箍筋约束再生混凝土受压应力-应变本构关系模型

为获得箍筋约束再生混凝土受压应力-应变关系曲线，对17个足尺再生混凝土圆形截面柱进行轴心受压试验，再生粗骨料取代率为50%，加载应变率为(10-6~10-4)/s，主要变化参数为纵筋配筋率和箍筋约束水平。结果表明：箍筋约束再生混凝土的初始弹性模量主要与棱柱体抗压强度有关，棱柱体抗压强度越高，初始弹性模量越大；峰值应力在箍筋侧向约束下显著增大，提高幅度为侧向压应力的4.17~8.77倍，当箍筋提供的侧向压应力较小时，峰值应力增大程度较大，当箍筋提供的侧向压应力较大时，峰值应力增大程度较小；峰值应变随配箍水平增大呈增大趋势。基于试验数据，提出了箍筋约束再生混凝土受压本构关系模型，上升段与Mander模型一致，下降段中引入曲线形状参数，以调整曲线陡峭程度，结果表明，所提出的约束本构关系模型与试验曲线吻合良好，可较好地反映再生混凝土下降段较为陡峭的特点。

Stress-strain constitutive model for stirrup-confined recycled concrete under compression

In order to obtain the stress-strain curves of stirrup-confined recycled concrete under compression, axial loading tests of seventeen full scale recycled concrete columns with circular cross section were conducted. The replacement ratio of recycled coarse aggregate was 50% and the strain rate of loading ranged from 10^-6/s to 10^-4/s. The main test parameters were longitudinal steel ratio and confinement level of stirrup. The results show that the initial elastic modulus of stirrup-confined recycled concrete is related to the prism compressive strength, and the higher the prism compressive strength, the greater the initial elastic modulus. The peak stress increases obviously when the recycled concrete is confined laterally by stirrup, and the increase ranges from 4.17 to 8.77 times of the lateral pressure. When the lateral pressure is relatively small, the increasing amplitude is large. On the contrary, the increasing amplitude is small when the lateral pressure is relatively large. Moreover, the peak strain increases with the increase of the confinement level of stirrup. In this paper, the stress-strain constitutive model for stirrup-confined recycled concrete under compression was proposed based on the test data. The ascending branch was similar to that of Mander model and the shape parameters were introduced to adjust the steepness of the descending branch. It is found that the proposed model is in good agreement with the experimental curves, and reflects that the descending stage of recycled concrete is much steeper than that of normal concrete.