Vulnerability assessment of buildings under windborne debris impact

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2021-08
Authors
Saini, Dikshant Singh
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Shafei, Behrouz
Alipour, Alice
Cho, In Ho
Sarkar, Partha
Durbin, Paul
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Civil, Construction, and Environmental Engineering
Abstract
This research presents a holistic computational framework to understand the extent and likelihood of damage to building envelopes against windborne debris hazard. This type of hazard is a major source of damage to residential and commercial buildings, incurring billions of dollars of property loss over the past few decades. Windborne debris hazard can be broadly divided to three stages, i.e., generation, flight, and impact. The debris flight mainly depends on the wind field surrounding the object, the initial condition of the object, and its mass and shape properties. The available numerical and experimental studies are limited to the two-dimensional (2D) autorotation of debris object, while such objects are found to exhibit complex three-dimensional (3D) spinning modes of autorotation in reality. In addition, the existing analytical models do not go beyond uniform winds. To address this research gap, the current research develops a debris flight trajectory prediction framework in the atmospheric boundary layer (ABL) using coupled computational fluid dynamics (CFD) and rigid body dynamics (RBD). Two important debris types, i.e., plate- and rod-type debris, are investigated. Verification of the debris trajectory model is performed by comparing the results with the data obtained from the past analytical and experimental studies. Upon validating the developed simulation framework, the flight trajectory in ABL winds is determined by calculating the displacement and angular velocity components of each debris type. For a holistic investigation, the study is extended to understand the effect of initial pitch and yaw angles, debris characteristics, mean wind velocity, and release height on debris flight. Finally, a set of models are developed based on the simulation results to predict the debris travel distance, as well as linear and angular velocities. The developed predictive models can be employed for designing the building envelopes that can provide adequate resistance against windborne debris hazard. In the second stage, this study investigates the performance of common building envelopes, such as structural insulated panels (SIPs) and wood frame shear walls, under windborne debris impact. Wood frame construction consists of horizontal diaphragms in conjunction with shear walls to support gravity loads and resist lateral loads originating from seismic and wind events. The existing literature shows that studies on wood frame shear wall structures are limited to cyclic and earthquake loads. Thus, the current study contributes to the literature by evaluating the damage to wood frame shear walls after windborne debris impact. For this purpose, the effects of a wide range of parameters, including the angle of attack, impact velocity, nail spacing, and moisture content, are examined on the extent of damage to the wood frame shear walls. The simulations are further extended to quantify the damage by evaluating the shear walls’ post-impact lateral load carrying capacity. This research effort is further extended to evaluate damage to SIPs under windborne debris hazard. For the SIPs, a high-fidelity finite element (FE) framework is developed to evaluate their perforation resistance. In this study, SIPs consisting of expanded polystyrene (EPS) sandwiched between two layers of metal skins are investigated. Upon validating the models, the performance of SIPs is investigated using several parameters, including deformation pattern, critical and residual velocity, and energy absorption. The vulnerability of the SIPs is determined by capturing the critical velocity, which is defined as the maximum velocity at which no perforations occur. Furthermore, a parametric study is conducted to examine the influence of mechanical and structural properties of face sheets and foam core on the perforation resistance of SIPs. The study on SIPs is further extended to double-layered wall panels. The main objective is to optimize the design configuration of SIPs subjected to windborne debris impact. For that purpose, a surrogate model-based multi-objective optimization is conducted to achieve a design with improved energy absorption capacity and impact resistance. Structural wall panels often sustain significant damage upon a single debris impact. Thus, these wall panels cannot resist multiple debris impacts at one location in one or consecutive windstorms. To investigate this critical aspect, this study investigates the impact response of aluminum foam panels subjected to repeated windborne debris impact. Impact simulations are carried out to study multiple debris impacts for a range of debris masses and velocities, core densities, core thicknesses, and face sheet thicknesses. The simulation results showed excellent performance of aluminum foam panels in resisting the single and multiple windborne debris impact, which has great importance to the construction industry.
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