ON INNOVATION IN STRUCTURES AND CONSTRUCTION Editors:

A. S. Elnashai (University of Illinois at P. J. Dowling (University of Surrey)

Urbana-Champaign)

Published Vol. 1:

Earthquake-Resistant Design of Masonry Buildings by M. Tomazevic

Vol. 2:

Implications of Recent Earthquakes on Seismic Risk by A. S. Elnashai & S. Antoniou

Vol. 3:

Design of Modern Highrise Reinforced Concrete Structures by H. Aoyama

Series on Innovation in Structures and Construction — Vol. 3 Series Editors: A . S. Elnashai & P. J. D o w l i n g

DESIGN OF MODERN HIGHRISE REINFORCED CONCRETE STRUCTURES

Editor

Hiroyuki Aoyama University of Tokyo, Japan

ICP

Imperial College Press

Published by Imperial College Press 57 Shelton Street Covent Garden London WC2H 9HE Distributed by World Scientific Publishing Co. Pte. Ltd. P O Box 128, Farrer Road, Singapore 912805 USA office: Suite IB, 1060 Main Street, River Edge, NJ 07661 UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE

British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library.

DESIGN OF MODERN HIGHRISE REINFORCED CONCRETE STRUCTURES Copyright © 2001 by Imperial College Press All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher.

For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher.

ISBN

1-86094-239-3

Printed in Singapore by Uto-Print

Preface Reinforced concrete (RC) as construction material has been used for a wide range of building structures throughout the world, owing to its advantages such as versatile architecture application, low construction cost, excellent durability and easy maintenance. However, its use in seismic countries and areas in the world has been limited to lowrise or mediumrise buildings, considering inherent lack of structural safety against earthquakes. In the last several decades, highrise RC buildings finally emerged in Japan, under the increased social need of more advanced types of RC buildings. Such a new type of structures was developed with the tremendous technical efforts for new high strength material, new design method, and new construction method, backed up by vast amount of research accomplishment. A five year national research project, entitled "Development of Advanced Reinforced Concrete Buildings using High Strength Concrete and Reinforcement", was conducted in 1988-1993 by the coalition of many research organizations in Japan with the Building Research Institute of the Ministry of Construction as the central key organization. The major incentive of this national research project was to further promote construction of highrise RC buildings as well as other advanced types of RC structures, by providing new high strength material and new design and construction methods suitable for such material. This national research project was simply referred to "the New RC" project. Now it is more than five years since the conclusion of the New RC project. It is quite clear that the project was successful and effective in finding numerous applications in the practical design and construction of advanced RC structures. This book was written as an effort to disseminate major findings of the project so as to help develop modern RC buildings in seismic countries and areas in the world. It consists of the following nine chapters. In Chapter 1, development and structural features of highrise RC buildings up to the onset of the New RC project are explained. It was the major motivation of the New RC project to develop even taller highrise RC buildings in seismic areas. Methods of seismic design and dynamic response analysis,

vi

Preface

prevalent at the time of New RC project initiation, are also introduced in this chapter. In Chapter 2, the development goal of the New RC project, development organizations and the outline of expected results are mentioned. Chapter 3 is entitled "high strength materials", and describes the development of high strength concrete and reinforcement and their mechanical characteristics. Chapter 4 describes the structural tests of New RC structural members such as beams, columns, walls, and so on, subjected to simulated seismic loading, and the evaluation methods of structural performance of New RC members and assemblies. Chapter 5 is entitled "finite element analysis", and describes the development of nonlinear finite element analysis models for New RC members, examples of analysis that supplement the structural testing of Chapter 4, and the guidelines for nonlinear finite element analysis. Chapter 6 introduces the New RC Structural Design Guidelines, emphasizing the new seismic design method for New RC highrise buildings, which basically consists of evaluation of seismic behavior through time history response analysis and static incremental load (push over) analysis. Also introduced in this chapter are several design examples. Chapter 7 intends to give an introductory explanation of dynamic time history response analysis to readers who are not quite acquainted with this kind of analysis, or to those who have experience in modal analysis or elastic analysis only. Computational models suitable for RC structures, general trends of seismic response of RC structures, and method of numerical analysis are presented. In Chapter 8, outline of a full-scale construction test and the New RC Construction Standard are presented. The construction standard is the compilation of standard specifications for New RC materials, their manufacturing and processing, and various phases of construction works. In the last Chapter 9, feasibility studies on three new types of buildings using high strength materials are mentioned, and highrise buildings utilizing New RC materials that were actually designed and constructed, or under construction, are introduced. Most chapters of this book were authored by persons who acted as secretaries of the relevant committees of the New RC project. This is the reason why relatively few literatures were referred to in each chapter of this book.

Preface

vii

The authors wish that the publication of this book will further promote the dissemination of the results of the New RC project into practice throughout the world, and will also encourage further research on the use of high strength and high performance materials to RC structures. Hiroyuki Aoyama

Contents

Preface

v

Chapter 1 RC Highrise Buildings in Seismic Areas Hiroyuki Aoyama

1

1.1. Evolution of RC Highrise Buildings 1.1.1. Historic Background 1.1.2. Technology Examination at the Building Center of Japan 1.1.3. Increase of Highrise RC and the New RC Project 1.2. Structural Planning 1.2.1. Plan of Buildings 1.2.2. Structural Systems 1.2.3. Elevation of Buildings 1.2.4. Typical Structural Members 1.3. Material and Construction 1.3.1. Concrete 1.3.2. Reinforcement 1.3.3. Use of Precast Elements 1.3.4. Preassemblage of Reinforcement Cage 1.3.5. Re-Bar Splices and Anchorage 1.3.6. Concrete Placement 1.3.7. Construction Management 1.4. Seismic Design 1.4.1. Basic Principles

1 1

ix

3 5 7 7 10 12 13 15 15 16 17 18 19 21 21 22 22

x

Contents

1.4.2. 1.4.3. 1.4.4. 1.4.5. 1.4.6.

Design Criteria and Procedure Design Seismic Loads Required Ultimate Load Carrying Capacity First Phase Design Second Phase Design 1.4.6.1. Calculation of Ultimate Load Carrying Capacity . 1.4.6.2. Ductility of Girders 1.4.6.3. Column Strength and Ductility 1.4.6.4. Beam-column Joints 1.4.6.5. Minimum Requirements 1.4.6.6. Imaginary Accident 1.4.7. Experimental Verification 1.5. Earthquake Response Analysis 1.5.1. Linear Analysis 1.5.2. Nonlinear Lumped Mass Analysis 1.5.3. Nonlinear Frame Analysis 1.5.4. Input Earthquake Motions 1.5.5. Damping 1.5.6. Results of Response Analysis 1.6. For Future Development 1.6.1. Factors Contributed to Highrise RC Development 1.6.2. Need for Higher Strength Materials

23 25 26 26 27 27 28 29 30 30 30 31 32 32 32 33 33 34 36 37 37 38

Chapter 2 The N e w R C Project Hisahiro Hiraishi

40

2.1. 2.2. 2.3. 2.4.

40 41 44 53 53 55 55 56 56 59

Background of the Project Target of the Project Organization for the Project Outline of Results 2.4.1. Development of Materials for High Strength RC 2.4.2. Development of Construction Standard 2.4.3. Development of Structural Performance Evaluation 2.4.4. Development of Structural Design 2.4.5. Feasibility Studies for New RC Buildings 2.5. Dissemination of Results

Contents

Chapter 3

N e w R C Materials

xi

61

Michihiko Abe Hitoshi Shiohara 3.1. High Strength Concrete 3.1.1. Material and Mix of High Strength Concrete 3.1.1.1. Cement 3.1.1.2. Aggregate 3.1.1.3. Chemical Admixtures 3.1.1.4. Mineral Admixtures 3.1.1.5. Mix Design 3.1.2. Properties of High Strength Concrete 3.1.2.1. Workability 3.1.2.2. Standard Test Method for Compressive Strength 3.1.2.3. Mechanical Properties 3.1.2.4. Drying Shrinkage and Creep 3.1.2.5. Durability 3.1.2.6. Fire Resistance 3.2. High Strength Reinforcing Bars 3.2.1. Reinforcement Committee 3.2.2. Advantages and Problems of High Strength Re-bars . . . . 3.2.3. Relationship of New Re-bars to Current JIS 3.2.4. Proposed Standards for High Strength Re-bars 3.2.4.1. General Outlines 3.2.4.2. Specified Yield Strength 3.2.4.3. Strain at Yield Plateau 3.2.4.4. Yield Ratio 3.2.4.5. Elongation and Bendability 3.2.5. Method of Manufacture and Chemical Component 3.2.6. Fire Resistance and Durability 3.2.6.1. Effect of High Temperature 3.2.6.2. Corrosion Resistance 3.2.7. Splice 3.3. Mechanical Properties of Reinforced Concrete 3.3.1. Bond and Anchorage 3.3.1.1. Beam Bar Anchorage in Exterior Joints 3.3.1.2. Bond Anchorage in Interior Joints

61 61 62 64 66 70 71 75 75 76 77 80 82 84 86 86 86 87 88 88 91 91 92 93 93 97 97 99 100 104 104 105 109

xii

Contents

3.3.1.3. Flexural Bond Resistance of Beam Bars 3.3.2. Lateral Confinement 3.3.2.1. Stress-strain Relationship of Confined Concrete . 3.3.2.2. Upper Limit of Stress in Lateral Reinforcement . 3.3.2.3. Buckling of Axial Re-bars 3.3.3. Concrete under Plane Stress Condition 3.3.3.1. Biaxial Loading Test of Plain Concrete Plate . . . 3.3.3.2. Tests of Reinforced Concrete Plate under In-plane Shear

Ill 113 113 120 121 122 123 124

Chapter 4 N e w R C Structural Elements Takashi Kaminosono

127

4.1. Introduction 4.2. Beams and Columns 4.2.1. Bond-Splitting Failure of Beams after Yielding 4.2.2. Slab Effect on Flexural Behavior of Beams 4.2.3. Deformation Capacity of Columns after Yielding 4.2.4. Columns Subjected to Bidirectional Flexure 4.2.5. Vertical Splitting of Columns under High Axial Compression 4.2.6. Shear Strength of Columns 4.2.7. Shear Strength of Beams 4.3. Walls 4.3.1. Flexural Capacity of Shear-Compression Failure Type Walls 4.3.2. Deformation Capacity of Walls under Bidirectional Loading 4.3.3. Shear Strength of Slender Walls 4.4. Beam-Column Joints 4.4.1. Bond in the Interior Beam-Column Joints 4.4.2. Shear Capacity of 3-D Joints under Bidirectional Loading 4.4.3. Shear Capacity of Exterior Joints 4.4.4. Concrete Strength Difference between First Story Column and Foundation 4.5. Method of Structural Performance Evaluation 4.5.1. Restoring Force Characteristics of Beams

127 128 129 136 141 147 152 156 162 169 170 178 183 189 191 196 203 206 209 209

Contents

xiii

4.5.1.1. Initial Stiffness 210 4.5.1.2. Flexural Cracking 210 4.5.1.3. Yield Deflection 211 4.5.1.4. Flexural Strength 214 4.5.1.5. Limiting Deflection 214 4.5.1.6. Equivalent Viscous Damping 214 4.5.2. Deformation Capacity of Columns 215 4.5.2.1. Flexural Compression Failure 215 4.5.2.2. Bond Splitting Along Axial Bars 216 4.5.2.3. Shear Failure in the Hinge Zone after Yielding . . 217 4.5.2.4. Shear Strength of Beams and Columns 219 4.5.3. Flexural Strength of Walls 219 4.5.4. Shear Strength of Beam-Column Joints 221 4.5.5. Connections of First Story Column to Foundation 224 4.5.5.1. Bearing Stress 224 4.5.5.2. Splitting Stress 224 4.5.5.3. Strengthening 225 4.6. Concluding Remarks 225 Chapter 5 Finite Element Analysis Hiroshi Noguchi

227

5.1. Fundamentals of FEM 5.2. FEM and Reinforced Concrete 5.2.1. History of Finite Element Analysis of Reinforced Concrete 5.2.2. Modeling of RC 5.2.2.1. Two-Dimensional Analysis and Three-Dimensional Analysis 5.2.2.2. Modeling of Concrete 5.2.2.3. Modeling of Reinforcement 5.2.2.4. Modeling of Cracks 5.2.2.5. Modeling of Bond between Reinforcement and Concrete 5.3. FEM of RC Members Using High Strength Materials 5.4. Comparative Analysis of RC Members Using High Strength Materials

227 229 229 232 232 232 234 234 234 235 236

xiv

5.5.

5.6.

5.7.

5.8.

Contents

5.4.1. Comparative Analysis of Beams, Panels and Shear Walls 5.4.2. Material Constitutive Laws 5.4.2.1. Uniaxial Compressive Stress-Strain Curves of Concrete 5.4.2.2. Compressive Strength Reduction Coefficient of Cracked Concrete 5.4.2.3. Confinement Effect of Concrete 5.4.2.4. Biaxial Effect of Concrete 5.4.2.5. Tension Stiffening Characteristics of Concrete . . 5.4.2.6. Shear Stiffness of a Crack Plane 5.4.2.7. Cracking Strength 5.4.2.8. Stress-Strain Relationship of Reinforcement . . . 5.4.2.9. Dowel Action of Reinforcement 5.4.2.10. Bond Characteristics 5.4.3. Analytical Models and Analytical Results 5.4.3.1. Analysis of Beam Test Specimens 5.4.3.2. Analysis of Panel Specimens 5.4.3.3. Analysis of Shear Walls 5.4.3.4. Conclusions FEM Parametric Analysis of High Strength Beams 5.5.1. Objectives and Methods 5.5.2. The Effect of Shear Reinforcement Ratio 5.5.3. Effects of Concrete Confinement Models with a Constant Value of pw<Jwy 5.5.4. Conclusions FEM Parametric Analysis of High Strength Columns 5.6.1. Objectives and Methods 5.6.2. Analytical Results 5.6.3. Conclusions FEM Parametric Analysis of High Strength Beam-Column Joints 5.7.1. Objectives and Methods 5.7.2. Comparison between Test and Analytical Results 5.7.3. Results of Parametric Analysis 5.7.4. Conclusions FEM Parametric Analysis of High Strength Walls

236 237 237 238 238 239 239 239 240 240 240 240 240 242 242 244 244 246 246 247 248 251 251 251 253 255 255 255 256 256 260 260

Contents

xv

5.8.1. Objectives and Methods 5.8.2. Outline of Research 5.8.3. Analytical Results and Discussions 5.9. FEM Parametric Analysis of High Strength Panels 5.9.1. Objectives and Methods 5.9.2. Analytical Results and Summary

260 260 262 265 265 265

Chapter 6 Structural Design Principles Masaomi Teshigawara

271

6.1. Features of New RC Structural Design Guidelines 272 6.1.1. Earthquake Resistant Design in Three Stages 273 6.1.2. Proposal of Design Earthquake Motion 273 6.1.3. Bidirectional and Vertical Earthquake Motions 273 6.1.4. Clarification of Required Safety 274 6.1.5. Variation of Material Strength and Accuracy in Strength Evaluation 274 6.1.6. Structural Design of Foundation and Soil-Structure Interaction 274 6.2. Earthquake Resistant Design Criteria 275 6.2.1. Design Earthquake Intensity 275 6.2.2. Design Drift Limitations 275 6.2.3. Design Criteria 276 6.3. Design Earthquake Motion 279 6.3.1. Characteristics of Earthquake Motion 279 6.3.2. New RC Earthquake Motion 279 6.3.3. Relation to Building Standard Law 280 6.4. Modeling of Structures 281 6.4.1. Modeling of Structures 281 6.4.2. Relation of Model and Earthquake Motion 281 6.4.2.1. Fixed Base Model 281 6.4.2.2. Sway-Rocking Model 282 6.4.2.3. Soil-Foundation-Structure Interaction Model . . . 282 6.5. Restoring Force Characteristics of Members 283 6.5.1. Dependable and Upper Bound Strengths 283 6.5.2. Member Modeling 284 6.5.3. Hysteresis 286 6.6. Direction of Seismic Design 286

xvi

Contents

6.6.1. Design Forces in Arbitrary Direction 6.6.2. Bidirectional Earthquake Input 6.6.3. Effect of Vertical Motion 6.7. Foundation Structure 6.8. Design Examples 6.8.1. 60-Story Space Frame Apartment Building 6.8.2. 40-Story Double Tube and Core-in-Tube Office Buildings 6.8.2.1. Double Tube Structure 6.8.2.2. Core-in-Tube Structure 6.8.3. Mediumrise Office Buildings (15-Story Wall-Frame, 15-Story Space Frame, 25-Story Space Frame)

286 289 289 289 291 291

Chapter 7 Earthquake Response Analysis Toshimi Kabeyasawa

315

7.1. Earthquake Response Analysis in Seismic Design 7.2. Structural Model 7.2.1. Three-Dimensional Frame Model 7.2.2. Two-Dimensional Frame Model 7.2.3. Multimass Model 7.2.4. Soil-Structure Model 7.3. Member Models 7.3.1. One-Component Model for Beam 7.3.2. Multiaxial Spring Model for Column 7.3.3. Wall Model 7.4. Nonlinear Response of SDF System 7.4.1. Displacement-Based Design Procedure 7.4.2. Correlation of Nonlinear Response to Linear Response 7.5. Numerical Analysis 7.5.1. Numerical Analysis of Equation of Motion 7.5.2. Release of Unbalanced Force

315 319 319 321 323 324 325 325 328 331 335 335

Chapter 8 Construction of N e w R C Structures Yoshihiro Masuda

345

299 299 305

310

337 341 341 343

Contents

8.1. Introduction 8.2. Full Scale Construction Testing 8.2.1. Objectives 8.2.2. Outline of Construction Testing 8.2.3. Concrete Mix 8.2.4. Reinforcement Construction 8.2.5. Concrete Construction 8.2.5.1. Fresh Concrete 8.2.5.2. Construction of Column Specimens 8.2.5.3. Construction of Frame Specimen 8.2.5.4. Measurement of Internal Temperature 8.2.5.5. Strength Development 8.2.5.6. Observation of Cracks on Frame Specimen . . . . 8.2.6. Conclusion 8.3. Construction Standard for New RC 8.3.1. General Provisions 8.3.2. Reinforcement 8.3.3. Formwork 8.3.4. Concrete 8.3.4.1. General 8.3.4.2. Concrete Quality 8.3.4.3. Material 8.3.4.4. Mix 8.3.4.5. Manufacture of Concrete 8.3.4.6. Placing and Surface Finishing 8.3.4.7. Curing 8.3.4.8. Compressive Strength Inspection Chapter 9 Feasibility Studies and Example Buildings Hideo Fujitani

xvii

345 345 345 346 349 354 356 356 357 360 366 366 371 374 375 375 375 376 377 377 377 383 384 386 387 388 388 391

9.1. Feasibility Studies 391 9.1.1. Highrise Flat Slab Buildings 391 9.1.1.1. Highrise Flat Slab Condominium with Core Walls 393 9.1.1.2. Highrise Flat Slab Condominium with Curved Walls399 9.1.2. Megastructures 407 9.1.2.1. OP200 Straight Type 407 9.1.2.2. OP300 Straight Type 408

xviii

Contents

9.1.2.3. OP300 Tapered Type 9.1.2.4. BR200 K-brace Type 9.1.2.5. BR200 D-brace Type 9.1.2.6. BR300 X-brace Type 9.1.2.7. Concluding Remarks 9.1.3. A Box Column Structure for Thermal Power Plant 9.2. Example Buildings

410 412 412 414 415 418 424

Index

437

Chapter 1

RC Highrise Buildings in Seismic Areas Hiroyuki Aoyama Department of Architecture, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan E-mail: [email protected]

1.1. 1.1.1.

Evolution of R C Highrise Buildings Historic

Background

The national research project on development of advanced reinforced concrete buildings using high strength concrete and reinforcement, usually referred to as the "New RC" project and on which basis this book was written, was planned and conducted in 1988-1993 in Japan under the leadership of the Japanese Ministry of Construction. This project was carried out on the background of quick development of highrise RC buildings since about 1975, in order to further promote the development and use of higher strength materials for highrise and other advanced types of RC buildings. This chapter is devoted to the introduction of the background of the New RC project, that is, the development of highrise RC buildings up to the onset of the New RC project in 1988. Reinforced concrete as building material was introduced to Japan around 1905. The first all RC building was a warehouse in Kobe, designed by Naoji Shiraishi, a professor of civil engineering of the University of Tokyo and a member of the Institute of Civil Engineers of the Great Britain, and constructed in 1906. The RC construction became popular in the subsequent years, for it was generally accepted as fire-proof and earthquake-proof construction, in contrast to combustible wooden construction or earthquake-crumbling brick construction. l

2

Design of Modem, High-rise Reinforced Concrete Structures

However the RC construction as building structure did not trace a favorable history since then. Regardless of its reputation as an "eternal" architecture, many RC buildings in Tokyo suffered heavy damage in 1923 Kanto earthquake. The behavior of RC in this earthquake disaster was generally inferior to concrete-encased or brick-encased steel buildings. This led to the development of composite steel and reinforced concrete (SRC) construction as a uniquely Japanese type of construction for Mghrise buildings. The traditional RC construction, on the other hand, was limited to buildings whose height did not exceed 20 m. This limitation was not explicitly prescribed in the building code, but was enforced by means of the administrative guidance. Any building taller than, say, seven stories had to be constructed by steel structure or SRC structure. This administrative guidance was carried over to post-war period. In 1950, five years after the end of the World War II, the new Building Standard Law was enforced to replace the old Urban Building Law, but the situation for RC construction was basically unchanged. Around 1980, the situation began to change rapidly. The RC construction was started to be used for taller buildings. This new trend included development of highrise wall-frame construction of 10 to 15 stories and highrise frame construction of 20 stories or higher, both for apartment buildings. The more important of the two developments was the latter, which was initiated by Kajima Construction Co. by completing an 18-story building in Tokyo, the Shiinamachi Apartment, in 1974, followed by another 25-story building also in Tokyo, Sun City G-Blook Apartment, in 1980, as shown in Fig. 1.1. It should be mentioned that all the big Japanese construction companies have

(a) Shiinamachi Apartment

(b) Sun City G-Building

Fig. 1.1. Early examples of RC highrise buildings.

RC Higkri.se Buildings in Seismic Areas

3

design sections within the company, and hence the structural design of these buildings was also done by Kajima. The Building Standard Law prescribed provisions for buildings up to 31 m in height in its original version of 1950, which was revised to extend the height limitation to 60 m in 1981. If one wants to build a taller building, its structural design, particularly the seismic design, has had to be subjected to the technical review of the Technical Appraisal Committee for Highrise Buildings of the Building Center of Japan, and subsequently a special permit of the Minister of Construction is issued. For the two Kajima buildings of highrise RC, this review was especially challenging, as it was the first experience for both design engineers and committee members to handle earthquake resistant highrise RC construction. Kajima had conducted an extensive research and development project within the company prior to designing these buildings. It included large-scale structural testing in the laboratory of beams, columns, and subassemblages, computer programs of advanced analysis technique for nonlinear static and dynamic earthquake response, and development of construction technology. With the help of vast experimental and analytical background data, Kajima could obtain technical appraisal for their first highrise RC buildings, leading to the special permission of the Minister of Construction. Kajima subsequently submitted 25- and 30-story apartment buildings for technical appraisal in 1983. Other big construction companies did not allow Kajima alone to go further in highrise RC construction. Taisei Construction Co. and Konoike-gumi Construction Co., among others, submitted similar proposal to the Building Center of Japan. In 1983-1984, it became almost like a violent competition of big construction companies to prepare for submission of highrise RC construction, regardless of the possibility to realize the projected plan.

1.1.2.

Technology of Japan

Examination

at the Building

Center

The Highrise RC Construction Technology Examination Committee was formed in 1984 in the Building Center of Japan under the chairmanship of Dr. Hiroyuki Aoyama, Professor of the University of Tokyo. The chairman was succeeded by Dr. Yasuhisa Sonobe, Professor of Tsukuba University, in 1986. The purpose of this committee was to control the spontaneous and violent competition of construction companies for highrise RC construction.

4

Design of Modern Highrise Reinforced Concrete Structures

In many countries where earthquake is not a potential risk for structural safety of buildings, highrise RC construction as tall as 30 stories is not uncommon. The country of Japan makes a sharp contrast to these countries not only for its high seismic risk, but also for its high level of protection demand against earthquake damage by the society. Under such a condition one would have to be prudent in the development of highrise RC construction. It was deemed insufficient to utilize the experience of highrise steel or SRC construction, and was deemed necessary to solve new problems proper to highrise RC construction. To this end the above-mentioned construction companies established new technologies associated with the design and construction of highrise RC buildings in the course of technical appraisal of the structural design of particular buildings. However this meant a dual object in the conduct of technical appraisal. The applicant of a highrise RC building — the design section of a construction company — had to show design capability for highrise RC construction by the compilation of experimental data, computer programs for nonlinear static and dynamic response analysis, and construction guidelines with practices, and so on, in addition to showing the design and analysis of the building project to be appraised, unless the construction company was a repeater of highrise RC such as Kajima. The Technical Appraisal Committee had to work on materials of the general nature as well as those specifically related to the building in question. Some companies wanted to obtain technical appraisal of a highrise RC building only in order to be recorded. In spite of having no prospect to realize the project, they compiled and submitted the materials of general character showing design capability for highrise RC to the Technical Appraisal Committee. This movement clearly added improper burden to the Committee. The Highrise RC Construction Technology Examination Committee was formed, as mentioned earlier, in 1984 in order to control undue competition of construction companies. It also helped release the Technical Appraisal Committee from the above-mentioned unfair burden. It was reorganized in 1992 as the Highrise RC Construction Technology Guidance Committee under the chairmanship of Dr. Yasuhisa Sonobe. The committee has been chaired by Dr. Shunsuke Otani, Professor of the University of Tokyo, since 1994 up to the present time. The Technology Examination Committee's work is different from that of the Technical Appraisal Committee in that there is no concrete project to

RC Highrise Buildings in Seismic Areas

5

be designed and constructed. Instead, applicants submit set of materials to demonstrate their capability to design and construct highrise RC buildings. The materials usually consist of structural design specifications, an imaginary building project designed accordingly, and construction specifications with emphasis on the quality control. Materials are frequently accompanied by reports of laboratory structural tests of RC members, laboratory and field tests of high strength concrete, and operation tests of various stages of construction. The structural design and construction specifications are required to fully reflect results and implications of these tests. One of the most important aspect of the examination is the operation test of the construction of a full-size mock-up, usually one- or two-storied and single- to double-span frame in two directions. Such an operation test is almost mandatory to the applicant, and is carried out in the presence of committee members. The construction operation test has been shown to be quite effective in the reform of understanding of both structural and construction engineers to account for new aspects of highrise RC, such as high viscosity of high strength concrete, preassembling of high strength re-bar cages, responsibility of contractor in the quality control of concrete and form works, separate concreting for columns and floor framing, proper use of concrete buckets, concrete pumps, vibrators, and so on. As an application to the technology examination involves construction technology, majority of applicants are construction companies. A few design firms have so far applied by forming a team with construction companies, or by preparing elaborate construction specifications to be applied to the contractor after bidding is settled.

1.1.3.

Increase

of Highrise

RC and the New RC

Project

The number of highrise RC buildings is steadily increasing since about 1985. Figure 1.2 shows annual numbers of highrise buildings that passed the technical appraisal of the Building Center of Japan, together with the breakdown into three structural categories of steel, SRC and RC. It is seen the number fluctuates greatly, presumably according to the construction business fluctuation, but the annual number for highrise RC construction shows steady increase since 1987. It is inferred that the increase since 1987 owes to the increase of construction companies that passed the technology examination of the Building Center of Japan, backed up by the beginning of brisk business condition at that time. After the peak of good business of 1990, the ratio of concrete construction

6

Design of Modern Highrise Reinforced Concrete Structures 120 110 100

- ns ®SRC

90 E 80 w

1

• RC

70 -

*3

^ t ° zo

60 50 40 30 20 10 0

-

79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 Year

Fig. 1.2. Annual highrise construction in Japan.

including SRC and RC to the total highrise construction became larger. In the average of recent ten years, steel, SRC and RC occupy approximately 70, 15 and 15 percent of total highrise construction, respectively. The total number of highrise RC at the end of 1997 exceeds 200. In 1987 when the New RC project was proposed at the Building Research Institute of the Ministry of Construction, the immediate arrival of highrise RC boom was quite apparent. The quick development of highrise RC construction owed to many factors, such as large scale structural testing, advanced analysis techniques, and development of construction technology. But the most significant and influential factor was the development of high strength concrete up to 42 MPa and high strength, large size reinforcing bars up to SD 390 D41 bars. The New RC project was an attempt to further promote the development of advanced RC construction in the seismic zones. As mentioned earlier, this national research project, development of advanced RC buildings using high strength concrete and reinforcement in its full name, was conducted as a fiveyear project in 1988-1993 under the leadership of the Japanese Ministry of Construction, with Building Research Institutes as the key organization. It was a very ambitious project to enlarge the scope of RC construction to a new height in the seismic countries such as Japan, probably to 200 m or higher. The technology developed in this project can be regarded as an attractive new technology to enhance the possibility of RC construction. Its influence was spread out to RC construction even before the end of the five-year project.


7

The increase of highrise RC after 1988 in Fig. 1.2 is the result of this influence, at least partly. As will be seen in Chapter 9 of this book, there are already more than 20 highrise RC buildings constructed, or under construction, as the direct result of this New RC project. 1.2. 1.2.1.

Structural Planning Plan of

Buildings

Highrise RC construction is currently used almost exclusively for apartment houses, because of better habitability provided by concrete. Floor plan of these buildings is generally regular, and symmetric with respect to one or two axes. Figure 1.3 shows a typical plan of buildings that were investigated in the technology examination of the Building Center of Japan. This is probably the most regular of the all, but other plans investigated in the technology examination were much alike. The variation employed in those plans included the following; slightly different span numbers in two directions, slightly different span

1200 5000

|

II

|

*" I m

°®

//

•

»

J

25000

©

®

5000 1200 |

I"

©

©

©,5°°

Fig. 1.3. Example of typical floor plan of RC highrise building.

8

Design of Modern Highrise Reinforced Concrete

Structures

lengths in two directions, varying span lengths in one direction, eliminating one span each at four corners, eliminating one or two central spans at four sides, and having a courtyard at the center. Thus it was apparent that designers of highrise RC buildings gave priority to structural characteristics, at least at the beginning in the stage of technology examination, by shaping the plan as simple as possible within the practicability limit. The span length of the building in Fig. 1.3 is 5 m in both directions. The span length of 5 m is much shorter than comparable SRC or steel buildings, but this was also typical for most of the buildings subjected to technology examination. The short span was adopted in order to limit the axial load on a column, and thereby reduce the seismic force acting on a column. Here lies a possibility for the New RC to liberate the structural constraint, that is, to enlarge the span by adopting higher strength materials.

Z9.0

(a)H729

n.a

36.0

(22,-2)X2

(b)H789(32,-4)

(c) H444

3B.5

2 .8

(d)H504

(25,-2)

(«) H425

(30,0)

(30,0)

(0H495

(29-1)

x 33.6

11.3

(g)H309

(25,0)

Fig. 1.4.

(h)H59S

(21.-2JX2

37.6

(i) H505

(30,-2)

Key plans of RC highrise buildings.

RC Highrise Buildings

in Seismic Areas

9

1 1

X

31.8

JZ.l

<j)H514

(k)H5B3

(25,-1)

(1)H466

(33-2)

(30,-1)

dampers wall

M j y.

(m) HB67

-

(26, - 2)

J-

(n)H706

(33,-1)

L

nH

r 3S. ?

(o)H5B0 (37,-1) (RC 13 Et±)

(p)HB84

Fig. 1.4.

(41,-1)

(Continued)

Figure 1.4 shows sixteen examples of structural key plan of highrise RC buildings actually constructed up to 1991. These drawings show columns and floor girders only, and cantilever balcony slabs are not shown. Floor opening for stairs and elevators are not shown either. X-marks denote courtyards and similar open bays. In the case of actual buildings, somewhat larger variations from the regular plan shown in Fig. 1.3 are apparent. Figures 1.4(a) to (h) are frame buildings without courtyard, (i) to (1) are frame buildings with courtyard, (m) is the

10

Design of Modern Higkri.se Reinforced Concrete

Structures

one with shear walls in one direction, (n) is a frame building with a special antiseismic device explained in the next section, (o) and (p) are the so-called tube structure buildings also described in the next section. However it will be seen that all buildings are shaped more or less like a tower with 30 m to 40 m in each direction. There is no slab-shaped buildings as contrasted to lowrise to mediumrise apartment buildings. Most buildings are equipped with balconies of continuous cantilever slabs around the periphery of the plan. A few examples have balconies inside the peripheral frame lines. It should be noted that there are no buildings with a structural core. The core system is better suited to office buildings, but not used for apartment houses. As a partial result of the New RC project, Chapter 9 of this book introduces an office building with hybrid structure, consisting of RC core and peripheral steel frames. Such a variation is not found in Fig. 1.4 where all buildings are for dwelling.

1.2.2.

Structural

Systems

Structural systems of highrise RC buildings currently constructed in Japan are classified into three categories; space frame system, space frame with seismic elements, and double-tube system. The space frame system consists of frames with uniform, or nearly uniform, span lengths in two directions. Unlike RC construction in overseas countries, all frames available in the plan are designed as moment resisting frames. This is because of high earthquake resistance required in Japan. By far this type is the most common in highrise RC construction. Figure 1.4 introduces twelve examples of space frame system, (a) to (1). Presence of a courtyard does not make any basic difference to the structural characteristics. What matters is the mixture of frames with variable number of spans. Compared to frames with multiple spans, frames with one or two spans are more susceptible to bending deformations resulting from axial deformation of columns under lateral loading, and it is usually required to analyze such structures by means of threedimensional structural analysis. One important consideration in a building with courtyard is the inplane stiffness of floor slabs as diaphragms. Due to the Japanese taste of enjoying sunshine in the dwellings, stairs and elevators are most often concentrated to the north side of the floor which is disadvantageous in this respect. It is then necessary to pay attention to the diaphragm stiffness at the north side of a


11

courtyard so that the floor slab openings of stairs and elevators will not cause any problem to the rigid slab assumption. The space frame with seismic elements refers to buildings like in Figs. 1.4(m) and (n). The first is the space frame building with shear walls. It is a well established fact that shear walls are quite effective in earthquake resistance, but it is limited to the past experience with lowrise to mediumrise RC buildings. It is believed that shear walls would be effective in highrise construction as well, but its performance would be different from lowrise buildings. The analysis and design of a space frame with shear walls will have to involve more sophisticated nonlinear analysis, static as well as dynamic. Presumably for this reason there are strikingly few examples of this type in the current highrise RC construction. Restriction in the interior architectural design by the presence of wall, and added complication in construction process, may also contribute to discourage the engineers from adopting shear walls. Figure 1.4(m) is one of rare examples of this type of construction where shear walls are provided in one direction only. When shear walls are provided in two directions, the spatial interaction would become more complicated. Challenge to such type of structures depend on engineers' courage. Another example in the space frame with seismic elements category is the building of Fig. 1.4(n). It is a space frame building having two axes of frames in the diagonal directions, with additional seismic dampers made of honeycomb shaped steel plates at several midspan of girders. These steel dampers yield at a small story drift, and absorb seismic energy through their elasto-plastic hysteresis, thereby reducing seismic effect on the RC space frames. It is an application of the so-called "structural control", usually referred to as passive seismic control. The third category in the structural systems is the double-tube system. A tubular structure here means plane frames with relatively short spans arranged into four-sided box. For an apartment building plan with a courtyard, exterior and interior peripheries can be used as this kind of tubes, such as shown in Figs. 1.4(o) and (p), hence they are called double tubes. Span length in the plane frames is usually 3 to 4 m, and the floor between the tubes spans over 10 m or so, which consist of floor slabs with subbeams or slabs with prestressing steel. The most important consideration in the structural design of double tubes is to ensure ductile behavior of short-span girders in the plane frames. Some examples utilize the so-called X-shaped reinforcement in the short girders.

12

Design of Modern Highrise Reinforced

1.2.3.

Elevation

of

Concrete

Structures

Buildings

Buildings for technology examination as well as those for actual construction have a common feature of regular shape in the vertical direction. Abrupt stiffness change between adjacent stories is carefully avoided. The total number of stories varies from 20 to 40 or more, and the story height is about 3 m, which is much smaller than office buildings. The short story height gives advantage in seismic design by reducing column moments for a given lateral load, and the fact that apartment houses do not require larger story height probably lead to the prosperity of current highrise RC construction. The first story above ground is usually occupied by entrance hall and other special purpose spaces, and hence has larger story height of 4 m or more. The aspect ratio, height to width ratio of the building, is less than 4 in all cases. Buildings usually have penthouse, consisting of RC frames with or without wall, or steel frames. Penthouses, containing elevator machinery and roof outlet from stairs, are often located off the center of gravity of typical floors, thus cause eccentricity to the main building body. It is also necessary to pay attention to the stress around the openings in the roof floor from the lateral seismic force of the penthouse. In case steel frames are used for a penthouse, the detail design of the connection to the main building is the point of major consideration. More than 80 percent of highrise RC buildings are built on basement stories. In the stage of technology examination many construction companies avoided basements for the sake of simplicity in structural design, but in actual practice basements are often needed for various architectural purposes. They also provide added safety and stability to seismic performance. The basement is generally provided with thick exterior retaining walls, which also serve as shear walls. Thus it has considerably larger lateral stiffness and strength than stories above ground. Care should be taken to account for possible reversed shear forces in the basement columns. Reversed column shear occurs when the basement story does not drift as much as the first story under lateral loading and first story column base moment is transmitted to the basement column. It contributes to the additional lateral force in the basement in the direction of lateral load, and also induces axial force in the first floor girders. It is also necessary to pay due attention to the transfer of lateral forces in the first floor slabs. In the first story lateral load is distributed more or less uniformly into column shear forces, but in the basement story most of the lateral load (more

RC Highrise

Buildings

in Seismic

Areas

13

than 100 percent when reversed shear forces occur in the basement columns) is carried by shear walls. Hence large amount of lateral load has to be transferred to shear walls through the first floor slabs acting as the diaphragm, and the floor slabs should be designed to account for this loading. The foundation of buildings may be directly supported by subsoil if it is firm enough, but in most cases pile foundation has to be employed. The most popular type of pile system is the bearing piles made by cast-in situ concrete, constructed by reverse circulation method or all casing method, or with partial replacement by continuous wall-piles. The foundation of buildings in these cases consists of pile-cap tie girders, strong and stiff enough to ensure monolithic performance of the building as a whole. The basement story shear walls add strength and stiffness to these foundation girders, but they are often reserved in the structural design as a surplus margin of safety. In case of pile foundation, foundation girders must be designed for flexure, shear and axial load considering the reaction to pile-top bending moment. 1.2.4.

Typical Structural

Members

Column section is usually square, with the maximum dimension of about 90 cm at the lower stories above ground. Figure 1.5 shows typical sections of columns. Axial reinforcement ratio is about 2 to 3 percent. To provide effective confinement to the core concrete, construction companies devised various types of lateral reinforcement for the technology examination, but in the more recent years it became a governing trend to use subhoops in the shape of Fig. 1.5(b) consisting of high strength deformed PC steel or flush butt welded (FB) rings.

12-D41 Spiral Hoop Ol6@75 Hoop D16(J)@75

(a) F i g . 1.5.

12-D41 Spiral Hoop Dtf)ll@80 Hoop #<J>11@80

(b) T y p i c a l c o l u m n sections.

14

Design

of Modern

Highrise

Reinforced

Concrete

Structures

To overcome large seismic overturning moment which produces dominating axial forces in the exterior columns in lower stories, additional axial bars (core bars) are frequently located in the central portion of these column sections. Some examples are shown in Fig. 1.6. Girders are of rectangular section with height not greater than 80 cm and with relatively large width of about 60 cm, providing space for four large diameter axial bars in a row, as shown in Fig. 1.7. Four-leg stirrups are generally used. High strength deformed P C steel is often used for stirrups to increase shear resistance. In most cases girders are located below the floor slab, and thus form a T-shaped section with the monolithic slab. But in a few cases wall girders were used in the exterior frames which consisted of girders below the slab and spandrels above the floor connected monolithically into girders of large depth. The prevalent architectural design to provide balconies around the floor plan prohibits the use of wall girders. When and where balconies are

J

D

r

i

->,

C«

cfl

n A

r-I

880 16-D41+8-D41 J. Hoop S.Hoop

16-D41+8-D41 Hoop DiJ)ll@60 #cj)ll@60 (b)

(a) Fig. 1.6.

E x t e r n a l c o l u m n s w i t h core bars.

J 3

0

c

3

3

3

C

W

c r

D

3

")

J U L

C

c

c r 1.

T

f

650

650

16-D41 Stirrup DD16-@100

14-D41 Stirrup © D i e - ® 100

Fig. 1.7.

T y p i c a l girder sections.

1


15

not provided, or when they are located inside the peripheral frame lines, wall girders can be used to increase strength and stiffness against lateral load. As mentioned earlier the story height of typical apartment houses is about 3 m. It is then essential to provide horizontal openings penetrating through the girder web for piping and air ducts. These openings must not pose any problem to the fiexural and shear strength of girders. For the practical reinforcement around such openings various prefabricated devices are available in the shape of multiple rings and spirals and so on, which have passed the technical appraisal of the Building Center of Japan.

1.3. 1.3.1.

Material and Construction Concrete

All highrise RC buildings use concrete with specified strength much higher than ordinary buildings, to cope with large axial forces in the columns. The number of stories is almost completely dictated by the concrete strength in the lowest story, as long as current floor plans and column sections are used. Concrete strength in the first story was either 36 or 42 MPa before 1988 when the New RC project was started. Compared with the concrete used for conventional RC lowrise construction of 21 or 24 MPa, this was already very high. Practical use of such high strength concrete required careful evaluation of construction technology including quality control. After the initiation of the New RC project, some construction companies started the use of even higher strength concrete, such as 48 MPa or in some cases 60 MPa before the results of the project were released. Evidently the New RC project created an atmosphere to welcome high strength material, and encouraged construction companies to develop their own voluntary project towards high strength concrete. It is a common practice to reduce strength in upper stories, with the minimum about 24 MPa. Most of highrise RC buildings are constructed by placing column concrete and that for floor system separately. This was quite a revolution in the Japanese construction practice, as the concrete casting into column and floor system simultaneously has been a common traditional practice for lowrise buildings. VH separate casting (which means casting separately into vertical and horizontal members) was deliberately adopted for highrise construction with the aim of maintaining good quality in the column concrete.

16


Concrete

Structures

In United States or other countries it is often observed that, in conjunction with the VH separate casting, different concrete strength is specified for columns and floor system, that is, higher strength for column concrete, and lower strength for floor slabs, girders, and beam-column joints. This practice is not used in Japan, and concrete of the same quality is specified for columns and floor system. Use of same concrete strength was probably accepted by most construction companies as a natural consequence from the previous custom of VH simultaneous casting. At the same time it can be also said that, although engineers are well aware of the importance of a good quality beamcolumn joint, they are not very much acquainted with, or not quite confident in, remedies for low strength concrete in a beam-column joint such as in the ACI Building Code. In some cases where lower strength concrete in the floor system is strongly required for construction economy, two types of concrete are used for floor system: same concrete as the column for the beam-column joint and some portion of surrounding girders and slabs, and lower strength concrete for the remainder of floor systems. Of course the construction joint of the two types of concrete in this case has to be treated with a special care. Concrete for the basement and foundation need not be so strong as the first story columns, but it is essential to ensure bearing strength just below the first story column base. Usual practice is to place somewhat stronger concrete than basement or foundation in some top layer portion below the column base.

1.3.2.

Reinforcement

The use of high strength and large size reinforcing bars is indispensable for highrise RC construction, to ensure seismic strength of the structure. Longitudinal bars up to 41 mm diameter (D41) with 390 MPa yield stress (SD390) are commonly used. After the New RC project was started in 1988, some attempts have been made to use bars with 490 MPa yield stress which had been specified in the Japanese Industrial Standard since several decades ago but had never been used extensively nor had been easily available in market. Lateral reinforcement consists of either D16 bars of 295 MPa steel or high strength deformed PC bars with 1275 MPa yield stress (Ulbon). This also sharply contrasts to the prevalent use of D10 and D13 bars of 295 MPa steel in lowrise buildings.


1.3.3.

Use of Precast

17

Elements

The use of precast members is advantageous for the efficient construction work with reduced work force. However considering the inevitable use of cast-inplace concrete at some critical portions such as diaphragm or joint of precast members, the extent of precasting in practice has received a divergence of opinions. Various degrees of precast application are spotted in the current practice. On one extreme end are buildings with all members cast-in-place. A popular and modest application is to use precast concrete formwork for composite floor slabs. Upper half of the floor slab is made by cast-in-place concrete to form the diaphragm for seismic loading, and the lower half is formed by precast slabs which also serve as the formwork for fresh concrete. Balcony cantilever slabs are often fully precast with elaborate architectural shape, best suitable for precast concrete construction. The use of precast girders is the next step. Precast girders have concrete up to the soffit of floor slabs in the cover, and the central portion is trough shaped. The upper portion is cast monolithically with the floor diaphragm. Bottom reinforcement is spliced at the beam-column joint or at the midspan, and top reinforcement is carried together with the precast unit and moved later to the prescribed position before concrete for upper portion is cast. It is easier to use precast units in only one of two orthogonal directions of a space frame. No matter precast units are used in one or two directions, it is essential that the units placed first in position must have only one layer of reinforcing bars in the bottom, as shown in Fig. 1.8. Columns are the most difficult to apply precast technique. When they are precast, there are currently available two kinds of technique. One is to use sleeve type splice for vertical bars located at the column bottom, as shown cast-in-situ concrete

.

n

\->\0

I

III

X

h ighr se

I

30 60 90 Concrete strength (MPa)

! 120

Fig. 2.1. Strength of materials and zones (I, II-l, II-2 and III) for research and development.

42


In contrast, the ranges of strength in the New RC project are much larger. Concrete from 30 to 120 MPa and steel from 400 to 1200 MPa are included. Comparing the zones for these ranges of material, it is obviously unrealistic to assume that behavior of New RC structures can be understood simply by extrapolating the knowledge of current RC structures. The area in Fig. 2.1 for the New RC was further divided into four zones, namely zones I, II—1, II—2, and III. Structures in these zones were studied by somewhat different tactics. Zone I corresponds to concrete up to 60 MPa and steel up to 700 MPa, which was assumed to be the direct target of the New RC project whose results could be compiled and put into practical use right at the conclusion of the five-year project in 1993. For this zone the extrapolation of the knowledge of current RC structures was thought to be relatively effective. On the contrary zone III corresponds to concrete from 60 to 120 MPa and steel from 700 to 1200 MPa, which was regarded as a future "dream". Basic characteristics of RC would have to be reexamined, and hence the project was not expected to produce much practical results. Basic subjects such as material characteristics and performance under loading of structural elements and members would be the major results for the zone III. Zones II—1 and II—2 are the combination of very high strength material and not-so-high strength material. Such combination would not have much practical significance, hence they were regarded to have secondary importance in the project. It would be relatively easy to use such combination of materials once zones I and III were completely understood. Objectives and corresponding final results of the project are summarized in Table 2.1. The first item was development of high strength materials. This required close cooperation of material engineers, structural engineers who must specify basic requirements, material supplier for cement, mineral and chemical admixtures, and steel manufacturers. The second item was investigation into properties of structural members, particularly framing members for the superstructure, under the action of seismic excitation. Experimental approach by conducting laboratory testing was indispensable in this aspect, but theoretical examination of experimental data was also emphasized in this project. The third item was development of design and construction guidelines. Here the word "guidelines" did not mean a type of guidelines that would specify full details of technology, but it was to give only fundamental considerations on principles for design and construction practice. Such a soft type of guidelines

The New RC Project

43

Table 2.1. Objectives of research and development and expected final results. Objectives (1) Development of high strength and high quality materials

Expected final results Methods for mix proportion and quality control of concrete (Zone I) Methods for production and use of reinforcement (Zone I) Principles for developing ultra-high strength materials (Zones II and III)

(2) Evaluation of basic properties of materials, structural members and frames

Methods for evaluation of basic properties of materials (Zones I—III)

(3) Development of design and

Structural design guidelines (Zone I)

construction guidelines

Methods for evaluation of basic properties of members and frames (Zones I—III)

Earthquake response evaluation guidelines (Zone I) Construction guidelines (Zone I) Development of criteria for structural design, earthquake response evaluation, and construction (Zones II and III)

(4) Feasibility study on RC buildings in Zone II—I

New type of highrise RC buildings

(5) Feasibility study on RC buildings in Zone III

New image of RC buildings (super-highrise)

(6) Trial design of a highrise boiler building in Zone II—I

A structure with steel superbeams and RC box supercolumns

was preferred in the worldwide trend towards the performance-based design. The above three items were expected, not only to produce final results as outlined in Table 2.1, but also to throw some light on the current RC technology towards the possible future revisions of specifications and standards. The fourth to sixth items in Table 2.1 were aiming at exploring the feasibility of new type of structures using the New RC material, although they were not essential parts of the project philosophically. It was expected that the New RC project would induce development of new technologies in various related fields, improve potential for international competition of construction industry, and contribute to the activation of the industry.

44


2.3.

Organization for the Project

The Building Research Institute of the Ministry of Construction was in charge of conducting the entire project. Research committees were set up in an organization called Japan Institute for Construction Engineering, to organize people from universities, Housing and Urban Development Corporation, makers of cement, admixtures and steel, and construction companies. The entire organization for the project is shown in Fig. 2.2. Technical Coordination Committee was the center of the committee tree. Research Promotion Committee consisting of representatives from sponsoring companies and Technical Advisory Board consisting of senior researchers of related fields helped the Technical Coordination Committee from financial and technical sides. These three committees were chaired by Dr. Hiroyuki Aoyama, Professor of the University of Tokyo (the affiliation at the time of the five-year project, same in the followings). Under the Technical Coordination Committee five technical committees were set up. Concrete Committee was chaired by Dr. Fuminori Tomosawa, Professor of the University of Tokyo; Reinforcement Committee by Dr. Shiro Morita, Professor of Kyoto University; Structural Element Committee by Dr. Shunsuke Otani, Associate Professor of the University of Tokyo; Structural Design Committee by Dr. Tsuneo Okada, Building Research Institute

9, Building Contractors Society

Japan Institute For Construction Engineering

Technical Advisory BRI Project \g— Team

Technical Coordination Committee

Research Promoting Committee

_jj Private Organization Housing & Urban Development ! Corporation

Cement Admixure ^ Makers

Concrete Committee

Re inforce m e nt Committee

Structural Element Committee

Working

Working

Working Group

Structural Design Committee

Working Group

Construction Manufact ring Committee

Working Group

AIJ, Universities

Fig. 2.2. Organization for research and development.

""*{ Private Organization

1 Private Organization |

The New RC Project 45 Table 2.2. Technical Coordination Committee. Position Chairman Vice-chairman

Secretary General Secretary

Member

Administrator

Name Aoyama, Hiroyuki Kamimura, Katsuro Okada, Tsuneo Morita, Shiro Murota, Tatsuro Tomosawa, Fuminori Otani, Shunsuke Masuda, Yoshihiro Hiraishi, Hisahiro Hirosawa, Mas aya Murakami, Masaya Sawai, Nobuaki Nishimukou, Kimiyasu Bessho, Satoshi Saida, Kazuo Noto, Hidekatsu Yamamoto, Kouichi Kurumada, Norimitsu Kidokoro, Motoyuki Habu, Hiroharu Takahashi, Yasukazu Yamazaki, Yutaka Nakata, Shinsuke Abe, Michihiko Kaminosono, Takashi Baba, Akio Teshigawara, Masaomi Shiohara, Hitoshi Fujitani, Hideo Kubo, Toshiyuki Akimoto, Toru Mori, Shigeo Ishikawa, Yukio

Affiliation* University of Tokyo Utsunomiya University University of Tokyo Kyoto University Building Research Institute University of Tokyo University of Tokyo Building Research Institute Building Research Institute Kogakuin University Chiba University Housing & Urban Develop. Co. Building Contractors Society Kajima Construction Co. Shimizu Construction Co. Steel Makers Club Kobe Steel Co. Cement Association Ministry of Construction Ministry of Construction Building Research Institute Building Research Institute Building Research Institute Building Research Institute Building Research Institute Building Research Institute Building Research Institute Building Research Institute Building Research Institute Japan Institute for Construction Japan Institute for Construction Japan Institute for Construction Japan Institute for Construction

Engineering Engineering Engineering Engineering

*As of March 31, 1993.

Professor of the University of Tokyo; Construction and Manufacturing Committee by Dr. Katsuro Kamimura, Professor of Utsunomiya University. These committees were in charge of making detailed research programs, implementing research works, and integrating research results in five particular fields. Tables 2.2 to 2.9 show the rosters of these eight committees, with due appreciation to the contribution of these committee members which was reflected in this book. Numerous working groups were formed as needed under the five technical committees, but the rosters had to be eliminated here because of the limitation of the space.

46

Design of Modern Highrise Reinforced Concrete Structures Table 2.3. Research Promotion Committee. Position Chairman

Name

Affiliation*

Aoyama, Hiroyuki

University of Tokyo

Vice-chairman Kamimura, Katsuro

Utsunomiya University

Secretary

Takahashi, Yasukazu Murota, Tatsuro

Building Research Institute Building Research Institute

Member

Okada, Tsuneo Tomosawa, Puminori Morita, Shiro Otani, Shunsuke Hirosawa, Masaya Koizumi, Shinichi Nishimukou, Kimiyasu Takata, Kenjo Moriguchi, Goro Ohmori, Kazuhiro Imazu, Yoshiaki Nakane, Jun Miki, Masahiro Nakae, Shintaro Bessho, Satoshi Kato, Takehiko Ono, Tetsuro Tamura, Ryoji Koitabashi, Michikata Higashiura, Akira Saida, Kazuo Nohmori, Masami Matsumoto, Hiroshi Harasawa, Kenya Heki, Hisashi Mogami, Tatsuo

University of Tokyo University of Tokyo Kyoto University University of Tokyo Kogakuin University Housing Urban Develop. Co. Building Construction Society Aoki Construction Co. Asanuma-gumi Construction Co. Ando Construction Co. Ohki Construction Co. Obayashi Construction Co. Ohmotc-gumi Construction Co. Okumura-gumi Construction Co. Kajima Construction Co. Kumagai-gumi Construction Co. Konoike Construction Co. Goyo Construction Co. Sada Construction Co. Sato Kogyo Construction Co. Shimizu Construction Co. Sumitomo Construction Co. Seibu Construction Co. Zenidaka-gumi Construction Co. Daisue Construction Co. Taisei Construction Co. Dainippon-doboku Construction Co. Ano, Shinji Takenaka Construction Co. Sugano, Shunsuke Chizaki Kogyo Construction Co. Ohkawa, Akinori Tekken Construction Co. Morimoto, Hitoshi Takusagawa, Masamitsu Tokai Kogyo Construction Co. Tokyu Construction Co. Yamamoto, Toshihiko Toda Construction Co. Motegi, Yuji Tobishima Construction Co.

Nakagawa, Mitsuo J

•—.—_

The New RC Project Table 2.3. {Continued) Position

BRI Secretary

Affiliation*

Name Yamanouchi, Jiro Taguchi, Renichi Yanagisawa, Nobufusa Toda, Tetsuo Koga, Kazuya

Nishimatsu Construction Co. Nissan Construction Co. Nippon Kokudo Kaihatsu Co. Hazama Construction Co. Haseko Corp.

Saitou, Junichi Teraoka, Masaru Wakabayashi, Hajime Maeda, Yasuji Abe, Osamu Endo, Katsuhiko Inaba, Masahiro Noto, Hidekatsu Yamamoto, Koichi Suzuki, Akinobu Kurokawa, Kenjiro Inaoka, Shinya Shimizu, Hideo Kurumada, Norimitsu Uchikawa, Hiroshi Tanaka, Mitsuo Nakano, Kinichi Nagashima, Masahisa Sakai, Masayoshi Takeda, Shigezo Furukawa, Ryutarou Sawamura, Hirotoshi Makino, Yoshihisa Maebana, Tadao Toda, Kazutoshi Kodama, Kazumi Kidokoro, Motoyuki Habu, Hiroharu Hiraishi, Hisahiro

Fukuda-gumi Construction Co. Pujita Construction Co. Fudo Construction Co. Maeda Construction Co. Matsumura-gumi Construction Co. Mitsui Construction Co. Mitsubishi Construction Co. Steel Makers Club Kobe Steel Co. Japan Steel Co. NKK Co. Kawasaki Steel Co. Sumitomo Metal Co. Cement Association Onoda Cement Co. Chichibu Cement Co. Osaka Cement Co. Mitsubishi Material Co. NKK Co. Japan Steel Co. Shin-nittetsu Chemical Co. Kawatetsu Kogyo Co. Sumitomo Metal Co. Kobe Steel Co. Chemical Admixture Association Nisso Master Builders Co. Ministry of Construction Ministry of Construction Building Research Institute

Masuda, Yoshihiro Abe, Michihiko Kaminosono, Takashi Teshigawara, Masaomi

Building Building Building Building

Research Research Research Research

Institute Institute Institute Institute

47

48

Design of Modern Highrise Reinforced Table 2.3. Position

Structures

(Continued) Affiliation*

Name

Shiohara, Hitoshi Pujitani, Hideo Kubo, Toshiyuki Administrator Akimoto, Toru Mori, Shigeo Ishikawa, Yukio

Concrete

Building Research Institute Building Research Institute Japan Institute for Construction Engineering Japan Institute for Construction Engineering Japan Institute for Construction Engineering Japan Institute for Construction Engineering


Table 2.4. Technical Advisory Board. Position

Name

Affiliation*

Chairman

Aoyama, Hiroyuki

University of Tokyo

Vice-chairman

Kamimura, Katsuro

Utsunomiya University

Advisor Secretary

Umemura, Hajime

University of Tokyo

Takahashi, Yasukazu Murota, Tatsuro


Member

Shiire, Toyokazu Tomii, Masahide Okada, Tsuneo Ogura, Kouichiro Kasai, Yoshio Kanoh, Yoshikazu Kishitani, Kouichi Sonobe, Yasuhisa Tomosawa, Fuminori Muguruma, Hiroshi Morita, Shiro Yamada, Minoru Watabe, Makoto Otani, Shunsuke Hirosawa, Masaya Kidokoro, Motoyuki Yokota, Mitsuhito Habu, Hiroharu

Kanagawa University Kyushu University University of Tokyo Meiji University Nihon University Meiji University Nihon University Tsukuba University University of Tokyo Kyoto University Kyoto University Kansai University Shimizu Construction Co. University of Tokyo Kougakuin University Ministry of Construction Ministry of Construction Ministry of Construction

Administrator

Kubo, Toshiyuki Akimoto, Toru

Japan Institute for Construction Engineering Japan Institute for Construction Engineering


The New RC Project

49

Table 2.5. Concrete Committee. Position

Name

Affiliation*

Chairman

Tomosawa, Fuminori

University of Tokyo

Secretary

Shimizu, Akiyuki

Tokyo Science University

Abe, Michihiko

Building Research Institute

Kamata, Eiji

Hokkaido University

Kawase, Kiyotaka

Niigata University

Kemi, Torao Daimon, Masaki Tanigawa, Yasuo Matsufuji, Yasunori Kittaka, Yoshinori

Ashikaga Institute of Technology

Member

Noguchi, Takafumi Hamada, Masaru Hisaka, Motoo Nakane, Jun Okamaoto, Kimio Matsuo, Tadashi Izumi, Itoshi Hiraga, Tomoaki Sakai, Masayoshi Kurumada, Norimitsu Kodama, Kazumi Kosuge, Keiichi Suguri, Hideaki Furuta, Hajime Aoki, Hitoshi Masuda, Yoshihiro Hiraishi, Hisahiro Baba, Akio Tanano, Hiroyuki Yasuda, Masayuki

Tokyo Institute of Technology Nagoya University Kyushu University Utsunomiya University University of Tokyo Housing & Urban Develop. Co. Materials Testing Center Obayashi Construction Co. Kajima Construction Co. Sato-kogyo Corp. Takenaka Construction Co. Toda Construction Co. NKK Co. Cement Association NMB Co. Denki Kagaku Co. Ministry of Construction Ministry of Construction Ministry of Construction Building Research Institute Building Research Institute Building Research Institute Building Research Institute Building Research Institute

Coop. Member Shiraishi, Kiyotaka Shiomi, Itsuo Sudo, Eiji

Building Research Institute Building Research Institute Building Research Institute

Administrator


Akimoto, Toru Ishikawa, Yukio

*As of March 31 1993.

50


Structures

Table 2.6. Reinforcement Committee. Affiliation*

Name

Position Chairman

Morita, Shiro

Kyoto University

Secretary

Noguchi, Hiroshi Shiohara, Hitoshi

Chiba University

Member

Kubota, Toshiyuki Tanaka, Reiji Tanigawa, Yasuo Matsuzaki, Ikuhiro

Kinki University Tohoku Institute of Technology Nagoya University Tokyo Science University

Wada, Akira Imai, Hiroshi Kaku, Tetsuzo Sakino, Kenji Hayashi, Shizuo

Tokyo Institute of Technology Tsukuba University Toyohashi Institute of Technology Kyushu University Tokyo Institute of Technology Tsukuba Technical College

Pujisawa, Masami


Kyoto University Shimizu Construction Co. Taisei Construction Co. Takenaka Construction Co. Yamamoto, Toshihiko Tokyu Construction Co. Fujita Construction Co. Teraoka, Masaru Kobe Steel Co. Yamamoto, Koichi New-Japan Steel Co. Suzuki, Akinobu Sumitomo Metal Co. Shimizu, Hideo Ministry of Construction Suguri, Hideaki Ministry of Construction Puruta, Hajime

Pujii, Shigeru Inada, Yasuo Hattori, Takashige Sugano, Shunsuke

Administrator

Aoki, Hitoshi

Ministry of Construction

Fukushima, Tbshio Masuda, Yoshihiro Hiraishi, Hisahiro

Building Research Institute Building Research Institute Building Research Institute

Baba, Akio Kato, Hirohito


Akimoto, Toru


Ishikawa, Yukio *As of March 31, 1993.

The New RC Project

51

Table 2.7. Structural Element Committee. Name

Position

Affiliation*

Chairman

Otani, Shunsuke

University of Tokyo

Vice-chairman

Watanabe, Pumio

Kyoto University

Secretary

Kaminosono, Takashi


Member

Fujitani, Hideo


Ohkubo, Masamichi Kanoh, Yoshikazu Takiguchi, Katsumi Nomura, Setsuro Minami, Koichi Kato, Daisuke Kabeyasawa, Toshimi Joh, Osamu Fujisawa, Masami Ichinose, Toshikatsu Bessho, Satoshi Kato, Takehiko Yoshizaki, Seiji Maeda, Yasuji

Kyushu Institute of Design Meiji University Tokyo Institute of Technology Tokyo Science University Fukuyama University Niigata University Yokohama National University Hokkaido University Tsukuba College of Technology Nagoya Industrial University Kajima Construction Co. Kumagai-gumi Construction Co. Taisei Construction Co. Maeda Construction Co.

Mitsui Construction Co. Ministry of Construction Ministry of Construction Aoki, Hitoshi Ministry of Construction Nakata, Shinsuke Building Research Institute Hiraishi, Hisahiro Building Research Institute Goto, Tetsuro Building Research Institute Teshigawara, Masaomi Building Research Institute Kato, Hirohito Building Research Institute

Endo, Katsuhiko Suguri, Hideaki Tsujikawa, Takao

Coop. Member Oka, Kohji


Administrator


Akimoto, Toru Mori, Shigeo


52


Structures

Table 2.8. Structural Design Committee. Position

Name

Affiliation*

Chairman

Okada, Tsuneo

University of Tokyo

Vice-chairman

Murakami, Masaya

Chiba University

Secretary

Yoshimura, Manabu

Member

Sugimura, Yoshihiro Matsushima, Yutaka Wada, Akira Akiyama, Hiroshi Hirosawa, Masaya

Tohoku University Tsukuba University

Kabeyasawa, Toshimi Kanda, J u n

Yokohama National University University of Tokyo Nagoya Institute of Technology Hokkaido University

Tokyo Metropolitan University Teshigawara, Masaomi Building Research Institute Pujitani, Hideo Building Research Institute

Kubo, Tetsuo Takizawa, Haruo Nakano, Yoshiaki Sawai, Nobuaki Izumi, Nobuyuki Yoshioka, Kenzo Abe, Isamu Ono, Tetsuro Saida, Kazuo Yamamoto, Masashi Ishida, Tadashi Toda, Tetsuo Suguri, Hideaki

University of Tokyo Housing &; Urban Develop. Co. Toda Construction Co. Obayashi Construction Co. Okumura-gumi Construction Co. Kohnoike-gumi Construction Co. Shimizu Construction Co. Tobishima Construction Co. Nishimatsu Construction Co. Hazama-gumi Construction Co. Ministry of Construction

Tsujikawa, Takao


Aoki, Hitoshi Kitagawa, Yoshikazu


Yamazaki, Yutaka


Nakata, Shinsuke


Yamanouchi, Hiroyuki Hiraishi, Hisahiro


Coop. Member Igarashi, Haruhito Administrator

Tokyo Institute of Technology University of Tokyo Kogakuin University



Akimoto, Toru

Tokyo Institute for Construction Engineering

Mori, Shigeo

Tokyo Institute for Construction Engineering

•As of March 31, 1993.

The New RC Project 53 Table 2.9. Construction and Manufacturing Committee. Position Chairman Vice-chairman Secretary Member

Coop. Member Administrator

Name Kamimura, Katsuro Morita, Shiro Tomosawa, Fuminori Masuda, Yoshihiro Shiohara, Hitoshi Kemi, Torao Tanaka, Reiji Imai, Hiroshi Shimizu, Akiyuki Fukushi, Isao Nakane, Jun Bessho, Satoshi Okamoto, Kimio Hattori, Takashige Izumi, Itoshi Sugano, Shunsuke Yamamoto, Koichi Abe, Michihiko Hiraishi, Hisahiro Yasuda, Masayuki Nishimura, Susumu Akimoto, Toru Ishikawa, Yukio

Affiliation* Utsunomiya University Kyoto University University of Tokyo Building Research Institute Building Research Institute Ashikaga Institute of Technology Tohoku Institute of Technology Tsukuba University Tokyo Science University Housing & Urban Develop. Corp. Obayashi Construction Co. Kajima Construction Co. Kajima Construction Co. Taisei Construction Co. Takenaka Construction Co. Takenaka Constructoin Co. Kobe Steel Co. Building Research Institute Building Research Institute Building Research Institute Building Research Institute Japan Institute for Construction Engineering Japan Institute for Construction Engineering

"As of March 31, 1993.

In addition, several cooperative research projects were organized between the Building Research Institute and volunteering companies. Figure 2.2 shows these cooperative research projects in the right hand side enclosed by dotted lines. The aim of the cooperative research covered the latter three objectives in Table 2.1, namely various feasibility studies of the New RC structures. Chapter 9 of this book deals with the results of these cooperative research projects.

2.4. 2.4.1.

Outline of Results Development

of Materials

for High Strength

RC

The first major effort was the development of high strength concrete and steel, together with their test methods and evaluation criteria. Figure 2.3 shows fresh high strength concrete at the slump test. High strength concrete

54

Design of Modem Highrise Reinforced Concrete Structures

Fig. 2.3. Concrete after slump test.

160 140 --W/(C+Si)=20%

120

~

100

m

80

//

-^1- -- -W/(C+Si)=25%

t -~W/C=35% W/C=65% V\ —

/ ,7

V)

.7 '

55

?/

60 40 20

0

w

V.

1

\

I'

0

0.1

0.2

0.3

0.4

0.5

0.6

Strain (%)

Fig. 2.4. Examples of stress-strain relationship of concrete.

with compressive strength greater than 40 MPa usually displays viscous iow. Handling of such viscous fresh concrete in the site requires special attention, as explained in Chapters 3 and 8 of this book. Figure 2.4 shows some examples of stress-strain relationship of concrete. Relatively linear ascending portion and steep descending portion are conspicuous characteristics of high strength concrete. Figure 2.5 illustrates stress-strain curve of USD 685 steel with specified yield point of 685 MPa that was newly developed for axial reinforcement, together with commercially available reinforcing bars and prestressing steel. As shown by dotted curves in Fig. 2.5, stress-strain relationships of steel in tension tends to lose yield plateau as yield point gets higher. The newly developed

The New RC Project

55

2,000

1,500 ' PC ban (0.86)

5

| New RC USD675(0.77) \

1,000

• SD590 (0.76)

w

' SD390 (0.67) 500 SD295(0.71)

"0

5

10

15 Strain (%)

20

25 30 Numbers in { ) indicate yield ratio.

Fig. 2.5. Examples of stress-strain relationship of reinforcing bars.

USD 685 was a successful attempt to produce high strength steel with well denned yield plateau. 2.4.2.

Development

of Construction

Standard

Major achievement in the construction engineering was the development of New RC Construction Standard. It is different from the current JASS (Japan Architectural Standard Specification) in the definition of concrete strength. In order to procure the specified strength in the structure with the maximum reliability, concrete strength in the New RC Construction Standard is defined by the strength of concrete in the structure, to be controlled by the strength development in the structure and in the cylinders under the corresponding curing condition. Essential features of the New RC Construction Standard are introduced in Chapter 8. 2.4.3.

Development

of Structural

Performance

Evaluation

A set of evaluation methods for structural performance of New RC elements and structural members was developed. Performance of elements here refers to beam bar anchorages to columns, buckling of compression bars, lateral confinement, planar RC panel elements subjected to plane stress conditions, and so on. Performance of structural members means items as indicated below: flexural behavior of beams and columns as influenced by axial load, bond

56


splitting along axial bars, and shear failure in the hinge zone; flexural and shear strength of walls; shear failure of beam-column joints; and connections of first story columns to foundations. Needless to say that monotonic loading as well as cyclic reversal of loading were considered. These evaluation methods, mostly in the form of equations, were developed primarily through theoretical studies, which were subsequently investigated by experiments for their adequacy and accuracy. In some aspects, however, empirical approaches were indispensable, which was judged appropriate for the complex structural material such as RC. Chapter 4 of this book is devoted to this development of performance evaluation methods. Chapter 5 was written as a plain guide for the readers to the nonlinear finite element analysis for RC elements and members, as it was shown in the New RC project that finite element analysis was such a powerful tool for structural engineering that it should have a wider application in the structural design in future.

2.4.4.

Development

of Structural

Design

New RC Structural Design Guidelines was developed mainly for earthquake resistance. It is based on the dynamic time history response analysis to earthquake ground motions with a clear definition of required safety. It is introduced in detail in Chapter 6 of this book. Figure 2.6 illustrates an imaginary building that was designed using the guidelines. It is a sixty-story apartment building, whose detail and structural design are also included in Chapter 6. Chapter 7 was written as an easy introduction to the earthquake response analysis, keeping those readers with no experience or little knowledge on the response analysis in mind. The guidelines were developed for highrise RC buildings, but it will be applicable to RC structures in general, and its philosophy should also be applicable to structures of other material.

2.4.5.

Feasibility

Studies for New RC

Buildings

Application feasibility studies were made for materials in Zones II and III in Fig. 2.1. They consist of the following three types of buildings. The first was a highrise flat slab building shown in Fig. 2.7. This building was assumed to be constructed using materials in zone II—I. Flat slab structures

The New RC Project

57

Fig. 2.6. Bird's eye view of a 60-story building.

Fig. 2.7. Highrise flat plate building utilizing high strength concrete.

have significant advantage for dwellings because of no girders protruding below the soffit of ioor slabs, in other words, from the ceilings. However its application in Japan has been quite limited in view of apparent deficit in seismic resistance. This feasibility study aimed at the breakthrough for this type of construction in the seismic areas with the use of high strength materials. It was shown to be quite feasible, and much future development is expected. The second was a series of highrise buildings based on the "megastructure" concept. Figure 2.8 shows an example of such structures with 300 m in height,

58


Fig. 2.8. Megastructure of 300 m high utilizing high strength materials.

I s 4&:>

Fig. 2.9. Highrise boiler building of thermal power plant.

consisting of five rnegastories each of which contains fifteen stories of substructures inside. Materials in zone III are to be used. The basic idea for this type of structures is that the megastructure constructed by high strength RC can be used for centuries as a kind of infrastructure to the society due to its superior durability and easy maintenance, whikf the substructure is relatively light and easily alterable according to the future change of occupancy or other changes of

The New RC Project

59

architectural needs. The feasibility study lead to the trial design of two groups of megastructures, having 200 m or 300 m in height. The third was a new type of thermal power plant boiler building shown in Fig. 2.9, consisting of four huge RC box columns housing a vertical boiler inside, suspended from the steel grid girders that connect top of four columns at the height of 100 m. Materials in zone II—1 were assumed. Laboratory experiment was conducted for a portion of box columns, and it was also shown that this type of structure was quite feasible by the use of New RC materials. 2.5.

Dissemination of Results

Bulky reports were compiled each year during the New RC Project of 19881993 by the research committees shown in Fig. 2.2, and disseminated to all parties involved in the project. Major findings were condensed into short summary papers and reported at the Annual Conventions of the Architectural Institute of Japan in each year. Occasional introductions at international meetings were also made (Refs. 2.1-2.3). In addition, seminars were organized each year for audiences from participating universities and construction companies. In October 1994, the Concrete Journal published 55-page articles in Japanese covering all features of the project (Ref. 2.4). Some portions of the results have already been in use in the construction of highrise concrete buildings. Standards for performance evaluation or design and construction guidelines have been partially incorporated into existing standards and guidelines. It is expected that such practical use of results of the New RC Project will increase. Objects of the feasibility studies, namely highrise flat slab buildings, highrise megastructure buildings, and thermal power plant boiler buildings, will be constructed eventually. It is deemed necessary that following items have to be attended appropriately in the near future. (1) JIS (Japanese Industrial Standards) for newly developed reinforcing steel with 685 MPa yield strength. (2) Incorporation of standard specification for high strength and superhigh strength concrete into existing standard specification and design standards. (3) Popularization of high strength and superhigh strength ready mixed concrete. (4) Acceptance and authorization of New RC design and construction guidelines at the Technical Appraisal Committee for Highrise Buildings of the Building Center of Japan.

60


T h e major contents of this book except C h a p t e r 7 are t h e translation of a report published by Building Research I n s t i t u t e in M a r c h 2001 (Ref. 2 - 5 ) .

References 2.1. Aoyama, H., Murota, T., Hiraishi, H. and Bessho, S., Development of advance reinforced concrete buildings with high-strength and high-quality materials, Proc. Tenth World Conference on Earthquake Engineering, Madrid, Vol. 6, July 1992, pp. 3365-3370. 2.2. Aoyama, H., Recent Development in seismic design of reinforced concrete buildings in Japan, Bulletin of the New Zealand National Society for Earthquake Engineering, 24(4), December 1991, pp. 333-340. 2.3. Aoyama, H. and Murota, T., Development of new reinforced concrete structures, Eleventh World Conference on Earthquake Engineering, Acapulco, Mexico, June 23-28, 1995. 2.4. Murota, T. et al., Feature articles on new reinforced concrete structures (in Japanese), Part I-VII, Concrete J. 32(10), October 1994, pp. 5-61. 2.5. Aoyama, H. et al., Development of advanced reinforced concrete buildings using high-strength concrete and reinforcement, Report No. 139, Buildings Research Institute, March 2001.

Chapter 3

New RC Materials Michihiko Abe Department of Architecture, Kogakuin University 1-24-2 Nishi-Shinjuku, Shinjuku-ku, Tokyo 163-8677, Japan E-mail: [email protected] Hitoshi Shiohara Department of Architecture, University of Tokyo 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan E-mail: [email protected]

3.1.

High Strength Concrete

Chapter 3 of this book is devoted to the description of high strength and high quality materials developed for the New RC project. The first section deals with the development and properties of high strength concrete, achieved by the effort of the Concrete Committee under the chairmanship of Dr. F. Tomosawa, Professor of the University of Tokyo. 3.1.1.

Material

and Mix of High Strength

Concrete

In order to obtain high strength of concrete, three methods are available in general. The first is to increase the strength of the binder, the second is to select aggregate with high strength, and the third is to improve the bond at the interface of aggregate and binder (Refs. 3.1 and 3.2). Among them, the most popularly adopted is the first method. This is because of the fact that the binder strength of concrete in the ordinary strength range is smaller than the strength of aggregate, hence the strength of 61

62


Structures

concrete is dictated by that of binder. The increase of binder strength requires the cement and mineral admixtures suitable for high strength, and reduction of water-binder ratio as the most effective means in terms of mix design. This is a well-known fact by the classical name of "water-cement ratio" theory. In addition, to maintain workability of concrete within the practical limit without increasing the unit water content while keeping the low water-binder ratio, that is, without increasing the unit binder content, it is necessary to develop chemical admixtures with high capability of dispersing cement and mineral admixtures. The increase of binder strength naturally results in producing concrete whose strength is strongly affected by the aggregate strength. Hence the selection of aggregate suitable for high strength concrete becomes an important issue. Finally, it is an established fact (Ref. 3.3) that the concrete strength depends microscopically on the structure of the transition zone between aggregate and binder. For the strength improvement of the transition zone, not only the reduction of water-binder ratio but also the use of mineral admixtures with ultrafine particle such as silica fume was found to be effective. Based on these general considerations for high strength of concrete, this subsection presents research accomplishment on the development of cement, chemical and mineral admixtures, and the selection of aggregate, both suitable for high strength, and achievement on the mix proportioning method of high strength concrete.

3.1.1.1.

Cement

A series of experiment was carried out in the New RC project with the aim of developing the cement suited for high strength concrete and of developing the quality standard of such cement, leading to test results as summarized below. Compressive strength of mortar with water-cement ratio of 25 to 65 percent was studied using ordinary, high-early strength, moderate heat, and type B blast furnace slag portland cement. As shown in Fig. 3.1, mortar strength is affected by cement type for water-cement ratio greater than 30 percent, but the difference is small for water-cement ratio of 25 percent. The figure also shows mortar strength for type B fly ash cement and for ordinary portland cement with silica fume, which resulted in lower strength even at the water-cement ratio of 25 percent.

New RC Materials 63

Ordinary Portland ceaent High-early-strength Portland ceaent Moderate heat Portland cement Type B blast furnace ceaent Type B fly-ash ceaent OPC with silica fume Age'-28 days

25

30

35

40

50

later-ceaent ratio (%) Fig. 3.1. ratio.

Strength of mortar with various cement types in the range of low water-cement

130 120 -

^

1 1

10

^>-

o

O

°

o 9 l d»1*

°

O>0

•

*

•

90

Jeo 70

i

40

I

60

I 80

I

I

100

Percentage of base cement (%) Fig. 3.2. Relationship between base cement percentage in particle size distribution controlled cement and mortar strength.

Setting and compressive strength tests were conducted of mortar with water-cement ratio of 30 percent and sand-cement ratio of 1.4, using ordinary, high-early strength, moderate heat, and type B blast furnace slag portland cement of various makers. High strength could be obtained by any cement, but the correlation between mortar strength and cement strength by JIS (Japanese

64


Structures

Industrial Standard) method was not observed. This indicates that JIS may not be sufficient as a quality standard of cement for high strength concrete. The fluidity of mortar and concrete using commercially available cement is greatly impaired when the water-cement ratio is low. To increase the fluidity of mortar with low water-cement ratio, particle size distribution controlled cement was manufactured on trial, by replacing part of ordinary portland cement by pulverized matter such as coarse particle portland cement or finely ground limestone. Tests of mortar and concrete were conducted using this particle size distribution controlled cement, and mortar with good fluidity (flow value of 200 mm) was obtained even with water-cement ratio of 20 percent or less. The fluidity of concrete using this cement at the water-cement ratio of 20 percent was also excellent, and as shown in Fig. 3.2, compressive strength of more than 100 MPa was achieved for the new cement with 60 to 80 percent base cement (40 to 20 percent replacement). Quality standards for cement to be used for concrete between 36 MPa and 60 MPa were developed, which will be explained in Chapter 8. 3.1.1.2.

Aggregate

The relationship between the quality of high strength concrete and the quality of aggregate was studied experimentally, to establish method for selection of aggregate suitable for high strength concrete. Major findings were as follows. Assuming that concrete is a two-element system of matrix (mortar) and coarse aggregate, and that mortar is another two-element system of matrix (cement paste) and fine aggregate, strength variation of concrete and mortar was studied by varying the amount of aggregate from various places while keeping the matrix quality constant. Figure 3.3 shows results for concrete. For both water-cement ratio of 25 percent and 35 percent, concrete was made using four different kinds of coarse aggregate, which are marked O, T, K and D. Compression tests were made at the age of 28 days. With the increase of unit coarse aggregate content of K or D, compressive strength decreased almost linearly, while it remained more or less constant with the increase of good quality aggregate such as O or T. Thus it is clear that coarse aggregate with inferior quality affects the strength of high strength concrete remarkably. Figure 3.4 shows a similar results as above for mortar. Using nine different kinds of sand of varying sand-cement ratio while keeping the water-cement ratio constant at 25 percent, mortar strength was tested at ages of 7 or 28 days. The compressive strength showed tendency to decrease as sand

New RC Materials

65

Unit coarse aggregate content (!/•*)

0 1

200

400

i

600 100 ° i

i

200

400

600

80

00

S\.

NX

^"&

• Hortar

oo

60

Nof-O A T

80

^v

vK

40

OD

(b) W/C = 35 X

(a) f/C = 25 %

Fig. 3.3. Relationship between unit coarse aggregate content and compressive strength of concrete using various kinds of coarse aggregate (O, T, K and D).

Sand-ceoent r a t i o 120

0.5

1.0

1.5

2.0

T

1

r

W/C=25% 110 ^^

100

Age^ 28 days

Si 90 •M SO

I 80 to

« S B3

OA1 70 - « A 2

©A3 ©A4

OB • C

i D vE

OF

D

|

90 80 70 N

A 60 Fig. 3.4. Relationship between sand-cement ratio and compressive strength of mortar using various kinds of sand ( A 1 ~ F ) .

66


8r~

Concrete

W=160kg/m',

Structures

Drying p e r i o d s months

Sfc... 20 22.5 25 25N 30

20 22.5 25 25N 30 w/B (%)

20 22.5 25 25N 30

Andesite

Limestone

Hard Sandstone

Pig. 3.5. Effect of kinds of coarse aggregate on the drying shrinkage of concrete.

content increases for all kinds of sand used, but the decreasing trend was more conspicuous for some sand, for example with marks D and E. A study into the effect of aggregate size, shape, and unit coarse aggregate content on the compressive strength was conducted. No effect was found of aggregate size and aggregate content on the concrete strength, but angular shape was found to be advantageous for high strength. Crushed hard sandstone, limestone, and andesite aggregates with BS (British Standard) crushing value of 15 to 20 were used for high strength concrete of 100 to 120 MPa compressive strength, to investigate Young's modulus at 28-day age and drying shrinkage at 6-month age. Limestone concrete showed higher Young's modulus of about 50 GPa compared to about 40 GPa of hard sandstone or andesite concrete. Drying shrinkage was also smaller for limestone concrete as shown in Fig. 3.5, which illustrates shrinkage strain after 6 months of drying period for concrete using three kinds of coarse aggregate and water-cement ratio ranging from 20 to 30 percent while keeping the unit water content of 160 kg/m 3 constant. All concrete except for 25N used the cement with 15 percent replacement by silica fume for the binder. High strength concrete with 120 MPa strength can be made by using selected aggregate, both coarse and fine, and the fluidity can be improved by using fine aggregate with adjusted fineness, i.e. by removing very fine component from the fine aggregate. 3.1.1.3.

Chemical

Admixtures

Various commercially available as well as newly developed chemical admixtures, generally known as air-entraining and high-range water-reducing agents,

New RC Materials

67

were compared in a series of unified tests. Concrete with four grades of compressive strength were considered. They were 40 MPa at water-cement ratio of 40 percent, 60 MPa at water-cement ratio of 30 percent, 80 MPa at waterbinder ratio of 25 percent of both plain concrete and concrete mixed with silica fume or ground granulated blast furnace slag, and 100 MPa at water-binder ratio of 22 percent of concrete mixed with silica fume or ground granulated blast furnace slag. Items such as relationship between unit water content and admixture addition ratio to achieve the target slump or air content, time variation of slump, setting time, compressive strength, drying shrinkage, and freezethaw resistance, were studied. As an example, the case of 60 MPa concrete at water-cement ratio of 30 percent is illustrated below. Figure 3.6 shows change with time of slump of concrete using various brands of chemical admixtures. Unit water content of 165 kg/m 3 was kept content, and air content was in the range of 3 to 4 percent. Some brands, e.g. marks A and G, showed larger slump loss with time than other brands. Figure 3.7 shows range of setting time of concrete with unit water content of 165 kg/m 3 and 150 kg/m 3 using the same ten brands of chemical admixtures as above. Some brands showed very long setting time, particularly when the unit water content was low. The drying shrinkage strain of concrete using certain brands of admixture was also found to be longer.

L_J 0

1 15

i 30

I 60

i 90

Time (min) Fig. 3.6. Change with time of concrete slump using various brands of air-entraining and high-range water-reducing agents.

68


Concrete

Structures

1250 Z l W=165kg/m3 H i W = 150kg/m 3 1000

•S

1

W/C=30%

750

D I

EH

500

250 S

A

B

_L C D

E

_L F

151

ri

G

H

I

Brand of admixtures

Fig. 3.7. Setting time of concrete using various brands of air-entraining and high-range water-reducing agents.

120 100

W/C=3Q% • W=165kg/m\ M W=165kg/m\ W& W=150kg/m 3 , H I W=150kg/m 3 ,

Air=3~4X Air=2 % Air=3~4 X *ir=2 *

I d e n o t e s r a n g e of max and min

80

20

4

[W

60 40

rfi

T

if"

i

I ll 28

i

91

Age (days)

Fig. 3.8. Compressive strength of high strength concrete using various brands of airentraining and high-range water-reducing agents.

New RC Materials

69

Nevertheless, compressive strength of concrete was satisfactory for all brands of admixtures. Figure 3.8 shows compressive strength for four different combination of unit water content and air content at five different ages. Watercement ratio of 30 percent was kept constant, aiming at compressive strength of 60 MPa. As can be seen in the figure, the target strength was more than satisfied at the age of 28 days. It was even cleared at 7 days in this test. The cases of higher strength concrete indicated the significance of air entrainment on the freeze-thaw resistance. Figure 3.9 is the results of freezing and thawing test of 80 MPa concrete with water-cement ratio of 25 percent, indicating the relationship of spacing factor and durability factor, which is the relative value of dynamic modulus of elasticity at the end of freezing and thawing test. For plain concrete without mineral admixture with air of 3 to 4 percent and plain concrete with ground granulated blast furnace slag, no reduction of durability factor was observed. However, plain concrete with low air content and plain concrete with silica fume showed inferior durability. Based on these unified tests, quality standard and usage guideline for chemical admixtures for 60 MPa high strength concrete were developed. Test data for higher strength concrete were not compiled into practical form as above at the present stage, but they are believed to throw some light into the future advancement of the concrete research.

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Mineral admixture ; not mixed : not mixed : silica fume ; blast furnace slag

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Fig. 3.9. Durability factor and spacing factor of concrete using various brands of airentraining and high-range water-reducing agents.

70


3.1.1.4.

Mineral

Admixtures

Mineral admixtures for high strength concrete are to replace a part of cement and form a part of binder. Admixtures such as silica fume, fly ash fume, ground granulated blast furnace slag, and etringite type special admixture were considered. Fly ash fume is obtained by processing fly ash at high temperature, thereby evaporating silicon dioxide whose boiling temperature is relatively low among substances in the fly ash, and then coagulating it at the lowered temperature for collection. Etringite was used to be known as cement bacillus, but the etringite type special admixture is a kind of mineral admixture mainly consisting of Type 2 anhydrous gypsum, with the aim of growing hardened binder body with fine structure by utilizing the growth of needle-shaped crystal of etringite (formed by the reaction of aluminate in the cement and gypsum). Followings are major findings of unified tests for mineral admixtures. Fluidity and compressive strength of cement paste, mortar and concrete were tested using silica fume or fly ash fume whose specific surface area was modified to range of 260 000 to 700 000 cm 2 /g. It was found that replacement of 10 to 15 percent of silica fume or fly ash fume lead to the maximum compressive strength. Greater specific surface area of fly ash fume resulted in the increase of strength. Workability, strength development and freeze-thaw resistance of mortar and concrete were studied using ground granulated blast furnace slag with specific surface area of 6000, 8000 and 10 000 cm 2 /g. The strength development was slow at low temperature, but strength was improved when the specific surface area was greater. Strength development of concrete with low water-binder ratio was measured where the binder consisted of three components of cement, ground granulated blast furnace slag, and silica fume or fly ash fume. The concrete with the three components showed greater increase of strength at long term than two component concrete. Properties of concrete with etringite type special admixture were investigated, and it was shown that increase of compressive strength of about 15 MPa was obtained by adding this admixture. Figure 3.10 shows the effect of curing condition on this kind of concrete, in terms of compressive strength at 28 and 91 days under four different curing conditions, i.e. exposed to air after 2, 4, 7, or 28 days of wet curing either in the form or under standard curing condition. Strength of cylinders under standard curing condition is shown in all four groups as a common reference. An exception in this figure is the leftmost group

New RC Materials

0 0

Strip at 2d tin, sealed

Strip at 2d. then standard-cured I Strip at 2d standard-cured 1(3 Strip at 2d standard-cured 2d than air-cured

Strip at 2d then air-cured

71

5d than aircured

Strip at 4d then air-cured fU Strip at 7d than air-cured

2 Strip at 2d standard-cured 25dthen air-cured • Strip at 28d than ail-cured

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(w/ad. ) (w/out ad.) (w/ad. ) (w/out ad. ) (w/ad.) (»/out ad. ) (w/ad.) (w/out ad.)

Fig. 3.10. Effect of curing condition on the compressive strength of concrete using etringite type special admixture.

where strength of sealed cylinders is shown, which was happened to be similar to that under standard curing. In each group strengths with and without etringite type admixture are compared. For all four curing conditions, strength increase due to addition of the admixture is clearly seen. Furthermore, this admixture improves the strength development in the concrete exposed in the air. Concrete with this admixture revealed strength comparable or even better strength compared to standard curing even after 4 or 7 days of wet curing condition. These mineral admixtures are very important for high strength concrete, especially in excess of 60 MPa, and the individual special features must be carefully considered in their practical use. 3.1.1.5.

Mix Design

Aiming at developing specification for mix design of high strength concrete of 60 to 80 MPa specified strength, procedure to determine water-cement ratio or

72


Concrete

Structures

water-binder ratio, unit water content, unit bulk volume of coarse aggregate, and dosage of chemical admixtures was studied to achieve the required average (proportioning) strength, air content and slump or slump flow. Major findings are summarized below. In order to find relationship between required average strength and watercement ratio or water-binder ratio, and relationship between unit water content or dosage of chemical admixture and workability, tests were made on the various concrete properties in the range of water-binder ratio of 15 to 40 percent and unit water content of 145 to 175 kg/m 3 , using air-entraining and high-range water-reducing agent, silica fume and ground granulated blast furnace slag 8000. For the same slump or slump flow of fresh concrete, it was found that flow speed of concrete was faster, hence the workability was better, when silica fume was used or when unit water content was increased. Furthermore, as shown in Fig. 3.11, compressive strength at ages of 7, 28 and 91 days increased in proportion to binder-water ratio in the range of water-binder ratio of 25 percent or more, but for lower water-cement ratio compressive strength did not increase with the increase of binder-water ratio. As shown in the figure, concrete with ordinary portland cement (OPC) showed the strength at 28 days of about 100 MPa, and concrete with silica fume replacement of 15 percent (OPC + SF) and concrete with ground granulated blast furnace slag 8000 replacement of 30 percent (OPC -I- BS) showed the strength at 28 days of about 120 MPa, both more or less constant for different binder-water ratio above 4. 140

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