UBC Theses and Dissertations
Nonlinear response of high-rise buildings: effect of directionality of ground motions Archila, Manuel
The response of high-rise buildings to strong ground shaking depends on ground motion parameters namely: intensity, frequency content, duration and horizontal ground motion directionality. The latter has been a concern to engineers for several decades in seismic design. The prediction of the direction where ground motion will hit the building is rendered difficult because in many regions faults are not mapped to a great extent, and for regions were fault locations are known accurate prediction of ground motion directionality is impeded because ground motions have unique wave propagation characteristics along its path. The purpose of this study was to evaluate the influence of ground motion directionality on the nonlinear dynamic response of a high-rise building. The influence of ground motion directionality was evaluated for a building case study. The building was 44 storey, and resembled general features of structural configuration commonly provided to reinforced concrete high-rise in Vancouver city. The nonlinear time history analysis (NLTHA) method was used to estimate seismic response of the building model to bi-directional ground shaking. This method was systematically applied for 40 ground motion component angles of incidence, which accounted for different ground motion directionalities ranging from 0 to 360 degrees. A suite of 3 pairs of horizontal ground motion representative of seismic hazard 2% in 50 years in Vancouver was considered for analysis. The ground motion directionality had significant effect over the calculated building seismic response. In some scenarios at critical angle of incidence the calculated floor displacements and interstorey drifts were 4 times as large as the displacements and drifts calculated for ground motion at 0 degrees angle of incidence. The largest building response envelope was obtained for several critical angles of incidence of the ground motion components. Critical angles of incidence were distributed over the entire building’s height. The relevance of ground motion directionality for seismic design of high-rise buildings was clearly demonstrated. The NLTHA used in conventional design practice still ignores ground motion directionality. It is concluded there is a need to develop the tools engineers can readily use to consider ground motion directionality in seismic design of modern high-rise buildings.
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