Abstract
Premature and simultaneous buckling of several steel braces in steel structures due to the prolonged duration of a seismic motion is one of the issues that must be addressed in the next version of Eurocode 8. In an effort to contribute towards the improvement of the seismic design provisions of Eurocode 8, an evaluation of the overall behavior of some steel building-foundation systems under the action of long duration seismic motions is performed herein by means of nonlinear time-history seismic analyses, taking into account soil–structure interaction (SSI) effects. In particular, the maximum seismic response results—in terms of permanent interstorey drifts, overturning moments and base shears of the steel buildings as well as of the permanent settlement and tilting of their foundations—are computed. It is found that the seismic performance of steel buildings when subjected to long duration seismic motions is: (i) acceptable for the two and five-storey fixed base steel buildings and for the two-storey steel buildings with SSI effects included; (ii) unacceptable for the eight-storey fixed base steel buildings and for the five and eight-storey steel buildings with SSI effects included. In all cases of steel buildings with SSI effects included, the seismic performance of the mat foundation, as expressed by the computed values of residual settlement and tilting, is always acceptable.
Highlights
Despite the fact that the effects of earthquake duration to damage of structures are well known [1], current seismic codes, e.g., Eurocode 8 [2], still make use only of spectral acceleration in order to define the design seismic load
It has been found out that the fixed base steel buildings fail in a total of three out of 33 cases studied, whereas the steel buildings founded on soil classes C and D, do not fail in any of the 66 cases studied
The fixed base steel buildings fail in a total of one out of 33 cases studied, whereas the steel buildings founded on soil classes C and D, fail in 42 out of 66 cases studied
Summary
Despite the fact that the effects of earthquake duration to damage of structures are well known [1], current seismic codes, e.g., Eurocode 8 [2], still make use only of spectral acceleration in order to define the design seismic load. The response/design spectrum is a snapshot of the total seismic response, providing the maximum value of the response index (displacement, velocity, acceleration) needed for a particular structure (in terms of its natural period) of interest considering its elastic or inelastic behavior. The duration is an important characteristic of earthquake ground motion and affects both the structural response and response of soils. Prolonged duration of earthquake ground motion is the decisive factor related to the fatigue and deterioration/degradation phenomena of structures and to the liquefaction and permanent displacements of soils. According to Trifunac and Novikova [5], the duration of earthquake ground motion depends on: (i) the duration of the rupture process (involves the released seismic energy, the ruptured area, the velocity of rupture and the shear wave velocity of the medium); (ii) the propagation path effects (through rocks or soft sediments); (iii) regional effects (topographic irregularities, trapped waves in a sedimentary basin) and (iv) local soil effects (geology of the recoding site)
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