Define shear lag effect

Shear lag is the non-uniform distribution of stress in a tension member when only part of its cross-section (e.g. one leg of an angle or the web of a channel) is connected to the gusset. The force enters through the connected element, so the stress is highest near the connection and the outstanding element is less effective, especially over a short connection length.

Because the outstanding leg does not carry its full share, the net section reaches its strength earlier than the full area would suggest. IS 800:2007 (cl. 6.3.3) therefore reduces the net-section strength using a factor $\beta=1.4-0.076\dfrac{w}{t}\dfrac{f_y}{f_u}\dfrac{b_s}{L_c}$ for the outstanding leg:

$$T_{dn}=\frac{0.9A_{nc}f_u}{\gamma_{m1}}+\frac{\beta A_{go}f_y}{\gamma_{m0}}$$

Shear lag is reduced by a longer connection length $L_c$ and by connecting the outstanding leg as well (e.g. with a lug angle).