The simply supported beam has a pin at A and a roller at B. Find the vertical support reaction RB.
Find RB (kN)
Show hints
- Use static equilibrium: ΣFy = 0 and ΣM = 0. Two unknowns, two equations.
- Take moments about A. RA passes through A, so it drops out and you get RB directly.
- Total downward load is 55 kN, so RA + RB = 55 kN.
Show the answer and the step-by-step solution
Static equilibrium: a body at rest has ΣFx = 0, ΣFy = 0 and ΣM = 0 about any point. Taking moments about one support removes that support’s reaction from the equation.
Free-body diagram
Replace the supports with reaction forces. A roller gives one vertical reaction; with only vertical loads the pin gives one vertical reaction too.
Equilibrium
Moments about A, counter-clockwise positive. Then vertical force balance.