Please use this identifier to cite or link to this item: http://hdl.handle.net/1946/12550
Response of linear-elastic structures to near-fault ground motions
Recorded earthquake ground motions in the near-fault regions have different and peculiar characteristics compared to that in the far-fault region. The main difference is a strong long period pulse in the velocity record due to forward directivity effects. This phenomenon can cause severe damage to flexible structures like high rise buildings. Seismic design codes are based on far-fault ground motion data and provisions for structures in near-fault regions are inadequate. In this study the main characteristics of near-fault ground motions are addressed. Time-history analyses are performed for linear-elastic steel frames of five different heights. The dataset used in this study contains acceleration records from 27 different earthquakes with total of 56 records. The near-fault strong-motion dataset used in this study was collected and processed by Rupakhety (2010). The time-history results of equivalent static storey forces for the frames differed increasingly from the linear distribution of equivalent static storey force method in EC8, as the total height of the frames increased. The Eurocode 8 (EC8) storey force distribution approximates the dynamic behaviour by considering only a single mode. Results from time history analysis suggests that for near-fault sites the linear distribution of equivalent static storey forces in EC8 might not satisfy the actual storey forces for the lower half of tall structures but for the upper half of structures the provision is excessive. Two models of storey force distribution are proposed for near-fault ground motion areas obtained by fitting a 5th and 3rd degree polynomials to the mean storey force distribution obtained from time-history analysis. The simpler of the two proposed models is tested with examples and proves to simulate storey forces better than the EC8 storey force method which is based on the response of the fundamental period of a structure.
Keywords: near-fault ground motion, forward directivity, time-history analyses, equivalent static storey forces, linear-elastic seismic response.