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. Equilibrium requires applied loads and support reactions to balance. Ideal truss analysis treats straight members as carrying axial tension (a pull) or compression (a squeeze) through pin joints, while a beam model must account for bending and associated stresses. Real structures introduce additional behaviours and design requirements. Symmetric central loading and ideal connections make vertical support reactions and simple force paths possible to compare.