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Case studies of damage to 19‐storey irregular steel moment‐frame buildings under near‐source ground motion

Earthquake Engineering & Structural Dynamics (Impact Factor: 1.9). 05/2007; 36(7):861 - 885. DOI: 10.1002/eqe.657

ABSTRACT This paper describes the three-dimensional nonlinear analysis of six 19-storey steel moment-frame buildings, designed per the 1997 Uniform Building Code, under strong ground motion records from near-source earthquakes with magnitudes in the range of 6.7–7.3. Three of these buildings possess a reentrant corner irregularity, while the remaining three possess a torsional plan irregularity. The records create drift demands of the order of 0.05 and plastic rotation demands of the order of 4–5% of a radian in the buildings with reentrant corners. These values point to performance at or near ‘Collapse Prevention’. Twisting in the torsionally sensitive buildings causes the plastic rotations on the moment frame on one face of the building (4–5% of a radian) to be as high as twice of that on the opposite face (2–3% of a radian). The asymmetric yield pattern implies a lower redundancy in the lateral force-resisting system as the failure of the heavily loaded frame could result in a total loss of resistance to torsion. Copyright © 2006 John Wiley & Sons, Ltd.

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    ABSTRACT: Currently, there is a significant campaign being undertaken in southern California to increase public aware-ness and readiness for the next large earthquake along the San Andreas Fault, culminating in a large-scale earthquake response exercise. The USGS ShakeOut scenario is a key element to understanding the likely effects of such an event. A source model for a M7.8 scenario earthquake has been created (Hudnet et al. 2007), and used in conjunction with a velocity model for southern California to generate simulated ground motions for the event throughout the region (Graves et al. 2008). We were charged by the USGS to provide one plausible realization of the effects of the scenario event on tall steel moment-frame buildings. We have used the simulated ground motions with three-dimensional non-linear finite element models of three build-ings (in two orthogonal orientations and two different connection fragility conditions, for a total of twelve cases) in the 20-story class to simulate structural responses at 784 analysis sites spaced at approximately 4 km throughout the San Fernando Valley, the San Gabriel Valley and the Los Angeles Basin. Based on the simulation results and available information on the number and distribution of steel buildings, we have recommended that the ShakeOut drill be planned with a damage scenario comprising of 5% of the estimated 150 steel moment frame structures in the 10-30 story range collapsing (8 collapses), 10% of the structures red-tagged (16 red-tagged buildings), 15% of the structures with damage serious enough to cause loss of life (24 buildings with fatalities), and 20% of the structures with visible damage requiring building closure (32 buildings with visible damage and possible injuries). This paper details the analytical study underlying these recommendations.
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