(1) Before the construction of reinforced concrete continuous box girder, special design should be made for full steel pipe supports and templates to ensure the construction quality and neat appearance of box girder.

Full-house bowl-buckle steel pipe support is adopted, and square wood is set at the top of the support. The bottom formwork of continuous beam adopts composite steel formwork, and the bottom formwork is lined with PVC board to eliminate flat-fell seam of formwork. The side formwork of box girder and the bottom formwork of wing plate adopt large formwork specially processed by steel plate according to the structural size, each formwork has an area of more than 6m2, and the internal formwork of box girder adopts wooden formwork. The bottom plate shall be provided with ventilation holes as designed, and steel pipes with D= 10cm shall be adopted. During construction, plug the steel pipe with a cork, pull out the cork after the box girder construction is completed, and clean the exhaust hole.

The support is preloaded with bagged sand and gravel, and the preloading load is not less than 80% of the beam's own weight. With the start of web construction, the pressure gradually decreases.

In box girder concrete construction, the bottom plate is poured first, then the web plate is poured, and then the top plate is poured. When pouring, pour from mid-span to fulcrum, and leave 0.8 ~ 1.0m at the top of each pier for final pouring. Steel bars are made in the processing shed, bound on site, and concrete is pumped into the mould.

2 reinforced concrete continuous box girder construction process is as follows:

Foundation treatment, cast-in-place concrete sleeper beam, erection of full steel pipe support, laying square timber, loading preloading, installing bottom formwork, installing bottom formwork wedge adjustment block, measuring bottom slab elevation (including pre-camber), binding bottom slab and web reinforcement, installing side formwork, installing end formwork, self-inspection and acceptance by supervision engineer, pouring bottom slab concrete, strengthening maintenance, installing internal formwork, pouring web slab concrete, strengthening maintenance, removing internal formwork and installing top slab.

(3) Construction preparation

Cast-in-place continuous beam construction is supported by full steel pipe supports, and the bearing capacity of foundation is particularly important. The quality of foundation treatment is directly related to the quality of continuous beam, and various construction preparations must be made before construction.

(1) Before construction, the erection and dismantling of the whole bridge bracket shall be designed and constructed in detail, and the structural mechanics shall be checked. The construction scheme shall be submitted to the supervision engineer for approval.

(2) Clear the empty ballast and floating soil in the whole bridge span, level the site, roll it, replace the soft foundation, and do a good job in temporary drainage system at the site, so that rainwater and sanitary water can be discharged smoothly. ?

(3) The support foundation shall be rammed twice with a heavy hammer, and the settlement under the static load of 60Kpa within two weeks shall not exceed 1cm. Then, gravel of 10cm shall be filled, rolled by a road roller for 2-3 times, and then plain concrete with a thickness of 15cm shall be poured as the support point of the support.

(4) Supporting construction

(1) The continuous beam is cast-in-situ with full bowl-shaped steel pipe support.

(2) According to the bracket design, set the bowl buckle steel pipe bracket, and use the corresponding wooden wedge with the slope of 1: 8 as the disassembly leveling block of the bottom die.

(3) In order to solve the deflection caused by factors such as bracket deformation, dead weight of continuous beam, live load, etc., preloading is carried out after bracket erection, and the preloading amount is 95% of the beam weight, so as to check the bearing capacity of bracket, reduce and eliminate inelastic deformation of bracket and uneven settlement of foundation, thus ensuring the pouring quality of concrete beam. With the construction of box girder concrete pouring, the pressure gradually decreases.

(4) The erection of the support should fully consider the vertical and horizontal slope of the beam according to the design. The support is 50cm wider than the bridge width, and the cantilever part is directly supported by the vertical support.

⑤ The support erection scheme shall be submitted to the supervision engineer for approval, and shall be checked and approved by the supervision engineer after the erection is completed.

5] Pre-camber setting

When installing supports and bottom formwork, pre-camber shall be set according to the design and specification requirements, and the pre-camber shall be distributed in a quadratic parabola within the beam span. According to the design requirements, the pre-camber of holes 8 and 9 of E ramp bridge is 2.5cm, that of other holes is 2.0cm, that of interchange 1 and 4 holes is 2.0cm, and that of holes 2 and 3 is 3.0cm.

[6] Vertical formwork

Detailed template design shall be carried out before formwork erection.

(1) Place the bearing accurately at the design position of the pier, then lay the bottom formwork and ensure that the bearing does not shift. (2) The bottom plate adopts composite steel formwork, the side plates, wing plates and web plates adopt specially designed composite large steel formwork, the internal formwork adopts wooden formwork, and the bottom plate is lined with PVC board to ensure smooth surface and eliminate flat-fell seam of formwork.

(3) The formwork shall be firmly spliced and connected, and the joints shall be tight and smooth to ensure no slurry leakage, and the release agent shall be painted. After the formwork is supported, check the elevation, axis, geometric size, connection state and support stability.

Primary reinforcement

The fabrication and processing of steel bars shall be carried out in strict accordance with Technical Specification for Construction of Highway Bridges and Culverts (JTJ04 1-2000).

(1) beam reinforcement is manufactured in the processing shed and bound on site. The reinforcement is welded on both sides, and each weld must be carefully checked.

(2) The connection points of steel bars should avoid the maximum stress section, and the joints should be staggered according to the construction technical specifications. The steel bars at the top of the middle pier top box girder and the bottom of the middle span box girder bottom plate shall not have joints.

(3) Measures must be taken at the welding site under climatic conditions that are not conducive to welding. When the ambient temperature is lower than 5℃, steel bars should be preheated before welding.

(4) The welding length of steel bar shall not be less than 5d.

⑤ If the specification, grade and diameter of steel bar change or the welder changes, the established welding parameters must be checked.

⑥ When arc welding is adopted, the length, width and thickness of the weld shall meet the specification requirements according to the varieties and models of covered electrode, and batch welding shall be carried out after the sample is qualified.

Being concrete pouring construction

The pouring sequence of concrete should be layered hole by hole from side span to the other end, but each span should be poured from the middle to both ends. The bottom plate, web plate and top plate are poured in three times along the section height of box girder, that is, before the next pouring, the surface of the concrete poured in the previous time is roughened, and then the lower concrete is poured.

Concrete pouring is transported by concrete truck, concrete is pumped into the mould and vibrated by plug-in vibrator. The temperature of pouring concrete should be controlled between 10-32℃.

Before pouring pumping concrete, the mixture ratio and specified test must be carried out and the written approval of the supervision engineer must be obtained. The pumping construction technology shall comply with the relevant provisions of Technical Specification for Concrete Pumping Construction.

Before pouring concrete, pump a part of cement mortar to wet the pipeline, and discard the concrete pumped for the first time until the concrete with consistent quality and good workability is discharged and approved by the supervision engineer.

Pump concrete continuously, and do not stop halfway. After the pumping operation is completed, the residual concrete in the pipeline should be discharged in time, and all the equipment should be thoroughly cleaned.

If it is necessary to shut down for special reasons, the shutdown time shall not exceed 30 minutes, and in hot weather it shall not exceed 10 minutes. When the pump is stopped, pump it several times at regular intervals to prevent concrete from condensing and blocking the pipeline. During pouring, designated persons shall check the stability of supports, templates, steel bars and embedded parts. , and deal with problems (looseness, deformation, displacement) in time.

When tamping vibration, the vibrator should be vertically inserted into the previous layer of concrete by 50-100 mm. The moving distance of the plug-in vibrator should not exceed 1.5 times of the effective vibration radius, and the pulling speed should be slow to avoid cavities and contact with reinforced concrete and embedded parts. The corners of formwork and the places beyond the reach of vibrator should be supplemented by pin vibration to ensure the compactness and smooth surface of concrete. Ensure that the beam will not be disturbed within 1.5-24h after concrete tamping.

When constructing concrete in hot climate, measures should be taken to keep the concrete temperature below 32℃. Measures to keep concrete temperature shall be approved by the supervision engineer.

During the construction of each part, pay attention to the embedding of relevant embedded parts.

Levies temporary working seam

In the process of continuous box girder construction, temporary working joints are left at the top of each pier.

Pier rigid support, bracket elastic support. When pouring box girder concrete, the bracket will have uneven settlement, so effective measures must be taken to avoid cracks in the box girder at the pier. Therefore, a temporary working joint is set at the pier top, and the working joint will be filled up after the concrete pouring of the beam body is completed, the support is stable and the settlement of the upper structure stops.

The width of the working joint is 0.8m ~ 1.0m, and the two ends are separated from the main girder by wooden boards. The wooden boards are reserved when pouring the concrete of the girder, and the holes through which the steel bars pass are reserved.

⑽ Health.

After the completion of concrete pouring, the concrete should be cured as soon as possible after the surface mud is collected.

The box girder of this bridge is covered with plastic sheets by sprinkling water, and the joints of plastic sheets should overlap 150mm and be bonded with adhesive tape. The connected plastic sheets make the whole box girder surface completely waterproof. And fix the plastic sheet to prevent it from being blown by the wind.

During the curing period, before the concrete strength reaches 2.5Mpa, it shall not bear the load of pedestrians, transportation tools, templates, supports, scaffolding, etc.

Special personnel shall be responsible for the maintenance, and the appropriate time interval shall be controlled according to the climatic conditions, so that the concrete surface will always be moist during the maintenance.

When the temperature is lower than 5℃, cover the beam to keep warm, and do not sprinkle water for health preservation.

⑾ Remove the bracket.

When the concrete strength of the box girder reaches 85% of the design strength, the frame can be removed and the bottom can be removed. The unloading rack must be unloaded slowly and symmetrically from the middle of the span to the fulcrums at both ends. It is forbidden to pile up heavy objects on the box girder that has just been unloaded.

⑿ Bridge quality control

The measured items of the main bridge project are carried out according to the following table.