Jump up to grab the beam above and pull up.

Start walking on the longer beam. Halfway across, the beam is not stable and it will start to collapse. You can either hang from the edge before the part that collapses and traverse to the other side or walk back, wait for the beam to collapse and jump over the gap.

When you clear this situation, jump to the next set of beams and walk to the other side. Then drop to the ground.