Stiffness Of Structural System Research Articles

Implications of Bond-Slip in Inelastic Dynamic Responses of Degrading Structural Systems

The influence of bond-slip behavior, shown by pinched hysteretic curves in the inelastic response of degrading structural systems, is investigated in this paper. Inelastic response spectra are calculated and compared for deteriorating structures with and without manifestation of bond-slip. The response spectra are generated by using a smooth hysteretic model with distinct degrading parameters that are calibrated to the generic inelastic envelopes. In addition to the ductility demands, degraded residual strengths and stiffness of structural systems after an earthquake are considered as the relevant response measures. These measures can serve as design parameters for structures that should remain functional after an extreme event. Based on the response spectra analyses, it is found that nonlinear responses of degrading structural systems with bond-slip develop larger ductility demands and greater loss of strength and stiffness than the responses without bond-slip. Numerical results show that, ductility demand is increased up to 25–100% with consideration of slip in the model, as well as residual strength and stiffness decreased up to almost half.

Effectiveness of simple approaches in mitigating residual deformations in buildings

AbstractDevelopments in performance‐based seismic design and assessment approaches have emphasized the importance of considering residual deformations. Recent investigations have also led to a proposed direct displacement‐based design (DDBD) approach which includes an explicit consideration of the expected residual deformations as an integral part of the design process. Having estimated the expected residual deformations in a structure, engineers are faced with the problem of reducing them to meet the targeted performance levels under pre‐defined seismic hazard levels. Previous studies have identified the post‐yield stiffness as a primary factor influencing the magnitude of residual deformations in single degree of freedom and multiple degree of freedom structures. In this paper, a series of simple approaches to increase the post‐yield stiffness of traditional framed and braced systems for the purpose of reducing residual deformations are investigated. These methods do not utilize recentring post‐tensioned technology. This contribution addresses the feasibility of altering the lateral post‐yield stiffness of structural systems by: (i) using different reinforcement materials with beneficial features in their stress–strain behaviour; (ii) re‐designing the section geometry and properties of primary seismic‐resisting elements; and (iii) introducing a secondary elastic frame to act in parallel with the primary system. The efficiency of each of these techniques is investigated through monotonic and cyclic moment‐curvature and non‐linear time‐history analyses. Of these approaches the design and introduction of an elastic secondary system was found to be most effective and consistent in reducing residual deformations. A simplified design approach for achieving the desired increase of a system's post‐yield stiffness is also presented. Copyright © 2007 John Wiley & Sons, Ltd.