Wind-induced dynamic responses of structures with outrigger systems

Abstract

A multi-degree of freedom lumped mass model with rotational springs was built to investigate the influence of outrigger system on the natural periods and mode shapes of a structure. The presence of outrigger system was found to significantly stiffen the structure, reducing the natural periods and distorting the mode shapes. The influences of outrigger system on the modal properties of a structure vary with the change of its number, locations and rotational stiffness. Wind-induced along-wind and across-wind responses of structures with and without outrigger system were analyzed, compared and discussed. It was found that the outrigger system can effectively decrease the along-wind responses (peak displacements and accelerations) and its influence is the most significant when it's located at the middle of the structural height. For across-wind responses, the outrigger system(s) could help with the prevention of vortex-induced resonance, if its location(s) is(are) appropriately chosen, by shifting the natural periods of the original structure without outrigger away from the frequency of vortex shedding. Two methodologies were proposed for the design of outrigger systems in two different scenarios, one with the number and locations of outrigger(s) preset and the other not. For the first scenario, the corresponding methodology is a checking process and for the second, it is a designing process. Both methodologies are aimed at preventing vortex-induced resonance and minimizing along-wind peak displacements and accelerations, satisfying related human comfort criteria for motions and lateral drifts requirements.