Terrain Exposure Research Articles

Wind-induced torsional loads on low buildings

Wind-induced instantaneous pressures on low building envelopes continuously vary in temporal and spatial dimensions and this may lead to significant torsional moments on the building's lateral load resisting system. Studies on wind-induced torsional loads on low buildings are very limited. Wind-induced torsion provisions in the American Society of Civil Engineers Standard (ASCE/SEI 7-10, 2010), the National Building Code of Canada (NBCC, 2010), and the European Code (EN 1991-1-4, 2005) were reviewed and compared for three gabled-roof (18.4°) low buildings. Significant discrepancies were found among the provisions of these wind standards in evaluating torsional wind loads on low buildings. In addition, wind-induced torsional loads on low buildings have been measured in a boundary layer wind tunnel. Three low buildings, with the same plan dimensions but different gabled-roof angles (0°, 18.4°, 45°) and two different heights (i.e. full, and half eave building height) were tested in simulated open and urban terrain exposures for different wind directions (from 0° to 180° every 15°). The experimental results were compared with current wind-induced torsional load provisions. It was found that NBCC (2010) underestimates the torsional moments on low buildings significantly.

Physical modeling of complex airflows developing above rural terrains

The rural atmospheric boundary layer (ABL) flow was reproduced in a wind tunnel at three different simulation length scales to investigate possible effects of the simulation length scale on flow characteristics. Performance of truncated vortex generators developed for part-depth ABL wind-tunnel simulations was tested in rural terrain exposure against the full-size Counihan vortex generators. A procedure to design the ABL developing above rural type terrain has been described. The 1:395 and 1:236 simulations were created as full-depth simulations, i.e., wind characteristics throughout an entire ABL were reproduced in the wind tunnel. The 1:208 simulation was a part-depth simulation, i.e., only a lower 70% of the ABL was experimentally modelled. The projected scaled-up ABL thicknesses are 395, 354, and 416 m full-scale in the 1:395, 1:236, and 1:208 simulations, respectively. Experimental results show similar trends in all three configurations not depending on the simulation length scale factor. This clearly indicates a possibility to physically, in the wind tunnel, reproduce the same rural atmospheric airflows at different simulation length scales.

A Study on the Equivalent Static Wind Loadings on the Arched Roof Frames of Low-Rise Buildings in Atmospheric Boundary Layers

A series of wind tunnel aerodynamic experiments were conducted to investigate the wind loads on the low-rise buildings with arched roofs. The wind loadings were calculated from the simultaneous measured wind pressures data over all of the models surfaces in a simulated open terrain exposure atmospheric boundary layer. With these data the equivalent static wind loads (ESWL) of fluctuating wind pressures acting on buildings frames were evaluated and the results of equivalent static wind loads were compared with the 2006 version design codes of wind loadings on buildings in Taiwan. The design codes suggested the direction of wind acting on the low-rise buildings roofs were normal to the ridges of roofs. In this study results shown, the equivalent static wind loads caused by the approaching turbulent flow may exceed the suggested values by codes. So the peak response of structural frames should be considered carefully.

Validating the MYSTIC three-dimensional radiative transfer model with observations from the complex topography of Arizona's Meteor Crater

Abstract. The MYSTIC three-dimensional Monte-Carlo radiative transfer model has been extended to simulate solar and thermal irradiances with a rigorous consideration of topography. Forward as well as backward Monte Carlo simulations are possible for arbitrarily oriented surfaces and we demonstrate that the backward Monte Carlo technique is superior to the forward method for applications involving topography, by greatly reducing the computational demands. MYSTIC is used to simulate the short- and longwave radiation fields during a clear day and night in and around Arizona's Meteor Crater, a bowl-shaped, 165-m-deep basin with a diameter of 1200 m. The simulations are made over a 4 by 4 km2 domain using a 10-m horizontal resolution digital elevation model and meteorological input data collected during the METCRAX (Meteor Crater Experiment) field experiment in 2006. Irradiance (or radiative flux) measurements at multiple locations inside the crater are then used to evaluate the simulations. MYSTIC is shown to realistically model the complex interactions between topography and the radiative field, resolving the effects of terrain shading, terrain exposure, and longwave surface emissions. The effects of surface temperature variations and of temperature stratification within the crater atmosphere on the near-surface longwave irradiance are then evaluated with additional simulations.

Topographic Effects on the Surface Radiation Balance in and around Arizona’s Meteor Crater

Abstract The individual components of the slope-parallel surface radiation balance were measured in and around Arizona’s Meteor Crater to investigate the effects of topography on the radiation balance. The crater basin has a diameter of 1.2 km and a depth of 170 m. The observations cover the crater floor, the crater rim, four sites on the inner sidewalls on an east–west transect, and two sites outside the crater. Interpretation of the role of topography on radiation differences among the sites on a representative clear day is facilitated by the unique symmetric crater topography. The shortwave radiation balance was affected by the topographic effects of terrain exposure, terrain shading, and terrain reflections, and by surface albedo variations. Terrain exposure caused a site on the steeper upper eastern sidewall of the crater to receive 6% more daily integrated shortwave energy than a site on the lower part of the same slope. Terrain shading had a larger effect on the lower slopes than on the upper slopes. At the lower western slope site the daily total was reduced by 6%. Measurements indicate a diffuse radiation enhancement due to sidewall reflections. The longwave radiation balance was affected by counterradiation from the crater sidewalls and by reduced emissions due to the formation of a nighttime temperature inversion. The total nighttime longwave energy loss at the crater floor was 72% of the loss observed at the crater rim.

Health and Usage Monitoring Algorithm Based on Terrain Identification for Mechanical Components on an Army Ground Vehicle System

The desire for enhanced functionality of Army vehicle systems has resulted in increasingly complex systems. This drive is in direct contention with another Army goal of improved reliability. Health and usage monitoring systems (HUMS) and remaining-life prognostics are being developed to address these conflicting goals. One of the major challenges of applying a HUMS to an Army wheeled vehicle system is that the development and per unit cost of the HUMS needs to be relatively low in comparison with typical high-cost applications such as aircraft. Simplified algorithms that derive terrain exposure from a basic set of sensors and estimate fatigue damage accumulated on components where loading comes primarily from terrain have been developed to meet this need. Various inputs and statistical parameters are evaluated for this model based on accuracy of terrain identification and quality of fatigue prediction on an example component. The generalized process and recommendations for application of this model to military ground vehicle systems are discussed.

Simplified terrain identification and component fatigue damage estimation model for use in a health and usage monitoring system

Improved reliability of military ground vehicle systems is often in direct conflict with increased functionality and performance. Health and Usage Monitoring Systems or HUMS are being developed to address this issue. Traditionally, HUMS applications have been limited to high-cost equipment such as aircraft. In order to apply a HUMS to a relatively inexpensive military ground vehicle, simplified algorithms that derive terrain exposure from a basic set of sensors and estimate fatigue damage accumulated on components whose loading comes primarily from terrain have been developed. Various inputs and statistical parameters are evaluated for this model based on accuracy of terrain identification and quality of fatigue prediction on an example component. The generalized process and recommendations for application of this model to military ground vehicle systems are discussed.

Using airflow modelling and spatial analysis for defining wind damage risk classification (WINDARC)

The main goal of the work was to develop a method for evaluating wind damage risk of the forest stands. The risk treated in the work represents relative ranking with values from 1 (the lowest risk) to 9 (the highest risk). In general, the damage risk is divided into a permanent and a temporary damage risk. Defining permanent risk areas is based on the existence of factors that cannot be influenced by man (the character of the soil, terrain and all climatic factors). The temporary damage risk is based on the characteristics of vegetation. Input parameters for calculating the damage risk are the soil, the vegetation and the terrain. GIS-based data are used for calculating damage risk based on the soil and damage risk based on the forest stands, respectively. An airflow model, developed within the computational fluid dynamics (CFD) programme FIDAP, is used for calculating terrain exposure classification (TEREX) which evaluates wind exposure of sites independently of current vegetation. Integrating TEREX with damage risk based on the soil yields permanent exposure classification (PERMEX), evaluating the risk of wind damage occurrence that cannot be influenced by man. A result of combining PERMEX with damage risk based on the forest stands is a complex regional wind damage risk classification (WINDARC) which represents current threat of forest stands from wind.

Wind pressures on buildings with stepped roofs

The paper describes an experimental study for the evaluation of wind pressures on buildings with roofs of two different heights, such as one building with roofs at two levels or, more commonly, two flat-roofed buildings in a row. The study is experimental and consists of an extensive series of tests in a boundary layer wind tunnel simulating the flow over an open country terrain exposure. The basic model of the study has been designed and constructed in sections so that it can represent flat roofs in steps of different relative heights and widths. The maximum height of the model is variable and can represent a building up to 60 m high. The results of the study for buildings with a two-level flat roof are discussed in the paper. Data are presented in pressure coefficient form (both mean and peak values) measured locally on a number of pressure taps placed at strategic locations on the roof and wall sections of the model. The results of the study are compared with the flat-roof specifications described in the American National Standards Institute wind standard and the National Building Code of Canada. It has been found that some modifications of these standards are required to accommodate the wind loading of these building configurations. In particular, the inclusion of positive pressure coefficients must be considered for stepped roofs. Key words: building, code, design, loads, pressure, roof, wall, wind.

Wind pressures on buildings with multi-level roofs

The objective of this study is the assessment of wind pressures on buildings with roofs on different heights, such as one building with roofs at various levels or, more commonly, a number of flat-roofed buildings in a row. The study is experimental and consists of an extensive series of tests in a boundary layer wind tunnel simulating the flow over an open country terrain exposure. The basic model of the study has been designed and constructed in sections so that it can represent flat roofs in steps of different relative heights and widths. The maximum height of the model is variable and can represent a building up to 60 m high. The paper presents and discusses the results of the tests for buildings with a two-level flat roof. Data are presented in pressure coefficient form (both mean and peak values) measured locally on a number of pressure taps placed at strategic locations on the roof and wall sections of the model. The results of the study are compared with the flat roof specifications provided by wind standards and codes of practice.

Design recommendations for wind loading on buildings of intermediate height

The National Building Code of Canada (NBCC) specifies wind loads for the design of tall (height, H > width, W) and low (H < 10 m, or H < W and H < 20 m) buildings. Since there are no specifications for the design of buildings of intermediate height, the present project has been undertaken to help define wind loads appropriate for the design of such buildings. The experimental study was carried out at the boundary layer wind tunnel of the Centre for Building Studies at Concordia University. The methodology used for this project consisted of testing five square building models (12, 25, 55, 100, and 145 m high) under conditions simulating strong turbulent wind blowing over an open country terrain exposure. Both the lowest and the tallest buildings were tested for validation purposes. Statistics of wind induced pressures were measured at several points and areas on the walls and the roof of all buildings for both normal and oblique wind directions. Experimental data show good agreement with previous studies of buildings of similar height tested under different environmental and proximity conditions. Results for the intermediate height buildings are presented in the paper. Wind pressures are compared with the NBCC specifications for low and tall buildings. Key words: building, code, design, loads, pressure, roof, wall, wind.

Estimating Detection Probabilities Fdr Search and Rescue

In planning visual search, operations, the allocation of Search and Rescue (SAR) resources may be dependent on the statistical probability that a missing aircraft or crash site can be detected if it is within given geographical areas. The present study was undertaken in order to relate probability of detection (POD) to the relevant environmental or contextual variables. Multidimensional scaling (MDS) and cluster analysis were used to determine the basic stimulus dimensions and characteristics that define different categories of search area. A simulated visual search task generated POD data for representative aerial views that contained synthetic crash sites. POD was a function of target contrast and terrain exposure. Limited field trials have indicated that data from the static visual displays were capable of providing reasonable estimates of detection in dynamic visual search.

Design and fabrication of a wind tunnel for building aerodynamics

A boundary layer wind tunnel has been designed and built at the Centre for Building Studies to be used for research and teaching purposes and small industrial projects as well. The tunnel is of the open return circuit type and has a working section about 12m (40ft.) long with a cross-section 1.8m × 1.8m (6ft. × 6ft.). The roof is of adjustable height to allow for zero longitudinal pressure gradient for various floor roughness characteristics simulating different terrain exposures. The maximum wind speed at the test section is 14m/s. The paper describes the requirements set and the problems encountered in the design and fabrication of the tunnel together with the practical solutions given. The geometry and flow characteristics of the tunnel have been based on economic and space availability considerations. Preliminary results of the performance of the wind tunnel are also presented.

Scale effects in wind tunnel testing of low buildings

Further analysis of wind loads derived from boundary layer wind tunnel experiments on low buildings sheds light on the question of scaling. Results are available for building models tested at three geometric scales under two different terrain exposures representing open country and suburban areas. Both mean and fluctuating pressure coefficients appropriate for both local and area loads have been examined. The errors introduced by using larger models are discussed and evidence is presented that a small relaxation of scale (up to a factor of 2) leads to errors of the order of 10% or less for all cases examined, except for the particular case of local pressure coefficients acting on building walls, which may be subject to non-conservative errors of the order of 25%.

Epidemic Trichophyton mentagrophytes infections in servicemen. Source of infection, role of environment, host factors, and susceptibility

Epidemic inflammatory dermatophytosis among US combat forces in Vietnam was caused by a pancreatopeptidase E-producing, small (a) mating type, zoophilic variety of<i>Trichophyton mentagrophytes</i>,a variety not ordinarily isolated in the United States. An abundant reservoir of zoophilic<i>T mentagrophytes</i>was discovered in commensal rats; carriage was frequent on normal-appearing perineal skin. Variations in prevalence and severity of infection were related to differences in clothing, wet terrain exposures, and duration of tropical service. Our findings suggest that (1) T mentagrophytes infections were acquired in Vietnam, possibly from rats; (2) risk of infection was directly related to degree of exposure to wet clothing; (3) Americans were distinctly more susceptible to T mentagrophytes infections than were adult Vietnamese.

Epidemic Trichophyton mentagrophytes Infections in Servicemen

Epidemic inflammatory dermatophytosis among US combat forces in Vietnam was caused by a pancreatopeptidase E-producing, small (a) mating type, zoophilic variety of<i>Trichophyton mentagrophytes</i>,a variety not ordinarily isolated in the United States. An abundant reservoir of zoophilic<i>T mentagrophytes</i>was discovered in commensal rats; carriage was frequent on normal-appearing perineal skin. Variations in prevalence and severity of infection were related to differences in clothing, wet terrain exposures, and duration of tropical service. Our findings suggest that (1) T mentagrophytes infections were acquired in Vietnam, possibly from rats; (2) risk of infection was directly related to degree of exposure to wet clothing; (3) Americans were distinctly more susceptible to T mentagrophytes infections than were adult Vietnamese.