lopezwind loads-asce7-05.pdf

7/27/2019 LopezWind Loads-ASCE7-05.pdf

http://slidepdf.com/reader/full/lopezwind-loads-asce7-05pdf 1/85

Workshop on Vertical Shelter from TsunamisCIAPR June 18-20 2012

Calculation of Wind LoadsAccording to PR Building

Code 2011Dr. Ricardo R. López Rodríguez,

Ph.D., P.E.

Professor of Civil Engineering

University of Puerto Rico at

Mayagüez, [email protected]

Earthquake Commission of CIAPR

1

Workshop on Vertical Shelter from Tsunamis

mailto:[email protected]

mailto:[email protected]




2

Some slides taken and adapted from FEMA presentation

by Adam Reeder, PE, CFM from presentation

Wind Provisions of the 2009 International Building

Code and International Residential Code




3




P646 on Wind Loading

4




Agenda

• Wind effects on structures

• About the PR Building Code

• Wind Load Provisions for Buildings

Definitions and terms used in all Procedures

Alternative Procedures of Analysis

– Simplified

– Analytical (Low rise or high rise)

– Wind Tunnel

• Examples of calculation of horizontal wind pressures

• Cylindrical Structures

5




Wind effects on structures

6

V I E N

T O

Rectangular BuildingsThe wind generates pressure in windward wall and

suction in leeward wall, lateral walls, and part of the roof.




Internal Pressures

7

There is always some

internal pressure, unless

the building is completely

open. Partially enclosed

buildings have the highest

internal pressures.

It is important for doors and

windows to resist the wind

pressure and impact of flying objects.




Effect of openings on internal pressure

Windward or leeward opening

8




Organization of the IBC

Chapter 1: Administration

Chapter 2: Definitions

Chapter 3: Use and Occupancy Classification

Chapter 5: General Building Heights and Areas

Chapter 6: Types of Construction

Chapter 14: Exterior Walls

Chapter 15: Roof Assemblies and Rooftop Structures

Wind Loads

13




Organization of the IBC

Chapter 18: Soils and Foundations

Chapter 19: Concrete

Chapter 21: Masonry

Chapter 22: Steel

Chapter 24: Glass and Glazing Chapter 25: Gypsum Board and Plaster

Chapter 34: Existing Structures

Chapter 35: Referenced Standards

Appendix H: Flood-Resistant Construction

14




Main vs Components




ASCE 7-05 – Wind Loads

Wind directionality factor, K d

22

Structure Type Directionality Factor, K d

Buildings

Main Wind Force Resisting System

Components and Cladding

0.85

0.85

Arched Roofs 0.85

Chimneys, Tanks and Similar Structures

Square

Hexagonal

Round

0.90

0.95

0.95

Solid Freestanding Walls and

Solid Freestanding and Attached Signs 0.85

Open Signs and Lattice Framework 0.85

Trussed Towers

Triangular, square, rectangular

All other cross sections

0.85

0.95




Exposure Categories

27

Exposure Category B





Exposure category

• Surface Roughness Category B, C or D

• Exposure Category B, C or D

• Wind Direction and Sectors

For each direction at which the wind loads are to be

evaluated, the exposure shall be determined for the two

upwind sectors extending 45° either side of the selected

wind direction.

The exposure resulting in the highest wind loads shall be

used to represent winds from that direction.

7-05 Does not use Exp. D in Hurricane Prone Coasts, 7-10 does

29





Topographic factor, K zt Wind Speed-Up over Hills, Ridges and Escarpments

30

H Height of hill or escarpment relative to the upwind terrain, in meters.

Lh

Distance upwind of crest to where the difference in ground elevation is half the

height of hill or escarpment, in meters.

x Distance (upwind or downwind) from the crest to the building site, in meters.

z Height above ground surface at building site, in meters.





Topographic factor, K zt Wind Speed-Up over Hills, Ridges and Escarpments

Kzt = (1 + K1 K2 K3)2

32

K1

Factor to account for shape of

topographic feature and maximumspeed-up effect.

K2

Factor to account for reduction in

speed-up with distance upwind or

downwind of crest.

K3

Factor to account for reduction in

speed-up with height above local

terrain.





Topographic factor, K zt • K1 is determined using the table below

Factor to account for shape of topographic feature and

maximum speed-up effect.

33

Hill Shape

K1/(H/Lh)

Exposure

B C D

2-D Ridges

(or valleys with -H) 1.30 1.45 1.55

2-D Escarpments 0.75 0.85 0.95

3-D Axisym. Hill 0.95 1.05 1.15

H

Height of hill or

escarpment relative tothe upwind terrain, in

meters.

Lh

Distance upwind of crest

to where the difference

in ground elevation is

half the height of hill or escarpment, in meters.





Topographic factor, K zt • K2 = (1 - )

Factor to account for

reduction in speed-up with

distance upwind or downwind of crest.

• K3 = e-γz/Lh

Factor to account for

reduction in speed-up with

height above local terrain.

34

hL

|x|

Lh

Distance upwind of crest to where the difference

in ground elevation is half the height of hill or

escarpment, in meters.

xDistance (upwind or downwind) from the crest to

the building site, in meters.

zHeight above ground surface at building site, in

meters.

μ Horizontal attenuation factor.

γ Height attenuation factor.

Hill Shape γ

μ

Upwind of

Crest

Downwind

of Crest

2-D Ridges

(or valleys with -

H) 3 1.5 1.5

2-D Escarpments 2.5 1.5 4

3-D Axisym. Hill4

1.5 1.5





Topographic factor,

Kzt = (1 + K1 K2 K3)2

35

Notes:

1.Linear interpolation

between values ispermitted.

2.For H/Lh > 0.5,

assume H/Lh = 0.5 for

finding K1 and

substitute 2H for Lh for

finding K2 and K3. 3.Multipliers assumewind approaches along

the direction of

maximum slope.





Gust Effect Factor, G

• G = 0.85 for rigid buildings and other structures

• G is determined by formula for flexible or dynamically

sensitive buildings or other structures

Flexible: natural frequency < 1

36

Note:

Where combined gust-effect factors and pressure

coefficients (GCp), (GCpi) and (GCpf ) are given in figuresand tables, the gust-effect factor shall not be determined

separately.





Enclosure classification

37

Open

Ao ≥ 0.8Ag

Ao = total area of openings in a wall that receives positive

external pressure, in m2

Ag = gross area of that wall in which Ao is identified, in m2

Partially

Enclosed

• Ao > 1.10Aoi AND

• Ao > 0.37 m2 OR Ao > 0.01Ag (whichever is smaller) AND

• Aoi / Agi ≤ 0.20

Aoi = sum of the areas of openings in the building envelope

(walls and roof) not including Ao, in m2

Agi = sum of the gross surface areas of the building envelope(walls and roof) not including Ag, in m2

Enclosed Not open or partially enclosed.




Velocity pressure qz

Velocity pressure

Factor Kz includes the effect of height




ASCE 7-05 and 7-10 – Wind Loads

Internal Pressure Coefficient, (GCpi)

39





Internal Pressure Coefficient, (GCpi)

40

Enclosure

Classification(GCpi)

Open 0.00

Partially Enclosed+0.55

-0.55

Enclosed+0.18

-0.18

Note:

Plus and minus signssignify pressures acting

toward and away from

the internal surfaces,

respectively.





Procedures for determining wind loads for Main Wind-Force Resisting System (MWFRS)

41

Procedure Application Location

Simplified Procedure Low-rise buildings Section 6.4

Analytical Procedure

Buildings of all heights

Distinguish low rise and

High-rise

Section 6.5

Wind Tunnel Procedure All buildings and other structures

Section 6.6




ASCE 7-05 – Simplified Procedure

MWFRS and C&C Simplified Procedure (Sec 6.4)

for Enclosed Low-Rise Bu i ld ings

• Applicability

Building has simple diaphragm and low-rise (h<60’)

Enclosed and meets WBD requirements

Building not classified as flexible Building is not subject to the following:

– Across-wind loading

– Vortex shedding

– Instability due to galloping or flutter

– Channeling effects – Buffeting in the wake of upwind obstructions

Building has a symmetrical cross section

Building exempted from torsional load cases

42




MWFRS and C&C Simple Procedure (Sec 6.4)

Enclosed Low-Rise Bu i ld ings


Step 1 Basic wind speed, V Sec 6.5.4

Step 2 Importance Factor, I Sec 6.5.5

Step 3 Exposure Category Sec 6.5.6

Step 4 Height and Exposure Adjustment, λ Fig 6-2

Step 5Design pressure at 30 ft ps30 shall be

determined

Fig 6-2

Step 6 Topographic amplification factor calculated. Sec 6.5.7

Step 7

Wall and roof pressures calculated. Check

Minimum

Sec 6.4.2.1.1 or

Sec 6.4.2.2.1

43

Fi 6 2 Si lifi d P d




Fig 6-2 Simplified Procedure

44




Fi 6 2




Simplified Method

Fig 6-2

Fig 6-2 Simplified Design Wind




Fig 6 2 Simplified Design Windpressure ps30

47

p

D i Si lifi d P d




=

Design pressure, Simplified Procedure





ASCE 7 05 Wind LoadsAnalytical Procedure

MWFRS and C&C Analytical Procedure (Sec 6.5)Enclos ed, Part ia lly Enclos ed and Open Bu i ld ings of A l l Heights

• Applicability

Building is regular-shaped

Building is not subject to the following:

– Across-wind loading

– Vortex shedding

– Instability due to galloping or flutter

– Channeling effects

– Buffeting in the wake of upwind obstructions

49




CIAPR June 18-20 2012

1. V and Kd (directionality)2. Importance, I

3. Exposure and height, Kz, Kh

4. Topographic Effect

5. Gust effect G6. Enclosure

7. Internal pressure GCpi

8. External Pressure Cp

9. Velocity pressure qz10. Design wind load p

Analytical Method - Procedure

Exposure Coefficient Kh and Kz





p

Internal press re coefficients





Internal pressure coefficients

53

Fig 6-6 Monoslope roof





g pExternal wall pressures

54

Fig 6 6 Cp for Analytical Method





Fig 6-6 Cp for Analytical Method

55

Fig 6 10 Low Rise Analytical Procedure





Fig 6-10 Low-Rise Analytical Procedure

56

Wall pressures

Windward: 1, 1E

Leeward: 4, 4E

Low Rise Force coefficients GCpf





Low Rise Force coefficients GCpf

57

Velocity pressure and wall pressures





Velocity pressure and wall pressures

Velocity pressure

Wall pressure, analytical method

Pressures for Analytical Procedure





Pressures for Analytical Procedure

ASCE 7 05 Wind Loads






Wind Tunnel Procedure (Section 6.6)

• Permitted for any building or structure

• Tests shall meet the following conditions:

Atmospheric boundary layer modeled for wind speed variation

Atmospheric turbulence modeled to match the same scale as

the building model Modeled building, surrounding building and topography scaled

properly

Modeled building and surrounding area is less than 8 percent

of the test section

Longitudinal pressure gradient accounted for

Reynolds number effects on pressure minimized

Response characteristics consistent with model

60

Cylindrical Structures





Cylindrical Structures

61

ASCE 7-05 does not consider buildings with shapes

different from rectangular or combinations of rectangular.

The only guidance for cylindrical structures is in thesection on Other Structures (Sec 6.5.15).

The total lateral load is calculated from equation 6-28

Other Structures





Other Structures

62

Fig 6-21 – Other Structures Coeff Cf





Fig 6-21 – Other Structures Coeff. Cf

63




CIAPR June 18-20 2012 64

Example





Example

65

Rectangular building

Plan dimensions 70’ x 70’

Height = 60’

Plan View

70’

70’

Elevation

24’

12’

12’

12’

Story

Heights

Solution using simplified procedure






66

V = 145 mph from Fig 6-1

I = 1.15 from table 6-1 and occupation Cat IV (or III)

Exposure Category = C

λ = 1.62 from Fig 6-2 with h=60’ and Exp C

Width of special zone A = 2a

• a < 0.10 (B) = 0.10 (70) = 7’

• a < 0.4 (h) = 0.4 (60) = 24’

• Select the smallest = 7’ but not less than

• a > .04 (B) = .04 (70) = 2.8’• a > 3’,

•Select a = 3’, 2a = 6’







67

Width of zone A = 6

Width of zone C = 70 – 2(6) = 58’ assuming zone A on both corners simultaneously

Horizontal pressures from Fig and roof angle ϴ = 0

Ps30 = 33.4 psf in zone A

Ps30 = 22.1 psf in zone C

Topographic factor Kzt =1 for flat terrain

Pressures =

• psA = 1.62(1)(1.15)(33.4) = 62.2 psf • psC = 1.62(1)(1.15)(22.1) = 41.2 psf

Fig 6-2 Simplified Design Wind





pressure ps30

68

p

PA = 33.4 psf PC = 22.1 psf



A l ti l M th d P d





1. V and Kd (directionality)2. Importance, I

3. Exposure and height, Kz, Kh

4. Topographic Effect

5. Gust effect G6. Enclosure

7. Internal pressure GCpi

8. External Pressure Cp

9. Velocity pressure qz10. Design wind load p

Analytical Method - Procedure

Solution using analytical procedure






71


Kd = 0.85 from Table 6-4

I = 1.15 from table 6-1 and occupation Cat IV (or III)

Exposure Category = C

For Low-rise buildings use Fig 6-10 and q = qh

• Select a = 3’, 2a = 6’

• Select values of GCpf for zones 1, 1E, 4, 4E

• GCpf1 = 0.40, GCpf1E = 0.61

• GCpf4 = -0.29, GCpf4E = -0.43



Solution using analytical procedureL i b ildi





Low-rise buildings

73

Design pressures

Use q = qh

Windward

p1 = 59.5(0.40 + 0.18) = 34.5 psf

p1E = 59.5(0.61 + 0.18) = 47.0 psf

Leeward

p4 = 59.5(-0.29 + 0.18) = -6.5 psf

p4E = 59.5(-0.43 + 0.18) = -14.9 psf

Solution using analytical procedureL i b ildi





Low-rise buildings

74

Forces per level, calculated adding the windward and

leeward pressures because they act in the samedirection.

Level Height

, ft

Ps1E+

4E, psf

Width

E, ft

Ps1+4,

psf

Width ,

ft

Force

Kips

1 30 61.9 12 41.0 58 93.6

2 12 61.9 12 41.0 58 37.5

3 12 61.9 12 41.0 58 37.5

4 6 61.9 12 41.0 58 18.7

Total 187.3







75

For comparison the solution was obtained neglecting the

low-rise classification


Kd = 0.85 from Table 6-4

I = 1.15 from table 6-1 and occupation Cat IV (or III) Exposure Category = C

Kzt = 1

G = 0.85 for rigid structures, T< 1sec

Enclosure classification = enclosed Internal pressure coefficients Fig 6-5, GCpi = ± 0.18







76

Obtain Kz from from Table 6-3 and z = level height

Velocity pressure coefficient,

Height, z, ft Kz qz, psf

24 0.94 45.5

36 1.01 53.1

48 1.08 56.8

60 1.13 59.5







77

Design pressures. No special regions, but pressure varieswith height

Use q = qz for windward pressures

Use q = qh for leeward pressures

Use qi = qh

Shape factors Cp = 0.8 windward, Cp = -0.5 leeward,

obtained from Fig 6-6






S s g y c p c

78

Forces per level

Level Z qz,

psf

Windw

qzGCp

Internal

qhGCpi

Leew

qhGCp

Windw

pLeew

p

Total

p

Area,

sqft

Force

kips

1 24 45.5 30.9 -10.7 -25.3 41.6 14.6 56.2 70x30 118.0

2 36 53.1 36.1 -10.7 -25.3 46.8 14.6 61.4 70x12 51.63 48 56.8 38.6 -10.7 -25.3 49.3 14.6 63.9 70x12 53.7

4 60 59.5 40.5 -10.7 -25.3 51.2 14.6 65.8 70x6 27.6

Total 250.9



Solution for Cylindrical Plan Building





y g

80

Or assuming rough surface Cf = 0.8

F = 51.6(0.85)(0.8)(70x60) = 147 kips

Summary of examples





y p

81

Calculated Base Shear ForcesProcedure Calculated Base

Shear Force, kips

% Difference

from Simplified

Procedure

Simplified 188.1 0

Analytical, Low-

rise

187.3 -0.4

Analytical 250.9 33.4

Cylindrical, other

structures, noteplan area is not the

same

92 for smooth

surface,147 for rough

surface

-51.1

-21.9






Basic wind speed, V, mph (m/s)

82

Figure 26.5-1A: Basic Wind Speeds for

Occupancy Category II Buildings andOther Structures

Figure 26.5-1B: Basic Wind Speeds for

Occupancy Category III and IV Buildingsand Other Structures



Questions?




CIAPR June 18-20 2012 84

Impacts of Wind Provisions onBuilding Components



Building Components

Load Paths and Connectors

Roof Systems

Windows, Doors and Openings

Wall Systems

Foundations

lopezwind loads-asce7-05.pdf

Documents