Windborne Debris Research Articles

LES study on aerodynamics of auto-rotating square flat plate by IBM and SAMR

Windborne debris is caused by severe wind events, such as typhoons and tornadoes. Among the various shapes, sheet-shaped debris has especially complex flight behavior due to the Magnus effect induced by autorotation. In this study, we simulate flows past an autorotating flat square plate pinned with a freely rotatable axis (one degree-of-freedom) and a free-flight flat square plate (six degrees-of-freedom). Therefore, the coupled model for fluid flow and a rigid body based on large-eddy simulation has been developed using the immersed-boundary method and block-structured adaptive mesh refinement to capture details of the vortex structures around the moving plate. This model has such efficiency of computation that the boundary of the moving plate can be treated as passing through a fixed mesh pattern represented by sufficiently fine Cartesian grids, avoiding time-dependent grid generation in a boundary-fitted manner. The aerodynamics of the auto-rotating flat plate was examined and confirmed to validate the present model. Moreover, the unsteady forces based on wake vortices in the process of successive deformation are identified, and their roles on autorotation are clarified. In the case of free flight, the sensitive instability of the axis during autorotation and the effects of translational motion on rotational motion are discussed.

Development of a windborne debris impact fragility curve for Cross-Laminated Timber using experimental testing

Cross-Laminated Timber (CLT) is an engineered wood product with high rigidity, dimensional stability, and desirable environmental properties. Because of these characteristics, it presents the potential to resist the impact loads associated with windborne debris in both tornadoes and hurricanes. Full-scale experimental debris impact testing was performed on 3-layer CLT in order to determine its response to debris impact loading scenarios. A variety of missile masses, speeds, and impact locations were tested to determine this response. Various forms of failure were observed including missile perforation, excessive backside deflection, and dislodgement of debris on the backside of tested panels. Analysis of the experimental data was then performed with the goal producing a debris impact fragility curve for CLT. The resulting curves were based on relating a missile's kinetic energy with the probability of failure as defined by relevant testing standards. The results of this study point towards 3-ply CLT having a high likelihood of surviving impacts from EF-2 and EF-3 level missiles with a decreased likelihood of surviving debris from EF-4 and EF-5 level events. For qualification as a material for safe rooms, thicker panels and additional connection design would be required.

Impact and Post-Impact Performance of Sandwich Wall Boards with GFRP Face Sheets and a Web-Foam Core: The Effects of Impact Location.

In recent years, load-bearing exterior sandwich wall boards have been adopted in civil engineering. The exterior walls of structures are often exposed to low velocity impacts such as stones, tools, and windborne debris, etc. The ultimate loading capacity, deformation, and ductility of sandwich walls are weakened by impact loads. In this study, the sandwich wall boards consisted of glass fiber reinforced plastic (GFRP) face sheets and a web-foam core. The core of wall boards was not the isotropic material. There was no doubt that the mechanical performance was seriously influenced by the impact locations. Therefore, it is necessary to carry out an investigation on the impact and post-impact performance of exterior wall boards. A comprehensive testing program was conducted to evaluate the effects of impact locations and impact energies on the maximum contact load, deflection, and contact time. Meanwhile, the compression after impact (CAI) performance of wall boards were also studied. The results indicated that the impact location significantly affects the performance of wall boards. Compared with an un-damaged wall board, the residual ultimate loading capacity of damaged wall boards reduced seriously, which were not larger than 50% of the designed ultimate loading capacity.

Vulnerability Analyses of Structural Insulated Panels with OSB Skins Strengthened by Basalt Fiber Cloth Subjected to Windborne Debris Impact

In this study, numerical simulations are conducted with a verified model to develop damage threshold curves for structural insulated panels (SIPs) with OSB skins strengthened by basalt fiber cloth subjected to windborne debris impact. Numerical models of the SIP with OSB skins strengthened by basalt fibre cloth at the front or back side are developed by using LS-DYNA. The accuracy of the numerical model is verified by comparing numerical results with laboratory testing data. Using the verified numerical model, intensive simulations are conducted to examine the influence of various parameters, including thickness of basalt fiber, location of basalt fiber layer, bonding strength between the basalt fiber cloth and the OSB skin, on the dynamic responses of the SIP. The debris penetration or fracture of the strengthened SIP that creates an opening is defined as failure of the panel in this study. Empirical formulae are derived on the basis of the numerical results to predict the thresholds of penetration velocity and projectile mass that lead to failure of the SIP. The empirical formulae can be straightforwardly used to assess the performance of the SIP with OSB skins strengthened by basalt fiber cloth subjected to windborne debris impact.

Lentil anthracnose: epidemiology, fungicide decision support system, resistance and pathogen races

Colletotrichum lentis causes anthracnose of lentil (Lens culinaris) in Canada that results in defoliation, stem girdling and severe yield losses, but the disease is rarely reported elsewhere. The pathogen survives as microsclerotia on lentil debris for up to 3 years when buried in the soil, but loses viability on the soil surface. Windborne debris spreads the pathogen to neighbouring fields, while seedborne infection is less important. Foliar fungicides were registered, and a fungicide decision support system was developed which assessed disease risk with 85% accuracy. Around 2300 L. culinaris accessions from 50 countries were screened for resistance. Congruently, two races – Ct1 and Ct0 – were identified on differential lentil lines. Resistant lines were generated by cycles of inoculation and selfing of single resistant plants which resulted in the following three accessions resistant to both races: VIR2633 (Georgia), VIR2058 and VIR2076 (Czech Republic), while six and 49 lines had resistance to Ct0 and Ct1, respectively. Ct1 resistance is controlled by recessive and dominant genes crt1 and CtR3 in variety ‘Indianhead’, ctr2 and CtR5 in accession PI345629 and CtR4 in PI320937. Molecular markers linked to Ct1 resistance were identified on linkage group six, close to Ascochyta lentis resistance, and were used to combine resistance to both pathogens in breeding lines. Two repeat rich regions in the intergenic spacer (IGS) of ribosomal DNA can be used to differentiate the two C. lentis races. Utilizing length polymorphisms in a 39 nucleotide repeat region showed the races were equally frequent among isolates collected between 1991 and 1999, while 95% belonged to race Ct0 in 2010, likely because lentil varieties are susceptible to race Ct0, but around one-third of the varieties had Ct1 resistance.

Exceptional atmospheric events resilience of the curtain wall

The paper presents the results of a research conducted on codes and standards adopted internationally for the design, construction and testing of hurricane- and tornado-resistant facades. These facades are built using technologies that pass tests in order to verify the resistance of both the frame and the glazed surface to the impacts caused by wind-borne debris during these extreme meteorological events. The aim of the research is the identification of the best practices that have been adopted, in order to increase the resilience of building envelopes to this weather phenomenon, evaluating the possible applicability of adopting the principles to the specific needs of the European and Italian market.

Numerical and experimental study of steel wire mesh and basalt fibre mesh strengthened structural insulated panel against projectile impact

Extreme wind events caused damages and losses around the world every year. Windborne debris impact might create opening on building envelop, which would lead to the increase in internal pressure and result in roof being lift up and wall collapse. Some standards including Australia Wind Loading Code (AS/NZS 1170:2:2011, 2011) put forward design criteria to protect structures against windborne debris impacts. Structural insulated panel with Oriented Strand Board skin and expanded polystyrene core has been increasingly used in the building industry. Its capacity was found insufficient to resist the windborne debris impact in cyclonic areas defined in the Australian Wind Loading Code. Therefore, such panels need be strengthened for their applications in construction in cyclonic areas. In this study, impact resistance capacities of seven structural insulated panels strengthened with steel wire mesh and basalt fibre mesh were experimentally and numerically investigated. The impact resistance capacities were identified by comparing the damage mode, residual velocity and unpenetrated length of projectile after impact. Experimental results clearly demonstrated the enhancement of the impact resistance capacities of panels strengthened with steel wire mesh and basalt fibre mesh. Finite element model was developed in LS-DYNA to simulate the dynamic response of the structural insulated panels under windborne debris impact. The accuracy of the numerical model was validated with the testing data.

Finite Element Analysis of Saferooms Subjected to Tornado Impact Loads

A Tornado is one of the most dreadful and unpredictable events in nature. Unfortunately, weather and geographic conditions make a large portion of the United States prone to this phenomenon. Tornado saferooms are monolithic reinforced concrete protective structures engineered to guard against these natural disasters. Saferooms must withstand impacts and wind loads from EF-5 tornadoes – where the wind speed reaches up to 150 m/s (300 mph) and airborne projectiles can reach up to 50 m/s (100 mph). The objective of this work is to evaluate the performance of a saferoom under impact from tornado-generated debris and tornado-dragged vehicles.Numerical simulations were performed to model the impact problem using explicit dynamics and energy methods. Finite element models of the saferoom, windborne debris, and vehicle models were studied using the LS-DYNA software. RHT concrete material was used to model the saferoom and vehicle models from NCAC were used to characterize damage from impacts at various speeds. Simulation results indicate good performance of the saferoom structure at vehicle impact speeds up to 25 meters per second. Damage is more significant and increases nonlinearly starting at impact velocities of 35 m/s (78 mph). Results of this study give valuable insight into the dynamic response of saferooms subjected to projectile impacts, and provide design considerations for civilian protective structures. Further work is being done to validate the models with experimental measurements.

Modelling wind fields and debris flight in tornadoes

This paper describes the derivation of a simple yet realistic engineering model of tornado wind and pressure fields. This novel model is shown to be capable of providing a method for predicting wind speed and pressure time histories and debris impact energies that can ultimately be used in the development of a rational risk-based design methodology for tornado wind loads on buildings. A stationary one-cell tornado vortex is first considered, and the circumferential and vertical velocities and pressure profiles derived from a simple assumption for radial velocity (that is bounded in the radial and vertical directions) and the use of the Euler equations. The generalisation of this model to a two-cell tornado form is then set out. This model is then used to investigate the trajectories of wind borne debris in tornado wind fields, and for the first time, this analysis reveals the important dimensionless parameters of the problem and the parameter boundary between falling and flying debris. An asymptotic long time solution for debris paths is also derived.

Multihazard Interaction Effects on the Performance of Low-Rise Wood-Frame Housing in Hurricane-Prone Regions

AbstractHurricanes represent multihazard events that include wind, windborne debris, storm surge, and rainfall hazards. Conventional risk analysis does not consider the interaction between these mu...

Damage modelling of aluminium panels impacted by windborne debris

Impact by flying debris in windstorms conditions has been a major contributor to damage to aluminium and other types of building facades. The damage so caused to cladding panels was mainly controlled by the amount of force that was developed at the point of contact between the debris object and the surface of the target. However, no codified design guidelines are currently available to quantify the required impact resistance of an aluminium panel for given storm scenarios. Current analytical expressions derived for analysing impact actions as reported in the literature are mostly based on the use of energy principles. The influence of the hardness of the debris object and the magnitude of the contact force has not been taken into considerations. Thus, the amount of deformation that is inflicted on the panel by the impact of a non-rigid projectile object can be over-stated. This paper presents an analytical expression that has been developed for estimating the severity of damage to the surface of a cladding panel (and to determine if leakage of rainwater from the panel can be resulted) for given mass of the debris object, velocity of impact, and importantly, parameters characterising the stiffness properties of the impactor object.

Experimental and numerical study of basalt fibre cloth strengthened structural insulated panel under windborne debris impact

Strong wind causes damages and losses around the world. The windborne debris carried by strong wind might impact on building and create openings on the building envelop, which might threaten the occupants and cause further damages to the building. To address this issue, some wind loading codes including the Australian Wind Loading Code (AS/NZS 1170:2:2011) give design requirements. The resistance capacity of oriented strand board skins structural insulated panel was investigated and proved having low resistance to the projectile impact, and could not meet the impact resistance requirement for application in cyclonic region C and D defined in Australian Wind Loading Code. In this study, basalt fibre cloth is used to strengthen oriented strand board structural insulated panel to increase its capacity to resist windborne debris impact. This paper presents experimental and numerical study of structural insulated panel with or without basalt fibre cloth strengthening under windborne debris impact. Five specimens with different configurations were tested. The dynamic responses were quantitatively compared in terms of residual speed of debris after impact. The results indicate that basalt fibre cloth enhanced the resistance capacity of oriented strand board structural insulated panel. A numerical model is developed in LS-DYNA to simulate the debris impact. The testing results are used to verify the accuracy of the numerical model, which can be used in subsequent parametric studies.

Numerical Study of Basalt Fibre Cloth Strengthened Structural Insulated Panel under Windborne Debris Impact

Strong winds happen around the world every year and cause enormous damages and losses. Besides large wind pressure, impact from windborne debris on building envelope is a major source of structural damage in strong winds. The debris lifted and carried by wind impacting on building envelop may create openings on building envelope which increase internal pressure of the building, and lead to roof lifting and even total building collapse. Preventing impact damage to structural wall and roof is therefore critical in extreme wind conditions. On the other hand Structural Insulated Panel (SIP) with Oriented Strand Board (OSB) skins is popularly used in the building industry. Previous studies revealed that such SIP panels had weak impact resistant capacity and do not meet the design requirements to resist windborne debris impact specified in Australian Standard (AS/NZS1170.2:2011) for their applications in cyclonic regions. To increase the capacity of such SIP panels against windborne debris impact, basalt fibre cloth was used to strengthen the panel. Laboratory tests found that SIP strengthened with basalt fibre cloth was effective in increasing its impact-resistant capacity. This paper presents the development of a reliable numerical model to predict the impact responses of basalt fibre cloth strengthened SIP panel in LS-DYNA. The accuracy of the numerical model is verified by comparing the numerical and experimental results. The validated numerical model provides a reliable tool to predict basalt fibre cloth strengthened SIPs.

Laboratory test and numerical study of structural insulated panel strengthened with glass fibre laminate against windborne debris impact

Cyclone and tornado as common nature disasters have caused devastating damages and losses around the world. In such events loose objects might be lifted and propelled by strong wind as the windborne debris, which is a potential hazard to the building facade because windborne debris impact may create openings on the building envelop, threaten the safety of occupants inside the building and cause further damages to the structure. Some wind loading codes e.g., the Australian Wind Loading Code (AS/NZS 1170:2:2011) specifies the design requirements to address this issue. On the other hand, structural insulated panel (SIP) has been increasingly used in building constructions owing to the advantages of thermal insulation and easy to build, but it is vulnerable to windborne debris impact owing to its insufficient impact resistance capacity. This disadvantage prevents the wide applications of SIP in regions with strong winds, such as the Cyclone region C and D defined in Australian Wind Loading Code. In this study, glass fibre laminate was used to strengthen SIP with OSB (Oriented Strand Board) skins to improve its capacity to resist windborne debris impact. One unstrengthened and six strengthened SIP panels were manufactured and tested by using a pneumatic cannon system. Two high speed cameras were used to capture failure modes and dynamic responses. The effectiveness of glass fibre laminate strengthening was examined and compared in terms of the residual velocity of the projectile. A numerical model was also developed to simulate the laboratory tests. The accuracy of the model was calibrated by the test results. The validated numerical model was then used to conduct more numerical simulations to obtain vulnerability curves of OSB skin SIP panels against windborne debris impact.

Numerical simulation of 3-D probabilistic trajectory of plate-type wind-borne debris

To address the uncertainty of the flight trajectories caused by the turbulence and gustiness of the wind field over the roof and in the wake of a building, a 3-D probabilistic trajectory model of flat-type wind-borne debris is developed in this study. The core of this methodology is a 6 degree-of-freedom deterministic model, derived from the governing equations of motion of the debris, and a Monte Carlo simulation engine used to account for the uncertainty resulting from vertical and lateral gust wind velocity components. The influence of several parameters, including initial wind speed, time step, gust sampling frequency, number of Monte Carlo simulations, and the extreme gust factor, on the accuracy of the proposed model is examined. For the purpose of validation and calibration, the simulated results from the 3-D probabilistic trajectory model are compared against the available wind tunnel test data. Results show that the maximum relative error between the simulated and wind tunnel test results of the average longitudinal position is about 20%, implying that the probabilistic model provides a reliable and effective means to predict the 3-D flight of the plate-type wind-borne debris.

Deterministic solutions for contact force generated by impact of windborne debris

Impact by windborne debris can cause severe and wide spread damage to building facades and other exposed installations. There is no clear guidance on how to estimate the amount of force generated by the impact of windborne debris when design codes of practices only provide estimates of the wind pressure. The model presented in this paper enables the value of the peak contact force generated by the impact of a piece of debris to be predicted. Results of calculations employing the derived relationships have been verified by comparison with experimental results across a wide range of impact scenarios. Once the impact action has been quantified the predicted impact force can be applied to the target in a quasi-static manner for predicting damage.

Experimental investigations of fabric material against projectile impacts

Air supported structures made of PVC coated polyester fabric materials have been used in industrial and commercial building constructions. If they are used in cyclonic regions, the structure envelop might be impacted by windborne debris. The windborne debris might perforate the fabric material, which not only results in total collapse of the structure, flying debris at high speed also imposes threats to people and facilities inside the structure. In this study, the penetration resistant capability of PVC coated polyester fabric material commonly used in air supported structures construction was tested by using a pneumatic cannon system. The impact loading from windborne debris equivalent to a timber projectile of 4kg mass as specified in the Australian Wind Loading Code (AS/NZS 1170.2:2011) was applied in the test. The failure and damage modes under various projectile impact scenarios were observed and compared. Its capability of resisting projectile impact was assessed. The performances of PVC coated polyester fabric material were examined quantitatively in terms of projectile residual velocity and energy absorption. The effects of various projectile velocity, impact location, fabric pretension and boundary condition on their penetration resistance performance were studied. The testing results will benefit construction designers involved in the fabric material applications in high wind speed area.

Detailing Steel Roof Decks to Control Damage from Wind-Borne Debris Impact

AbstractStructurally hardened safe rooms are a proven strategy for enhancing life safety during tornadoes and other severe wind events. Performance criteria for safe rooms include resistance to both wind pressure and impact from wind-borne debris. This paper presents the results of a test program evaluating debris impact resistance of light-gauge steel decking for use as roof cladding on safe rooms. Particular attention is given to the modes of damage caused by debris impact and strategies for controlling and mitigating such damage. Recommendations are provided for detailing lap joints and bearing connections and for selecting appropriate support spacing. This information will aid design engineers in detailing light-gauge steel roof decks for use in tornado safe rooms. Recommendations provided in this paper are also applicable to other scenarios where steel roof decks are at risk of wind-borne debris impact.

Cross-laminated Timber Tornado Safe Room as a Stand-alone Module

A tornado safe room is typically a small interior room such as an office or a bathroom which is strengthened in order to provide occupants with near-absolute protection during extreme loading events such as tornadoes. The loads associated with extreme wind loading events are generally in the form of wind induced pressures or impact loading from windborne debris. These rooms are designed to be structurally independent so as to maintain their integrity given the destruction of the surrounding structure. Prefabrication of such rooms as a stand-alone module can be an important advantage since the proper installation of the connection system is particularly critical to its structural performance. Furthermore, the safe room may be fabricated with utility services such as plumbing, electrical, and HVAC systems. Cross-laminated Timber (CLT) is an innovative engineered wood product that has been increasingly used in building construction over the past decade. It is a massive timber slab with excellent strength and stiffness properties as well as remarkable fabrication precision and dimensional stability. In this study, the feasibility and potential for a modular tornado safe room constructed out of CLT panels is discussed. Such structures may represent viable solutions for difficulties associated with residential safe room construction providing a safe, more sustainable, and potentially economic alternative to conventional systems.

Experimental analysis of a stochastic model for estimating wind-borne compact debris trajectory in turbulent winds

The impact of flying debris against building envelopes during high winds is a major source of structural damage. For example, damage produced by Hurricanes Katrina and Ike in the United States on the facades of tall buildings, located in urban areas, has been documented. It is therefore of relevance to analyze the vulnerability of tall buildings to debris-induced non-structural damage in the general context of performance-based wind engineering. In order to analyze the random trajectory of debris in highly turbulent winds, a numerical model combined with a probability-based algorithm was recently proposed by the authors (Moghim and Caracoglia, 2013). This model investigates the trajectory of “compact debris”, defined as point-mass objects of negligible mass moments of inertia and for which the aerodynamics is predominantly controlled by the drag force. The model replicates both the inherent randomness in debris properties and the effect of wind shear and atmospheric turbulence to estimate debris trajectory and the likelihood of impact against vertical building facades in a probabilistic setting.This paper describes the comparison between numerical model results and wind tunnel experiments. Tests were carried out in the Northeastern University׳s small scale wind tunnel in both smooth flow and grid-generated turbulent flow. The motion of spheres and cubes, simulating compact debris objects, was investigated in two dimensions (2D) on a vertical plane.The 2D motion of compact objects of various sizes was captured by a high-speed digital camera at different flow speeds. Experimental results showed to be consistent with numerical simulations. They also confirmed that not only mean flow speed but also turbulence features can have a non-negligible effect on the trajectory of compact objects.