Research On Seismic Response Modification Factor Of Cold-Formed Thin-walled Steel Storage Racks Structure

With the rapid development of the logistics industry,the application of cold-formed thin-walled steel storage racks structure is increasing day by day.China is a multi-earthquake country.The effect of earthquake on storage racks structure can’t be ignored.Seismic response modification factor is key factor in determining the seismic force based on the bearing capacity of the seismic design.It is also an important basis for determining the ductile inelastic response spectrum based on performance seismic design.Therefore,it is important to research the seismic response modification factor of storage racks structure for the safety and economy of storage racks structure seismic design.The high-rise storage racks structure with spine bracing which is widely used is object to be researched.Based on the preliminary study results of the semi-low-cycle pushover test of three-storey three-span storage racks structure with no spine bracing,finite element model is compared with the experimental results to verify the accuracy of the finite element model.And based on the relevant parameters of the finite element model,the hysteretic model and the Rμ-μ-T relations for the storage racks structure with spine bracing were firstly studied.Then,the static pushover analysis was carried on storage racks structure with spine bracing which is widely used in the practical engineering.The weak parts and failure mechanism of the storage racks structure with spine bracing was found.And based on the Rμ-μ-T relations for the storage racks structure with spine bracing,the ductility reduction factor,the overstrength factor and the seismic response modification factor of cold-formed thin-walled steel storage racks structure were determined.Meanwhile,the impact on these coefficients of story numbers and storage racks form were discussed.Finally,incremental dynamic analysis was carried on to verify the accuracy of pushover calculations.The dynamic response and collapse mechanism of the storage racks structure in different leveling intensity were further discussed.The seismic response modification factor of storage racks structure with spine bracing was determined by dealing with IDA curve.And the results were compared with pushover analysis.Combined with the two methods,seismic response modification factor of storage racks structure with spine bracing was given for seismic design.Based the researches above,the main conclusions are obtained as follows:1.The pinching and sliding characteristics of storage racks structure with spine bracing is more obvious compared with the storage racks structure with no spine bracing.The shear-slip hysteretic model can be used as the hysteretic model of storage racks structure with spine bracing for studying the Rμ-μ-T relationship.Through the single-degree-of-freedom dynamic time-history analysis program,Rμ-μ-T which is used for storage racks structure with spine bracing was got by amending the Rμ-μ-T relationship that has been proposed for clough model.2.Based on the Rμ-μ-T relationship,the seismic response modification factor,the ductility reduction factor and the overstrength factor of cold-formed thin-walled steel storage racks structure were determined by pushover analysis.It showed that seismic response modification factor and ductility reduction factor increase with the increase of story numbers.The overstrength factor is showed decreasing with the increase of the story numbers.The ductility reduction factor,the overstrength factor and the seismic response modification factor of the standard structure are all bigger than the single structure.3.The IDA analysis showed that the weak parts of the storage racks structure under the earthquake mainly appeared in the bottom spine bracing controlling areas.The standard structure and single structure are all shown as the bottom row spacers,the spine bracing and the partial columns failure.Compared the seismic response modification factor determined by IDA analysis with pushover analysis,the devitation is very small,which verified the accuracy of the Rμ-μ-T relationship of the storage racks.The seismic response modification factor of the standard structure and the single structure is different.RMI specification which doesn’t subdivide the form of storage racks and only stipulates a single R value is rough.