| The U-shaped steel-concrete composite beam is formed by U-shaped steel filled witn concrete.The U-shaped steel is formed by welding the cold bending thin-walled steels or taking thin steel plate into the cold bending directly.The essential connectors are designed to ensure the combined action.This composite beam is a new type of composite flexural component,which has been researched widely and has been applied in engineering project in recent years.The composite beams with U-shaped steel section have many advantages,such as higher loading capacities,higher fire resistance,better ductility and faster construction speed.In this paper,the design ideas of researchers about U steel-concrete composite beams are summarized in recent years.At the same time,six new type of the cold-form U-shaped steel-concrete composite beams are designed.as for the innovation of this composite beam:Firstly,The U shaped-steel beam is designed to a closed section by welding the steel truss at the edge of the U shaped steel,which can enhance its stability and strengthen the restraining effect of the internal concrete.Secondly,on the interface between steel beam and flange plate,shear reinforcement is set up to resist horizontal shear force and prevent the flange plate from lifting.Thirdly,The unexpected failure could be prevented by setting up the Longitudinal reinforcement on the bottom of the composite when a fire breaking out.Then,test research and numerical simulation has been carried out in this article to study this new type of the cold-form U-section steel-encased concrete composite beams.The main work is as follows:(1)Six new type of the cold-formed U-shaped steel-concrete composite beams were fabricated and tested.The faiure modes,load-deflection curves,load-strain cueves,the distribution of strain along the height direction and the deflection curves under different load level of beams are analyzed from the static test of six simply supported specimens.The influences of studs,Longitudinal reinforcement of the bottom of the beam,shear connector and steel truss are studied.(2)The finite element software ABAQUS is used to develop the model to analyse the flexural behavior of the cold-formed U-shaped steel-encased concrete composite beams.By comparing with the experimental results,the accuracy of finite element results is validated.Then the new typical composite beams are analyzed to study its working mechanism.At last,the influences of material strength,thickness of steel plate,width and deprh of section on the bending behavior of composite beams are analyzed.Design suggestions of this new typical composite beam is also presented.(3)According to the relating design codes and based on the plastic design method,the formula for calculating the bending capacities of the cold-form U-section steel-encased concrete composite beam is proposed,and its accuracy is validated by comparing with experimental results.The formula for calculating the stiffnees of the cold-formed U-shaped steel-encased concrete composite beams is proposed based on the reduced rigidity method. |
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