Open structure wind loads

Tekla Structural Designer
2021
Tekla Structural Designer

Open structure wind loads

Tekla Structural Designer provides a quick means to apply wind loads to structural members, ancillaries, and equipment in open structures.

Entities are loaded as follows:

  • Structural members (beams, columns etc)
    • wind pressure is determined, load is then calculated from this pressure, a shape factor and the area exposed to the wind (including fire protection if relevant)

  • Ancillary pipework and cable trays
    • wind pressure determined, load is then calculated from this pressure, a shape factor and a calculated effective area (based on largest pipe for pipework and height for cable trays) (including insulation if relevant)

  • Ancillary ladders, guardrails and staircases
    • wind pressure determined, load is then calculated from this pressure, a shape factor and a user defined effective area.

  • Equipment
    • wind pressure determined, a point load is then calculated from this pressure, a shape factor and a user defined effective area.

Wind pressure

Wind pressure can be determined either by running the wind wizard to create a wind model, or by manually by creating a simple wind load.

Wind load calculation for members and ancillaries

Wind load is determined as two full length UDLs, one acting in local y (minor) and one acting in local z (major) on the member.
Full UDLMajor
  =  
z x Cf x Effective Areaxy x Cos(θ) x Sin(φ) / L
Full UDLMinor
  =  
z x Cf x Effective Areaxz x Sin(θ) / L

where

z
  =  
wind pressure calculated at the height of the member for that wind direction (for vertical member average is taken at top and bottom level)
Cf
  =  
shape factor
Effective Areaxy
  =  
effective area of member in xy
Effective Areaxz
  =  
effective area of member in xz
θ
  =  
angle of the wind to the member x axis projected vertically into the horizontal plane
φ
  =  
angle of the member to the horizontal plane
L
  =  
length of the member

Wind load calculation for equipment

Wind load is determined as a single point load and applied to the CoG of the equipment at mid height.
FWind
  =  
z x Cf x Effective Areaxz x Sin(θ) + Effective Areayz x Cos(θ))
Fx
  =  
FWind x Cos(θ)
Fy
  =  
FWind x Sin(θ)

where

z
  =  
wind pressure calculated at the height of the equipment for that wind direction
Cf
  =  
shape factor
Effective Areaxy
  =  
effective area of equipment in xy
Effective Areaxz
  =  
effective area of equipment in xz
θ
  =  
angle of the wind to the equipment x axis projected vertically into the horizontal plane
L
  =  
length of the equipment
Note: All wind loads considered are horizontal, no vertical loading is considered.

Shape factors and effective area factors

The default shape factors ( Cf) come from the document ‘Wind Loads For Petrochemical And Other Industrial Facilities’ published by ASCE. These and the effective area factors assigned to new members/ancillaries can be edited as follows:
  • For new members/ancillaries - from Model Settings > Loading > Wind Loading
  • For existing members/ancillaries - from the Properties window

Assumptions and limitations

Assumptions
  • All wind loads are assumed to act perpendicular to the members, equipment and ancillaries
  • Applicable for all 1D structural members irrespective of their characteristic except
    • analysis elements
    • DELTABEAM
    • FABSEC beams
Limitations
  • Only currently applicable for US, EC and IS wind codes
  • Cannot be applied on structural walls
  • Shielding effect is not considered
  • There are no frictional wind forces accounted on any surfaces

Open structure wind loads report

An Open Structure Wind Load report can be generated for the open structure loads in user defined wind load cases on members, ancillaries and equipment.

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