ML19260C073
| ML19260C073 | |
| Person / Time | |
|---|---|
| Issue date: | 11/02/1979 |
| From: | Jeng D Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML19260C066 | List: |
| References | |
| NUDOCS 7912180321 | |
| Download: ML19260C073 (9) | |
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EARTHOUAKE DAMAGE OBSERVATION REPORT BY DAVID C. JENG STRUCTURAL ENGINEERING BRANCH, DSS 1.
General Damage Descriotion The earthquake which struck.along a 150 mile band of the U. S. Mexico border caused most of the damages in the agriculturally rich Imperial Valley.
In El Centro, Mexicali and Brawley areas, walls buckled, ceilings fell in, gas and water lines ruptured. Several places along the All American Canal including irrigation lines and road ways were damaged. Some spots of moderate liquefaction were observed. Fires broke out. A highway bridge in Brawley area was extensively damaged. Mcbile homes toppled off their foundations and plate glass windows sprayed spears of shattered glass and many parapets of buildings fell off from the roofs. Severe damages occurred at the six story County Service Building in El Centro. About 40 to 100 people were injured, but apparently only three were hosoitalized, including a woman who suffered a heart attack. Preliminary monetary loss due to the earthquake was estimated to be 12-16 million dollars.
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Highlights of Structural Damaces County Service Building This building is a six story reinforced concrete building which is supported by peripheral columns with interior core shear walls. The most severe damages occurred at the first story level resulting in bursting / compression failures of the columns, and their supporting beams and slabs. The building was extensively instrumented for recording earthquake motions at various floor levels. The building may have experienced as high as 0.4g horizontal ground acceleration based on discussions with local building officials and O
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. con ting engineers. There appeared to be no failure of the building foundation which is primarily a friction type pile foundation supported by a 10 f t. thick layer of clay underlain by more than 50 ft saturated silt and sand layers. Level readings taken after the earthquake indicate no significant settlement of the pile foundation and no indication of lique-faction was observed in the general vicinity of the building.
Accoraing to Mr. John Hess, a local earthquake / soil engineering consultant, the.re was an eye-witness who was outside the building when the earthquake hit. The eye-witness observed a sequential failures o f the first story columns starting from the south-enst corner column of the building which is most closely oriented to the epicenter. Bursting / compression failures of the column base to floor junctions were accompanied by scalling of con-crete and fracture and ripping off of tie-bars and some vertical reinforcing steels. Failures were also observed at junctions of the column tops to beam girders and slabs at the 2nd story and upper levels especially at the east panel of the building.
The spalling/ compression failures of column base potentially raise a cuestion as to whether the placemthi of the tie bars ir. terms of their hooking angles, extension lengths and tie spacing; was adequa:e and met applicable require-ments of the 1963 ACi luilding Code which was said to be the reference code for the building design. The observed sequer tial failures of the columns tend to suggest a possible prt: dominance of h)rizontally tr?tvelling surface waves with destructive energy approaching from the south-eest corner dir-ections to the building. The time-delayed f111ures also may imply the "? "
effect and its accompanying torsional / rocking response widely treated in
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_:s the staff review of the Diablo Canyon OL application. This observed fact may also lead to a senario of torsional failure of the first story column due to the building's extremely low torsional resistance capacity arrange-ment. This can be partly attested by the fact that the eastern most panel of the building suffered the most severe damage (2-3 ft. tilting and settlement of floors) as compared to that of the west side panal where a N-S oriented shear wall along the edge of the building is provided.
Another implication of the sequential damage to the building on the staff's soil-structure interaction analysis position may pertain to the issue on wave patterns aporoaching to a structure (i.e., horizontally travelling shear waves vs vertically propagating shear waves). A more definite answer to this question can only be developed after results of related future studies are made available to the profession. According to one source, the building was also instrumented for measuring of torsional effects of earth-quake. If this is the case, then the data obtained should contribute to our future resolution of an issue regarding the need for designing nuclear power plants for torsional seismic inputs.
One additional item which could be suggested for post-earthquake research is to take core sa3.ples of the failed columns, beams and slabs to determine their "as built strength" and assess their impiciations on the building failure.
Two important preliminary lessons learned from this case are that:
1 Proper detailing of column ties and provision of adequate tie bqrs are absolutely necessary for a sound design of reinforced concrete structure, ii Provision of adequate peripheral (not interior core) shear walls in re'a.ced concrete structures is extremely important f,e an ear-..
.e resistant design of reinforced concrete structures.
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Steam Plant Tank Roof Failure Two tanks of the steam plant located on Dogwood Road in El Centro appeared to have failed due to sloshing effects of the tank fluid. The sloshing for:es caused bucklino failure of the steel roofs of the tanks. The sloshing motion appeared to have taken place with respect to an axis generally paralleling the f ault line. This sloshing orientation appears to imply that the energy of sloshing was transmitted primarily along a direction normal to the fault line which seems a reasonable occurrence for a location very close to the fault line'(near field case).
One key lesson learned from this damage is that the sloshing effect of tanks during an earthquake is an important factor requiring serious analysis and design consideration. The staff may need to reassess the adequacy of its present design criteria for seismic sloshing consideration and emphasize the importance of this review.
Steam Plant Damages to Seismic Lateral Sucocrts and Picing Several seismic lateral supports and struts were damaged during the earth-quake primarily at their connection points to other members providing lateral force resistance. It was indicated that the plant probably was des'gned for 0.29 seismic loads, however, based on the observed motions at the plant, it may have been subjected to motions of 0.3g to 0.4g ground acceleration. Itwasalsoindicatedthata4"/feedwaterpipewasbroken during the earthquake.
In general, however, the plant did not suffer major damages and stood fairly well against the earthquake, although some turbines have tripped due to the intense shaking.
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. - A seismoscope recording of the earthquake traces including those of the many after shocks was obtained. This recorded data are yet to be analyzed by researchers to shed important information of the steam plant response to the earthquake.
There was also an indication of some up lifting of one of the tanks at the steam plant which on its downward moving path crushed a pipe that happened to roll under the tank. This seems to indicate a fairly significant vertical acceleration and rocking motion of the tank to cause a separation of the tank base from the supporting floor.
Con ercial Building Damages in El Centro Many cocnercial/ residential buildings in El Centro were damaged to various degrees. Discussion and joint inspection with Mr. B. Johns of the City's Building Inspector covering the damaged area indicated that:
i Some 28 buildings including the County Service Building were severely damaged to require official condemnatien action, 11 Some additional 24 buildings were moderately damaged to the extent that the residents of these buildings were advised that their continued occupancy of the buildings would be at their own risk, although, official condemnation of the buildings will not be imposed. These damages need to be repaired for future safe occupancy.
iii Some additional 70 buildings suffered minor to moderate damages resulting in significant financial losses.
The follcwing represents typical damages suffered by those buildings in downtown El Centro area.
1 Collapse of columns and walls ii Collapse of roofs and separation of roofs from walls iii Fractures of slabs and beams iv Differential settlements of masonry columns and walls v
FC'ure of parapets and chiminies n
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. vi Cracking of walls and columns vii Cracking, tilting and settlement of masonry and brick, walls and columns viii Cracking and Settlement of sidewalks and paved roadways ix Shattering of windows and door glass It is important to note that most of the recently built one or two story masonry / brick buildings stood well against the earthquake primarily due to their compliance in design with present version building code requirements.
Older buildings seem to have suffered more damages then the newer ones, although some solidly built old brick buildings also stood well against the earthquake. After shocks, especially the larger ones (magnitude 4-5), may have in some instances exacerbated the damages of these buildings incurred during the first earthquake shaking.
Failure of Bridae Near Brawley A highway bridge failure primarily due to a failure in the bridge abutment witn slumping of the road way a;proach fills. It was not known as to whether the failure was caused by liquefaction of the abutment support medium or due to severe shaking of the abutment walls. Some other timber bridges of minor county roads also were reported to have failed during the earthquake.
Failure of Tanks of the Tank Farm Welds between the cylindrical shell and the base plate of some steel tanks at the tank farm were reported to have been ripped apart due to the intense up and down shaking as well as rocking motion of the earthquake resulting in some spillages of the oil. This damage should caution the NRC staff to adopt more rigorous analysis / design procedures in staff review of Category I tanks' design ade:aacy.
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Wavino Action Of Ground Surface Curina Earth:uake According to an eyewitness to the earthquake, who was thrown down to the ground by the earthquake, an extremely high frequency waving motion of the ground was literally observed during the shaking. He could feel that the earthquake energy was apprcaching him from the general epicentral direction.
This observation tends to attest to the existence of surface waves travelling near ground surface.
Sand Boils and Liouefaction Several sand boiling and !;quefaction phenomena took place on Herber road and along the all American Canal next to the Highway 98.
Irrigation canals and highways were damaged due to the soil failures although most of the damages were already repaired or in the process of being required. The attached map shows some key locations of this type of failures.
Faultino Trace Observation Obvious faulting traces can be observed at Herber road and at point near the intersection of highways 111 and 528 and other locations as marked on the attached map. The faulting widths were in the order of 6" to 10" and : lear trend of the trace can be observed across the flat agricultural field.
It appears that this type of soil medium failure experience would call for NRC staff's future emphasis in its review of Category I structural foundations with regard to potential hazard from medium instability failures. Particularly, in the SEB areas of review, more rigorous requirements regarding foundation mat and piling design analysis with due consideration of potential of liquefaction may have to be implemented.
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Preliminary Lessons Learned Which Are Imoortant To Future Safety Review Based on the above discussion of the earthquake damages, the following important points snould be properly considered and reflected in the future reviews of Category I structures:
i Proper placement of tie-bars for reinforced concrete columns, including its hooking arrangements, extension or embedment lengths, steel area and spacings, is one of the key factors to failure or non-failure of the columns during earthquake, therefore, strict adherance to applicable code requirements is indispensable to the structural safety. The SRP.should be revised to provide more specific requirements and criteria covering this aspect of design, ii Sloshing effects of fluids in a tank during earthquakes can cause fail-ures of safety related tanks and future staff review depth covering this area should be increased. The SRP should also be revised to provide more specific criteria and guidance on this subject to facilitate the
- review, iii Lay out of Category I structures should be encouraged to have a series of peripherally located sheer wall's. Use of peripheral open column support systems with interior core walls arrangements should be dis-couraged and when submitted by applicants for review, should be examined with utmost care and adequate analysis to ensure its structural safety against earthquakes, iv Records obtained in the County Service Building and the Steam Plant as r7 well as other free field records of the earthauake should be utilized, as 7-appropriate, in future formulation of related staff positions (e.g.,
+u ductility, surface wave and "15" effects, failure mode assessment of structures, soil-structure interaction analysis) and the need of a technical c
assistance program with this objective in mind should be develooed thru coordination among pertinent.NRR technical branches in the near future for implementing the objective.
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