Moment Distribution for Sidesway Frame

Unsymmetrical frame will experience sidesway. Prior to the moment distribution process, we should establish two analysis cases using principle of superposition.

The first case is where the frame subjected to original loading and a horizontal reaction R that resists the frame from sidesway. Moment distribution is conducted, and the value of R is calculated using equilibrium equations. The value of R denotes the force required to stop the frame from sidesway.

In case two, we apply only horizontal force R at the same node, but in opposite direction. Unit moment is assumed developed in vertical members as FEM due to sidesway, caused by the force R. Moment distribution in this case, determine the internal moment in all members when unit FEM is developed in vertical member. The value of R on the other hand, denotes how much force is needed to cause one unit FEM in vertical member.

Given the actual force required to resist sidesway (from case one), we can deduce that is the pulling force that causes the frame sidesway under original loading condition. Then, we can determine how much unit FEM is developed by dividing it with R from case two. Finally, additional moment due to sidesway can be calculated for all members, by applying the principle of superposition.

The following introduces the solution of sidesway frame using moment distribution method. Watch the video above for full details.