A multiscale framework for the risk analysis of urban building envelope systems subject to windborne debris considering the directional effect of tropical cyclones

Windborne debris poses a significant threat to the envelope systems of urban high-rise buildings during tropical cyclones (TCs). The time varying feature of TC surface wind makes it inadequate to ignore the wind direction effect in the analysis of the windborne debris risk to envelop systems. To address this issue, this paper proposes an integrated framework that spans the entire process from TC generation based on physical stochastic sources, to local urban wind environment simulations, and to detailed debris flight trajectory modeling and impact fragility analysis of envelope systems. This framework establishes a multiscale perspective for analyzing the uncertainty propagation associated with the windborne debris risk from regional meteorological scale to local urban scale and debris scale. First, the joint probability distribution of TC maximum wind speed and surface wind direction is derived based on TC wind hazard assessment technique. Next, the urban wind field is simulated by a computational fluid dynamics (CFD) model, and the debris flight trajectory in the local wind environment is simulated by a rigid-body dynamical model. The urban wind field model and debris flight trajectory model are then used to estimate the fragility of the envelope system given specific wind speeds and directions. Finally, the annual occurrence rate that the number of damaged glazing units exceeds certain thresholds is derived using the total probability theorem. A 100-m high-rise building located in Shanghai is used to illustrate the application of the proposed framework. A detailed analysis of the illustrative application is presented and the results show that ignoring wind direction effects may overestimate the risk of windborne debris to envelope systems.