Stress-Strain Relation Models for Square Contined Reinforced Concrete Columns

为了评估钢筋混凝土构件的极限强度和塑性，有必要采用混凝土轴向应力-应变关系模型，该模型实际反映了混凝土在最大应力后下降部分范围内的行为。本文通过两组试验，提出了一种较为实用的方形约束钢筋混凝土柱应力-应变关系模型。在系列i中，15根方形柱，每根150mm × 530mm高，包含不同排列的方形钢箍，仅受同心轴向力。在系列1的基础上，提出了应力-应变关系模型。考虑了环箍约束的最大应力增量和最大应力下的轴向应变增量。该模型还考虑了方形约束的影响，采用了截面核心混凝土的折减系数。折减系数计算为受箍有效约束的核心混凝土面积与未受有效约束的核心混凝土面积之比。在系列2,8中，一侧固定和另一侧自由型方形柱，每个180mm方× 500mm高（加载部分），包含与系列1中两种类型相同的箍布置，不仅要承受高轴力，还要承受剪切力和弯矩。系列2的6个试件在水平千千顶保持2DY、4DY、8DY顶位移恒定的情况下承受偏心轴向力，其中dy为受拉主筋屈服位移。(系列2 - 1)。系列2的两个试件在等轴力作用下（系列2-2）承受水平剪切力。利用提出的应力-应变关系，模拟了系列2试件的基弯矩-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.