室内环境下UHPC非线性徐变特性研究

Experimental Study on Nonlinear Creep of UHPC in Indoor Environments

为研究超高性能混凝土(UHPC)非线性徐变阈值与特性,对不同初始龄期加载与应力比的圆柱体UHPC试件开展室内环境下徐变试验,测试试件在加载100 d期间的轴向与环向应变。根据试验结果,计算UHPC在不同应力比下的徐变系数、非线性徐变放大系数与名义泊松比,分析普通混凝土非线性徐变放大系数模型对UHPC的适用性,得到适用于UHPC的非线性徐变放大系数模型。结果表明:UHPC的徐变类似于普通混凝土,但UHPC的非线性徐变特性更显著,其非线性徐变阈值为0.3 f_(c)(f_(c)为混凝土抗压强度);传统的普通混凝土徐变模型高估了UHPC的非线性徐变阈值且低估了非线性徐变放大系数;UHPC的名义泊松比在加载后增长显著,表明非线性徐变与试件内微裂缝扩展有关;本文模型计算结果与试验结果吻合较好,最大相对残差仅9.9%,可用于UHPC非线性徐变计算。

Cylindrical ultra-high performance concrete(UHPC)specimens with different initial loading ages and stress/compressive strength ratios were prepared for creep tests in indoor environments,to study the nonlinear creep threshold and creeping characteristics of UHPC.The axial and circumferential strains of the specimens were measured within a load-applying duration of 100 days.In accordance with the test results,the creep coefficient,nonlinear creep amplification coefficient and nominal Poisson′s ratio of UHPC under multiple stress/compressive ratios are calculated,and the applicability of the numerical model of nonlinear creep amplification coefficient of normal concrete to the UHPC is analyzed,and a nonlinear creep amplification coefficient model for UHPC is developed.It is shown that the creep of UHPC is similar to that of normal concrete,but revealing more distinctive feature of nonlinear creep,with a nonlinear creep threshold of 0.3 f_(c)(f_(c)refers to the compressive strength of concrete).The creep prediction models of normal concrete overestimate the nonlinear creep threshold of UHPC,while underestimate the nonlinear creep amplification coefficient.After loading,the nominal Poisson′s ratio of UHPC gets a significant increase,indicating that the nonlinear creep is related to the propagation of microcracks in the specimens.The numerical simulations with the proposed model agree well with the test results,with a maximum relative residual error of 9.9%,indicating it is applicable to calculate the nonlinear creep of UHPC.