پاسخ دریفت لرزه ای سازه های فولادی با مهاربند الاکلنگی و کمانش ناپذیر
Abstract
1- Introduction
2- Seismic analysis of 3-D steel structures
3- Seismic response results
4- Synopsis and conclusions
Acknowledgement
Appendix A. Supplementary data
Research Data
References
Abstract
A numerical comparison study of the interstorey and the residual interstorey seismic drifts of steel structures equipped with the seesaw system and buckling-restrained braces is carried out. This investigation involves inelastic time-history seismic analyses of 2-, 5- and 8-storey 3-D steel structures, with specific orientation of columns and configuration of braces, for the design basis earthquake. The effects of soil-structure interaction and seismic incident angle are also considered in these analyses. Comparison of the seismic drift responses experienced by the seesaw-braced and the buckling-restrained braced steel structures, reveals different peak interstorey drift values but in many cases similar drift concentration along the height of the structures. Furthermore, the seesaw-braced steel structures exhibit, in general, larger peak residual drifts than buckling-restrained braced steel structures.
Introduction
After a major seismic event, the integrity of a structure, e.g. its capacity for immediate occupancy, should be certified via the explicit consideration of seismic response indexes such as the peak drifts. Focusing on steel structures, several studies, e.g. Ref. [1], have demonstrated the necessity to consider residual (permanent) drifts after an earthquake. Residual drifts, i.e. permanent drifts caused by yielding, permit the evaluation of the seismic performance of a steel structure regarding deformation and damage to its elements. In regions where repeated earthquakes can take place in a short period of time, the occurrence of a second or a third earthquake (not necessarily aftershocks of the first earthquake), increases the collapse risk of a steel structure if its residual drifts are significant [2]. The importance of residual drift has been also recognized as a key design parameter of novel seismic force resisting systems for steel structures, e.g., Refs. [3,4]. The limit value of 0.5% for residual drifts has been established as the threshold beyond which any repair of a structure is unfeasible in comparison to its rebuilding [5].
Over the past 20 years, buckling-restrained braces (BRBs) have shown an increased popularity in China, Japan, Taiwan, United States and other countries, as a primary force-resisting system for steel structures [6]. More recently, BRBs have also been applied for the seismic retrofit of older non-ductile structures [7]. BRBs, due to their stable and symmetric cyclic hysteretic response, have the advantage of developing full plastic strength in both tension and compression, providing, thus, significant energy dissipation and ductility without exhibiting strength degradation. The main disadvantage associated with BRBs is their tendency to cause storey drift concentration, i.e. accumulation of significant storey drifts in a few storeys without a more or less “uniform” distribution along the height of a structure, which inevitably leads to large residual storey drifts [8].