氯盐环境下预损伤UHPC-HPC组合梁抗弯性能

Flexural behavior of pre-damaged UHPC-HPC composite beams in chloride corrosion environment

为了提高普通钢筋混凝土梁的耐久性,设计了一种超高性能混凝土(UHPC)-高性能混凝土(HPC)组合梁新型结构,开展了锈蚀后UHPC-HPC组合梁的抗弯性能试验,研究了氯盐侵蚀后组合梁抗弯承载力降低的机理,分析了腐蚀程度、截面形式与预损伤对其抗弯性能的影响;引入钢筋屈服强度折减系数、截面积折减系数与混凝土预损伤系数,提出了锈蚀后UHPC-HPC组合梁抗弯承载力计算方法,并验证了计算方法的可行性。分析结果表明:锈蚀后梁体抗弯承载力降低主要原因为钢筋抗拉强度下降,梁体刚度退化与韧性减弱,钢纤维阻裂效果削弱;锈蚀后UHPC-HPC组合梁的破坏表现为跨中附近出现1条主裂缝或加载点附近出现2条主裂缝;UHPC-HPC组合梁的受力过程分为线弹性、裂缝发展和屈服3个阶段,梁体截面混凝土应变基本符合平截面假定;侵蚀时间越长,组合梁的开裂荷载和承载力降低越大,通电快速侵蚀10 d时,降幅分别达16.2%和10.9%;锈蚀后T形梁比矩形梁开裂早,前者的开裂荷载比后者降低8.1%,后期刚度下降较快;预损伤显著影响梁的整体刚度,预加载后梁的整体刚度降低,混凝土损伤后的预损伤系数为0.984;锈蚀率越大,钢筋的屈服强度与截面积折减系数越小,变化趋势符合二次抛物线;锈蚀后UHPC-HPC组合梁抗弯承载力的计算值与实测值吻合良好,两者之比的平均值为0.998,标准差为0.020。

In order to improve the durability of ordinary reinforced concrete beams,a new structure of ultra-high performance concrete(UHPC)-high performance concrete(HPC)composite beam was designed,and the flexural behavior of the UHPC-HPC composite beam after chloride corrosion was tested.The decrease mechanism of flexural capacity of the composite beam after chloride erosion was studied,and the effects of erosion degree,section form and pre-damage on the flexural behavior were analyzed.The yield strength reduction coefficient,cross-sectional area reduction coefficient of steel bar and pre-damage coefficient of concrete were introduced to propose the calculation method of flexural capacity of the UHPC-HPC composite beam after corrosion,and the feasibility of the calculation method was verified.Analysis results show that the main reasons for the decrease in the flexural capacity of the beam after corrosion are the decrease in the tensile strength of steel bars,the degradation of the stiffness and toughness of the beam,and the weakening of the crack resistance effect of steel fibers.The failure of the UHPCHPC composite beam after corrosion is characterized by one main crack near the mid-span or two main cracks near the loading point.The stress process of the UHPC-HPC composite beam is divided into three stages:linear elasticity,crack development and yield.The concrete strain of the beam section basically conforms to the assumption of plane section.The longer the erosion time is,the more the cracking load and the flexural capacity reduce.When the beam is energized and eroded rapidly for 10 d,the reductions reach 16.2%and 10.9%,respectively.The T-beam cracks earlier than the rectangular beam,the cracking load of the former is 8.1%smaller than that of the later,and the stiffness decreases faster in the later stage after corrosion.The predamage significantly affects the overall stiffness of the beam,the overall stiffness decreases after pre-loading,and the pre-damage coefficient after the concrete damage is O.984.The larger the corrosion rate is,the smaller the yield strength and the cross-sectional area reduction coefficient of the steel bar are,and the change trend conforms to the quadratic parabola.The calculated flexural capacity of the UHPC-HPC composite beam after corrosion is in good agreement with the measured value,the average ratio of the two is 0.998,and the standard deviation is 0.020.10 tabs,14 figs,31 refs.