Wind Load Based on SNI 1727:2013 / ASCE 7-10 Ryan R. Setiadi, ST
Main Parts of a Structure in Wind Load
• Main Wind Force Force Resisting System (MWRS) (MWRS) An assemblage of structural elements assigned to provide support and stability for the overall structure. The system generally receives wind load from more than one surface. ASCE Chapter 27.
•
Components and Cladding (C & C) Elements of the building envelope that do not qualify as part part of the main wind force -resisting system. ASCE Chapter 30 .
Basic Wind Pressure equation The basic form of the pressure equation: p = q [G Cp – (G Cpi)] Internal pressure (see next slide)
Where surface – p = a wind pressure on a surface pressure. This is the pressure due to a moving fluid on a flat – q = velocity pressure. plate – G = gust factor. The gust factor accounts for dynamic interaction between the flowing air and the structure – C = pressure coefficient. The pressure coefficient accounts for varying pressure across a surface. surface.
Location of Pressure •
ASCE ASCE 7 prov provid ides es mean means s for for com compu puti ting ng for force ces s on on vari variou ous s surfaces. – The building envelope surfaces experience experience pressure on both sides (i.e. external and internal). Internal pressure are only happen if building enclosed classification are partial enclose or enclosed
Enclosed classification
Must Consider Internal Pressure
Internal Pressure
Internal Pressure Coefficients, ( GC pi ) stagnant • Internal pressure is fairly easy because the air is relatively stagnant and the shape of the structure does not affect it’s magnitude.
• As gusting is not a concern internally, the gust factor and the pressure coefficient are combined. – (GC pi ) •
The magnitude of the internal pressure coefficient is strictly dependent on the enclosure classification.
•
The pressure can be both positive or negative (i.e. suction) depending on the direction of the wind relative to opening for partially enclosed or enclosed buildings. – Both internal pressures must be considered.
Internal Pressure Coefficients, ( GC pi )
External Pressure Coefficients, C p • As external surfaces are subject to “flowing” air, the pressure varies considerably on the building surface depending on structural configuration and direction of the wind. •
Coefficients also depend on whether the resulting forces are to be used to design/analyze: – Main Wind-Force Resisting Systems – Components & Cladding
The Gust Factor, G
• Factor accounting for: – Gustiness and turbulence – Gust frequency – Gust size • Integral scale longitudinal longitudinal and lateral
– Frequency of structure – Structural damping – Aerodynamic admittance – Gust correlation
The Gust Factor, G • For stiff buildings and stiff structures – G = 0.85 • For flexible buildings and other structures – Calculate “by a rational analysis that incorporates incorporates the dynamic properties of the main wind-force resisting system.”
Must calculate Gust Factor for flexible building with frequency < 1 herz
Velocity Pressure •
qz =Velocity Pressure = 0.613 x Kz x Kzt x Kd x V 2 (N/m2)
– – – – –
Constant 0.613 V = Basic wind speed in m/s Kz = Exposure Coefficient Kzt = Topographical Factor Kd = Wind Directionality Factor
Wind Speed There is no wind map in Indonesia, based on TPKB consensus in Jakarta, wind speed can be taken by Vs = 39.1 m/s for strength design and Vs = 32 m/s for serviceability design. HB 212-2002 Design Wind Speeds Speeds for the Asia-Pacific Region Region report report from AS/NZS AS/NZS recomm recommend end to used used Vs = 32 m/s for servicea serviceability bility design design and and Vs = 40 m/s for ultimate ultimate design design in Indonesia region. region.
Exposure Coefficient (Kz)
Exposure Category (see next slide) ASCE 7-10 PAGE 250 for MWRS (Structure) ASCE 7-10 PAGE 317 for C&C Kz factor are dependent of height about ground
Exposure Category
Exposure A: This exposure category does not exist in the hurricane prone region of the country. Deleted since ASCE 7-02 7-02
Exposure B: Urban and suburban areas, wooded areas, areas with many closely spaced obstructions.
In jakarta, we used this exposure category
Exposure C: Open terrain with scatter obstructions. Airports, areas that are generally flat open country.
Exposure Category
Exposure D: Flat, unobstructed areas and water surfaces outside hurricane prone regions
Topographical Factor, Kzt Only if this condition apply, otherwise used Kzt = 1.0
Topographical Factor, Kzt
Topographical Factor, Kzt
ASCE 7-10 page 252
Wind Directionality Factor, Kd
ASCE PAGE 250 !!!
Example 1 Wind Load Calculation 10 m
Building type : Multi Million Business Office Location : Jakarta, Jakarta, Indonesia Dimension : 10 m x 6 m floor plan, with with 30 m height
30 m
Find wind load for structure and component cladding (C&C)
General Step by step Note : for risk category, usually only used 1.0 factor Wind speed used 39.1 m/s
Example 1 Concrete Building 10 m
Find velocity pressure : qz =Velocity Pressure = 0.613 x Kz x Kzt x Kd x V 2 (N/m2)
Step 1, find V Strength design V = 39.1 m/s 30 m
Step 2, find Kzt Building definitely definitely not in hill, ridges, ridges, or escarpment, used Kzt = 1.0
Example 1 Concrete Building 10 m
Find velocity pressure : qz =Velocity Pressure = 0.613 x Kz x Kzt x Kd x V 2 (N/m2)
Step 3, find Kd :
30 m
ASCE PAGE 250 !!!
Used kd = 0.85 both for structural load and C&C
Example 1 Concrete Building 10 m
Find velocity pressure : qz =Velocity Pressure = 0.613 x Kz x Kzt x Kd x V 2 (N/m2)
Step 4, find Kz Used Exposure Class B 30 m
Kz for Structure
ASCE PAGE 261 !!!
Kz for Component & Cladding
ASCE PAGE 317 !!!
Example 1 Concrete Building 10 m
Find velocity pressure : qz =Velocity Pressure = 0.613 x Kz x Kzt x Kd x V 2 (N/m2)
qz = 0.613 x Kz x 1.0 x 0.85 x 39.1^2 qz = 796.5 x Kz
30 m Used different Kz for every elevation
Example 1 Concrete Building 10 m
30 m
Example 1 Concrete Building 10 m
Next find wind load :
p = q [G [G Cp Cp – (G Cpi Cpi)] Step 1, find Gust factor (G)
30 m
Assumed G = 0.85 in this example, example, otherwise calculate gust factor in ASCE 7-10 Chapter 26.9 (need to find structural period first)
Example 1 Concrete Building 10 m
Next find wind load :
p = q [G [G Cp Cp – (G Cpi Cpi)] Step 2, find internal pressure coef (G Cpi)
30 m
Example 1 Concrete Building 10 m
Next find wind load :
p = q [G [G Cp Cp – (G Cpi Cpi)] Step 2, find external pressure coef (Cp) for MWRS (NEXT SLIDE) 30 m
Next Slide
ASCE PAGE 267 !!!
Leeward wall Windward wall
Side wall
Example 1 Concrete Building 10 m
Next find wind load :
p = q [G [G Cp Cp – (G Cpi Cpi)] Step 2, find external pressure coef (Cp) for MWRS
30 m
For wall pressure :
Example 1 Concrete Building 10 m
Next find wind load :
p = q [G [G Cp Cp – (G Cpi)] pi)] Step 2, find external pressure coef (Cp) for MWRS
30 m
For roof pressure : Roof pressure coefficients, Cp, with the wind normal to the 10 m face For h/L = 30/6 = 5 > 1.0, and < 10 ° , two zones are specified in ASCE 7-10 Fig. 27.4-1 of the Standard (red box next slide)
ASCE PAGE 267 !!!
Example 1 Concrete Building 10 m
Next find wind load :
p = q [G [G Cp Cp – (G Cpi)] pi)] Step 2, find external pressure coef (Cp) for MWRS
30 m
For roof pressure : First value 0 to h/2, Cp = -1.3 and h/2 to h, Cp = -0.7 Second value Cp = -0.18 from 0 to h (not show here)
Example 1 Concrete Building 10 m
Next find wind load :
p = q [G [G Cp Cp – (G Cpi)] pi)] Step 2, find external pressure coef (Cp) for MWRS
30 m
For roof pressure : Roof pressure coefficients, Cp, with the wind normal to the 6 m face are shown in following Table. For h/L = 30/10 = 3 > 1.0, and < 10° , same like wind normal to 10 10 m face.
Example 1 Concrete Building 10 m
Next find wind load :
p = q [G [G Cp Cp – (G Cpi)] pi)] Step 3, Wind Load for structure (MWRS) Next slide 30 m
Wind load to building structure
Unit N/m2
illustration l oad for case max pressure
730 N/m2
Negative pressure mean wind pressure away from building face
327 N/m2
678 N/m2 Wind Load to 6 m face
149 N/m2
451 N/m2
10 m
WIND DESIGN DESIGN LOAD LOA D CASE CA SE FOR MWRS
WIND DESIGN DESIGN LOAD LOA D CASE ILLUSTRATION
Example 1 Concrete Building 10 m
Next find wind load :
p = q [(G Cp) – (G Cpi) Cpi)]] Step 4, find external pressure coef (GCp) for C&C
30 m
ASCE have different Cp for several case in in C&C Part 1. Low Rise Building Part 2. Low Rise Building (Simplified) Part 3. Building with h > 18.3 m Part 4. Building with h < 18.3 m Only part 3 are show here
Example 1 Concrete Building 10 m
Next find wind load :
p = q [(G Cp) – (G Cpi) Cpi)]] For wall and roof, used Figure 30.6-1 ASCE 7-10 page 348 (Next Slide) 30 m
Location number
for simplification, this example only used min value
for simplification, this example only used max value
Pressure Coefficient
WIND LOAD FOR C&C
WIND LOAD FOR C&C
WIND LOAD FOR C&C
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing
25 m 5m
10 m
100 m
25 m 25 m 50 m
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing Building type : Warehouse Location : Banten, Banten, Indonesia Wind speed : 39.1 m/s Exposure category : Type C
Find wind load for structure (MFWRS)
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing Find velocity pressure : qz =Velocity Pressure = 0.613 x Kz x Kzt x Kd x V 2 (N/m2)
Step 1, find V Strength design V = 39.1 m/s
Step 2, find Kzt Building definitely definitely not in hill, ridges, ridges, or escarpment, used Kzt = 1.0
Step 3, find Kd
ASCE PAGE 250 !!!
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing Find velocity pressure : qz =Velocity Pressure = 0.613 x Kz x Kzt x Kd x V 2 (N/m2)
qz = 0.613 x Kz x 1.0 x 0.85 x 39.1^2 qz = 796.5 x Kz
for simplified simplified calculation calculation because this this building are are low rise, we will used only single single value of Kz. Find Kz based on Table 28.3-1 note 1. 'If h < 4.6 m
then: Kh = 2.01*(15/zg)^(2/a) 2.01*(15/zg)^(2/a)
'If h >= 4.6 m then: Kh = 2.01*(z/zg)^(2/a) 2.01*(z/zg)^(2/a) A and zg taken from Table 26.9-1 26.9-1 z = mean roof height = 10+5/2 = 12.5 m Kz = Kh = 2.01*(z/ 2.01*(z/zg)^( zg)^(2/a) 2/a) Kz = 1.0 1.05 5 So, qz = 796.5 796.5 x Kz = 836 N/m2 N/m2
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing Next find wind load :
p = q [G [G Cp Cp – (G Cpi Cpi)] Step 1, find Gust factor (G) Used 0.85 in this example
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing Next find wind load :
p = q [G [G Cp Cp – (G Cpi Cpi)] Step 2, find internal pressure coef (G Cpi)
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing Next find wind load :
p = q [G [G Cp Cp – (G Cpi Cpi)] Step 2, find external pressure coef (Cp) for MWRS For this case, we will used envelope procedure (Section 28) that only applied to enclosed and partially enclosed low rise building. building. Requirement to used this procedure procedure : 1. The building is a regular-shaped building or structure as defined in section 26.2.
2. Low rise building Mean roof height (h) (h) = 10 + 5/2 = 12.5 12.5 m < 18 m Ratio h/B = 10/50 < 1.0 Ratio h/L = 10/100 10/100 < 1.0 Condition satisfied
Used interpolation for our case, angle = tan^-1(5/25) = 11.3 degree
ASCE PAGE 301 !!!
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing Next find wind load :
p = q [G [G Cp Cp – (G Cpi Cpi)] Step 2, find external pressure coef (Cp) for MWRS
Example Example 2 – Warehous Warehouse e Metal Metal Build Building ing Wind load MWFRS:
p = q [G [G Cp Cp – (G Cpi Cpi)]
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design (Other Structures)
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
ASCE 7-10 table 26.6 page 250
ASCE 7-10 table 27.3-1 page 261
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
ASCE 7-10 7-10 table 29.5-1 page 312
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
Example Example 3 – Wind Load Load Reaction Reaction For Vessel Vessel Foundation Foundation Design Design
Summary Wind Load on Pier
Summary Wind Load on Pier
END OF THIS PRESENTATION PRESENTATION
