Gypsum-based Lightweight Materials Design For CFS Wall And Compression Performance Of The Infilled Walls

During the service of cold-formed steel(CFS)wall,such problems as Cavity inside,studs without lateral restraint and easily to local buckling,limited the application of CFS buildings.In this paper,Flue gas desulfurization(FGD)gypsum was used as a main raw material to prepare a series infilling materials,to solve the problems and promote the application of this green residential system.The main contents of this paper are as follows:1.Gypsum modification for the preparation of the infilled materials of CFS wall.The limestone/gypsum process was the main process of FGD.After calcinations,the gypsum it produced which was called FGD building gypsum had several problems such as rapid hydration speed,severe bleeding and rapid hardening.The particle distribution and microstructure were analyzed by laser particle size analyzer,porosity tester and scanning electron microscope.It was found that there were a large number of fissures inside,which leads to a larger inner surface area,and the crystallizations of hemihydrates gypsum were incomplete.These were the main reasons for the problems before.After find the reasons,the improvement measures were put forward.In order to solve the problems of poor water resistance,low pH value and low strength of gypsum,Portland cement and Fly ash were used as modifying materials.This paper suggested that when the ratio of cement to fly ash to gypsum was 3:3:14,the composite cementious material have certain water resistance and alkalinity,and at the same time,the FGD gypsum which was an industrial solid waste can be utilized as much as possible.Compared to unmodified gypsum,the durability of CFS in modified gypsum was increased by 16-39 times.And it was further guaranteed with the use of corrosion inhibitor2.Wall infilling materials design based on Rheology parameters and the physical and mechanical properties of the materials.Considering about the floating trend of lightweight aggregate in slurry,the Stability criteria and the terminal floating velocity was calculated by using rheological parameters,and a new mix proportion design method of modified gypsum-based lightweight materials was raised.The reliability of this method was verified by experiments.The physical and mechanical properties of Glazed hollow bead(GHB)-modified gypsum lightweight materials and expanded polystyrene(EPS)-modified gypsum based lightweight materials were acquired.In view of the special stress-strain characteristics,through analyzing the stress-strain curve shapes,the stress-strain equations were established by using subsection fitting method.Physical meanings of the parameters in the equations were clear.The stress-strain showed that GHB-modified gypsum lightweight materials had better plastic deformation ability,whereas EPS-modified materials exhibited greater brittleness.3.Vertical compression performance analysis of CFS walls filled with gypsum-based lightweight materials.Eight full-scale CFS walls were designed in order to investigate the change of vertical compression performance when the wall filled with modified gypsum lightweight materials.The failure modes,load-deformation relations,load-strain relations,compressive stiffness and compressive bearing capacity under vertical load were studied through loading tests.Based on the results,the wall was modeled and parameter analyzed by ABAQUS.The results showed that in the filled walls,the studs would appear to strength failure instead of buckling failure because of the surrounded of the filling material.Compared with the unfilled walls,the vertical bearing capacity and compressive stiffness of the filled walls were significantly improved.When the filled walls reached to their maximum loads,the encased studs were in or close to yield state,while the filling material cannot make full use of its bearing capacity.On the basis of the result of experiment and ABAQUS analyses,a modified superposition method was proposed to quantify the vertical bearing capacity of the filled walls,and the reduction factor(?)of studs was suggest to 0.85,while the reduction factor(?)of filling materials was 0.6.The computation results tend to be more secure than experimental and ABAQUS values,which were worthy of adoption in design.The out-of-plane equivalent bending rigidity formula of the filled walls was derived by superposition method,and the stability calculation method was given in this paper.