定/变轴力下墩柱剪切模型评估及抗震性能分析

Evaluation of shear models and seismic performance of RC columns under the constant/variable axial loads

关键词:  变轴力  RC墩柱  剪切失效模型  拟静力  抗震性能分析

Key words:  variable axial load  reinforced concrete column  shear failure model  quasi-static loading  seismic performance analysis

摘要:

近断层强竖向地震作用下,桥梁墩柱中产生的显著变轴力可能会削弱墩柱的抗剪性能,甚至导致墩柱发生剪切脆性破坏。然而,目前国内外常基于纤维模型研究竖向地震动对RC墩柱抗震性能的影响,忽略了墩柱的剪切退化性能；或基于定轴力假设得出的剪切模型研究强竖向地震下复杂变轴力对墩柱抗震性能的影响,导致采用不同剪切模型得出的结论差别较大。为此,基于已有定轴力和变轴力墩柱拟静力试验结果,评估3种代表性剪切模型的有效性并给出建议,包括基于强度的剪切失效模型和两种基于变形的剪切失效模型。另外,设计一组定/变轴力作用下墩柱拟静力对比模拟工况,分析变轴力对RC墩柱抗震性能的影响。结果表明:采用不同的剪切模型研究墩柱的抗震性能将产生较大区别,变轴力作用下这一差别更加明显；变轴力对墩柱抗震性能的影响主要表现为墩柱更早地发生剪切失效,且发生更严重的抗剪性能退化。本文为变轴力作用下墩柱剪切性能模拟提供了合理建议,为近断层RC墩柱的抗震性能评估及设计提供理论依据。

Abstract:

Under strong vertical earthquakes near-fault lines, significant variable axial forces generated in bridge RC columns may weaken the shear resistance of RC column and even lead to shear failure. However, current research both domestically and internationally typically focuses the influence of vertical ground motion on seismic performance of RC columns based on fiber models, neglecting the shear degradation performance of the columns. Alternatively, studies based on shear models derived from fixed axial force assumptions investigate the effects of complex variable axial forces on the seismic performance of columns under strong vertical seismic actions. This leads to substantial differences in conclusions drawn from various shear models. In this context, based on quasi-static cyclic loading column model tests under constant and variable axial load, the accuracy of three representative shear models is evaluated, including one strength-based model and two deformation-based failure models, and a suggested model was provided. Moreover, a new numerical quasi-static loading test under constant and variable axial load is designed to study the effect of variable axial load on the seismic performance of RC column. Results indicate that the seismic performance of columns obtained by using different shear failure models show great disparity, especially for the case of variable axial load. The influence of variable axial loads focuses on the seismic performance of RC column mainly manifests in earlier initiation of shear failure and severer shear degradation. This paper provides valuable insights for simulating the shear performance of columns under variable axial loads, offering a theoretical basis for the seismic evaluation and design of RC columns located in the near-fault region.