October Bulletin

NCEER BULLETIN


The Quarterly Publication of NCEER

Volume 8, Number 4, October 1994


Earthquake Site Response and Seismic Code Provisions

by Geoffrey R. Martin and Ricardo Dobry

This article presents the authors' review of events leading up to and recommendations resulting from an NCEER-supported workshop on earthquake site response and seismic code provisions. The three-day workshop was held at the University of SouthernCalifornia in 1992. The recommendations included new methods for classifying soil factors which, with minor modifications, have been approved for inclusion into the 1994 edition of NEHRP Seismic Provisions. Comments and questions should be directed to either Professor Geoffrey Martin, University of SouthernCalifornia, (213) 740-9124 or Professor Ricardo Dobry, RensselaerPolytechnic Institute (518) 276-6934.

Background

In current versions of design guidelines or codes for the seismic design of buildings, such as the 1991 NEHRP Provisions and theUniform Building Code, a site or soil factor is incorporated inequivalent lateral force equations based on standardized elasticresponse spectra. This format, which uses four soil factors inmost codes, is illustrated in figure 1.

The need to re-examine the soil categories and site factors (Sfactors) used in building code site response provisions arose dueto new research data developed since current building codeprovisions were formulated in the mid 1970's as part of an Applied Technology Council study (soil categories S1 through S3,except for S4 provisions, which were added following the 1985 Mexico City earthquake). Research by Seed et al. (1976) formed the basis for the site categories S1, S2 and S3. In addition, many concerns were expressed in relation to the appropriateness of existing definitions of site classes for site factors. Concerns included difficulties or ambiguities in classifyingsites using the given definitions, the lack of inclusion ofnonlinear or earthquake intensity effects on the S factors andthe need to include factors reflecting variations in short periodresponse. Extensive research data and new knowledge on siteresponse effects gained in recent years further highlighted theneed for revisions.

In October 1991, a workshop on the effects of site soilconditions on earthquake ground motions (supported by NCEER and chaired by Robert V. Whitman) was held at the State University ofNew York at Buffalo (Whitman, 1992). The timing of this workshop was considered particularly appropriate, in that the Structural Engineers Association of California (SEAOC) had recently madeplans for a major effort to review earthquake ground motion parameters for design and the Building Seismic Safety Council(BSSC) was beginning a cycle of effort leading to the 1994revisions of the NEHRP recommended provisions on seismic design. During the 1991 workshop, efforts were made to produce specific recommendations for changes to site effects provisions in current codes and additional related research to address the concerns expressed above. Questions considered included:

These questions were seen as fundamental to short term revisions to code guidelines planned for 1994. The workshop favored an approach that retained a small number of categories (no more than five), but with a matrix of soil factors for each category. This matrix could provide for factors such as the impedance contrast between the soil profile and the underlying rock, intensity of ground motion (non-linearity problem), nature of the ground motion (influence of possible source effects) and variation of site effects with spectral ordinate periods of interest. It was felt that this scheme permitted a reasonable and workable balance between over-simplicity and undue complexity. The matrix of soil factors for each site category could have two (or possibly three) columns corresponding to different periods on a response spectrum plot. Horizontal rows in the matrix would then give "corrections" for additional factors.

The 1991 workshop concluded that there was a need for studies to develop specific recommendations concerning soil factors. These studies should investigate the influence of a number of important parameters, so as to determine whether or not they have significant influence upon site effects. Significant factors could then be quantified for code-based design calculations.

Several research efforts related to the above needs were noted to be in progress at the time, including:

To effectively coordinate on-going research studies and to ensurethat maximum use was made of available results in the code-updating efforts of SEAOC and BSSC, it was recommended at the 1991 workshop and at the urging of Robert Whitman that acoordinating committee be formed. The following workshop attendees were designated as members of this committee: C.B.Crouse, R. Dobry, I.M. Idriss, W.B. Joyner, G. Martin and M.Power. The committee met at the end of the workshop to plan its future activities, which included subsequent meetings and a further workshop to address critical issues and to develop consensus recommendations to the BSSC. The November 1992 workshop was the outcome of the committee activities.

The 1992 Workshop

A three-day workshop, the NCEER/SEAOC/BSSC Workshop on Site Response During Earthquakes and Seismic Code Provisions, was held at the University of Southern California in November 1992. Theworkshop was the result of extensive planning by the above workshop committee. The workshop was sponsored by NCEER, SEAOCand BSSC, and was funded by the National Science Foundation, NCEER and the U.S. Geological Survey. Background material was mailed to all participants prior to the workshop, including:

The workshop was attended by over 65 participants from the geosciences, and geotechnical and structural engineering. In compiling a list of participants to invite to the workshop, the committee recognized the need to have representatives covering abroad range of disciplines and interests including:

Draft proposals for new site coefficients were presented at theworkshop by R.D. Borchert, R. Dobry and R.B. Seed and, although somewhat independent, showed similarities in many areas. With strong direction from breakout session moderators, a general consensus was developed during the final plenary session as to the direction in which modifications to existing code provisions should take.

The subsequent workshop recommendations are summarized in a memorandum prepared by Rinne and Dobry (1992) to a BSSC technical subcommittee. Extracts from this memorandum are used below in summarizing the workshop recommendations.

The recommended site categories were specified in terms of the average shear wave velocity in the upper 100 feet of a soil profile, as shown in table 1. Exceptions included soils with greater than a 10 foot thickness of soft clay and site conditions where site specific studies were recommended.

The proposed methodology for constructing response spectra is based on the current acceleration and velocity-based effectivepeak accelerations (Aa and Av) presented in maps 3 and 4 of the1991 NEHRP Provisions (for rock, assumed class B). However, the method could be easily modified for other spectral maps which may eventually be adopted in the provisions. The two-factor approach for constructing free-field acceleration response spectra is shown in figure 2. The anchor spectrum corresponding to thecurrent S1 spectrum from rock (class B) is modified by site coefficients applicable to short period motion Fa and long periodmotion Fv. It should be noted that these spectra are intended to cover the period range of about 0.2 seconds to 3.0 seconds, or the portion of the spectra controlled by nearly constant spectral acceleration and velocity in the classic Newmark-Hall method. The method does not address the period range between 0 and about 0.2 seconds, and thus cannot be used to amplify peak acceleration or other high frequency spectral values. The factors Fa and Fv are a function of Aa and Av, respectively, and of site classification as shown in tables 2 and 3.

 

 

The methodology, site classes, and spectral site coefficients Fa and Fv were based on draft proposals submitted to the workshop by three investigators: R.D. Borcherdt, R. Dobry, and R.B. Seed. These three draft proposals, developed independently but using the same general ground rules, took advantage of extensive research efforts by a number of researchers on the subject of site response, which intensified after the 1989 Loma Prieta earthquake and in preparation for the workshop. Analytical and empirical studies by K. Aki, R.D. Borcherdt, W.B. Joyner, W.Silva, M. Ordaz, R. Dobry, G.R. Martin, R.V. Whitman, J. Taylor, R.B. Seed, and I.M. Idriss played especially important roles in the preparation of the three draft proposals and in the discussions at the workshop.

It is appropriate to briefly review some of these studies and the role they played in defining the site classes and values of Fa and Fv.

W. Silva: Study of response of rocks of different stiffnesses. This study helped define site class A0 and the corresponding Fa and Fv.

K. Aki: Empirical studies of earthquake records, and especially the coda wave arrivals, which helped bound the Fa and Fv values at low levels of shaking for various site conditions.

R.D. Borcherdt: Empirical studies from nuclear ex-plosions and Loma Prieta records obtained on a variety of site conditions up to about 0.10 g peak acceleration on rock. These studies showeda consistent, although widely scattered, relationship between lowand high-period site response and average shear wave velocity inthe top 100 feet of the soil profile, which greatly influencedthe recommended site classes.

M. Ordaz: Empirical studies of records at more than 30 stationson soft clay obtained in Mexico City in recent years, whichconfirmed the influence of average shear wave velocity on siteamplification.

W.B. Joyner: Empirical studies of Loma Prieta records, which supplemented Borcherdt's results and added useful information about the influence of a soft clay layer thickness on low- and high-period site amplification.

R.B. Seed and I.M. Idriss: Very comprehensive analytical and empirical studies of site response of a number of site conditions. The analytical methods were empirically calibrated to the Loma Prieta strong motion records prior to their use for higher levels of shaking.

R. Dobry and G.R. Martin: A large number of analytical studiesof site response for a wide range of site conditions. Theseparametric studies were especially helpful in the evaluation of thickness boundaries for soft soils and exceptions needing sitespecific analytical studies.

R.V. Whitman and J. Taylor: Analytical site response studies,including parametric calculations and analyses of response ofsoil profiles representative for several U.S. cities.

These and other studies resulted in the three draft proposals presented by Borcherdt, Dobry and Seed at the workshop, which after verifying that there were no substantial differences between them were merged during the workshop into the consensus proposal described in figure 2 and tables 2 and 3. It is emphasized that the proposed values of Fa and Fv in tables 2 and3 for low Aa = 0.1 g(approximately) and Av = 0.1g (approximately) are firmly grounded in empirical results, especially from theLoma Prieta earthquake. At these low levels of rock acceleration, the values of Fa and Fv obtained from the empiricaland analytical studies agree well, and this provided acalibration point for the analytical techniques used (mostlyone-dimensional equivalent linear and nonlinear codes). On theother hand, the values of Fa and Fv at high Aa and Av such as 0.4g are mostly based on these calibrated analytical techniques.

While the Fa and Fv values of tables 2 and 3 appear to representa significant increase in the current S factors, this increase is less significant when compared to the relative spectral values for various conditions presently in the UBC and the NEHRPCommentary.

Some comment on the risk levels and uncertainties relative to the recommended method is appropriate. The method generally applies to the 90% probability of non-exceedance in 50 years that forms the basis for present codes. It does not, however, incorporatethe uniform risk approach used in the spectral maps. The areas of uncertainty and the method used in dealing with it can besummarized as follows:

1. Users of the current Aa and Av map values should recognize that these maps were prepared over 20 years ago, based on historical data available at the time and mean attenuation relationships that do not account for variability. In addition, the values are truncated to 0.40 g maximum. These effects may lead to unconservative results particularly in high seismic zones near active faults. Site specific studies are recommended within 10 km of an active fault to better evaluate near fault conditions.

2. The Fa values in table 2 generally represent mean values based on the limitations of the studies. There is considerable uncertainty at higher rock input motions due to limited empirical data and analyses. In addition, the degree of uncertainty in these values is not incorporated into the method which could have either over- or under- conservative implications depending on the site.

3. The Fv values in table 3 generally represent values of the mean plus about one standard deviation from the mean because the actual value is highly variable depending on the specific period being considered, site conditions and input motion. In the period range of highest site amplification (typically associated with resonance near the site period), the proposed Fv values are well below the mean, while at periods of relatively low amplification, they are much higher than the mean. The selection of mean plus one standard deviation was made to provide better protection for the high amplification period range although it is still below the mean based on both analytical and empirical results near the site period.

Conclusions

The recommendations described in this article, with some refinements, have been recommended by the BSSC for inclusion in the 1994 NEHRP seismic design provisions. (Refinements included complementary site category definitions based on standard penetration blowcounts and undrained shear strengths.) The site categories are now more clearly defined, and reflect the effects of nonlinear soil behavior as well as observational data from recent earthquakes. The site factor modifications clearly provide improvement to the short comings of the existing factors.

In commenting on the effects of the new provisions, Rinne (1994) noted that the main impact of the new site factors is the dramatic increase in soft soil amplification in areas of low seismicity throughout the country. The inclusion of the short period Fa factor will affect designs in all areas since the current code uses Fa = 1. However, the effect is particularly significant in low to moderate seismic areas. Rinne (1994) cites the example of the eastern part of the country characterized on NEHRP maps with Aa and Av less than or equal to 0.10 g. For this case, the equivalent static force with the new coefficients may increase 20 to 250 percent for short period structures and 20to 60 percent for long period structures depending on the soil conditions. On the other hand, the increase for structures in the highest seismic zones in the west is less than 10 percent. The reason for this is the nonlinearity of soil modulus and damping properties which decreases soil amplification at higher input motion.

References

Jacob, K., (1990) "Seismic Hazards and the Effects of Soils on Ground Motions for the Greater New York City Metropolitan Region", Geotechnical Aspects of Seismic Design of the N.Y.C.Metropolitan Area; Risk Assessment, Code Requirements and DesignTechniques, Metropolitan Section, ASCE, New York, N.Y., Nov.13-14, 1990.

Martin, G.R. editor, (1994), Proceedings, NCEER/SEAOC/ BSSCWorkshop on Site Response During Earthquakes and Seismic CodeProvisions, University of Southern California, November 18-20,1992, in preparation.

NEHRP, Recommended Provisions for the Development of Seismic Regulations for New Buildings, 1991 Edition, FEMA 222.

Rinne, E. and R. Dobry, (1992), "Preliminary Site Response Recommendations", Memorandum to Roland Sharpe, Chair TS-2, BSSC, December 11, 1992.

Rinne, Edward E., (1994), "Development of New Site Coefficients for Building Codes," Proceeding of the Fifth U.S. National Conference on Earthquake Engineering, Chicago, Vol. III, pp. 69-78.

Seed, H.B., C. Ugas, and J. Lysner, (1976), "Site DependentSpectra for Earthquake Resistant Design," Bulletin of theSeismological Society of America, Vol. 66, No. 1, February, 1976.

Whitman, R.V. editor, (1992), Proceedings from the Site Effects Workshop, University at Buffalo, October 24-25, 1991, Technical Report NCEER-92-0006, National Center for Earthquake Engineering Research, February 29, 1992.


Development of Reliability-Based Design Criteria by Y.K. Wen, H.H. Hwang, and M. Shinozuka

This article is excerpted from Development of Reliability-BasedDesign Criteria for Buildings Under Seismic Load, which is aforthcoming NCEER technical report. Comments and questions shouldbe directed to Professor Y.K. Wen, University of Illinois atUrbana-Champaign, (217) 333-1328.

Introduction

In designing buildings and structures to withstand seismic loads,code requirements and provisions have been traditionally based on experience and periodically revised after each disastrous earthquake. Most current code procedures define a single "design earthquake" corresponding to a prescribed probability of exceedance in a given period of time. Estimates of peak (oreffective) ground acceleration or related ground motion parameters are provided for the regions of interest. These groundmotion parameters are then multiplied by a series of factorswhich are determined largely based on judgment and experience and often calibrated in such a way that the resulting designs do not deviate significantly from the acceptable practice at this time.Therefore, despite their simplicity and ease of use, the current seismic design provisions oversimplify a complex problem; there are many inherent assumptions built into the approach which often are not easily understood by or are "transparent" to thedesigners. Another significant shortcoming is the inability toquantify the reliability of the final design; against either unserviceability or ultimate failure. In other words, the reliability of the structural system so designed is unknown and undefined. Building codes so far have been aiming at design based on life safety. Damage and economic loss suffered during an earthquake may be just as important an issue as life safety, a fact accentuated by the Northridge earthquake in SouthernCalifornia. A study has been carried out to address the problem of reliability in current code provisions, and develop and calibrate reliability-based design procedures. Some highlights of this study are summarized in the following article, details of which can be found in Wen et al. (1994).

Current Design Procedures

Some representative current code procedures used or recommendedin countries of high seismicity have been reviewed from the reliability point of view, including the Uniform Building Code (UBC, 1991) and Department of Energy (DOE) Design Guidelines (1990) in the U.S., Taiwan Code, Japan PRESSS Design Guidelines(1993), and New Zealand Code of Practice (1984). The emphasis of this review was on the risk criteria used in the selection of design earthquakes, and how safety and satisfactory performance requirements of the structures were incorporated into the procedure. The first three procedures are similar in that they are basically single-level design methods where life safety is the major concern. The DOE Guidelines, however, assign a different level of design earthquake to each of the four categories of buildings (including nuclear structures) accordingto the potential hazard in the event of failure and the proportionally reduced annual exceedance probabilities.

The last two procedures are two-level designs intended to ensure serviceability as well as life safety. Both have explicit provisions for enforcement of proper inelastic structural response behavior (capacity design). The PRESSS Guidelines represent the most recent effort of modernizing building design.The building is designed to form a strong-column weak-beamfailure mechanism. The basic philosophy of this design procedureis to avoid large plastic deformation, concentrate damage inlimited locations, and brittle failure (Otani et al., 1992). Unlike UBC and DOE, no importance factor is used and the performance of the structure is strictly enforced by the explicit consideration of adequate strength of the structure at various drift levels after the structure becomes inelastic (staticpush-over test). On the other hand, the risks of design earthquakes are not as clearly defined as in UBC and DOE. Current code procedures generally do not specify structural performance goals in terms of probability. The exception is the DOE Guidelines, in which a specific structural performance goal and a corresponding annual probability of failure to achieve the goal are given for each structural category.

Reliability Implied in Current Codified Designs

The procedures reviewed are similar in concept and format; the design base shears, however, vary greatly. Also the reduction factors for dissipating energy and ductility capability vary widely (by a factor as high as three) for different structural frames in the same building code and for the same type of frame in different building codes. The risk implication is obviously important but difficult to fathom in these code provisions. A larger base shear by itself does not necessarily mean safer design; neither does a stricter drift limit. Since seismic environments and construction practice in these countries are so different (e.g., use of interior frames to carry lateral loads in Japan and Taiwan, but not in the U.S.) and there are so many uncertainties associated with seismic loads, simple comparison ofdesign base shears or drift limits may lead to erroneous conclusions. The only rational method of assessing adequacy of code procedures is to take the loading environments and uncertainties into consideration and measure the degree of satisfactory performance of codified designs by the probabilityof reaching the specified limit states over a given time period. Some recent results are summarized in the following paragraphs.

A study of the reliability of steel frame buildings designed for seismic loads in accordance with UBC has recently been carried out (Wen et al. 1992). Two sites in Southern California were considered: Imperial Valley, 5 km from the Imperial Fault, and downtown Los Angeles. The future ground motions at the site were modeled as nonstationary random processes whose intensity andfrequency content vary with time. The parameters of the groundmotion depend upon the source, path, and site properties. Six low-rise steel buildings were designed according to UBC; (OMRSF,SMRSF, CBF, EBF, D/CBF, and D/EBF). One 5-story building using each of the above framing systems was designed for Zone 4 inaccordance with the 1988 UBC. The risks of limit states in termsof interstory drift thresholds being exceeded were evaluated for a time window of 50 years.

Parallel to the above effort, an investigation of the reliability of reinforced concrete structures in Japan designed according tothe 1993 PRESSS Guidelines, which are similar in concept to the1990 AIJ Guidelines with slight modifications, was also carriedout (Saito and Wen, 1994). The methodology follows that of Wenet al. (1992) with the same emphases on uncertainty in theseismic excitation. Two sites were chosen: Sendai and Tokyo. Twobuildings, one 7-story and one 12-story reinforced concretemoment-resisting frames, were studied. Figure 3 shows theresults. The reliability of a typical multistory steel frame building designed according to the Taiwan code and located inTaipei was also evaluated (Loh et al., 1994). The building haseight stories with four bays in the strong direction and three bays in the weak direction. Both SMRSF and EBF systems were considered. The construction details were according to practicein Taiwan. The treatment of the seismic risk and ground motionsat the site as well as the response analysis follow Wen et al.(1992). The results are also shown in figure 3. The comparatively much larger responses of the SMRSF building can be attributed tothe fact that the fundamental natural period of the building of1.6 seconds happens to coincide with that of the Taipei basin.

The above reliability evaluation of buildings designed according to current codes are based on analysis and calculation. Due to the extremely complex behavior of both excitation and response of the structures during earthquakes, these estimates represent results from one approach to this difficult problem. The reliability of the codified design can also be estimated from an entirely different approach based on the expected building performance as estimated by experts. These experts are experienced structural engineers who can give their opinions regarding building performance in future earthquakes based on performance and damage surveys of buildings in past earthquakes. Such a survey has been recently conducted by the Earthquake Engineering Research Institute for buildings designed according to the 1991 UBC (Holmes and Tubbesing, 1994). The results are used herein as conditional probability of damage given the occurrence of an earthquake, which in combination with the site seismic risk, provides a reliability estimate of buildings against damage and collapse. The resulting 50-year probabilities of exceedance of the five damage states for buildings designed according to UBC are shown in figure 4.

The 50-year probabilities shown in figures 1 to 4 can be described as performance curves of buildings designed in accordance with current code procedures in which the uncertainty in seismic loads and the structural system and nonlinear behaviors are properly considered. With the exception of the Imperial Valley site, the 50-year risk of the serviceability limit state (0.5% interstory drift) being exceeded is generally on the order of 0.5 (approximately 10^-2 per year). The ultimate limit state (1.5% drift) has a 50-year risk of 0.05 (10^-3 per year) or lower.

In a reliability-based design, target performance curves may be chosen based on the importance of the structure and the objective of the design is to ensure that such curves are satisfied at least at some key points corresponding to, for example, serviceability and ultimate limits.

Reliability-Based Bi-Level Design Procedure

With the exception of DOE guidelines, current code procedures generally do not set building performance goals in terms of probability. In view of the large uncertainty normally associated with seismic load, however, the performance of buildings and structures against future earthquakes can be assured only in terms of probability of the performance goal being exceeded. There is, therefore, an obvious need for design procedures in which the factors and coefficients are calibrated based on reliability. Also, although the majority of code procedures are designed only for life safety, the lessons learned from the Northridge earthquake have shown the importance of potential large loss due to content damage and interruption of service. Therefore, a bi-level or multiple-level design with consideration of the serviceability, ultimate and other limit states such as collapse is needed.

Within the context of the current code format, one can adjust the factors and coefficients in the provisions in such a way that the resulting design will have desirable (target) reliabilities against specified limit states. This is commonly referred to as "code calibration." In the current code procedures, the design earthquake is determined based on probability which obviously has an impact on the reliability of the design. In addition, the load factors which account for the overall uncertainty in the loading, the importance factor which accounts for the different levels of performance required of the buildings, and the drift limits, will also affect the reliability of the design. The design earthquake and these factors and limits are, therefore, the subjects for calibration. They are also interconnected as far as the overall reliability of the structure is concerned such that selection of one of these design values without considering the others may lead to inconsistent reliability. The only rational method of determining the design values is calibration according to explicit target reliabilities against specified limit states. Factors based on consideration of structural dynamics, soil condition, ductility capacity and so on should be risk neutral and not subjected to calibration.

Within the current code format, one can select key reliability-related factors as design variables represented by a vector X and proceed to the code calibration process by minimizing the difference between the target reliability and that of the design as follows (Wen 1993):

in which i refers to limit state and j refers to the type of structure under consideration; (ij is the weight assigned to each case; pij (x) is the probability of the i-th limit state of structure type j resulting from the design with the design variable vector X and is the target probability of the j-th limit state. In checking the safety of the design, it is most convenient to express the limit state function in terms of the load effect and structural resistance variables; or in other words, the reliability problem is formulated in the load effect space. In formulating the design criteria, however, it is more convenient to directly specify the criteria in terms of loads. In this case, the design variables X take the form of load and resistance factors and the above minimization would assure that the resulting load and resistance factors lead to designs which satisfy the target reliabilities for all limit states and types of structures under consideration as much as possible.

To illustrate the procedure, a simple design example is provided. The problem was to determine the load factors for dead, live and earthquake loads so the resulting design has reliabilities equal to the target values against serviceability and ultimate limit states, respectively. That is, the effort was focused on calibration of load factors, otherwise design procedures in the 1992 NEHRP provisions were followed. For simplicity, only one- and two-story, five-bay Special Moment Resisting Steel Frame (SMRSF) structures were considered. The site was in downtown Los Angeles. For the purpose of demonstrating the procedure, the dead load factor of 1.3 as recommended in the 1992 NEHRP provisions was used and the attention was focused on factors for live and seismic loads. The serviceability limit was chosen to be an interstory drift of 0.5% of story height and the ultimate limit was 1.5% of story height. Strictly speaking, a nonlinear programming solution procedure is required and the computation can become excessive since, in search of the minimum point, repeated designs and reliability evaluations are needed, dependent on the number of iterations required. To alleviate this difficulty, a response surface method was used which approximates the objective function by a second order polynomial and as a result, allows control over the calculations required (Wen 1993). In the analysis, the frames have been assigned equal weights and the ultimate limit state was assigned a weight ten times that for the serviceability limit state, reflecting the seriousness of the consequence of exceeding the limit states. In actual code calibration, the weights may be determined based on consensus among professionals experienced in assessing consequences of exceeding different limit states. The load factors obtained from the minimization of the response surface are shown in table 1 for a few selected combinations of target limit state probabilities. Note that each combination corresponds to specifying two check points in the target probabilistic performance curve that the structure has to satisfy. The load factors are seen to be more sensitive to the change in ultimate limit state probability, though it is also somewhat influenced by the serviceability limit state probability. In this example, the drift limits were not considered, which can also be included as a design variable for calibration since they usually play a dominant role in the reliability of multi-story buildings. Calibration including drift limits based on a population of low- to mid-rise steel buildings is currently under investigation.

Table 1: Load factors as functions of target 50-year limit state probability

Target for

Serviceability 0.30 0.30 0.50 0.50 0.70 0.70

Target for Ultimate

Limit 0.05 0.10 0.05 0.08 0.05 0.10

Live Load 1.00 1.00 1.00 1.10 1.00 1.00

Earthquake Load 1.35 1.18 1.28 1.20 1.24 0.68

References

Architectural Institute of Japan (AIJ), (1990), "Design Guidelines for Earthquake Resistant Reinforced Concrete Building Based on Ultimate Strength Concept."

Holmes, W., and Tubbesing, S., editors, (1994), "Expected Seismic Performance of Buildings," EERI Report.

Japan PRESSS Guidelines Working group (S. Otani, Chair), (1993), "Ultimate Strength Design Guidelines for Reinforced Concrete Buildings."

Kennedy, R.P., Short, A.S., McDonald, R.R., McCann Jr., M.W., Murray, R.C., and Hill, J.R., (1990), "Design and Evaluation Guidelines for Department of Energy Facilities Subjected to Natural Phenomena Hazards," UCRL-15910, United States Department of Energy.

Loh, C.H., Jean, W.Y. and Wen, Y.K., (1994), "Evaluation of Seismic Reliability of Steel Buildings in Taiwan," Second International Conference on Stochastic Mechanics, June 13-16, Athens, Greece.

New Zealand Code of Practice for General Structural Design and Design Loading for Buildings (1984), NZS 4203.

Otani, S., Kubo, T., Okada, T., and Nomura, S., (1992), "Outline of AIJ Guidelines for RC Buildings," Proceedings of the Tenth World Conference on Earthquake Engineering, Madrid, Spain.

Saito, T. and Wen, Y.K., (1994), "Seismic Risk Evaluation for Reinforced Concrete Buildings in Japan Designed in Accordance with the 1990 AIJ Guidelines," Structural Engineering Research Report No. 587, U. of Illinois.

United States Department of the Interior, USGS, (1988), "Probabilities of Large Earthquakes Occurring in California, on the San Andreas Fault," Open-File Report 88-398.

Wen, Y.K., (1993), "Reliability-Based Design Under Multiple

Loads," Structural Safety, Volume 13, pp. 3-19.

Wen, Y.K., Foutch, D.A., Eliopoulos, D., and Yu, C.Y., (1992), "Evaluation of Seismic Reliability of Steel Building Designed According to Current Code Procedures," Proceedings of the Tenth World Conference on Earthquake Engineering, Madrid, Spain.

Wen, Y.K., Hwang, H., and Shinozuka, M., (1994), "Development of Reliability-Based Design Criteria for Buildings Under Seismic Load," Technical Report 94-0023 National Center for Earthquake Engineering Research, University at Buffalo, August 1, 1994.


Users Group Established for IDARC Computer Program

by A. Reinhorn

NCEER has established a users group for interactive support in the use of the Inelastic Damage Analysis of Reinforced Concrete (IDARC) computer program. The users group will obtain support from the developers at the University at Buffalo and the University of Central Florida in the start-up operations and routine operation of the program. Users group members will obtain updates to the program. Based on feedback from users, the program developers will provide further improvements and enhancements which will be included in subsequent versions. The developers will provide limited assistance in the use of the program and some professional advice.

Members of the users group will receive the current version of the program along with a users manual and examples, as part of their membership. The users will be able to obtain updated versions of the program at a discounted fee.

A one-time enrollment fee will be charged for membership as follows: university and research institutional user fees are $275, commercial user fees are $550, and foreign users will be charged an extra $25 for shipping the materials.

The establishment of the users group also comes with the release of a new version of the program, IDARC2D - Version 3.1. This new version includes corrections to the previous programs based on feedback from previous users. Moreover, the new version includes the following new features:

The new version (i.e., Version 3.1) was developed for use on any of the following operating systems: PC/DOS, UNIX or VMS; note that there are special features in the PC/DOS version. This unified version was extensively tested with experimental data and other computer models. Technical information on this latest version is described in NCEER Technical Report NCEER-92-0022, IDARC Version 3.0: Inelastic Damage Analysis of Reinforced Concrete Structures (available from NCEER Publications for $15.00) and in the subsequent users manual.

New members of the users group will receive Version 3.1 as part of their membership. For additional details, contact Professor Andrei M. Reinhorn at the University at Buffalo, phone (716) 645-2114, ext. 2419, email: ciereina@ubvms.cc.buffalo.edu or Professor Sashi K. Kunnath at the University of Central Florida, phone: (407) 823-0176, email: kunnath@galileo.engr.ucf.edu.

The developers are currently working on a project to retrofit structures using supplemental damping. A future release, Version 3.2, will include modeling supplemental damping devices, i.e., fluid, viscoelastic, hysteretic and friction devices. This version is currently being verified using the results of recently completed shaking table experiments of a reinforced concrete structure equipped with various damping devices.


National Science Foundation Conducts Site Review of NCEER's Program

On October 20-21, NCEER hosted a mid-term review of its research and implementation activities. The review panel was selected by the National Science Foundation (NSF) and the Panel's mission was to advise the NSF on NCEER's plans and status for Years 9 and 10. Panel members were selected for their expertise in the field and included: Dr. Neil Hawkins, panel chairman, University of Illinois at Urbana-Champaign; Dr. Daniel J. Alesch, University of Wisconsin at Green Bay; Dr. Jean-Lou Chameau, Golder Associates; Dr. W.D. Liam Finn, University of British Columbia; Dr. Helmut Krawinkler, Stanford University; Dr. Stephen Mahin, University of California at Berkeley; Ms. Suzanne Dow Nakaki, Englekirk and Nakaki; and Dr. William Petak, University of Southern California.

Dr. Aaron Bloch, Provost of the University at Buffalo, welcomed the review team to Buffalo and spoke of the University's long term commitment to the engineering program. Dr. William Anderson of the National Science Foundation and Dr. Neil Hawkins, chair of the site review panel, set the stage for the review panel members by stating the panel's mission and outlining the agenda for the meeting.

NCEER Director Dr. George Lee and NCEER Deputy Director Dr. Ian Buckle presented an overview of NCEER activities. Research Accomplishments in selected project and program areas were then presented. Speakers and topics were: Dr. Daniel Abrams, Buildings; Dr. Tsu T. Soong, Protective Systems; Dr. Barclay Jones, Socioeconomic Issues; Dr. Tsu T. Soong, Nonstructural Components; Dr. Thomas O'Rourke, Lifeline Geotechnical Engineering; Dr. Masanobu Shinozuka, Lifeline Systems Analysis; Mr. Ronald Eguchi, Lifeline Societal Issues; and Dr. Ian Buckle, Highways. The next segment of the meeting featured Knowledge Transfer Accomplishments. Speakers and topics were: Dr. Ian Buckle, Standards and Guidelines; Dr. Tsu T. Soong, Industrial Partnerships; Ms. Patricia Coty, Information Service and Publications; Ms. Andrea Dargush, Education and Public Awareness; and Dr. George Lee, International Cooperation.

The Research and Implementation Plan for Years 9 and 10 was presented on Friday morning. In addition to the Research Accomplishments speakers noted above, Dr. Steven Horton spoke on Seismic Hazards and Ground Motion, and Dr. Masanobu Shinozuka spoke on Risk and Reliability. Dr. George Lee covered the Knowledge Transfer program.

Other meeting participants included Dr. S.C. Liu and Dr. M.P. Singh of the National Science Foundation, Dr. James Yao, Chairman of NCEER's Oversight Committee, Dr. Jose Roesset, Chairman of NCEER's Scientific Advisory Committee, Dr. Geoffrey Martin, Dr. Andrei Reinhorn, and Dr. Kathleen Tierney, members of NCEER's Research Committee, and NCEER senior staff members.

The panel spent Friday afternoon in an executive session and is expected to provide its recommendations to NSF in November.


Annual Principal Investigators Meeting

The annual principal investigators meeting was held at the University Inn and Conference Center in Buffalo, New York on October 28-30. NCEER Director Dr. George Lee welcomed the group to Buffalo and provided a brief overview of the National Science Foundation site review (see related article in this issue). He thanked the investigators for their cooperative responses to the numerous requests for information made by NCEER staff prior to the site review.

NCEER Deputy Director Dr. Ian Buckle then reviewed the many meetings and activities NCEER has been involved in during the past year. Among these were five workshops and six committee meetings, as well as the hosting of two meetings independent of NCEER - the Applied Technology Council (ATC) board meeting and ASCE's Technical Committee on Lifeline Earthquake Engineering Executive Committee meeting. He indicated that requests to NCEER for earthquake-related information has continued to increase. In partial response to these requests, the Information Service has participated in the development of a CD-ROM entitled "Earthquakes and the Built Environment," which was developed by NISC, Inc. as part of a cooperative venture between NCEER, NISEE at the University of California at Berkeley, and the Newcastle Earthquake Project, Australia, featuring each agency's respective databases (see section "News from the Information Service")

Next, Research Committee Chairman Masanobu Shinozuka discussed plans for Year 10. He stressed that investigators should concentrate on finishing incomplete research and encouraged development of monographs, workshops and other methods of knowledge transfer. He indicated that for the first time, investigators had been assigned to specific breakout discussion sessions, to better promote system integration between Project and Program areas.

The balance of Friday and Saturday were dedicated to technical breakout sessions. Sessions and session chairs included: Buildings, Dr. Daniel Abrams (Masonry) and Dr. Andrei Reinhorn (Concrete) for Dr. Peter Gergely; Lifelines, Dr. Masanobu Shinozuka; Intelligent and Protective Systems, Dr. Tsu T. Soong; Socioeconomic Issues, Dr. Barclay Jones; Nonstructural Components, Dr. Tsu T. Soong; and Risk and Reliability, Dr. Masanobu Shinozuka. Sessions were scheduled at alternating times to avoid overlap and to encourage multidisciplinary participation.

Following Saturday's breakout sessions, Dr. Ian Buckle presented an overview of NCEER's knowledge transfer activities. Some session chairs then presented brief reports regarding the research plan for Year 9 and any identified challenges discussed during the breakout sessions. On Sunday, participants resumed meeting in technical discussion groups.


Highway Seismic Research Council

NCEER hosted a meeting of the Highway Seismic Research Council (HSRC) on September 22-24 at the University Inn and Conference Center in Buffalo. The meeting was held so that the HSRC could review Year 1 progress and research results with Highway Project researchers, and to discuss the Year 2 research plan on the two FHWA-sponsored contracts (i.e., Seismic Vulnerability of Existing Highway Construction Project 106, and Seismic Vulnerability of New Highway Construction Project 112).

On Thursday, September 22, George Lee and Ian Buckle welcomed the HSRC and project researchers, and turned the meeting over to the HSRC co-chairs, Joanne Nigg and Joe Nicoletti. Members of the Highway Project Research Committee (HRC) provided overviews on each of the Year 1 and Year 2 research tasks in six technical sessions, and selected tasks were discussed in more detail by the respective task principal investigators. HRC member Maury Power introduced Session I on Seismic Hazard and Ground Motion; Ian Buckle led Session II on Performance Criteria, Structural Details, and Design Issues for existing construction; Geoff Martin introduced Sessions III and VI on Foundations and Soils for existing and new construction, respectively; Masanobu Shinozuka intro-duced Session IV on Analysis, Earthquake Protective Systems, Fragility, and Risk; and John Mander led Session V on Performance Criteria, Structural Details, and Design Issues for new construction.

An important aspect of the meeting was the presentation of the draft master plan on Project 106 by Ian Buckle. Project 106 consists of an interrelated series of tasks in each of the technical areas noted above. However, the final product of the project is intended to address the seismic vulnerability of all elements of the U.S. highway system as well as for the highway system as a complete network. The master plan attempts to provide a focus to each of the various tasks and individual research products into a three-volume seismic vulnerability and retrofitting manual. As presented by Ian Buckle, Volume I will cover the seismic risk analysis of highway systems, Volume II will cover the evaluation, assessment, and retrofit of highway bridges, and Volume III will contain the evaluation, assessment, and retrofit of tunnels, retaining structures, slopes and

pavements.

During the discussion of the master plan with the HSRC, it became clear that Volume II is the most well developed at this time. New research tasks in Years 3 and 4 will concentrate on studies to address the issues important to Volumes I and III and for which limited guidance is currently available.

HSRC members and project researchers participated in technical breakout sessions to further the discussions on each of the Year 1 and Year 2 tasks on September 23, and initiated discussions on the preliminary research plan for Year 3. The HSRC broke into its two groups (Coordination Group and Technical Group) and met in executive session on Saturday morning, while the researchers continued to discuss and coordinate the various research tasks and approaches. Prior to adjournment at noon on Saturday, the HSRC co-chairs briefly reviewed the concerns and recommendations that the two HSRC groups would be formally submitting via their written reports on the meeting. Based on these reports, it appears that the Highway Project is on schedule and, for the most part, proceeding according to plan. The HSRC did, however, make a number of suggestions that should improve the overall focus of, and products resulting from, the project.


U.S.-Hungary Cooperative Research in Earthquake Engineering

NCEER has signed a cooperative research agreement with the Technical University of Budapest, Hungary. Two researchers from Budapest visited the University at Buffalo and Cornell University in April, 1994. Dr. Peter Gergely, NCEER Research Committee member from Cornell University, finalized plans for the coordinated research program. Research will initially concentrate on simplified methods for including nonlinear dynamic effects in building codes.


Seismic Repair of Multi-Story Concrete Buildings

by M. Flett

On October 4, 1994, Michael Rojansky, vice president and group manager of EQE International, presented a seminar at the University at Buffalo entitled "Seismic Repair of Multi-Story Concrete Buildings," sponsored by NCEER. The seminar featured a discussion of the seismic evaluation and repair of two telecommunications buildings, one damaged in the 1989 Loma Prieta earthquake and the other during the 1994 Northridge earthquake.

Both structures were multi-story reinforced concrete shearwall buildings that featured irregularities. Damage to each building was illustrated with numerous slides. The repair program was complicated by the fact that each building was required to maintain full operations during the repair procedures. This necessitated stringent controls of dust, vibration, noise, and electromagnetic interference. In developing the seismic repair criteria, observed damage was calibrated with response spectra analyses based on acceleration records obtained at nearby locations. Additional design considerations included soil structure interaction, minimizing or removing various structural irregularities, pounding of adjacent buildings, and special investigations into the dynamic behavior of lightweight concrete shear walls.

For more information on this seminar, contact Dr. Rojansky at (415) 989-2000.


Fifth U.S.-Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures Against Soil Liquefaction

The Fifth U.S. Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures Against Soil Liquefaction was held September 29 - October 1, 1994 in Snowbird, Utah. Snowbird is near Salt Lake City, Utah, several kilometers from the Wasatch fault zone. This fault zone is considered to be the longest and most active normal-slip fault in North America.

The workshop was organized by Professor Thomas O'Rourke of Cornell University on behalf of NCEER and Professor Masanori Hamada of Waseda University on behalf of the Association for the Development of Earthquake Prediction (ADEP). In addition, members of the Utah engineering and scientific communities, especially T.L. Youd of Brigham Young University, S. Musser of the Utah Department of Transportation, and G. Christianson and W. Black of the Utah Geological Survey actively participated in the organization of the workshop.

Over 100 engineers, academicians and government officials participated in the workshop, representing the U.S., Japan, Canada, Mexico and Venezuela. Opening remarks were made by Professor K. Kubo, Vice President of ADEP and Professor Emeritus of the University of Tokyo and by Professor M. Hamada of Waseda University. Professor T.L. Youd of Brigham Young University welcomed the participants to the workshop. The workshop was divided into technical sessions as follows: Liquefaction and Lifeline Performance During Past Earthquakes, chaired by Professors K. Kubo, T.L. Youd, M. Hamada and T. O'Rourke; Mechanisms of Liquefaction and Large Ground Deformation, chaired by Professors I. Towhata, A. Elgamal, G.R. Martin and Dr. N. Yoshida; Liquefaction and Dynamic Response of Underground Structures, chaired by Professors S. Yasuda and H.E. Stewart; Mitigation of Earthquake and Liquefaction Effects, chaired by Dr. S. Iai and Mr. R.T. Eguchi; Lifeline Performance During Earthquakes, chaired by Dr. I. Katayama and Professor M. O'Rourke; and Liquefaction and Lifeline Performance During Earthquakes, chaired by Professor F. Miura and Dr. T.L. Holzer. Over 45 papers were presented in these sessions.

Workshop participants were taken on a field trip by the Utah Geological Survey to several trenches crossing the Wasatch fault zone, where evidence of previous surface faulting was preserved in the form of rupture planes and colluvial wedges in the walls of the trenches. This evidence is a striking reminder that the Salt Lake Valley is an active seismic area. Over 80 percent of Utah's 2.3 million residents live and work in the vicinity of the fault zone.

The Fifth U.S.-Japan Workshop was not only an international event, but a forum for engineers and utility personnel in the Salt Lake City area to learn about state-of-the-art developments and to participate in the presentations and discussions as experienced members of a community which must implement seismic resistant design of lifeline facilities and countermeasures for soil liquefaction.

The proceedings from this workshop will be available through NCEER in early 1995.

Workshop participants visited several trenches crossing the Wasatch fault zone where evidence of previous surface faulting could be observed.


Earthquake Education Activities in New York State

by Katharyn Ross

September 5, 1994 at 12:30 a.m. was the fiftieth anniversary of the Cornwall, Ontario - Massena, New York earthquake. According to Sam Jacobs, Massena resident, "I thought a giant had pulled up the house and was shaking it. The windows were rattling out of their panes and everyone was screaming because they were scared to death. Everyone on my street ran out in their nightclothes and were looking down at Alcoa Aluminum Plant because they guessed the Nazis had bombed the plant. Eventually, we had realized it was an earthquake." The event was a magnitude Mw = 5.8.

To commemorate this earthquake, a workshop for educators was held July 28-30, 1994 in Massena, New York. It was sponsored by NCEER, and cosponsored by the New York State Geological Survey, the New York Emergency Management Office, the National Earth Science Teachers Association, and the Science Teachers Association of New York State.

The workshop included group presentations on topics such as liquefaction in the St. Lawrence Valley, structural and nonstructural mitigation, and post-earthquake psychological stress. Hands-on sessions involved workshop participants in exercises on the built environment, soil-sand-water: the earthquake connection, using literature and music to teach about earthquakes, treating a class to creative tectonic lessons; and three earthquake damage tours one of Massena, one of Massena Center, and one of Cornwall, Ontario. Participants received a draft tour guide which included background on each stop and discussion topics that could result.

The workshop featured sixteen speakers from both the United States and Canada, including two Massena residents. Theresa Sharp, Massena Town Historian, talked about "Massena in the 1940's: Setting the Stage for the 1944 Earthquake" and Sam Jacobs shared his recollections of the event. Although the primary focus of this workshop was on the 1944 Cornwall-Massena earthquake, Dorothy Tao of NCEER's Information Service made a presentation on the Attica, New York earthquake of 1929 and Gary Nottis from the New York State Geological Survey made one on the Rockaway Beach earthquake of 1884.

The tour of selected damage sites in Massena included 16 stops. Among these were the First Baptist Church at the corner of Main and East Orvis Streets where cracks in the masonry can still be seen and the cemeteries on West Orvis and Beach Streets where rotated and shifted monuments can be observed. Investigations conducted by seismologists and geologists revealed that cemetery monuments were damaged in about 11 cemeteries in the Cornwall, Ontario - Massena, New York area after this earthquake. To assist educators in using cemeteries for meaningful lessons, workshop participants were given a guide sheet on what can be learned about earthquakes in a cemetery.

In addition to the workshop, a Town Meeting was held Thursday, July 28, 1994 at the Massena Town Hall Auditorium. Dr. Frank Revetta, Geology Professor at the State University of New York at Potsdam spoke about the local seismic network and earthquakes in the "North Country," Gary Nottis discussed the Cornwall-Massena earthquake, and Daniel O'Brien, from the New York State Emergency Management Office told attendees how to economically prepare for an earthquake by doing one thing every day of the week. Local residents that attended also shared their recollections of the Cornwall-Massena earthquake.

A final version of the tour guide with some accompanying lessons is being completed by the New York State Geological Survey and NCEER. A slide set is also being organized to accompany this guidebook. In addition, representatives of the Newburgh Free Academy have videotaped the workshop and are planning to make available, for a small fee, shortened versions of the workshop that highlight particular aspects, e.g., liquefaction. For more information, contact Katharyn Ross, NCEER, phone: (716) 645-3391.


NCEER Committee Meetings

Oversight Committee

The Oversight Committee met in Buffalo on August 8, 1994 to review NCEER's program in research and implementation and to provide guidance in the development of NCEER's long term plans. NCEER's Director George Lee, Deputy Director Ian Buckle and Research Committee Chairman Masanobu Shinozuka presented highlights from NCEER's research program. The Committee discussed the upcoming National Science Foundation site review and NCEER's role under the National Earthquake Hazard Reduction Program.

Scientific Advisory Committee

The Scientific Advisory Committee met in Buffalo on July 27-28, 1994. The Committee reviewed and discussed the Year 9 research and implementation plan, which incorporated comments and recommendations provided by the Committee to NCEER during the March meeting. Research Committee members were on hand to provide further discussion and information on the Year 9 plan.


First H. Bolton Seed Medal Awarded to I.M. Idriss

The H. Bolton Seed Medal, awarded by ASCE for the first time this year, will go to Izzat M. Idriss of the University of California, Davis, where he is a civil engineering professor and directs the university's Center for Geotechnical Modeling. Dr. Idriss also serves on NCEER's Highway Seismic Research Council.

Specifically, Dr. Idriss is being honored for his "outstanding contributions to teaching, research and practice in geotechnical earthquake engineering." Idriss, who worked for the firm of Woodward-Clyde Consultants for some 20 years, will present the first Seed Medal Lecture, in November 1995, at the University of California, Berkeley, where Seed was a member of the university's engineering faculty.

The Seed Medal was awarded for contributions to geotechnical aspects of earthquake engineering, an area in which the late Harry Seed, for whom the eponymous medal is named, accomplished pioneering advances.

- Reprinted with permission from ASCE News, August 1994.


M. Shinozuka Receives 1994 Theodore von Karman Medal

Dr. Masanobu Shinozuka, Chairman of NCEER's Research Committee, Received the ASCE 1994 Theodore von Karman Medal. Dr. Masanobu Shinozuka, Norman John Sollenberger Professor of Engineering at Princeton University, was awarded the 1994 Theodore von Karman Medal by the Engineering Mechanics Division of the American Society of Civil Engineers (ASCE). The medal is awarded in recognition of distinguished achievements in engineering mechanics that are applicable to any branch of civil engineering. Professor Shinozuka is the only person who has been honored by all three of the major awards associated with the Engineering Mechanics Division of ASCE. The other two awards are the N.M. Newmark Medal which was awarded to him in 1985, and the A.M. Freudenthal Medal in 1978.

Professor Shinozuka served as NCEER Director from 1990 through 1992. He is now chairman of the NCEER Research Committee. His research interests are reliability based structural design, stochastic continuum and discrete mechanics, structural analysis, design, and risk assessment under earthquake, wind and other natural and man-made hazards, numerical analysis of complex stochastic structural systems, and structural control. He was elected an Honorary Member of the ASCE in 1993, and elected to the National Academy of Engineering in 1978.


NCEER Technical Reports

Eight New Reports Reviewed

NCEER technical reports are published to communicate specific research data and project results. Reports are written by NCEER-funded researchers, and provide information on a variety of fields of interest in earthquake engineering. The proceedings from conferences and workshops sponsored by NCEER are also published in this series. To order a report reviewed in this issue, fill out the order form and return to NCEER. To request a complete list of titles and prices, contact NCEER Publications, University at Buffalo, Red Jacket Quadrangle, Box 610025, Buffalo, New York 14261-0025, phone: (716) 645-3391; fax: (716) 645-3399; or email: nceer@ubvm.cc.buffalo.edu. Abstracts from recently published reports are given below.

Seismic Energy Based Fatigue Damage Analysis of Bridge Columns: Part I - Evaluation of Seismic Capacity G.A. Chang and J.B. Mander, 3/14/94, NCEER-94-0006, 240 pp., $20.00

This is the first part of a two-part series on the seismic energy based fatigue damage analysis of bridge piers. This first part was concerned with the computational modeling of energy absorption (fatigue) capacity of reinforced concrete bridge columns by using a cyclic dynamic Fiber Element computational model. The results may be used with a hysteretic rule to generate seismic energy demand. By comparing the ratio of energy demand to capacity, inferences of column damageability or fatigue resistance can be made. A complete analysis methodology for bridge columns was developed. The hysteretic behavior of ordinary mild steel as well as high threadbar prestressing reinforcement - stability, degradation and consistency of cyclic behavior - is explained. An energy based universally applicable low cycle fatigue model is proposed. A hysteretic model for confined and unconfined concrete subjected to both tension or compression cyclic loading is developed. The model is also capable of simulating gradual crack closure under cyclic loading. A cyclic inelastic strut-tie (CIST) model is developed, in which the comprehensive concrete model stress-strain proved to be suitable. A fiber element based column analysis program UB-COLA is also developed, which is capable of accurately predicting the behavior of reinforced concrete columns subjected to inelastic cyclic deformations. The program is useful in predicting the failure model of high axial load columns. For shear critical columns, the cyclic inelastic behavior is accurately simulated through the CIST modeling technique.

Seismic Energy Based Fatigue Damage Analysis of Bridge Columns: Part II - Evaluation of Seismic Demand G.A. Chang and J.B. Mander, 6/1/94, NCEER-94-0013,164 pp., $15.00

This is the second part of a two-part series on the seismic energy based fatigue damage analysis of bridge piers. This second part deals with the determination of energy and fatigue demands on bridge columns. A smooth asymmetric degrading hysteretic model is presented, capable of accurately simulating the behavior of bridge piers. The model parameters are determined automatically by using a system identification routine integrated into a computer program OPTIMA. The program can use either real experimental data or simulated experiment results from a reversed cyclic loading Fiber Element analysis. An SDOF inelastic dynamic analysis program was implemented capable of using different hysteretic models. Spectral results were produced by using the smooth model presented which had been calibrated with full-size bridge column experimental data to determine global parameters to simulate column behavior. Design recommendations regarding the assessment of fatigue energy are made based on the results obtained through the nonlinear dynamic analysis. A complete methodology of seismic evaluation of existing bridge structures is proposed, which incorporated the traditional strength and ductility aspects plus the fatigue energy demand. The relevance of fatigue aspects for the seismic design of new bridge structures is also demonstrated. It is shown that the present code use of force reduction factors, that are independent of natural period, are unconservative for short period stiff structures. Recommendations are made for force reduction factors to be used in fatigue resistant design.

NCEER-Taisei Corporation Research Program on Sliding Seismic Isolation Systems for Bridges: Experimental and Analytical Study of a System Consisting of Sliding Bearings and Fluid Restoring Force/Damping Devices P. Tsopelas and M.C. Constantinou, 6/13/94, NCEER-94-0014, 220 pp., $20.00

This report describes the results of an experimental study of the behavior of a bridge seismic sliding isolation system consisting of flat sliding bearings and fluid restoring force/damping devices. Earthquake simulator tests have been performed on a model bridge structure both isolated with this system and non-isolated. The experimental results demonstrate a marked increase of the capacity of the isolated bridge to withstand earthquake forces. Analytical techniques are used to predict the dynamic response of the system and the obtained results are in very good agreement with the experimental results.

Generation of Hazard-Consistent Fragility Curves for Seismic Loss Estimation Studies H. Hwang and J-R. Huo, 6/14/94, NCEER-94-0015,172 pp., $15.00

This report presents an analytical method for generating fragility curves and corresponding damage probability matrix for structures subject to earthquakes. In the proposed method, seismic hazards, local soil conditions, and nonlinear building behavior are systematically considered, and all the uncertainties in seismic, site, and structural parameters are taken into account. For an illustration, the proposed method is used to generate fragility curves and damage probability matrix for Smith Hall on the main campus of the University of Memphis, which is located close to the New Madrid seismic zone. The expected damage cost is also estimated based on the 1993 replacement value of the building.

Sliding Mode Control for Seismic-Excited Linear and Nonlinear Civil Engineering Structures J. Yang, J. Wu, A. Agrawal and Z. Li, 6/21/94, NCEER-94-0017,112 pp., $15.00

Control methods based on the theory of variable structure system (VSS) or sliding mode control (SMC) are presented for applications to seismic-excited linear, nonlinear and hysteretic civil engineering structures. Emphasis is placed on continuous sliding mode controls using only the measured information from a limited number of sensors installed at strategic locations. Furthermore, controllers are proposed for applications to parametric control, including the use of active variable stiffness (AVS) systems and active variable dampers (AVD). Under suitable conditions, a complete compensation of the structural response can be achieved. Among the contributions of this report are the establishment of saturated controllers, controllers for static output feedback, parametric control, etc. The robustness of the control methods, the application of the static output feedback controllers, the control effectiveness in case of actuator saturation and the applicability to parametric control are all demonstrated by numerical simulation results. Applications of the control methods to linear buildings, fixed-based buildings with large ductility, base-isolated buildings using lead-core rubber bearings and elastic nonlinear structures are presented.

Study of Seismic Isolation Systems for Computer Floors V. Lambrou and M.C. Constantinou, 7/19/94, NCEER-94-0020, 216 pp., $20.00

The work described in this report concentrated on the development and testing of computer floor seismic isolation systems by utilizing devices of established effectiveness in the seismic isolation of buildings and shock isolation of military equipment. A computer floor system with a raised floor and a generic slender equipment was constructed. It was isolated by spherically shaped sliding bearings and was highly damped either by utilizing high friction in the bearings or by installing fluid viscous dampers. The spherically shaped bearings provided the simplest means of achieving long period in the isolation system under low gravity load. The isolation system prevented rocking of the cabinet on top of the isolated floor and substantially reduced its acceleration response in comparison to that of a conventional computer floor. An analytical study was also conducted in order to extend the results to a range of parameters which could not be tested.

Proceedings of the U.S.-Italy Workshop on Guidelines for Seismic Evaluation and Rehabilitation of Unreinforced Masonry Buildings

Edited by D. Abrams and G.M. Calvi, 7/20/94, NCEER-94-0021, 290 pp., $20.00

In an effort to assist in the development of engineering procedures for the seismic evaluation and rehabilitation of unreinforced masonry buildings, designed, if at all, for gravity loads only, this workshop volume compares the Italian and American experience in these areas. The intent of the workshop was to review hazard mitigation for URM buildings as a whole. Thus, workshop topics included architectural issues in building preservation and rehabilitation, development of Eurocode 8 and FEMA-BSSC-ATC-33, case studies of retrofitting projects and in situ testing methods for masonry construction. The workshop program called for introduction of each general topic, followed by the presentation of a paper on that topic from one Italian and one American participant, and by group discussion. Accordingly, this volume offers 16 paired papers, as well as the complete text of the workshop resolutions concerning future research and cooperation in this field.

NCEER-Taisei Corporation Research Program on Sliding Seismic Isolation Systems for Bridges: Experimental and Analytical Study of a System Consisting of Lubricated PTFE Sliding Bearings and Mild Steel Dampers P. Tsopelas and M.C. Constantinou, 7/22/94, NCEER-94-0022, 166 pp., $15.00

This report describes the results of an experimental study of the behavior of a bridge seismic isolation system consisting of lubricated flat sliding bearings and mild steel dampers. Earthquake simulator tests have been performed on a model bridge structure both isolated with this system and non-isolated. The experimental results demonstrate that the system is capable of maintaining the forces transmitted to the substructure at a preset limit, however at the expense of significant permanent displacements. Analytical techniques are used to predict the dynamic response of the system and the obtained results are in good agreement with the experimental results.

Technical Report Order Form

  Name    

  Address 

     

     

   City/State/Zip   

   Country     

   Telephone____________________Telefacsimile     


   Shipping Options:

   Third Class - U.S.                                  
First Class - U.S
    no additional charge)                                 
(add $3 per title)
   Surface International                               
Airmail International
        (add $5 per title)                                   
    (add $9 per title)

Report Number Authors Price Shipping Total Make checks payable to the "Research Foundation of SUNY" For a complete list of technical reports, call NCEER Publications at (716) 645-3391; fax: (716) 645-3399.


News from the Information Service

Earthquakes and the Built Environment Index on CD-ROM

by Patricia Coty

The culmination of years of work has resulted in a new computerized CD-ROM index to be published by NISC, Inc. this fall, Earthquakes and the Built Environment, which will include three databases: Quakeline (NCEER), Earthquake Engineering Abstracts (NISEE at U/C Berkeley), and Newcastle Database (Newcastle Earthquake Project, Australia). Earthquakes and the Built Environment provides 90,000 records drawn from these important files and from the collections of the research libraries at Buffalo and Berkeley. The various files can be searched concurrently (by default), individually, or in any combination. A valuable feature of the search software included on the CD-ROM is that any records that appear in more than one database are merged, so that search results do not contain duplicate citations.

Quakeline (1987-present) provides more than 25,000 citations and abstracts covering the literature of earthquake engineering and natural hazards mitigation. The NCEER Information Service at the University at Buffalo produces the database. About 4,000 records are added each year to Quakeline. Also included as a separate file on the CD-ROM are another 25,000 citations to the books, reports, journals and other materials on earthquake engineering and related subjects held in the University at Buffalo collection. Coverage is strong in the area of earthquake engineering hazards mitigation.

Earthquake Engineering Abstracts (1984-present) provides more than 25,000 citations and abstracts on earthquake engineering and earthquake hazards mitigation. The National Information Service for Earthquake Engineering (NISEE) maintains the database at the Earthquake Engineering Research Center (EERC), University of California at Berkeley. About 3,700 records are added each year. Also included as a separate file on the CD-ROM are another 12,000 citations to reports, monographs, serials, conference proceedings, slides, and videotapes contained in the NISEE library collection. Coverage on the 1989 Loma Prieta, California earthquake is particularly strong.

Newcastle Earthquake Database (1989-present), from the Newcastle Earthquake Project at the Newcastle Region Library of Australia, provides over 2,000 citations and abstracts specifically on the 1989 Newcastle earthquake. Coverage on structural and geological factors is strong, as is coverage on topics related to the earthquake's aftermath, such as counselling, reconstruction, and insurance.

The records included on the CD-ROM are bibliographic, not full text, and most contain abstracts. All items have location information, so that users can identify where to request a loan or photocopy of the desired material. The topics covered include earthquake engineering, earthquake prediction, natural hazards mitigation, planning and public policy; seismology; engineering seismology; wind engineering; seismometry; dynamic properties of soils, rocks, and foundations; structural dynamics; earthquake-resistant construction; tsunamis; effects and aftermath of earthquakes; properties of materials and components; socioeconomic aspects of disasters; relevant general theory and technique; seismic retrofit; earthquake preparedness; and other related subjects.

Source materials include journals, conference proceedings, technical reports, books, publications of worldwide academic, professional, and governmental organizations, archival records, building reports, codes, and standards, newspaper articles, slide sets, theses, videotapes, and software.

A high percentage of the Quakeline records are based on conference papers; this is balanced by a high concentration of journal literature in the Earthquake Engineering Abstracts database. The small incidence of duplication between the various databases is resolved by the publisher's software, which creates special composite records that provide all relevant information without the inconvenience of duplicate citations. The composite records contain the information shared by two or more source records, plus any data that is unique to a record, such as library location.

The CD-ROM can be used with any DOS-capable PC (IBM compatible), either single station or network, with 512k RAM available. Any CD-ROM drive will suffice.

Orders for the CD-ROM can be placed through NISC, Inc. at (410) 243-0797 or fax: (410) 243-0982. Or, contact Carol Kizis, NCEER Information Service, University at Buffalo, c/o SEL, 304 Capen Hall, Buffalo, NY 14260-2200, phone: (716) 645-3377; fax: (716) 645-3379; e-mail: nercak@ubvms.cc.buffalo.edu for additional details.


Bulletin Board

Engineering for Extreme Winds: 1995

A two and one-half day short course entitled Engineering for Extreme Winds: 1995 will be presented at Texas Tech University on February 1-3, 1995 by the Wind Engineering Research Center. The topics to be discussed include wind definition, wind-induced damage, interpretation of the ASCE 7-93 standard, discussion of changes proposed in the ASCE 7-95 standard and their effects on loads, design for hurricane winds, and design for tornadoes. A set of lecture notes, a copy of the ASCE 7-93 standard, and a guide to the use of the wind load provisions will be provided to each attendee. For additional information and application forms, contact Birgit Rahman, Division of Continuing Education, Texas Tech University, Box 42191, Lubbock, TX 79409-2191, phone: (806) 742-2352, or fax: (806) 742-2318.

Third International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics

The Third International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics will take place April 2-7, 1995 in St. Louis, Missouri. The confer-ence will provide a forum for geotechnical, structural and civil engineers, seismologists, geologists, and teachers in eng-ineering schools to discuss recent activity and advances that have been made in the 14 themes covered by the conference. For more information and registration materials contact the Conference Chairman Dr. Shamsher Prakash at University of Missouri-Rolla, Continuing Education Department, 103 ME Annex, Rolla, MO 65401-0249, phone: (314) 341-4200, fax: (314) 341-4992.

SSRC Proceedings Available

Orders are now being taken for the Proceedings of the 1994 Structural Stability Research Council 50th Anniversary Conference held June 21-22, 1994 at Lehigh University in Bethlehem, Pennsylvania. The 410-page book contains 27 papers by invited speakers from all over the world. The special anniversary conference theme was "SSRC - Link Between Research and Practice." Each session began with a keynote speech followed by presentations on topics germane to selected SSRC task groups and task reporters. The cost is $40 U.S. (SSRC members only); $50 U.S. (non-members), postage paid. To order, write to SSRC Headquarters, Fritz Engineering Laboratory, 13 E. Packer Avenue, Lehigh University, Bethlehem, PA 18015, fax: (610) 758-4522.

Bulletin of the New Zealand National Society for Earthquake Engineering

The Bulletin of the New Zealand National Society for Earthquake Engineering is dedicated to the advancement of the science and practice of earthquake engineering. The quarterly publication provides a forum for the exchange of ideas and expertise. The Bulletin is of interest to all those involved with earthquakes and their effects: engineers, scientists, architects, insurers, contractors, and the libraries they use. Papers for consideration are welcome.

For more information about the New Zealand National Society for Earthquake Engineering and/or the Bulletin, contact: The Secretary, New Zealand National Society for Earthquake Engineering, PO Box 312, Waikanae, New Zealand, phone and fax: (+644) 04-293-3059.

Pacific Conference on Earthquake Engineering (PCEE '95)

The Pacific Conference on Earthquake Engineering (PCEE '95) will take place on November 20-22, 1995 in Melbourne, Australia. The organizing committee invites authors to submit technical papers on fundamental, experimental, computational, and practical aspects of design and research topics in earthquake engineering. Areas of particular interest are: intraplate seismicity and zonation, soil response and soil-structure interaction, design in areas of low seismicity, seismic isolation, building codes, insurance, earthquake disaster mitigation, lifelines, retrofitting of existing structures, steel/concrete/timber/URM structures, nonstructural elements and components, and recent large/damaging earthquakes. Abstracts of approximately 300 words should be submitted no later than December 31, 1994. Authors should note their subject area at the top of the abstract.

For more information and registration forms, contact Barbara Butler, PCEE '95, PO Box 829, Parkville, Victoria 3052, Australia, phone: (+61) 3-344-6712, fax: (+61) 3-344-4616.


NCEER BULLETIN

is Published By:

National Center for Earthquake Engineering

Research State University of New York at

Buffalo Red Jacket Quadrangle Box 610025

Buffalo, NY 14261-0025

Editor: Jane Stoyle

Associate Editor: William Wittrock

Illustration and Photography: Hector Velasco

Production and Mailing List: Laurie McGinn

Administrative Support: Marjorie Buscher

Contributors:

P. Coty, NCEER Information Service

R. Dobry, Rensselaer Polytechnic Institute

I. Friedland, NCEER

M. Flett, NCEER Information Service

H. Hwang, Memphis State University

G. Martin, University of Southern California

A. Reinhorn, University at Buffalo

K. Ross, NCEER Education Specialist

M. Shinozuka, Princeton University

Y.K. Wen, University of Illinois