Natural periods of braced steel frames designed to EC8

Günaydın, Egemen
A two-phase study was undertaken to investigate the fundamental period of concentrically braced steel frames (CBFs) designed according to Eurocode 8. In the first phase, typical office buildings were studied by conducting two types of designs which are called as iterative and non-iterative. Non-iterative design is composed of obtaining final period by designing the structure with lower bound expression in Eurocode 8 while iterative design is similar to the non-iterative one but an updating of periods was considered in order to converge assumed and final periods. Different overstrength provisions are considered in the study. Lower bound expression in Eurocode 8 results in shorter periods which indicates that this expression can be safely utilized. The lower bound represented by Tremblay (2005) is also admissible except for some cases including shorter periods. In the second phase, a simple expression is derived for estimating the design base acceleration for braced frames proportioned according to Eurocode 8. This method requires inelastic top story drift values which were obtained from structures designed in the first phase using iterative method. These drifts were represented by simple expressions utilizing data fitting techniques. The method gives suitable first order estimate for the design base acceleration.