Characterizing wind-structure interaction for performance-based wind design of tall buildings

Abstract

Performance-based wind design (PBWD) has been receiving a great deal of attention from the wind and structural engineering communities. This is specifically highlighted with the release of the ASCE pre-standard for PBWD (2019). The PBWD of tall building requires a series of steps one of which is the interaction parameter, i.e. characterizing the interaction of the tall building with the wind field. In the studies involving slender structures-such as tall buildings, it is essential to consider this interaction parameter which is a function of the time-varying aerodynamic loads. The aerodynamic loads consist of the turbulent loads due to fluctuating wind, known as buffeting loads, and the self-excited loads resulting from the interaction of the structural motions with wind, referred as aeroelastic loads. Flexible structures can become unstable at a critical wind speed, known as flutter speed, wherein a diverging motion of the structure occurs. Aerodynamic instability that is caused by self-excited loads generally doesn’t occur in tall buildings within their design wind speeds but certainly needs to be considered in a wind-structure interaction analysis, particularly when tall buildings become increasingly slender and are allowed to enter post-elastic region. This study aims to characterize the interaction parameter in the PBWD of tall buildings by including the self-excited loads in its response analysis corresponding to the three-degree-of-freedom response motions of the building in along-wind, across-wind, and torsional directions. For this purpose, the flutter derivatives that are used to represent the self-excited loads in frequency domain are first obtained from wind tunnel tests of scaled section models of the structure and then converted into approximate coefficients known as Rational Function Coefficients (RFC) as part of Rational Function Approximations (RFA) of the self-excited loads in Laplace or time domain. The wind loads on a structure in time domain are calculated by combining both the buffeting loads and self-excited loads associated with the calculated RFC. The non-linear structural behavior of a 44-story and a 60-story tall building each is studied using nonlinear dynamic time-history analysis in extreme wind conditions and then observed for any flutter-like instabilities. The concept PBWD is applied considering the performance objective involving those associated with occupant comfort and structural or non-structural damages.