Eccentricity of load causing tension stress from bolt group centroid.
Tesnsion load eccentricity
Bolt tension
$$ T_{1_{bg}} = {{\left({ P_{bg} \cdot e_{t_{bg}} }\right) \over \left({ 2 \cdot n_{c_{bg}} \cdot s_{r_{bg}} \cdot {\left({ n_{r_{bg}} ^ 2 - 5 }\right) \over \left({ 2 \cdot \left({ n_{r_{bg}} - 1 }\right) }\right)} }\right)}} $$