Research On Temporary Brace System Of Basement Roof Slab Under The Load Of Large Crane

Steel structure has many advantages such as light weight,high strength,good seismic performance,and convenient construction,so it is widely used in construction engineering.However,there are still many problems in the steel structure installation and construction process.Especially when a large crane is used to hoist the steel structure,the load of the crane will affect the existing structure to a certain extent.To ensure construction safety,temporary brace systems are often used to strengthen the existing structure.Considering the construction cost and convenience,the selection of temporary brace system under different crane loads and the strengthening performance of the brace system for existing structures are issues worthy of attention.This thesis combines an example of the steel structure installation project in the exhibition center of a large-scale complex project in Xi’an.The SAP2000 finite element software was used to establish a structure model,uses the bridge module in SAP2000,and defines the lane along the crane travel area according to the traveling route planned by the crane.The vehicle is defined as a general vehicle,the corresponding wheelbase and axle load are specified according to the type of crane,and the traveling speed of the crane is assumed to be 1m/s.The effect of the crane load on the basement roof is simulated,and the basement roof is calculated and analyzed.The linear and nonlinear stability analysis of the temporary support system selected for the basement roof is carried out,and its multi-order buckling mode and the nonlinear stability bearing capacity considering the initial defects are obtained,which provides a reference for the selection of this kind of engineering support system.The main research results are as follows:1.By defining different vehicle loads,a comparative analysis of the mechanical performance of the basement roof slab under different cranes was carried out.When the large cranes are moving on the basement roof slab,QAY300,QAY200 and QY90 K cranes have a larger impact on the load-bearing capacity,stress and deformation of the basement roof slab than QAY180 and QY60 K cranes.Under the selected crane load,the load-bearing capacity of the basement roof slab can meet the requirements of large cranes,but the maximum tensile stress of the bottom of the slab and part of the top of the slab has exceeded the ultimate tensile stress of the concrete,and the slab will crack and fail.and the deformation has exceeded its deflection limit,and the width of the crack at the bottom of the slab will reach0.26 mm.Exceeding the specification minimum crack width limit,the slab deflection reaches30.43 mm,which exceeds the specification deflection limit.During crane hoisting operations,under the action of the reaction of the crane legs,the QAY300 crane leg reaction is the largest,and the QY60 K crane leg reaction is the smallest.The bearing capacity of the basement roof slab cannot meet the requirements of the crane hoisting operation under selected crane leg reaction.but the maximum tensile stress of the bottom of the slab and part of the top of the slab has exceeded the ultimate tensile stress of the concrete,and the slab will crack and fail.and the deformation has exceeded its deflection limit.the width of the bottom crack is0.47 mm,which exceeds the minimum crack width limit of the specification,and the deflection of the slab is 55.12 mm,exceed the specification deflection limit.2.The full-floor bracing and strengthening plan was adopted for the crane walking path,and the steel pipe column back-to-top support plan was adopted during hoisting operations.The semi-rigidity of the nodes is considered,and the full-floor support system node torque is40N·m.Through linear and nonlinear stability analysis and comparison of the stability of the brace system with differences spacing of ledgers and standards and different specifications of steel pipe columns.the results show that the change of the spacing of ledgers has a greater impact on the bearing capacity of the brace system than that of the standards.The non-linear bearing capacity considering the initial defects is significantly lower than the linear bearing capacity.The wall thickness,length and initial defects of the steel pipe prop have a great influence on its bearing capacity.3.Considering the initial defects of the brace system,the nonlinear stability analysis of the brace system shows that the nonlinear ultimate bearing capacity is significantly lower than the linear critical bearing capacity.The reduction can reach to 52.38% for the full-floor brace system,and the reduction can be up to 47.99% for the steel pipe column prop.4.After the full brace system is added to the basement roof slab,under different crane loads,the tensile stress distribution at the bottom of the slab has been significantly improved.The tensile stress of the slab is reduced by 61%～73% compared with that before reinforcement,and the maximum tensile stress of the slab is less than the ultimate tensile stress of the concrete,the full brace system has a very good reinforcement effect to basement roof slab.