To a designer of a nonlinear structure, there is nothing more attractive than a real or fictitious ground motion time history whose response spectrum matches the target design spectrum. Frequency-domain scaled, design spectrum compatible time histories (DSCTH) are widely used in analysis and design of special structures, particularly seismic-isolated buildings. Their use has been even mandated by some code provisions. At the first glance, it seems that DSCTH records furnish designers of earthquake resistant structures with a consistency and compatibility bridge between the two very different worlds of elastic and inelastic response. Closer examination, as presented in this paper, reveal however that there are significant potential problems associated with uncontrolled use of DSCTH records in seismic design. It is shown that the use of design spectrum compatible time histories can lead to exaggeration of displacement demand and energy input. This in turn can distort the expected performance of the structure when subjected to design earthquake ground motions.

The 2009 NEHRP Provisions modified the definition of horizontal ground motion from the geometric mean of spectral accelerations for two components to the peak response of a single lumped mass oscillator regardless of direction. These maximum-direction (MD) ground motions operate under the assumption that the dynamic properties of the structure (e.g., stiffness, strength) are identical in all directions. This assumption may be true for some in-plan symmetric structures, however, the response of most structures is dominated by modes of vibration along specific axes (e.g., longitudinal and transverse axes in a building), and often the dynamic properties (especially stiffness) along those axes are distinct. In order to achieve structural designs consistent with the collapse risk level given in the NEHRP documents, we argue that design spectra should be compatible with expected levels of ground motion along those principal response axes. The use of MD ground motions effectively assumes that the azimuth of maximum ground motion coincides with the directions of principal structural response. Because this is unlikely, design ground motions have lower probability of occurrence than intended, with significant societal costs. We recommend adjustments to make design ground motions compatible with target risk levels.

Artículo de publicación ISIConcepción, near the southern end of the fault rupture zone of the offshore Maule, Chile earthquake, suffered signifi cant damage to all types of structures. Tall reinforced concrete buildings in the region were also affected, some severely. Spectacular collapse and partial collapse were experienced in two buildings, and many buildings had failure of thin shear walls that lacked suffi cient boundary element confi nement. Concrete spalling and crushing occurred and reinforcing steel buckled and were sometimes fractured

Artículo de publicación ISIThere are many modern tall buildings in Santiago that were subjected to the 27 February 2010 earthquake in Chile. Although there was not widespread damage in Santiago, there was notable damage to some tall concrete buildings that may have resulted from lack of proper detailing, the absence of 135° seismic hooks and inadequate confi nement of walls in the boundary zones. These caused buckling of the main bars and tension compression failure of the walls

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