SMIP 2012 Seminar

A recently completed California Strong Motion Instrumentation Program (CSMIP) data interpretation project used recorded ground and floor motion data to evaluate a key ASCE/SEI 7-05 (and 7-10) equation for seismic design of acceleration-sensitive building nonstructural components. CSMIP motions from 73 earthquakes recorded in 151 fixed-base buildings were used in the evaluation. An improved equation was developed with two categories of revisions. First, the current code formula considers a linear relationship between the peak floor acceleration (PFA) and relative height of the component in the building with a roof PFA that is three times that of the peak ground acceleration. The analyses of the recorded motions showed that improved results could be obtained by using a nonlinear relationship and by considering both the building approximate period, Ta, and the level of ground motion. Second, the code formula considers a component amplification factor, ap, that takes values between 1.0 and 2.5 depending on the flexibility of the nonstructural component. Analyses showed that component amplification factor can be better represented using a three-segment spectrum composed of a linear rise from 1.0 to maximum value of ap at short periods, a flat segment with the maximum value of ap at medium range periods, and a nonlinear decaying segment at longer periods. The shape and amplitude of the spectrum was found to vary depending on Ta.

Kinematic soil-structure interaction (SSI) results from the incoherent nature of ground motions, which causes the motions of foundation slabs to generally be reduced from those in the free-field at high frequencies. We compare two models of kinematic SSI utilized in engineering practice: one based on finite element analysis and the second based on a semi-empirical approach. Predictions from both approaches are compared for two well-instrumented structures to observed transfer functions. The results show (1) the two models produce very similar transfer function estimates and (2) the model predictions are generally consistent with observations.

Seismic response records from the CSMIP database are used to formulate expressions for the expected value of damping ratios as a function of available regressors. The paper discusses the source of the high variance in the identification of damping and proposes mechanisms for the correlation between fundamental building frequency and damping as well as for the observation that damping increases with the mode number. The data analyzed is restricted to cases where the ground accelerations exceed 0.05g and the values obtained, not surprisingly, prove notably larger than those of previous studies, where very small amplitude vibrations were used. Reduced to the most basic observation the results show that the damping ratio of steel buildings (for linear but not ambient level vibration) is typically larger than the widely used 2%, while 5% is reasonable for concrete.

Modern performance-based seismic evaluation of buildings calls for nonlinear analysis of the structural system to estimate seismic demands and assess building performance. The availability of new software with expanded capabilities is gradually making it more feasible to conduct fully nonlinear simulations of building systems. However, at present, there are no readily available guidelines to aid a structural engineer in the process of building an appropriate nonlinear model of the system. As an initial step towards developing such guidelines, the suitability of three widely used computer programs (SAP2000, Perform-3D and OpenSEES) for seismic evaluation of buildings is investigated in this project by utilizing response data recorded from instrumented buildings and comparing the performance of different nonlinear models and methods in terms of their predictive abilities and response sensitivity to modeling choices. Preliminary findings from a preliminary set of simulations on a 9-story steel moment frame building are reported in this paper.

In this study we simulated and analyzed strong ground motion data recorded in the Humboldt Bay and Eureka areas during the M6.5 Ferndale area earthquake of January 2010. The scope of the presented work was two-fold. First, we investigated the main aspects of seismic wave generation and propagation, including kinematic rupture process and 3D wave propagation scattering. Our goal is to analyze their potential effects on seismic motion recorded at free field stations across Humboldt Bay and Eureka, and test the performance of a standard broadband strong ground motion simulation technique. Second, using non-linear site response analysis, we investigated the effects of shallow sedimentary layers on strong ground motion recorded by the Humboldt Bay geotechnical array. Our study provides insight into the composition of the wave field during the earthquake and an improved understanding of how the wave field is affected by the local 3D structure and the non-linear response of the shallow sediments of the Humboldt Bay..

The One Rincon Hill Tower in San Francisco is the tallest concrete core shear wall structure in California. After completion of the construction, the building was extensively instrumented in 2012 with 72 sensors in a joint effort by the California Strong Motion Instrumentation Program of the California Geological Survey and the National Strong Motion Program of the U.S. Geological Survey. This paper describes the sensor locations in the building and the instrumentation objectives. Data of the building ambient vibration obtained by the instrumentation system and results of preliminary analysis are also presented and discussed.

A 64-story, performance-based design building with reinforced concrete core shear-walls and unique dynamic response modification features (tuned liquid sloshing dampers and buckling-restrained braces) has been instrumented with a monitoring array of 72 channels of accelerometers. Ambient vibration data recorded are analyzed to identify modes and associated frequencies and damping. The low-amplitude dynamic characteristics are considerably different than those computed from design analyses, but serve as a baseline against which to compare with future strong shaking responses. Such studies help to improve our understanding of the effectiveness of the added features to the building and help improve designs in the future.

The need for functioning hospitals after a major earthquake is obvious and rarely disputed. While emergency field hospitals, medical tents, and air-lifts to available facilities are often used to supplement for damaged hospitals, they will never provide a sufficient substitute. Only modern health care facilities, located within the damaged region and capable of functioning at full capacity can adequately provide the needed medical assistance. The Health and Safety code requires insofar as practicable California hospital buildings to continue to provide services after a disaster and designed and constructed for forces generated by earthquake, gravity, and wind. While the expected operational performance of new hospital buildings can be estimated with a reasonable degree of accuracy, the performance of existing structural, non-structural and operational components are more difficult to ascertain. The degree of nonstructural damage or inherent structural damage can be difficult to ascertain immediately after a seismic event. Current seismic codes have come a long way since the start of seismic design. However there is a large inventory of the hospital buildings that predate modern seismic codes. Even hospital buildings designed with modern seismic codes have not been seriously tested in a large urban earthquake. With practical and monetary limits to laboratory testing, it makes sense to instrument hospital buildings to determine actual performance in an earthquake. There is also a need for use of the instrument recordings to provide automated damage indicators in these instrumented hospital buildings. Such instrumented damage indicators are required to supplement the traditional visual inspections immediately after a seismic event to make quick and reliable decision on whether to evacuate damaged buildings

The new Bay Bridge East Span is comprised of four major structures. From west to east they are: (1) the Yerba Buena Island Transition Structure, (2) the Self- Anchored Suspension Bridge, (3) the Skyway, and (4) the Oakland Touchdown Approach. The entire East Span is being targeted for opening on Labor Day weekend of 2013 (more information is available at http://www.baybridgeinfo.org). The entire structure is 3.5 km (2.2 miles) long.