Displacement Demands Of Structures Research Articles

A Winkler-based model for inelastic response of soil–structure systems with embedded foundation considering kinematic and inertial interaction effects

In this paper, a parametric study is carried out on the ductility and displacement demands of structures with embedded foundation considering nonlinear soil–structure interaction (SSI). The soil–embedded foundation interaction is simulated using the beam on Winkler foundation concept. The bilinear behavior is also assumed for the equivalent single-degree-of-freedom (SDOF) structure. Effect of key parameters including fundamental period, level of inelasticity, soil flexibility, embedment ratio, and slenderness ratio on the seismic demands is examined. A family of soil–structure systems are analyzed subjected to a group of 33 ground motions recorded on alluvium deposits. Both sway and rocking components of foundation input motion are applied to the system. Results reveal that foundation embedment generally increases the ductility demand of the SDOF system. Moreover, the kinematic interaction (KI) effect on ductility demands is more prominent for structures with deep embedment ratios. As the aspect ratio increases, the role of rocking input motion on ductility and displacement demands becomes more noticeable. It is also concluded that the nonlinear SSI can increase the displacement demand of interacting systems as compared to the equivalent linear soil model. Based on the obtained results, a simplified expression is proposed to estimate the displacement ratio for soil–structure systems with embedded foundation considering KI effects.

Considering Soil-Nonlinearity Effect on Seismic Performance Evaluation of Structures based on Pushover Analysis

According to the most of current seismic codes, nonlinear soil behavior is commonly ignored in seismic evaluation procedure of the structures. To contribute on this matter, a pushover analysis method incorporating the probabilistic seismic hazard analysis (PSHA) is proposed to evaluate the effect of nonlinear soil response on seismic performance of a structure. The PSHA outcomes considering soil nonlinearity effect is involved in the analysis procedures by modifying the site-specific response spectrum. Results showed that incorporation of nonlinear soil behavior leads to an increase in displacement demand of structures which should accurately be considered in seismic design/assessment procedure. Results of implemented procedure are confirmed with the estimated displacement demand including soil-structure interaction (SSI).

C1 in Displacement Coefficient Method for Taiwan to Estimate Maximum Inelastic Displacement Demands of Existing Structures

ABSTRACTThe coefficient C1 in the displacement coefficient method of FEMA-273/356 is the modification factor to relate the expected maximum displacements of elasto-plastic inelastic SDOF systems to displacements calculated for linear response. It permits the estimation of maximum inelastic displacements from maximum elastic displacements for structures with known lateral strength (usually, the existing structures). Recently, an improved C1 has been presented in FEMA-440 because it was shown that the C1 in FEMA-273/356 underestimates the maximum inelastic displacement demands of structures significantly. However, the improved C1 in FEMA-440 was derived from the earthquake ground motions recorded in California. In addition, it was mentioned in FEMA-440 that “caution should be used when extrapolating the results presented in the report for ground motions and site conditions that differ”. Because the characteristics of earthquakes occurred in Taiwan are different from those occurred in California, the coefficient for used in Taiwan needs to be modified. The objective of this paper is to propose appropriate C1 for use in Taiwan.

Assessment of current nonlinear static procedures on the estimation of torsional effects in low-rise frame buildings

The capability of current nonlinear static procedures in capturing torsional effects was evaluated by comparing their estimates to the “exact” results, obtained from nonlinear response history analyses under a ground motion ensemble scaled to 3 different hazard levels. Two different types of eccentricities were considered. In the first case, the mass center of the floor of a symmetric plan structure was shifted in one direction to create a uni-directional eccentricity and in the other case a structure with a plan asymmetry in both horizontal directions was used. Results of numerical analyses show that far-fault and near-fault ground motions have similar influences on the displacement demand of structures as far as torsional effects are concerned. The recent nonlinear static procedures proposed for asymmetric buildings were found to be effective in capturing torsional effects whereas the classical nonlinear static procedure developed originally for planar systems significantly underestimates torsional rotation demands in structures.