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Estimation of Wind-Driven Rain Intrusion through Building Envelope Defects and Breaches during Tropical Cyclones
Abstract
Wind-driven rain (WDR) intrusion through building envelope defects and breaches is a major source of damage to building interior components and contents during hurricane landfall. The extent of total building interior damage (damage to building interior components, utility, and contents) is a function of the total volume of WDR intrusion which in turn is dependent on the size of openings, wind speed, and rain intensity. Currently, the volume of rainwater intrusion through a given opening on a building façade is estimated using a semiempirical model with use of parametric information based on engineering judgment. This paper presents a test-based WDR intrusion model which uses values of parameters developed through testing of building models under simulated WDR conditions. The model estimates the total volume of rainwater intrusion through an opening as a summation of WDR volume attributable to direct impinging raindrops and surface runoff rainwater from the undamaged envelope area. Test-based WDR intrusion data measured using a building model with simulated envelope defects and breaches were used to validate the applicability of the new WDR intrusion model to full-scale buildings. Comparison between model estimation results and WDR intrusion measurements through simulated window sill cracks and envelope breaches demonstrated reasonable agreement. The model presented herein can be used to predict the WDR intrusion and subsequent interior damage to low-rise buildings during tropical storms and hurricanes.
... Also, typically due to the deflection of air and rain, the deposit of rain is higher on the top and sides of a building in comparison to the remaining surfaces. Baheru et al., (2014a) and Vutukuru et al. (2020) identified that water intrusion into a building can be attributed to three categories: pathways, sources and driving forces, as shown in Figure 1. (Vutukuru et al. 2020) Specific to hurricane-prone regions in the U.S., damage assessment studies published by the Federal Emergency Management Agency (FEMA) following the active 2004 and 2005 Atlantic hurricane seasons identified several instances where significant losses to building interiors and contents directly resulted from water intrusion through various openings and breaches of the building envelope (FEMA 2005a(FEMA , 2005b. ...
... Existing risk assessment models include FEMA-HAZUS (discussed in Subramanian et al., 2014) and the Florida Public Hurricane Loss Model (FPHLM) (discussed in Baheru et al. 2014). However, the interior damage is treated as a function of the total volume of water entering a building, which is calculated based on semi-empirical models with assumed WDR parameters and engineering judgement (Baheru et al., 2014a). Due to a lack of quantitative data, there is a possibility of high-level uncertainty in the estimated water volume in these semi-empirical methods. ...
... Chowdhury et al. (2011) conducted similar experiments with the 6-fan WOW system to investigate water intrusion volumes through commonly installed roof vent devices. Baheru et al. 2014a andBaheru et al., 2014b reported their efforts to simulate hurricane-level wind and WDR conditions with the 12-fan WOW facility at FIU. Under these simulated conditions, Baheru et al., 2014c conducted a detailed study of water deposition on the façade of a 1:4 scale residential building model to improve the risk assessment methodology in the FPHLM. ...
Executive Summary The objective of the proposed research is to experimentally and analytically assess wind-induced water intrusion through typical sliding glass door systems installed in residential mid-rise buildings. Another aim of this project is to investigate the wind-driven-rain (WDR) impact with and without the presence of common shuttering systems, namely aluminum storm panels and accordion-style shutters. This project investigated water intrusion through a full-scale sliding glass door system installed on a large-scale building model. To accomplish the goals, wind-driven-rain (WDR) tests were conducted for multiple wind directions, test durations and wind speeds to study their effects on water intrusion through the sliding glass door system. Water intrusion effects were studied with respect to wind speed, test duration, and wind direction for configurations with and without shuttering systems. Pressure equalization across shuttered sliding glass doors was also investigated. The following list summarizes the research findings: The highest differential pressure on the sliding glass door occurred at the 0° wind direction and it decreased in magnitude as the model was rotated toward 45°. Shutters provided a sheltering effect and resulted in a lower and more uniform pressure differential on the sliding glass door when compared to the non-shuttered test cases. Significant water intrusion was observed for all test configurations during the 130 mph wind speed tests. Substantial differences in the water intrusion volumes were observed between the aluminum storm panel configuration and the accordion shutter system configuration. There was a general trend that the volume of water intrusion increased as the test duration increased. This trend was most significant for the aluminum storm panels at 100 mph. Results at lower wind speed suggest that oblique wind directions may be vulnerable to high levels of water intrusion. This study demonstrated that significant levels of water intrusion can occur during conditions well below design-level. This project also demonstrated that variability could exist among various shuttering systems with regards to their potential sheltering effect for reducing water intrusion. More research is needed to investigate the impact of different shutter installation methods, types, and geometries to discover optimal installation techniques for potentially reducing water intrusion effects. Future research should more thoroughly investigate water intrusion at oblique angles under higher wind speed conditions to confirm this observation. The new knowledge regarding will help quantify usefulness of shutters to reduce the risk of WDR intrusion. The Florida Public Hurricane Loss Model (FPHLM) can use the test-based data to estimate WDR loss reduction benefit provided by shutters using a risk modeling platform. The data also provide means for minimizing water intrusion. Thus, the research is important for Florida and Floridians in terms of understanding WDR intrusion and what types of shutters may help to reduce water intrusion. The research activities helped in training students with expertise in hurricane damage mitigation. The team plans to disseminate project results through journal publication and report. Also, video recording of the testing is planned to be made publicly available by FIU IHRC/EEI to demonstrate the water intrusion, helping researchers, stakeholders, and citizens to observe water penetration through the sliding glass door. Section 2 page 3 Introduction The use of shuttering systems on windows, doors and sliding glass doors is a common practice in hurricane-prone regions, such as Florida. Internal pressurization due to a broken window/door is not desirable during extreme wind events because this may lead to catastrophic damage to the building. Florida Building Code (FBC) recommends the use of shutters primarily to protect the building façade from flying debris. Shutter components are typically product-rated to resist the impact during hurricanes based on standardized testing methodologies. However, it is unclear whether various shutter systems can provide additional resistance to water intrusion into the buildings. To address this question, a previous study was performed at the FIU Wall of Wind Experimental Facility that investigated water intrusion through shutters, impact resistant and unprotected windows against hurricane force wind speeds on a large-scale building model with a 1:4 scale raindrop size distribution (RSD). The results showed that there was a significant decrease in the water intrusion for the shuttered and impact resistant windows compared to unprotected windows. Hence, it was concluded that in addition to providing resistance against flying debris, shutters may also provide resistance to water intrusion into the building. To expand on these results to other building components, the current project studies the effect of shutters on a full-scale sliding glass door. For this purpose, a building with full-scale sliding glass door model was tested against simultaneous wind and rain starting with wind speeds ranging from tropical storm to a major hurricane range. Further, a full-scale RSD (based on Tokay et al., 2008 Gamma model) is better simulated at WOW during the current testing. The objective of the proposed research is to experimentally and analytically assess wind-induced water intrusion through typical sliding glass door systems installed in residential mid-rise buildings. Another aim of this project is to investigate the WDR impact with and without the presence of common shuttering systems, namely aluminum storm panels and accordion-style shutters. The results may help develop an understanding of the difference(s) between shutter types for rain intrusion vulnerability. To accomplish these goals, water tests were conducted for multiple wind directions, test durations and wind speeds to study their effects on water intrusion. Pressure equalization across shuttered sliding glass doors was also investigated.
... Since they represent one of the main structural systems in the coastal areas, they contribute significantly in the total hurricane-induced losses [9]. Specifically, if excluding the areas where storm surge is the prevailing damage cause, wind-induced loads, windborne debris and wind-driven rain ingress [10][11][12][13] are the dominant mechanisms by which hurricane inflict the damage. Therefore, it is important to assess the hurricane-induced damage/loss in the affected areas under a changing climate which will allow for the development of effective and appropriate risk mitigation strategies. ...
... Content loss is due to damage to any component not attached to the building (e.g., furniture and appliances) and is assumed to occur when water enters the interior of the building due to breach in the enclosing. It should be noted that the amount of rain intrusion depends on the rain event duration and the wind speed itself [10]. Several studies have reported high correlation coefficients between the rain intensities and wind speeds, which can reach values between 0.85 and 0.82 [53][54][55]. ...
... Several studies have reported high correlation coefficients between the rain intensities and wind speeds, which can reach values between 0.85 and 0.82 [53][54][55]. On the other hand, with the increasing duration of the rain event, the total rain intrusion through defects, driven by wind, will increase [10]. ...
Hurricanes are considered as one of the most devastating natural hazards. Their induced risk is expected to significantly increase with the changing climate conditions. Residential buildings are specifically highly vulnerable to hurricane winds. Therefore, accurate assessment of hurricane induced losses under changing climate conditions is crucial to assist in the development of the best mitigation strategies. In this paper, a stochastic hurricane risk assessment framework accounting for several climate scenarios is developed to assess the hurricane-induced losses of residential buildings located in hurricane-prone regions. Specifically, a total of 10,000 years of synthetic storms will be generated for both ‘observed climate’ and ‘future climate’. The future climate models correspond to the worst-case scenario SSP5-8.5 and are simulated based on two global climate models. Then a physics-based wind model is coupled with the synthetic tracks to generate the hazard probabilities. To accurately capture the upper tail effects, the Gaussian kernel density estimation function is proposed in this study. The effects of the variability of climate change models on the wind hazard and its induced losses are quantitatively evaluated. The average annual regional loss is selected as the decision variable. The framework is applied to a one-story single-family wood frame residential building in three different cities, namely Atlantic City, Miami and Galveston. Three mitigation strategies are evaluated, with varying degrees of structural mitigation, by comparing the corresponding losses incurred under different climate change scenarios. It is shown that, due to the disproportionate variation of hurricane intensity and frequency over the coastal areas, the estimated annual losses with the consideration of several mitigation strategies change unevenly from one location to another. Also, the selection of inappropriate probability density function to estimate the wind distribution might underestimate the hurricane-induced loss which is mainly due to its incapability to accurately capture the upper tail ends of the wind distribution.
... Although the importance of damage to the building envelope of engineered systems due to local actions has been documented (e.g. Pita et al., 2012;Barbato et al., 2013;Baheru et al., 2015), the majority of the work in this area has focused on describing performance in terms of the response of the structural system. Other aspects that are generally ignored are the damage and losses generated by the action of local wind pressures, the water ingress, and debris impact. ...
... These sources of risk have the potential to induce damage to the envelope components, and subsequent losses, through the actions of dynamic internal and external wind pressure, dynamic structural responses, debris impact, and rainwater ingress (e.g. Kareem, 1986;Minor , 2005;Baheru et al., 2015;Minor , 1994). Among these actions, significant interaction exists, e.g. ...
... Barbato et al., 2013;Pita et al., 2012;Unnikrishnan and Barbato, 2016) have been proposed. While for low-rise residential buildings the important role played by the building envelope in dictating performance is well understood (Pita et al., 2012;Barbato et al., 2013;Baheru et al., 2015), the same cannot be said for engineered structures, e.g. multistory buildings. ...
The adoption of performance-based wind engineering (PBWE) is rapidly becoming recognized as a fundamental step to reducing the economic losses induced by severe windstorms. A number of PBWE frameworks for the assessment of engineered building systems such as high-rise structures have been introduced. Although these frameworks have resulted in significant progress toward the efficient and effective estimation of performance within a PBWE setting, there is still a significant lack of frameworks that can holistically model the performance of the envelope systems of engineered buildings, notwithstanding how these systems are often critical to the overall performance of engineered buildings. The lack of research on this topic is mainly due to the high complexity of modeling the interdependent physical processes leading to damage. These processes include the 3D turbulent wind flow, wind-driven-rain and rainwater runoff, flying debris, internal/external wind pressures, structural dynamic responses, story drift/net pressure-induced envelope damages, debris impact-induced damages, and water ingress. As analytical solutions do not exist for this type of problem, efficient computational frameworks must be developed. To address this situation, this research presents a performance-based wind engineering framework that integrates system-level structure and envelope performance assessment. In particular, the external surface pressure is generated through a wind tunnel-enabled proper orthogonal decomposition (POD)-based non-Gaussian simulation framework while the stochastic internal pressures at envelope openings are modeled through a nonlinear coupled system of equations derived through the application of the unsteady-isentropic form of the Bernoulli equation and the principle of mass conservation. Linear modal analysis or high-fidelity nonlinear finite element methods (FEM) are used in modeling the dynamic structural responses as well as any subsequent damage. To predict the envelope component damage, suites of coupled fragility functions are derived to account for the effect of multiple demands acting simultaneously. As a concurrent hazard event, wind-driven rain is modeled in a separate computational fluid dynamics (CFD) domain where the mean wind flow is solved through a 3D Reynolds-averaged Navier-Stokes (RANS) equation with realizable emph{k}-epsilon model. Based on this mean wind flow, the wind-driven rain is solved through an Eulerian-multiphase model with turbulent dispersion considered. For efficiently estimating probabilistic performance metrics in terms of the total repair cost and amount of water ingress, the framework is further integrated into a conditional stochastic simulation framework where the uncertainties in the hazard inputs, such as wind speed, stochasticity of the aerodynamic loads, wind direction, and rainfall intensity are propagated to the system responses. Finally, the effect of the hazard duration on the performance metrics is investigated. In this respect, in place of the classic assumption of a nominal wind and rain hazard of 1-hour duration, a synthetic tropical cyclone approach is adopted in which the entire duration of the hurricane is simulated resulting in time-varying inputs of wind speed, wind direction, and rainfall intensity. A comprehensive comparison, in terms of a full range of probabilistic performance metrics, is carried out illustrating the limitations of current practice.
... The semi-empirical winddriven rain (WDR) model and numerical analysis using computational fluid dynamics (CFD) are two options for the rainwater intrusion evaluation (e.g. Pita et al. 2012;Baheru et al. 2015). The CFD approach provides a more detailed assessment of WDR at a price of greatly increased complexity and cost in both modelling and computation. ...
... Because of the computationally intensive procedure involved in their CFD approach, only the impinging rain on one roof corner was explicitly calculated, and rainfall on other roof areas were estimated based on the calculated values at the roof corner (Dao 2010). The semi-empirical WDR models were adopted by Pita et al. (2012) and Baheru et al (2015) to evaluate rainwater intrusion through roof and wall openings as well as building deficiencies and cracks. The pioneering study by Pita et al. 17 (2012) proposed the method to assess rainwater intrusion for houses in the US subjected to hurricanes based on event-based hurricane wind and rainfall models as well as the semiempirical WDR model. ...
... Several model parameters in Pita et al. (2012) are assigned with assumed values which are left for estimation and calibration by experiments. Baheru et al. (2014) and Baheru et al (2015) further conducted both wind tunnel and full-scale tests to estimate these parameters in the WDR model for low-rise residential buildings subjected to hurricanes. Johnson et al. (2018) further extended the method by Pita et al. (2012) ...
Non-cyclonic windstorm is a major natural peril that causes substantial economic losses to housing in New South Wales, Victoria and southeastern Queensland where the majority of Australia’s population live. Housing in non-cyclonic regions of Australia comprises a large portion of metal-clad contemporary houses with complex hip-roof geometries. According to post-damage surveys, wind-induced losses to Australian contemporary houses mainly result from direct wind damage to roof and windows as well as associated rainwater damage to building interior and contents. Construction defects have also been observed as a major contributor to housing damage during windstorms. There is a lack of systematic approaches to assess wind and rainfall losses for metal-clad contemporary houses in non-cyclonic regions of Australia with an explicit modelling of construction defects. Risk mitigation and climate adaptation aim to improve building resilience to wind hazards and reduce economic losses associated with wind damage under a changing climate. Although several mitigation/adaptation measures for Australian housing have been proposed in the literature, quantitative evaluations of their cost-effectiveness are still limited. There is a need for a quantitative decision support model to assist relevant decision-makers and stakeholders in choosing appropriate mitigation/adaptation measures for the protection of houses against wind hazards.
This PhD research develops a probabilistic risk assessment (PRA) and decision support framework for metal-clad contemporary houses subjected to non-cyclonic windstorms. The PRA framework integrates hazard modelling for extreme wind speed and associated rainfall, reliability-based wind damage assessment for roof system and windows, rainwater intrusion evaluation and economic loss estimation. A probabilistic construction defect model including five types of defects in roof connections is also developed, which can be readily integrated into the PRA framework to account for the reduced roof reliability and performance due to defective roof components. A scenario-based approach is adopted to include climate change impact on extreme wind speed and associated rainfall. The developed PRA framework is illustrated on representative metal-clad contemporary houses in two Australian cities − Brisbane and Melbourne (i.e. capital cities in Queensland and Victoria). Risk-based decision models are employed to provide decision support to identify cost-effective measures for risk mitigation and climate adaptation. The magnitude of uncertainty and decision-makers’ risk preferences (i.e. risk aversion, risk-neutrality and risk proneness) are taken into account in the decision-making. The implications for mitigation/adaptation decisions with the consideration of insurance and economic incentives are also discussed.
The PRA and decision analysis results suggest that rainwater damage to building interior and contents is a major contributor to economic risks for Australian contemporary houses subjected to non-cyclonic windstorms. Installing window shutters is a promising mitigation/adaptation measure for homeowners in Brisbane to implement. Climate change has a marginal influence on the cost-effectiveness of mitigation/adaptation measures. The outputs of this PhD research can assist insurance and re-insurance industries in catastrophe risk management, government agencies in disaster planning and management, and homeowners in choosing cost-effective mitigation/adaptation measures to protect their home against windstorms. This research paves the way towards a more resilient residential community under wind hazards.
... El problema de la interacción entre la lluvia y un edificio ha sido estudiado por Straube (1998), Straube y Burnett (2000), Blocken et al. (2005Blocken et al. ( , 2010Blocken et al. ( , 2012, y Choi (1993Choi ( , 1994 pero no para el caso de tormentas tropicales. Investigaciones recientes por Baheru et al. (2013aBaheru et al. ( , 2013bBaheru et al. ( , 2014 son las primeras en cuantificar experimentalmente el impacto de la lluvia y el escurrimiento de agua sobre un inmueble en condiciones típicas de un huracán. El enfoque de este artículo es la integración de los resultados de estos ensayos con el modelo de daño exterior del FPHLM (2012), para cuantificar el volumen de agua que penetra en un edificio y el subsecuente daño interior. ...
... Experimentos a gran escala se llevaron a cabo en el "Muro de Viento" de la Florida International University de Miami para medir el factor de admitancia de lluvia (FALL) y el coeficiente de escurrimiento de superficie (CES) para un edificio de un piso con techo a dos aguas, techo a cuatro aguas, y techo plano, para varias velocidades y direcciones de viento. Los resultados detallados de los ensayos se encuentran en Baheru et al. (2013aBaheru et al. ( , 2013bBaheru et al. ( , 2014. ...
... Como ya comentamos más arriba, Baheru et al. (2014) produjeron mapas de contorno de FALL y CES sobre la superficie de un edificio para 3 direcciones de viento (0, 45, y 90 grados). Estos resultado fueron extrapolados a otras direcciones basado en la simetría del edificio, y los mapas de contorno se simplificaron en mapas de zonas (ver Figuras 1 y 3). ...
... Field studies have been conducted to categorize wind and wind-driven rain's impact on each of these components (FEMA 2005a, b). Large-scale testing has been conducted to observe the effects that rain penetration can have on residential windows, walls, and full-scale structures (Baheru et al. 2014a;Salzano et al. 2010;Lopez et al. 2011;Bitsuamlak et al. 2009;Baheru et al. 2014b). This section summarizes recent efforts to study hurricane-associated wind-driven rain on wood-frame residential structures, as WDR provides the necessary conditions for fungal biodeterioration (wood moisture content above 30%, temperatures above 25°C). ...
... In addition, they found that self-adhered and heavy secondary water barriers performed better than nailed and light secondary water barriers (Bitsuamlak et al. 2009). Baheru et al. (2014b) in testing a small enclosed structure at Wall of Wind further found that the volume of moisture intrusion through small structural defects (such as a window sill crack) can be greater than that through large building envelope breaches from wind borne debris (Baheru et al. 2014a, b). Consequently, nonstructural components and cladding likely pose a substantial risk for moisture intrusion leading to structural biodeterioration. ...
The increasing frequency of high-intensity hurricanes and associated flooding can expose residential structures to severe moisture intrusion and initiate fungal biodeterioration of structural elements. This state-of-the-art review discusses the effects of moisture intrusion from hurricane events and subsequent biodeterioration in residential wood-frame structures in the southeast United States. The review is structured to follow the timeline of progressive biodeterioration. Moisture intrusion during the hazard event is considered through post-hazard damage assessments and experimental efforts. Fungal decay inception and propagation are considered from a plant pathology view, including the limited engineering literature on the mechanical effects of decay. The long-term impacts of biodeterioration on housing and residents are explored through a social-science based discussion of pre-hazard risks and post-disaster recovery. Additionally, recommendations are suggested to prevent and mitigate wood degradation. The review found that little effort has been conducted at the scale of timber framed structures to evaluate the effects of biodeterioration from a structural engineering viewpoint, nor have existing efforts considered the long-term effects of wood rot on housing availability or health.
... [17,9]). Recently, these WDR methods have been extended to evaluate the amount of rainwater intrusion through building envelope breaches during hurricanes for timber-framed houses in the US [21,22,45,8,36,43]. Although the CFD approach provides a more detailed assessment of WDR, it increases the complexity and cost in both modelling and computation [11]. ...
... where A G is the area of the gap (mm 2 ), and f v is a velocity ratio that accounts for the speed change of air as it passes through small gaps, cracks and openings on buildings [8]. As shown in Table 5, the f v value is assumed to follow a normal distribution with a mean of 2.50 and a standard deviation of 0.30 which is estimated based on the environmental design guide CIBSE [20] for air infiltration driven by wind through small gaps in buildings. ...
Severe windstorms cause millions in losses annually for housing in Southeast Australia that has more than half of Australia’s population. The risk assessment for housing in these non-cyclonic regions is the key to assessing the cost-effectiveness of relevant wind mitigation measures to reduce economic losses. This study develops a probabilistic risk assessment framework to evaluate the wind and rain losses for new Australian contemporary houses correctly built and inspected to current standards that are subjected to non-cyclonic windstorms, which integrates the hazard modelling for extreme wind and associated rainfall, reliability-based wind damage assessment, rainwater intrusion evaluation and economic loss modelling. The risk analysis was conducted for metal-roofed contemporary houses in Brisbane and Melbourne, and the efficacy of the proposed risk assessment framework was demonstrated by comparing with inferred insurance loss data. It was found that rainwater damage to building interior and contents is the major contributor to annual expected economic losses associated with windstorms, whereas wind damage to roof cladding and windows comprises a small portion of annual losses. Preliminary model outputs also indicate that houses in Brisbane are generally subject to more losses than houses in Melbourne. However, modelling assumptions that lead to these results have yet been fully validated.
... Choi 1994a; Blocken & Carmeliet 2002). Recently, these WDR methods have been extended to evaluate the amount of rainwater intrusion through building envelope breaches during hurricanes for timber-framed houses in the US (Dao 2010;Dao & van de Lindt 2010;Pita et al. 2012;Baheru et al. 2015;Johnson et al. 2018;Pant & Cha 2019). Although the CFD approach provides a more detailed assessment of WDR, it increases the complexity and cost in both modelling and computation (Blocken & Carmeliet 2010). ...
... where AG is the area of the gap (mm 2 ), and fv is a velocity ratio that accounts for the speed change of air as it passes through small gaps, cracks and openings on buildings (Baheru et al. 2015). As shown in Table 5, the fv value is assumed to follow a normal distribution with a mean of 2.50 and a standard deviation of 0.30 which is estimated based on the environmental design guide CIBSE (2015) for air infiltration driven by wind through small gaps in buildings. ...
Severe windstorms cause millions in losses annually for housing in Southeast Australia that has more than half of Australia’s population. The risk assessment for housing in these non-cyclonic regions is the key to assessing the cost-effectiveness of relevant wind mitigation measures to reduce the economic losses. This study develops a probabilistic risk assessment framework to evaluate the wind and rain losses for Australian contemporary houses subjected to non-cyclonic windstorms, which integrates the hazard modelling for extreme wind and associated rainfall, reliability-based wind damage assessment, rainwater intrusion evaluation and economic loss modelling. The risk analysis was conducted for metal-clad contemporary houses in Brisbane and Melbourne. It was found that damage to building interior and contents 18 caused by rainwater intrusion associated with extreme winds is the major contributor to the annual expected economic losses, and houses in Brisbane are generally subjected to higher losses than houses in Melbourne.
... The test results by Baheru et al. (2014a) also revealed that the RAF values are sufficiently independent of wind speed in tropical cyclone wind conditions to justify extrapolating the results to various wind speeds in the vulnerability model presented in the following sections. ...
... When evaluating roof components, the Lref corresponds to the projection of the roof plan dimension parallel to the wind direction (i.e., roof width for wind normal to the ridge, roof length for wind parallel to the ridge, and diagonal roof dimension for oblique wind direction). Fig. 5 illustrates the concept of reference surface runoff area (rectangle) for SRC quantification on the roof surface (Baheru et al. 2014a); L 1 is the roof length and L 2 is the projected roof width excluding the roof slope. Similar to the RAFs, the test results revealed important insights on surface-runoff rainwater accumulation specific to hurricanes conditions. ...
Recent large-scale tests provided valuable insight into the wind driven rain deposition distribution and subsequent water surface run-off for low-rise buildings in hurricane conditions. These tests led to better understanding of the phenomena associated with water intrusion through the building envelope, one of the predominant factors contributing to interior damage from hurricanes. This paper incorporates those test results within a vulnerability model along with a directionality scheme to model the effect of change of wind direction on water deposition on building facades to quantify the volume of rainwater ingress into a building through building defects and breaches of building components in order to improve the prediction of insured losses. This paper describes the model enhancement and implementation, and the resulting changes in the vulnerability model.
... The studies have focused on providing a foundation that can be used, based on the PEER framework [7,13,52] to evaluate wind-excited tall buildings and other structures (i.e., bridges). Afterward, various studies were conducted, and several frameworks for residential buildings as well as different engineered systems were proposed [11,12,16,[117][118][119][120][121][122][123][124][125][126][127][128][129][130][131]. ...
... Regarding the WDR loading on facade, Blocken and Carmeliet [63] published a review paper in 2004 and summarized the methods in quantifying WDR load on building façade, i.e. experimental, numerical, and semi-empirical. In 2015, Mirrahimi et al. [64] emphasized the [25] SM WD RSh Arch et al. [26] SM WD RSh Vutukuru et al. [27] SM -FD Raji et al. [28] SM WD RSh Cho et al. [29] SM RI, WS BG FM Blocken et al. [30] FS --Tang et al. [31] FS RI, WS, WD -Blocken et al. [32] FS -FD Blocken et al. [33] FS --Nore et al. [34] FS --Briggen et al. [35] FS -FD Wang et al. [36] FS RSD, RI, WS, WD FD CFD RANS LPT Blocken et al. [30] FS --Tang et al. [37] FS RSD, WS, WD -Blocken et al. [38] FS RI, WS, WD -Blocken et al. [39] FS RI, WS BG Blocken et al. [40] FS --Blocken et al. [41] FS -FD Abadie et al. [42] FS --Briggen et al. [35] FS -FD Abuku et al. [43] FS RI, WS -Blocken et al. [44] FS RI BG Blocken et al. [45] FS -BG Blocken et al. [46] FS Foroushani et al. [47] FS RI, WS, WD FD Blocken et al. [48] FS RSD, WS -Ge [49] FS RI, WS, WD -Jiang et al. [50] FS --Kubilay et al. [51] FS RSD, RI, WS FD Khalilzadeh et al. [22] FS/SM WD -EM Huang et al. [52] FS RSD, WS -Huang et al. [53] FS --Kubilay et al. [23] FS RSD, WS -Kubilay et al. [54] FS RSD, WS -Wang et al. [19] FS WD -Raghavan et al. [55] FS RI FD Wang et al. [ importance of experimental data for the validation of numerical and semi-empirical methods in order to predict WDR loading on buildings. Blocken et al. [11] in 2013 reviewed façade response to WDR, i.e. the second part of WDR; and the rainwater runoff from building facades and the difficulties of runoff quantification were discussed. ...
Wind-driven rain (WDR), as one of the environmental loads, is an important factor in designing durable and climate-resilient buildings. The negative consequences of moisture intrusion caused by WDR include degradation of surface material, frost damage, salt efflorescence, structural cracking, interior damage, etc. WDR has been extensively studied through experimental measurements, numerical simulations, and semi-empirical methods. The previous WDR studies can be categorized into two areas: the study of WDR loading on buildings and the investigation of façade response to the impinging raindrops. While previous studies have investigated the characteristics of WDR loading on façade, such as the wetting pattern on various building configurations, i.e. stand-alone (isolated), street canyon, building-array, urban area. This review paper synthesizes results from the previous studies and provides a comprehensive summary and comparison of research approaches and their outcomes regarding quantification of WDR loading on building facades. The effect of meteorological and geometrical parameters on the interaction of WDR and buildings has been discussed. A cross-comparison of the WDR results has been performed based on previous experimental, CFD, and semi-empirical studies. The effectiveness of RANS and LES approaches has also been discussed. This paper shows that WDR results depend on the CFD approach selected and on the type of WDR modeling techniques used, i.e. Lagrangian Particle Tracking (LPT), and Eulerian Multiphase (EM). It is important to consider turbulent dispersion for the lower part of the windward façade in the case of high-rise buildings in CFD simulations. Finally, the review highlights potential research gaps in WDR.
... reliability integral), to the performance assessment of wind excited tall buildings and long span bridges. Since these initial research efforts, PBWE has seen an explosion of interest with numerous frameworks being proposed for both residential buildings (Rosowsky and Ellingwood, 2002;Barbato et al., 2013;Baheru et al., 2015;Peng et al., 2016;Unnikrishnan and Barbato, 2017) as well as engineered systems (Ciampoli et al., 2011;Griffis et al., 2013;Spence and Kareem, 2014;Bernardini et al., 2015;Judd and Charney, 2015;Chuang and Spence, 2017;Cui and Caracoglia, 2018;Judd, 2018;Chuang and Spence, 2019;Ierimonti et al., 2019;Micheli et al., 2019;Mohammadi et al., 2019;Cui and Caracoglia, 2020;Ouyang and Spence, 2020). ...
This paper surveys the rapidly growing field of performance-based wind engineering (PBWE) of engineered systems, with focus on not only how PBWE has evolved since its early incarnations inspired by performance-based seismic engineering, but also the unique challenges of PBWE and the research that continues to emerge to tackle them. The limitations of traditional prescriptive wind design approaches are discussed with the aim of illustrating how such approaches are inadequate for providing acceptable building performance during extreme wind events, thus motivating why performance-based strategies for wind engineering are gaining traction and are poised to complement, if not replace, current approaches to wind design. In this respect, the current state of knowledge on the factors that affect building performance via extreme structural response, damage to the envelope system, and nonstructural components, is reviewed and challenges are identified. Lastly, the potential benefit of integrating optimization methods is identified while acknowledging the computational difficulty associated with such approaches.
... To simulate the rotation of the hurricane, the values of WDR1 and WDR2 are distributed in ratios α and β over the eight possible wind direction octants (Johnson et al., 2018) (see Fig. 3). Fig. 3. Example of wind-driven rain distribution Baheru et al. (2015) produced zonation plots of rain admittance factors (RAF) and surface runoff coefficients (SRC) for CR-LR models given 0°, 45°, 90° wind directions. Fig. 4 is an RAF zonation plot for 0° wind direction. ...
... Wind-induced damage to residential buildings can be classified as direct damage to structural or envelope systems and indirect water intrusion damage to the interior of buildings such as interior drywall or furniture (Baheru et al. 2015;Pasch et al. 2005). Recent hurricanes showed that structural systems of residential buildings built in accordance with modern and updated codes have performed well compared to older existing houses. ...
Coastal residential buildings have suffered significant damage during recent hurricanes, which illustrates the poor performance of coastal structures. This paper reviews the performance of coastal residential buildings with respect to direct and indirect damage, and subsequent mitigation techniques are discussed according to hurricane wind and flood-related hazards. The results show that building systems other than conventional wood frames have better performance during strong hurricanes. Regardless of building materials and systems, envelope systems and roofs are more susceptible to wind-induced damage compared to structural components. Therefore, selecting adequate connection systems, suitable wind-resistant materials, and appropriate installation methods for wall/roof coverings can significantly reduce the level of wind-induced damage. Regarding flood-related hazards, surge and subsequent wave heights cause inevitable damage to non-elevated or low elevated buildings once a flood reaches the first-floor level. Furthermore, many elevated buildings surviving a flood can still be vulnerable to wind-induced damage, particularly envelope systems due to the fact that the house would be exposed to higher wind pressures. As a result, selecting the appropriate foundation system and using flood-resistant materials below the base flood elevation can reduce flood-induced damage to residential buildings in coastal regions.
... Over the last two decades, a significant amount of research has been focused on the development of performance-based wind engineering (PBWE). This has led to the introduction of a number of frameworks for the implementation of PBWE in the assessment of both engineered building systems (e.g., high-rise buildings) (Jain et al. 2001;Ciampoli et al. 2011;Smith and Caracoglia 2011;Petrini and Ciampoli 2012;Chuang and Spence 2017;Cui and Caracoglia 2018;Ierimonti et al. 2019) as well as nonengineered building systems (e.g., low-rise residential buildings) (Rosowsky and Ellingwood 2002;Barbato et al. 2013;Baheru et al. 2015;Peng et al. 2016;Unnikrishnan and Barbato 2017). Although the importance of damage to the building envelope of engineered systems due to local actions has been documented (e.g., Williams and Kareem 2003;Vega and Koke 2008;Beers 2011), the majority of work in the area of PBWE frameworks for engineered systems has focused on describing structural and nonstructural performance in terms of the response of the structural system, i.e., damage and losses generated by the action of local wind pressures and debris impact are not generally modeled. ...
The adoption of performance-based wind engineering (PBWE) is rapidly becoming recognized as a fundamental step to reducing
the huge economic losses caused by severe windstorms. This has led to the recent introduction of a number of PBWE frameworks for the
assessment of engineered building systems such as high-rise structures. Although these frameworks have resulted in significant progress
toward the efficient and effective estimation of performance within a PBWE setting, there is still a significant lack of frameworks that can
holistically model the performance of the envelope system of engineered buildings. Recognizing how accurate prediction of losses occurring
during severe windstorms, such as hurricanes, cannot be made without detailed modeling of the losses caused by damage to the envelope
system, this paper introduces a new PBWE framework that is focused on the performance assessment of the envelope system. The proposed
framework is based on integrating a recently proposed building envelope damage model into a conditional stochastic simulation framework
in which the directional wind and concurrent rain hazard is explicitly modeled together with the stochastic nature of the local wind pressure.
By incorporating loss models, performance estimates are provided in terms of annual exceedance rates of system-level metrics such as repair
costs. A full-scale building example is presented to illustrate the practicality of the proposed PBWE framework.
... (Barbato et al., 2013;Pita et al., 2012;Unnikrishnan and Barbato, 2016)] have been proposed. While for low-rise residential buildings the important role played by the building envelope in dictating performance is well understood (Pita et al., 2012;Barbato et al., 2013;Baheru et al., 2015), the same cannot be said for engineered structures, e.g. multistory buildings. ...
The performance assessment of wind-excited multi-story building systems is undergoing a period of rapid change with a number of performance assessment frameworks being proposed that are based on the principles of performance-based design. Having said this, there is still a significant lack of computational frameworks that can holistically treat the building envelope of this class of building systems. Indeed, the majority of research in this direction has focused on estimating damages and losses due to excessive structural response, notwithstanding the important role played by other damage mechanisms, such as those driven by excessive dynamic pressures. This paper introduces a computational framework that can holistically treat multiple damage mechanisms during the performance assessment of building envelopes of wind-excited engineered systems. In particular, interdependent envelope damage states driven by dynamic internal/external wind pressures and structural responses are modeled through multiple dependent fragility functions. Consequences are modeled in terms of the envelope components' final damage states as well as the ingress of wind driven rain. By setting the framework in a simulation environment , probabilistic estimates of the performance metrics are provided as output. A full scale application is presented illustrating the proposed framework.
... Damage to roof covering is historically recognized as a leading building performance problem during high wind events. In hurricanes, rainwater entering a building through damaged roofs can cause major damage to interior finishes and contents (Baheru et al., 2014a;FEMA, 2009). Permeable roof coverings are mostly made of roofing elements attached to an underlying support system and overlapping each other with interlocking patterns. ...
Full-scale experiments were conducted to investigate wind loading on roof tiles in hip, ridge, and perimeter locations, identified from past storms as main points of damage initiation. The objectives were to: (i) provide test-based data on wind-induced loads for tiles, and (ii) evaluate characteristics of near-surface flows to assess tile loading models. The experiments included pressure measurements on the external surface and in the cavity underneath the tiles, and wind speed measurements near tile surfaces. The highest net uplift pressure (computed as external pressure minus the cavity pressure) was observed on the gable end ridge tiles. Except for a few non-critical cases, due to effects of pressure equalization net uplift was lower than external surface uplift. Mean wind speeds at tile surfaces were recorded that were up to 55% higher than the mean wind speed at mid-roof height in the approach flow. Two alternative models that use wind speeds near the tile surface to determine net design wind loads on tiles were investigated. The results showed that the models can underestimate wind loading. However, when used with appropriate parameters, the models can produce results comparable to those obtained using ASCE's external pressure coefficients in conjunction with pressure adjustment factors.
... High dynamic wind suctions created at the surface of a roof due to wind flow separation (or conical vortices) coupled with positive internal pressures are the main cause of damage to the roof systems. Water leaking through a failed roofing system during rain accompanied wind storms can result in major damage to interior contents, disrupt the functionality of critical and essential facilities, and even cause ceiling weakening and collapse which can result in injury to the occupants [1][2][3]. Currently, the performance of metal roofs under wind load is evaluated by undertaking physical tests to assess their capability to withstand a ''design load" as provided by wind loading codes and standards. The ability of such tests to assess the true performance of the roof system depends on how well the tests represent the true wind loading actually experienced in wind storm conditions. ...
The current methods for evaluating the adequacy of metal roofs in withstanding wind-induced loads involve undertaking uniform uplift pressure tests. These methods may not be truly representative of real conditions, and might set higher minimum design requirements than necessary in some cases, and in others they could underestimate effects of very localized peak pressures. This research work presents results of a full-scale experimental study conducted under more realistic wind loading with the panels installed as they would be in the American Society for Testing and Materials (ASTM) E1592 test chamber. The research objectives were to (i) measure the uplift roof pressure experience by mono-sloped standing seam metal roofs and compare them with the provisions of the American Society of Civil Engineers (ASCE) 7-10 standard, (ii) evaluate the performance of standing seam roofs under high winds, and (iii) compare the deflections and failure modes observed under more realistic wind loading to uniform loading tests. The research has provided test based data on aerodynamic loading of two types of standing seam metal roofs (i.e. vertical-leg and trapezoidal), as well as their performances under high wind speeds. Significantly higher pressure was recorded on the trapezoidal roof. This showed that roof panel profile and perimeter eave attachments can significantly affect uplift pressures. The ASCE 7-10 standard was observed to underestimate corner wind suctions on trapezoidal roof. Lower deflections were recorded by the vertical-leg roof owing to its higher stiffness and lower suctions experienced. The ASTM E1592 test protocol was observed to produce higher deflections and more conservative failure wind speeds than those experienced in the current tests. However, entirely different failure modes were observed between the uniform and dynamic tests. This was attributed to wind-induced vibrations that were observed in the current tests that are not present in the ASTM E1592 test, which is entirely static. The current research results may suggest future directions to enhance the existing testing standards.
... The issue of impinging rain and the building vs. driving rain interaction has been studied by Straube and Burnett [6], [7], Blocken et al. [8] and others [9], although not under tropical storm conditions. Recent efforts by Baheru et al. [10], [11], [12] are the first to quantify the fraction of direct impinging rain and accumulated surface runoff on a building system under simulated hurricane conditions. The focus of this paper is the combination of these test results with the exterior and interior damage model developed for the FPHLM [13], [14], to quantify the volume of water penetrating into a building and the subsequent interior damage. ...
This study investigates the resilience of informally-constructed light-frame timber houses in Puerto Rico, a region where households with limited resources face significant risks from climate hazards, notably hurricanes. This study conducts a component-based, performance-based wind engineering assessment of informally-constructed house typologies, defined based on extensive fieldwork, under both existing and projected future climate conditions. Key findings highlight the effectiveness of certain mitigation strategies, such as reinforcing roof-to-wall connections, in significantly reducing the probability of failure. Fully-mitigated cases, which involve applying mitigation measures to the roof envelope, roof-to-wall connections, and shear walls, exhibited annual probabilities of failure that are much closer to, but do not necessarily meet, the threshold targeted by American building standards (i.e., ASCE 7). The results also show a dramatic increase in probability of failure of these houses projected by the adopted climate change model scenarios, driven by the increased frequency and intensity of hurricanes in Puerto Rico. Results from feedback from those working in the informal construction sector also identify challenges hindering the effective implementation of mitigation measures in Puerto Rican communities, including a lack of knowledge about how to implement the mitigation strategies and barriers related to real and perceived costs. Taken together these results underscore the urgent need for changes in building practices and revising building standards and suggesting potentially feasible mitigation strategies to improve those practices.
Despite recent advancements in hurricane hazard characterization and a better understanding of the vulnerabilities of the built environment to hurricane-related hazards, coastal communities still face considerable losses due to extensive damage from hurricanes. Designing and constructing the most vulnerable types of buildings, that is, residential buildings, to be considered as resilient structures can play a significant role in maintaining the functionality of these communities after strong hurricane events. To construct buildings that can maintain or recover functionality in a timely manner after a hurricane event, an organized and clear understanding of the vast extent of hurricane hazards that could disrupt the functionality of buildings is crucially important. This knowledge could enable investigators to pursue research gaps and illuminate less-understood aspects of hurricane-induced failure mechanisms to effectively limit loss of functionality in residential buildings after hurricanes. With this intention, this paper presents a review of the damage mechanisms for different kinds of hurricane-related hazards in low-rise residential buildings and tries to synthesize information in the literature, building codes, and guidelines to identify research gaps. Based on the highlighted gaps, the paper suggests future research endeavors to augment the existing knowledge regarding hurricane-induced loss of functionality through refined or new research methodologies. The paper concludes with a brief discussion on the benefits, limitations, and future directions of the performance and functionality-based design in the context of hurricane engineering and loss assessment in low-rise residential buildings.
Wind-driven rain (WDR), as one of the environmental loads, is an important factor in designing durable and climate-resilient buildings. The negative consequences of moisture intrusion caused by WDR include degradation of surface material, frost damage, salt efflorescence, structural cracking, interior damage, etc. WDR has been extensively studied through experimental measurements, numerical simulations, and semi-empirical methods. The previous WDR studies can be categorized into two areas: the study of WDR impinged on buildings and the investigation of surface reactions to the impinging raindrops. While previous studies have investigated the characteristics of WDR impinged on façade, such as the wetting pattern on various building configurations, i.e. stand-alone (isolated), street canyon, building-array, urban area. This literature review synthesizes results from the previous studies and provides a comprehensive summary and comparison of research approaches and their outcomes regarding quantification of WDR on buildings. A cross-comparison of the WDR results has been performed based on previous experimental, and CFD, semi-empirical studies. The effectiveness of RANS and LES approaches has also been discussed. The report shows that WDR results depend on the CFD approach selected and on the type of WDR modeling techniques used, i.e. Lagrangian Particle Tracking (LPT), and Eulerian Multiphase (EM). It is important to consider turbulent dispersion for the lower part of the windward façade in the case of high-rise buildings in CFD simulations. The effect of meteorological and geometrical parameters on the interaction of WDR and buildings, and used methods of three key papers have been discussed. Finally, the review highlights potential research gaps in WDR.
Asphalt shingles constitute more than 80% of the roofing materials in current residential housing in the United States. Many post-disaster surveys have reported the failure of these roofing elements below the design level wind event. Research to realistically model the aerodynamics of asphalt shingles at full-scale is limited, resulting in knowledge gaps in peak wind loads and effects of permeability. In this study, the aerodynamics and wind resistance of asphalt shingles are studied by using a monoslope roof tested at Florida International University's Wall of Wind Experimental Facility. Results from both aerodynamic and failure assessment test protocols showed that shingles near the upper corners of the roof were subjected to high suctions due to cornering winds. This presents a critical loading case for which asphalt shingle roofing systems are not typically tested using current standard tests. Moreover, the extent of permeability underneath the shingles was observed to vary with the spatial location of shingles and wind direction. Finally, the comparison of area-averaged peak Cp values obtained from this study with GCp plots in ASCE 7-16 Standard showed that these provisions, which do not consider the effects of permeable roofing elements (e.g., shingles), can underestimate wind loads on asphalt shingles.
Rainwater penetration on building façades has a significant impact on the durability, hygrothermal performance, and habitability of buildings. This research characterises the directional exposure of Mexican façades to rainwater penetration by identifying wind-driven rain (WDR) and driving rain wind pressure (DRWP) throughout the country. For this purpose, climatic datasets of daily resolution gathered at 527 weather stations between 2003 and 2018 were analysed. As a result, isopleth maps of annual scalar values of WDR, DRWP, and the approximate orientation of their directional maxima were produced. The joint risk of rainwater penetration (defined by both factors) and the applicability of novel extrapolation that estimates the maximum directional exposures anywhere in Mexico from scalar results are also discussed. Additionally, the influence of certain tropical cyclones on the exposure was characterised, leading to the identification of preliminary patterns associated with these temporary WDR and DRWP exposures. Such extreme climatic events can cause, in a short interval of time, as much WDR as that occurring during the rest of the year and DRWP that is 2–5 times higher than the mean annual value. In general, the highest level of hazard of rainwater penetration on façades was identified west of the Isthmus of Tehuantepec and on the coast of the state of Veracruz.
Posthurricane surveys have shown that building interior damage often results from water intrusion into the building interior. The interior damage can make up 50%–100% of the total building loss; therefore, its accurate evaluation and quantification are necessary for estimation of hurricane losses. In this research, water propagation into a building’s interior was experimentally investigated. Large-scale building models with gable and hip roofs were tested for three exterior damage states. The results showed that for the light damage state, the very small area of the roof and wall defects and breaches does not allow wind circulation inside the building, and as a result, the rain affected only localized areas with defects. However, for the more severe damage states, the areas of breaches were large enough to allow wind circulation inside the building, and the water propagation path is highly affected by the internal wind flow. The findings from the current study can be implemented in hurricane loss models and improve their accuracy by estimating the water distribution inside the building.
Maintaining communications during major hurricanes is critically important for public safety operations by first responders. This requires accurate knowledge of the propagation channel during hurricane conditions. In this work, the authors have carried out ultra-wideband (UWB) channel measurements during hurricane conditions ranging from Category-1 to Category-4, generated at the wall of wind facility of Florida International University. Time-domain P410 radios are used for channel measurements. From the empirical data analysis in time domain, they developed an UWB statistical broadband channel model for hurricanes. In particular, they characterise the effects of rain and wind speed on large-scale and small-scale UWB propagation parameters considering both line-of-sight (LOS) and non-LOS (NLOS) links. Their experimental results show that number of multipath components reduce considerably with wind driven rain (WDR) and with link obstruction (NLOS scenario). Several remarks are also provided that can help explain the behaviour of UWB propagation characteristics under WDR.
Roofing is one of the most vulnerable parts of the building envelope in a residential structure, often damaged during extreme wind events such as hurricanes or tornadoes. Conventional roofing systems in residential buildings mostly consist of separate the main wind force resisting system (MWFRS) and components and cladding (C&C). High wind uplift forces often cause partial or full destruction of one or more of these elements, leading to water intrusion and losses of interior contents. This study focuses on the design, development, and testing of a new composite roofing system that integrates the functionalities of the MWFRS and C&C. The new system is composed of lightweight concrete panels reinforced with fiber-reinforced polymer mesh and rods. The architectural shape of a conventional residential roof with high profile tiles was adopted for the composite roof panels to help provide the requisite structural stiffness and strength of the MWFRS, while maintaining similar C&C aesthetics and avoiding failure of individual tiles that often become wind-borne debris. The panel system was subjected to a battery of tests under equivalent wind loads. In addition, three connections for the system were designed and validated through testing. The panel-to-wall connection provided ample continuity of the vertical load path; the panel to panel connection was found adequate for shear transfer; and the ridge connection allowed for load transfer between the windward and leeward sides of the roof. Tests demonstrated the structural viability of the new system as an alternative to conventional roofs, making it ideal for residential buildings in hurricane zones and tornado alleys. The purpose of the paper is to present details of the system and their structural reliability. Durability and constructibility issues, including cracking, are the object of future work.
Wind-driven rain is one of the main sources of damage to building interior and contents during hurricane landfall. Recently, vulnerability models for hurricane induced total building interior damage (damage to building interior components, utilities, and contents) have been widely developed for prediction of property loss in relation to determination of insurance premiums and development of damage mitigation techniques and guidelines. However, the prediction capabilities of these models have been limited due to the lack of field and experimental data on some specific model parameters. This paper presents an experimental study being conducted to develop test-based data on wind-driven rain intrusion through building envelope breaches caused by strong wind and wind-borne-debris. The study aimed at investigating parameters such as rain admittance factor (RAF) and surface runoff coefficient for different wind directions. The dataset may be used to increase the accuracy and prediction capabilities of existing catastrophe (CAT) models.
The study of wind-driven rain (WDR) has shown a significant progress in past few decades. The applications of semi-numerical and computational fluid dynamics (CFD) methods have shown major advances to reasonably estimate the amount WDR impinging on building facade. The agreement witnessed between numerical results and actual measurements on existing buildings reinforces the above fact. However, standardized testing methodology for WDR which can produce reliable and repeatable test results is still in its development stage. Buildings' component-wise testing methods for WDR effects prescribed in standards and building codes are limited to a simplified application of water with a uniform and cyclic static pressure. The study presented herein focuses on the representation of WDR and the different parameters involved in simulation of WDR in full and large-scale testing facilities. As to the holistic testing approach, many parameters are involved in determining the amount of rain water deposition on building envelope. These parameters consist of wind field characteristics (wind speed profile and turbulence intensity), rain rate, raindrop size spectrum and its integral parameters (drop number concentration and liquid water content per unit volume of air, mean-weight and volume median diameters etc.) and rain duration. The terminal raindrops velocity also has a direct effect on the calculations of WDR rate and in the determination of the level of impact caused by raindrops on building façade. The paper also discusses the processes involved in hurricane level WDR simulation using a 2-fan WDR generator at Florida International University (FIU). The objective is to develop flow management techniques using a 2-fan prototype system that can be applied to simulate the target parameters at the large-scale 12-fan Wall of Wind hurricane wind and rain simulator. WDR is generated using different type of nozzles arranged in a grid pattern with a controlled discharge rate. Rainfall data (drop size distribution and rain rate) collected during tropical cyclones have been used as target for simulating realistic WDR at the testing facility and preliminary results are presented and discussed.
A new full scale testing apparatus generically named the Wall of Wind (WoW) has been built by the researchers at the International Hurricane Research Center (IHRC) at Florida International University (FIU). WoW is capable of testing single story building models subjected up to category 3 hurricane wind speeds. Depending on the relative model and WoW wind field sizes, testing may entail blockage issues. In addition, the proximity of the test building to the wind simulator may also affect the aerodynamic data. This study focuses on the Computational Fluid Dynamics (CFD) assessment of the effects on the quality of the aerodynamic data of (i) blockage due to model buildings of various sizes and (ii) wind simulator proximity for various distances between the wind simulator and the test building. The test buildings were assumed to have simple parallelepiped shapes. The computer simulations were performed under both finite WoW wind-field conditions and in an extended Atmospheric Boundary Layer (ABL) wind flow. Mean pressure coefficients for the roof and the windward and leeward walls served as measures of the blockage and wind simulator proximity effects. The study uses the commercial software FLUENT with Reynolds Averaged Navier Stokes equations and a Renormalization Group (RNG) k- turbulence model. The results indicated that for larger size test specimens (i.e. for cases where the height of test specimen is larger than one third of the wind field height) blockage correction may become necessary. The test specimen should also be placed at a distance greater than twice the height of the test specimen from the fans to reduce proximity effect.
Wind loads on low-rise buildings in general and residential homes in particular can differ significantly depending upon the laboratory in which they were measured. The
differences are due in large part to inadequate simulations of the low-frequency content of
atmospheric velocity fluctuations in the laboratory and to the small scale of the models used
for the measurements. The imperfect spatial coherence of the low frequency velocity
fluctuations results in reductions of the overall wind effects with respect to the case of
Characteristics of the raindrop size distribution in seven tropical cyclones have been studied through impact-type disdrometer measurements at three different sites during the 2004–06 Atlantic hurricane seasons. One of the cyclones has been observed at two different sites. High concentrations of small and/or midsize drops were observed in the presence or absence of large drops. Even in the presence of large drops, the maximum drop diameter rarely exceeded 4 mm. These characteristics of raindrop size distribution were observed in all stages of tropical cyclones, unless the storm was in the extratropical stage where the tropical cyclone and a midlatitude frontal system had merged. The presence of relatively high concentrations of large drops in extratropical cyclones resembled the size distribution in continental thunderstorms. The integral rain parameters of drop concentration, liquid water content, and rain rate at fixed reflectivity were therefore lower in extratropical cyclones than in tropical cyclones. In tropical cyclones, at a disdrometer-calculated reflectivity of 40 dBZ, the number concentration was 700 ± 100 drops m−3, while the liquid water content and rain rate were 0.90 ± 0.05 g m−3 and 18.5 ± 0.5 mm h−1, respectively. The mean mass diameter, on the other hand, was 1.67 ± 0.3 mm. The comparison of raindrop size distributions between Atlantic tropical cyclones and storms that occurred in the central tropical Pacific island of Roi-Namur revealed that the number density is slightly shifted toward smaller drops, resulting in higher-integral rain parameters and lower mean mass and maximum drop diameters at the latter site. Considering parameterization of the raindrop size distribution in tropical cyclones, characteristics of the normalized gamma distribution parameters were examined with respect to reflectivity. The mean mass diameter increased rapidly with reflectivity, while the normalized intercept parameter had an increasing trend with reflectivity. The shape parameter, on the other hand, decreased in a reflectivity range from 10 to 20 dBZ and remained steady at higher reflectivities. Considering the repeatability of the characteristics of the raindrop size distribution, a second impact disdrometer that was located 5.3 km away from the primary site in Wallops Island, Virginia, had similar size spectra in selected tropical cyclones.
Most residential buildings use a natural ventilation process by which overheated air inside buildings is vented out and fresh air is pulled in to replace it. Proper ventilation helps maintain a comfortable temperature inside buildings, maintain indoor air quality, increase energy efficiency, and prevent moisture damage. Vents are necessary to prevent heat and moisture buildup and contribute to the longevity of building components. However, the vents are subjected to wind loading and can be the path for water infiltration during hurricane events. Limited research has been performed on water intrusion through various types of vents in residential buildings to relate such water intrusion to the vent mechanism and the differential pressures that the vents are subjected to during hurricanes. The objectives of this research were to perform full-scale holistic testing of vents subjected to simulated hurricane-level wind and wind-driven rain to evaluate such relations and vent performance under hurricane conditions. Two building models incorporating a variety of vents were tested using the wall-of-wind facility. It was found that the extent to which water intrusion increased with higher positive differential pressure across the vent for various angles of attack can be affected significantly by the vent mechanism. DOI: 10.1061/(ASCE)NH.1527-6996.0000039. (C) 2011 American Society of Civil Engineers.
Hurricanes present a serious financial threat to the Gulf Coast and eastern seaboard of the United States. This paper is the first in a set of companion papers that detail a comprehensive mechanistic loss model for wind and rainwater intrusion damage to light-frame wood buildings. In this paper the structural and hazard modeling for a passing hurricane is explained and demonstrated. The structural model consists of a nonlinear nail model integrated into a finite-element model, and a hazard model is developed using a combination of existing wind tunnel data and a rainwater intrusion model. A methodology to compute the rainwater entry volume is presented. The approach differs from previous methods in that it allows any time period to be examined by dividing the hurricane passage period into smaller increments of time and allows both load and resistance to change from time period to time period. Thus, the time and location of damage and rainwater intrusion is known. The companion paper utilizes the volume of rainwater calculated herein and presents a systematic mechanistic approach to damage state modeling and the related financial loss.
Wind-driven rain (WDR) is among the important environmental variables that affect the performance and durability of building enclosure systems. Although the need to investigate multi-level effects of WDR on building structures has increased through time, the available methods of investigation have been generally limited to field study and application of computational fluid dynamics. This paper investigates the parameters of tropical storm and hurricane-level WDR and presents a methodology of experimental simulation of WDR that may complement the two other investigation methods. Tropical cyclone WDR data acquired through National Aeronautics and Space Administrations’ Tropical Rainfall Measuring Mission ground validation program were used to study the characteristics of tropical storm and hurricane-level WDR and derive the values of target parameters, which were later used in the experimental simulation process. Procedure for determination of target WDR rate, simulation of raindrop size distribution and its integral parameters, and selection of type and number of nozzles are discussed in detail. Similarity requirements and important scaling considerations of WDR simulation were addressed. The procedure was used to simulate WDR using the 12-fan Wall of Wind facility at Florida International University. The experimental simulation results, presented herein, demonstrated satisfactory representation of target rainfall intensity and raindrop size distribution in the test setup. The WDR simulation methodology presented herein may be used for simulation of WDR in testing facilities to evaluate water intrusion in buildings during tropical cyclones, develop solutions to promote functional longevity of building envelope, and enhance current simplified test protocols given in international standards.
Interior damage is a significant portion of overall building damage caused by hurricanes. Most of the vulnerability models in the literature assess interior damage by expert opinion or with empirical functions of the envelope damage. Interior damage to buildings at low to moderate wind speeds is mainly caused by the ingress of water through breaches in the building's envelope. The parameters that govern water intrusion include wind speed, rain rate, rain duration, raindrop size distributions, exterior building damage, and shape of the building. The amount of ingressed water is proportional to the breach sizes as well as the uncertain meteorological phenomena. This paper presents a novel approach to estimate the interior building damage caused by hurricanes by simulating the co-occurrence of wind, rain and envelope damage and by converting ingressed water into interior damage. The simulation rationale is described and some preliminary qualitative results are introduced via a sample case. The approach presented herein has been implemented in the Florida Public Hurricane Loss Model (FPHLM).
The probability of occurrence of extreme rainfall rates is reviewed. The drop-size distributions associated with a range of high rainfall rates are examined using data from tropical storms and hurricanes. Mean drop-size distributions are presented for a range of high rainfall rates, as well as a -distribution fit to the entire set of normalized drop-size distributions. This fit forms the basis for a model drop-size distribution for intense rain. The goodness of fit of the model is examined by comparing it with independent drop-camera measurements of high-rain-rate distributions from several geographic locations. The slope of exponential fits to the distributions are examined for constancy with rainfall rate, and are generally found to decrease with increasing rainfall rate.
Light-frame wood buildings represent most of residential structures throughout the United States. Approximately half of the U.S. population lives within 50 miles of the coast with many of those dwellings in the Gulf Coast region or along the eastern seaboard, both of which can be negatively impacted by hurricanes. The majority of damage during a hurricane is the result of wind-driven rainwater entering a building through openings caused by strong wind. To date, wind fragility approaches to examine the probability of damage to a light-frame wood building have focused only on component or subassembly strength, thereby providing information up to the point of first failure of the building envelope. These previous analyses, while valuable, will not allow hurricane engineering research to progress to fully mechanistic loss modeling, which is needed to mitigate losses caused by these events. In this paper a methodology to develop fragility curves and fragility surfaces for the volume of rainwater intrusion is summarized and demonstrated on an example structure. To do this, nonlinear structural analysis, computational fluid dynamics, and reliability theory are combined with particle dynamics for rainwater trajectory modeling, essentially providing the first fragilities of their kind and going beyond first failure of the building envelope. It should be emphasized that it is the methodology that is the focus and some level of calibration is still necessary.
A new full-scale testing apparatus generically named the Wall of Wind (WoW) has been built by the researchers at the International Hurricane Research Center. The paper discusses the development of a full-scale testing methodology that can be adopted for assessing wind-driven-rain intrusion through the building envelope. The current phase of FIU's WoW is capable of testing full-scale single story building models subjected up to 56m/s (125mph) wind speeds and 762mm/h (30in./h) of rain. Emphasis has been placed on generating a wind field with a proper boundary-layer profile and turbulence characteristics. Artificial rain has been generated by continuously pumping water through a plumbing system with regularly placed spray nozzles. A large wind and wind-driven-rain field 6.7m wide by 4.8m high (∼22ft wide by ∼16ft high) has been produced, which can engulf the test specimen completely. For example, an assessment of roof secondary water barrier effectiveness in preventing water intrusion is presented. Six different roof secondary water barriers have been investigated. The amount of water intruded through the secondary water barrier and the visual observation of failure have been used as performance indexes. In addition, external and internal pressure measurements, required to explain rain intrusion mechanisms were carried out. Roof slope effects on water intrusion have been investigated by testing three different slopes (2:12, 4:12 and 6:12). Results indicated the following (i) as the slope increases the intrusion decreases, (ii) self-adhered secondary water barrier performed better than nailed secondary water barriers, and (iii) heavy secondary water barriers performed better than light secondary water barriers.
The weather resistance design of building facades requires adequate knowledge on the wind and rain environment around the building. It is important to know both the wind speed as well as the associated rainfall intensity impinging onto the building faces. However, wind-driven-rain around a building is complicated and it is a topic not well understood. Usually with speed and rain intensity are considered separately and their values for weather resistance design are just guesses based on engineering experience. A method is proposed in the present paper, where wind-driven-rain intensities impinging on building faces are calculated taking into account all the relevant factors such as the interactions between wind, rain and building, and also the joint probability of occurrence of wind and rain. The method comprises the following steps: (a) using computational fluid dynamics method to calculate the flow pattern around a building, (b) raindrop trajectories in the flow field are obtained by solving the force equations, (c) obtain the probability of joint occurrence of wind and rain from the analysis of meteorological records, (d) rainfall intensities on building faces are computed as a function of return period by coupling (b) and (c). The method is applied onto a rectangular building located in Sydney and the extreme wind-driven-rain intensities on various portion of its faces calculated.
The reliable measurement of pressures on low-rise buildings in the atmospheric boundary layer (ABL) flow remains a challenge, as has been shown by the large discrepancies among results obtained in different wind tunnel facilities or even in the same wind tunnel. Two major causes of the discrepancies are the difficulty of simulating large-scale, low-frequency turbulent fluctuations uniformly across laboratories and the small scale of models in typical civil engineering wind tunnels. To address these issues, it was proposed that a simplified flow be used in laboratory simulations, rather than a conventional ABL flow. In the simplified flow the reference mean wind speed is larger than the mean wind speed of the ABL flow, and the low-frequency fluctuations present in the ABL flow are suppressed; that is, the peak energy of the missing low-frequency fluctuations is supplied in the simplified flow by the increment in the mean wind speed, which may be regarded as a flow fluctuation with zero frequency. High-frequency turbulent fluctuations, which typically affect flow reattachment, are approximately the same in the ABL and the simplified flow. Because, over small distances, low-frequency fluctuations are highly coherent spatially for small low-rise buildings with dimensions of up to approximately 20 m (e.g., single-family residential homes), the peak aerodynamic effects of the two flows may be hypothesized to be approximately the same. Preliminary experimental results obtained in University of Western Ontario's ABL wind tunnel facility and Florida International University's small-scale Wall of Wind facility are shown to support this hypothesis. The use of the proposed simplified flow is currently being tested by the authors for application to computational wind engineering (CWE) applications. Such use eliminates the need to simulate the lower frequency fluctuations of the boundary layer flow and thus makes it possible to achieve practical CWE calculations, and it is advantageous in experiments from the points of view of measurement accuracy, model scaling, repeatability of the simulations, and computational efficiency. DOI:10.1061/(ASCE)EM.1943-7889.0000508. (C) 2013 American Society of Civil Engineers.
Measurements of the raindrop size distribution (RSD) have been collected
in tropical cyclones and hurricanes with an impact type disdrometer
during the past three Atlantic hurricane seasons. The measurements were
taken at Wallops Island, Virginia, Lafayette, Louisiana, and Orlando,
Florida. The RSDs from the remnants of tropical cyclones or hurricanes
at 40 dBZ agreed well with each other where the mean mass diameter was
1.65-1.7 mm, and the total concentration had a range of 600 to 800
drops/m3. Assuming the normalized gamma size distribution, the shape
parameter will be 5-8 to satisfy the observed rain rate of 18-20 mm/hr.
If the observations were taken during the extratropical phase of the
storm where the tropical cyclone merges with a frontal system, the
composite spectra at 40 dBZ include more large drops and less small to
mid-size drops, typical for continental thunderstorms. Thus, the mean
mass diameter was larger, while total concentration, and rain rate was
less in extratropical cyclones than in tropical cyclones.
A simplified numerical model for rainwater runoff on building facades is presented, evaluated and discussed. The variation of runoff film thickness is described by a first-order hyperbolic partial differential equation. This equation is derived from the continuity equation, to which the wind-driven rain (WDR) intensity and the
capillary absorption flux by the wall are added as source/sink terms, and from the adoption of the parabolic
velocity profile of the Nusselt solution for a simplified representation of thin film flow. Two major model
simplifications are the adoption of the Nusselt solution for (1) statistically-steady, developed films, in spite of
actual wave behaviour, and for (2) transient, developing films, in spite of the actual moving contact line
complexity. Both simplifications are directly related to surface tension effects. Concerning the first
simplification, a selective review of the literature, including experimental laboratory data, confirms the validity
of the Nusselt solution for representing the time-averaged properties of thin film flow, up to film Reynolds
numbers of 1000, in spite of the actual wave behaviour. Concerning the second simplification, the runoff model is evaluated by a comparison with available on-site measurements of rainwater runoff from a building facade exposed to WDR, indicating a fair qualitative and quantitative agreement. Specific attention is given to a discussion of the possibilities and limitations of the runoff model. The runoff model can easily be integrated into 2D and 3D building envelope heat-air-moisture transfer (BE-HAM) models, but further research on the simplifications and assumptions of the runoff model is required.
Researchers at the International Hurricane Research Center (IHRC), Florida
International University (FIU), are working in stages on the construction of a large state-of-
the-art Wall of Wind (WoW) facility to support research in the area of Wind Engineering. In
this paper, the challenges of simulating hurricane winds for the WoW are presented and
investigated based on a scale model study. Three wind profiles were simulated using
airfoils, and/or adjustable planks mechanism with and without grids. Evaluations of flow ....
This paper presents the results of an experimental investigation of the momentum threshold required to damage residential window glazing when impacted by roof shingles and wooden dowels Shingles are among the most common sources of debris in hurricane winds, and they have been observed to be a major contributor to the breach of windows. Wooden dowels represent lightweight vegetation type windborne debris (e g. twigs, branches). Custom launching apparatuses were constructed to achieve controllable and repeatable flight modes and speeds for the debris. More than 600 annealed residential window glass specimens were tested to quantify the momentum threshold and damage accumulation The shingle impact experiments were conducted using varying shingle sizes, flight modes, impact angles, shingle age, impact speeds, glass specimen thicknesses, dimensions, and edge boundary conditions. The wooden dowel impact experiments include varying wooden dowel diameters and angles of impact Vulnerability curves are provided for unprotected window glass as a function of momentum, debris type, flight mode, and angle of impact Published by Elsevier Ltd
In the past, different calculation models for wind-driven rain (WDR) have been developed and progressively improved. Today, the models that are most advanced and most frequently used are the semi-empirical model in the ISO Standard for WDR (ISO), the semi-empirical model by Straube and Burnett (SB) and the CFD model by Choi, extended by Blocken and Carmeliet. Each of these models is quite different, and to the knowledge of the authors, no comparison of these models has yet been performed. This paper first presents a detailed overview of the three models, including new insights in similarities between these models and relations with recent research results. Based on this overview, it provides a comparison focused on the extent to which the different influencing parameters of WDR are implemented in the models. It shows that the implementation of the influencing parameters is most pronounced for the CFD model, less pronounced for the ISO model and least pronounced for the SB model. It is also shown that in the two semi-empirical models, the values of the wall factor W (for ISO) and the rain admittance function RAF (for SB), which have the same definition in both models, can differ more than a factor 2 from each other. The two models can therefore provide very different results. They also require differently defined reference wind speed values as input. The overview and the comparison in this paper provide the basis for future comparison studies and future improvements of the semi-empirical models.
1:40 scale wind-tunnel modelling of the Silsoe 6 m Cube at the University of Auckland is reported. In such situations, it is very difficult to model the full turbulence spectra, and so only the high-frequency end of each spectrum was matched. It is this small-scale turbulence that can directly interact with the local flow field and modify flow behaviour. This is illustrated by studying data from tests conducted in a range of European wind tunnels. It is recommended that spectral comparisons should be carried out by using turbulence-independent normalising parameter, such as plotting fS(f)/U2 against reduced frequency f=nz/U. Using parameters such as the variance and integral length scale can easily mask major differences. It is noted that it is the size of the tunnel that limits the low-frequency end of the spectra, and so the longitudinal and transverse turbulence intensities were lower than in full scale. In spite of this similar pressure distributions are obtained. Some differences are observed and these are partially attributed to the reduced standard deviation of wind directions, which affects both the observed mean and peak pressures by reducing the band of wind directions occurring during a run centred on a particular mean direction. The reduced turbulence intensities also affect the peak-to-mean dynamic pressure ratio. However, since the missing turbulence is at low frequencies, the peak pressures appear to reduce in proportion. By expressing the peak pressure coefficient as the ratio of the extreme surface pressures to the peak dynamic pressure observed during the run, reasonable agreement is obtained. It is argued that this peak–peak ratio is also less sensitive to measurement system characteristics or analysis method, provided the measurement and analysis of the reference dynamic pressure is comparable with that used for the surface pressures.
The weather resistance design of building facades requires adequate knowledge on the wind and rain environments around the building. In the present paper a numerical method for the simulation of wind-driven-rain around a building is proposed. The model involves two components. Flow around the building is computed by solving the k-ϵ two equation turbulence model. Movements of raindrops in the wind field are calculated by considering the forces acting on the droplets. Raindrop trajectories are then calculated by solving the equations of motion.Wind-driven-rain around rectangular buildings of different aspect ratios are investigated. Raindrops trajectories for droplets of different sizes are calculated. Their velocities and directions of impingement on various locations of the building are computed. The amount of rain water and its intensity falling onto different parts of the building surface are obtained.The effects of wind speed, rainfall intensity and building geometry on wind-driven-rain are investigated. It is observed that the movements of the smaller raindrops (less than 1mm) are strongly influenced by the local flow around the building. For wide buildings, they are swept upwards over the top of the front face at an angle of more than 45 degrees to the horizontal. The amount of rain water hitting the front face is observed to be strongly influenced by the wind speed. For the same building geometry, the average rain intensity on the front face for wind speed of 20 m/s is 10 times that for 5 m/s. Different locations on the faces of the building also received very different amount of rainfall. The upper quarter of the front face received much more rainfall than the sum of the remaining three quarters.
With the specific intention to provide experimental data for model development and model validation, a new measurement setup for wind, rain and wind-driven rain (WDR) has been designed and installed at the Laboratory of Building Physics (Katholieke Universiteit Leuven). This paper focuses on the new measurement setup and on the obtained measurement results. The CFD-based design and the installation of the measurement setup are outlined and samples of the database containing the wind, rain and high-resolution WDR measurements are provided and discussed. This paper also provides the link to a website from which the experimental WDR database can be downloaded. Finally, the use of these data to determine WDR coefficients and their use in WDR assessment are briefly addressed.
Development of test-based wind-driven rain intrusion model for hurricane induced building interior and contents damage.” Ph.D. dissertation Florida International Univ
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© ASCE
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FEMA-HAZUS. (2009). "HAZUS MH MR3." Multi-hazard loss estimation methodology: Hurricane model, FEMA, Washington, DC.
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public hurricane loss projection model (FPHLPM), Laboratory for
© ASCE
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Flow resistance: A design guide for engineers
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Development of effective approaches to the large-scale aerodynamic testing of low-rise buildings.” Ph.D. dissertation Florida International Univ
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aerodynamic testing of low-rise buildings." Ph.D. dissertation, Florida
International Univ., Miami, FL.
Hydrothermal performance of buildings-Calculation and presentation of climatic data-Part 3: Calculation of a driving rain index for vertical surfaces from hourly wind and rain data
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presentation of climatic data-Part 3: Calculation of a driving rain
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Hurricane vulnerability of commercial-residential buildings
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