Study On Bending Performance Of Concrete Composite Slabs Using Semi-prefabricated Slabs Without Extended Bars

With the steady and rapid development of China's society and economy,the problem of high energy consumption in the construction industry has become increasingly prominent,and a series of policies have been issued to fully support the the industrialization of construction.At present,reinforced concrete composite slabs are widely used in the floor of prefabricated buildings in China.Compared with the traditional concrete composite slabs,the rigidity of the prefabricated slabs and the overall performance of the composite slabs are better than that of the ordinary concrete composite slabs due to the restraint effect of the steel bar truss on the concrete.The current design codes require that the two-way concrete composite slab needs monolithic connection joints,and the prefabricated slab needs to reserve the extended reinforcement,which will cause a series of problems.This paper proposes two new connection joints that do not extend the reinforcement on the prefabricated slab,and designs and tests the bending performance of the two new connection joints.The main work and achievements are as follows:(1)The two-point symmetrical static loading test of five steel bar truss reinforced concrete composite slabs with connection joints were completed.By the comparison of the failure process and damage states,strain distribution characteristics,load-deflection curves and characteristic load values of the specimens,the bending performance of each specimen has been studied.The experimental results show that the two connection joints avoid the early failure result from cracks along the transverse direction at laminated face,which is safer and more reliable than the close joint on the technical specification.Under the same reinforcement condition,increasing the thickness of the post-cast layer or the yield strength of the additional reinforcement could effectively increase the stiffness and bearing capacity of the specimen.The slab with stepped joint could achieve the same bending performance as the slab with post-cast joint after reasonably setting the additional reinforcements.(2)The uniform static loading test of four steel bar truss reinforced concrete twoway composite slabs were completed.By the comparison of the failure process and damage states,strain distribution characteristics,load-deflection curves and characteristic load values of the specimens,the bending performance of each specimen has been studied.The experimental results show that the failure process and modes of two-way composite slabs using two new connection joints are similar to that of the cast-in-place two-way composite plates,showing obvious two-way stress characteristics,which indicate that the two new connection joints proposed in this paper could effectively withstand the bending moment,and could be used for two-way composite slabs.The joint at the mid-span will greatly weaken the stiffness and bearing capacity of the two-way composite slab,which should be avoided in engineering.(3)Based on the test data,it is verified that the calculation method of bending bearing capacity in Code for Design of Concrete Structures(GB50010-2010)could be applied to concrete composite slabs with two new connection joints and post-cast joint,and reinforcement design methods of two new joints on one-way slab are proposed;Based on the yield-line theory,the calculation method for the bearing capacity of the two-way composite slabs with two new connection joints and post-cast joints is obtained;the theoretical calculation formula of the maximum deflection of the two-way concrete composite slabs is derived,and the practical calculation method for the maximum deflection of the two-way composite slabs with two new connection joints and post-cast joints is obtained.The paper contains 52 figures,15 tables and 106 references.