ANALYTICAL PREDICTIONS OF STRENGTH AND DEFLECTION OF LIGHT GAUGE. STEEL FRAME / WOOD PANEL SHEAR WALLS
C. Y. Chen, A. F. Okasha and C. A. Rogers
Department of Civil Engineering & Applied Mechanics, McGill University, Montreal, Canada
E-mail: colin. rogers@mcgill. ca
It is anticipated that the construction of buildings that incorporate light gauge steel frame/wood panel shear walls as primary lateral load resisting elements will increase across Canada in coming years. At present, a codified method for the prediction of shear wall strength and stiffness is not available in Canada. For this reason an investigation of various analytical prediction methods was completed. The racking strength and stiffness of steel frame/wood panel shear walls have been shown to be highly dependent on the behaviour of the sheathing connections. An experimental program involving over 200 small-scale tests was first carried out to establish the performance of steel stud to wood sheathing connections. This information was then utilized in a comparison of five existing analytical/mechanics based methods to predict the strength and deflection of wood framed shear walls. These existing analytical methods were adapted for use with the steel framed walls. A comparison of the predicted strength and deflection values was then made with the results of full-scale shear wall tests. Based on the comparison between test and predicted shear wall response the elastic models presented by Kallsner & Lam were recommended for use to predict the lateral resistance and deflection of light gauge steel frame/wood panel shear walls under monotonic and cyclic loading. At the same time, the shear capacity and initial stiffness as measured from tests of single sheathing connections with an edge distance of 25 mm, and which were evaluated using an equivalent energy approach, were recommended as the input connection parameters for both the strength and deflection models.
A typical light gauge steel frame / wood panel shear wall is composed of cold-formed steel studs and tracks that are connected with self-drilling/tapping screws to either plywood or OSB sheathing. Guidelines for the design of these shear walls do not exist in current Canadian codes. A design method for the calculation of in-plane shear stiffness and strength has been proposed for use with the 2005 NBCC (NRCC, 2005) (Branston, 2004), however this method is reliant on the results of full-scale testing. Eventually, with the proven applicability of an analytical model, researchers could extend the results of small-scale connection tests to aid in the design of full size shear walls. For this reason a study was carried out to evaluate the possibility of using existing analytical methods, which were originally developed for the design of wood framed shear walls, to predict the in-plane shear stiffness and deflection of steel frame / wood panel shear walls. Methods by Kallsner & Lam (1995), Easley et al., (1982) and McCutcheon (1985) were adapted for use with steel frame shear walls. Since all of these methods are based, to a large extent, on the stiffness and strength properties of the individual sheathing connections in a wall, tests were carried out by Okasha & Rogers (2004) to identify the connection properties. With the results of the sheathing connection tests Chen (2004) then compared the analytical predictions with the results of shear wall tests.