Theoretical And Experimental Study On Short-term Stiffness Of Composite Slab With Lattice Girder

Composite slabs with lattice girder,as a common horizontal member in current engineering,have a very different forcing mechanism in construction and use stage.The influence of lattice girder on the stiffness of filigree slabs and composite slabs is controversial.Therefore,this thesis studies the mechanical properties and short-term stiffness of filigree slabs and composite slabs.The details are as follows:1、The static load test of three filigree slabs is carried out.The test results show that the upper bar of the lattice girder has a large strain value,which reveals that the bare part of lattice girder has a certain contribution to the stiffness of the filigree slabs under the short-term design condition.The static load tests of four precast slabs were carried out,including three composite slabs with lattice girder and one precast slab without lattice girder.The test results show that the deflection of the mid-span measured by the test has no obvious difference between the precast slab without lattice girder and the composite slab with lattice girder in the same thickness,so the composite slab can be treated as the precast slab.Changing the layout direction of the lattice girder has a certain impact on the shear resistance of the composite slabs.2、The short-term stiffness formula of 《Code for design of concrete structures》 is used to calculate the deflection of 3 filigree slab speciments.The result shows that the actual stiffness contribution of lattice girder is smaller than the equivalent section stiffness calculated by equal elastic modulus method.To solve this problem,regression analysis of14 filigree slabs in this thesis and literatures is carried out.It is concluded that stiffness of the lattice girder calculated by equal elastic modulus method should be multiplied by the reduction factor of 0.6.3、The short-term stiffness formula of 《Code for design of concrete structures》 is used to calculate the deflection of 3 composite slabs.The result shows that the calculation deflection result is smaller than the test result,which indicates that the stiffness value calculated by the equal elastic modulus method is larger.The stiffness contribution of the lattice girder to the composite slabs is less than 3% of the total,and the influence on the final calculation deflection result is only 0.02 mm.On the basis of the arrangement of lattice girder,the calculation deflection method of composite slab is discussed according to isotropy and anisotropy.4、The short-term stiffness parameters of filigree slabs and composite slabs are analyzed,and six groups of parametric analysis specimens are designed.The finite element analysis results show that the lattice girder has a great influence on the filigree slabs,and the top bar of lattice girder can significantly inhibit the rapid degradation of stiffness after the cracking of filigree slabs.Then,the influence of lattice girder on composite slabs is modest.When changing the numbers and the design height of lattice girder,the cracking moment and mid-span deflection of composite slabs will not change greatly.