You have two parallel I-beams. A trolley with 4 wheels runs on top, and carries a total load of say 10kN. How would you evaluate the torsion? angle theta = TL/GK where (for an I beam) K = [2bt^3 + (d - 2t)(thickness of web)^3] / 3 and t = thickness of flange But, how would you calculate the torque T? Say if the beams were 1m apart, if torque was simply 10kN x 0.5m, then the beam would roll over. For the equation; tau = T/Q how do you calculate Q for an I beam?