how do loads form - avant-garde engineering llc ......) 17 load adjustments and reductions roof live...

Loads on StructuresLoads on StructuresThe ASCE/SEI–7 CodeThe ASCE/SEI–7 Code

A lecture assembled for the course onStatics and Strength of Materials

by Jason E. Charalambides PhD, PE, M.ASCE, AIA, ENV_SP

Data composed exclusively by author(only for educational purposes)

2

How do Loads FormHow 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 certainlydifferent 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 ona point, therefore they are to be considered as Point Loads.

Reciprocally, loads that occur throughout a linear element or throughout an area are considereddistributed load. For reasons of simplicity they are mostly considered Uniformly Distributed sinceit is impossible to determine special locations of higher or lower concentration if that wouldoccur.

3

Definitions

4


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 differencebetween a static load and a dynamic load is that the former is anticipated to always beevident, whilst the latter may appear at given times at constant frequencies or at randompoints in time.

An example of a static load could be that of a piece of equipment such as the A/C unit on theroof of a building. Per contra, the random vibrations caused by an earthquake, the constantfrequency vibrations caused by constant wind loads, or an impact are to be considered asdynamic loads. Variations in dynamic loading can be attributed to changes in appliedacceleration, mass, direction of movement, pressure or speed of movement.

This course is mainly focused on static loads although instantaneous impact can also beaddressed as it can be resolved through the use of principles of simple statics.

5


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 dueto the fact that it is a living person only but because it is a typeof load that can move and it is relatively variable. Everythingthat is superimposed on, or temporarily attached to, a structurebut not that of the material utilized in its construction or ofanything permanently attached to it, is considered as LiveLoad. Examples would be people, machinery, equipment,appliances, furniture etc.

The material that is used to build that beam is considered DeadLoad. Any constant load in a structural system that is causedby the weight of the elements and any permanent attachmentsor accessories is considered Dead Load.

6


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 certainlydifferent 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 ona point, therefore they are to be considered as Point Loads.

Reciprocally, loads that occur throughout a linear element or throughout an area are considereddistributed load. For reasons of simplicity they are mostly considered Uniformly Distributed sinceit is impossible to determine special locations of higher or lower concentration if that wouldoccur.

7

Loads on Buildings

8

Standardized Load CombinationsStandardized Load Combinations

How loads are evaluated: Some loads can be easily determined. The specific weight of concrete fro example is known to

be 150pcf. Once the volume of beams, columns, slabs, etc, is known, it is easy to calculate thetotal weight of these elements. The aforementioned are dead loads.

It is also possible to determine loads based on statistical precedence. E.g., the average weightof stacks in a library is approximately 125psf, whilst the reading areas are approximately 60psf.These are live loads.

Note that there is a difference in estimating dead loads and live loads. Every type of loadingactually has a different variance of precision. Therefore it is rational to consider applying asafety factor in calculations.

For this class, we will almost exclusively be using a factor of 1.2 (i.e. augmenting by 20%) forDead Loads, and a factor of 1.6 (augmenting 60%) for Live Loads. This is actually one of thestandard formulae that are provided in the IBC and the ASCE/SEI-7 code.

9

Load CombinationsLoad Combinations

ASCE Standard Load Combinations: Ideally a designer would try all possible scenarios and select the one that provides the largest

loading as governing:

Again, for this class we will be applying the 2nd combination unless a special situation is to beaddressed.

Loads before factorization are determined as “Service Loads” as opposed to “Design Loads”that are the values of the loads after factorization.

1.2⋅Dead Load+1.6⋅Live Load+0.5⋅Roof Live Load1.2⋅Dead Load+1.6⋅Roof Live Load+Live Load οr 0.8⋅Wind Load1.2⋅Dead Load+1.6⋅Wind Load+Live Load+0.5⋅Roof Live Load1.2⋅Dead Load+Earthquake Load+Live Load+0.2⋅Snow Load0.9⋅Dead Load+Earthquake Load οr 1.6⋅Wind Load

1.4⋅Dead Load

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How Heavy Are The MaterialsHow Heavy Are The Materials

Every material has it's own distinctcharacteristics.

A cubic foot of concrete may weigh approximately150lbf, may have the capacity to take approximately4000lbf on every square inch of it in compression, it isconsidered as not good at all in tension, and it maytake very slight deformations before it cracks.

Structural steel such as A36 will weigh about 490pcf, willeasily take 36000psi either in compression or tension,and it can deform greatly before it fractures. These arematerials that are used in building extensively, butmore specifically these are materials that are used forthe structure mostly, thus they will be used in order tosupport other things, such as the gypsum boardassemblies of walls, or the glass fenestration, the tiling,the plumbing system and fixtures etc.

Weights of Common Building MaterialsMaterial Load

Brick (4” - on wall) 40 psfCurtain wall (aluminum & glass) 15 psf (avg)Earth (Soil) 100 – 130 pcfGlass (1/4”) 3.3 psfGranite 170 pcfGypsum board (1/2”) 1.8 psfHardwood floor (7/8”) 2.5 psfHeavy aggregate concrete block 83 pcfMarble 165 pcfPlaster (1/2”) 4.5 psfPlywood (1/2”) 1.5 psfQuarry tile (1/2”) 5.8 psfReinforced concrete 150 pcfRoofing (5-ply) 6 psfShingles (asphalt) 2 psfSteel decking 2.5 psfSuspended acoustical ceiling 1 psfTerazzo 2 1/2” sand cushion 27 psfWater 62.4 pcfWood @ 20% moisture 30 – 40 pcf

11

How Heavy Are The MaterialsHow 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 goodestimate of what will be the total loads that eachstructural member shall be supporting.

The table here provides some good references ofmaterial weights and how they can be distributed.

Weights of Common Building MaterialsMaterial Load

Brick (4” - on wall) 40 psfCurtain wall (aluminum & glass) 15 psf (avg)Earth (Soil) 100 – 130 pcfGlass (1/4”) 3.3 psfGranite 170 pcfGypsum board (1/2”) 1.8 psfHardwood floor (7/8”) 2.5 psfHeavy aggregate concrete block 83 pcfMarble 165 pcfPlaster (1/2”) 4.5 psfPlywood (1/2”) 1.5 psfQuarry tile (1/2”) 5.8 psfReinforced concrete 150 pcfRoofing (5-ply) 6 psfShingles (asphalt) 2 psfSteel decking 2.5 psfSuspended acoustical ceiling 1 psfTerazzo 2 1/2” sand cushion 27 psfWater 62.4 pcfWood @ 20% moisture 30 – 40 pcf

14

Estimating and Adjusting LoadsEstimating 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 conditionsthat Structural Engineers need to apply.

For the most part, other disciplines of the building industry do not engage in thismanner in significant depth other than being generally familiarized with the conceptand 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 7-16code of Minimum Design Loads for Buildings and Other Structures. Specific mostapplicable extracts for different loads are presented here with examples solved.

15

Load Adjustments and ReductionsLoad Adjustments and Reductions

Interior Live Loads: For interior space where the value of Ar·KLL is larger than

400sqft, where KLL is the live load element factor (see table),and Ar is the tributary area in square feet, live loads can bereduced according to the following conditions:

where L is the reduced live load per square foot,L0 is the initial (unreduced) design live load persquare foot.

L=L01⋅[0.25+ 15√K LL⋅Ar ]

Live load element factorElement KLL

Interior column 4Exterior columns without cantilever slabs 4Edge columns with cantilever slabs 3Corner columns with cantilever slabs 2Edge beams without cantilever slabs 2Interior beams 2All other members 1

16


Interior Live Loads cont.: Special conditions apply for the following:

L shall not be less than 0.5·L0 for members supporting one floor and L shall not beless than 0.4·L0 for members that support at least two floors.

Live loads exceeding 100psf and for passenger vehicle garages shall not bereduced for members supporting one floor. If members support two or morefloors, live loads can be reduced by 20%.

For structural members in one and two-family dwellings supporting more than onefloor an alternative formula can be used: where L01, L02,...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 atleast equal to X.)

L=0.7⋅(L01+L02+...)

17


Roof Live Loads: For roof live loads the following conditions apply:

where 12<Lr<20 and where Lr is the reduced roof live load per square ft of horizontal projectionsupported by the member, and L0 is the unreduced design roof live load per square foot ofhorizontal projection supported by the member. The reduction factors R1 and R2 are determinedas follows:

And

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 32.

Lr=L0⋅R1⋅R2

R1=1 for Ar≤ 200 ft 2

R1=1.2−0.001⋅Ar for 200 ft 2

<Ar<600 ft 2

R1=0.6 for Ar ≥ 600 ft2

R2=1 for F ≤ 4 R2=1.2−0.05⋅F for 4<F<12 R2=0.6 for F ≥ 12

18


Snow Loads: For flat roofs the following formula applies

where pf refers to the load of a flat roof, Ce is the exposure condition, Ct is the thermal condition, I is the Importance factor that is based on the Risk category, and pg 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 thefull extent. It is more than adequate at this stage for designers to be aware of this material andspecialize in application of these codes as professionals.

p f =0.7⋅Ce⋅Ct⋅I s⋅p g

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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 pg notexceeding 20psf, the formula is adjusted to:

where Is is the importance factor (ranging between 0.8 and 1.2 in the ASCE/SEI 7)

Where pg exceeds 20psf the formula is adjusted to:

For sloped roofs the formula used is the following: where ps refers to the total snow load acting on the horizontal projection of the sloped

surface, Cs is the roof slope condition, and pf 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 andthen factored by the slope condition.

pm=I s⋅pg

pm=20⋅I s

ps=Cs⋅p f

20

Load Adjustments ExampleLoad Adjustments Example Snow Load calculation:

A non heated garage facility is situated in a plain terrain inKansas city MO, where the ground Snow load is 20psf .Calculate the design snow load on the roof:

As the roof is flat in this particular case, per guidelines andtables of the ASCE/SEI 7 code, Ce=0.8 due to the openarea, Ct=1.2, and Is=0.8.

Therefore,

Due to the fact that the snow load does not exceed 20psf thealternative formula needs to be examined also:

By comparison, the second case of 16psf governs.

p f =0.7⋅0.8⋅1.2⋅0.8⋅(20psf )=10.75psf

pm=I s⋅pg=0.8⋅20psf =16 psf

21

Load Adjustments ExampleLoad Adjustments Example

Snow Load calculation: A semicircular dome of diameter 50ft carries a typical 20psf . Calculate the design live load on

the roof: With a diameter of 50ft on a complete semicircular dome, the maximum height will be

equivalent to the radius, i.e. 25ft. Thus the factor F would be equal to:

Therefore,

The tributary area would be 1963.5sqft so the factor R1 is 0.6. Solving for Lr:

However, according to the conditions stated above, Lr cannot deceed the value of 12psf whichis the value that finally governs.

F= RiseSpan

⋅32=( 2550 )⋅32=16→ F=12

R2=1.2−0.05⋅F=1.2−0.05⋅12=0.6 (default value too)

Lr=0.6⋅0.6⋅20psf =7.2psf

MINIMUM DESIGN LOADS

17

Table 4-1 Minimum Uniformly Distributed Live Loads, Lo, and Minimum Concentrated Live Loads

Occupancy or Use Uniform psf (kN/m2) Conc. lb (kN)

Apartments (see Residential)

Access fl oor systems Offi ce 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 fl oor) 60 (2.87)a

Lobbies 100 (4.79)a

Movable seats 100 (4.79)a

Platforms (assembly) 100 (4.79)a

Stage fl oors 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/m2)

Catwalks for maintenance access 40 (1.92) 300 (1.33)

Corridors First fl oor 100 (4.79) Other fl oors, 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))

300 (1.33)

Finish light fl oor plate construction (on area of 1 in. by 1 in. (25 mm by 25 mm))

200 (0.89)

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

Trucks and buses c

Handrails, guardrails, and grab bars See Section 4.5

Helipads 60 (2.87)d,e

Nonreducible

e,f,g

Hospitals Operating rooms, laboratories 60 (2.87) 1,000 (4.45) Patient rooms 40 (1.92) 1,000 (4.45) Corridors above fi rst fl oor 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 fi rst fl oor 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)

Continued

c04.indd 17 4/14/2010 11:00:42 AM

CHAPTER 4 LIVE LOADS

18


Offi ce buildings File and computer rooms shall be designed for heavier loads based

on anticipated occupancy Lobbies and fi rst-fl oor corridors 100 (4.79) 2,000 (8.90) Offi ces 50 (2.40) 2,000 (8.90) Corridors above fi rst fl oor 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 fi xed seats (fastened to the fl oor)

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 roomsa and corridors serving them 100 (4.79)

Roofs Ordinary fl at, 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 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 fl oor Single panel point of lower chord of roof trusses or any point

along primary structural members supporting roofs over manufacturing, storage warehouses, and repair garages

2,000 (8.9)

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 fi rst fl oor 80 (3.83) 1,000 (4.45) First-fl oor 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) 300r

One- and two-family dwellings only 40 (1.92) 300r

Table 4-1 (Continued)

c04.indd 18 4/14/2010 11:00:42 AM

MINIMUM DESIGN LOADS

19


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 fl oor 100 (4.79) 1,000 (4.45) Upper fl oors 75 (3.59) 1,000 (4.45) Wholesale, all fl oors 125 (6.00)a 1,000 (4.45)

Vehicle barriers See Section 4.5Walkways 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 specifi c 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 Specifi cations; however, provisions for fatigue and dynamic load allowance are not required to be applied. d Uniform load shall be 40 psf (1.92 kN/m2) 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.gA 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 fl oors 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 confi gurations 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 confi gurations 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/ft2 (0.48 kN/m2).n Where uniform roof live loads are reduced to less than 20 lb/ft2 (0.96 kN/m2) in accordance with Section 4.8.1 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.

Table 4-1 (Continued)

c04.indd 19 4/14/2010 11:00:43 AM

CHAPTER 4 LIVE LOADS

20

Table 4-2 Live Load Element Factor, KLL

Element KLLa

Interior columns 4Exterior columns without cantilever slabs 4

Edge columns with cantilever slabs 3

Corner columns with cantilever slabs 2Edge beams without cantilever slabs 2Interior beams 2

All other members not identifi ed, 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, KLL is permitted to be calculated.

c04.indd 20 4/14/2010 11:00:43 AM

1

ASCE Webinar –ASCE 7-10 Wind Load Provisions 1

ASCE 7-10Wind Load Provisions

(Part 2)

Maps and Wind Design Provisions

byWilliam L. Coulbourne, P.E., M.ASCE

Applied Technology Council(ATC)


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

2


ASCE 7-10Wind 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


700 Year RP Winds

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 = 0.00143, MRI = 700 Years).

Location Vmph (m/s)Guam 195 (87)Virgin Islands 165 (74)American Samoa 160 (72)Hawaii Special Wind Region Statewide

Puerto Rico

110(49)

115(51)

150(67) 160(72)

170(76)

115(51)

115(51)150(67)

140(63)120(54)

130(58)

170(76)160(72)

180(80)

180(80)

170(76)160(72)

150(67)

140(63)

140(63)

150(67)

140(63)

130(58)

120(54)

115(51)

110(49)

150(67)

120(54)130(58)140(63)

160(72)

160(72)

150(67)140(63)

130(58)

120(54)

110(49)

Special Wind Region

3


New V700/√1.6 vs. ASCE 7-05

140

130

150

140

140

130

110

120130150

110

110


1700 Year RP Winds


Location Vmph (m/s)Guam 210 (94)Virgin Islands 175 (78)American Samoa 170 (76)Hawaii Special Wind Region Statewide Puerto Rico

115(52)

120(54)

160(72) 170(76)

180(80)

120(54)

120(54)

130(58)140(63)

150(67)160(72)

170(76) 180(80)

150(67)160(72)

170(76)180(80)

190(85)

200(89)

200(89)

160(72)

150(67)

140(63)

130(58)

120(54)

160(72)

150(67)

165(74)

165(74)

160(72)150(67)

140(63) 130(58)120(54)

115(51)

115(51)

120(54)

130(58)

140(63)

150(67)

Special Wind Region

4


300 Year RP Winds


Location Vmph (m/s)Guam 180 (80)Virgin Islands 150 (67)American Samoa 150 (67)Hawaii Special Wind Region Statewide

Puerto Rico

100(45)

105(47)

140(63) 150(67)160(72)

105(47)

105(47)

110(49) 140(63)

150(67)

140(63)

130(58)

130(58)

150(67) 160(72)

130(58)

140(63)

120(54)

110(49)

105(47)

170(76)

170(76)

130(58)

140(63)

120(54)

150(67)

150(67)

140(63) 130(58)120(54)

110(49)105(47)

105(47)

110(49)

120(54)

130(58)140(63)

Speical Wind Region


Wind speeds at selected locations

Location 6.1/700V

ASCE 7-05 Exposure C

Exposure C Exposure D Bar Harbor, Maine 97 95 103 Boston, MA 106 103 112 Hyannis, MA 117 112 122 New Port, RI 117 109 119 Southampton, NY 120 110 119 Atlantic City, NJ 114 102 111 Wrightsville Beach, NC 132 119 129 Folly Beach, SC 131 115 125 Miami Beach 145 136 148 Clearwater, FL 128 115 125 Panama City, FL 129 107 116 Biloxi, MS 138 129 140 Galveston, TX 131 119 129 Port Aransas, TX 134 117 127 Hawaii 105 103 112 Guam 170 155 168

5


ASCE 7-10 MWFRSAlternative 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

Design Procedures

Chapter 27

Directional Procedure

(all heights method)

6


Chapter 27 Directional Procedure

Velocity Pressure: (27.3)

qz (qh)= 0.00256 Kz Kzt Kd V2 (Eq. 27.3-1)

where:

qz = velocity pressure at height z

qh = velocity pressure at mean roof height h



Chapter 27

where: q = velocity pressure

G = gust effect factor

Cp = external pressure coefficient

qi = velocity pressure at mean roof height h

GCpi = internal pressure coefficient

p = qGCp – qi(GCpi)

7



Design Procedure (Table 27.2-1):1. Wind Speed V (Figure 26.5-1 maps)2. Wind Directionality Factor Kd (26.6, Table 26.6-1)

3. For each wind direction:Exposure Category (26.7)Velocity Pressure Exposure Coefficient Kz, Kh (Table 27.3-1)


Wind Directionality Factor, Kd

8


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


Exposure BSuburban

9


Exposure BUrban


Exposure Bwith a Hole

10


Exposure C


Exposure C(<1500 ft of B)

11


Exposure D


Table 27.3-1 Velocity Pressure Exposure

Coefficients, Kh and Kz

1.891.771.56(152.4)500

1.861.731.52(137.2)450

1.821.691.47(121.9)400

1.781.641.41(106.7)350

1.731.591.35(91.4)300

1.681.531.28(76.2)250

1.611.461.20(61.0)200

1.581.431.17(54.9)180

1.551.391.13(48.8)160

1.521.361.09(42.7)140

1.481.311.04(36.6)120

1.431.260.99(30.5)100

1.401.240.96(27.4)90

1.381.210.93(24.4)80

1.341.170.89(21.3)70

1.311.130.85(18)60

1.271.090.81(15.2)50

1.221.040.76(12.2)40

1.160.980.70(9.1)30

1.120.940.66(7.6)25

1.080.900.62(6.1)20

1.030.850.57(0-4.6)0-15

(m)ft

DCB

ExposureHeight above ground level, z

12


Table 26.9-1 Terrain Exposure Constants



Design Procedure (Table 27.2-1 continued):

4. Topographic Factor, Kzt (26.8, Table 28.8-1)

5. Gust Effect Factor G or Gf (26.9)

6. Enclosure Classification (26.10)

7. Internal Pressure Coefficient GCpi (26.11,

Table 26.11-1)

8. External Pressure Coefficients Cp, GCpf

(Figures 24.4-1-3) or force coefficients Cf

(Figures 27.4-4-7)

13


Fig. 26.8-1 Topographic Factors, Kzt


Fig. 26.8-1 Topographic Factors, Kzt

14


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. 26.9-6, 26.9-7, 26.9-8 and 26.9-9, using Table 26.9-1.

For flexible or dynamically sensitive structures as defined in Section 26.2, Gf shall be calculated by Eqs. 26.9-10, 26.9-11, 26.9-12, 26.9-13, 26.9-14, 26.9-15a, 26.9-15b and 26.9-16, using Table 26.9-1.


26.10 Enclosure Classification

Buildings, Open:

A building having each wall at least 80% open.

Mathematically, Ao > 0.8Ag where:

Ao = Total area of openings in a wall that receives positive external pressure, in sq. ft.

Ag= Gross area of that wall in which Ao is identified in sq. ft.

15


26.10 Enclosure Classification

Buildings, Partially Enclosed:If the following two conditions are satisfied:

1. Ao > 1.1Aoi

2. Ao > 4 sq. ft or >0.01Ag, whichever is smaller, & Aoi<0.2Agi

where:

Aoi = The sum of the areas of openings in the building envelope (walls & roof) not including Ao, in sq. ft.

Agi = The sum of the gross surface areas of the building envelope (walls & roof) not including Ag, in sq. ft.


26.10.3 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

16


Table 26.11-1 Internal Pressure Coeff, GCpi

+0.18-0.18Enclosed Buildings

+0.55-0.55Partially Enclosed

Buildings

0.00Open Buildings

GCpiEnclosure Classification



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

17


Fig. 27.4-1

External Pressure

Coefficient, Cp for

MWFRS


Fig. 27.4-1 Cp for MWFRS: Walls

18


Fig. 27.4-1 Cp for MWFRS: Roofs


Fig. 27.4-1 Cp for MWFRS

27.4-2

19


Part 2 – Enclosed Buildings with h ≤ 160 ft.

Wind pressures obtained directly from tables (Table 27.6-1)

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



Pressure pz (psf):

pz = p0 (1 - z / h) + (z / h) ph

p0

ph

z

pz

Table values

20



php0


Roof Pressure Zones

Roof Shapes:• Flat• Gable• Hip• Monoslope• Mansard

Roof Pressures - MWFRS

21


Exposure CTable for Roof,Adjustment factors for other exposures

V (MPH)Roof ZoneRoof SlopeHeight h (ft)

Pressure (psf)(Two load casesfor sloped roofs)


28.4.1 Part 1-MWFRS Envelope Procedure

Chapter 28

where: qh = velocity pressure at mean roof

height h GCpf = external pressure coefficient GCpi = internal pressure coefficient

p = qh[(GCpf) – (GCpi)]

22


Fig. 28.4-1 GCpf for MWFRS: h < 60 ft


Fig. 28.4-1 GCpf for MWFRS: h < 60 ft

23


Fig. 28.4-1 GCpf for MWFRS

There are 9 notes that describe the application of these coefficients and the torsional load cases.


where: ps = simplified design pressure for surfaces A-H

λ = adjustment factor

Kzt = topographic adjustment

Ps30 = pressures read from tables

Part 2 - Envelope Method - MWFRS

ps = λKztps30

24


28.6.1 Part 2 – MWFRS Envelope Procedure

Completely revised for 7-02. This version first appeared in IBC 2000. 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, low-

rise building with flat, gable or hip roof shape.


Part 2 - Simplified Method - MWFRS

25


Part 2 - Envelope Method - MWFRS


Other MWFRS External Pressure Coefficients

Domed Roofs– Figure 27.4-2 Arched Roofs – Figure 27.4-3 Monoslope Roofs (and other shapes) –

Figure 27.4-4-7 Chimneys, Tanks, & Roof Equip – Figure

29.5-1 Walls and Solid Signs – Figure 29.4-1 Open Signs & Lattices – Figure 29.5-2 Trussed Towers – Figure 29.5-3

26

Components & Cladding(Chapter 30)

Pressure Coefficients


C&C Pressure Equations

Low-rise buildings with h ≤ 60 ft. based on Envelope Procedure

Buildings with h ≥ 60 ft. based on Directional Procedure

Buildings with h ≤ 160 ft. based on Simplified Method (pressures in Table 30.9-1)

p = qh[(GCp) – (GCpi)]

p = q(GCp) – qi(GCpi)

p = ptable(EAF)(RF)Kzt

27


Fig. 30.4-1 GCp for C & C-Walls: h < 60 ft


Fig. 30.4-1 GCp for C & C-Walls

28


Fig. 30.4-2A GCp for C&C-Gable Roofs:h < 60 ft

For < 7o


Fig. 30.6-1 GCp for C & C: h > 60 ft

29


Chapter 29 Other Structures/Appurtenances

Design Force – Solid freestanding walls and solid

signs:

F = qh G Cf As (Eq. 29.4-1)

Design Force – Other Structures

F = qz G Cf Af (Eq. 29.5-1) where:

q = velocity pressure Cf = force coefficients As = gross area of solid sign or wall Af = projected area normal to wind


Parapets – Chapter 27

30


Parapets – Chapter 27

where:pp = combined net pressure on parapetqp = velocity pressure at the top of parapetGCpn = combined net pressure coefficient

= +1.5 for windward parapet= - 1.0 for leeward parapet

h = hp = height at top of parapet

pp = qpGCpn

Wind Load Cases

Torsional Loadings

31


Traditional Method - Load Cases


Envelope Method - Load Cases

32


Simplified Method h ≤ 160 ft. Load Cases

Appendix D

Cases A – F to consider

Torsional load cases are those shown in Figure 27.4-8 and shown here as the traditional load cases


2.3.2 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

how do loads form - avant-garde engineering llc ......) 17 load adjustments and reductions roof live...

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