Reinforcement Of Large Transportation Bridges

1.1 Bridge Overview

The bridge span composition is 14m+14m+14m=42m, and the bridge deck cross-section composition is 2.0m (sidewalk) + 26m (carriage) + 2.0m (sidewalk) = 30.0m. The upper structure adopts ordinary reinforced concrete continuous slab, and the construction of the slab beam is completed by one-time integral cast-in-place on the support. A total of 4 slabs are arranged throughout the bridge, with a thickness of 70cm, a width of 750cm at the top of the slab, a width of 450cm at the bottom of the slab, and a cantilever length of 150cm. C40 concrete is used, and the steel bars are all grade II steel bars.

The pier adopts a lotus-shaped solid slab pier with a pier thickness of 80cm, a top width of 250cm, and a bottom width of 100cm. The cap is a rectangular section, reinforced concrete structure, and a thickness of 150cm. The pile adopts bored piles with a pile diameter of 100cm and is designed according to friction piles. The abutment adopts a pile-column light abutment with a column diameter of 80cm and a friction pile diameter of 100cm. The substructures are all made of C30 concrete except that the piles are made of C25 underwater concrete.

The bridge deck pavement has the same thickness, the thickness is 10cm, and the spacing is 10cm to 10cm. The cast-in-place bridge deck concrete is C40 waterproof concrete.

1.2 Bridge diseases

Before the bridge reinforcement design, the status of the bridge was tested. The test results show that the main diseases of the bridge at present are the transverse cracks of the slab beam and the deflection of part of the bridge span. Part of the wet joints between the slabs and beams cracked longitudinally, seeped water, and locally powdered concrete. The bridge deck pavement has mesh cracking and a long longitudinal joint, the expansion joint is blocked, the rubber strip is partially damaged, and the concrete in the anchoring area is cracked. In the substructure, the pier body is partially honeycombed.

2.1 Bridge reinforcement design

According to the calculation results of the structure response of heavy vehicles passing under the bridge before reinforcement, it can be seen that the bearing capacity of the upper and lower structures of the bridge is far from the requirements. For the traditional reinforcement of the upper slab beam with enlarged cross-section (reinforcement by sticking steel plates, and external prestressed reinforcement, none of them can effectively solve the problem of insufficient bearing capacity of the upper and lower structures. Therefore, the reinforcement plan of the bridge is to increase temporary piers.

2.1.1Temporary buttress setting method selection

After analysis, when heavy vehicles cross the bridge, the main control reinforcement design items are the bearing reaction force of the slab beam at the middle pier and the resultant force of the vertical force on the top of the middle pier. In order to control the supporting reaction force at the original pier under the heavy vehicle and the vertical force of the pier top, the vertical compressive rigidity of the new temporary supporting pier should be ensured. After calculation and analysis, it is determined to adopt the form of temporary concrete supporting piers, adopting 80cm and 80cm square pier columns, and set up two rows of supporting piers for each span of 3# slab beam under the partial load mode.

2.1.2Support treatment

Because the original supports of the bridge are provided with multiple fixed supports and single supports, the slabs and beams are connected by wet joints of cast-in-place concrete. Under various temporary buttress setting schemes, excessive longitudinal and transverse bridge loads will be generated at the original bridge pier support when heavy vehicles pass the bridge. This problem was compared and analyzed by using the space finite element program. After comparing the calculation results, it was found that although the numerical value of the vertical and horizontal reaction force was smaller than that of the grid model. However, when all the front 14 axles of the heavy vehicle were on the bridge, the longitudinal and lateral extreme values reached 921kN and 269.4kN respectively. Therefore, in order to ensure that the supports are not damaged when heavy vehicles pass the bridge, some fixed supports and one-way supports of the original bridge should be temporarily replaced before crossing the bridge.

2.1.3Reinforcement design of plate beam joint area

The finite element model of the bridge entity is established by using the space finite element program, and the force on the joint area of the plate and girder under the bridge is studied. Under the condition of temporary replacement of the slab girder support to relieve the surplus longitudinal and lateral constraints, when all the 14-axis steel bridges are on the bridge, the maximum value of the transverse stress increase at the bottom of the slab girder joint area is 5.06MPa. In order to assist the force in the joint area of the plate beams, cross partitions were added between the 2#, 4# beams and the 3# beams, and the section steel connecting rods were added in the area between the partitions. After calculation, the concrete stress increment in the original joint area of the slab beam after the diaphragm reinforcement is reduced to 2.49MPa locally, and the maximum stress increment of the transverse diaphragm is 3.72MPa. After the diaphragm concrete cracks, the tensile stress is transferred to the bottom steel plate and longitudinal steel bars of the diaphragm.

2.2 Bridge reinforcement plan

After calculation and comparison analysis, the following reinforcement schemes are adopted for the bridge:

(1) Repair and treat the diseases in the wet joint area of the beam.

(2) Reinforce the 3# beam by adding temporary buttresses. Two temporary buttresses will be added for each span, and the temporary buttresses will be expanded foundation and column piers.

(3) Set concrete diaphragms between 2#, 4# slab beams and 3# slab beams, and set section steel supports in the area between the diaphragms to support the force of the flange plates of the slab beams.

3. Construction process

(1) Sealing and grouting the cracks in the wet joint area of the slab beam, chiseling and removing the aging and loose concrete in the joint area to a solid part, and repairing it with epoxy mortar until it is flush with the original surface.

(2) Cast-in-place temporary buttress concrete foundation and temporary buttress pier column.

(3) Reinforcement planting, steel tying and welding are carried out on both sides of the 2#, 3# and 4# beams, and self-leveling concrete with cross-parts and steel support rods are installed between the cast beams.

(4) Set up jacks after leveling the top of each temporary support pier. The single-point target lifting force of each support pier is (200/2kN, 600/2kN, 600/2kN, 600/2kN, 500/2kN, 500kN/ 2. 70/2kN). After the lifting is completed, the bottom of the beam is copied and the jack is unloaded.

(5) Riverbed protection construction.

(6) Remove all temporary buttress piers and restore river paving and slope protection in front of the platform.

4 Conclusion

In actual transportation, the large-size transport vehicle group passed the bridge safely and smoothly. When the equipment passed the bridge, the professional team monitored the bridge, and the results showed that the bridge deformation and other parameters were basically consistent with theoretical calculations. After the equipment passed the bridge, the professional team inspected the bridge. The inspection results showed that the major equipment passed the bridge this time without causing damage to the bridge.