Key points of standardized construction of cast-in-place beam?

What are the key points of standardized construction of cast-in-place beams? The following is a detailed introduction of Zhong Da Consulting for your reference.

The Manual for Standardized Construction of Cast-in-place Beams has compiled ultra-detailed technical pictures and texts, including general construction requirements, support and formwork design, construction technology and construction points, which is very suitable for field frontline construction personnel to learn. Take a quick look!

1, general requirements

1. 1 Review the design documents, the construction scheme of cast-in-place beam has been approved, and technical disclosure will be made to the construction team.

1.2 Reasonable choice of support forms, different construction geological conditions and stress conditions, different options, when the height-width ratio of the support is less than or equal to 2, the shaped bowl-buckle full-house support is generally adopted, and the steel pipe column combined support is generally adopted when crossing the existing road.

1.3 Due to the large amount of supports, templates, steel bars, cement and preloading materials used in cast-in-place construction, materials should be organized to enter the site in advance.

2. Support and formwork design

2. 1 Scaffold-type scaffolds shall be fabricated and assembled with standardized, serialized and universal steel members.

Support should be installed according to the requirements of construction drawing design. The vertical pole should be vertical, and the node connection should be reliable. The support of post-cast strip must be specially designed and reinforced to avoid the support from sinking or collapsing after tensioning.

2.2 Pre-camber setting of support should be considered according to the design requirements. If there is no provision in the design, it can be calculated according to relevant specifications and methods. The camber of other points is distributed in a straight line or quadratic parabola across the midpoint.

2.3 Support preloading Support preloading method can use sandbags or precast concrete blocks for preloading, and the preloading weight and time should meet the design and specification requirements. Stability observation should be strengthened to ensure the safety of stent preloading. Once the deformation is found not to converge, measures such as unloading or emergency evacuation should be taken immediately. Loading and unloading procedures must be carried out in strict accordance with the structural characteristics and the approval of the supervision engineer.

3. Building technology

Cast-in-place beam construction adopts the method of erection of supports on site, sectional binding of steel bars and sectional layered pouring of concrete. The construction process is as follows:

Foundation treatment → erection of support → full hole preloading → installation of bottom formwork and support → binding of reinforcement (bottom, web and beam) → installation of side formwork → pouring of bottom, web and beam → installation of internal formwork → binding of roof reinforcement → pouring of roof concrete → prestressed tensioning grouting → dismantling of formwork and support.

4. Key points of construction

4. 1 The compaction degree of the original ground for supporting foundation treatment reaches 90%, and 20cm gravel is paved.

Use 15cm25 concrete or 20 cm3: 7 lime soil 15cm25 concrete to ensure the safety of cast-in-place construction. The bearing capacity of foundation for cast-in-place construction should generally be above 200KPa, and there is no soft substratum. The treatment range of foundation shall be at least 0.5m wider than that of mounting bracket. After the foundation is treated, an annular drainage ditch should be set around the support as soon as possible to avoid rain soaking the foundation and causing settlement and deformation.

4.2 Concrete pouring

1) Concrete shall be poured at one time as far as possible. The mix proportion of concrete should be put forward by the laboratory.

Before trial fitting, and approved by the supervision engineer. The mixing of concrete should be strictly controlled according to the construction mixture ratio.

2) Concrete shall be poured horizontally and obliquely in sections, symmetrically across the bridge (even settlement shall be eliminated), and it shall be continuously pushed from the low end to the high end along the bridge direction. For the box girder with the same cross section, when pouring concrete, the web plate should be poured first, then the bottom plate should be poured from the working opening, and finally the top plate concrete should be poured. In the process of concrete pouring, it should be fully vibrated and compacted, and no vibration leakage or excessive vibration is allowed. When closing the roof, workers should step on the prepared bench and close the surface backwards. No stepping on footprints.

4.3 Concrete curing After concrete is poured, it will be covered with geotextile, and then it will be cured with water after secondary slurry collection. The curing time shall not be less than 7 days. In winter, the roof of cast-in-place beam is tightly wrapped around the ground with tarpaulin, and a stove is placed to boil water for health. After the concrete is poured on the roof, cover it with a plastic film, and then cover it with a quilt and a layer of striped cloth. When the temperature is below -5℃, steam curing should be considered.

4.4 template removal and unloading

1) For non-prestressed structures, the non-load-bearing formwork can only be removed after the concrete strength reaches 2.5MPa, and the removal of the load-bearing formwork should be carried out according to the requirements of the specification.

2) For prestressed beams, the load-bearing formwork should be removed after the prestressed tendons are tensioned and grouted, and the grouting strength reaches certain requirements, so as to avoid the adverse effects caused by the tensioning of beam concrete.

4.5 construction matters needing attention

1) Set up an escalator and hang a safety net around it. One side of the pedestrian should be provided with a safe passage.

2) There should be working platforms on both sides of the support, and safety fences with a height not less than 1.50m should be set on the side, and safety nets should be hung on the side.

3) For roads with closed traffic, isolation railings, eye-catching signs and speed limit signs should be set according to the actual situation on site, and indicator lights should be set at night.

4) PVC pipes should be used to lead the drainage holes on the bridge or interchange area to the drainage ditch or sewer. The bottom side of the flange of the wing plate is provided with a drip tank.

5) Cast-in-place box girder end formwork must use steel formwork.

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