Internal Force Calculation Of Concrete Composite Slab With Lattice Girders Adopting Monolithic Connection Without Gap

The manufacturing technology of concrete composite slab with lattice girders combines the prefabrication and cast-in-place technology,and the mid span joints parallel to the short direction and the lattice girders in the span are usually arranged.This kind of construction method will cause the change of the long and short direction stiffness of the composite slab,and then lead to the change of the two direction internal force of the composite slab compared with the ordinary reinforced concrete slab.At present,there is a dispute on whether to consider the influence of joint mode and lattice girders on the internal force of composite plate in the current code.Therefore,based on the theoretical calculation,experimental research and numerical simulation,this paper studies the mechanical performance and internal force calculation method of composite slab.The details are as follows:（1）The full-scale static load tests of four composite slab without gap and two contrast slabs are carried out.The contrast slabs include one composite slab with post pouring strip and another common precast slab without lattice girders.The test results show that both post cast strip and no gap joints can transfer internal forces well,and the two-way mechanical performance of composite slabs with lattice girders is similar to that of common precast slab.If the thickness of the post pouring layer is too small,it is easy to cause tearing failure of the composite surface.The construction of the lattice girders being perpendicular to the joint will weaken the shear capacity of the composite surface.（2）The moment adjustment coefficient of composite slab with lattice girders is determined;Based on the elastic thin plate theory,ignoring the influence of the joint mode in the composite slab,and using the equal elastic modulus method to consider the influence of the lattice girders,the moment adjustment coefficient of the simply supported composite two-way slab on four sides is calculated and analyzed.The results show that the internal force distribution of the composite two-way slab will be changed by the configuration of the lattice girders.The bending moment adjustment coefficient in both directions is in the range of 0.95 ～ 1.05.The arrangement of the lattice girders being perpendicular to the joint is not conducive to the two-way stress of the slab.（3）The finite element analysis software ABAQUS is used to simulate the composite slab and cast-in-place slab.The finite element analysis results are in good agreement with the theory and experiment,and the moment adjustment coefficient is analyzed.The results show that the change of length width ratio and total slab thickness will not make the moment adjustment coefficient of two-way composite slab exceed the range of 0.95 ～ 1.05.If the thickness of post pouring layer is too small,the moment adjustment coefficient of the short direction will be greater than 1.05,which should be avoided in design.