Pan Zuanfeng, Cao Dong, Zeng Bin, Wang Yuwei
State Key Lab of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China.
Department of Structural Engineering, Tongji University, Shanghai 200092, China.
Materials (Basel). 2022 Sep 28;15(19):6742. doi: 10.3390/ma15196742.
Creep affects the long-term deformation of concrete structures. Nonlinear creep further overestimates the safety factor of structures and affects the safety service performance. The coupling of creep and a damage model considering the rate effect is conducive to accurate prediction of nonlinear creep, but the iterative process of strain makes the calculation method more complex. The purpose of this study is to propose a nonlinear creep explicit method that considers the damage evolution of concrete under compression. Two groups of axial compression members with compressive stresses of 0.2 fc and 0.4 fc were made. Considering the law of concrete damage evolution under uniaxial compression, coupled with elastic creep and damage incremental strain, the lower limit of the medium stress level that gives rise to nonlinear creep is analyzed. The concrete nonlinear creep amplification coefficient with a loading age of 28 days and loading duration of 360 days is studied with consideration for the uncertainty of relative humidity and the theoretical thickness of the component. On this basis, the explicit calculation formula of the nonlinear creep amplification coefficient related to the concrete axial compressive strength and stress level is given. The results indicate that the nonlinear creep amplification coefficient increases nonlinearly with an increase in the stress level, and, when the compressive stress level ratio is higher than 0.6, the nonlinear creep amplification coefficient increases significantly; when the stress level is determined, the creep amplification coefficient decreases gradually with an increase in the compressive strength of the concrete. It is suggested that a stress level range of 0.35~0.75 should be used for the study of a nonlinear creep amplification factor under the medium stress state.
徐变影响混凝土结构的长期变形。非线性徐变会进一步高估结构的安全系数，并影响结构的安全服役性能。徐变与考虑率效应的损伤模型的耦合有利于非线性徐变的精确预测，但应变的迭代过程使计算方法更加复杂。本研究的目的是提出一种考虑混凝土受压损伤演化的非线性徐变显式方法。制作了两组压应力分别为0.2fc和0.4fc的轴心受压构件。考虑混凝土单轴受压损伤演化规律，结合弹性徐变和损伤增量应变，分析了引起非线性徐变的中等应力水平下限。考虑相对湿度和构件理论厚度的不确定性，研究了加载龄期为28天、加载持续时间为360天的混凝土非线性徐变放大系数。在此基础上，给出了与混凝土轴心抗压强度和应力水平相关的非线性徐变放大系数的显式计算公式。结果表明，非线性徐变放大系数随应力水平的增加而非线性增大，当压应力水平比高于0.6时，非线性徐变放大系数显著增大；当应力水平确定时，徐变放大系数随混凝土抗压强度的增加而逐渐减小。建议在中等应力状态下研究非线性徐变放大系数时，应力水平范围取0.35~0.75。
