Wind load on inclined member

Applies To
Environment: ALL
Area: Load Generation
Subarea: Wind Load Generation
Original Author:Sye Chakraborty, Bentley Technical Support Group

How is wind load calculated on inclined members when Open Structure option is chosen ?


The open wind load on an inclined member is calculated based on the projected area of obstruction. The wind intensity is multiplied by the projected area of obstruction offered by the inclined member to find the total force which is subsequently divided by the member length to arrive at the value for the udl on the inclined member.


Let the wind intensity = w kN/m2 ( blowing horizontally )

Actual member Length = L m

B=width of area of obstruction in m

Angle of inclination of the inclined member to the horizontal = a

Projected member length ( vertical )  = Lprojected = L sina

Projected area of obstruction = A = B x Lprojected = B x Lsina

Total load on the projected surface = w x B x Lsina

So udl on the member = w x B x Lsina / L = w x B x sina .... Equation 1


Now please refer to the attached model. The member 1 is vertical, member 2 is inclined at 60 to the horizontal and member 3 is at 30 degree to the horizontal.


Substituting the following values in equation 1,

w= 1 kN/m2

For W12X14 section oriented as shown in the model, B = flange width = 10.084 cm = 0.10084 m


For the member 1 ( vertical ) udl = 1 x 0.10084 x sin90 =  0.101 kN/m

For the member 2 ( at 60 deg  )  udl = 1 x 0.10084 x sin60 =  0.087 kN/m

For the member 3 ( at 30 deg  )  udl = 1 x 0.10084 x sin30 =  0.050 kN/m