I. Overview of the Project
A bridge is an important part of expressway, which surrounds the east of the city. The superstructure is a five-span prestressed concrete continuous box girder with equal cross section, and the substructure is a pile-column structure. The span is 25.5 m+40 m+63 m+40 m+40 m, and the total length is 208.5m m. The bridge is a two-frame six-lane separated bridge. The design load standard is automobile-super class 20, trailer-120. The box girder of this bridge adopts a single-box and double-chamber section, with a top width of 12.5m, a bottom width of 8.0m, a cantilever length of 2.75m on both sides, a beam height of 2.7m, a side web thickness of 70cm, a middle web thickness of 30cm and a top and bottom plate thickness of 20cm.
Prestressed box girder adopts 50 # concrete. 12-7 Φ 5 high-strength steel strand is used for web longitudinal prestressed steel strand, 15-7 Φ 5 high-strength steel strand is used for top and bottom longitudinal prestressed steel strand, Ryb = 1860 MPa, and the anchorage system is VLM 15- 12 and/kloc-0. The box girder adopts integral cast-in-place construction. First, the middle part of 63m span is poured, and the prestressed steel beam is tensioned, and both ends are tensioned. Then pouring the second mid-span part, tensioning the prestressed steel beam, and adopting a single-end tensioning mode; Finally, the side span part is poured, and the prestressed steel beam is tensioned, and the single-end tensioning method is adopted. The pier body of the main pier adopts reinforced concrete square column pier with variable cross section, and the foundation adopts group pile foundation.
Second, the design basis
2. 1 Design and construction drawing of a bridge.
2.2 the bridge construction supervision unit "bridge construction".
2.3 Technical Standards for Highway Engineering Design (JTJ001-97) promulgated by the Ministry of Communications; General Code for Design of Highway Bridges and Culverts (JTJ 021-89) promulgated by the Ministry of Communications; Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts promulgated by the Ministry of Communications (JTJ 023-85); Code for Design of Foundation and Foundation of Highway Bridges and Culverts (JTJ 024-85) issued by the Ministry of Communications; Technical Code for Construction of Highway Bridges and Culverts (JTJ 041-2000) issued by the Ministry of Communications; Code for Seismic Design of Highway Engineering (JTJ 004-89) issued by the Ministry of Communications; Technical Specification for Highway Maintenance issued by the Ministry of Communications (JTJ 073-96); Technical Specification for Strengthening and Repairing Concrete Structures with CFRP (Draft for Review) issued by China Engineering Construction Standardization Association (March 5438+0, 2006).
Third, the construction status quo
A bridge was constructed at the bridge of the project management department of the first bid section of a road and bridge company. During the construction of right -2 section box girder (section 9-9), the steel beam extension of R4 steel beam with inner web only reaches 50% of the design value and has been grouted. The construction does not meet the design requirements. Therefore, it is necessary to carry out necessary reinforcement design and construction.
Fourth, the test results
According to the original design documents and construction status, QJX program and Super Sap program are used to analyze the plane bar system and spatial structure respectively. The analysis and calculation results show that under the most unfavorable load combination, there is no tensile stress at the lower edge of the mid-span and the upper edge of the pier top of 1, but there is almost no stress reserve. Compared with the original design idea, the bridge should have a certain stress reserve under the most unfavorable load. Because the construction tension is not in place, these two sections are not in harmony with the stress reserve and safety of the whole bridge, and the stress reserve has been lost. Compared with other parts of the whole bridge, it is a weak section, which will have a certain impact on the durability and safety of the bridge.
Five, the basic idea of steel bar design
According to the bridge structure recheck calculation, combined with the site construction conditions (except the right -2 section box girder and R4 steel beam with internal web, the bridge construction can meet the requirements of design and relevant codes), the local bridge (the second span) needs to be reinforced to ensure that the structure meets the design requirements. After analysis and comparison, according to the provisions of the current bridge design code and considering the actual stress of the bridge, this reinforcement design puts forward two reinforcement schemes: external prestressing and sticking steel plates and carbon fibers. The external prestressing scheme is an active reinforcement scheme, but the construction is difficult, so it is necessary to check and maintain the external prestressing tendons regularly during operation. The scheme of sticking steel plate and carbon fiber is a passive afterloading scheme, but it is convenient to construct and does not need maintenance during operation.
Scheme 1: External prestress scheme. This scheme is an active post-loading scheme, that is, external prestress is applied at the position where the prestressed steel beam R4 is not tensioned to meet the design requirements, so that the existing bearing capacity limit state and normal service limit state of the bridge can be improved to the design requirements.
Scheme 2: Bonding steel plate and carbon fiber scheme This scheme is a passive reinforcement scheme. First, the steel plate is pasted on the upper edge of 1 pier, and then the carbon fiber cloth is pasted on the bottom of the box girder of the second span along the axis direction of the bridge, so that the existing bearing capacity limit state and normal service limit state of the bridge can meet the design requirements.
Six, the main reinforcement materials
Scheme No.1
1. No.50 concrete is adopted for the concrete toothed plate, and its quality requirements meet the requirements of Technical Specification for Construction of Highway Bridges and Culverts JTJ04 1-2000-2000.
2. The design of ordinary steel bars adopts Grade I and Grade II, which must comply with the relevant provisions of the national standard (GB 1499-84-84).
3. The prestressed steel bar is designed with epoxy all-inclusive non-stick steel strand, and the finished bundle model is OVM-S Ⅲ (conforming to ASTM A4 16-90A standard, the nominal diameter of single strand steel strand is 15.24mm, the cross-sectional area is 140mm2, the standard strength is Ryb = 1860mpa, and it is elastic.
4. OVM is adopted for anchorage. TS 15- 19 anchorage.
5. Steel is A3 steel.
6. Other rebar planting: K80 1 glue or Hilti HiT-HY 150 glue is used. Anchor bolts and anchor clips: Hiltihad-T-M 16 special anchor bolts and anchor clips are used. Anti-corrosion material: Flitwick series special steel structure anti-corrosion material is adopted.
Option 2
1, carbon fiber: C-30 carbon fiber cloth, with a thickness of 0. 167mm and a standard tensile strength of ≥ 3400 MPa; Elastic modulus ≥ 2.0×105 MPa; ; Elongation ≥ 1.4%.
2. Sticking carbon fiber material: using supporting special bottom resin, leveling material and impregnating resin.
3. Steel plate: M 16 steel is adopted.
4. Bolts: M 16 high-strength bolts are used.
5. Bonded steel plate material: epoxy cement.
Seven, the main steps of reinforcement construction scheme
Scheme 1: external prestressing scheme
1, reinforcement method According to the design and construction status of the bridge, combined with the structural review calculation of the bridge, this scheme adopts the method of adding external prestress in the box to make the stress of the box girder meet the original design requirements.
2. Maintenance and reinforcement order The maintenance and reinforcement of this bridge will be carried out in stages. The first stage: drilling diaphragm beam (used for threading steel strand) at the fulcrum section of 1 pier; The second stage: adding concrete toothed plates and steel guide blocks in the box; The third stage: tensioning prestressed steel tendons; The fourth stage: anti-corrosion treatment and cleaning up construction waste. The specific construction sequence is as follows: preliminary preparation → erection of facility platform → drilling of transverse diaphragm beam of box girder → planting toothed plate steel bar and placing steel guide block → pouring concrete → piercing pipe → stretching external beam → anti-corrosion treatment → removing construction waste.
Scheme 2: Sticking steel plate and carbon fiber scheme
1, reinforcement method According to the design and construction status of the bridge, combined with the structural review calculation of the bridge, this scheme adopts the methods of sticking steel plates on the upper edge of the fulcrum section of 1 pier and sticking carbon fibers on the bottom of the box girder of the second span (sub-middle span), which greatly improves the ultimate bearing capacity and normal service limit state of the box girder.
2. Maintenance and reinforcement order The maintenance and reinforcement of this bridge will be carried out in stages. The first stage: the installer builds scaffolding and platforms; The second stage: sticking carbon fiber cloth on the bottom plate of the second span (secondary middle span); The third stage: 1 Stick steel strip on the upper edge of pier fulcrum section; The fourth stage: box girder surface painting; Stage 5: Dismantle the construction support and platform, and remove the construction garbage. The specific construction sequence is as follows: preliminary preparation → building a platform for constructors → sticking carbon fiber cloth on the bottom plate → sticking steel belt on the top surface of fulcrum → fastening anchor bolts of steel belt → painting the surface of box girder → dismantling construction supports and platforms to remove construction waste.
Eight, steel construction technology
Scheme 1: external prestressing scheme
1, planting rebar and pouring toothed plate.
1. 1, lofting, plane lofting according to the position and size of the toothed plate given in the steel bar construction drawing, and indicating the specific position.
1.2. Drilling and hole treatment: according to the layout of the construction drawing, drill a blind hole with a depth of 16 cm and a diameter of about 18 ~ 20 mm at the position where the new toothed plate is added, and use compressed air to remove the floating dust in the hole;
1.3, roughening of concrete on contact surface;
1.4, planting portal anchor bar and single anchor bar: planting portal anchor bar and single anchor bar with 80 1 glue or HiT-HY 150 glue; Put the high-strength adhesive into the syringe, and inject the medicine into the hole from the bottom of the blind hole to ensure complete filling. Remove rust spots and sundries of anchor bars, and slowly insert anchor bars into the bottom of blind holes, with the length in the blind holes not less than 15cm. Field mechanical properties test should be carried out for reinforcement planting. When the tensile stress of steel bar exceeds 200MPa, the anchorage of planting steel bar must be in good condition.
1.5, welding steel bar to form skeleton net;
1.6. pouring the toothed plate: after the skeleton is formed, the formwork is supported according to the shape of the toothed plate, and then concrete is poured to form the toothed plate. Pay attention to the concrete mixture ratio when pouring, strengthen vibration to make the concrete dense, and avoid cavities and honeycomb pits.
1.7. Tooth plate maintenance: After pouring a new tooth plate, the maintenance should be strengthened, and the stretching work can only be carried out after the cube strength reaches over 85%.
2. Install the steel steering block.
2. 1, lofting according to the drawing;
2.2. Drill holes with Hilti's special drill;
2.3, hole cleaning;
2.4. Install HAD-T-M 16 anchor bolts and anchor cards with installation tools;
2.5, put the steel steering block, and paste the steel steering block with concrete with epoxy resin;
2.6, tighten the nut.
3. Unbonded steel strands with epoxy coating are used for tensioning and anchoring steel strands, tooth plate anchor sealing, and prestressed steel strands inside and outside the anti-corrosion box. The standard strength is 1860MPa, the diameter is φj 15.24, and the model is OVM-S Ⅲ. See the design drawing for prestress arrangement. Adding new prestressing tendons to the fabric: all prestressing tendons are covered with epoxy unbonded tendons, and the specific type is OVM-S Ⅲ, that is, unbonded steel strand bundles are placed in pe pipes, which are filled with epoxy resin and covered with film, and grease layers are coated between high-strength steel wires. The anchorage adopts OVM. Type TS 15- 19. Because the newly-added prestressed tendons are close to the top plate, bottom plate or web plate of box girder, be careful not to damage the PE sheath outside the steel strand when passing through the prestressed tendons.
Tensioning prestressed tendons: after the prestressed tendons are in place and the concrete strength reaches 85% of the design value, tensioning can be carried out. The controlled stress under the anchor is 1 1 16MPa. Prestressed tendons shall be tensioned in strict accordance with the relevant technical requirements of Technical Specification for Highway Bridge and Culvert Construction (JTJ04 1-2000). Tensioning machines and tools should be calibrated by qualified units, and the tonnage and elongation should be strictly controlled during tensioning. During the tensioning process, the new tooth plate area and steering block area should be treated. Anchor sealing, steel guide block protection and external prestressing tendon protection: after external prestressing tendon is tensioned, the anchorage should cover the concave template and seal the anchor according to the manufacturer's requirements. Firstly, the steel steering block is derusted, then epoxy resin is evenly coated, and finally Flitwick series special steel structure anticorrosive materials are coated. The corrosion of steel steering block and the damage of steel strand should also be checked regularly.
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