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Failure of one-story precast structures consisting of cantilever columns connected by simply supported beams was widely reported throughout the epicentral regions of the last devastating earthquakes in Turkey. As a single degree of freedom system, precast columns are designed by using the elastic spectrum given in the seismic code and by considering a seismic load reduction factor which takes into account the inelastic behavior of the columns under seismic loads. Although the existing seismic codes consider near-fault shaking effects in the development of elastic response spectra, they do not currently consider the increased inelastic demands that may occur during near-fault ground motion. The current study consists of nonlinear time history analyses of various hypothetical columns having geometric and mass properties which are being used in Turkish precast industry and the evaluation of damage indexes (DI) in terms of peak ground velocity (PGV) and peak ground acceleration (PGA) of the used strong ground motions. It is achieved that near-fault earthquakes create more damages on the columns. This might be one of the main reasons for the collapse of several one-storey precast buildings which were well designed according to the seismic codes in the district of existing faults. The obtained PGV versus DI charts prove that if one increase the sectional dimensions and/or longitudinal reinforcement ratio of the column, the possible damage from near-fault shaking effects could be reduced. 123 938 Bull Earthquake Eng (2010) 8:937-953 Fig.

Seismic isolation, with its capability of reducing floor accelerations and interstory drifts simultaneously, is recognized as an earthquake resistant design method that protects contents of a building along with the building itself. In research studies, superstructures of seismically isolated buildings are commonly modeled as idealized shear buildings. Shear building representation corresponds to an idealized structure where the beams are infinitely stiff in flexure and axially inextensible; columns are axially inextensible; and rigid floors are supported on these columns. Although it is more convenient to model and analyze a shear building, such an idealization may influence the seismic responses of seismically isolated buildings. This study presents a comparison of the seismic performances of seismically isolated buildings with superstructures modeled as shear buildings to those with full three dimensional superstructures. Both linear and nonlinear base isolation systems with different isolation periods and superstructures with different number of stories are considered.

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A variant of modal pushover analysis (VMPA) is presented to evaluate the seismic performance of the structures. The suggested procedure is based on an iterative process in which secant stiffnesses are used both at the element level and in the modal response. VMPA diverges from the existing modal pushover analyses for the following reasons: (1) mode compatible adaptive forces are applied to the structure at each iteration step, (2) the application of the equal displacement rule in combination with secant stiffness based linearization in the spectral displacement (S d )-spectral acceleration (S a ) relation eliminates the necessity to produce a modal capacity diagram for each mode. The displacement controlled algorithm determines the single ordinate of the modal capacity diagram corresponding to the target displacement demand for the nth mode (S dn_p , S an_p ) by reducing elastic spectral acceleration (S an_e ) to converge to the plastic acceleration (S an_p ). A Matlab based computer program known as DOC3D-v2 is developed to implement the proposed procedure. To verify the success of the suggested procedure, 9-and 20-storey LA SAC buildings are analysed, and the resulting demands are compared with several existing procedures, such as the extended N2, MPA and MMPA, as well as nonlinear time history analyses performed for two different set of acceleration records. VMPA yields enhanced results in terms of storey drifts, especially for the 20-storey LA building, compared with the other methods. Although the storey displacements and drifts are largely consistent with nonlinear time history analysis results, conservative estimates are obtained for the storey shear forces.Keywords Nonlinear static procedure Á Pushover analysis Á Adaptive pushover analysis Á Multi-mode analysis Á Higher mode effect