| The cold-formed steel(CFS)framed structure system using sprayed lightweight mortar(SLM)acted as a new-type of low-and mid-rise green energy-saving buildings,not only has some advantages of traditional CFS framed structures with sheathing such as light-weight and easy to work with,but also could simplify the detailing of constructions,improve the thermal,acoustic,fire resistance and shock resistance performance significantly,avoid knocking walls to appear the hollowing sense,solve the limitation of wall hanging,and increase the global stability as well as the load bearing capacity of structures.Therefore,this new-type of structure system conforms to the basic requirements of the new rural construction and urbanization construction in China.In order to study the seismic behavior of CFS framed shear walls with SLM in the new-type of structure systems,the experimental research,numerical study and theoretical analysis were carried out,and the design method of seismic behavior would be proposed,which could provide the basis for the application and promotion of this structure system in seismic areas.Firstly,through tests of two CFS frames and eight CFS framed shear walls with SLM under reversed cyclic loading,the failure process and pattern were observed,and detailed discussions on hysteretic loops,strength,stiffness,ductility and energy absorption were given.The experimental results indicated that both the lateral stiffness and load bearing capacity of CFS frames were low,so that it was uneconomical to ignore the interaction effect between steel frames and sheathing in design.CFS framed shear walls with SLM were failed by the local buckling at the bottom of end studs and the relative slippage between the steel frame and SLM outside.Although the mortar layers had cracks,the overall stability and integrity of walls were well-preserved at the ultimate stage.Because of the strong interaction between the steel frame and SLM outside,the load bearing capacity,lateral stiffness and ductility of CFS framed shear walls with SLM were considerably high.Because the connections of the knee elements were weak,there was not much improvement on the lateral stiffness and load bearing capacity of the wall specimens.The fitting of the knee elements with connections strengthening locally or steel-strap X-shaped bracings could increase the load bearing capacity by 16%-29% or 14%-22%,respectively.Based on above test results,the finite element analysis was conducted to simulate the shear behavior of CFS steel framed shear walls with SML under monotonic horizontal loading by the software ANSYS,where the load-slip curves of nonlinear spring elements were used to simulate the interaction between SLM and CFS frames.The calculated results agreed well with the test results,so the parameter analysis on the shear behavior of shear walls was carried out based on the correct finite element model.The analysis results indicated that the load bearing capacity of walls using steel grade Q345 or LQ550 could be increased by 15%or 28%,respectively,compared to that of walls using steel grade Q235.The thickness of end studs had a significant influence on the shear capacity of walls,and 1.5-mm-thick end studs could increase the load bearing capacity of walls by 66%,compared to 0.8-mm-thick end studs.However,the thickness of tracks and blockings as well as the number of blockings in the skeleton of walls had little influenced on the the lateral stiffness and load bearing capacity of walls.According to the results of the experimental research and finite element analysis,the theoretical calculation formulas of the lateral stiffness and load bearing capacity of CFS framed shear walls with SLM were proposed,and the calculated results agreed with the experimental and finite element analysis results.Based on the failure modes of shear walls,four performance levels,namely full operation,temporary operation,life safety and collapse prevention,were put forward,and the drift angle limit were determined as 1/1000,1/550,1/200 and 1/120 on four performance levels,respectively.According to the principle of equivalent safety coefficient,the partial safety factor of resistance γ_R was determined as 1.602,and the design values of CFS shear walls with SLM were suggested.According to the results of theoretical analysis,the base shear method was used to seismic checking to a two-storey CFS framed structure with SLM.The computing results indicate that both the stiffness and load bearing capacity of this new-type of the structure meet the requirments under eight-degree frequently occurred horizontal earthquake action,and the structure has certain safety reserves.Finally,according to the characteristic of envelope curves in test specimens and the results of theoretical analysis,the degenerated four-linear envelope curve model and the Pivot hysteretic model were established to simulate the hysteretic behavior of CFS framed shear walls with SLM.This simplified hysteretic model,which agreed well with the hysteretic loops of test specimens,could provide the theoretical basic for the elastic or elasto-plastic time history analysis of CFS framed structure system with SLM. |
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