Prediction of spatially distributed seismic demands in specific structures: Ground motion and structural response

Abstract

The efficacy of various ground motion intensity measures (IM's) in the prediction of spatially distributed seismic demands (Engineering Demand Parameters, EDP's) within a structure is investigated. This has direct implications to building-specific seismic loss estimation, where the seismic demand on different components is dependent on the location of the component in the structure. Several common intensity measures are investigated in terms of their ability to predict the spatially distributed demands in a 10-storey office building, which is measured in terms of maximum interstorey drift ratios and maximum floor accelerations. It is found that the ability of an IM to efficiently predict a specific EDP depends on the similarity between the frequency range of the ground motion which controls the IM and that of the EDP. An IM's predictability has a direct effect on the median response demands for ground motions scaled to a specified probability of exceedance from a ground motion hazard curve. All of the IM's investigated were found to be insufficient with respect to at least one of magnitude, source-to-site distance, or epsilon when predicting all peak interstorey drifts and peak floor accelerations in a 10-storey RC frame structure. Careful ground motion selection and/or seismic demand modification is therefore required to predict such spatially distributed demands without significant bias.

Component correlations in structure‐specific seismic loss estimation

“…0.5x10x(10 -1)x9) and 495 correlation coefficients for the peak interstorey drifts and peak floor accelerations, respectively. The similar trends observed in the 9 different arithmetic means in each plot suggests that their is not an overly significant variation in the correlation vs. n fs trend for ground motion intensities resulting in elastic response through to collapse [23,24]. The solid lines provide simple piecewise linear fits to the data with equation inset in each figure.…”

“…The seismic loss estimation results presented are for a typical New Zealand 10 storey office building, and include losses resulting from damage of structural, non-structural, and contents components. Details on the seismic hazard, input ground motions and seismic response analyses can be found in Bradley et al [23], while component inventory data is given in Bradley et al [24]. The five different assumptions regarding correlations are: (i) all correlations zero; (ii) all correlations perfect; (iii) all bestestimate partial correlation; (iv) EDP|IM correlations perfect and DS|EDP and L|DS correlations zero; (v) EDP|IM correlations perfect and DS|EDP and L|DS best-estimate partial correlation.…”

“…one column for each ground motion and one row for each EDP i value being monitored), the correlation coefficient for EDP i and EDP j can then be computed by: The correlations of the N edp different EDP values being monitored are defined by a N edp x N edp symmetric correlation matrix with 0.5 N edp (N edp -1) unique correlation coefficients. Figure 2 illustrates the lower-triangular portion of the correlation matrix based on the seismic response analyses of the 10 storey office building discussed in Bradley et al [23,24]. In Figure 2, EDP numbers 1-10 are the peak interstorey drift ratios on floors 1-10, and EDP numbers 11-21 are peak floor accelerations on the 1 st -roof floors.…”

“…Such ground-motion independent methods therefore do not enable the computation of EDP|IM correlations as given in Equation (16). In the following paragraphs a simple EDP|IM correlation model is developed for multi-storey buildings based on the structural analysis results of Bradley et al [23,24] which can be used in conjunction with such ground motion independent simplified methods. Figure 3a and 3b illustrate the relationship between the correlation coefficient and the number of floors separation, n fs , (equivalent to j i EDP EDP  ) for peak interstorey drifts and peak floor accelerations, respectively.…”

“…In Figure 3a and 3b, each point is one correlation coefficient, and each dashed line is the arithmetic mean of the correlations for a specific IM level. The 50 ground motions, 21 EDPs and 9 IM levels used in Bradley et al [23,24] gives a total of 405 (i.e. 0.5x10x(10 -1)x9) and 495 correlation coefficients for the peak interstorey drifts and peak floor accelerations, respectively.…”