9. Wind Design

1 Dynamic Loads Wind Design Richard L Wood, 2018 Page 1 of 31 9. Wind Design Lesson Objectives: 1) Define basic definitions within wind Design including: Main Wind Force Resisting System and Components and Cladding. 2) Select appropriate building enclosure classification from open building, partially enclosed building, and enclosed building classifications. 3) Determine the basic wind Design speed from the mapped values within ASCE 7-16. 4) Compute Design wind pressures from ASCE 7-16 through selection of wind directionality factor, exposure category and surface roughness , any topographical effect, and the gust effect factor. 5) Outline the process to analyze a general and regular building using the MWFRS Directional Procedure as outlined within Chapter 27. Background Reading: 1) Read _____.

2 Wind Nomenclature: 1) _____ or MWFRS - assembly of structural elements that provide support and stability under wind loads. a. This consists of the various components, namely: building foundation, structural floor members (joists, beams, and framing systems) columns, roof trusses, structural bracing, walls, and diaphragms that transfer loads. b. MWFFRS experiences external pressures and forced induced from wind loads which may cause: i. _____ pressures on windward walls ii. _____ pressures on leeward walls, side walls, and roof systems iii. May cause collapse of surfaces due to _____ _____ Dynamic Loads Wind Design Richard L Wood, 2018 Page 2 of 31 2) _____ include elements of the building envelope that are not considered part of the MWFRS. a. Select _____ examples include: purlins, studs, roof decking, and roof trusses.

3 B. Select _____ examples include: wall coverings, curtain walls, roof coverings, exterior windows, and/or doors. c. Elements of components and cladding may be considered as part of the MWFRS under certain Design scenario. d. Components and cladding experience both _____and _____ external pressures. At sharp edges (corners, wall and roof junctions, etc.), the air flow separates which creates _____ and _____ _____ positive and negative pressures. e. Complex aerodynamic effects exist and are dependent on the shape of the structure. As a result, components and cladding are subject to failures resulting from numerous factors. 3) _____ are caused by a permeability in a building and/or when the wind enters the building through a dominant opening. a. When determining the total wind pressure, the internal pressure may be _____ _____ from the external pressures.

4 B. The _____ of the internal pressure depend on whether the building is open, partially enclosed, or enclosed according to the definitions prescribed in ASCE 7-16. 4) _____ - building having each wall at least 80% open. One example is a rigid frame building having no side walls. 5) _____ - building which meets both of the following statements: a. The total area of openings in a wall that receives positive external pressure exceeds the sum of the areas of openings in the balance of the building envelope (walls and roof) by more than 10%, and b. The total area of openings in a wall that receives positive external pressure exceeds four (4) square feet or of the area of that wall, whichever is smaller, and the Dynamic Loads Wind Design Richard L Wood, 2018 Page 3 of 31 percentage of openings in the balance of the building envelope does not exceed 20% 6) _____ - building that does not comply with the requirements for open or partially enclosed buildings.

5 Wind Loads by ASCE 7-16 and 7-10 (Similar Process): 1) The basic _____ to determine wind loads can be located in Figure of ASCE 7-16 or shown here in Figure 1. Figure 1. Outline for determining wind loads, from ASCE 7-16. Dynamic Loads Wind Design Richard L Wood, 2018 Page 4 of 31 General Requirements - Basic Design Wind Speed: 1) ASCE 7-16 has developed _____ for the United States and all its territories by occupancy category. 2) This can be found as Figures - In these notes, these figures are shown in Figures 2-7. 3) Note Design wind speeds can be found by location using the _____, shown in Figure 8. 4) The values provided are nominal Design 3-second gust wind speeds in miles per hour (m/s in the parenthesis) at 33 feet (10 meter) above ground for exposure C category 5) _____ is permitted between contours.

6 6) Island and coastal areas outside the last contour shall use the last week speed contour of the coastal area. 7) Mountainous terrains, gorges, ocean promontories, and special wind regions shall be examined for _____. 8) Wind speeds correspond to various values between on the mapped occupancy: a. Category _____ _____% probability of exceedance in 50 years, mean recurrence interval of _____ years b. Category _____ _____% probability of exceedance in 50 years, mean recurrence interval of _____ years c. Category _____ _____% probability of exceedance in 50 years, mean recurrence interval of _____ years 9) Regional climatic data is permitted for the estimation of basic wind speeds. Refer to section Dynamic Loads Wind Design Richard L Wood, 2018 Page 5 of 31 Figure 2.

7 Basic wind speeds mapped for occupancy category I (part one). Dynamic Loads Wind Design Richard L Wood, 2018 Page 6 of 31 Figure 3. Basic wind speeds mapped for occupancy category I (part two). Dynamic Loads Wind Design Richard L Wood, 2018 Page 7 of 31 Figure 4. Basic wind speeds mapped for occupancy category II (part one). Dynamic Loads Wind Design Richard L Wood, 2018 Page 8 of 31 Figure 5. Basic wind speeds mapped for occupancy category II (part two). Dynamic Loads Wind Design Richard L Wood, 2018 Page 9 of 31 Figure 6. Basic wind speeds mapped for occupancy category III. Figure 7. Basic wind speeds mapped for occupancy category IV. Dynamic Loads Wind Design Richard L Wood, 2018 Page 10 of 31 Figure 8. Design wind speeds by latitude and longitude. (Available at: ).

8 Note this is for ASCE 7-10 loads, the updated version has not been released to date. Dynamic Loads Wind Design Richard L Wood, 2018 Page 11 of 31 General Requirements Wind Directionality Factor: 1) The wind directionality factor, _____, shall be determined from Table from ASCE 7-16 (herein shown as Table 1). 2) Note this directionality factor shall only be included in determining wind load when the load combinations specified in ASCE 7-16 Section and are used for Design . 3) The effect of wind directionality in determining wind loads in accordance with Chapter 31 (wind tunnels) shall be based on an analysis for wind speeds that conforms to the requirements of ASCE 7-16 Table 1. Wind directionality factor. Dynamic Loads Wind Design Richard L Wood, 2018 Page 12 of 31 General Requirements Exposure Category: 1) For each wind direction, the _____ shall be based on the ground surface roughness that is determined from natural _____, _____, and constructed _____.

9 2) A ground surface roughness within each 45-degree ( radian) sector shall be determined for a distance upwind of the site as defined in and from the categories defined below. a. The highest wind load shall be used to represent the winds from that direction. b. Surface roughness B: Urban and suburban areas, wooded areas, or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger. c. Surface roughness C: Open terrain with scattered obstructions having heights generally less than 30 ft ( m). This category includes flat open country and grasslands. d. Surface roughness D: Flat, unobstructed areas and water surfaces . This category includes smooth mud flats, salt flats, and unbroken ice. 3) An exposure category shall be determined in accordance with one of the following three: a.

10 Exposure B: For buildings with a mean roof height of less than or equal to 30 ft ( m), Exposure B shall apply where the ground surface roughness , as defined by Surface roughness B, prevails in the upwind direction for a distance greater than 1,500 ft (457 m). For buildings with a mean roof height greater than 30 ft ( m), Exposure B shall apply where Surface roughness B prevails in the upwind direction for a distance greater than 2,600 ft (792 m) or 20 times the height of the building, whichever is greater. b. Exposure C: shall apply for all cases where Exposures B or D does not apply. c. Exposure D: shall apply where the ground surface roughness , as defined by Surface roughness D, prevails in the upwind direction for a distance greater than 5,000 ft (1,524 m) or 20 times the building height, whichever is greater.