LATERAL BEHAVIOUR OF LIGHT FRAMED WALLS IN RESIDENTIAL STRUCTURES

In attempt to use conventional methods to calculate the ductility demand factor (μ) for lightframed clad residential structures, it was found that this key parameter varies substantially depending on the definition of the yield displacement. The difficulty in defining the yield displacement is due to the fact that there is not a suitable equivalent elasto-plastic model to fit highly non-linear load-deflection curves. Typical plasterboard clad wall frames exhibit such high non-linearity and stiffness degradation. Based on experimental and analytical results, a strong relationship was found between the initial period (Ti), ground period (Tg), and equivalent elastic period (T). Four different analytical models showed similar linear trend between Ti/Tg and T. As the ratio Ti/Tg increased, T decreased. With a reliable equivalent elastic period and soil category, μ was calculated based on the equal displacement approach. Thus, the observed variation in μ using this approach can be explained in rational engineering terms, unlike the situations when conventional methods are used. Consequently, the ductility reduction factor (Rμ) was calculated for different wall configurations. For some typical wall design and construction practices, the overstrength was estimated to range between 1.5 and 5 depending on which components of the wall boundary conditions are included in the design process. Having established the ductility reduction factor and the overstrength factor, the response modification factor, which is used in most seismic codes, can be evaluated. However, presenting the ductility reduction and overstrength factors separately may be more appealing as the designer can better predict the behaviour of the structure and more appropriate structural optimisation can be achieved.