Seismic Performance And Design Methods On Shear Energy Dissipation Multi-Storey Cold-Formed Steel Frame-Braced Structures

The traditional cold-formed steel(CFS)composite wall is prone to have misalignment at the joints of wall panels and damage of self-tapping screw connections under earthquake,resulting in obvious pinching of the hysteretic curve.The shear bearing capacity and the energy dissipation capacity of the wall are difficult to meet the seismic demand in high intensity areas.The energy dissipation segment(EDS)made of low yield point steel has the advantages of high initial stiffness,stable hysteretic performance,excellent fatigue performance and simple fabrication process.Combined with bracing members in CFS structures to form CFS shear energy dissipation frame-braced structures,which can not only improve the lateral performance of the structure,but also can concentrate the damage on the low yield point steel EDS to realize the "efficient seismic resistance" feature that the damaged components can be replaced after the earthquake.This paper focuses on the seismic performance and related design methods of the structure.The main contents are as follows:(1)The CFS shear energy dissipation frame-X and K-shaped braced structures with EDS were proposed,and the experimental studies on the seismic performance of two X-shaped and eight K-shaped braced structures were completed.The test parameters included the energy dissipation panel’s aspect ratio,width to thickness ratio,whether the panel was stiffened or slotted.In addition,the repair and replacement process of the EDS after the earthquake was simulated in the test,and the technical points and repairability indexes of the repair process were evaluated.The effects of the parameters on the failure characteristics,load-interstorey drift hysteretic curves,skeleton curves,strain-displacement curves,ductility and energy dissipation capacity of the specimens were obtained through the tests.The test results showed that the new structures proposed in this paper had a typical yield sequence of "EDS before frame" with a plump hysteretic curve and good energy dissipation capacity.The design objective that the damage was mainly concentrated on the energy dissipation panel was realized.The mechanical performance of the repaired specimens was almost consistent with that of the original specimens,which verified the rehabilitation capability of the structures.(2)The refined finite element models of the specimens were established based on ABAQUS software.After the correctness of the analysis model was verified by the test results,the test parameters were broadened to carry out parametric analysis.The effects of energy dissipation panel’s aspect ratio,width to thickness ratio,initial geometric imperfections,strength ratio and stiffness ratio of the panel to main frame,and aspect ratio of main frame on the structural performance were investigated.The recommended values of each parameter were put forward aiming at excellent energy dissipation capacity and reasonable failure mode.Then simplified analytical models of the braced structures were established,the calculation method of the elastic lateral stiffness of the structure was derived based on the deformation coordination relationship,and the calculation method of the shear bearing capacity of the structure was derived based on the principle of virtual work and superposition principle.(3)The ABAQUS simplified analytical model of multi-storey CFS shear energy dissipation frame-K-shaped braced structure was established and its accuracy was verified by the comparison with shake table tests.Subsequently,the damping effects of different lateral resisting structures in CFS frames were compared,as well as the effects of different bracing arrangement schemes,including planar and vertical arrangement schemes on the seismic performance of the structures.The results showed that in the plan arrangement,the K-shaped braces with EDS should be arranged in the four corners of the structure.In the elevation arrangement,for the structure with uniform vertical stiffness,the through-height arrangement was the best.If the economy of the structure needed to be considered,the arrangement below 1/2 height of the structure was a more effective arrangement scheme.(4)The restoring force model of the multi-storey CFS shear energy dissipation frame-braced structure was established.On this basis,a direct displacement-based seismic design method considering damage control was proposed for the multi-storey CFS shear energy dissipation frame-braced structure,and the seismic performance target of the new structure was established,so that the CFS frame remained basically elastic while the EDS can be replaced under the rare earthquakes to realize the design concept of "damage control".The method was then used to design a 6-storey CFS shear energy dissipation frame-K-shaped braced structure,and the design steps were described in detail.