Self-locking bi-foldable load bearing segments are disclosed that can be used in applications such as ladders or ramp. First and second sections of the segment are foldably coupled to transition between an open configuration and a folded configuration. The first and second sections can include rungs pivotally attached to rails that can be further transitioned from the folded configuration to a collapsed configuration, but not transitioned from the open configuration to the collapsed configuration. Openings in the side walls of the rails allow the rungs to pivot in one direction, but not an opposite direction. In the open configuration, the openings of the first and second sections may be oriented opposite, and the direction of allowed rotation of the rungs of the first section and second section are opposite, restricting compression of the rails together. In the folded configuration, the openings of the first and second sections can be oriented the same to allow rotation of the rungs and compression of the rails together.