Seismic Performance Analysis And Resilience Assessment Of LEM-filled CFS Composite Wall Structure

In recent years,Chinese government made great efforts to promote the rural vitalization.The new livable green prefabricated rural residence has become the research and application hot spots.The main structural types of rural housing in China are masonry-timber,masonry and brick mixed structures,which induces some outstanding problems such as low degree of industrial construction,waste of human and material resources,poor anti-disaster capacity.This paper proposed a novel type of green and low-carbon,assembled cold-formed steel composite wall structure filled with light EPS polymer(LEM-filled CFS composite wall),in which the LEM-filled CFS composite wall is the main bearing component.The LEM-filled CFS composite wall is consisted of CFS framing,light EPS polymer and sheathing.LEM-filled CFS composite wall could be prefabricated in the factory,which causes less on-site wettable operation and high assembled degree.The light EPS polymer is made of industrial waste including polystyrene particles desulfurized gypsum,which could lead recycle of waste and energy saving and environmental protection.Thus,it complies with the policies of low-carbon development in China.However,the seismic performance of LEM-filled CFS composite wall is not systematically investigated.There is still lack of calculation model and design method of this type of composite wall.Moreover,seismic performance of the LEM-filled CFS composite wall structure is also limited.In order to explore the seismic performance,design method and seismic resilience of LEMfilled CFS composite wall structure,the following work is carried out in this paper:(1)In this paper,12 specimens were designed and tested including a pure CFS wall without filling material,seven integral LEM-filled CFS composite walls,and four spliced LEM-filled CFS composite walls assembled using three separated.The test considered the influence of LEM type,sheathing type,X-shaped bracing,wall opening.The failure patterns,load-displacement relationships,feature values,ductility,stiffness and energy dissipation were systematically analyzed and asserted.The research results indicated that the LEM restricted the global instability and global buckling of wall stud.The LEM could also enhance the anchorage of self-tapping screw to avoid its pulling out and fracture.The LEM provided confining effects for the wall stud and they could work interactively,significantly improving the shear strength and stiffness of the wall.Besides,the spliced composite walls also exhibited excellent seismic response.(2)Based on the previous experimental investigation,the calculation method on the axial strength of LEM-filled CFS composite wall was proposed considering the interactive work between the CFS framing and LEM.Simultaneously,the modified soften strut-and-tie model is proposed considering the improvement provided by the rib lath and X-shaped bracing to calculate the shear strength of the composite wall.Considering the connection performance of steel strip and self-tapping screw between the two prefabricated walls,the shear strength of spliced composite wall could be calculated.The calculation results coincided well with the test results.(3)Based on the existing simplified method of pure CFS wall steel,the equivalent simplified analysis model of LEM-filled CFS composite wall was established considering the work mechanism of LEM under shear and connection between sheathing and self-drilling screws.Then,nonlinear simplified analysis models were established by software Open SEES.The simulated results were validated by test results.Besides,the effects of axial compression ratio,width height ratio,filling material thickness and strength on the performance of cyclic response were studied.It provided a foundation for the further research of structural dynamic response analysis.(4)A four-liner simplified model of skeleton curve(elastic point,yield point,peak point and ultimate point)was proposed considering the mode of bending failure and shearing failure.The calculation methods of the four feature points were also proposed.According to the typical test hysteresis loop and considering the characteristics of stiffness degradation,slipping and pinching,the hysteretic rules of the composite walls were determined.Then,the hysteretic rule was determined according to the feature of hysteretic curves in cyclic tests.Based on the four-liner skeleton curve and hysteretic rule,the restoring-force model was developed to provide a reference for the further analysis.(5)After determining the multi performance objectives under various earthquake intensities,the direct displacement-based design(DDBD)method was used to design the archetype structures.The equivalent viscous coefficient used in the DDBD method was calculated according to the restoring-force model.Then,2-,4,and 6-story LEMfilled CFS archetype structures were respectively designed,and the structure models were established and explored by nonlinear time history analysis.The inter-story drift and residual inter-story drift were adopted to evaluate the seismic response of the LEMfilled CFS composite wall structures.(6)Based on FEMA P58 and the abovementioned 2-,4,and 6-story LEM-filled CFS archetype structures,the fragility curve of the composite wall was defined.The resilience model of the structure after determining the demand parameters and conducting the nonlinear time-history analyses.the seismic resilience of the three structures located on soil class D were evaluated through the parameters of residual story drift,repair time,repair cost,and casualties under design-based earthquake.