ON THE NATURAL FREQUENCIES OF INFILLED FRAMES.

Three approximate models are considered for the evaluation of the first few natural frequencies and associated mode shapes of infilled frames. The reasonableness of the models is checked with the available experimental results and with the corresponding finite element solution. The models include the multiple strut model, shear-flexure analogy, and an equivalent plane frame model. Besides presenting the approximate models, the effect of frame-infill separation in reducing the fundamental frequency is investigated and an empirical relation is presented in this regard. Also some of the factors influencing the frame-infill contact lengths are studied and this indicates that the contact lengths are highly sensitive and indeterminate. Some constructional methods for avoiding separation and ensuring effective composite action between the frame and infill are also suggested.