Loads on Structures The ASCE/SEI 7 Code. A lecture assembled for the course on Statics and Strength of Materials

Transcription

1 Loads on Structures The ASCE/SEI 7 Code A lecture assembled for the course on Statics and Strength of Materials by Jason E. Charalambides PhD, PE, M.ASCE, AIA, ENV_SP Data composed exclusively by author (only for educational purposes) How do Loads Form Types of Loads: Besides the Dead and Live loads, the other types considered as standard loads are Ice (D), Earthquake (E), Flood (F), Lateral Earth Pressure (H), Roof Live Load (Lr) which is certainly different from the Live Load that is meant to be experienced inside a building, Rain (R), Snow (S), and Wind (W). Three special types that are more rare are the Extra Ordinary Event Load (A), and the Self Straining Load (T) and the Wind on Ice (Wi). It is important to note that some loads, such as a human standing on a cantilever beam occur on a point, therefore they are to be considered as Point Loads. Reciprocally, loads that occur throughout a linear element or throughout an area are considered distributed load. For reasons of simplicity they are mostly considered Uniformly Distributed since it is impossible to determine special locations of higher or lower concentration if that would occur. 2

2 Definitions 3 How do Loads Form The various types of loads: There is a multitude of loads and loading patterns that can be applied to a structure or to individual structural members. Most loads are static and some are dynamic. The difference between a static load and a dynamic load is that the former is anticipated to always be evident, whilst the latter may appear at given times at constant frequencies or at random points in time. An example of a static load could be that of a piece of equipment such as the A/C unit on the roof of a building. Per contra, the random vibrations caused by an earthquake, the constant frequency vibrations caused by constant wind loads, or an impact are to be considered as dynamic loads. Variations in dynamic loading can be attributed to changes in applied acceleration, mass, direction of movement, pressure or speed of movement. This course is mainly focused on static loads although instantaneous impact can also be addressed as it can be resolved through the use of principles of simple statics. 4

3 How do Loads Form Types of Loads: There are factors that subject a structure to loads. A person standing on a beam, is defined a Live Load (L). That is not due to the fact that it is a living person only but because it is a type of load that can move and it is relatively variable. Everything that is superimposed on, or temporarily attached to, a structure but not that of the material utilized in its construction or of anything permanently attached to it, is considered as Live Load. Examples would be people, machinery, equipment, appliances, furniture etc. The material that is used to build that beam is considered Dead Load. Any constant load in a structural system that is caused by the weight of the elements and any permanent attachments or accessories is considered Dead Load. 5 How do Loads Form Types of Loads: Besides the Dead and Live loads, the other types considered as standard loads are Ice (D), Earthquake (E), Flood (F), Lateral Earth Pressure (H), Roof Live Load (L r ) which is certainly different from the Live Load that is meant to be experienced inside a building, Rain (R), Snow (S), and Wind (W). Three special types that are more rare are the Extra Ordinary Event Load (A), and the Self Straining Load (T) and the Wind on Ice (W i ). It is important to note that some loads, such as a human standing on a cantilever beam occur on a point, therefore they are to be considered as Point Loads. Reciprocally, loads that occur throughout a linear element or throughout an area are considered distributed load. For reasons of simplicity they are mostly considered Uniformly Distributed since it is impossible to determine special locations of higher or lower concentration if that would occur. 6

4 Loads on Buildings 7 Standardized Load Combinations How loads are evaluated: Some loads can be easily determined. The specific weight of concrete fro example is known to be 150 pcf. Once the volume of beams, columns, slabs, etc, is known, it is easy to calculate the total weight of these elements. The aforementioned are dead loads. It is also possible to determine loads based on statistical precedence. E.g., the average weight of stacks in a library is approximately 125 psf, whilst the reading areas are approximately 60 psf. These are live loads. Note that there is a difference in estimating dead loads and live loads. Every type of loading actually has a different variance of precision. Therefore it is rational to consider applying a safety factor in calculations. For this class, we will almost exclusively be using a factor of 1.2 (i.e. augmenting by 20%) for Dead Loads, and a factor of 1.6 (augmenting 60%) for Live Loads. This is actually one of the standard formulae that are provided in the IBC and the ASCE/SEI-7 code. 8

5 Load Combinations ASCE Standard Load Combinations: Ideally a designer would try all possible scenarios and select the one that provides the largest loading as governing: 1.4 Dead Load 1.2 Dead Load +1.6 Live Load +0.5 Roof Live Load 1.2 Dead Load +1.6 Roof Live Load+Live Load οr 0.8 Wind Load 1.2 Dead Load+1.6 Wind Load +Live Load+0.5 Roof Live Load 1.2 Dead Load +Earthquake Load +Live Load +0.2 Snow Load 0.9 Dead Load +Earthquake Load οr 1.6 Wind Load Again, for this class we will be applying the 2 nd combination unless a special situation is to be addressed. Loads before factorization are determined as Service Loads as opposed to Design Loads that are the values of the loads after factorization. 9 How Heavy Are The Materials Every material has it's own distinct characteristics. A cubic foot of concrete may weigh approximately 150lbf, may have the capacity to take approximately 4000 lbf on every square inch of it in compression, it is considered as not good at all in tension, and it may take very slight deformations before it cracks. Structural steel such as A36 will weigh about 490 pcf, will easily take psi either in compression or tension, and it can deform greatly before it fractures. These are materials that are used in building extensively, but more specifically these are materials that are used for the structure mostly, thus they will be used in order to support other things, such as the gypsum board assemblies of walls, or the glass fenestration, the tiling, the plumbing system and fixtures etc. Weights of Common Building Materials Material Load Brick (4 - on wall) 40 psf Curtain wall (aluminum & glass) 15 psf (avg) Earth (Soil) pcf Glass (1/4 ) 3.3 psf Granite 170 pcf Gypsum board (1/2 ) 1.8 psf Hardwood floor (7/8 ) 2.5 psf Heavy aggregate concrete block 83 pcf Marble 165 pcf Plaster (1/2 ) 4.5 psf Plywood (1/2 ) 1.5 psf Quarry tile (1/2 ) 5.8 psf Reinforced concrete 150 pcf Roofing (5-ply) 6 psf Shingles (asphalt) 2 psf Steel decking 2.5 psf Suspended acoustical ceiling 1 psf Terazzo 2 1/2 sand cushion 27 psf Water 62.4 pcf 20% moisture pcf 10

6 How Heavy Are The Materials Cont.: It is important to have a good reference of how much weight these materials produce in order to have a good estimate of what will be the total loads that each structural member shall be supporting. The table here provides some good references of material weights and how they can be distributed. Weights of Common Building Materials Material Load Brick (4 - on wall) 40 psf Curtain wall (aluminum & glass) 15 psf (avg) Earth (Soil) pcf Glass (1/4 ) 3.3 psf Granite 170 pcf Gypsum board (1/2 ) 1.8 psf Hardwood floor (7/8 ) 2.5 psf Heavy aggregate concrete block 83 pcf Marble 165 pcf Plaster (1/2 ) 4.5 psf Plywood (1/2 ) 1.5 psf Quarry tile (1/2 ) 5.8 psf Reinforced concrete 150 pcf Roofing (5-ply) 6 psf Shingles (asphalt) 2 psf Steel decking 2.5 psf Suspended acoustical ceiling 1 psf Terazzo 2 1/2 sand cushion 27 psf Water 62.4 pcf 20% moisture pcf 11

7 Estimating and Adjusting Loads Other than some specific formulae, the process is very straightforward: Load adjustments/reductions This is a very specific sub-chapter that is particularly applicable to special conditions that Structural Engineers need to apply. For the most part, other disciplines of the building industry do not engage in this manner in significant depth other than being generally familiarized with the concept and understanding that certain conditions allow standard loading to be reduced. For more details about it, you are advised to refer to the most current ASCE/SEI 7-16 code of Minimum Design Loads for Buildings and Other Structures. Specific most applicable extracts for different loads are presented here with examples solved. 14

8 Load Adjustments and Reductions Interior Live Loads: For interior space where the value of A r K LL is larger than 400 sqft, where K LL is the live load element factor (see table), and Ar is the tributary area in square feet, live loads can be reduced according to the following conditions: [ 15 ] L=L K LL A r where L is the reduced live load per square foot, L 0 is the initial (unreduced) design live load per square foot. Live load element factor Element KLL Interior column 4 Exterior columns without cantilever slabs 4 Edge columns with cantilever slabs 3 Corner columns with cantilever slabs 2 Edge beams without cantilever slabs 2 Interior beams 2 All other members 1 15 Load Adjustments and Reductions Interior Live Loads cont.: Special conditions apply for the following: L shall not be less than 0.5 L 0 for members supporting one floor and L shall not be less than 0.4 L 0 for members that support at least two floors. Live loads exceeding 100psf and for passenger vehicle garages shall not be reduced for members supporting one floor. If members support two or more floors, live loads can be reduced by 20%. For structural members in one and two-family dwellings supporting more than one floor an alternative formula can be used: L=0.7 ( L 01 +L ) where L 01, L 02,... are the unreduced live loads of each floor level. The total reduced Live load "L" shall not bear a value lower than the initial unreduced live load of any given floor, (e.g. floor X carries "X" value of unreduced Live load. L needs to be larger or at least equal to X.) 16

9 Load Adjustments and Reductions Roof Live Loads: For roof live loads the following conditions apply: Lr= L 0 R 1 R 2 where 12<L r <20 and where L r is the reduced roof live load per square ft of horizontal projection supported by the member, and L 0 is the unreduced design roof live load per square foot of horizontal projection supported by the member. The reduction factors R 1 and R 2 are determined as follows: R 1 =1 for A r 200 ft 2 R 1 = A r for 200 ft 2 < A r <600 ft 2 R 1 =0.6 for A r 600 ft2 And R 2 =1 for F 4 R 2 = F for 4<F<12 R 2 =0.6 for F 12 where for pitched roof the factor F=number of inches per linear foot, and for an arch or dome, F=rise to span ratio multiplied by a factor of Load Adjustments and Reductions Snow Loads: For flat roofs the following formula applies p f =0.7 C e C t I s p g where p f refers to the load of a flat roof, C e is the exposure condition, C t is the thermal condition, I is the Importance factor that is based on the Risk category, and p g is standard ground snow load. These values need to be obtained from sources of codes such as the IBC or the ASCE/SEI 7 Due to the extensive amount of information contained in those codes, these data are not engaged to the full extent. It is more than adequate at this stage for designers to be aware of this material and specialize in application of these codes as professionals. 18

10 Load Adjustments and Reductions Snow Loads cont.: Special conditions apply for the following: A minimum roof snow load pm single slope, hip and gable roofs with slopes not exceeding 15º and to curved roofs with vertical angle from eave to crown not exceeding 10º and p g not exceeding 20 psf, the formula is adjusted to: p m =I s p g where I s is the importance factor (ranging between 0.8 and 1.2 in the ASCE/SEI 7) Where pg exceeds 20 psf the formula is adjusted to: p m =20 I s For sloped roofs the formula used is the following: p s =C s p f where p s refers to the total snow load acting on the horizontal projection of the sloped surface, C s is the roof slope condition, and p f is the above mentioned load of a flat roof. Thus, in order to determine the load on a sloped roof, the load on the horizontal projection needs to be calculated first and then factored by the slope condition. 19 Load Adjustments Example Snow Load calculation: A non heated garage facility is situated in a plain terrain in Kansas city MO, where the ground Snow load is 20 psf. Calculate the design snow load on the roof: As the roof is flat in this particular case, per guidelines and tables of the ASCE/SEI 7 code, C e =0.8 due to the open area, C t =1.2, and I s =0.8. Therefore, p f = (20 psf )=10.75 psf Due to the fact that the snow load does not exceed 20 psf the alternative formula needs to be examined also: p m =I s p g = psf =16 psf By comparison, the second case of 16 psf governs. 20

11 Load Adjustments Example Snow Load calculation: A semicircular dome of diameter 50 ft carries a typical 20 psf. Calculate the design live load on the roof: With a diameter of 50 ft on a complete semicircular dome, the maximum height will be equivalent to the radius, i.e. 25 ft. Thus the factor F would be equal to: F= Rise Span 32= ( ) 32=16 F=12 Therefore, R 2 = F= =0.6 (default value too) The tributary area would be sqft so the factor R 1 is 0.6. Solving for L r : L r = psf =7.2 psf However, according to the conditions stated above, L r cannot deceed the value of 12 psf which is the value that finally governs. 21

12 MINIMUM DESIGN LOADS Table 4-1 Minimum Uniformly Distributed Live Loads, L o, and Minimum Concentrated Live Loads Occupancy or Use Uniform psf (kn/m 2 ) Conc. lb (kn) Apartments (see Residential) Access floor systems Office use 50 (2.4) 2,000 (8.9) Computer use 100 (4.79) 2,000 (8.9) Armories and drill rooms 150 (7.18) a Assembly areas and theaters Fixed seats (fastened to floor) Lobbies Movable seats Platforms (assembly) Stage floors 60 (2.87) a 100 (4.79) a 100 (4.79) a 100 (4.79) a 150 (7.18) a Balconies and decks 1.5 times the live load for the occupancy served. Not required to exceed 100 psf (4.79 kn/m 2 ) Catwalks for maintenance access 40 (1.92) 300 (1.33) Corridors First floor 100 (4.79) Other floors, same as occupancy served except as indicated Dining rooms and restaurants 100 (4.79) a Dwellings (see Residential) Elevator machine room grating (on area of 2 in. by 2 in. (50 mm by 50 mm)) Finish light floor plate construction (on area of 1 in. by 1 in. (25 mm by 25 mm)) Fire escapes 100 (4.79) On single-family dwellings only 40 (1.92) Fixed ladders See Section 4.5 Garages Passenger vehicles only 40 (1.92) a,b,c c Trucks and buses Handrails, guardrails, and grab bars See Section 4.5 Helipads 60 (2.87) d,e Nonreducible 300 (1.33) 200 (0.89) Hospitals Operating rooms, laboratories 60 (2.87) 1,000 (4.45) Patient rooms 40 (1.92) 1,000 (4.45) Corridors above first floor 80 (3.83) 1,000 (4.45) Hotels (see Residential) Libraries Reading rooms 60 (2.87) 1,000 (4.45) Stack rooms 150 (7.18) a,h 1,000 (4.45) Corridors above first floor 80 (3.83) 1,000 (4.45) Manufacturing Light 125 (6.00) a 2,000 (8.90) Heavy 250 (11.97) a 3,000 (13.40) e,f,g Continued 17

13 CHAPTER 4 LIVE LOADS Occupancy or Use Uniform psf (kn/m 2 ) Conc. lb (kn) Office buildings File and computer rooms shall be designed for heavier loads based on anticipated occupancy Lobbies and first-floor corridors 100 (4.79) 2,000 (8.90) Offices 50 (2.40) 2,000 (8.90) Corridors above first floor 80 (3.83) 2,000 (8.90) Penal institutions Cell blocks 40 (1.92) Corridors 100 (4.79) Recreational uses Bowling alleys, poolrooms, and similar uses Dance halls and ballrooms Gymnasiums Reviewing stands, grandstands, and bleachers Stadiums and arenas with fixed seats (fastened to the floor) 75 (3.59) a 100 (4.79) a 100 (4.79) a 100 (4.79) a,k 60 (2.87) a,k Residential One- and two-family dwellings Uninhabitable attics without storage 10 (0.48) l Uninhabitable attics with storage 20 (0.96) m Habitable attics and sleeping areas 30 (1.44) All other areas except stairs 40 (1.92) All other residential occupancies Private rooms and corridors serving them 40 (1.92) Public rooms a and corridors serving them 100 (4.79) Roofs Ordinary flat, pitched, and curved roofs 20 (0.96) n Roofs used for roof gardens 100 (4.79) Roofs used for assembly purposes Same as occupancy served Roofs used for other occupancies o o Awnings and canopies Fabric construction supported by a skeleton structure 5 (0.24) nonreducible 300 (1.33) applied to skeleton structure Screen enclosure support frame Table 4-1 (Continued) 5 (0.24) nonreducible and applied to the roof frame members only, not the screen 200 (0.89) applied to supporting roof frame members only All other construction 20 (0.96) Primary roof members, exposed to a work floor Single panel point of lower chord of roof trusses or any point 2,000 (8.9) along primary structural members supporting roofs over manufacturing, storage warehouses, and repair garages All other primary roof members 300 (1.33) All roof surfaces subject to maintenance workers 300 (1.33) Schools Classrooms 40 (1.92) 1,000 (4.45) Corridors above first floor 80 (3.83) 1,000 (4.45) First-floor corridors 100 (4.79) 1,000 (4.45) Scuttles, skylight ribs, and accessible ceilings 200 (0.89) Sidewalks, vehicular driveways, and yards subject to trucking 250 (11.97) a,p 8,000 (35.60) q Stairs and exit ways 100 (4.79) 300 r One- and two-family dwellings only 40 (1.92) 300 r 18

14 MINIMUM DESIGN LOADS Table 4-1 (Continued) Occupancy or Use Uniform psf (kn/m 2 ) Conc. lb (kn) Storage areas above ceilings 20 (0.96) Storage warehouses (shall be designed for heavier loads if required for anticipated storage) Light 125 (6.00) a Heavy 250 (11.97) a Stores Retail First floor 100 (4.79) 1,000 (4.45) Upper floors 75 (3.59) 1,000 (4.45) Wholesale, all floors 125 (6.00) a 1,000 (4.45) Vehicle barriers See Section 4.5 Walkways and elevated platforms (other than exit ways) 60 (2.87) Yards and terraces, pedestrian 100 (4.79) a a Live load reduction for this use is not permitted by Section 4.7 unless specific exceptions apply. b Floors in garages or portions of a building used for the storage of motor vehicles shall be designed for the uniformly distributed live loads of Table 4-1 or the following concentrated load: (1) for garages restricted to passenger vehicles accommodating not more than nine passengers, 3,000 lb (13.35 kn) acting on an area of 4.5 in. by 4.5 in. (114 mm by 114 mm); and (2) for mechanical parking structures without slab or deck that are used for storing passenger vehicles only, 2,250 lb (10 kn) per wheel. c Design for trucks and buses shall be per AASHTO LRFD Bridge Design Specifications; however, provisions for fatigue and dynamic load allowance are not required to be applied. d Uniform load shall be 40 psf (1.92 kn/m 2 ) where the design basis helicopter has a maximum take-off weight of 3,000 lbs (13.35 kn) or less. This load shall not be reduced. e Labeling of helicopter capacity shall be as required by the authority having jurisdiction. f Two single concentrated loads, 8 ft (2.44 m) apart shall be applied on the landing area (representing the helicopter s two main landing gear, whether skid type or wheeled type), each having a magnitude of 0.75 times the maximum take-off weight of the helicopter and located to produce the maximum load effect on the structural elements under consideration. The concentrated loads shall be applied over an area of 8 in. by 8 in. (200 mm by 200 mm) and shall not be concurrent with other uniform or concentrated live loads. g A single concentrated load of 3,000 lbs (13.35 kn) shall be applied over an area 4.5 in. by 4.5 in. (114 mm by 114 mm), located so as to produce the maximum load effects on the structural elements under consideration. The concentrated load need not be assumed to act concurrently with other uniform or concentrated live loads. h The loading applies to stack room floors that support nonmobile, double-faced library book stacks subject to the following limitations: (1) The nominal book stack unit height shall not exceed 90 in. (2,290 mm); (2) the nominal shelf depth shall not exceed 12 in. (305 mm) for each face; and (3) parallel rows of double-faced book stacks shall be separated by aisles not less than 36 in. (914 mm) wide. k In addition to the vertical live loads, the design shall include horizontal swaying forces applied to each row of the seats as follows: 24 lb per linear ft of seat applied in a direction parallel to each row of seats and 10 lb per linear ft of seat applied in a direction perpendicular to each row of seats. The parallel and perpendicular horizontal swaying forces need not be applied simultaneously. l Uninhabitable attic areas without storage are those where the maximum clear height between the joist and rafter is less than 42 in. (1,067 mm), or where there are not two or more adjacent trusses with web configurations capable of accommodating an assumed rectangle 42 in. (1,067 mm) in height by 24 in. (610 mm) in width, or greater, within the plane of the trusses. This live load need not be assumed to act concurrently with any other live load requirement. m Uninhabitable attic areas with storage are those where the maximum clear height between the joist and rafter is 42 in. (1,067 mm) or greater, or where there are two or more adjacent trusses with web configurations capable of accommodating an assumed rectangle 42 in. (1,067 mm) in height by 24 in. (610 mm) in width, or greater, within the plane of the trusses. At the trusses, the live load need only be applied to those portions of the bottom chords where both of the following conditions are met: i. The attic area is accessible from an opening not less than 20 in. (508 mm) in width by 30 in. (762 mm) in length that is located where the clear height in the attic is a minimum of 30 in. (762 mm); and ii. The slope of the truss bottom chord is no greater than 2 units vertical to 12 units horizontal (9.5% slope). The remaining portions of the bottom chords shall be designed for a uniformly distributed nonconcurrent live load of not less than 10 lb/ft 2 (0.48 kn/m 2 ). n Where uniform roof live loads are reduced to less than 20 lb/ft 2 (0.96 kn/m 2 ) in accordance with Section and are applied to the design of structural members arranged so as to create continuity, the reduced roof live load shall be applied to adjacent spans or to alternate spans, whichever produces the greatest unfavorable load effect. o Roofs used for other occupancies shall be designed for appropriate loads as approved by the authority having jurisdiction. p Other uniform loads in accordance with an approved method, which contains provisions for truck loadings, shall also be considered where appropriate. q The concentrated wheel load shall be applied on an area of 4.5 in. by 4.5 in. (114 mm by 114 mm). r Minimum concentrated load on stair treads (on area of 2 in. by 2 in. [50 mm by 50 mm]) is to be applied nonconcurrent with the uniform load. 19

15 CHAPTER 4 LIVE LOADS Table 4-2 Live Load Element Factor, K LL Element Interior columns 4 Exterior columns without cantilever slabs 4 Edge columns with cantilever slabs 3 Corner columns with cantilever slabs 2 Edge beams without cantilever slabs 2 Interior beams 2 All other members not identified, including: 1 Edge beams with cantilever slabs Cantilever beams One-way slabs Two-way slabs Members without provisions for continuous shear transfer normal to their span a In lieu of the preceding values, K LL is permitted to be calculated. K LL a 20

16 ASCE 7-10 Wind Load Provisions (Part 2) Maps and Wind Design Provisions by William L. Coulbourne, P.E., M.ASCE Applied Technology Council (ATC) ASCE Webinar ASCE 7-10 Wind Load Provisions 1 Agenda Wind speed maps Design procedures Directional (all heights) Envelope (simplified) Simplified (buildings up to 160 ft. in height) MWFRS and C&C Load Cases ASCE Webinar ASCE 7-10 Wind Load Provisions 2 1

17 ASCE 7-10 Wind Speed Maps Speeds are for ultimate event Maps for 3 Risk Categories (I, II, III and IV) Wind Speeds along the Hurricane Coastline were revised in 1998 to 3- sec peak gust Importance Factor is included in the speeds given in the maps ASCE Webinar ASCE 7-10 Wind Load Provisions Year RP Winds 115(51) 120(54) 110(49) 130(58) 140(63) 115(51) 115(51) 140(63) 150(67) 150(67) 140(63) 130(58) 120(54) 110(49) 160(72) 170(76) 140(63) 150(67) 160(72) 170(76) 110(49) 115(51) 150(67) 120(54) 130(58) 140(63) 180(80) 180(80) 160(72) 160(72) 120(54) 130(58) 140(63) 150(67) Special Wind Region Location Vmph (m/s) Guam 195 (87) Virgin Islands 165 (74) American Samoa 160 (72) Hawaii Region Statewide Special Wind 150(67) 160(72) 170(76) Puerto Rico Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10m) above ground for Exposure C category. 2. Linear interpolation between contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions. 5. Wind speeds correspond to approximately a 7% probability of exceedance in 50 years (Annual Exceedance Probability = , MRI = 700 Years). ASCE Webinar ASCE 7-10 Wind Load Provisions 4 2

18 New V 700 / 1.6 vs. ASCE ASCE Webinar ASCE 7-10 Wind Load Provisions Year RP Winds 120(54) 130(58) 115(52) 140(63) 150(67) 120(54) 160(72) 120(54) 150(67) 160(72) 160(72) 150(67) 140(63) 130(58) 120(54) 115(51) 170(76) 180(80) 150(67) 160(72) 170(76) 180(80) 190(85) 165(74) 165(74) 115(51) 120(54) 130(58) 140(63) 150(67) 120(54) 160(72) 200(89) 130(58) 140(63) 150(67) 200(89) Special Wind Region Location Vmph (m/s) 160(72) 170(76) Guam 210 (94) Virgin Islands 175 (78) 180(80) American Samoa 170 (76) Hawaii Special Wind Region Statewide Puerto Rico Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10m) above ground for Exposure C category. 2. Linear interpolation between contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions. 5. Wind speeds correspond to approximately a 3% probability of exceedance in 50 years (Annual Exceedance Probability = , MRI = 1700 Years). ASCE Webinar ASCE 7-10 Wind Load Provisions 6 3

19 300 Year RP Winds 105(47) 100(45) 110(49) 120(54) 130(58) 105(47) 140(63) 105(47) 130(58) 140(63) 140(63) 130(58) 120(54) 110(49) 105(47) 130(58) 140(63) 150(67) 150(67) 160(72) 105(47) 105(47) 170(76) 150(67) 150(67) 110(49) 120(54) 130(58) 140(63) 110(49) 140(63) 120(54) 130(58) Speical Wind Region Location Vmph (m/s) Guam 180 (80) Virgin Islands 150 (67) American Samoa 150 (67) Hawaii Region Statewide Special Wind 170(76) 140(63) 150(67) 160(72) Puerto Rico Notes: 1. Values are nominal design 3-second gust wind speeds in miles per hour (m/s) at 33 ft (10m) above ground for Exposure C category. 2. Linear interpolation between contours is permitted. 3. Islands and coastal areas outside the last contour shall use the last wind speed contour of the coastal area. 4. Mountainous terrain, gorges, ocean promontories, and special wind regions shall be examined for unusual wind conditions. 5. Wind speeds correspond to approximately a 15% probability of exceedance in 50 years (Annual Exceedance Probability = , MRI = 300 Years). ASCE Webinar ASCE 7-10 Wind Load Provisions 7 Wind speeds at selected locations Location ASCE 7-05 Exposure C V 700 / 1.6 Exposure C Exposure D Bar Harbor, Maine Boston, MA Hyannis, MA New Port, RI Southampton, NY Atlantic City, NJ Wrightsville Beach, NC Folly Beach, SC Miami Beach Clearwater, FL Panama City, FL Biloxi, MS Galveston, TX Port Aransas, TX Hawaii Guam ASCE Webinar ASCE 7-10 Wind Load Provisions 8 4

20 ASCE 7-10 MWFRS Alternative Design Procedures Chapter 27 (Directional Procedure) Part 1: Buildings of all heights Part 2: Simple diaphragm buildings with h 160 ft. (pressures read from tables) Chapter 28 (Envelope Procedure) Part 1: Enclosed or partially enclosed low-rise buildings Part 2: Simple diaphragm buildings with h 60 ft. (pressures read from tables) Chapter 31 - Wind Tunnel Procedure ASCE Webinar ASCE 7-10 Wind Load Provisions 9 Design Procedures Chapter 27 Directional Procedure (all heights method) 5

21 Chapter 27 Directional Procedure Velocity Pressure: (27.3) q z (q h )= K z K zt K d V 2 (Eq ) where: q z = velocity pressure at height z q h = velocity pressure at mean roof height h ASCE Webinar ASCE 7-10 Wind Load Provisions 11 Directional Procedure Chapter 27 p = qgc p q i (GC pi ) where: q = velocity pressure G = gust effect factor C p = external pressure coefficient q i = velocity pressure at mean roof height h GC pi = internal pressure coefficient ASCE Webinar ASCE 7-10 Wind Load Provisions 12 6

22 Directional Procedure Design Procedure (Table ): 1. Wind Speed V (Figure maps) 2. Wind Directionality Factor K d (26.6, Table ) 3. For each wind direction: Exposure Category (26.7) Velocity Pressure Exposure Coefficient K z, K h (Table ) ASCE Webinar ASCE 7-10 Wind Load Provisions 13 Wind Directionality Factor, K d ASCE Webinar ASCE 7-10 Wind Load Provisions 14 7

23 26.7 Exposure Categories B Suburban, use as DEFAULT unless others apply >60% to 80% of all buildings are in this category C Open country, 1500 ft creates this category D Water, including on hurricane coast! It s about Flow Characteristics vs. Surface Roughness ASCE Webinar ASCE 7-10 Wind Load Provisions 15 Exposure B Suburban ASCE Webinar ASCE 7-10 Wind Load Provisions 16 8

24 Exposure B Urban ASCE Webinar ASCE 7-10 Wind Load Provisions 17 Exposure B with a Hole ASCE Webinar ASCE 7-10 Wind Load Provisions 18 9

25 Exposure C ASCE Webinar ASCE 7-10 Wind Load Provisions 19 Exposure C (<1500 ft of B) ASCE Webinar ASCE 7-10 Wind Load Provisions 20 10

26 Exposure D ASCE Webinar ASCE 7-10 Wind Load Provisions 21 Height above ground level, z Exposure Table Velocity Pressure Exposure Coefficients, K h and K z ft (106.7) (121.9) (137.2) 500 (152.4) ASCE Webinar ASCE 7-10 Wind Load Provisions 22 (m) (0-4.6) (6.1) (7.6) (9.1) (12.2) (15.2) (18) (21.3) (24.4) (27.4) (30.5) (36.6) (42.7) (48.8) (54.9) (61.0) (76.2) (91.4) B C D

27 Table Terrain Exposure Constants ASCE Webinar ASCE 7-10 Wind Load Provisions 23 Directional Procedure Design Procedure (Table continued): 4. Topographic Factor, K zt (26.8, Table ) 5. Gust Effect Factor G or G f (26.9) 6. Enclosure Classification (26.10) 7. Internal Pressure Coefficient GC pi (26.11, Table ) 8. External Pressure Coefficients C p, GC pf (Figures ) or force coefficients C f (Figures ) ASCE Webinar ASCE 7-10 Wind Load Provisions 24 12

28 Fig Topographic Factors, K zt ASCE Webinar ASCE 7-10 Wind Load Provisions 25 Fig Topographic Factors, K zt ASCE Webinar ASCE 7-10 Wind Load Provisions 26 13

29 26.9 Gust Effect Factor, G For rigid structures as defined in Section 26.2, G shall be taken as 0.85 or calculated by Eqs , , and , using Table For flexible or dynamically sensitive structures as defined in Section 26.2, G f shall be calculated by Eqs , , , , , a, b and , using Table ASCE Webinar ASCE 7-10 Wind Load Provisions Enclosure Classification Buildings, Open: A building having each wall at least 80% open. Mathematically, A o > 0.8A g where: A o = Total area of openings in a wall that receives positive external pressure, in sq. ft. A g = Gross area of that wall in which A o is identified in sq. ft. ASCE Webinar ASCE 7-10 Wind Load Provisions 28 14

30 26.10 Enclosure Classification Buildings, Partially Enclosed: If the following two conditions are satisfied: 1. A o > 1.1A oi 2. A o > 4 sq. ft or >0.01A g, whichever is smaller, & A oi < 0.2A gi where: A oi = The sum of the areas of openings in the building envelope (walls & roof) not including A o, in sq. ft. A gi = The sum of the gross surface areas of the building envelope (walls & roof) not including A g, in sq. ft. ASCE Webinar ASCE 7-10 Wind Load Provisions Wind Borne Debris Regions Glazed openings in Risk Category II, III, IV buildings requires protection Exception Glazing located over 60 ft. above ground and over 30 ft. above aggregate-surfaced roofs shall be permitted to be unprotected ASCE Webinar ASCE 7-10 Wind Load Provisions 30 15

31 Table Internal Pressure Coeff, GC pi Enclosure Classification GC pi Open Buildings Partially Enclosed Buildings Enclosed Buildings ASCE Webinar ASCE 7-10 Wind Load Provisions 31 Directional Procedure Base method in ASCE 7 for 30+ years. Best representation of actual pressures. Best method to adapt to unusual buildings. Examples in Seminar 3 Traditional Methods ASCE Webinar ASCE 7-10 Wind Load Provisions 32 16

32 Fig External Pressure Coefficient, C p for MWFRS ASCE Webinar ASCE 7-10 Wind Load Provisions 33 Fig C p for MWFRS: Walls ASCE Webinar ASCE 7-10 Wind Load Provisions 34 17

33 Fig C p for MWFRS: Roofs ASCE Webinar ASCE 7-10 Wind Load Provisions 35 Fig C p for MWFRS ASCE Webinar ASCE 7-10 Wind Load Provisions 36 18

34 Part 2 Enclosed Buildings with h 160 ft. Wind pressures obtained directly from tables (Table ) Derived from Directional Procedure Building must be enclosed with simple diaphragm Building may be any plan shape and roof geometry Must determine L/B ratio to use table ASCE Webinar ASCE 7-10 Wind Load Provisions 37 Part 2 Enclosed Buildings with h 160 ft. Pressure p z (psf): p z = p 0 (1 - z / h) + (z / h) p h p h p z Table values z p 0 ASCE Webinar ASCE 7-10 Wind Load Provisions 38 19

35 Part 2 Enclosed Buildings with h 160 ft. p 0 p h ASCE Webinar ASCE 7-10 Wind Load Provisions 39 Roof Pressures - MWFRS Roof Pressure Zones Roof Shapes: Flat Gable Hip Monoslope Mansard ASCE Webinar ASCE 7-10 Wind Load Provisions 40 20

36 Height h (ft) Roof Slope Roof Zone V (MPH) Pressure (psf) (Two load cases for sloped roofs) Exposure C Table for Roof, Adjustment factors for other exposures ASCE Webinar ASCE 7-10 Wind Load Provisions Part 1- MWFRS Envelope Procedure Chapter 28 p = q h [(GC pf ) (GC pi )] where: q h = velocity pressure at mean roof height h GC pf = external pressure coefficient GC pi = internal pressure coefficient ASCE Webinar ASCE 7-10 Wind Load Provisions 42 21

37 Fig GC pf for MWFRS: h < 60 ft ASCE Webinar ASCE 7-10 Wind Load Provisions 43 Fig GC pf for MWFRS: h < 60 ft ASCE Webinar ASCE 7-10 Wind Load Provisions 44 22

38 Fig GC pf for MWFRS There are 9 notes that describe the application of these coefficients and the torsional load cases. ASCE Webinar ASCE 7-10 Wind Load Provisions 45 Part 2 - Envelope Method - MWFRS p s = λk zt p s30 where: p s = simplified design pressure for surfaces A-H λ = adjustment factor K zt = topographic adjustment P s30 = pressures read from tables ASCE Webinar ASCE 7-10 Wind Load Provisions 46 23

39 Part 2 MWFRS Envelope Procedure Completely revised for This version first appeared in IBC There is a slightly different simplified version in the current IBC. Wind pressures obtained from tables. MWFRS based on the Envelope Procedure contained in Part 1 of Chapter 28. Pressures are applied to vertical and horizontal projected areas. Building must be enclosed, simple diaphragm, lowrise building with flat, gable or hip roof shape. ASCE Webinar ASCE 7-10 Wind Load Provisions 47 Part 2 - Simplified Method - MWFRS ASCE Webinar ASCE 7-10 Wind Load Provisions 48 24

40 Part 2 - Envelope Method - MWFRS ASCE Webinar ASCE 7-10 Wind Load Provisions 49 Other MWFRS External Pressure Coefficients Domed Roofs Figure Arched Roofs Figure Monoslope Roofs (and other shapes) Figure Chimneys, Tanks, & Roof Equip Figure Walls and Solid Signs Figure Open Signs & Lattices Figure Trussed Towers Figure ASCE Webinar ASCE 7-10 Wind Load Provisions 50 25

41 Components & Cladding (Chapter 30) Pressure Coefficients C&C Pressure Equations Low-rise buildings with h 60 ft. based on Envelope Procedure p = q h [(GC p ) (GC pi )] Buildings with h 60 ft. based on Directional Procedure p = q(gc p ) q i (GC pi ) Buildings with h 160 ft. based on Simplified Method (pressures in Table ) p = p table (EAF)(RF)K zt ASCE Webinar ASCE 7-10 Wind Load Provisions 52 26

42 Fig GC p for C & C-Walls: h < 60 ft ASCE Webinar ASCE 7-10 Wind Load Provisions 53 Fig GC p for C & C-Walls ASCE Webinar ASCE 7-10 Wind Load Provisions 54 27

43 Fig A GC p for C&C-Gable Roofs:h < 60 ft For < 7 o ASCE Webinar ASCE 7-10 Wind Load Provisions 55 Fig GC p for C & C: h > 60 ft ASCE Webinar ASCE 7-10 Wind Load Provisions 56 28

44 Chapter 29 Other Structures/Appurtenances Design Force Solid freestanding walls and solid signs: F = q h G C f A s (Eq ) Design Force Other Structures F = q z G C f A f (Eq ) where: q = velocity pressure C f = force coefficients A s = gross area of solid sign or wall A f = projected area normal to wind ASCE Webinar ASCE 7-10 Wind Load Provisions 57 Parapets Chapter 27 ASCE Webinar ASCE 7-10 Wind Load Provisions 58 29

45 Parapets Chapter 27 p p = q p GC pn where: p p = combined net pressure on parapet q p = velocity pressure at the top of parapet GC pn = combined net pressure coefficient = +1.5 for windward parapet = for leeward parapet h = h p = height at top of parapet ASCE Webinar ASCE 7-10 Wind Load Provisions 59 Wind Load Cases Torsional Loadings 30

46 Traditional Method - Load Cases ASCE Webinar ASCE 7-10 Wind Load Provisions 61 Envelope Method - Load Cases ASCE Webinar ASCE 7-10 Wind Load Provisions 62 31

47 Simplified Method h 160 ft. Load Cases Appendix D Cases A F to consider Torsional load cases are those shown in Figure and shown here as the traditional load cases ASCE Webinar ASCE 7-10 Wind Load Provisions Strength Design Load Combinations Wind load factor changed in 2010 Edition: Old: LF = 1.6 New: Load factor from 1.6 to 1.0; load factor is built into the MRI for the maps For ASD design, new load factor is 0.63, reduced from 1.0 ASCE Webinar ASCE 7-10 Wind Load Provisions 64 32