Discontinuities include corners of walls roof ridges roof eaves gable ends and

Discontinuities include corners of walls roof ridges

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Discontinuities include corners of walls, roof ridges, roof eaves, gable ends, and roof overhangs. Components and cladding are individual structural components such as rafters, studs, sheathing panels, and nails. Wind force areas are the surface areas that are tributary to the specified structural component. d) Exposure B includes terrain with buildings, wooded areas, or other obstructions approximately the height of a single-family dwelling (Surface Roughness B) extending at least 2600 ft. or 20 times the building height (whichever is greater) from the site. Exposure B applies to most urban and suburban areas. Exposure B is the least severe wind exposure. Exposure C applies where Exposures B and D do not apply. Exposure D applies to unobstructed flat terrain (including mud flats, salt flats and unbroken ice) (Surface Roughness D) extending a distance of 5000 ft. or 20 times the building height (whichever is greater) from the site. Exposure D also applies to building sites adjacent to large water surfaces outside hurricane prone regions. Exposure D is the most severe wind exposure. ______________________________________________________________________
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Chapter 2 Solutions Page 13 of 19 Problem 2.18 a)A mean recurrence interval of 50 years (annual probability of exceedence of 0.02) generally applies to basic wind speeds in ASCE 7 Fig. 6-1. b)A mean recurrence interval of 100 years applies to wind pressures for essential and hazardous facilities (I= 1.15). c)The mean roof height above ground (hmean) is used to determine the height and exposure factor (λ). ______________________________________________________________________ Problem 2.19Kzt= 1.0 a) V= 120 mph ASCE 7 Figure 6-1B for Tampa, FL b) I= 1.15 ASCE 7 Table 6-1 and IBC Table 1604.5 for essential facility (Category IV) c) λ= 1.0 ASCE 7 Figure 6-2 for Exposure B and mean roof height of 30 ft. d) ASCE 7 Figure 6-2 for flat roof Zone ps30(psf) ps= λKztI ps30(psf) Wall A 22.8 26.2 Wall B - 11.9 - 13.7 Wall C 15.1 17.4 Wall D - 7.0 - 8.05 Roof E - 27.4 - 31.5 Roof F - 15.6 - 17.9 Roof G - 19.1 - 22.0 Roof H - 12.1 - 13.9 Roof Overhang EOH- 38.4 - 44.2 Roof Overhang GOH- 30.1 - 34.6 e) ASCE 7 Figure 6-3 for flat roof. Assume 10 ft2tributary area (effective wind area). Wind pressures would be lower for larger tributary areas. Zone pnet30(psf) pnet= λKztIpnet30(psf) Roof 1 10.5 - 25.9 12.1 - 29.8 Roof 2 10.5 - 43.5 12.1 - 50.0 Roof 3 10.5 - 65.4 12.1 - 75.2 Wall 4 25.9 - 28.1 29.8 - 32.3 Wall 5 25.9 - 34.7 29.8 - 39.9 Roof Overhang 2 - 37.3 - 42.9 Roof Overhang 3 - 61.5 - 70.7
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Chapter 2 Solutions Page 14 of 19 Problem 2.20 Kzt= 1.0 V= 90 mph ASCE 7 Figure 6-1 for Denver, CO I= 1.15 ASCE 7 Table 6-1 and IBC Table 1604.5 for essential facility (Category IV) Ridge height = 22 ft + (3/12)(50 ft/2) = 28.25 ft hmean= (22 ft + 28.25 ft)/2 = 25.1 ft λ= 1.35 ASCE 7 Figure 6-2 for Exposure C and hmean= 25.1 ft. 0.4hmean= 0.4(25.1 ft) = 10.1 ft 0.1b= 0.1(50 ft) = 5 ft a= lesser of {0.4hmeanor 0.1b} = 5 ft 2a= 10 ft Roof angle = arctan (3/12) = 14.0 degrees a) ASCE 7 Figure 6-2 for roof angle of 15º (Wind direction perpendicular to gable ridge). [Note that this solution is for a tabulated roof angle of 15º. Interpolation of tabulated values for a 14º roof slope would provide results within 2%.] Zone ps30(psf) ps= λKztIps30(psf) Wall A 16.1 25.0 Wall B - 5.4 - 8.4 Wall C 10.7 16.6 Wall D - 3.0 - 4.7 Roof E - 15.4 - 23.9 Roof F - 10.1 - 15.7 Roof G - 10.7 - 16.6 Roof H - 7.7 - 12.0 a) ASCE 7 Figure 6-2 for roof slope of 0° (Wind direction parallel to gable ridge) Zone ps30(psf) ps= λKztIp
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