电测法确定低强混凝土裂缝起裂和等效裂缝长度

该文设计了3种低强度混凝土三点弯曲切口梁,测试研究其双K断裂参数。试验中采用标距为5 mm和10 mm的应变片以半桥连接方式测量预制裂缝的起裂荷载,比较其工作性,发现应变片测量起裂荷载具有强度敏感性,短标距应变片更适宜测量本试验用低强度混凝土的裂缝起裂。试验中另沿韧带方向布置4组半桥应变片,根据各测点处拉应变回缩时的荷载与裂缝口张开位移,计算裂缝发展至测点高度时刻的等效裂缝长度,并与此时的实际缝长比较,结果表明双K断裂模型在预测裂缝长度方面具有较好的适用性。

DETERMINATION OF CRACK INITIATION AND EQUIVALENT CRACK LENGTH OF LOW STRENGTH CONCRETE USING STRAIN GAUGES

The double-K fracture parameters of three low strength concretes are investigated using three point bending notched beams. In the tests, half-bridge strain gauges with lengths of 5 mm and 10 mm are used to determine the initial cracking load of the pre-cast cracks. Comparison of their workability results show that strain gauges are sensitive to material strengths and short ones are more suitable for low strength concrete. Four other half-bridge strain gauges are arranged along the fracture ligament. When the tensile strain of the gauge decreases, the factual crack has propagated to the measuring point. With the load and the crack mouth opening displacement at this moment, the corresponding equivalent crack length can be calculated and then compared with the actual one. Results show that double-K fracture model can be well applied to predict crack lengths in concrete.