Gable Roof Buildings Research Articles

Effects of roof geometry on tornado-induced structural actions of a low-rise building

Continued loss of property and lives in tornadoes including the 23-person death toll resulting from the Lee County AL tornado on March 3rd 2019 reflects the ever-present vulnerability of the community to tornadoes, and necessitates improvement in building standards for more accurately predicting such extreme loads. This article investigates effects of three roof geometries: flat, gable, and hip, on maximum overall and local wind-induced uplift, shear and moment on low-rise buildings by a translating tornado. To explore local structural actions, maximum of five frames along the longer horizontal dimension of each building were considered. Maximum structural actions, independent of building orientation and its distance to the center of the tornado-track were calculated, with results showing that a flat roof building experiences the largest amount of overall uplift, overall shear, local uplift, and moment. Only local shears on a hip roof building were equal to or larger than those of a flat roof building for same frame locations. This study also showed that gable and hip roof buildings experience moments of similar magnitudes, whereas a gable roof performs better against shear and a hip roof performs better against uplift. Experimentally-calculated structural actions were compared with predictions of ASCE7-16, with results showing that ASCE7-16 under-predicts overall and local uplifts, and moments, while over-predicts shear for all roof geometries. The maximum under-prediction of overall and local uplifts using ASCE7-16′s procedure were 41% and 55%, respectively, both for a gable roof building. Internal frames experienced maximum under-prediction of uplifts, which makes them a vulnerable location of low-rise buildings that are built in compliance with ASCE7-16 building standard. Finally, correction factors were introduced to modify and improve accuracy of ASCE7-16 in prediction of structural actions on low-rise buildings with different roof geometries.

Effects of roof geometric details on aerodynamic performance of standing seam metal roofs

Standing seam metal roofs are one of the most commonly used types of roofs especially because of their additional durability and ease of construction. The performance of such roofs under extreme wind events like hurricanes depends on their structural strength and aerodynamic characteristics. Large-scale experimental testing was performed at the NHERI Wall of Wind Experimental Facility (WOW EF) using a 1:10 scale model of a gable-roof building with double-lok trapezoidal seam roof panels along with eave and rake (gable) attachments. The results showed that the geometric features considerably modify the aerodynamic roof pressures. The standing seams along with both types of attachments reduced the peak suction at roof corners as compared to a bare surface roof by as much as 70% and 45% on an individual tap and area-average basis, respectively. In addition, mean uplift pressure reduction was observed. The power spectral densities of pressure fluctuations at most individual taps were also reduced with the addition of attachments. Also, the correlation between the pressures at different taps was significantly decreased in most cases, resulting in reduced area-averaged pressures due to the effects of the standing seams. However, as shown in a previous full-scale study, wind-induced vibrations can lead to damage of such roofs and thus dynamic effects should be carefully considered for design purposes.

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

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 load-ing 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 versus short side of the building).

Effect of Gable Roof Angle on Streamlines and Pressure Coefficient for an Isolated Building

The airflow characteristics around and within an isolated gable roof building was investigated using CFD simulation based on steady RANS computation. Model validation and grid sensitivity analysis were conducted to ensure the reliability of the results. Three different roof pitches of gable roof namely 15º, 25º and 35º were considered in this study. The model validation results show well agreement with those of Tominaga et al. (2015). In general, the streamline and pressure coefficient were found to be significantly depending on the roof pitch. The streamline shows the velocity at the inlet opening and outlet opening increased as the roof pitch increase except the roof opening outlet increased between 15º and 25º then decreased between 25º and 35º. The spatial distribution of pressure coefficient at the windward side and the interior of the building decreased as the roof pitch increased. The difference in the flow fields of 25º and 35º roof pitch is large with the presence of window and roof opening relative to the difference between 15º and 25º roof pitch. In terms of spatial distribution of pressure coefficient and streamline, steeper roof pitch is more preferable.

Low-rise gable roof buildings pressure prediction using deep neural networks

This paper presents a deep neural network (DNN) based approach for predicting mean and peak wind pressure coefficients on the surface of a scale model low-rise, gable roof building. Pressure data were collected on the model at multiple prescribed wind directions and terrain roughness. The resultant pressure coefficients quantified from a subset of these directions and terrains were used to train a DNN to predict coefficients for directions and terrains excluded from the training. The approach can leverage a variety of input conditions to predict pressure coefficients with high accuracy, while the prior work has limited flexibility with the number of input variables and yielded lower prediction accuracy. A two-step nested DNN procedure is introduced to improve the prediction of peak coefficients. The optimal correlation coefficients of return predictions were 0.9993 and 0.9964, for mean and peak coefficient prediction, respectively. The concept of super-resolution based on global prediction is also discussed. With a sufficiently large database, the proposed DNN-based approach can augment existing experimental methods to improve the yield of knowledge while reducing the number of tests required to gain that knowledge.

Numerical Simulation Analysis of Wind Interference Effects on Low-rise Gable Roof Buildings

Numerical Simulation Analysis of Wind Interference Effects on Low-rise Gable Roof Buildings

Ventilation performance of single zone occupied space in ancient Myanmar multistage roof buildings

Roof ventilation gives passive cooling effect in removing hot air from tropical climate buildings. However, little is known about the impacts of building parameters on the passive cooling effect in ancient Myanmar multistage roof buildings. The authors believe that this is the first study to assess the ventilation performance of multistage roof buildings taking into account their typologies, ventilation modes and climatic parameters. This paper presents the ventilation performance of two roof typologies by varying defined parameters from studies in computational fluid dynamic simulations. Simulations were generated by using the 3D steady Reynolds Averaged Navier Stokes equations and k-ε turbulence models. The results of CFD studies revealed that the presence of gable vents allowed better indoor air movement although the indoor air turbulence was depended on the intensity of exterior wind speed and roof typology. It was found that the single gable roof buildings increased the indoor airspeed with insignificant indoor air temperature improvement for thermal comfort. The results of this CFD study substantiate the findings of another dynamic simulation study and support the conclusion that the three-stage roof buildings have more potential to improve a better thermal and ventilation performance if they have gable vents.

Thermal performance in single-zone occupied space ancient Myanmar multistage roof buildings

Multistage roofs are dominant features in the ancient Myanmar buildings. They describe the cultural context, social status and are a response to the local climates. However, little is known about the thermal performance of multistage roof buildings. The authors believe that this is the first study to access the thermal performance of multistage roof buildings taking into account their typologies, ventilation modes and roof materials. The findings revealed that the three-stage roof buildings received a shorter duration of a year for thermal discomfort compared to the single gable roof buildings. However, there were insignificant improvements in annual mean air temperature by using three-stage roofs. On the other hand, the roof space of three-stage roof buildings received a very high indoor air temperature that caused abandon roof spaces apart from acting as a response to the local climate contexts. The study highlights that the beautiful use of Le-baw allows adding the gable vents easily for better ventilation performance. The results from this study substantiate the findings of another computational fluid dynamic simulation and support the conclusion with a discussion that the three-stage roof buildings have more potential to improve a better thermal performance if they have gable vents.

Interference effects on wind loads of gable-roof buildings with different roof slopes

The influence of roof slope and building spacing on wind interference effects is investigated in a group of low-rise gable-roof buildings with wind tunnel test. When the wind direction is perpendicular to the roof ridge, wind suctions on the gable roof of 10° in the central and downstream building are significantly reduced. When the roof slope is 35°, notable increase in wind suctions on the upstream and central building appears when the spacing ratio is smaller than 2.0. When the roof slope is 10°, the minimum interference factors (IF) of the most unfavorable suctions on the edge and central buildings are 0.36 and 0.26 respectively. When the roof slope is 35°, middle roof-ridge area of the edge building away from the central building displays significant amplification when the spacing ratio ranges from 0.25 to 4.0. Other roof ridge area experiences shielding effects, and the minimum IF is smaller than 0.7. For the central building, the roof corner area experiences amplification effects, and other roof areas exhibit obvious shielding effects when the spacing ratio is smaller than 1.0. IFs in the middle roof area change from around 0.8 to 1.4 when the spacing ratio increases from 1.0 to 3.0.

Wind Tunnel Experiments and CFD Simulations for Gable-Roof Buildings with Different Roof Slopes

Wind Tunnel Experiments and CFD Simulations for Gable-Roof Buildings with Different Roof Slopes

Numerical study of wind pressure on low-rise buildings induced by tornado-like flows

This paper presents large-eddy simulation of tornado-induced pressures and forces on flat-roofed and gable-roofed low-rise buildings. The simulation is carried out with respect to an ISU-type tornado simulator and the simulation results are compared with available laboratory and field data. The present study shows that tornado-induced wind pressures have very different characteristics than those caused by boundary layer flows. The distribution and magnitude of wind pressures around the building models depend significantly on the distance between tornado vortex and building model. The roof angle does not alter the integrated wind loads on the gable-roofed building models significantly, but the local pressure on building surfaces, especially on the roof, depends obviously on the roof angle. However, this dependence is similar to that in boundary layer winds, although the value of the pressure coefficient is different due to pressure drop accompanying the tornado. In addition, the present study shows that the same horizontal profile of mean tangential velocity do not necessarily result in the same wind loads on building models in a tornado because of the difference in vortex structures.

Study on localised wind pressure development in gable roof buildings having different roof pitches with experiments, RANS and LES simulation models

In this study, the influence of different roof pitches on the mean pressure distributions around isolated buildings subject to different wind directions were investigated with wind tunnel tests, 3D steady Reynolds-averaged Navier-Stokes (RANS) simulation and large eddy simulation (LES). Wind tunnel experiments were conducted to obtain mean pressure distributions around buildings having three commonly used roof pitches, namely, 1:5, 2:5 and 3:5. The critical high suction areas created by conical vortices were identified, and the influence of roof pitch on these critical areas with high localised pressures was investigated under various wind directions. In addition, computational fluid dynamics (CFD) analysis was performed, and the performance of RANS and LES were evaluated and compared with the results measured from the wind tunnel tests by considering both the accuracy of results and computational cost. The assessment on RANS and LES was used to determine the best guidelines for the flow problems involved in this study.Results from the RANS show good agreement with the experimental results on pressure distribution when the building is subject to perpendicular wind directions. However, a significant improvement was found using LES over RANS in the prediction of near-building flow field and localised pressure under oblique wind directions but with an increased computational cost by a factor of more than 80. Furthermore, the high suction pressures are observed to be more critical on buildings with a lower roof pitch under both perpendicular and oblique wind directions. This indicates that a low roof pitch should be applied with caution especially in windstorm-prone areas.

Tornado-induced wind loads on a low-rise building: Influence of swirl ratio, translation speed and building parameters

Significant parameters that influence tornado-induced wind loads on low-rise buildings are yet to be fully explored. In the current study, the influence of tornado parameters such as swirl ratio and translation speed and building’s spatial parameters such as its distance from the tornado mean path and its orientation with respect to the tornado’s translation direction on tornado-induced wind loads are investigated. A low-rise gable roof building with a roof angle of 35 degrees and a square plan area is chosen for this study. Laboratory simulated tornadoes with two swirl ratios with different ground-surface pressure characteristics, and three translation speeds were used. The 1:200-scaled building model that was used for this study was located on both sides of the simulated tornado’s mean path at several locations up to the distance of several tornado-core radii. At locations where maximum loadings occurred, orientation of the building was changed to explore its effect on peak loads. Results show significantly larger peak load coefficients for the tornado with lower swirl ratio which were comparable to its peak ground surface pressure drop. Peak roof uplift on the building located at the tornado’s mean path is smaller by 6–19% for the lower-swirl tornado case and up to 16% for the higher-swirl tornado case, compared to the other locations, for the three translation speeds investigated. For simulated tornado with lower swirl ratio, measurements showed that peak roof uplift increases with increase in translation speed when building is located on tornado mean path, whereas peak roof uplift decreases with increase in translation speed at locations other than tornado mean path. For tornado with higher swirl ratio, increase in translation speed does not change the maximum peak uplift load. Building experiences maximum horizontal and uplift loads at building orientation angle of −45° and 0° for lower swirl tornado case and −45° and −30° for higher swirl tornado case, respectively, with respect to the translation direction of the tornado.

Experimental and numerical study on mean pressure distributions around an isolated gable roof building with and without openings

In this study, the influence of opening position and wind direction on pressure distribution around isolated gable roof buildings with and without openings were investigated. Computational Fluid Dynamics (CFD) simulations were performed and compared with wind tunnel experimental results. One of the aims of this study was to develop well-defined design guidelines for typical gable roof structures, identifying critical localised pressure rises due to different wind attack angles. Existing international standards provide limited design guidelines for localised wind pressure distribution of such buildings, especially in cases where there are openings. Wind tunnel experiments were conducted to obtain mean pressure distributions of critical areas of the building under different wind directions with four different opening configurations, namely, an enclosed building, a building with one windward opening, a building with one windward opening and one sidewall opening, and a building with one windward opening and two sidewall openings. A CFD-based numerical simulation approach was used to create a virtual wind tunnel in the computational domain. Sensitivity analyses for grid resolutions and turbulence models of simulations were performed for the building with a windward opening.Results from the numerical simulations show good agreement with the experimental results on pressure distribution. The validated models were used to identify critical areas of the buildings that must be considered in the design stage. The relevant pressure coefficients are presented and compared with the standards. The importance of performing a comprehensive wind study using a numerical approach or wind tunnel tests is highlighted.

Wind Directional Effect on a Single Storey House Using Educational Wind Tunnel

Wind tunnel testing of single-storey isolated building with 1: 100 scale down model was carried out in an open circuit wind tunnel without roughness elements facilities. The gable roof building model with 30˚ roof pitch was studied for wind directions of 0˚, 30˚, 45˚, 60˚ and 90˚. Pressure measurements were performed on all the walls and the roof (Zone 1, 2, 3, 4 and 5) of the building model with wind speed of 12 m/s. The results showed that the high suctions were generally induced by the 90˚ wind direction for Zone 1 and 60˚ and 90˚ wind directions for Zone 2. Mostly, high suction was also observed in case of 45˚ and 60˚ wind direction in Zone 3. In zone 4 and zone 5, high suction was generally induced by the 0˚ wind direction.

Turbulence and Air Exchange in a Two-Dimensional Urban Street Canyon Between Gable Roof Buildings

We experimentally investigate the effect of a typical building covering: the gable roof, on the flow and air exchange in urban canyons. In general, the morphology of the urban canopy is very varied and complex, depending on a large number of factors, such as building arrangement, or the morphology of the terrain. Therefore we focus on a simple, prototypal shape, the two-dimensional canyon, with the aim of elucidating some fundamental phenomena driving the street-canyon ventilation. Experiments are performed in a water channel, over an array of identical prismatic obstacles representing an idealized urban canopy. The aspect ratio, i.e. canyon-width to building-height ratio, ranges from 1 to 6. Gable roof buildings with 1:1 pitch are compared with flat roofed buildings. Velocity is measured using a particle-image-velocimetry technique with flow dynamics discussed in terms of mean flow and second- and third-order statistical moments of the velocity. The ventilation is interpreted by means of a simple well-mixed box model and the outflow rate and mean residence time are computed. Results show that gable roofs tend to delay the transition from the skimming-flow to the wake-interference regime and promote the development of a deeper and more turbulent roughness layer. The presence of a gable roof significantly increases the momentum flux, especially for high packing density. The air exchange is improved compared to the flat roof buildings, and the beneficial effect is more significant for narrow canyons. Accordingly, for unit aspect ratio gable roofs reduce the mean residence time by a factor of 0.37 compared to flat roofs, whereas the decrease is only by a factor of 0.9 at the largest aspect ratio. Data analysis indicates that, for flat roof buildings, the mean residence time increases by 30% when the aspect ratio is decreased from 6 to 2, whereas this parameter is only weakly dependent on aspect ratio in the case of gable roofs.

Retrofitting building roofs with aerodynamic features and solar panels to reduce hurricane damage and enhance eco-friendly energy production

Wind-induced negative pressure on roofs of low-rise buildings is a major source of losses and community disruption. Vortex suppression technologies may reduce wind loads on buildings; however, it is challenging to implement an effective strategy to reduce wind loads on roofs with minimal loads on the mitigation feature itself. In this paper, the performance of different aerodynamic mitigation features is investigated in a comparative study. The results show that solar panels are relatively effective in reducing wind-induced uplift forces on a flat roof. Compared with all mitigation features presented, the airfoil is the most effective in reducing uplift loads, with promises to proceeding research in this area. In addition, the study investigates wind impact on a gable roof building with different configurations of solar panels, to reduce wind-induced loads on the host building while maintaining a visually appealing installation to permit broad usage and application. Pressure coefficients on roofs and solar panels from both computational fluid dynamics (CFD) simulations and laboratory experiments are compared. The study shows that the optimal roof/solar panel combination reduces wind loads on low-rise buildings, i.e. improves the performance, in addition to providing ecofriendly energy especially when power outage is expected.

An experimental study to assess the effect of soffit louvered vents on wind loads and wind driven rain intrusion on low rise buildings

Wind-driven rain (WDR) intrusion in buildings during hurricanes often leads to significant damage to building interior and contents, causing major losses. Many buildings in hurricane-prone U.S. coastal states are fitted with soffit vents with louvers that are designed to close during high winds and reduce rain intrusion. This paper focuses on the topic of WDR intrusion through soffit vents and, in particular, studies the effects of louvered soffit vents on (i) reduction of water intrusion, and (ii) overall aerodynamic loading of buildings’ roofs. A gable and a hip roof building retrofitted with open and closed vents were tested at the Wall of Wind (WOW) experimental facility. WDR intrusion studies were carried out only on the hip roof building, while wind pressure distributions were estimated for the gable and hip roof buildings. Results from the WDR intrusion study indicate a marked reduction in water intrusion for the closed vent roofs. Moreover, the net mean and peak pressure coefficients for the closed vent roofs are reduced in magnitude (less suction) compared to the open vent roofs. Future research is recommended to study the effect of different vent sizes and locations, besides considering other roof types (e.g. mono-slope).

Numerical Simulations of Wind-induced Mean Interference Effects between Two Low-rise Buildings with Gable Roof

In this study, numerical computations for wind pressure of low-rise buildings were conducted in order to investigate wind-induced mean interference effects between the buildings. The primary purpose is to make clear the characteristics of wind pressure distribution on low-rise gable roof building considering interference effects, so as to put forward practical wind-resistant design method and measures. Various ranges of arrangement modes, arrangement distances and wind direction angles were considered based on the numerical simulation method which was verified by wind tunnel test. Results showed that there are the most obvious wind-induced mean interference effects on cornice of interfered building for two same low-rise building. As for the arrangement of low-rise buildings, the tandem arrangement is largest, followed by staggered arrangement and less is parallel arrangement.

Automatic Detection of Low-Rise Gable-Roof Building from Single Submeter SAR Images Based on Local Multilevel Segmentation

Low-rise gable-roof buildings are a typical building type in shantytowns and rural areas of China. They exhibit fractured and complex features in synthetic aperture radar (SAR) images with submeter resolution. To automatically detect these buildings with their whole and accurate outlines in a single very high resolution (VHR) SAR image for mapping and monitoring with high accuracy, their dominant features, i.e., two adjacent parallelogram-like roof patches, are radiometrically and geometrically analyzed. Then, a method based on multilevel segmentation and multi-feature fusion is proposed. As the parallelogram-like patches usually exhibit long strip patterns, the building candidates are first located using long edge extraction. Then, a transition region (TR)-based multilevel segmentation with geometric and radiometric constraints is used to extract more accurate edge and roof patch features. Finally, individual buildings are identified based on the primitive combination and the local contrast. The effectiveness of the proposed approach is demonstrated by processing a complex 0.1 m resolution Chinese airborne SAR scene and a TerraSAR-X staring spotlight SAR scene with 0.23 m resolution in azimuth and 1.02 m resolution in range. Building roofs are extracted accurately and a detection rate of ~86% is achieved on a complex SAR scene.