Study On Longitudinal Shear Behavior Of Long-span Profiled Steel Sheet-Concrete Composite Slabs

Profiled steel sheet-concrete composite slabs are widely used in floor systems of steel structures and steel-concrete composite structures buildings because of their good bearing capacity,fast constructional speed,economic and security advantages.With the vigorous development of the construction industry,it is difficult to meet the needs of practical engineering to use traditional composite slabs with small span.And long-span and large-space structures are emerging.The application of long-span composite slabs can not only increase the clear height of buildings,but also reduce the layout of partition beams of large space floor and the welding of corresponding studs,which can speed up the construction progress and save the project costs,and has important practical significance.The one-sided connection between profiled steel sheet and concrete interface determines that the interaction between profiled steel sheet and concrete interface is difficult to achieve the same good interoperability as that between concrete and reinforcement.The failure mode of the composite slab under the action of external load is mainly controlled by the interaction ability between the profiled steel sheet and the concrete interface,and the bearing capacity is mainly controlled by the longitudinal shear bearing capacity of the profiled steel sheet and the concrete interface.The longitudinal shear bearing capacity of profiled steel sheet and concrete interface is mainly influenced by the section form and surface characteristics of the profiled steel sheet,the anchorage condition of the end of the composite slab,the thickness of the profiled steel sheet,the shear span ratio,the span height ratio,the mode of loading and so on.The longitudinal shear design methods of composite slabs mainly include the m-k design method based on the full-scale tests of composite slabs with small span an d the partial shear bonding design method which established based on the partial shear bonding theory(PSC method).There is no definite design methods and guidance suggestions for the design of long span composite slabs.The design method of composite slabs in the Code for Design and Construction of Composite Slabs is limited to m-k method.The design idea is relatively simple,the effect of failure modes on bearing capacity is not considered,and there is no definite design method for long-span composite slabs.In this paper,the systematic experimental study and theoretical analysis of three kinds of long-span composite slabs,such as trapezoidal-profile,dovetail-profile and re-entrant-profile,were carried out,the details are as follows:The push-out tests on 48 small size composite slabs including 9 trapezoidal-profile,18 dovetail-profile and 21 re-entrant-profile specimens were conducted under transverse and alternating loads.The interaction mechanism between profiled steel sheet with different cross-sectional forms and concrete interface was studied.The longitudinal shear behavior of the interface between profiled steel sheet with different cross-sectional forms and concrete was analyzedr,and the influences of the cross-sectional form of profiled steel sheet and the transverse load on the longitudinal shear behavior of composite slabs were investigated.The constitutive relationships of interface shear resistance of the profiled steel sheet with different cross-sections were proposed.The bearing capacity tests on 11 trapezoidal-profile and dovetail-profile,as well as 15 re-entrant-profile full-scale composite slabs were conducted.The main parameters include span of composite slab,anchorage condition at the end,thickness of profiled steel sheet,additional reinforcement at the bottom of slab,etc.Results show that the ductile longitudinal shear failure or bending failure occurs in the composite slabs with long span under external load,and the failure mode is related to the interface type.The stud anchorage at the end has a significant impact on the failure mode and bearing capacity of composite slab,and the bearing capacity of composite slabs with different spans,cross-section types and span-height ratios increases by different degrees,and the increase tends to decrease with the increase of span.Increasing the thickness of the composite slab and the thickness of the profiled steel sheet can effectively improve the bearing capacity,bending stiffness and deformation capacity,as well as the anti-slip ability of the interface.The additional tension reinforcement at the bottom of the composite slab can effectively improve the mechanical behavior of the composite slab,the bearing capacity can be greatly improved,and the stiffness of the composite slab at the later stage of loading can be significantly enhanced.In addition,aiming at the problems of low stress development and non-crushing of concrete in the middle span of compression zone in the test process,the bearing capacity of composite slab normal section was studied,and some suggestions on the reduction of concrete strength in calculating the bearing capacity of long span composite slab normal section were put forward.In the design of longitudinal shear bearing capacity of composite slab,based on the test data and different national codes,the m-k method was used to calculate the bearing capacity of unanchored and anchored composite slabs.Results show that the bearing capacity calculated by different specifications is obviously differentr,especially for long-span composite slabs,the calculation results tend to be conservative.Based on the theoretical analysis of interface shear resistance of long-span composite slabs,the distribution rules of interface shear stress of composite slabs in the ultimate state were studied.The design method of internal force balance in four-point equidistant loading mode was proposed.In addition,the longitudinal shear bearing capacities of the interface between profiled steel sheet and concrete of composite slabs with different spans were compared and analyzed through push-out method,PSC method and internal force balance method.The results show that both the internal force balance method and the PSC method can be used to accurately evaluate the longitudinal shear behaviors of long-span composite slabs.