Gable Roof Buildings Research Articles

Characterization of the wind loads and flow fields around a gable-roof building model in tornado-like winds

An experimental study was conducted to quantify the characteristics of a tornado-like vortex and to reveal the dynamics of the flow-structure interactions between a low-rise, gable-roof building model and swirling, turbulent tornado-like winds. The experimental work was conducted by using a large-scale tornado simulator located in the Aerospace Engineering Department of Iowa State University. In addition to measuring the pressure distributions and resultant wind loads acting on the building model, a digital Particle Image Velocimetry system was used to conduct detailed flow field measurements to quantify the evolution of the unsteady vortices and turbulent flow structures around the gable-roof building model in tornado-like winds. The effects of important parameters, such as the distance between the centers of the tornado-like vortex and the test model and the orientation angles of the building model related to the tornado-like vortex, on the evolutions of the wake vortices and turbulent flow structures around the gable-roof building model as well as the wind loads induced by the tornado-like vortex were assessed quantitatively. The detailed flow field measurements were correlated with the surface pressure and wind load measurements to elucidate the underlying physics to gain further insight into flow-structure interactions between the gable-roof building model and tornado-like winds in order to provide more accurate prediction of wind damage potential to built structures.

Interference Effect on Wind Loads on Gable Roof Building

Wind loads and its effects on the roof and walls constitute an important part in building design. This paper discusses the wind tunnel study on wind loads on gable roof building with interference of boundary wall. The pattern of wind load distribution on a test building at gable roof building has been studied in a wind tunnel on a 1:25 geometrical scale model in the presence of a boundary wall and reported in this paper. The size of building model is based on commonly available low rise gable roof buildings in India. A building with roof extend overhang has been used and data obtained under a simulated wind condition for open country and suburban terrain in a Boundary Layer Wind Tunnel at Indian Institute of Technology Roorkee, India. The study provides information on pressure variations on overhang, roof and wall surface of gable roof building due to interference effect of a boundary wall. It has been observed that pressure values reduce significantly due to presence of boundary wall. In general, it has been found that with an increase in the distance between the building and the boundary walls, maximum interference effect occurs on overhang, roof and wall surface of building at different distances of boundary wall and then the effect tapers off. Further possible issues have also been discussed for the interference effect on wind loads on gable roof building.

Radar Imaging Simulation for Urban Structures

With the recent advent of very high resolution (VHR) spaceborne synthetic aperture radar (SAR) sensors such as TerraSAR-X and COSMO-SkyMed, the potential to use SAR simulators is increasing. In this letter, we propose a novel radar imaging simulator that is relatively simple to implement and that finds a balance between accuracy and efficiency. The main goal of the proposed method is to obtain a precise simulation of the geometry of objects in SAR images rather than a detailed radiometric simulation. The simulator is based on an extended ray-tracing procedure to determine which surfaces of a generic object contribute to the backscatter. The backscatter contributions are calculated by means of a Lambertian-specular mixture model. The simulator has already been employed successfully in a methodology for 3-D reconstruction of man-made objects from single detected VHR SAR imagery. Here, we illustrate its work on two rather different structures, a rectangular gable-roof building and an Egyptian pyramid.

Visualization of flow structures around a gable-roofed building model in tornado-like winds

Tornadoes are violently rotating columns of air extending from thunder storms to the ground. While extensive studies have been conducted to assess wind loads and flow structures around building models in strong winds, most of the previous investigations were conducted with straight-line winds. Bienkiewicz and Dudhia (1993) found that the wind loads acting on building models in tornado-like winds would be significantly higher (3–5 times) compared to those in straight-line winds with the same wind speed. This suggests that it is incorrect, or at least incomplete, to use a conventional straight-line wind tunnel running at maximum tornado wind speed to investigate wake flow features as well as the resultant wind loads acting on buildings in tornado-like winds. While several studies on building models in tornado-like winds have been conducted recently by measuring wind loads and/or surface pressure distributions (Sengupta et al. 2008; Mishra et al. 2008a, b), very little in the literature can be found to provide detailed flow field measurements to elucidate the flow–structure interactions of building models with tornado-like winds. In this communication, we report an experimental study to quantify the characteristics of the wake vortex and turbulent flow structures around a gable-roofed building model in tornado-like winds using a high-resolution particle image velocimetry (PIV) system. The objective of the present study is to elucidate underlying physics for a more accurate prediction of damage potentials of tornado-like winds to buildings.

Building Height Retrieval From VHR SAR Imagery Based on an Iterative Simulation and Matching Technique

Experimental airborne synthetic aperture radar (SAR) systems achieve spatial resolutions of approximately 10 cm, whereas the new spaceborne very high spatial resolution (VHR) SAR sensors onboard the TerraSAR-X and COSMO-SkyMed satellites achieve spatial resolutions down to 1 m. In VHR SAR data, features from individual urban structures (i.e., buildings) can be identified by their characteristic settings in urban settlement patterns. In this paper, we present a novel concept for the height estimation of generic man-made structures from single detected SAR data. The proposed approach is based on the definition of a hypothesis on the height of the building and on the simulation of a SAR image for testing that hypothesis. A matching procedure is applied between the estimated and the actual SAR image in order to test the height hypothesis. The process is iterated for different height assumptions until the matching function is optimized, and thus, the building height is estimated. The efficiency of the proposed method is demonstrated on a set of 40 flat- and gable-roof buildings using two submeter VHR airborne and two 1-m resolution TerraSAR-X SAR scenes all acquired from the same residential area in Dorsten, Germany. The results show that, in the absence of string disturbing effects, the method is able to estimate the height of flat- and gable-roof buildings in the submeter data to the order of a meter, while the accuracy for the meter resolution spaceborne data is lower but still sufficient to estimate the number of floors of a building.

Analysis of Gable-Roofed Building Signature in Multiaspect InSAR Data

The spatial resolution of state-of-the-art synthetic aperture radar sensors enables the structure analysis of urban areas. The appearance of buildings in magnitude images in settlements is dominated by the effects of the inherent oblique scene illumination. In urban residential districts, salient pairs of parallel lines of bright magnitude are often caused by direct reflection and double-bounce signal at gable-roofed buildings. In this letter, the magnitude and interferometric phase signature of gable-roofed buildings are discussed to extract reliable building features for reconstruction. The analysis contains signature changes by varying illumination and building geometry. The presented approach is aiming at the reconstruction of gable-roofed buildings by a knowledge-based analysis considering the discussed effects. The reconstruction results are assessed by using a high-resolution LIDAR surface model as ground truth.

Tornado-Induced Wind Loads on a Low-Rise Building

Current design wind loads for buildings and other structures are based upon model tests in low-speed boundary-layer wind tunnels that generate straight-line winds. Winds resulting from tornadoes that can occur during extreme weather events such as thunderstorms or hurricanes differ greatly from conventionally conceived atmospheric boundary-layer winds. This paper presents transient wind loads on a one-story, gable-roofed building in a laboratory-simulated tornado and compares them with the provisions of building standards. Tornadoes were simulated in smooth, open terrain with vortex core diameters from roughly five to twelve times the plan dimension of the building model (0.46 to 1.06 m). A 1:100 scale model of a building with dimensions of 9.1 m×9.1 m×6.6 m and gable roof angle of 35° was used for this study. Comparisons of peak loads measured in this study showed that tornado-like vortices can generate load coefficients greater than those prescribed by ASCE 7-05 for straight-line wind over open terrain....

Component and Cladding Wind Loads for Soffits

The wind induced failure of soffits of low rise structures is a failure mechanism commonly observed in post hurricane damage investigations. The failure of the soffits has the potential to allow both wind and water to enter the attic space of the building. The current US national wind loading standard (ASCE 7) provides no guidance as to the wind load requirements for the design of soffits. In order to address this deficiency, wind tunnel tests on 1:50 scale models of one-, two-, and three-story hip and gable roof buildings were performed where measurements of the wind induced pressures and suctions on the soffits, roofs, and walls were obtained. The wind tunnel tests were performed in open and suburban terrain conditions, with and without surrounding buildings in place. The results of the tests clearly show that the soffit pressures are nearly fully correlated with nearby wall pressures, and a simple and accurate solution to the soffit loading deficiency in ASCE 7 is to prescribe that the component and cladding pressures for use in the design of soffits be identical to the component and cladding loads used for the design of wall components.

Mean Wind Pressure Coefficients on Surfaces of Gable-Roofed Low-Rise Buildings

To build an aerodynamic database for low-rise buildings, a series of pressure measurement wind tunnel tests were carried out on flat-, gable- and hip-roofed low-rise buildings in a simulated suburban wind field. Contours of statistics of point wind pressure coefficients on surfaces of the buildings were then drawn and disclosed on a website. The present study focuses on the mean wind pressure coefficients on roofs and walls of gable-roofed low-rise buildings for wind parallel or perpendicular to the roof ridges. The effects of building geometric parameters, height/breadth ratios, depth/breadth ratios and roof pitches, on the mean wind pressure coefficients on the building surfaces, which were sorted into four kinds of surfaces, upwind & downwind roof surfaces, crosswind surface, windward surface and leeward surface, are discussed. Based on these discussions, some new equations of the mean wind pressure coefficients are fitted as functions of building geometric parameters and the veracity of these fitted equations are compared with present test results and literatures.

Low-rise gable roof wind loads: Characterization and stochastic simulation

Mitigation of the damage caused by windstorms to low-rise buildings is a high priority in the wind engineering community. The development of cost-effective methods to withstand the effects of extreme winds can be advanced through improved modeling of wind loads acting on low-rise roof structures. This study explores the effects of the spatial and probabilistic characteristics of pressure fields on the aggregate uplift acting on roof panels of low-rise gable roof buildings representative of typical homes. Pressure time histories obtained at roof locations for buildings of varying roof slope at several angles of incidence in the boundary layer wind tunnel at Clemson University are used to characterize the correlation statistics between tap locations and model the marginal probability density function at individual tap locations. This information is incorporated into a multi-variate non-Gaussian simulation algorithm to study the effects of various levels of correlation on the aggregate uplift on sheathing panels. Comparisons are made between the simulated aggregate uplift and ASCE 7–98 provisions [Minimum Design Loads for Buildings and Other Structures, ASCE 7-98 Standard, American Society of Civil Engineers, New York [1]] as well as laboratory generated failure capacities for sheathing panels.

Effect of building length on wind loads on low-rise buildings with a steep roof pitch

A wind tunnel model study was carried out on long, low-rise buildings with a steep roof pitch to determine the effect of the length-to-span aspect ratio on the external wind pressure distributions. The study showed a significant increase in the magnitude of the negative pressure coefficients on the leeward roof and wall, with an increase in aspect ratio, for oblique approach winds. These large suction pressures also generate large design wind load effects on the frames near the gable-end. The 1989 edition of the Australian standard for wind loads, AS 1170.2-1989 was found to underestimate the wind loads on steep pitch gable-roof buildings of aspect ratio greater than 3, on areas near the windward gable-end, and hence the critical bending moments in the supporting structural frames. The current Australian/New Zealand wind load standard, AS/NZS 1170.2-2002 specifies increased negative pressure coefficients on the leeward half of high pitch roof buildings, and critical bending moments in the supporting frames calculated from these distributions agree quite well with values obtained from the wind tunnel study. However, other major standards severely underestimate the critical bending moments, and the effective pressure coefficients producing those bending moments, especially on the leeward roof slope.

Application of artificial neural network for determination of wind induced pressures on gable roof

Artificial Neural Networks (ANN) have the capability to develop functional relationships between input-output patterns obtained from any source. Thus ANN can be conveniently used to develop a generalised relationship from limited and sometimes inconsistent data, and can therefore also be applied to tackle the data obtained from wind tunnel tests on building models with large number of variables. In this paper ANN model has been developed for predicting wind induced pressures in various zones of a Gable Building from limited test data. The procedure is also extended to a case wherein interference effects on a gable roof building by a similar building are studied. It is found that the Artificial Neural Network modelling is seen to predict successfully, the pressure coefficients for any roof slope that has not been covered by the experimental study. It is seen that ANN modelling can lead to a reduction of the wind tunnel testing effort for interference studies to almost half.

Experimental Evaluation, Simulation and Optimization of a Commercial Heated-Air Batch Hay Drier: Part 1, Drier Functional Performance, Product Quality, and Economic Analysis of Drying

This paper considers the engineering design, operation, functional performance, product quality, and economic analysis of a natural gas heated-air batch hay drier that operates with an automatic bale wagon. The automatic bale wagon and a track are used for loading and off-loading stacks of alfalfa and timothy hay en masse to and from the drier. The newly developed batch hay drier has two identical drying units in a gable roof building, and each drying unit has a large axial flow fan which forces about 450 m 3/min of air by negative pressure through 22-32 t (a maximum of five stacks) of small rectangular hay bales placed to dry on the perforated extended metal grate floor of the drier. Top plenum swing-away frames, with attached polyethylene curtains, were used for effectively sealing the vertical sides and one end of the hay stacks. Batches of hay, initially at about 25-40% moisture content wet basis (w.b.) were successfully dried to 12-15% final moisture content in 17-37 h at moderate drying air temperatures of 45±5°C. The drying capacity was 1·0 t dried hay/h, specific fuel consumption 26 m 3/t, specific energy consumption 4790 kJ/kg water evaporated, and drying energy cost Canadian $5·82/t when hay was dried from an initial moisture content of 30% w.b. to a final value of 15% w.b. The hay produced by the drier was of high quality with an attractive green color.