Eccentric Load Cases

Eccentric load cases are produced according to Fig. 7.1 (it is reproduced below).

Eccentric Loads on Rigid Diaphragms

An eccentric wind load on a rigid diaphragm is represented with a point load offset from mass center with a distance of e_x (or e_y) measured perpendicular to wind direction. The point load equals to combined windward and leeward surface load on the diaphragm. In order to apply wind loads as shown in Figure 7.1, loading eccentricity is calculated as follows:

Total windward face force: $F_{w} = c_{p e w} \frac{b}{2}$
Total leeward face force: $F_{l} = c_{p e l} b$
Moment: $M = F_{w} \frac{b}{6} = (c_{p e w} b^{2}) (\frac{1}{2}) (\frac{1}{6})$
Total force: $\sum F = F_{w} + F_{l}$
Eccentricity: $e = \frac{M}{\sum F} = \frac{c_{p e w} b}{6 c_{p e w} + 12 c_{p e l}}$

Eccentric Loads on Semirigid Diaphragms

Wind pressure loads on windward and leeward surfaces are separately applied as shown in the Figure 7.1 (i.e., they are not combined as in the case of rigid diaphragms). Hence, an eccentricity with b/6 is used for wind pressures on windward surface whereas no eccentricity is applied for wind pressures on leeward surface.