轴力对RC中间节点抗震受剪承载力影响规律分析

ANALYSIS ON THE INFLUENCE OF AXIAL FORCE ON SEISMIC SHEAR CAPACITY OF RC INTERIOR JOINTS

  • 摘要: 对钢筋混凝土(RC)梁柱节点进行抗震受剪承载力计算是确保节点抗震性能的关键措施,我国《混凝土结构设计规范》(GB 50010−2010)的计算公式考虑轴力影响时目前暂时采用权宜性做法,其原因在于轴压力对节点受剪承载力的影响方式复杂、已有研究成果尚未充分澄清其影响规律。在OpenSees平台上,对梁柱节点单元(Beam-Column Joint Element, BCJE1)模型、考虑斜压杆双向应力扩散效应的BCJE2模型,以及将节点区离散为斜向混凝土压杆、水平及竖向钢筋弹簧的MBCJE模型的适用性进行了校核;选取合适的梁柱组合体原型试件,通过系列变化轴压力,采用模拟效果更优的MBCJE模型、BCJE2模型对RC节点及梁柱组合体进行参数分析。分析结果表明,节点剪压比\nu 高(\nu \geqslant 0.3)时,节点损伤较严重,增大轴压力会降低组合体的延性,且轴压力较大或较小时轴力对节点峰值剪应力的有利影响均明显降低,GB 50010−2010的节点抗震受剪承载力计算式未充分考虑该特点,存在隐患;节点剪压比中等(0.2 \leqslant \nu < 0.3)时,按GB 50010−2010的计算方法考虑轴压力的有利影响基本可行,但轴压比较小时宜适当提高节点配箍;剪压比较低的节点(\nu < 0.2)可按GB 50010−2010的受剪承载力计算方法确定节点配箍。

     

    Abstract: Calculating the seismic shear capacity of reinforced concrete (RC) beam-column joints is a key measure to ensure the seismic performance of the joints. The calculation formula in the Code for Design of Concrete Structures (GB 50010−2010) temporarily adopts an expedient method when considering the influence of axial force, which is related to the fact that the influence of axial force is complex and the existing research results have not clarified the effect of axial force. On the OpenSees platform, the applicability of the Beam Column Joint Element (BCJE1) model, the BCJE2 model considering the bidirectional stress dispersion effect of diagonal compression member, and the MBCJE model which discretizes the joint area into diagonal concrete compression members, horizontal and vertical steel bar springs, have been calibrated in this paper. The appropriate prototype of beam-column sub-assemblage specimens were selected, and the BCJE2 and MBCJE models with better simulation results were used to perform the parametric analysis of RC joints and beam-column sub-assemblage through a series of changes in axial load. The results show that when the shear-compression ratio of joint \nu is higher (\nu \geqslant 0.3), the joint damage is serious; increasing the axial load will reduce the ductility of the sub-assemblage, and the beneficial influence of the axial load on the peak shear stress of the joint will be significantly reduced when the axial compression load is large or small. The formula for calculating the seismic shear capacity of the joint in GB 50010−2010 does not fully consider this relationship, and there is a potential problem. When \nu is medium (0.2 \leqslant \nu < 0.3), it is generally feasible to consider the beneficial effect of axial force according to the calculation method of GB 50010−2010, but the stirrup of joint should be appropriately increased when the axial compression ratio is small. When \nu is low (\nu < 0.2), the stirrup of joints can be determined according to the calculation method for the shear capacity of joint in GB 50010−2010.

     

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