SMIP 1989 Seminar

​The purpose of the Strong Motion Instrumentation Program (SMIP) is to improve methods to protect California citizens and property from earthquake-induced structural hazards. Toward this end, the program records strong earthquake shaking in structures and at ground response sites to obtain the data necessary for the improvement of seismic design codes. SMIP also promotes and facilitates the improvement of seismic codes through data utilization projects. The SMIP89 Seminar is a component of that effort.

Focal mechanisms affect the pattern of the peak accele​rations of the October 1, 1987 Whittier Narrows earthquake and its October 4 aftershock. The peak accelerations observed on 21 Strong Motion Instrumentation Program and 22 United States Geological Survey accelerograms correlates well with the ratio of shear wave amplitude computed from the thrust mechanism of the mainshock and the strike-slip mechanism of the aftershock. This correlation means that seismic energy is radiated from the fault with close to the standard double-couple radiation pattern at the frequencies 3 to 6 Hz corresponding to the peak accelerations.

The October 1, 1987, Whittier Narrows ML 5.9 earthquake produced a pattern of peak acceleration and intensity that showed a marked geographical asymmetry: the west and northwest regions had larger values than those to the east. A possible cause of this asymmetry was the earth's subsurface geological structure that managed to attenuate or defocus more severely the seismic waves that travelled east of Whittier than those travelling west or northwest. To investigate the subsurface S-wave structure we chose to consider a refraction profile generated by two natural sources, the Whittier Narrows earthquake and the July 8, 1986, North Palm Springs ML 5.9 earthquake, 135 km due east of Whittier Narrows. After analyzing strong motion data from the mainshocks, high-gain vertical seismograms of aftershocks, and synthetic seismograms we conclude that the strong motion data are consistent with a simple layered medium with a Poisson ratio of approximately 0.25.

This paper summarizes parts of a project that is concerned with an assessment of the damage potential of the ground motions recorded during the October 1, 1987 Whittier Narrows earthquake. Damage potential is defined here as the seismic demand imposed on building structures with due consideration given to representative structural response characteristics. The demand parameters considered in this study include strength demand, ductility demand, and energy and cumulative damage demands. The seismic demands are predicted from ground motion recordings, utilizing simplified elastic and inelastic bilinear SDOF structural models.

A study is made of the performance of two reinforced concrete bearing wall buildings subjected to recent California earthquakes. The buildings are analyzed to verify modeling techniques. The buildings are compared with similar buildings in Chile, and based on the comparison, conclusions are drawn from the Chilean practice regarding likely performance in strong US earthquakes. Design recommendations are made.

This study focuses on the correlation of analytical predictions with the measured seismic response of two reinforced concrete moment resisting frames during the October 1, 1987 Whittier Narrows earthquake. The first building is a five story warehouse with a flat slab and a perimeter frame and the second is a twenty story hotel with moment resisting frames in both directions. Both buildings have a regular, rectangular, symmetric layout. To study the seismic response three dimensional models of the two buildings were subjected to the accelerations recorded at the base. The study assesses the effect of modeling assumptions on the fundamental period and the response of the buildings.

The 1987 Whittier Narrows Earthquake (ML = 5.9) shook two dams, the Puddingstone and Cogswell Dams, which were instrumented as part of the California Strong Motion Instrumentation Program (CSMIP). The resulting recorded accelerograms provided a valuable opportunity to investigate and evaluate the accuracy and reliability of conventional geotechnical procedures for evaluation of dynamic response characteristics of earth and rockfill dams. This paper presents the results of these studies, which provide insight regarding current techniques for dynamic soil property evaluation and the applicability of one-, two- and three-dimensional analytical procedures to evaluation of the dynamic response of these types of dams.

Six earthquakes have ken recorded since 1980 on the overpass of Highway 101 at Painter Street in Rio Dell, California, just south of Eureka. Finite element models of the bridge have been constructed and the natural frequency results compared with the recorded motions. Analysis of the experimental data tends to identify the first six modes of vibration. Modeling the backfill-abutment- superstructure interaction is key to the analytical modeling to describe response. Torsional modes of vibration of the individual spans appear heavily influenced by the skew implying use of very simple bridge models should he approached cautiously for such short spans.

This research project is devoted to interpreting the earthquake time history response records of three buildings that experienced strong motion during two recent Southern California temblors. The earthquake response interpretation has been aided by the information obtained from the ambient vibration tests of these buildings as well as developing a linear finite element model of each structural system. In addition some cursory building response results have been gleaned from the spreadsheet analyses of these earthquake records. The buildings and the earthquake records include: a.) Palm Springs Desert Hospital - Roof level excitation of 0.62g was recorded during the 8 July 1986 Palm Springs earthquake. b.) Burbank Pacific Manor - Roof level excitation of 0.54g was recorded during the 1 October 1987 Whittier Narrows earthquake. c.) UCLA Math-Science Building - Roof level excitation of 0.l4g was recorded during the 1 October 1987 Whittier Narrows earthquake.