| At present,China is vigorously promoting prefabricated buildings,and the application of prefabricated structures in daily buildings is becoming more and more extensive.At present,the prefabricated floor slabs used mainly include truss reinforced concrete laminate(60mm thick floor),reinforced truss floor deck(profiled steel plate floor),prestressed concrete laminate,etc.,and the traditional full hall support mode or temporary support frame are used during construction.In this thesis,a new type of mold-free concrete floor rebar truss composite plate(referred to as HJ rebar truss plate)is proposed,the bottom plate is only20mm thick,and the efficiency of factory production,hoisting transportation and site installation is doubled.HJ rebar truss plate retains the form of rebar truss in traditional rebar truss plate,reduces the thickness of the floor under the premise of ensuring that the bearing capacity,deflection and cracks meet the requirements in the construction stage,and replaces the profiled steel plate or 60mm concrete floor with a 20mm concrete floor as a permanent formwork for cast-in-place concrete layer.The steel truss with a spacing of 200mm not only effectively increases the rigidity of the composite plate but also solves the lifting point problem of HJ steel truss plate,which has the advantages of light weight,easy transportation and hoisting.The bottom plate of the HJ rebar truss plate is thin and easy to crack during the construction stage.This thesis mainly studies the supporting span of HJ rebar truss plate in the construction stage,and the main research contents are as follows:(1)The material properties of the concrete floor were tested to obtain its elastic modulus,tensile strength and compressive strength.The results show that by adding a certain amount of polypropylene fiber(PP fiber),the tensile strength of the floor concrete can reach 4.5MPa,the compressive strength can reach 55MPa,and the elastic modulus is 2×104N/mm~2.(2)SAP2000 finite element analysis was used to calculate and analyze HJ rebar truss plates with different spans.The lower floor slab of 90 steel truss specifications was modeled and analyzed,the influence of upper and lower chord steel bar stress,floor concrete stress and floor deflection on the support span was discussed,the main influencing factors of the span in the construction stage of HJ steel truss plate were clarified,and the calculation span selection table was preliminarily determined.(3)Referring to the combined section theory,the HJ rebar truss plate is simplified to the concrete material section,and the corresponding simplified calculation formula is given,and the applicable span of HJ rebar truss plate is determined by formula calculation.(4)Four kinds of truss heights of 60mm,80mm,100mm and 120mm were selected,and according to the changes of the diameter of the upper and lower chord steel bars of the steel truss,the diameter of the upper winding steel bar was 10mm and 12mm,and the diameter of the lower chord steel bar was 8mm,and 10 HJ steel truss plate specimens were made,and the test was carried out by heavy loading and on-site poured concrete loading.Through the analysis of the test data,it is found that the stress-strain deflection of the concrete floor steel truss composite plate increases significantly under a certain span,and temporary support needs to be erected,which further verifies the erection spacing of temporary support.The test data was compared with the calculation results,which fully verified the accuracy of the selection table. |
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