Beam Bridge Reinforced

1. Project overview

Longyu Bridge is located in Jinan, Jinan Ring Expressway, and its bridge deck width varies from 28m to 37m. The upper structure is (7×22)+(5×22)+(5×22)m reinforced concrete continuous box girder, with a beam height of 1.3m.

2. There is a disease in the bridge

2.1 Cracks in the bottom of the beam

The bridge has small cracks on the bottom of the box girder. The width of the cracks is within 0.1mm, and they are mainly distributed in the 1/3 span, middle span and 2/3 span of each hole. The crack length is about 35-120cm, and some are longer. Even through.

2.2 Cracks in the mid-span web

There are multiple vertical cracks within 2-5m of each hole of the upper and lower box girder of the bridge. The width of the cracks is generally 0.15-0.2mm, and the widest point is 0.35mm. Most of the cracks have been vertically penetrated.

3. Preliminary analysis of structural checking and crack causes

The upper part of Longyu Bridge is an ordinary reinforced concrete structure. In the case of combination I, the calculated value of the largest crack in the negative bending moment on the top of the pier is 0.13mm, and the calculated value of the largest crack in the positive bending moment area in the middle of the span is 0.15mm. In the case of combination II, the calculated value of the largest crack in the negative bending moment area on the top of the pier is 0.14mm, and the calculated value of the largest crack in the positive bending moment area in the mid-span is 0.18mm.

4. Treatment plan

According to the on-site investigation, the following treatment plan is adopted: crack grouting treatment for the cracks of the cast-in-place box girder bottom plate, web and wing plate width ≥ 0.15mm. For cracks with a width <0.15mm, the surface is sealed. For cracks with a width of ﹥0.2mm, in addition to the crack grouting treatment, two layers of carbon fiber cloth are used to reinforce it. The carbon fiber cloth should cover the crack area completely, and leave the anchorage length.

5. Construction of reinforced bridges with carbon fiber cloth

5.1 Advantages of strengthening bridges with carbon fiber cloth

5.1.1. No increase in dead load and section size

The weight of the carbon fiber cloth is only 200-300g/m2, and the design thickness is 0.111-0.167mm. In addition, the self-weight of the epoxy resin series bonding materials is also very light, and the impact on the weight of the entire structure and the clearance under the bridge is negligible. At the same time, the carbon fiber cloth can be pasted in multiple layers. According to the reinforcement requirements, the carbon fiber cloth can be overlapped and pasted in one part to fully meet the reinforcement requirements.

5.1.2. It can be adapted to different component shapes and is very convenient to form.

Due to the extremely strong conformability of carbon fiber cloth, it can be constructed at will according to the change of the structure shape, thereby reducing the difficulty of construction, reducing construction costs, shortening the construction period, and generating huge social and economic benefits.

5.1.3, simple construction

The method is simple in process, does not require large-scale equipment, templates, fixtures and supports, and is simple and easy to operate, so the working surface required during construction is small.

5.1.4. Adopt carbon fiber cloth to reinforce and reinforce, without producing new damage to the original structure

The carbon fiber cloth reinforcement system uses epoxy resin series bonding materials for pasting, without the need to set anchor bolts and excavate concrete. Therefore, it will not cause new damage to the damaged structure, and it can avoid conflicts with the original steel bars and prestressed cables in the structure when drilling and cause new problems.

5.1.5, can effectively close the cracks of concrete

The carbon fiber cloth (sheet) is pasted on the surface of the concrete, which not only closes the cracks in the concrete, but also restricts the generation and expansion of cracks in the concrete structure due to its high-strength and high-modulus characteristics, changing the shape of the cracks and turning wide and deep cracks into Scattered micro cracks, thereby improving the overall rigidity of the concrete components.

5.1.6. Carbon fiber cloth (sheet) has excellent chemical resistance. Carbon fiber cloth (sheet) is a composite material that is almost non-corrosive and magnetic, and has good heat resistance. It can not only withstand cement alkaline When used in corrosive environments such as salt erosion, its life span is also longer.

6 Concluding remarks

The Longyu Bridge has been in operation for 2 years after treatment, and no further proliferation and expansion of cracks have been found. Practice has proved that carbon fiber cloth can effectively restrain crack propagation, improve the crack resistance of concrete, reduce shrinkage deformation, obviously improve the physical and mechanical properties of concrete components, and improve the fatigue resistance of components, which is of reference value for the maintenance and reinforcement of other similar projects.