Reveal wind loading of tornadoes and hurricanes on civil structures towards hazard-resistant design

Extreme winds impacting civil structures lead to death and destruction in all regions of the world. Specifically, tornadoes and hurricanes impact communities with severe devastation. On average, 1200 tornadoes occur in the United States every year. Tornadoes occur predominantly in the Central and Southeastern United States, accounting for an annual $1 billion in economic losses, 1500 injuries, and 90 deaths. The Joplin, MO Tornado in 2011 killed 161 people, injured more than 1000, destroyed more than 8000 structures, and caused$2.8 billion of property loss. Hurricanes occur predominantly on the United States East coast regions and along the coast of the Gulf of Mexico, accounting for $21.2 billion in economic losses and 159 deaths on average each year ($19.4 billion per event). Data has shown that hurricanes have stricken coastal cities more frequently and more intensely. In 2020, 30 named storms formed in the Atlantic Ocean and 13 of them have progressed into hurricanes. The goal of this research is to investigate the true loadings of extreme winds on civil structures in order to design safer buildings and communities. To accomplish this goal, research has been conducted to properly model these winds using physical and numerical simulation (chiefly computational fluid dynamics simulation), investigate the wind characteristics of extreme winds, and determine how these winds impact civil structures (wind effects), which is required to conduct a hazard-resistant design --Abstract, page iv

Revealing Bluff-Body Aerodynamics on Low-Rise Buildings under Tornadic Winds using Numerical Laboratory Tornado Simulator

Tornadoes result in death and property loss in communities around the world. To quantify the actions of tornadoes on civil structures, researchers have built physical laboratory tornado simulators to simulate tornadoes in the lab environment and tested building models in the simulated tornadic wind field, which is similar to wind tunnel testing when quantifying the wind effects induced by straight-line winds. Unfortunately, physical tornado simulators are much less common than straight-line wind tunnels, leading to the lack of research on bluff-body aerodynamics on civil structures under tornadic winds. Considering that it is expensive to conduct experimental testing in physical tornado simulators, numerical models of physical tornado simulator has been developed using computational fluid dynamics (CFD) simulations. However, they have not been validated at the level of pressure distribution on the structural surface of the testing model. In this study, the numerical model developed for the large-scale tornado simulator of the Missouri University of Science and Technology (Missouri S&T), which is based on the numerical simulation of the entire process of the physical testing in tornado simulator, will be validated by the measured data on the building model tested in the physical tornado simulator. Then, through the validated numerical simulation model, the bluff-body aerodynamics of buildings under tornadic winds will be revealed. To be specific, CFD simulation is first applied to model the entire process of experimental testing of a low-rise building model in the physical tornado simulator. Then, the obtained results are compared with laboratory-measured data to evaluate the effects of the building model on the wind field and the surface pressure on the building model. Then, the bluff-body aerodynamics on low-rise buildings under tornadic winds will be revealed based on the data obtained from numerical simulations using the relationship between streamline pattern change and velocity magnitude change (mass continuity theorem) and using the relationship between the velocity magnitude change and the pressure change (Bernoulli\u27s theorem), as well as the flow separation and vortex shedding

Wind Effects on Dome Structures and Evaluation of CFD Simulations through Wind Tunnel Testing

In the Study, a Series of Wind Tunnel Tests Were Conducted to Investigate Wind Effects Acting on Dome Structures (1/60 Scale) Induced by Straight-Line Winds at a Reynolds Number in the Order of 106. Computational Fluid Dynamics (CFD) Simulations Were Performed as Well, Including a Large Eddy Simulation (LES) and Reynolds-Averaged Navier–Stokes (RANS) Simulation, and their Performances Were Validated by a Comparison with the Wind Tunnel Testing Data. It is Concluded that Wind Loads Generally Increase with Upstream Wind Velocities, and They Are Reduced over Suburban Terrain Due to Ground Friction. the Maximum Positive Pressure Normally Occurs Near the Base of the Dome on the Windward Side Caused by the Stagnation Area and Divergence of Streamlines. the Minimum Suction Pressure Occurs at the Apex of the Dome Because of the Blockage of the Dome and Convergence of Streamlines. Suction Force is the Most Significant among All Wind Loads, and Special Attention Should Be Paid to the Roof Design for Proper Wind Resistance. Numerical Simulations Also Indicate that LES Results Match Better with the Wind Tunnel Testing in Terms of the Distribution Pattern of the Mean Pressure Coefficient on the Dome Surface and Total Suction Force. the Mean and Root-Mean-Square Errors of the Meridian Pressure Coefficient Associated with the LES Are About 60% Less Than Those Associated with RANS Results, and the Error of Suction Force is About 40–70% Less. Moreover, the LES is More Accurate in Predicting the Location of Boundary Layer Separation and Reproducing the Complex Flow Field Behind the Dome, and is Superior in Simulating Vortex Structures Around the Dome to Further Understand the Unsteadiness and Dynamics in the Flow Field

Role of a Laboratory Tornado Simulator in Achieving Tornado-ready Communities

Tornado research is verified by using data from full-scale tornadoes, but this data is difficult and dangerous to obtain. In order to investigate the wind effects of tornadoes on buildings and communities, the use of tornado simulators in the laboratory setting has been employed. These simulators allow for the measurement of the pressures and forces on model versions of full-scale buildings and contribute to the knowledge base that wind engineers and structural engineers can draw on for designing safe homes and facilities. To these ends, a small-scale simulator was constructed in the Wind Hazard and Mitigation Laboratory on the university campus of the Missouri University of Science and Technology. Additionally, testing has been performed in this simulator, and the results compared to numerical simulation and full-scale radar-measurements, to determine the efficacy of the simulator. A large-scale simulator is planned for construction based on these results

Investigation of Structural Failure Modes Induced by Tornadoes through Post-Event Surveys

Tornadoes are violent, short-lived wind phenomenon that can result in catastrophic damage to homes and property. Often times, the occurrence of tornadoes is unpredictable and emergency alerts offer short notice. This leads to families and individuals taking shelter in their own homes or nearby buildings that may not have safe rooms available. The failure of buildings may endanger people\u27s lives. As such, it is imperative to investigate the failure modes of civil structures under tornadoes in order to properly design tornado-resistant buildings. In this study, a comprehensive literature review will be conducted on structural damage to investigate the failure modes caused by real-world tornadoes. To be specific, this research includes the identification of common damage conditions (such as the discontinuity of the load path resulting in the failure of structural components and the breaching of building envelopes resulting in the failure of nonstructural components). The overall goal behind this research is to improve the safety and welfare of the families and individuals living in high tornado risk areas by increasing the knowledge base regarding tornadoes, ultimately making recommendations to update existing building codes in an economically accepted manner

A Review of the Characteristics of Tornadic Wind Fields through Observations and Simulations

Tornadoes are violently rotating columns of air that may be produced by convective clouds and storms, and can produce substantial property damage, injuries, and deaths. To mitigate these losses and encourage accurate modeling and research in the field of civil engineering, with the goal of improving civil structure design, a comprehensive review of field measurements, lab simulations, and computational fluid dynamics (CFD) simulations of tornadoes is conducted. From this review, several tornadoes are examined and their characteristics presented. Specifically, characteristics of these tornadoes are provided in the following form: velocity of the wind field, pressure distribution associated with the wind field, tornado core radius, and flow structure (i.e., single vortex versus multiple vortices; for single vortex, one-celled versus two-celled). In addition, the driving forces behind tornadoes and the relationships between damage and reported intensity are examined, and the physical and numerical simulation of tornadoes conducted in civil engineering are reviewed. This paper is intended to provide a baseline review so that more accurate simulations of tornadic wind fields in civil engineering research can be made by providing some field-measured data from the meteorology community. This will benefit individual safety, community resilience and awareness, and simulation accuracy for future research

Revealing Bluff-Body Aerodynamics on Low-Rise Buildings under Tornadic Winds using Numerical Laboratory Tornado Simulator

Tornadoes result in death and property loss in communities around the world. To quantify the actions of tornadoes on civil structures, researchers have built physical laboratory tornado simulators to simulate tornadoes in the lab environment and tested building models in the simulated tornadic wind field, which is similar to wind tunnel testing when quantifying the wind effects induced by straight-line winds. Unfortunately, physical tornado simulators are much less common than straight-line wind tunnels, leading to the lack of research on bluff-body aerodynamics on civil structures under tornadic winds. Considering that it is expensive to conduct experimental testing in physical tornado simulators, numerical models of physical tornado simulator has been developed using computational fluid dynamics (CFD) simulations. However, they have not been validated at the level of pressure distribution on the structural surface of the testing model. In this study, the numerical model developed for the large-scale tornado simulator of the Missouri University of Science and Technology (Missouri S&T), which is based on the numerical simulation of the entire process of the physical testing in tornado simulator, will be validated by the measured data on the building model tested in the physical tornado simulator. Then, through the validated numerical simulation model, the bluff-body aerodynamics of buildings under tornadic winds will be revealed. To be specific, CFD simulation is first applied to model the entire process of experimental testing of a low-rise building model in the physical tornado simulator. Then, the obtained results are compared with laboratory-measured data to evaluate the effects of the building model on the wind field and the surface pressure on the building model. Then, the bluff-body aerodynamics on low-rise buildings under tornadic winds will be revealed based on the data obtained from numerical simulations using the relationship between streamline pattern change and velocity magnitude change (mass continuity theorem) and using the relationship between the velocity magnitude change and the pressure change (Bernoulli\u27s theorem), as well as the flow separation and vortex shedding

Identification of Existing Stress in Existing Civil Structures for Accurate Prediction of Structural Performance under Impending Extreme Winds

To accurately predict structural performance under impending extreme winds, it is imperative to identify the existing stressing condition in critical structural components before a hazard (intrinsic stress, referred to as existing stress hereafter). The identified existing stress should be added onto the stress induced by future extreme winds in order to determine the real structural performance under these conditions. To identify the existing stress, a novel approach is proposed in this study based on the connection between the unknown existing stress-existing strain curve and the measured stress—strain curve. This approach takes advantage of the known strain information when the material yields. Therefore, an approach to determine when the material yields is also developed. The proposed identification approach does not require any information on previous loads or load effects. Two numerical simulations and one laboratory test are conducted to validate the proposed identification approach. The obtained results demonstrated that the proposed approach is able to identify the existing stress with high accuracy and can be potentially implemented in practical applications

Influence of a Community of Buildings on Tornadic Wind Fields

To determine tornadic wind loads, the wind pressure, forces and moments induced by tornadoes on civil structures have been studied. However, in most previous studies, only the individual building of interest was included in the wind field, which may be suitable to simulate the case where a tornado strikes rural areas. The statistical data has indicated that tornadoes induce more significant fatalities and property loss when they attack densely populated areas. To simulate this case, all buildings in the community of interest should be included in the wind field. However, this has been rarely studied. To bridge this research gap, this study will systematically investigate the influence of a community of buildings on tornadic wind fields by modeling all buildings in the community into the wind field (designated as the Community case under tornadic winds ). For comparison, the case in which only a single building is included in the tornadic wind field (designated as the Single-building case under tornadic winds ) and the case where a community of buildings are included in the equivalent straight-line wind field (designated as the Community case under straight-line winds ) are also simulated. The results demonstrate that the presence of a number of buildings completely destroys the pattern of regular circular strips in the distribution of tangential velocity and pressure on horizontal planes. Above the roof height, the maximum tangential velocity is lower in the Community case under tornadic winds than that in the Single-building case under tornadic winds because of the higher surface friction in the Community case; below the roof height, greater tangential velocity and pressure are observed in the Community case under tornadic wind fields, and more unfavorable conditions are observed in the Community case under tornadic winds than under the equivalent straight-line winds

Influence of Turbulence Modeling on Cfd Simulation Results of Tornado-Structure Interaction

Tornadic wind flow is inherently turbulent. A turbulent wind flow is characterized by fluctuation of the velocity in the flow field with time, and it is a dynamic process that consists of eddy formation, eddy transportation, and eddy dissipation due to viscosity. Properly modeling turbulence significantly increases the accuracy of numerical simulations. The lack of a clear and detailed comparison between turbulence models used in tornadic wind flows and their effects on tornado induced pressure demonstrates a significant research gap. To bridge this research gap, in this study, two representative turbulence modeling approaches are applied in simulating real-world tornadoes to investigate how the selection of turbulence models affects the simulated tornadic wind flow and the induced pressure on structural surface. To be specific, LES with Smagorinsky-Lilly Subgrid and k-ω are chosen to simulate the 3D full-scale tornado and the tornado-structure interaction with a building present in the computational domain. To investigate the influence of turbulence modeling, comparisons are made of velocity field and pressure field of the simulated wind field and of the pressure distribution on building surface between the cases with different turbulence modeling