Wind and the Built Environment U.S. Needs in Wind Engineering and Hazard Mitigation (1993) / Chapter Skim
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3. Wind-Engineering Research Needs
3. Wind-Engineering Research Needs
Pages 55-78
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From page 55... ...
Reentrainment of exhaust gases from laboratory building fume hood exhausts into building ventilation systems and local dispersion of toxic gas releases or of toxic fiances from accidental spills represent health and safety issues to which wind engineering can make major contributions to eliminate or reduce the hazard. These are areas that do not have adequate design methodologies at present.
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From page 56... ...
These methodologies include physical modeling using atmosphenc, boundary-layer wind tunnels; numerical modeling taking advantage of powerful computing capability; and full-scale field measurements to vend predictions made by physical and/or numerical modeling. In addition, innovative experimental approaches, such as tornado simulation, are required to address particular problems (Lund and Snow, 1991~.
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From page 57... ...
A wide variety of wind tunnel tests are available on a commercial or research basis to define wind effects on structures. A plastic model of a
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From page 58... ...
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From page 59... ...
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From page 60... ...
For small projects such as single- or multiple-family dwellings, small commercial structures, or industrial buildings, wind turmel tests are often too costly relative to the overall project cost. For these structures, which make up the overwhelming bulk of construction in the United States, reliance must be placed on building codes to define wind loads.
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From page 61... ...
Still needed are improved numerical algorithms, protocols for easy implementation of parallel processing, and improved graphical display software. For many years, empirical mathematical models have been used for the prediction of pollutant dispersion by winds.
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From page 62... ...
Along with these expenments, physical modeling in the wind tunnel and numencal modeling should be planned to develop improved modeling technologies. Innovative Experimental Approaches Although boundaIy-layer wind tunnels provide a major too} for exploring wind loads on structures, they cannot provide all necessary experimental capability.
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From page 63... ...
Otherwise, a very large wind tunnel can impose the wind loads by winds occurring in nature. Research is needed to determine the most effective method for testing these structures and to design and build such facilities.
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From page 64... ...
Although w~nd-Ioad codes specify local wind pressures, wind tunnel tests often find significant variations from that loading. One of the largest local pressures on a building is frequently found near a corner of the roof.
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From page 65... ...
An analytical component of wind-Ioad research emphasizing chaos theory might provide advances in understanding these complex w~nd-Ioad mechanisms. Low Buildings A few research projects have been funded by the metal buildings industry to study design loads appropriate for small buildings.
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From page 66... ...
Information on code description of wind loading for low buildings needs to be expanded to cover more representative building shapes, and code provisions need to be made easier for designers to apply. Wood frame structures in particular do not have clearly deDned paths for transfer of wind loads from point of application to the ground.
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From page 67... ...
Flexible structures are susceptible to the dynamic loading and response effects discussed earlier under bluff body aerodynamics. There is no universal definition of a flexible structure to set it apart for separate attention by a designer, so not all flexible structures are recognized as such by designers.
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From page 68... ...
Current damping practice includes the use of tuned mass dampers (massive weights near a building top that are attached to the building frame through spnngs) , nscoelastic dampers (thousands of small devices placed throughout a building to dissipate kinetic energy in the structured, or aerodynamic fanugs (changes in the structure shape to reduce the wind loads causing the motion technique used on bridges but not practical for buildings)
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From page 69... ...
Wind speeds at various return intervals are the essential input for the design of conventional fixed structures. For these relatively stiff structures, ondy the steady wind effects are of interest and they typically contribute less than 10 percent of the total environmental Toads.
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From page 70... ...
The fluctuating nature of wind causes cyclic loadings on roof and wall panels of buildings. In a siow-mov~ng hurricane, such cyclic loadings can cause fatigue failures of these panels, resulting in their removal and consequent wind and water damage to the building interior.
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From page 71... ...
The factors that influence the magnitude of And loads on a building, addition to wind speed, are the terrain surrounding the building, the shape of the building, arid the desired safety of the building frame and components. The mode} building codes use some of these factors from the ANSI/ASCE 7-~8, modify some factors based on experience, or ignore some of the factors as a part of tradition.
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From page 72... ...
Needed improvements to the ANSI/ASCE 7-~8 include better wind-speed definition; improved wind directionality; improved gust factor models; inclusion of torsional wind loads (twisting about the vertical axis of buildings) ; improved local pressure prediction and overall frame loads through a fancily of loading coefficients for various building shapes; improved alongwind dynamic loading prediction model; inclusion of a workable across-wind mode]
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From page 73... ...
Several cities, including Boston, San Francisco, and Pittsburgh, require that wind tunnel tests be performed for all projects in which the wind speeds are likely to cause pedestnan comfort problems. However, even where cities have w~nd-speed requirements, no attempts have been made to account for thermal comfort.
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From page 74... ...
However, present Gaussian-Wpe or other empincal models are inadequate to describe pollution dispersion in a number of situations, and wind tunnel or numerical modeling is required to adequately address these situations, which include dispersion in winds about buildings, complex terrain, nonuniform roughness (urban or industrial settings) , blowing dust or particulates, area or volume sources, mobile sources, mountain valley wind systems (thermally driven flows)
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From page 75... ...
Research in time and spatial variations of wind gusts and their dynamic effect on turbine rotors should be pursued vigorously to understand cyclic loading on the rotor structure and to mitigate fatigue failures. Soil Erosion Soil erosion by wind is a global problem that induces both on-site and off-site damage.
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From page 76... ...
A strong research effort is needed to better define wind loads in a codified fob for small projects, such as housing for single or multiple families, small commercial structures, or industrial buildings, which comprise the overwhelming bulk of construction in the United States. For these types of structures, wind tunnel tests are often too costly to consider; thus reliance must be placed on building codes to define wind loads.
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From page 77... ...
In tandem with these experiments, physical modeling in the wind tunnel and numerical modeling should be planned to develop improved modeling technologies.
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From page 78... ...
15. Research is needed to develop better numerical models and more economical wind tunnel testing methods for prediction of fume hood exhausts to ensure that the public is not endangered by the reingestion of exhausts into air intake systems.
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