Concrete Bridge Strengthening

Project Overview

CYTS Beichuan River Bridge is a highway bridge across the river. The total length of the bridge is 100.84m, which is a 5×20m prefabricated simply supported beam bridge, with a calculated span of 19.5m. The bridge deck has a net width of 7 and the sidewalk is 2×2.5m. The design load of the bridge is car-1-20, the checked load is trailer-1100, and the crowd load is 3.5kN/m. It can be seen from Figure 1 that the bridge is hinged by 2 side plates and 7 middle plates. The dimensions of the middle and side plates are shown in Figure 2 and Figure 3. The bridge is a passage connecting the old and new living quarters to maintain the normal life of the residents in the new living quarters. It is decided to lay the corresponding pipelines along the bridge side beams on both sides of the channel steel to enter the living area. The load on each side of the pipeline is simplified by calculation to a uniform load q=6kN/m. It is required to calculate whether the safe and normal operation of the bridge can meet the requirements after the load is increased. If it is not satisfied, the reinforcement design is carried out.

Section Strength Check

The mid-span bending moment of the control design is calculated by calculation = 2394kN·m. Ignoring the influence of structural steel bars, considering that the bridge has been built and operated for a period of time, taking the beam bearing capacity reduction factor = 0.8, the bearing capacity of the calculated section of the flexural member M_j=2303kN·m is less than M_u2394kN·m. It can be seen from the calculation that the bearing capacity of the front section of the concrete beam of the bridge cannot meet the requirements of normal and safe operation, and the flexural bearing capacity of the concrete beam should be strengthened.

According to the owner's requirements and site conditions, it was decided to use CFRP for reinforcement.

CFRP Reinforced Design

The bridge is reinforced with Horse carbon fiber cloth and structural glue, that is, a layer of CFRP is pasted on the bottom of the concrete beam to improve the flexural bearing capacity, and a U-shaped anchor is added at the two supports and at the mid-span section. After calculation, the reinforced area Af=1054mm2 on the cross section, the cross-sectional bearing capacity of the reinforced member M_j=3060kN·m>M_u=2394kN·m.

Reinforcement Effect of CFRP

The bridge was reinforced in strict accordance with the construction technology of CFRP reinforced concrete beams. After the completion of the reinforcement construction, the bridge was tested, and it was found that the bearing capacity of the bridge section was greatly improved, the stress state was improved, the concrete cracks in the tension zone were reduced or even closed, and the overall stability and durability of the beam body was enhanced. At present, the operation of the bridge is in good condition, and no peeling or peeling of the carbon fiber cloth has been found, let alone any driving safety problems.