Bridge

The span of a bridge is 37m, and the bottom surface of the mid-span beam is about 4.5m from the water surface. It is an assembled uniform cross-section oblique leg rigid frame bridge. Both ends of the bridge deck are simply supported, and the upper ends of the oblique legs are rigidly connected to the bridge deck. It was built in 1987 with a design capacity of 100t. Due to actual needs, the bridge was reconstructed in February 2008. After the transformation, the bridge is required to be able to pass a flatbed trailer carrying 105t cargo. The flatbed trailer has a dead weight of 41t and a total weight of 146t.

Considering that the load far exceeds its design load, theoretical calculations are first carried out based on actual working conditions. This working condition belongs to the combination of load combination III in the code, structural gravity (constant load) and trailer. According to the requirements of the specification, the bridge components shall be checked and calculated for compression, bending and shearing.

After calculation, it is found that under the action of the self-weight of the bridge and the trailer load, the control conditions of the control section can meet the requirements of the specification. However, the oblique section shear strength of the three-element 3-node section and the shear strength of the joint surface are insufficient, so it must be reinforced.

Since the river channel where the bridge is located is an important waterway, if traditional glued steel plates are used for reinforcement, scaffolding must be built in the center of the riverway. This will affect water traffic and the construction period will be longer. It is also not suitable to use outsourcing to increase the cross-sectional size of the component or prestress reinforcement, so consider the use of carbon fiber materials to strengthen the bridge structure.

There are two types of carbon fiber used in this reinforcement: one is a plate-like material with a hard texture that can be pasted on the surface of the component. It is suitable for the flexural reinforcement of beams and is used to improve the flexural bearing capacity. Another silk-like material with a softer texture. It is used for winding or making U-shaped hoop. The glue can automatically penetrate the surface to make the fiber better stick to the concrete. It is suitable for constraining concrete and improving its ductility or shear resistance. . The adhesive is epoxy resin, which is composed of cement, bottom glue, surface glue and curing agent.

Based on the results of theoretical analysis, it was decided to adopt the following reinforcement scheme for the bridge: first, the inclined beam legs were reinforced, and carbon fiber cloth was wound within 50 cm from the 3 nodes to the support to improve the ductility at the nodes. Within 200cm of the 3-node to the mid-span direction, paste U-shaped carbon fiber along the beam to improve the shear resistance of the 3-node.

Then the bottom of the beam is strengthened by bending, using carbon fiber plate, and two pieces of each beam bottom, starting from the horizontal distance of 200cm from the support, and continue to the other end at the horizontal distance of 200cm from the support.

As overweight vehicles crossing the bridge are accidental events, and considering that with the increase of the bridge construction time, the bearing capacity of its piers and foundations will gradually increase, so no other reinforcement measures are adopted for the substructure of the bridge.