What are the types of steel truss bridges

Steel truss bridges can be divided into simply supported beam bridges, continuous beam bridges, and cantilever beam bridges.
① Simple supported beam bridge: The main beam is simply supported on the pier and abutment, and each hole works independently without being affected by pier and abutment displacement. The solid belly type main beam has a simple structure and simple design. During construction, a single main beam can be successfully erected using a self-propelled or combined gantry crane. But the holes of the simply supported beam bridge are not continuous, and vehicles will jump when passing through the broken joints, affecting the increase of vehicle speed. Therefore, there is a tendency to make the main beam simply supported and the bridge deck in a continuous form. As the span of a simply supported beam bridge increases, the internal force of the main beam will sharply increase, and the materials used will correspondingly increase. Therefore, large-span bridges generally do not use simply supported beams.
② Continuous beam bridge: The main beam is continuously supported on several piers. Under load, there are positive and negative bending moments on different sections of the main beam, and the absolute values of bending moments are smaller than those of simply supported beams of the same span bridge. In this way, the amount of main beam materials can be saved. Continuous beam bridges usually consist of 3-5 holes in a single unit, with no bridge deck joints within the unit, providing a more comfortable driving experience. When constructing a continuous beam bridge, the main beam can be erected as a simply supported beam hole by hole and then connected to each other to form a continuous beam. Alternatively, it can be extended from the piers and abutments in segments and finally connected to form a continuous beam. In the past one to twenty years, the top pushing method has been successfully used in the installation of prestressed concrete continuous beams, which involves continuously making beam bodies section by section on the embankment at one (or both ends) of the bridge, making construction more convenient. The main beam of a continuous beam bridge has both positive and negative bending moments, making its construction quite complex. In addition, the main beam of a continuous beam bridge is a statically indeterminate structure, and the uneven settlement of piers and abutments can cause changes in the internal forces of each hole in the beam body. Therefore, continuous beams are generally used on bridges with good foundation conditions and large spans.
③ Cantilever beam bridge: also known as extended arm beam bridge. It is a bridge that extends a short arm from a simply supported beam to one or both ends. This type of bridge can be either a single cantilever beam bridge or a double cantilever beam bridge. Cantilever bridges often place simply supported hanging beams on short arms, connecting them to form multi span cantilever beams. A bridge opening with short arms and hanging beams is called a cantilever hole or hanging hole, and a bridge opening supporting short arms is called an anchor hole. The two ends of each hanging hole in a cantilever beam bridge are deck joints, and the deflection at the cantilever end is also relatively large. The driving conditions are not improved compared to a simply supported beam bridge. The length of a cantilever beam is longer than that of a simply supported beam of the same span, making construction and installation more difficult. For prestressed concrete cantilever beam bridges, cantilever assembly or cantilever pouring methods are often used for construction. In order to adapt to the development of cantilever construction method and ensure that the internal force state of the main beam is the same as during construction, a type of prestressed concrete T-shaped rigid frame bridge emerged without anchor holes, and the short arm and pier body that are suspended are directly fixed on the facade, forming a prestressed concrete T-shaped rigid frame bridge. This type of bridge developed after the 1950s.