Large-Scale Experimentation Using the 12-Fan Wall of Wind to Assess and Mitigate Hurricane Wind and Rain Impacts on Buildings and Infrastructure Systems

Wind hazards are one of the most disastrous events that frequently occur in the United States. Hurricane Irma, which hit the southeast coast in 2017, left a majority of damage concentrated on low-rise buildings and wooden construction in its wake. As revealed by recent hurricane damage reconnaissance, hardware-type roof-to-wall connections are especially vulnerable to high wind suction. There is only limited research on the assessment of wind loads on these roof-to-wall connections, which are important components of the wind load path. Hence, it is essential to have realistic estimates of wind effects on these connections to ensure a safe design. To fill this fundamental knowledge gap, an extensive large-scale aerodynamic testing study has been recently conducted at the NSF-Natural Hazard Engineering Research Infrastructure (NHERI) Wall of Wind (WOW) Experimental Facility (EF) to investigate wind actions resulting from simulated hurricane force winds. A wooden gable roof building of a large length scale of 1:4 was adopted for this study. Seven trusses were used to construct the roof and were connected to the top plate of the side walls. Load cells were mounted at the roof-to-wall connection (RTWC) level to measure the effective net wind-induced forces. The model was tested under different wind directions varying from 0 to 360 • with an increment of 5 • under varying wind speeds. In addition, three different configurations, i.e., one enclosed and two partially enclosed, were considered to assess different internal pressure scenarios that affect the net loading on the roof-to-wall connections and the overall roof system. The RTWC force coefficients distribution along the entire roof was obtained. The results were compared to force coefficients recommended by ASCE 7-16 version for the cases of Main Wind-Force Resisting System (MWFRS) and Component and Cladding (C&C). The experimental results were in between MWFRS and C&C values based on the ASCE provisions in general. However, for partially enclosed case, some values slightly exceeded those based on the ASCE C&C provisions. Also, the overall uplift on the roof was found to be dependent on the location of the opening (i.e., opening on long side vs. short side of the building).

Section: Introductionmentioning

confidence: 94%

Section: Instrumentationmentioning

confidence: 99%

Experimental Assessment of Wind Loads on Roof-to-Wall Connections for Residential Buildings

Feng

Chowdhury

Elawady

et al. 2020

“…The open jet test section (6 m wide and 4.3 m high) allows large-scale aerodynamic testing for low-rise buildings and full-scale testing on building components such as, among others, rooftop equipment, roof pavers, and wall cladding elements. Design details and testing capabilities of the WOW EF, along with three case studies, are provided in Chowdhury et al (2017).…”

Section: Wall Of Wind Experimental Facility (Wow Ef)mentioning

confidence: 99%

Aerodynamic Mitigation of Wind Uplift on Low-Rise Building Roof Using Large-Scale Testing

Azzi

Habte²,

Elawady

et al. 2020

During strong wind events such as hurricanes and thunderstorms, building roofs are subjected to high wind uplift forces (suctions), which often lead to severe roofing component damage and possibly, water intrusion. It is therefore crucial to accurately estimate peak suctions (negative pressures) on roofs for design purposes and to develop mitigation devices to reduce wind uplift and possible damage. Past research suggests that mitigation devices, in various forms and configurations, can significantly reduce wind effects on buildings' roofs. Perforated parapets have been shown by many researchers to be one of the most effective and low-cost mitigation devices for reducing roof suction. However, such devices contain perforations of critical functionality that may be Reynolds number Re dependent. Therefore, it is essential to study their functionality and possible Re dependency in wind tunnel testing. This paper focuses on investigation of Reynolds number Re similitude aspects of porous devices and large-scale model testing of discontinuous porous parapets to estimate their roof uplift reduction efficacy that would be representative of the prototype (full-scale) conditions. Large scale (1:8) experiments were implemented at the 12-Fan Wall of Wind Experimental Facility (WOW) at Florida International University (FIU) to achieve adequate local Reynolds number Re to ensure realistic results. In this study, a relatively smaller ratio of parapet height to roof height has been considered as compared to previous studies. The paper delineates the step-by-step design of the parapets based on kinematic similitude requirements cited in the literature. The goal was to achieve a discontinuous porous parapet design that provides similar uplift reduction efficacy as compared to those reported in the literature, but with lower height and smaller length to ensure cost-effectiveness, ease of installation, and architectural aesthetics of the retrofitted building. The effects of perforated parapets on both individual tap and area-averaged pressure coefficients were explored. The results indicated a maximum of 45% reduction in individual tap peak pressure coefficients at the corner roof and a 40% reduction in area-averaged peak pressure coefficients. The study showed that low-height ratio perforated parapets could be as effective as those reported in the literature with higher height ratios.

“…The WOW EF, designated in 2015 as one of the National Science Foundation's Natural Hazards Engineering Research Infrastructure (NHERI) Experimental Facilities (EFs), is a stateof-the-art wind engineering research facility consisting of a 2 × 6 array of fans; each fan being powered by a 700 horsepower electric motor. The 12-fan WOW system produces a wind field that is 4.3 m high and 6.1 m wide (Gan Chowdhury et al, 2017). The WOW EF is capable of producing wind speeds of up to ∼70 m/s that is equivalent of a category five hurricane as per Saffir-Simpson scale.…”

Section: Wow Experimental Setup and Instrumentationmentioning

confidence: 99%

Mitigation of Aerodynamic Uplift Loads Using Roof Integrated Wind Turbine Systems

Chowdhury

Moravej

Zisis

et al. 2019

Coastal areas of the US are affected by extreme wind events, including hurricanes. Roofs are the most vulnerable building components as they are often damaged by high wind uplift forces acting on the edges and corners. This study investigates the application of a mitigation strategy, in the form of an Aerodynamics Mitigation and Power System (AMPS) (US Patent, Gan Chowdhury et al., Patent Number: US 9,951,752 B2, April 2018), designed to simultaneously reduce wind damage and provide power to buildings. The system consists of horizontal axis wind turbines, integrated to roof edges with or without gutters. Four sets of testing on a flat roof low rise building model (without gutters)-including a bare deck configuration (i.e. without AMPS) and three cases where the roof corner was fitted with AMPS-were conducted at the Wall of Wind Experimental Facility at Florida International University. In one of the configurations, the wind turbines were placed slightly above the roof edge, while in the other two configurations, the turbines were placed closer to the roof edge. Wind directions tested ranged from 0 • to 90 • (considering roof geometric symmetry). Estimation of areaaveraged mean and peak pressure coefficients were made for various locations on the roof for the three different configurations, and compared with the case of no mitigation. Results show that for wind directions tested, significant reduction in mean and peak pressure coefficients (reduced suction) were obtained in those cases where the wind turbines were placed closer to the roof edge as compared to the bare roof deck case. Flow visualization studies showed that the turbines helped to disrupt the conical vortices caused by cornering winds, thereby reducing the wind uplift forces on the roof. This study shows that the AMPS can be utilized to prevent wind-induced damage to the roof. Future research will include estimation of the: (1) potential wind energy production using the mitigation system under various wind conditions, (ii) effectiveness of AMPS in mitigating wind loading on other kinds of buildings (e.g., gable and hip roof buildings), and (iii) load transferred from the system to the roof.