Approximate parameter for semi-rigid `Khorjineeʹ connections in dynamic torsional response of steel structures

A comprehensive forced vibration test has been performed on the half-scale models of typical Iranian four storey steel structures for identification of the dynamic behavior of semi-rigid connections known as `Khorjinee connectionsʹ. In this paper, results of the test in the form of torsional frequency spectra of floor acceleration and displacement response of the structure for three cases of various gravity loads of the floors have been discussed. Dynamic characteristics of a structure, namely, natural frequencies, mode shapes, damping ratio and center of rigidity of flooors, based on the assumed connectionʹs stiffness have been obtained and compared to the characteristics of the mathematical model. Eleven mathematical models similar to the corresponding experimental models with different uncoupled torsional to lateral frequency ratio, eccentricity ratio, dimensions of plan ratio, and the connectionʹs stiffness have also been studied to examine their effect on dynamic response.