How can a bridge pass a load to its supports?

A bridge must carry a load across a gap to supports. A beam does this partly by bending. A triangular frame can carry squeezing forces in some members and pulling forces in others. With a centred load on this symmetric model, the supports share the upward force equally. Pulling is called tension; squeezing is called compression. Beams and trusses distribute forces differently. A loaded beam develops bending, with tension and compression in different regions. In an ideal pin-jointed truss, loads at joints produce axial forces in members. Our symmetric triangle has compressed diagonal members and a tension tie. Both designs transfer the applied load to supporting points.