| In resent years, low-rise cold-formed thin-wall steel framing dwellings spring up in our country. The cold-formed steel framing wall, made of cold-formed steel framing, outer wallboard (OSB, steel panel etc.) and inner wallboard (gypsum wallboard etc.) connected by self-drilling screws, is the major load bearing member in the low-rise cold-formed thin-wall steel framing dwelling. Therefore, it is meaningful to study the shear performance of cold-formed steel framing walls for constituting related codes and accelerating popularization and application of low-rise cold-formed thin-wall steel framing dwelling systems in our country.Because of many influencing factors, the theoretical calculation of the shear performance of the cold-formed steel framing wall is very difficult. In the world, the shear performance of cold-formed steel framing walls is studied mostly by test, which is uneconomical and disadvantageous for practical design and constituting codes. For recent research status, the analysis and study of cold-formed steel framing walls on the influencing factors of shear performance, the calculation of lateral stiffness and deformation checking, the calculation of the maximum shear resistance, determination of the design value of shear resistance are carried out by test, finite element numerical analysis, theoretical formula derivation in this paper.The shear performance of sixteen full-size (2.4m by 3m) specimens of high strength cold-formed steel framing wall are studied in this paper. The walls are made of 550MP_a cold-formed steel C-section studs, 550MP_a cold-formed steel rib panels and gypsum wallboards. By test of four types of walls, double boards, single gypsum wallboard, single steel rib panel and steel X-strap bracing on both sides, under monotonic loading without vertical compression loading, cyclic loading without vertical compression loading and cyclic loading with vertical compression loading, the properties of shear load carrying capacity and the structural ductility factor for the specimens are obtained. Experimental results show that the shear resistance of specimens under monotonic loading is higher than that of specimens under cyclic loading for all types of walls; the sum of the shear resistance of walls with single gypsum wallboard and 0.8 that of walls with single steel rib panel is near to the shear resistance of walls with double boards; the shear resistance of walls with steel X-strap bracing on both sides is 60%～67% that of walls with double boards; the structural ductility factors for the specimens with double boards are between 1.731 and 2.384.Based on experimental study on the shear performance of cold-formed steel framing walls carried out by our studying team in this paper and in 2003 and 2004, the finite element analysis models of walls are established, in which the material nonlinearity and geometric nonlinearity are considered. A detailed parameter analysis is carried out after the finite element analysis models have been verified by test data, including wall framing thickness, yield strength of wall framing, wallboard thickness, cross section of wall stud, rib height of steel rib panel, stud spacing, stud height, vertical loading, wall detail, setting steel X-strap bracing on one side, monotonic and cyclic loading and so on. And many beneficial conclusions and data are obtained by the finite element parameter analysis, which provide a powerful foundation for the subsequent theoretical analysis. A problem worthy to be said is that the spring element is used successfully to simulate the contact problem caused by steel rib panel after shear buckling contacting the wall studs and large numbers of contact elements are avoided to be used, which offers a new idea for simulating contact problems by the finite element method.The simplified calculation model of the lateral stiffness of cold-formed steel framing walls is put forward to deduce the theoretical calculation formula of the lateral stiffness of walls. Based on the theoretical calculation formula, test data and finite element analysis results, the practical calculation formulae of the lateral stiffness and the lateral deformation checking formulae of four types of walls, single gypsum wallboard, single OSB( oriented strand board), single steel rib panel and steel X-strap bracing on both sides, under the horizontal wind load, the horizontal frequent earthquake and the horizontal rare earthquake, are proposed. And the calculation results of the practical calculation formulae of the lateral stiffness of walls agree well with experimental data and finite element results. Meanwhile, a conclusion that the lateral stiffness of walls with double boards is equal to the sum of that of walls with corresponding single board is drawn.The calculation model of the maximum shear resistance of the cold-formed steel framing wall is proposed by studying the possible failure modes of the walls under the horizontal force. Based on the calculation model, experimental data and finite element analysis results, the practical calculation formulae of the maximum shear resistance of four types of walls, single gypsum wallboard, single OSB( oriented strand board), single steel rib panel and steel X-strap bracing on both sides, are obtained. And the calculation results of the formulae are consistent with test data and finite element analysis results.In our country, the design value of shear resistance must be used in the shear design of cold-formed steel framing walls. However, less experimental research on the shear performance of the cold-formed steel framing wall is carried out at home, so the probability statistics and reliability analysis can't be adopted to obtain the shear resistance partial coefficient and the design value of shear resistance of the cold-formed steel framing wall. To meet the design requirement in domestic practical projects, the resistance partial coefficient and seismic adjustable coefficient of walls are calculated approximately by using the allowable stress design method about this kind of wall in American code and combining American code with Chinese code. And the partial coefficient expression of the shear resistance of the cold-formed steel framing wall is given in this paper, which is suitable for Chinese design code and has the equivalent safety degree to American design code. The expression can be for design reference in the practical project at home. |
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