2019 CSCE Annual Conference - Laval (Greater Montreal) Conference
Dr. Girma Bitsuamlak, Western Univeristy
Dr. Solomon Tesfamariam, University of British Columbia
The architectural and structural forms of the recent generation of tall buildings show a trend towards complex geometry, reduced weight, stiffness, and damping properties, leading to an increased excitation by the wind. Therefore, the strength and stiffness requirements due to wind load usually govern the design of tall buildings. The current building codes in the US, Canada, and Europe recognize the first significant yielding point (i.e., linear-elastic design) as an ultimate limit state, which could result in the uneconomical and conservative design of tall buildings. The main reasons behind the provision of the linear-elastic design of tall buildings are the non-load reversal nature of wind load (uni-directional mean component in the drag direction), damage accumulation due to the longer duration of wind storms, and unsymmetrical yielding (cyclic excursions to the plastic range are in one direction). Considering the economics and safety of owners and the society, classical linear-elastic design arguments should be re-examined with consideration of performance-based design approaches, innovative technologies, and materials. In this paper, we critically examined the ductility demand, the effect of wind duration, hysteretic energy, and the rate of damage accumulation to introduce ductility-based design in wind engineering. For this purpose, a parametric study is conducted using non-linear time history analysis of bilinear and self-centering single-degree-of-freedom (SDOF) systems subjected to artificially generated wind load time histories. The parameters considered are critical damping ratio, post-stiffness yielding ratio, strength reduction factor, wind duration, and turbulence intensity. Results of the parametric study reveal that, for the bilinear SDOF systems with a fundamental frequency greater than 0.2Hz, designed considering a ductility capacity of 2 and 5, the elastic design force can be reduced up to 12% and 35%, respectively. However, for designs involving higher ductility demand, damage accumulation could trigger the failure of structural systems. Moreover, for bilinear SDOF systems, the results of the study are extended to define a new ultimate limit state (controlled inelasticity-limit state) with explicit consideration of both ductility demand and rate of damage accumulation. On the other hand, the results of the self-centering systems indicate their efficiency in controlling the damage accumulation under wind load. Therefore, we suggest the use of self-centering systems for the design of flexible buildings considering ductility demand greater than 2. Finally, for both bilinear and self-centering systems, new strength reduction factors are proposed.