Study On Mechanical Properties Of Lightweight Precast Concrete Composite Slab

At present,the most commonly used horizontal prefabricated components in prefabricated structures are traditional steel truss concrete composite slabs and welded steel plate bottom formwork steel truss floor support slabs.The former has the advantages of improving assembly rate,reducing on-site formwork support,and accelerating construction progress.However,the thickness of traditional reinforced truss concrete composite slabs is 100 mm or at least 20 mm thicker than that of commonly used cast-in-place slabs.The components have a larger self weight,high transportation costs,and high carbon emissions.At the same time,there are problems such as steel bar collision,difficulty in joint treatment,and slurry leakage that delay the construction period,which is not in line with the original intention of prefabricated structures to save construction time and be green and environmentally friendly;The latter has advantages such as smaller thickness compared to composite slabs,simple welding process operation,easy bottom mold connection,and effective prevention of slurry leakage.However,the welded steel plate bottom mold of the steel truss floor support slabs have corrosion and other problems during use.Therefore,this paper combines the advantages of the thin bottom formwork and light weight of the traditional steel truss floor deck and the cooperative stress of the prefabricated layer of the steel truss composite slab,and proposes a new type of steel truss lightweight precast concrete composite slab.The thickness of the fine aggregate concrete detachable bottom formwork is only 15 mm or 20 mm.The steel mesh is prefabricated in the bottom formwork.The steel mesh can work together with the bottom formwork in the construction stage.The advantages of laminated floor slab are: the thickness is the same as that of traditional cast-in-place floor slab,without increasing the slab thickness;Post-cast concrete shall be poured on site to wrap the surface rebar and bottom rebar,vibrated and compacted,which is equivalent to cast-in-place concrete slab;The bottom chord rebar of the laminated slab is exposed,which is visual and convenient for on-site acceptance.This paper will study its mechanical properties through tests,finite element simulation,parameter analysis and short-term stiffness theoretical calculation.The main research contents are as follows:(1)Six lightweight precast concrete composite slabs are designed and manufactured according to national codes and standards,and their static load test scheme is designed,the deflection,crack development and stress strain of the composite slab are observed during the test.The results show that the composite slab is basically under elastic stress in the construction stage,and conforms to the assumption of plane section.(2)Simulate static load tests during the construction phase using ABAQUS finite element software,and compare and analyze the results with the test results.The analysis results indicate that the load deflection curve and load strain curve are basically consistent with the experimental trend,verifying the effectiveness and feasibility of the finite element model established in this paper.Both the steel plate mesh and the steel bar are in an elastic state,and the steel plate mesh can work synergistically with the concrete in areas with significant tensile damage.(3)Through control variable method,various design parameters of lightweight precast concrete composite slab are analyzed,such as whether to dispose steel mesh,fine aggregate concrete strength,fine aggregate concrete bottom formwork thickness and truss rebar diameter,and reasonable design parameters are proposed.(4)By using the equivalent moment of inertia method of replacing the steel bar section with the concrete section,a short-term stiffness calculation formula for composite floor slabs was derived.The short-term stiffness correction coefficient was fitted using SPSS software.The calculation results showed that the formula can be generalized and has good applicability.Calculate the maximum unsupported span selection table for commonly used types of laminated floor slabs through formulas for designers to choose from.