A steel truss bridge is a structural system between beams and arches. It consists of a bending-resistant upper beam (or slab) structure integrally combined with a load-bearing lower column (or pier) structure. Due to the rigid connection between the beams and columns, the beams are unloaded by the bending stiffness of the columns. The entire system is a compression-bending structure, and also a thrust structure. It is a type of bridge where the main load-bearing structure is a rigid frame. It increases the clearance height under the bridge and is commonly used as an overpass.
Based on the force diagram, it can be classified into fixed-end rigid frame bridges, double-hinged rigid frame bridges, and three-hinged rigid frame bridges, etc.; based on the elevation type, it can be classified into portal rigid frame bridges, straight-leg rigid frame bridges, inclined-leg rigid frame bridges, V-shaped pier rigid frame bridges, and T-shaped rigid frame bridges, etc.; based on the number of spans, it can be classified into single-span rigid frame bridges and multi-span rigid frame bridges, etc.; based on whether there is horizontal thrust support, it can be classified into thrust-supported rigid frame bridges and thrust-free rigid frame bridges, etc.
This type of bridge features negative bending moments at the nodes, which reduces the positive bending moment at mid-span of the lintel. It has a very small structural height, making it well-suited for overpasses and elevated road bridges, and it also saves on materials. In contrast, the lintels and columns of reinforced concrete rigid frame bridges are generally required to be cast integrally in situ, resulting in a low degree of prefabrication. Under vertical loads, this type of bridge generates horizontal thrust at the column bases, placing high demands on the foundation.