Research on Reinforcement Technology for Cover Beam Structures of in-service Bridge

In order to determine a suitable reinforcement technology for the cover beam structure of a bridge in service, a model of a bridge in Shanxi Province was created and analyzed. Three different reinforcement methods were simulated using the finite element method, and these methods were then compared and analyzed. The results indicate that all three reinforcement methods can enhance the bridge’s performance, with the effectiveness ranked as follows: increasing the cross-section, applying external prestress, and attaching steel sheets. Considering factors such as economy, feasibility, and safety, it is recommended to reinforce the cover beam of the bridge by strengthening the external prestressed ribs in combination with affixing steel plates. This approach not only effectively reduces the stress and displacement of the cover beam structure but also redistributes the stress on the cover beam. Importantly, this method does not hinder bridge traffic and minimizes the impact on the clearance under the bridge.


Introduction
In recent years, with the rapid development of China's economy, the bridge industry has been vigorously developed, bridge construction technology has continued to progress, countless new bridges have been erected, and China's bridge construction has made brilliant achievements [1].At the same time, China's bridge industry has also ushered in a huge challenge, the existing part of the bridge facilities construction time is premature, in the process of its long-term use, the surface of the bridge has different degrees of fatigue cracks, the performance and service life of the bridge adversely affect, but if it is directly rebuilt, it not only costs a lot of manpower, material resources and financial resources, but also causes a waste of resources.In order to avoid the above problems, it is necessary to pay attention to the reinforcement of the bridge, especially the substructure of the bridge to improve the durability and bearing capacity of the bridge [2][3][4][5][6].
Shao Bin [7] studied the cover beam structure of a reconstructed long-span bridge, combined theoretical analysis and finite element simulation methods, and compared and optimized the reinforcement scheme of the cover beam, and the results showed that by adding temporary support to reduce the span of the cover beam and rebuild the force system of the structure, the long-span cover beam could be cut off and transformed safely and conveniently.Qiao Guowei [8] summarized the construction points of this technology by introducing the advantages of carbon fiber materials and their use in bridge reinforcement, in order to extend the service life of bridges.Ma Geng [9] studied the actual reinforcement effect of carbon fiber reinforced bridge through the solid bridge load test, and analyzed the degree and reasons for the increase in the bearing capacity of the main beam after carbon fiber reinforcement.Li Ming [10] proposed a bridge substructure reinforcement technology based on the rotary spray method, and the results show that this method can enhance the ability of the cantilever of the cover beam to resist negative bending moment, realize the reinforcement optimization of the bridge substructure, and improve the tensile force and stress yield response of the bridge substructure.
Since most of the general small and medium-sized bridges adopt simple support beam structure, the cover beam is the most important force-bearing structure in addition to the superstructure, and its structure plays a role in the bridge structure.However, people often do not pay much attention to the importance of cover beams in bridge design, and the current bridge design codes for cover beams are not very detailed, resulting in different degrees of disease after the completion of the bridge for a period of time, and even the normal use of the bridge has a great impact, so the research on the reinforcement technology of the cover beam structure of the bridge in service is of great significance in the maintenance and reinforcement of the bridge body.

Comparative study on the performance of cover beam before and after reinforcement
This section takes a multi-span bridge on National Highway NO.208 as an example to analyze and study the reinforcement method of the cover beam.The 1#, 2# and 6# cover beams of the bridge have problems such as steel corrosion, cease peeling and expose the ribs, and the finite element model of the whole bridge is established through Midas civil and FEA, and the diseases are quantified and applied to the model, and different reinforcement methods are simulated, and the superiority of various methods is compared and analyzed.The finite element model of the bridge is shown in figure 1, the whole bridge is simulated by beam elements, the two ends of the beam are constrained by general support, the elastic connection between the beam and the cover beam, the elastic connection between the cover beam and the pier, the elastic connection between the bottom of the pile foundation and the pier tie beam, and the bottom of the pile foundation is constrained by consolidation.The self-weight coefficient is 1.04, the overall temperature rise is set to 23°C, and the overall cooling is set to -23°C.The stress and displacement of the bridge are shown in figures 2 and figure 3.   The substructure of the bridge has not suffered serious diseases, and from the perspective of economy, it is not suitable to use the method of changing the structural system for reinforcement, so this section analyzes the reinforcement effect of applying in external prestressing reinforcement, pasting steel sheets, and increasing the cross-section of components:

External Prestress Reinforcement
In external prestressing reinforcement achieves the reinforcement effect by anchoring and installing prestressed ribs at the top of the cover beam, and the prestress size of the construction tension is 1395MPa.The stress and displacement of the reinforced bridge are shown in figure 4 and figure 5.According to the finite element calculation results, after the reinforcement by in external prestressing reinforcement, the stress of the bridge structure is redistributed, and the applied prestress cancels out part of the constant load and live load, and the stress and displacement of the bridge structure are greatly improved.The stress of the cover beam part is reduced by 4.6%~15.3%,and the compressive stress on the outside of the NO.1#, 2# and 6# cover beam becomes tensile stress; After applying the prestress, the displacement of the 1#, 2# and 6# cover beams was reduced by 2.2%~5.5%.

Paste the steel sheet
When using pasted steel sheet to reinforce the cover beam, high cementing agent and high strength bolts and other materials are used to paste and fix the steel plate, the steel plate model is Q235, the elastic modulus and ratio of Poisson are 200GPa and 0.25, the density is 7.85g/cm 3 , and the bolt model is M12×130.The size of the pasted steel plate is 2.95m long× 1.2m wide × 0.08m thick, and the steel plate is arranged at the peeling and exposed ribs of the cover beam, and the pasted steel plate is anchored with high-strength bolts.The reinforcement position of the pasted carbon fiber plate is shown in figure 6, and the stress and displacement of the reinforced bridge are shown in figure 7 and figure 8.According to the finite element calculation results, after the reinforcement by pasting steel plate method, the stress and displacement of the bridge structure have changed, the stress of the cover beam part has been reduced by 3.3%~11.1%,and the force on the outside of NO.1#, 2# and 6# cover beam has changed, and the compressive stress in this part has increased by 2.3%.After pasting the steel plate, the displacement of the NO.1#, 2# and 6# cover beams was reduced by 1.7%~4.4%.

Increase the cross-section of the component
When using increasing the cross-sectional area of the member for reinforcement, keep the beam, pier and infrastructure unchanged, and increase the area by widening the NO.1#, 2# and 6# cover beams along the radial direction of the bridge span, as shown in figure 9, where the red part is the widened part of the cover beam.The stress and displacement of the reinforced bridge are shown in figure 10 and figure 11.According to the finite element calculation results, after the reinforcement by increasing the section method, the stress and displacement of the bridge structure have been greatly improved, and the stability has been greatly improved.After pasting the steel plate, the stress of the NO.1#, 2#, 6# cover beam was reduced by 16.5%~21.5%;The displacement of the NO.1#, 2#, and 6# cover beams was reduced by 3.5%~6.5%.

The reinforcement method of the cover beam performance improvement is preferred
In the previous section, taking a multi-span bridge on the National Highway 208 line as an example, the cover beam of the bridge was reinforced by applying in external prestressing reinforcement, pasting steel sheets, and increasing the section of the component, and the stress and displacement of the bridge under various reinforcement methods were calculated through the finite element software, and the middle section of the cover beam and the adjacent section of the cover beam were selected as the key sections, and the sections 1~6 were numbered respectively, and the number was shown in figure 12, and the stress values and displacement values of each key section were summarized in table 1 and 2    In order to demonstrate the superiority of various reinforcement methods, figure 13 and figure 14 give a line plot of the bridge stress and displacement under different reinforcement methods: It can be seen from table 1, 2 and figure 13,14 that the reinforcement has the greatest impact on the key cross-section 2 of the cap beam, and the effect of reinforcement by increasing the cross-section of the cap beam is the best, and the effect of pasting the steel sheet is the worst.For the stress value, the stress in the middle of the 6# cap beam is the largest when it is not reinforced, which is -12097.8kN/m2;After being reinforced by the increased cross-section method, the stress in the middle of the 6# cap beam was -9506.4kN/m2,which was reduced by 21.4%.The stress value decreased by 9.5% after applying external prestress.The stress was reduced by 5.7% after the steel sheet was attached.For the displacement value, the middle part of the 6# cap beam was the largest when it was not reinforced, which was 0.4543cm, and after being reinforced by the increased section method, the middle part of the 6# cap beam was 0.4252cm, which was reduced by 6.4%.The displacement value decreased by 5.5% after applying external prestress.The displacement was reduced by 4.4% after pasting the steel sheet.

Conclusions
The effects of the three reinforcement methods are, in turn, enlarged cross-section, tensile external prestress, and pasted steel sheet.Although the effect of enlarging the section is good, it can effectively reduce the displacement and stress of the cover beam and eliminate the disease, but the construction is more complicated and affects the passage of the bridge deck.Tensile in external prestressing reinforcement can also reduce displacement and stress, and the prestressed ribs are light, which will not increase the self-weight of the bridge, but this method cannot repair the side spalling and exposed rib disease of the cover beam.Pasting steel sheets can effectively treat cover beam diseases, but the reinforcement effect is limited.Based on comprehensive consideration, it is recommended that the combined combination of tensile external prestress and pasted steel plate to strengthen the cover beam, which can not only effectively reduce the stress and displacement of the cover beam, but also redistribute the stress of the cover beam without affecting the passage on the bridge.

Figure 1 .
Figure 1.Finite element model of bridge.

Figure 6 .
Figure 6.Schematic diagram of reinforcement by pasting steel plate method.

Figure 9 .
Figure 9. Schematic diagram of enlarging the section of the cover beam.

Figure 12 .
Figure 12.Schematic diagram of key section number.

Figure 13 .
Figure 13.Line diagram of stress in key sections Figure 14.Vertical displacement line of key sections