考虑梁轴向约束效应的RC梁柱节点受力机理及抗震性能试验研究

钢筋混凝土（RC）框架梁受弯损伤会发生轴向伸长，周边构件（抗侧力构件、现浇板）对梁伸长的约束作用会在梁中产生不可低估的轴力，从而影响梁柱构件和节点的抗震性能以及结构的强震破坏模式。分析了梁中约束轴力对节点抗剪受力机理的影响，设计了6个1/2比例的RC梁柱子结构试件，采用可直接量测约束轴力的等效约束装置代替周边构件对梁伸长的约束作用，通过低周往复加载试验考察了梁轴向约束效应对节点抗剪需求、抗剪承载力以及损伤破坏模式的影响。结果表明，约束轴力对抗剪需求的影响比抗剪承载力的影响明显，梁轴向约束效应产生的轴力较大，且随梁弯曲变形的增大而增加。与无约束试件相比，考虑梁轴向约束效应的试件节点抗剪需求增大了1.14~2.22倍，节点区斜裂缝宽度较大，损伤情况更加严重。

EXPERIMENTAL INVESTIGATION OF BEAM ELONGATION EFFECTS ON THE MECHANISM AND SEISMIC PERFORMANCE OF RC FRAME JOINTS

Reinforced concrete(RC)beams tend to elongate after flexural cracking and yielding.The elongation is restrained by the surrounding structural components in the RC frame and therefore axial comprehensive force is formed.The seismic performance and failure modes of RC frame joints are affected by the unexpected axial compressive force.The influence of axial restraint force on the shear transfer mechanism of the joints was analyzed.Six 1/2-scale RC beam-column subassemblies,four of which were restrained by an equivalent device,were tested under cyclic loading to study the impacts of the beam elongation on the seismic shear demand,strength and failure modes.The results show that the beam elongation effects on the seismic shear demand were more obvious than those on the strength.The beam elongation caused large compressive axial force in beams with the increase of the beam bending deformation.Compared with the unrestrained specimens,the shear demand of the joints due to the axial restraint force was increased by 1.14~2.22 times.The widths of the inclined cracks in the joint area were larger,and the damage to the joints were relatively more serious in the axially restrained specimens.