钢-超高性能混凝土组合板开裂荷载正交试验及计算方法

Orthogonal test and calculation method of cracking load of steel-ultra-high performance concrete composite specimen

为了研究钢-超高性能混凝土(UHPC)轻型组合桥面结构的横向抗弯开裂性能,综合考虑配筋率、保护层厚度、UHPC层厚度和栓钉间距4个影响因素,对40个钢-UHPC组合板试件进行受弯开裂正交试验.结果表明,未配筋构件裂缝数量少且裂缝扩展较快,配筋可以提高构件的开裂刚度,加强裂缝扩展阶段,使构件出现多元开裂特性.配筋率对开裂应力的影响最大,其次是保护层厚度,然后是栓钉间距,UHPC厚度对开裂应力的影响较小.在配筋率较高时减小保护层厚度,开裂应力提高幅度较大.UHPC厚度为45 mm的组合板的开裂应力为18.7~27.8 MPa,UHPC厚度为60 mm的组合板的开裂应力为17.2~27.4 MPa,远超虎门大桥的工程需求.根据现有规范公式计算钢-UHPC组合结构开裂荷载偏保守.根据密集配筋钢-UHPC组合结构特点,提出钢筋应力和开裂荷载计算方法,计算结果和试验实测结果较吻合.

An orthogonal test was accomplished on 40 steel-UHPC composite specimens,in order to study the transverse bending cracking behavior of steel-ultra-high performance concrete(UHPC)lightweight composite deck.Four influence factors were considered,including reinforcement ratio,cover thickness,thickness of UHPC layer,and spacing of studs.Results show that the number of cracks in the unreinforced members is small and the cracks expand rapidly.The reinforcement can increase the cracking stiffness of the specimens and enhance the crack propagation stage,which makes the members exhibit multiple cracking characteristics.For the cracking stress of UHPC,the most significant factor is the reinforcement ratio,followed by the cover thickness and then the spacing of stud shear connectors,whereas the depth of UHPC layers is observed to have limited influence.Reducing the cover thickness can increase the cracking stress greatly when the reinforcement ratio is high.The cracking stress values of the composite plates with thickness of UHPC layer of 45 mm and 60 mm were 18.7~27.8 MPa and 17.2~27.4 MPa,respectively,which is far beyond the engineering requirements of the Humen Bridge.It is too conservative to calculate the cracking load of the steel-UHPC composite structures according to the formulas in the existing code.Calculation methods of reinforcement stress and cracking load were proposed according to the characteristics of dense reinforced steel-UHPC composite structure.The calculated values obtained by the proposed calculation method are in good agreement with those from tests.