Practical Lessons from the Loma Prieta Earthquake (1994) / Chapter Skim
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3. Buildings
3. Buildings
Pages 69-104
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From page 69... ...
Assuming these experts are correct, then results of a major earthquake close to a major urban area would be grim, and the Loma Prieta earthquake should be treated as a wake-up call. Because there were few surprises, it seems logical that knowledge of building performance in earthquakes has advanced to the point where we can forecast building performance in the next event based on lessons learned not only from Loma Prieta but from all past earthquakes.
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From page 70... ...
These lessons were extracted from the research report summaries and from discussions with practicing professionals familiar with the Loma Prieta earthquake. The paper does not focus on the details of research or observations but on what are perceived to be the major lessons.
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From page 71... ...
Legislation responding to the Loma Prieta earthquake required the California Seismic Safety Commission, in cooperation with the State Architect, to "develop a State policy on acceptable levels of earthquake risk for new and existing state-owned buildings and submit their policy to the Legislature for consideration by January 1, 1991." That document, Report No. SSC 91-1 (California SSC, l991b)
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From page 72... ...
After the Loma Prieta earthquake, the August 1990 Earthquake Engineering Research Institute newsletter reported that the National Science Foundation and the U.S. Geological Survey awarded approximately $4.1 million in grants to do various studies.
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From page 73... ...
Unfortunately, the mere availability of the knowledge does not necessarily transfer the knowledge or, in terms of seismic design, become useful in solving a design problem. Not all research is accepted out of hand, and it generally goes through a consensus process before it becomes an accepted theory.
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From page 74... ...
It should also be applied to the areas where the most impact can be gained. Illustrations of the role of research generated by the Loma Prieta earthquake were the CALTRANS tests of retrofit confinement for concrete columns.
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From page 75... ...
They are building high-use specialty structures and are doing the research to support their design concepts. The Loma Prieta earthquake has left many opportunities for research.
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From page 76... ...
Before the Loma Prieta earthquake, "earthquake proof" was still a term that was used. Post-earthquake things have changed.
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From page 77... ...
This law (SB 920) was signed by the governor about one month before the Loma Prieta earthquake.
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From page 78... ...
The Loma Prieta earthquake moved that evaluation from just the safety or collapse mitigation to the determination of the level of damage and, therefore, post-earthquake occupancy potential. This latter functionality requirement puts a strain on the level of knowledge of the engineering and research community.
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From page 79... ...
With the help of damage assessment volunteers and outside assistance from other agencies, the tagging of buildings for continued occupancy was accomplished. The tagging procedure and the lessons learned are discussed in Structural Engineers' Association of California (SEAC)
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From page 80... ...
It is paramount that those who have had to deal with this before share their information with those who may someday face the issue. A Question of Perspective Clearly the Loma Prieta earthquake introduced to the engineering community a genuine anomaly when it was found that a building could be not a "good" seismic performance structure although it was not heavily damaged.
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From page 81... ...
Interestingly enough, the city has been witness to some of the most intriguing engineering manipulations by competent engineers for finding ways to make beneficial use of that procedure. However, like the manipulation of the buildingperiod calculation in the more creative seismic design efforts, the procedure requires that one use the same logic before the earthquake as after the earthquake, thus resulting in consistent solutions.
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From page 82... ...
Evaluation of Risk: A Challenge The Seismic Safety Commission's acceptable risk could clearly be used as the scaling factor for the political bodies in determining what levels of risk are acceptable in the future, again taking into account return periods. Remembering
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From page 83... ...
This, however, is not the reality of the modern project, nor of the staffing capabilities of the average building department. The building official, without even considering the Loma Prieta earthquake, faces a difficult problem with both the plan checking and site inspections of buildings.
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From page 84... ...
Strong Motion Instrumentation The Strong Motion Instrumentation Program was the recipient of a major payoff in the Loma Prieta earthquake. The investment in instrumentation yielded numerous strong-motion records.
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From page 85... ...
Such information is vital to the total assessment of seismic risk to a community and would be useful in establishing priorities for funding as well as for mitigation programs. Some Perspective Regarding perspective on the interface between seismic design and the seismological experts, there does not seem to be any research being generated to identify the attributes mentioned above.
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From page 86... ...
This same group, the SEAC, has continued that effort year to year basically without funding and has continued to perfect a workable and effective code. It is not perfect, but while reflecting on the Loma Prieta earthquake and what did not suffer damage, it is appropriate to understand that the level of seismic safety was achieved not by accident but by the unselfish efforts of the engineering community with the help of active researchers.
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From page 87... ...
Good design, good construction, and good quality-control do result in high levels of performance despite the inadequacies some may claim exist in our knowledge of earthquakes. Breaking this down, it appears that for the Loma Prieta earthquake the requirements of the Uniform Building Code yield results consistent with its intent.
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From page 88... ...
The Loma Prieta earthquake taught the public that they can be affected dramatically by the simple closure of a building, which takes away their home, place of worship, or place of work. Given this perspective, functionality has become a new issue.
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From page 89... ...
The Profile of the Damaged Building This brings the discussion to where the focus of research on buildings is, especially in the post-Loma Prieta earthquake time frame. The hazards are clear, and the majority of the hazards are identifiable as unreinforced masonry, non-ductile concrete, and residential construction anywhere in seismic zone 4.
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From page 90... ...
Pre-Loma Prieta earthquake this was accepted, however, it is no longer professionally acceptable to fail to inform the owner of the realistic performance expectations of a design. Given this reality, owners are finding it difficult to retrofit at a functionality level, and without some financial incentives, the stock of truly historic buildings will be gone in the next major earthquake.
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From page 91... ...
Correlation with the recorded Loma Prieta earthquake results of actual building measurements should help with insight into this subject. Non-Engineered Structures A more difficult issue is facing the structures that have little or no engineered design and do not comply with the letter of the code.
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From page 92... ...
These results, compared with the findings of the Loma Prieta earthquake ground-motion data, should give a better understanding of the effectiveness, or lack thereof, of non-ductile frames. Extending the ground-motion data into other parts of the United States will prove useful.
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From page 93... ...
When viewing the shear wall damage, it is apparent that basic application of shear wall principles would have been a more effective mitigation measure than the application of more-complex code provisions. Stated another way: would the application of more-complex concrete shear wall provisions have improved the performance of buildings in the Loma Prieta earthquake?
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From page 94... ...
It would be unfortunate to have the data of this limited event extended to rationalize modifications in the basic approach to static design, which in fact demonstrated good results in the Loma Prieta earthquake. CONCLUSIONS Acceptable Risk For any location within the United States, there are data that describe the environmental earthquake risk as best we know it today.
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From page 95... ...
If the more complex structures use concepts not specifically stated in the code, how are officials to enforce compliance? There were numerous structures damaged in the Loma Prieta earthquake, which for legal reasons will go unnamed, and in which there were design or construction errors that technically should have been found within the purview of the building-department program.
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From page 96... ...
The findings published in a Report on Posting of a hazardous building might have some impact on the persons wishing to enter the building, but how would the hazard be reduced for those adjacent to the URM structure? The lesson is simple and well known; unreinforced masonry buildings are potentially hazardous.
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From page 97... ...
Ground Motion Data The focus on the instrumental data from the Loma Prieta earthquake is credible, but the research effort needs to be directed toward results that will benefit the knowledge of the designers of buildings throughout the United States. To this end, the prediction of the spectral characteristics of sites throughout the country would be a direct and needed goal.
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From page 98... ...
Report on the Loma Prieta Earthquake of 1989, Sacramento, California. California SSC.
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From page 99... ...
National Clearinghouse for Loma Prieta Earthquake Information: Catalog April 1991 Catalog November 1991 Catalog April 1992 Catalog November 1992 National Info....ation Service for Earthquake Engineering/Loma Prieta Project. Earthquake Engineering Research Center, 1302 South 46th Street, Richmond, California 94804-4698.
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From page 100... ...
Stephen Mahin, University of California, Berkeley The Loma Prieta earthquake provided the first major opportunity in two decades for the earthquake engineering profession in the United States to assess its design procedures. While the region of intense ground motion was relatively remote, significant motions did develop in the vicinity of many major engineered structures.
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From page 101... ...
While short-term reconnaissance style studies are carried out, few financial and personnel resources are available for sustained and directed engineering studies of these types. The Loma Prieta earthquake also raises many questions.
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From page 102... ...
William Holmes, Rutherford & Chekene We have heard many comments how, since the Loma Prieta earthquake, engineers have had to deal with policy makers or make policy themselves, much more so than ever before such as how to define performance objectives and acceptable risk. We need to settle some of these policy issues on where to put our mitigation resources.
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From page 103... ...
It is difficult to identify the extent to which the building has really been damaged. Lastly, the Loma Prieta earthquake brought to light a whole set of adjacency hazards.
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