Study On Bending Capacity Of Cold-formed Steel Double-limb U Box Beams

Cold-formed thin-walled steel has been widely used in the construction industry because of it’s superior mechanical properties.At present,there are many researches on cold-formed thin-walled single-limb members at home and abroad.However,there is no specific design method for the double limb build-up section members in the specification due to the variety of the section forms.In order to solve this problem and provide reference for engineering practice,the following studies are carried out in this paper:1.In this paper,the flexural performance of 12 cold-formed steel double-limb U-shaped build-up box girders have been tested.The failure modes,load-displacement curves,load-strain curves and mid-span section strain distributions of each specimen were obtained.The influence of screw spacing and web opening on failure mode and bending capacity of split box girder is analyzed.The test results show that the failure modes are the local buckling failure of flange and web in pure bending section.When the opening ratio is 0.4,the impact of web opening on the ultimate load of box girder is small and can be ignored.When the open hole ratio is 0.7,the existence of holes will obviously reduce the ultimate bearing capacity of box beams.When the screw spacing increases from 150 mm to 300 mm,the bending capacity of the split box girder decreases slightly.2.The finite element software ABAQUS was used to model the cold-formed steel doublelimb U-shaped build-up box girders,and the failure mode and load-displacement curve of the specimen were obtained,which were corresponds with the test result greatly.On this basis,36 groups of finite element models were analyzed,and the effects of flange width-thickness ratio,section width-width ratio,screw spacing and opening size on the bending performance of the cold-formed steel double-limb U-shaped build-up box girders were investigated.The results show that the increase of flange thickness and section height can significantly improve the bending capacity of the split box girder.The increase of screw spacing will slightly reduce the bending capacity of the split box girder.When the web opening ratio is less than 0.4,the web opening has little influence on the bearing capacity of the split box girder,but when the web opening ratio is greater than 0.4,the web opening will greatly weaken the flexural performance of the split box girder.3.The calculation method of flexural capacity of the cold-formed steel double-limb Ushaped build-up box girders in current Chinese and American codes and existing literature is introduced,and evaluated and verified by test data.The results show that the prediction results of flexural capacity by simple superposition method are conservative because the splicing effect is not taken into account.However,the method of JGJ 227-2011 produces large errors in test results.Based on the simple superposition method and the finite element parameter analysis,this paper proposes a method for calculating the flexural capacity of cold-formed steel doublelimb U-shaped build-up box girders with web openings considering the splicing effect.The results show that this method can predict the flexural capacity of cold-formed thin-walled box girders.