Effect of lightweight cladding panels on the seismic performance of moment resisting steel frames

This paper focuses on the seismic design of moment resisting steel frames endowed with structural lightweight cladding panels. The aim is to investigate the possibility to profit from their contributing effect on both the serviceability and the ultimate limit states of the structure. An original design procedure is proposed, where the stiffening action provided by cladding panels is taken into account in order to increase the lateral stiffness of the bare frame, which is designed according to the strength only. In order to assess the reliability of the proposed solution a number of non-linear dynamic time-history analyses are presented and discussed. With this aim, accurate mathematical models interpreting the cyclic response of both screwed and welded lightweight steel panels have been set up and implemented into a general purpose computer program. The main parameters affecting the seismic performance of the system, namely the frame configuration, the mechanical and hysteretic characteristics of cladding panels and their distribution throughout the frame, are investigated. On the one hand, the obtained results show that the proposed design procedure leads to more rational and economic solutions, allowing for an important reduction of the sizes of the main structural members. Also, it is shown that the requirements for cladding panels in terms of both strength and stiffness are not excessive. On the other hand, it is apparent that the cladding panels provide an improvement on the global seismic performance at the conventional ultimate limit state also, even though such an effect is largely dependent on the above influential parameters. A simplified procedure to account for such an effect is also proposed.