Classification structure of reinforced concrete beams

Reinforced concrete beams can be divided into rectangular beams, T-beams, I-beams, channel beams and box beams according to their cross-sectional forms. According to its construction method, it can be divided into cast-in-place beam, precast beam and precast cast-in-place composite beam. According to their reinforcement types, they can be divided into reinforced concrete beams and prestressed concrete beams. According to its structure diagram, it can be divided into simply supported beam, continuous beam, cantilever beam, main beam and secondary beam.

The typical reinforcement structure of reinforced concrete beams is shown in figure 1. In the section that mainly bears the bending moment, longitudinal reinforcement is arranged along the lower part of the beam to bear the tensile force caused by the bending moment. In the section where bending moment and shear force * * * act together, transverse stirrups and diagonal reinforcement are arranged to share the shear force and bending moment with longitudinal reinforcement * * *. Inclined steel bars are generally formed by bending longitudinal steel bars, so they are also called bent steel bars. In order to fix the position of stirrups and make them form a rigid skeleton with longitudinal reinforced bars, vertical bars must be set in the beams. When the beam is high, in order to ensure the stability of the steel skeleton and bear the stress caused by concrete shrinkage and temperature change, longitudinal structural steel bars with a diameter of not less than 10 mm should be set on the side of the beam every 300 ~ 400 mm along the beam height and connected with tie rods. In order to ensure that the steel bar is not corroded and closely bonded with concrete, the minimum thickness of the concrete protective layer on the side of the steel bar in the beam is 25mm (for prefabricated members with higher concrete grade, it can be reduced to 20mm). The stirrup is not less than 15mm from the concrete surface. In order to effectively use high-strength steel, avoid concrete cracking or reduce the crack width, and improve the stiffness of the beam, all or part of the longitudinal reinforced bars of the beam can be prestressed (see prestressed concrete structure).