Research On The Buckling Of Cold-formed Thin-wall Steel Lipped Channel Under Axial Compact

The cold-formed thin-wall steel members have widely used in various constructions and structures due to its advantages of light weight,high strength,and easy to process and produce in batch.These buildings,especially used as military construction,might suffered from high intense earthquake,high wind pressure and the impact load.However,the research on the dynamic buckling modes and failure of common open-section cold-formed thin-wall steel members like Csection or Z-section under impact load is quite lacking,which also affects the evaluation of such sorts of structures in the design and construction,especially the construction safety after disasters.The explicit design items over constructions subjected to impact load is not contained in the current various countries' specification for the design of cold-formed thin-wall steel,for example,Chinese and North American Specifications.Therefore,it is urgent and significant to study on the buckling of open-section cold-formed thin-wall steel member under impact load.Firstly,several drop hammer tests with the different impact speed were conducted to study the dynamic buckling of the selected C-section cold-formed thin-wall steel member.The high speed camera and Vic-2D analysis software were applied to obtain and analyze the occurring and growing of the buckling and the axial displacement and the residual deformation of the samples.Then,a numerical simulation model was established by Abaqus to take nonlinear buckling analysis,in which had considered the strain rate strengthening effect and geometric nonlinearity and introduced a specific combination of each FEM buckling mode and its participation ratios as initial imperfection based on the indentifying the main buckling mode through the generalized beam theory.The accuracy of simulation was verified by the high consistency of the residual deformation and the axial displacement of the channel steel samples and the hammer's axial speed with the tests' results.The simulation and tests' results indicated: The buckling of the C-section steel member under impact load is allergic to the initial geometric imperfection.The lip will lose its bearing capacity firstly and the stiffening effect on the flange,consequently,the load capacity of the flange and web decreased,eventually lead the total steel member to failure.Accordingly,there will be a serious hidden danger that the C-section steel members with defects,especially in the lip,used in the construction might subjected to impact load.A transition to high order non symmetric distortional buckling mode was discovered while the samples suffered an impact of about or above 10m/s with drop hammer of 50 kg.Moreover,the dynamic buckling critical point increases with the impact velocity and stress wave propagation,In addition,the propagation of stress wave plays the major role in the dynamic buckling of the channel steel section.Finally,axial compressive loading tests of damaged and intact samples have been carried out using by the WAW-2000 microcomputer controlled electro-hydraulic servo universal testing machine.The C-section steel members' residual deformation and load-displacement curves were analyzed and the relationship between the impact energy and the residual bearing capacity was obtained.