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Design of Multistory Reinforced Concrete Buildings for Earthquake Motions JOHN A. BLUME President, John A. Blume & Associates, Etzgineers San Francisco, California NATHAN M. NEWMARK Head, Department of Civil Engineering, University of Illinois Urbana, Illinois LEO H. CORNING Clzief Consulting Structural Engineer, Portland Cenient Association Chicago, Illinois Publislzed by PORTLAND CEMENT ASSOCIATION 5420 Old Orchard Road, Skokie, Illinois 60077 @ Portland Cement Association 7967 All rights reserved-no part of this book may be reproduced in any form without permission in writing from the publi~her,e xcept by a rez~iewer zuho zuishes to quote brief passages in connection with a review written for inclusion in magazine or newspaper. Printed in the United States of America FIFTHP RINTING LIBRARYO F CONGRECSAST ALOG CARD NUMBER 61- 1 7264 This publication is based on the facts, tests, and authorities stated here- in. It is intended for the use of professional personnel competent to evaluate the significance and limitations of the reported findings and who will accept responsibility for the application of the material it con- tains. Obviously, the Portland Cement Association disclaims any and all responsibility for application of the stated principles or for the accu- racy of any of the sources other than work performed or information developed by the Association. The activities of the Portland Cement Association are limited to scientific research, the development of new or improved products and methods, technical service, promotion and educational effort (including safety work) , and are primarily designed to improve and ex- tend the uses of portland cement and concrete. The manifold program of the Association and its varied services to cement users are made possible by the financial support of its member companies in the United States and Canada, engaged in the manufacture and sale of a very large proportion of all portland cement used in thesc two countries. A current list of member companies will be furnished on request. Foreword The publication of this volume in 1961 was a landmark event in the history of design and construction of multistory reinforced concrete buildings in regions of significant seismicity. The authors wrote in their preface, "...earthquake-resistant design is not yet capable of complete and rigorous execution solely by means of mathematical analysis, design codes, specifications, or rules of procedure. It is an art as well as a science. ..." These words are as true today as they were thirty years ago. However, this volume gave earthquake-resistant design of multistory reinforced concrete buildings more of a scientific basis than it ever had before. Available experimental information was compiled on the behavior of reinforced concrete members under reversed cyclic loading. The inelastic deformability and energy-absorbing capacity of different types of members were considered in developing design criteria to assure appropriate energy-absorbing capacity in an earthquake resistant reinforced concrete structure. Recom- mendations were given to enable the designer to provide the necessary inelastic deformability in reinforced concrete buildings. These recommendations, generally speaking, have stood the test of time, and have been responsible for satisfactory performance of reinforced concrete buildings in a number of earthquakes, thereby saving many lives. In the thirty years since its publication, this volume has become a classic in its own right - one of a very few classics in our technical literature. Communications have been received at PCA from time to time inquiring why the volume is not updated. The reason, truly, is a strong reluctance to tamper with a classic. In the sixties, seventies and eighties, much has of course been learned about earthquake ground motion, and about the behavior and characteristics of structures and structural components when subjected to such ground motion. The knowledge has come from actual observation, and analytical as well as extensive experimental studies. With gain in knowledge, however, has also come the realization that the complexities of earthquake-resistant design are more formidable than had been suspected earlier. Earthquake-resistant design today is more of an advanced art as well as an advanced science than it was in 1961. For a comprehensive update on developments in this field since 1961, the reader is referred to two major sources: I) a three-volume set of proceedings of a workshop on Earthquake-Resistant Reinforced Concrete Buildings Construction (ERCBC) sponsored by the National Science Foundation, and held at the University of California, Berkeley in July 1977 with Professor V.V. Bertero as organizer, and 2) a Special Publication (SP-127) entitled, "Earthquake Resistant Concrete Structures: Inelastic Response and Design," edited by this writer, and issued by the American Concrete Institute in 1991. As of this writing, a comprehensive, new design manual entitled, "Design of Concrete Buildings for Earthquake and Wind Forcesn (EB113), is in the process of being published jointly by the Portland Cement Association and the International Conference of Buildings Officials. This manual will provide updated design information and examples to structural engineers designing reinforced concrete buildings for wind or earthquake resistance. In view of a continuing demand on the part of the profession for this classic volume by Blume, Newmark and Corning, the Portland Cement Association is pleased to issue this fifth reprint. Skokie, Illinois S. K. Ghosh November 1991 CONSIDERABkLnEow ledge has been gained in the last three decades about the phenomena of ground motion, the characteristics of structures, and their behavior in earthquakes. In addition, much has been learned about the response of various vibrating systems to such motion. Despite this progress and coin- cidental development of earthquake design criteria and codes, the unknowns and the complexities are still so great that earthquake-resistant design is not yet capable of complete and rigorous execution solely by means of mathematical analysis, design codes, specifications, or rules of procedure. It is an art as well as a science, and requires experience and judgment on the part of the engineer, as well as sensitivity to the true nature of the problem including the behavior of materials and structures subject to various types and degrees of motion. Above all it is necessary to have an understanding of the manner in which a structure absorbs the energy transmitted to it by an earthquake and the maximum amount of motion or energy the structure can sustain. It is intended that this manual will furnish current information pertaining to these topics and specifically to the earthquake-resistant design of multistory reinforced concrete buildings. The authors and the Portland Cement Asso- ciation emphasize, however, that neither this manual nor any earthquake code, spectral analysis, or other procedure can supplant the sound professional judgment of engineers familiar with the earthquake problem. Earthquakes can be expected in presently active earthquake areas of the world, and probably in many of the apparently dormant areas as well. Engi- neers have learned from experience how to design and to construct buildings to resist the effects of earthquake motions, but the relatively simple empirical rules that have been developed as a result of experience may not always be the most satisfactory and may not result in the most economical construction. The objective is to proportion a structure in such a way that it can survive without damage in a moderate earthquake and without major structural damage as the result of the most severe earthquake reasonably predictable during the anticipated life of the structure. Furthermore, the structure should not collapse even when subjected to the motions of an earthquake of abnormal intensity. It is assumed, of course, that no structure would be located directly over an active known fault. The problem involves more than merely achieving an adequate design. The objectives of the design must be attained in the actual construction of the building. The development of design specifications and construction procedures for earthquake-resistant structures has been and, in fact, still is an evolutionary process. Although most design specifications involve the concept of a statically equivalent lateral design force, the appropriate choice of the equivalent static force is governed by the dynamic behavior of the structure. The design of earthquake-resistant structures is basically a dynamic and not a static problem. For a working understanding of the problem, one must consider inelastic defor- mation and energy absorption and must take into account the periods of vibration of the structure and the nature of the resistance of the structure under all conditions to which it is likely to be subjected. Many of these factors can be taken into account implicitly rather than explicitly. An advantage of having a code or design specification to follow is that it helps to remind the designer of some important aspects of the behavior of the structure that he might otherwise overlook. Many materials can be used for earthquake-resistant construction. Whatever the material, there are ways of using it that are most efficient and economical in resisting the motions and forces produced by earthquakes. The purpose of this manual is to present basic principles of earthquake-resistant design, with particular application to the design of multistory reinforced concrete buildings. Consideration is given to the dynamic behavior of reinforced concrete members and to methods of design that pro\ride the necessary strength and ductility to resist earthquake effects. Tiecommendations are given not only for design but for construction procedures and inspection to ensure, to the greatest possible degree, the achievement of the aims of the designer. The underlying principles in the development of modern codes for seismic design are discussed. In particular, recommendations for normal design procedures are based on the 1959 report, Recomm~ndedL at~ralF orce Requzrements, prepared by the Seismology Committee of the Structural Engineers Association of California, because the recommendations are the most recent and are considered to present the most rational code-type design requirements developed to date. In order to emphasize the true nature of the problem, however, con- siderable space in this manual is devoted to matters of dynamic movement, inelastic resistance, and energy absorption. The general procedures described, which are basic in the subject of structural dynamics, may be used in the analysis of very tall, slender, or unusual reinforced concrete buildings to supple- ment the design specifications. The reader will find in Chapter 1 a general description of earthquake ground motion and the effects of such motion on the dynamic behavior of simple spring- mass systems having one degree of freedom. The concept of the response spec- trum is introduced, and general predictions of earthquake response spectra are given for single-degree-of-freedom systems. Also considered in this chapter are the behavior of simple inelastic systems and the response spectra charac- terizing their action for certain earthquake motions. The more complex behavior of systems having many degrees of freedom is considered in Chapter 2. An illustrative example is given in Chapter 2 of the behavior of a three-story structure to indicate the general characteristics of the response of a complex system as compared with that of a simple system. The behavior of multi-degree-of-freedom systems in the inelastic range is considered, as well as the effects of foundation and soil conditions and other factors. Methods are given in this chapter for computation of the natural periods of vibration of a building. In Chapter 3, the principles of earthquake-resistant design, as distinct from analysis, are considered. The significance of design specifications and in particular of the SEAOC design code is discussed, and guidance is given for estimating the period of vibration and the required ductility of a proposed structure in order that it will have the appropriate characteristics to resist earthquake motions. A detailed discussion of design codes and specifications is given in Chapter 4, with particular emphasis on the SEAOC recommendations. The method of using these to obtain an adequate design of a reinforced concrete building is described. Consideration is given to the way in which the various elements of a building can absorb energy, and general concepts are presented to permit the designer to take account of the ways in which the structure may be designed so as to resist earthquake motions and forces. In Chapter 5, consideration is given to the behavior of reinforced concrete members under both static and dynamic loads. The strength, the stress-strain relationships, and the ductility or energy-absorbing capacity of members of different types are considered in detail with a view toward developing the criteria that the designer must adopt in order to assure the appropriate energy- absorbing capacity and ductility in his design. Consideration is given to members subjected primarily to flexure or to combined flexure and axial load. The effects of reversed loading on a building are considered to enable the designer to make necessary provision to prevent damage from the reversal of motion. The ways in which the principles developed in Chapter 5 are applied in the design of reinforced concrete frames are described in Chapter 6. Recommenda- tions are given to enable the designer to provide the necessary ductility in reinforced concrete buildings. These recommendations involve the selection of the strength of concrete and type of reinforcement, the amount and arrange- ment of the reinforcing steel, and special details that are desirable at joints and connections, in shear walls, and in other aspects of reinforced concrete buildings. Throughout the manual and particularly in Chapters 5 and 6, it is the intention of the authors that the provisions of the Building Code Requirements for Reinforced Concrete (ACI 318-56) of the American Concrete Institute are generally applicable to buildings constructed in seismic as well as nonseismic areas. However, because of the unique conditions to which structures may be subjected in severe earthquakes, certain more stringent design requirements and details are recommended. In order to demonstrate the procedures and principles described, an illustrative design example is given in Chapter 7. This example, pertaining to a 24- story reinforced concrete frame building, illustrates the steps to be taken in estimating the period to be used, the determination of the seismic forces accord- ing to the SEAOC code, and the design of typical columns, beams, and connections. Because of the importance of construction procedures and the inspection necessary to ensure that the appropriate procedures are being carried out, Chapter 8 presents recommendations for construction and inspection of reinforced concrete in buildings. Recommendations are given to assure adequate control of the quality of concrete and placement of steel, and methods are described to enable the inspector to carry out his responsibilities systematically and effectively. A description of some of the steps involved in a dynamic review of a typical design, with particular reference to the design example given in Chapter 7, is presented in Appendix A. Appendix B is a description of the reserve energy technique for the design and rating of structures in the inelastic range. Its application is illustrated by a review of the design example of Chapter 7. A verbatim reprint of the SEAOC Seismology Committee Recommended Lateral Force Requirements, July 1959, with subsequent changes and corrections, is included as Appendix C. For the convenience of the reader, all references cited in the manual have been numbered consecutively and are listed in Appendix D. A summary of the notation used repeatedly in the body of the manual is given in Appendix E. The notation used conforms to generally accepted symbols to the extent possible. Because of the scope of the manual, it has been necessary to assign meanings to certain symbols which commonly have distinctly different meanings in different areas of science or engineering. The transcription of the SEAOC Recommended Lateral Force Requirements in Appendix C is a verbatim copy; therefore any notation used in the body of the manual which differs from that in the SEAOC code is indicated in the list of notation in Appendix D. Acknowledgment This manual was prepared for the Portland Cement Association by the authors with the help of Alfred L. Parme, principal engineer, and John A. Sbarounis, structural engineer, Advanced Engineering Group of the Portland Cement Association. The authors wish to express their appreciation to their associates for their valued assistance in the studies leading to the preparation of the manual, and for their help in writing. Grateful acknowledgment is made to Dr. Chester P. Siess, professor of civil engineering, and Dr. Mete A. Sozen, associate professor of civil engineering, TJniversity of Illinois, Urbana, and to H. J. Sexton, vice president and chief engineer, and Roland L. Sharpe, vice president, of John A. Blume & Associates, Engineers, San Francisco. The detailed review and con- structive criticism of the manuscript by Stephenson B. Barnes, consulting structural engineer, Los Angeles, and John F. Meehan, supervising structural, engineer, California State Division of Architecture, Sacramento, are also grate- fully acknowledged. The work of many authors, investigators, and committees of technical organi- zations has been drawn upon in writing the manual. It has been the authors' intention to give full credit by references throughout the text to the bibliography in which are listed the sources of all data, charts, and information cited or reproduced. It is hoped that all to whom credit is due have been included. Any omissions are inadvertent.