The status quo of bridge structural strengthening technology

According to statistics, the number of existing bridges in China has reached 735,000. At present, most of the existing bridges tend to be aging. Coupled with the rapid growth of traffic and heavy and overloaded vehicles, the number of bridges that need to be reinforced and repaired each year is on the rise. Although the traditional bridge strengthening technology is very mature, each has its shortcomings. The ideal strengthening technology should meet the following characteristics: obvious strengthening effect, unsuitable construction technology, small impact on traffic volume, short construction period, simple and economical maintenance.

Traditional bridge structural strengthening technology

1. Enlarged structural section strengthening method. This method is generally achieved by increasing the concrete area on the surface of the beam or increasing the number of stressed steel bars, which can not only improve the bearing capacity and durability of the old beam, but also repair the original damage of the beam. However, the construction period of this method is relatively long, which affects the traffic volume in the initial stage and increases the weight of the structure after strengthening.

2. External prestressing method. This method applies prestress by prestressing the lower edge of the beam to be strengthened, which can effectively offset part of its own weight and effectively restrain the deformation of the beam structure and the expansion of the crack width. The disadvantage of this technology is that the construction process is relatively complicated, and the later maintenance cost after strengthening is relatively high.

3. Sticking steel plate strengthening method. This method uses a bonding agent to bond the steel plate and the old beam to be reinforced to achieve the effect of improving the rigidity and bearing capacity of the beam. Although this method is simple to construct, it is expensive and the steel plate is susceptible to rain erosion and rust, which weakens the strengthening effect.

Application of new technology of bridge structural strengthening

1. Bonding fiber composite material strengthening method

The technical method often used in actual engineering is the sticking carbon fiber cloth and plate strengthening method, and it is mostly used for sticking and strengthening the bridge pier in highway bridges. The disadvantage of this method is that the rigidity of the component after strengthening is not significantly increased, and the high-strength performance of carbon fiber cloth cannot be fully utilized, and the fire resistance of carbon fiber cloth is poor.

Advantage of carbon fiber strengthening

• Easy installation

• Corrosion resistance

• Short construction period

• No maintenance required

• Light weight, no influence to original structure

• Low cost, cost effective compared with other methods

2. Prestressed carbon fiber laminate strengthening technology

This method uses a special anchor to fix the high-strength carbon fiber laminate on the bottom of the beam member to be reinforced. Special carbon fiber laminate glue is used to cement the concrete and carbon fiber laminate, and the pre-stressed carbon fiber laminate is pre-stressed before the glue is cured to realize the full utilization of the high-strength tensile strength of the pre-stressed carbon fiber laminate. So as to improve the problem of insufficient carrying capacity of old bridges. The prestressed carbon fiber laminate is made by soaking the carbon fiber laminate with resin, curing it in a prefabricated mold, and performing continuous stretching and extrusion before preforming. With extremely high tensile strength, the tensile strength of the material reaches 2800 MPa, and the strengthening effect is very ideal.

The advantages of this strengthening technology method are:

• The construction is simple and fast, and the beam weight will not increase after strengthening;

• After the beam is reinforced, there will be no stress hysteresis in the structure;

• After the strengthening is completed, the bearing capacity of the beam is significantly improved, and the development of cracks and harmful deformation of the beam can be effectively restrained.

3. SRAP strengthening technology

The SRAP strengthening method adopts a new technical concept of prestressing the beam. This strengthening technology makes full use of the high-strength performance of the zinc-locked soft steel wire bundle (SR strengthening material) and the multi-functional alumina glycan resin mortar (AP resin mortar) for waterproof, corrosion resistance and strong adhesion. Apply external prestress and use resin mortar to repair the original damage of beam concrete to achieve the effect of strengthening. The external prestress is applied by using a spiral buckle to fix the steel wire bundle on an expansion bolt that is fixed to the bottom of the beam in advance, and the external prestress is applied by tightening the screw buckle with the opposite direction of the thread.

The main feature of this method is that the load-bearing capacity of the beam can be improved by applying external prestress, and AP resin mortar can be used to repair the original damaged part of the beam. The mechanical properties of AP mortar and bridge concrete are very similar. Alumina is used to improve the corrosion resistance of the beam and enhance the shrinkage compensation effect of the beam. The addition of glycan tackifier not only improves the adhesion, but also moisturizes the hardened material. In addition, AP mortar can be applied to the surface of the beam, and it can also be sprayed for strengthening. The strengthening technology has simple construction technology, low economic cost, good strengthening effect, and the reinforced bridge can effectively enhance the ability to resist fatigue cyclic loading.