Experimental Research On Shear Performance Of New-Type Cold-Formed Steel Load Bearing Walls

As a new distinctive structure system, cold-formed steel structure (CFSS) has the advantages of light weight, high performance, green environmental protection, energy conservation, rapid construction speed and so on. Although CFSS has been widely applied in low-rise residential apartments in Europe, Unite States, Australia, Japan and other regions, it is still in the initial stage in our country. Considering the large population in our country, it has more realistic significance to extend low-rise strut residential buildings to mid-rise buildings. So our research group raised a new-type cold-formed steel load bearing wall. Experimental tests and numerical simulation were performed in this paper to study its shear performance, and simplified methods of calculation for shear strength were proposed. The main contents and conclusions are as follows:1. The experimental program was based on twelve full-scale wall tests with different assemblies. The specimens were tested under either monotonic load or cyclic load considering the vertical load. Factors such as the sheathing material, studs section, edge distance of screws, and thicknesses of sheathing were considered. The following conclusions can be drawn. (1) Screw connections failure resulted in the failure of the walls. (2) The shear resistance of the specimen sheathed with double-layer wallboards was 55.96% higher than the specimen sheathed with single-layer. (3) When the thickness of bolivian magnesium boards increased from 12 mm to 15 mm, the shear strength raised by 22.77%. (4) The studs section and the edge distance of screws didn't make obvious difference to the shear behavior. (5) The shear strength of the walls sheathed with gypsum wallboards for the face layer combined with bolivian magnesium boards for the base layer were higher than the walls sheathed with gypsum wallboards for both layers, but their ductility would be falling.2. OpenSeeS finite element software was used here to simulate the lateral performance of cold-formed steel load bearing walls. The comparison between the numerical simulations and test results indicated that the finite element models can be used effectively to obtain the ultimate capacity, maximum error within 10%. What's more, pinching4 material constitutive model can simulate the hysteretic characteristics of screw connections, and the hysteresis loops obtained from OpenSeeS presented significant pinch effect. A detailed parameter analysis was carried out after the finite element models had been verified by tests date, including studs spacing, screws spacing. The main conclusions were as follows. (1) No meaningful difference was observed when the studs spacing was changed from 400 mm to 600 mm. (2) The shear strength of the walls mainly related to the peripheral screws spacing, insensitive to the screws spacing of middle studs.3. The transfer mechanism and failure modes of cold-formed steel wall for resisting horizontal force were analyzed in this paper.Then the paper deduced two kinds of simplified methods to calculate the shear strength of cold-formed steel walls:the global analysis method and analogy to the bolts(the elastic method and the ultimate strength method). On the basis of other scholars' methods, some reasonable improvements were made to the global analysis method considering the test failure modes and the results of numerical simulation. The screws on the side columns bear the horizontal shear, ignoring the screws on the intermediate column of wall plate. The ratio of the calculated results to the experimental results was 0.88-1.11. The elastic method and the ultimate strength method reference the calculation method of eccentric shear of bolt group. The calculated results of the elastic method were smaller than the actual value, and the maximum error was 21%. The calculated results of the ultimate strength method were higher than the actual value, and the maximum error was 19%.