Wind Load Calculation

The wind loads acting on the structure, for IRC, changes with the structural height, and exposure condition (Plain or Terrain with obstructions). Substructure calculates the wind pressure first, using Table 1 as in IRC 6-2000 as follows.

On the bridge location. When calculating the wind pressure, Substructure uses the following:

Cap Elevation + Girder Height + Slab Depth + kerb Height

The program uses this height and plain/non plain terrain option, to interpolate the exact value of pressure. You must define:

Gust factor G
Drag Coefficient, Cd

Then click the Generate button and the program computes the pressure, P, as explained above.

The program computes the total transverse wind pressure acting on the substructure, superstructure and uplift pressure and generate the cap, bearing and column forces.

Wind on Superstructure

F_t = P_z × A₁ × G x Cd

where

F_t	=	transverse force applied on superstructure
A₁	=	area of superstructure exposed in transverse direction

The program distributes the force, F_t, as a cap load.

Wind on Substructure

Compute Ft as shown in above formula, but this time, calculate:

F_{t_col} = P_z × A_col × G x C

F_{t_cap} = P_z × A_cap × G x C

where

A_col and A_cap

the column and cap areas, respectively, in transverse direction

Distribute F_{t_col} as a column load and F_{t_cap} as a bearing load.

The program computes longitudinal force as 25% of wind load acting in transverse direction.