| The development of building industrialization forward new requirements for building technology,and the development of residential building industrialization to green prefabricated energy-saving building is an important way to improve the level of building industrialization.Based on the traditional cold-formed steel composite wall,the research group governed by tutor proposed the fabricated cold-formed steel-high strength foamed concrete-straw slab shear wall structure system,referred to as FCCSS shear wall structure.High strength foamed concrete is poured into a space composed of straw board and cold-formed steel skeleton.Based on the good thermal insulation performance of straw board and foamed concrete,the structure can achieve the integration of thermal insulation and load-bearing maintenance performance.The straw board made with waste straws belongs to the category of green building materials.Steel frame and part of straw board were prefabricated in factory,which is a prefabricated building.The following problems were found in the study on compressive and seismic performance of FCCSS shear walls:1)The in-filled foamed concrete layered casting on site has poor integrity,which affected the uniformity of the wall shear-resistance.2)There is obvious bond slip between vertical cold-formed steel and foamed concrete,and the cooperative working ability needs to be improved.3)It is impossible to observe the failure development during the loading process of foamed concrete and the force-transferring mechanism of the wall is not clear.4)The industrialization level needs to be improved.To solve the above problems,this paper conducts multi-scale research from foamed concrete material to wall local composite specimen and wall component,and proposes the seismic performance experimental and theoretical research of composite wall based on the improvement of bond anchorage between cold-formed steel and foamed concrete and the improvement of prefabrication and assembly process.The cold-formed steel-foamed Concrete(CFSFC)composite walls studied in this paper are intended to be used in multi-storey village residential structures.Details of research are summarized as follows:(1)Research on the performance improvement of foamed concreteIn order to improve the integrity and uniformity of the wall as well as the bond-anchorage between the cold-formed steel and foamed concrete,the performance of foamed concrete needs to be improved.Based on the characteristics of hydrolysis and alkaline performance of silane coupling agent,the strength enhancement technology of foamed concrete is proposed.In combination with the strength enhancement technology,the foamed concrete of four grades A06,A07,A08 and A09 are prepared by mixing fly ash drifter,silica fume and fiber with different content,and the compression test,splitting tensile test and material thermal conductivity test are carried out.The test results can be found that the A07 foamed concrete has similar compressive strength of A12 concrete and thermal insulation property of A06.This new kind of foamed concrete solves problems including disharmony between insulation and strength,easy to collapse,crack in large area of foamed concrete.(2)Research on bond-anchorage between cold-formed steel and foamed concreteThe influences of the strength of foamed concrete,anchor-length of cold-formed steel,the number of rolled edge punching holes in the steel webs and the number of self-tapping screws in the steel flange on the bond-slip performance between cold-formed steel and foamed concrete are studied through the monotonic and cyclic repeated loading tests.The following conclusions can be drawn from the monotonic loading test:1)the failure modes and the mechanism of bond slip of specimens are different with different configuration;2)the load-slip curves of specimens with rolled edge punching holes in the web or with self-tapping screws in the flange have obvious peak platform in the ultimate load zone,and the descending curve is gentle and there is no obvious residual segment;3)the ultimate bearing capacity increases with the increase of the steel anchorage length and the number of the self-tapping screws,but the increase amplitude decreases slightly.The following conclusions can be drawn from the cyclic repeated loading test:1)the failure modes of the specimens are similar,and the deformation recovery lags behind during unloading process;2)the ultimate bearing capacity under compression direction is greater than under tension;3)regarding to syntectonic specimens,the damage under repeated loading is severer than monotonic loading,and the ultimate bearing capacity and the average bond strength are smaller than that under monotonic loading.Based on the monotonic loading test,the four stages bond-slip constitutive relation model can predict the bond slip curve shape and characteristic values of specimens well.While,the predicting accuracy of the bond-slip constitutive relationship under cyclic loading based on the degradation three linear model needs to be improved.(3)Experimental study on seismic performance of CFSFC composite walls9 CFSFC composite walls,1 FCCSS shear wall and 1 traditional cold-formed steel composite wall are tested to study the seismic performance of CFSFC composite walls.The affecting factors include the foamed concrete stress,holes arrangement in the steel web,steel spacing,axial compression ratio,aspect ratio,window opening in wall,and so on.The following test results can be observed:1)the damage modes of CFSFC wall include that the straw board at the vertical joint is seriously torn and the foamed concrete is densely packed with intersecting oblique cracks,which are finally crushing collapsed and the self-tapping screws were broken as well as the steel of end columns are occurred with local buckling;2)the load-displacement hysteretic curve of CFSFC composite wall shows obvious characteristics of stiffness and strength degradation,slip and pinching,and no obvious yield point;after the maximum bearing capacity,there is peak platform area,which make the stress failure of the CFSFC walls become shear failure with certain ductility;3)the shear bearing capacity of CFSFC walls is 18.2%higher than that of FCCSS shear wall,and the slip degree of cold-formed steel and foamed concrete is lighter than that of FCCSS wall.This phenomenon indicates that the rolled edge punching holes can effectively improve the bond-anchorage between steel and foamed concrete,so as to improve the integrity of the wall and the anti-lateral bearing capacity.(4)Calculation of shear capacity of CFSFC composite walls:softened strut-and-tie slip analysis model and the formula of bearing capacityBased on the damage mechanism of the CFSFC composite walls,softened strut-and-tie model of the reinforced concrete shear wall and direct shear truss model of foamed concrete,a softened strut-and-tie slip model reflecting failure mode and the forced mechanism of the CFSFC composite walls was proposed,and the calculated results are in good agreement with the experimental values.The failure mode and forced mechanism of CFSFC composite walls are different from that of traditional cold-formed steel and light steel-light concrete structure.It is difficult to quantitatively analyze the distribution spacing of straw fibers.The existing calculation formula for the bearing capacity of shear walls,which takes into account the distribution spacing of horizontal reinforcement,is not applicable to CFSFC walls.Based on the softened strut-and-tie slip theoretical model,a formula for calculating the shear capacity of CFSFC walls is proposed.The calculation results can be used to predict the shear capacity of the wall with deviation in less thaną10%.The contribution of each component of the walls to the shear bearing capacity is calculated by using the formula of shear bearing capacity.When the vertical steel ratio is less than 0.5%,the shear bearing capacity contribution rate of steel is 4.3%-9.6%,and that of straw slab is about 22%-29%.The shear bearing capacity contribution of steel can be ignored in the design of CFSFC composite wall.When the vertical steel ratio is with scope of 0.5%to 0.85%,the shear contribution rate of straw slab and vertical steel is close to each other.The calculated bearing capacity can be multiplied by the reduction coefficient for engineering design.Considering the economic benefits and shear bearing capacity,it is suggested that the maximum ratio of vertical section steel should be 0.5%.(5)Restoring force model of CFSFC composite wallsBased on the experimental load-displacement skeleton curve of CFSFC walls,a skeleton curve model based on secant stiffness degradation is established by using the discrete coordinate method.The formulas with high precision for calculating the elastic stiffness and shear bearing capacity,is deduced based on the softened strut-and-tie slip model.Based on the experimental hysteresis curve of CFSFC walls,the hysteresis rule is analyzed,and the conclusion that the shape of the hysteresis loop in the rising stage is controlled by the historical maximum displacement can be observed.Combining the pinch point and the starting point of the slip stage,the curve of the rising stage is divided into four stages with monotonically varying stiffness.A four-line nonlinear hysteretic model which can reflect the wall stiffness degradation and slip and pinching characteristics is established as follows:the first unloading stage and the second loading stage are represented by the Richard-Abbott curve model,and the first and third loading stages are represented by straight lines.The software Origin2020b was used to identify the parameters in each segment of the mathematical model,and the calculated hysteresis curve was highly consistent with the experimental hysteresis curve.The restoring force model is achieved based on secant stiffness degradation and a four-line segment nonlinear hysteretic model.Its expression is intuitive and its parameters are easy to identify,which can provide a basis for the nonlinear dynamic analysis of CFSFC composite wall house.(6)Suggestions on seismic design of CFSFC composite wallsBased on the cold-formed steel-foamed concrete bond anchorage test and wall seismic performance test,the design suggestions of each component of the wall are proposed by comprehensively considering the structure and shear performance of the CFSFC composite walls.Suggestions on the wall construction process,fire prevention and waterproof design are also put forward,which are intended to provide reference for the application design of wall engineering. |
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