|RESEARCH INTO PRACTICE
Session Chair: Gary C. Hart
Professor of Civil Engineering
University of California at Los Angeles
An Assessment of Earthquake Engineering Research
and Testing Capabilities in the United States
Daniel P. Abrams
Professor of Civil Engineering
University of Illinois at Urbana-Champaign
Recommendations made over the last twenty-two years for improving experimental capabilities in the United States are briefly summarized as a preface to a presentation of findings from a recent workshop on the subject. The workshop was held in response to a need expressed in the NEHRP Reauthorization Act of 1994 for the President to conduct an assessment of earthquake engineering research and testing capabilities in the United States. With sponsorship of the National Science Foundation and the National Institute of Standards and Technology, the Experimental Research Committee of the Earthquake Engineering Research Institute held a meeting of the nations top experimental researchers and earthquake engineers to offer their ideas and opinions on (a) the present state of research facilities, (b) the need for new facilities, (c) options for multinational cooperation, (d) projected costs for construction, (e) operation and maintenance of new research facilities, (f) options for funding of future experimental earthquake engineering research, and (g) the feasibility of developing a comprehensive national research program. Recommendations from the workshop on each of these topics are presented.
The SAC Steel Program and Guideline Developments in the U.S.
Stephen A. Mahin
Byron L. and Elvira E. Nishkian Professor of Civil Engineering
University of California at Berkeley
President, California Universities for Research in Earthquake Engineering
Many steel frame buildings suffered brittle fractures in their welded beam to column connections during the January 17, 1994 Northridge earthquake. Damage varied in intensity, from micro-cracking to complete fractures of beams or columns. Damaged structures were observed throughout the epicentral region, in old and new structures, in tall and short ones, both privately and publicly owned.
In the immediate aftermath of the earthquake, the California Office of Emergency Services initiated a program to reduce earthquake hazards in steel frame structures. The program was carried out by the SAC Joint Venture, comprised of the Structural Engineers Association of California, the Applied Technology Council, and the California Universities for Research in Earthquake Engineering. The Federal Emergency Management Agency (FEMA) significantly expanded the scope of this effort to include surveys of the performance of steel buildings, detailed analytical and experimental investigations of damaged and undamaged steel buildings, and assessment of the state of the art. In addition, a preliminary experimental investigation of full-size beam to column connections was conducted to examine the behavior of conventional pre-Northridge details and to validate the reliability of various recommendations for repairing or upgrading damaged connections and for constructing new ones.
The topical investigations conducted to date have been reviewed and used to develop Interim Guidelines. The Interim Guidelines contain:
Information on damage to steel buildings during the Northridge earthquake
A unified classification system for reporting damage
Procedures for inspecting and evaluating structures to determine appropriate post-earthquake actions
Procedures for repair and modification of damaged steel frames
Procedures for design and construction of new steel frames
Information on materials, welding, inspection and quality control
The Interim Guidelines suggest that historic practices used in the design and construction of welded steel moment frame structures do not provide adequate levels of reliability and safety and should not continue to be used. Following strong earthquake ground shaking, welded steel moment frames should be subjected to rigorous evaluations to determine the extent and implications of any damage sustained. Risk to public safety associated with continued occupancy of existing undamaged welded steel moment frame buildings is probably no greater than that associated with many other types of existing buildings with known seismic vulnerability.
A second three-year phase is about to begin with additional FEMA funding. It will enable the SAC Steel Program to conduct further investigations leading to more reliable and cost effective solutions to the steel problems revealed by the Northridge earthquake.
Inelastic Design Considerations: From Research Into Practice
John A. Blume Professor of Engineering
Department of Civil Engineering
Seismic design has been, and in most cases still is, based on purely elastic concepts. A few basic principles combined with much judgment are being used to define seismic design loads for which an elastic design is performed based on member forces (or stresses) and elastic stiffness. In parallel with elastic design go more than 30 years of research on inelastic behavior of structures, which has provided fundamental as well as detailed knowledge on dynamic and cyclic response characteristics of structures and their elements. As this knowledge finds its way into practice, and as the public, regulatory agencies, and the engineering profession request, or focus on, fulfillment of explicit performance objectives, the need is being recognized for a more realistic representation of actual physical phenomena in the seismic design and evaluation process. In severe earthquakes, in which life safety and collapse prevention become overriding performance objectives, inelastic considerations control seismic performance in most structures. In many cases, these considerations can not be represented adequately in elastic models.
The presentation focuses on the following three related issues: (1) it summarizes research that provides the foundation for inelastic design considerations, (2) it summarizes ongoing professional efforts that focus on the explicit incorporation of inelastic concepts in the design process, and (3) it paints a subjective picture of the potential of a design methodology in which inelastic concepts are considered explicitly and comprehensively.
SPECIAL STRUCTURES AND SYSTEMS
Session Chair: Sami F. Masri
Professor of Civil Engineering
University of Southern California
Energy Concepts and Structural Control
Tsu T. Soong
Professor, Department of Civil Engineering
State University of New York at Buffalo
This talk touches upon two areas of Professor Housners contributions to earthquake engineering that have had a major impact on the earthquake resistant design and seismic retrofit of structures. These two areas are energy-based design concepts and structural control. Energy-based design philosophy has been largely responsible for the development of innovative structural control technologies and, as a result, considerable attention has been paid to passive and active structural control research in recent years. Passive control systems encompass a range of materials and devices for enhancing damping, stiffness, and strength and can be used both for new design and for rehabilitation of aging or deficient structures. In recent years, serious efforts have been undertaken to develop the concept of energy dissipation, or supplemental damping, into a workable technology. Active systems and some combinations of passive and active systems, so-called hybrid systems, are force delivery devices integrated with real-time processing evaluators/controllers and sensors within the structure. They must react simultaneously with the hazardous excitation to provide enhanced structural behavior for improved service and safety. Remarkable progress has been made in both areas of research and implementation. This talk presents an overview of some of the basic control concepts as applied to civil engineering structures and provides examples of current full-scale applications of these technologies.
Bridge Retrofit Research and Implementation in California
Professor of Structural Engineering
Department of AMES
University of California, San Diego
In direct response to recommendations in the Governors Board of Inquiry report following the 1989 Loma Prieta earthquake, Caltrans has significantly expanded seismic retrofit research programs and accelerated bridge retrofit implementations over the past six years. The problem-focused research efforts that resulted from these Board of Inquiry recommendations are discussed by means of examples of experimental and analytical research, the resulting retrofit technology development, and examples of field installations. Examples presented will include, but not be limited to, the bridge column retrofit with steel and advanced composite jackets, the footing retrofit with reinforced concrete overlays and additional piles, the retrofit of the San Francisco Double Deck Viaducts, and the retrofit of flared bridge columns. The emphasis in the presentation will be on problem-focused research and retrofit technology development based on analytical models, laboratory component testing, and large scale prooftesting.
Seimic Analysis of Tanks:
From Housners Pioneering Study to Todays State of Knowledge
Medhat A. Haroun
Director, University of California Study Center in Cairo, Egypt
Professor, Department of Civil and Environmental Engineering
University of California, Irvine
George Housner, as he has often done in many fields of earthquake engineering, has laid the foundation for the advancement of the seismic analysis of liquid storage tanks. In his pioneering work, some forty years ago, Housner developed a simplified method for the seismic analysis of rigid tanks which recognized that these systems have two distinct response characteristics: the impulsive (short period) components and the convective (long period) components. His method has formed the basis for the design of storage tanks for many years to follow and has served as the cornerstone for future advancements in the field. In the late seventies, the so-called Haroun-Housner mechanical model was developed to take into consideration the wall deformability of anchored tanks. Since Housners original work, numerous enhancements of the analysis of tanks have been made, most notably, by Veletsos, Clough, Haroun, and their associates, to include explicitly tank flexibility, support effects, and various nonlinearities.
The most recent advancement in the seismic analysis of tanks has dealt with the nonlinear time-dependent response of unanchored ground-based tanks. For these tanks, the overturning moment caused by the hydrodynamic pressure tends to lift the shell off its foundation. Computer models capable of simulating this complex seismic behavior were developed taking into consideration large amplitude liquid sloshing and the geometric, material and contact nonlinearities of the tank shell and the base plate using the finite element method. The computer simulation included the following features: a variational principle that forms the basis for the numerical discretization of nonlinear fully-coupled liquid-structure interaction problems with free surface sloshing; an up-to-date finite element technique for the linearity; potential flow modeling using an efficient Eulerian finite element; free surface of the contact/uplift analysis by a Lagrange multiplier technique employed to enforce both displacement compatibility and force transmissibility constraints along the unknown contact surface; and an efficient time integration technique developed specifically to solve liquid-structure interaction problems.
The presentation includes a summary of the historical development of the seismic analysis of liquid storage tanks since Housners pioneering work and it highlights the most recent advances in the field and their implications on enhancing seismic design procedures.
Earthquake Analysis, Design and Safety Evaluation of Concrete Dams
Anil K. Chopra
Johnson Professor of Civil Engineering
University of California at Berkeley
Progress in earthquake engineering can often be traced back to the damaging effects of earthquakes. Alarmed by the damaged school buildings during the 1933 Long Beach earthquake, the California Legislature passed the Field Act. The spectacular damage to the Olive View Hospital during the 1971 earthquake led to the stringent code for design of hospitals. The damage to freeway structures during the same earthquake prompted Caltrans to revise its design procedure and to develop retrofit concepts. These design and retrofit schemes were improved again after the experience with the performance of freeway structures during the 1989 Loma Prieta earthquake. Finally, the 1994 Northridge earthquake brought to the fore the concern about blind thrust faults and surprised the profession in that steel frame buildings are not as earthquake-resistant as we had presumed.
The 1967 Koyna earthquake was a watershed event in the history of earthquake engineering for concrete dams. A dam designed by standard procedures of the time had been structurally damaged during the earthquake, which surprised the dam engineering profession. This event inspired serious research on earthquake engineering for concrete dams. In 1970 George Housner wrote about the significance of the seismic events at Koyna Dam. Since then, over the past twenty-five years, earthquake analysis of dams has come a long way, advancing from rule-of-thumb methods to very simple pseudostatic analyses to procedures that recognize the dynamics of the dam-water-foundation rock system. It is the story of this progress that will be presented in this talk.
The current state of knowledge about earthquake response analysis of concrete dams will be summarized, along with its application to the earthquake-resistant design of new dams and to the seismic safety evaluation of existing dams. The limitations of the traditional analysis procedures will be identified, the factors that should be considered in dynamic analysis of dam-water-foundation rock systems will be discussed, and linear analysis procedures for simplified response spectrum analysis and refined response history analysis available to the profession will be summarized. The presentation will include examples of the application of these analysis procedures to seismic design and safety evaluation of dams.
Linear analyses of dams subjected to the very intense ground motions expected in highly seismic areas may indicate that the computed tensile stresses exceed the available tensile strength of concrete, indicating that the dam is likely to crack. Similar analyses of an arch dam may show that the tensile stresses in the arch direction exceed the compressive arch stresses prior to the earthquake, implying cyclic opening and closing of the vertical contraction joints during vibration. For these reasons nonlinear response of concrete dams has been a subject of increased research activity during recent years. However, the interpretation of the results of such analyses to predict the damage to a dam and to evaluate its safety remains a challenge, especially for government agencies responsible for dam safety. Additional research is needed to develop reliable methods for predicting damage to dams that experience intense earthquakes with spatial variability in ground motion along the canyon, as was the case at Pacoima Dam during the 1994 Northridge earthquake.
Nuclear Power Plants and Nuclear Production Facilities
William J. Hall
Professor Emeritus of Civil Engineering
University of Illinois at Urbana-Champaign
This talk begins with a brief description of George Housners key role in the seismic design of special and commercial nuclear power plants, as well as nuclear production facilities. This road map of Georges leading part in this effort is based on the speakers personal knowledge, as well as deductive research on the matter. George Housner was the pioneer in developing seismic design criteria for such facilities, and in making the case for the importance of such design considerations.
There follows a brief history of the development of such facilities and systems, with particular emphasis on the advances that have been made in the field in the relatively short time it has been in existence. This section of the presentation leads naturally into some observations about current technical efforts in the United States directed toward reduction of cost of new commercial nuclear power plants, with the goal of bringing about a resurgence of interest in nuclear power as a major energy source. The talk concludes with some brief comments about the importance of interrelationships between technical and societal issues as they relate to nuclear matters.
LOOKING TO THE FUTURE
Session Chair: Mihran S. Agbabian
Professor Emeritus of Engineering
Civil Engineering Department
University of Southern California
Looking back at the Housner years is the way to chart the future of Earthquake Hazard Mitigation. Back to the Future is the best way to describe what we are discussing at this Symposium that honors George Housner.
Dr. Housner was a co-founder of the Earthquake Engineering Research Institute in 1949, with the goal of the advancement of the science and practice of earthquake engineering, and the solution of national earthquake engineering problems. He has personally fulfilled this challenge and developed the state of the art more than anyone else in the scientific community. He took the leadership role in organizing the California Universities for Research in Earthquake Engineering, and in recent years became the principal advisor on the new technology of structural control. His publications, starting with Characteristics of Strong-Motion Earthquakes in 1947, have laid the foundation of the science of earthquake hazard mitigation.
There are now thousands of scientists and engineers who are building on the pioneering work of Housner. These persons are Housners children. I say this by quoting a Russian scientist during the Soviet years who was visiting the United States in 1979 as the leader of the delegation of exchange scientists on Construction in Seismic Regions. I heard him say to Dr. Housner, We are all your children. There is no better testimony in honoring our father of earthquake engineering.
Future Earthquake Education in the Earth Sciences
Bruce A. Bolt
Professor of Seismology (Emeritus)
Departments of Geology and Geophysics and Civil Engineering
University of California, Berkeley
Geology and geophysics enter into earthquake hazard reduction (and hence earthquake engineering) because there is the need to specify earthquake source location, size, activity rate, mechanism, rupture process and so on. Seismology further has the responsibility of providing ways to construct appropriate seismic ground motions for structural design and hazard assessment. Many recent inferences, field measurements, and estimation procedures on these topics have not yet been worked through in the classroom. In the future, additional attention in text books and courses must be given to three-dimensional seismic wave propagation properties, including lateral refraction and scattering, together with better explanations of nonlinear wave interactions at the source and site.
New educational emphasis must be given to forensic earthquake studies so that more quantitative correlations can be made in practice between recorded seismic motions and observed intensity (in both surficial geology and engineered structures). Better understanding of formulating and working inverse problems is needed. Closer integration of courses in strong motion seismology and earthquake engineering must emerge if the full promise of cost-efficient damage minimization is to be achieved.
Trends and Directions of Civil Engineering Education
James T.P. Yao
Professor of Civil Engineering
Texas A&M University
To date, many workshops and conferences have been held to discuss engineering education. During this past decade, the National Science Foundation has been supporting projects to further improve engineering education including the eight Engineering Education Coalitions. These Coalitions involve approximately 60 institutions of higher learning. They are pursuing various approaches with such common goals as (a) to develop innovative and integrated curricula, (b) to incorporate new technologies in teaching, and (c) to increase the number of engineering graduates from underrepresented groups. The American Society of Civil Engineers (ASCE) held a Civil Engineering Education Conference in Denver, Colorado on 8-11 June 1995. In preparation for this conference, a workshop was held in Dallas, Texas on 22-25 September 1995 with 23 educators and 23 practitioners. In addition, more than 200 position papers were circulated to 400 interested members and friends of ASCE from 1992 through Spring 1995. These efforts resulted in the following four educational initiatives:
Integration of Technical Subjects, Communication, Leadership Training, Management and Teamwork into Curricula, and Implementation of Results of NSF Coalitions
Practitioner Involvement in the Education Process
Professional Degrees (Post-baccalaureate)
In this paper, current trends and future directions of civil engineering education will be presented and discussed in honor of Professor George Housner as a leader and role model of engineering educators.
Earthquake Response/Recovery or Earthquake Mitigation:
What Should be Done and Who Should Pay for It?
Robert D. Hanson
Professor of Civil Engineering
University of Michigan
(on IPA assignment with the Federal Emergency Management Agency)
Recent earthquake experiences in California, namely the Loma Prieta earthquake of 1989 and the Northridge earthquake of 1994, have created a new climate of expectations from the public, building owners, local and state public officials, and the federal government. Many of these expectations are based on a misunderstanding of the purposes of earthquake resistant design codes and the resulting construction. They expected earthquake-proof buildings and received damaged buildings.
For the private sector this has increased interest in techniques to minimize damage, to assure post-earthquake operation, and to control construction or rehabilitation costs. For the public sector this has increased efforts to mobilize the maximum amount of federal dollars to repair damaged buildings, to upgrade damaged buildings to new building earthquake resistant design levels, and to rehabilitate undamaged buildings (mitigation) to new building design levels. This extraordinary demand for federal dollars is causing a serious consideration of revisions to the Stafford Disaster Relief Act to reduce the federal exposure in the next earthquake disaster. This paper focuses on the impact of building officials interpretations of codes and legislative actions to maximize federal disaster relief through earthquake damage upgrade triggers, and some actions being considered for revision of federal disaster relief legislation regarding response/recovery and mitigation.
LOOKING TO THE FUTURE II
Session Chair: Robin Shepherd
Professor of Civil Engineering, Emeritus
University of California at Irvine
SEAOCs Vision 2000:
A Conceptual Framework for Performance-Based Seismic Engineering
Chris D. Poland
Chairman, SEAOC Vision 2000 Committee
President, Degenkolb Engineers
The Recommended Lateral Force Requirements of SEAOC (Structural Engineers Association of California) have historically targeted a limited set of design objectives and focused chiefly on the design of the primary structural system. Recognizing that this is no longer sufficient, SEAOC has begun the development of a new generation of performance-based engineering provisions embracing a broader scope of design and construction quality assurance issues and yielding more predictable seismic performance over a range of earthquake demands. These procedures will address a broad range of performance objectives considering life-safety, structural and nonstructural damage control, and maintenance of function over a range of earthquake hazards. The performance-based procedures will embrace new design and analysis approaches to more directly address the inelastic response of structures and to provide alternative procedures to better achieve defined seismic performance objectives. To date, SEAOC has developed a conceptual framework for this new generation of design guideline.
Performance-based engineering begins with the selection of performance objectives and identification of seismic hazards; continues with conceptual, preliminary and final designs, design acceptability checks and design review; and concludes with quality assurance during construction and building maintenance after construction. Each step is pursued to a greater or lesser extent, depending on the rigor of design required to meet the selected performance objectives. Abbreviated methodologies can be used for simple structures with modest performance objectives.
The design and acceptability check steps vary depending on the design approach selected and the performance objectives. Building design approaches have been defined and include Comprehensive Design, Displacement, Energy, General Force/Strength, Simplified Force/Strength, and Prescriptive Approaches. Acceptability analysis procedures outlined include the General Elastic Analysis Procedures, Component-Based Elastic Analysis Procedure, Capacity Spectrum Procedure, Pushover Analysis Methods, Dynamic Nonlinear Time History Analysis, and the Drift Demand Spectrum Analysis. Other methods will be considered and added as they are identified and shown to be usable.
The conceptual framework thus far defined must next be developed into guidelines and then into code provisions, before it can be uniformly applied in building design. Some of the concepts are easily developed; others will require considerable research and trial design applications before they can be developed into a usable form. In the transitional phase from current seismic design practice to performance-based engineering design, it is anticipated that new provisions will be incrementally developed from the existing provisions to assure that a smooth transition is made.
Collaborations For Earthquake Loss Reduction
Richard N. Wright
Director, Building and Fire Research Laboratory
National Institute of Standards and Technology
George Housner and his colleagues have long warned the earthquake community and the nation of the need for actions to reduce catastrophic potential earthquake losses. Recent earthquakes in California and in Japan have shown that even well prepared areas are vulnerable to severe losses of life and property, and to catastrophic secondary economic losses. Indeed, nowhere in the nation are we well prepared for earthquake loss reduction. The Federal government is addressing the needs for loss reduction efforts in major policy studies: Administration Policy Proposals, The National Mitigation Strategy, the National Earthquake Strategy, the Plan for Development and Adoption of Seismic Standards for Lifelines, and Recommendations for Large Scale Testing Facilities. The recommendations and status of these studies is reported. An important feature of each is the dependence on collaborations between the private sector and federal, state and local governments. These include collaborations between earth scientists, social scientists, and engineers concerned with research, practice and education. Success in earthquake loss reduction requires understanding, commitment of resources, and partnership among all these groups.
Midterm Report of the International Decade for Natural Disaster Reduction
Professor, School of Civil Engineering
The International Decade for Natural Disaster Reduction (IDNDR) was first proposed by Dr. Frank Press, then President of the National Academy of Sciences, in his keynote address to the 8th World Conference on Earthquake Engineering held in San Francisco in 1984. The International Association of Earthquake Engineering immediately endorsed the proposal to promote the IDNDR in the earthquake engineering community and related fields. In 1986, the Advisory Committee on the IDNDR was organized and chaired by Prof. G.W. Housner under the auspices of the National Research Council, the National Academy of Sciences and National Academy of Engineering. The Committee published a booklet entitled Confronting Natural Disasters in 1987. This was the first concrete activity taken by the US organization. In 1988, Dr. Press called 31 specialists from various countries to discuss how to promote the IDNDR in the world. Professor Housner was representing the United States, and in this way, the United States was the leading country in the beginning of the IDNDR. After the United Nations adopted the resolution to support the IDNDR, however, the activities of the United States were not influential for worldwide promotion of the IDNDR, even though the national committees for the IDNDR were organized by the federal government and academia.
Professor Housner had been waiting patiently for something to happen in the developed countries of the world and under the auspices of the United Nations. Nothing happened except the holding of many meetings that produced no active action for reducing natural disasters of the world. Then Prof. Housner suggested that something be done only in the earthquake engineering community. The World Seismic Safety Initiative has been organized and accepted during the 10th World Conference on Earthquake Engineering held in Madrid in 1992. Only WSSI has mounted continuing efforts to promote the IDNDR in the world, particularly in developing countries.
Session Chair: Wilfred D. Iwan
Professor of Civil Engineering
California Institute of Technology
Director, Caltech Earthquake Engineering Research Laboratory
Closing Remarks by George W. Housner
C. F. Braun Professor of Engineering, Emeritus
California Institute of Technology