Arindam Gan Chowdhury

Wall of Wind Full-Scale Destructive Testing of Coastal Houses and Hurricane Damage Mitigation

Abstract Damages during extreme wind events highlight the weaknesses inherent in coastal residential building construction and underscore the need for improving the structural performance of typical residential buildings. Also, there is a tremendous concern for the existing stock of buildings that are not sufficiently designed and constructed to an acceptable building code. Conducting research to better understand simultaneous hurricane-induced wind, rain, and debris effects on the built environment will lead to innovative design technologies that can mitigate hurricane wind damage. The International Hurricane Research Center (IHRC) at the Florida International University (FIU) has developed a new research approach to better understand categories 1 to 5 hurricane-induced effects on residential buildings and other structures through full-scale, destructive testing, much the same way that the automobile industry tackled the crash worthiness issue or the earthquake community approached building safety. This research will foster the development of novel mitigation techniques to improve our built environments resilience to hurricane impact. To develop these advanced techniques, we will subject test models of representative building structures or appropriate portions of such structures to hurricane-induced wind–rain–debris effects in a controlled and repeatable environment using the Wall of Wind testing apparatus developed by the IHRC. Through such full-scale destructive testing, performance-based evaluation, and failure-mode analysis, innovative mitigation techniques will be developed. Wall of Wind experimentation has the potential for revolutionizing our building and retrofitting practices.

Aerodynamic Mitigation of Roof and Wall Corner Suctions Using Simple Architectural Elements

Thispaperpresentstheuseofsimplearchitecturalelementssuchasaerodynamicmitigationdevicesforreducinghighwind-induced suctions occurring at roof and wall corners of low-rise buildings where wind-induced building envelope failures usually initiate. The architectural elements considered in the current study include trellises (pergolas), roof extensions of gable ends (gable end ribs), ridgeline extensions(ridgerib),andsidewaysextensionsofwalls (wallribs). Asmall-scalemodelofresidential villawastestedinaboundarylayer wind tunnel for two different roof geometries (gable and hip). Moreover, selected cases were investigated at the Wall of Wind, a large-scale testing facility, to investigate scale effects. The effectiveness of these architectural elements in reducing high suction (negative pressure) was assessed bycomparingthewind-inducedpressuremeasurementsobtainedbeforeandafterintroducingtheelements.Basedontheresultsobtainedforthe worstwindangleofattacks,thepeaksuctionwasreducedafterintroducingthearchitecturalelementsby65%atgable-endcorners,60%closeto roof ridges, 45% at soffits, 35% at wall corners, and 25% at eaves. These simple architectural elements, which can be retrofitted to the stock of existing homes or incorporated into the design of new buildings, can be used as aerodynamic mitigation devices for reducing peak suction at critical locations of the building envelope. DOI: 10.1061/(ASCE)EM.1943-7889.0000505.

Wind-Loading Effects on Roof-to-Wall Connections of Timber Residential Buildings

AbstractExtensive damage to residential wood-frame buildings caused by failures of roof-to-wall connections during extreme wind events underscores the need to improve their performance. Most of these connections use mechanical connectors, e.g., metal clips and straps (sometimes referred to as hurricane clips and hurricane straps). The allowable capacity of these connectors is based on results of unidirectional component tests that do not simulate multiaxial aerodynamic loading effects induced by high wind events. The objective of this research was to facilitate a better understanding of these loading effects on roof-to-wall connections of a typical low-rise gable roof residential structure subjected to combined impacts of wind and a potential breach of the building envelope. Large-scale experiments on a heavily instrumented building model generated multiaxial aerodynamic loading data on roof-to-wall connections for various wind angles of attack and internal pressure conditions. The results showed the seve...

Simplified Wind Flow Model for the Estimation of Aerodynamic Effects on Small Structures

The reliable measurement of pressures on low-rise buildings in the atmospheric boundary layer (ABL) flow remains a challenge, as hasbeenshownbythelargediscrepanciesamongresultsobtainedindifferentwindtunnelfacilitiesoreveninthesamewindtunnel.Twomajor 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 thana conventionalABL flow.In thesimplified flowthe referencemeanwind speedislarger thanthemean 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 Ontarios ABL wind tunnel facility and Florida International Universitys 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 eliminatestheneedtosimulatethelowerfrequency fluctuationsoftheboundarylayer flowandthusmakesitpossibletoachievepracticalCWE 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.

Study of the Capability of Multiple Mechanical Fasteners in Roof-to-Wall Connections of Timber Residential Buildings

One of the most critical connections in wood frame construction is that of the roof rafter and the top plate of the wall. This type of connection typically uses mechanical fasteners, such as metal straps or clips fastened with nails. Manufacturers base the allowable capacity of connections with one fastener on results of tests performed on such connections. However, it is assumed in current design practice that the capacity of a connection with two mechanical fasteners is twice the capacity of a connection with a single fastener. Implicit in this practice is the assumption that the connection’s capacity is proportional to the number of fasteners per connection joint. This approach, based as it is on testing a single fastener per joint, disregards the fact that the failure modes of a connection joint may depend on the number of fasteners per joint. This paper presents results of tests that establish this fact. The results, based on testing with three types of wood (spruce pine fir, southern yellow pine, an...

Wind Effects on Roofs with High-Profile Tiles: Experimental Study

AbstractHurricane wind–induced damage to the roofs of residential buildings has raised concerns regarding design provisions and construction practices. Current code provisions on wind loads on roofs are mainly based on testing of building models that do not include the architectural details of roofing materials. Past research has indicated that net pressures on roof tiles can differ significantly from external pressures on bare roofs and depend on wind direction, the location of the tile, and whether the eaves are sealed. This study presents experimental pressure measurements that confirm existing findings and provide more extensive results on wind loads on high-profile roof tiles. Four different roof models with bare and tiled roof decks were tested. Pressures on the external surfaces of the tiles, within the cavity space, and in the joint space between two overlapping tiles were measured to evaluate their effects on the net peak pressures on the tiles. Area-averaged peak pressure coefficients obtained f...

Study on roof vents subjected to simulated hurricane effects

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.

Triaxial Load Testing of Metal and FRP Roof-to-Wall Connectors

The allowable capacity of conventional roof-to-wall metal connectors is based on results of unidirectional component tests that do not simulate triaxial aerodynamic loading effects induced by high-wind events. The results of wind and wind-driven rain tests conducted at a full-scale facility were used to create a database on aerodynamic and aerohydrodynamic load effects on roof-to-wall connectors. Based on these results, three axial mean force components (triaxial mean loads) were combined into a series of resultant mean force vectors. A new test protocol was then developed for roof-to-wall connectors under simulated triaxial loading as opposed to simple uniaxial loading. The findings confirm that current testing methods tend to overestimate the actual load capacities of metal connectors. The performance of a nonintrusive roof-to-wall connector system using fiber-reinforced polymer (FRP) ties was also tested and compared with that of a traditional metal connector under simulated aerodynamic loads. The test...

Estimation of Wind-Driven Rain Intrusion through Building Envelope Defects and Breaches during Tropical Cyclones

AbstractWind-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 facade 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 ...

Assessment of ASCE 7-10 Standard Methods for Determining Wind Loads

AbstractThe purpose of this paper is to discuss issues associated with ASCE 7-10 standard methods for determining wind loads on buildings and other structures that warrant comment, correction, or improvement. The assessment is intended to serve as a resource in the development of a new version of the ASCE 7 standard and to stimulate a wider participation in that development by the structural engineering community. Issues discussed in the paper include: wind speeds in nonhurricane regions; alternative analytical methods for determining wind loads and wind effects on main wind force resisting systems and components and/or cladding; aerodynamic pressure coefficients; pressures on rooftop equipment; component and cladding pressures on arched roofs; and the wind tunnel procedure. It is noted that the ASCE 49 standard essentially covers wind tunnel testing, rather than the wind tunnel procedure, of which wind tunnel testing is only a part.