Stress-Strain Relation Models for Square Contined Reinforced Concrete Columns

为了评估受弯破坏钢筋混凝土构件的极限承载力和延性，必须采用能实际反映混凝土在最大应力后下降段范围内性能的混凝土轴向应力-应变关系模型。为了提出一个更符合实际的方约束钢筋混凝土柱的应力-应变关系模型，本文进行了两个系列的试验，第一系列试验中，15根150 mm × 530 mm高的方柱，每根方柱都有不同的方箍布置方式，只承受同心轴力。在系列1的基础上提出了应力-应变关系模型.考虑了环向约束对最大应力和最大应力处轴向应变的影响。该模型还考虑了方形约束的影响，采用截面核心混凝土折减系数。折减系数计算为核心混凝土有效约束面积与核心混凝土非有效约束面积的比值。在系列2中，8个一侧固定，另一侧自由的方形柱，每个180 mm × 500 mm高（加载部分），两种类型的系列1包含相同的箍布置，不仅受到高的轴力，而且受到剪切力和弯矩。系列2中的6个试件在水平千斤顶维持的2DY、4DY和8DY的恒定顶位移下承受偏心轴力，其中dy为受拉主筋的屈服位移。（系列2-1）。系列2的两个试样在恒定轴向力下经受水平剪切力（系列2-2）。利用所提出的应力应变关系，模拟了系列2的弯矩-曲率关系.

In order to evaluate ultimate strength and suctility of flexurally failing reinforced concrete members, the use of axial stress - strain relation models of concrete, which represent behaviors of concrete practically as far as in the range of descending part after maximum stress, will be necessary. In this study, two series of experiments were conducted in order to propose a more practical stress - strain relation model for square confined r/c columns.In series i, 15 square columns, each 150mm square by 530mm high, containing different arrangements of square steel hoops were to concentric axial force only. The stress - strain relation model was proposed based on the results of series 1. The increments of maximum stress and axial strain at maximum stress by hoop confinement were considered. The effects of square confinement were also considered in this model, using reduction factors of core concrete of sections. the reduction factors were calculated as ratios of area of core concrete confined effectively by hoops to that of core concrete confined not effectively.In series 2, 8 one side fixed and another side free type square columns, each 180 mm square by 500 mm high ( loaded portion ), containing same arrangements of hoops with two types of series 1 were subjected to not only high axial force but shear force and flexural moment. Six speximens of series 2 were subjected to eccentric axial force under constant top displacement of 2DY, 4DY and 8DY maintained by a horizontal jack, in which dy is a yielding displacement of tensile main bars. (series 2-1). two specimens of series 2 were subjected to horizontal shear force under constant axial force (series 2-2). The base moment - curvature relations of speciments of series 2 were simulated using the stress - strain relations proposed.