building technology
The overall construction process is as follows: support foundation treatment → support erection → support static load preloading → support pre-camber setting → formwork fabrication → beam reinforcement fabrication → concrete construction → maintenance → prestress application → grouting → maintenance → support removal.
Full house support installation and foundation treatment
(1) The foundation shall be compacted with a degree of compaction ≥90%, and then hardened with C20 concrete. After the concrete reaches a certain strength, install full-house support. Before scaffold erection, the elevation of concrete surface should be measured, the elevation of beam bottom surface should be calculated, and then vertical rods with different lengths should be configured to ensure that the adjustable height of U-shaped scaffold is within 30cm.
(2) After the scaffold erection is completed, measure and release the elevation control points on the pier shaft or cushion stone scaffold, then adjust the jacking thread to the design elevation, lay the longitudinal square wood (called longitudinal beam) on the adjustable jacking thread, lay the transverse square wood (called cross beam) on the longitudinal beam with a spacing of 0.3m, and lay the bottom die on the cross beam.
Support arrangement, its structural form is as follows:
The vertical spacing of vertical poles is 90cm, and the horizontal spacing of vertical poles is divided into two parts, the range of web is 60cm, the range of bottom plate and flange plate is 90cm, and the spacing of vertical poles is 120cm. At the chamfer of the end span, the vertical and horizontal density is 30cm (the calculation of the support and formwork is omitted). In order to ensure the overall stability of the support, every three rows of transverse vertical poles and every three rows of longitudinal vertical poles are provided with a bracing.
Supporting preloading
(1) The purpose of preloading the support is to check the safety of the support, ensure the construction safety and eliminate the inelastic deformation of the foundation, which is beneficial to the linear control of the bridge deck. Calculate the pre-camber setting value and adjust the bracket.
(2) Preloading weight: the pre-loading weight is the dead weight of box girder.
(3) Settlement observation: In order to know the settlement of the bearing, survey control points are arranged in advance, which are located at two fulcrums, two spans 1/4 and three points on each section. Measure the elevation of each survey control point before preloading. After loading 50% and 100%, the elevation of each control point shall be re-measured. After loading 100% preloading load, the elevation of each control point shall be re-measured every 24 hours. If the measured data no longer changes, it means that the foundation and support have basically settled in place; otherwise, preloading with load is needed until the foundation and support settle in place (according to experience, it usually takes 3-5 days).
(4) Pre-camber adjustment
After the preloading is completed, according to the preloading result, adjust the elevation of the support through the adjustable jacking, and set the pre-camber.
template
(1) bottom formwork: the box girder bottom formwork is made of bamboo plywood special for bridges, with a thickness of 15mm and a smooth surface. Under the bamboo veneer, lay a square wood with a longitudinal length of 10cm* 10cm, with a center spacing of 30cm, that is, a clear spacing of 20cm, to ensure the flatness and integrity of the formwork. Pay attention to the template seam on the square wood, otherwise adjust the position of the square wood appropriately. Before laying the bottom formwork, place the bridge bearing and install the bearing according to the relevant regulations or design instructions.
(2) External formwork and flange formwork: the external formwork and flange formwork panel of box beam are made of 15mm thick bamboo veneer, and the stiffening rib is made of 10cm× 10cm square timber, which is directly supported on the floor square timber.
(3) Internal formwork: the internal formwork of box girder adopts self-made wooden formwork. In order to facilitate the removal of the internal model from the box girder, a working hole of 1000* 1000mm is set on the top plate of the box girder14. After taking out the internal mold, pour the working hole with the same label material and seal it. Note that the seams of the formwork must be tightly closed. If there are gaps, paste them with broadband tape to avoid slurry leakage.
Beam structure
(1) The processing and installation of steel bars shall be carried out in accordance with relevant regulations and design. There are a large number of embedded bellows in the web and bottom plate. In order not to damage the bellows, all welding should be carried out before the bellows is embedded, and no welding should be carried out as far as possible after the pipeline is installed. When there is a contradiction between ordinary steel bar and corrugated pipe, the position of steel bar should be moved appropriately, and the positioning steel mesh should be installed accurately to ensure the accurate position of pipeline.
(2) Concrete pouring and curing: When pouring concrete, the construction shall be carried out in strict accordance with the specification requirements. Before the initial setting of the first layer of concrete, the second layer of concrete should be poured to ensure that there is no cold joint between layers. The vibrating of concrete should be carried out in strict accordance with the scope of action of the vibrator to prevent leakage, under-vibration and over-vibration. When the prestressed pipe or steel bar is dense and the gap is small, it should be equipped with a 30-type small-diameter internal vibrator. When vibrating, steel bars shall not be dragged or collided with prestressed pipes or steel bars. Control slump and workability of concrete.
Prestressed pipeline layout and beam penetration
Prestressed pipes are metal bellows. In the process of manufacture and installation, be careful not to deform and crack the bellows, and ensure the size. Then, arrange the bellows according to the positions shown in the design drawings and fix them with positioning ribs. The laid pipeline must be smooth and free from bending angles, and the bellows should be provided with exhaust holes at the highest position.
Prestressed construction
(1) Pre-stressed tensioning equipment shall be calibrated before use, and the linear regression equation of oil pump shall be determined, and the pressure gauge reading shall be calculated according to the pulling force of jack. During construction, double control shall be implemented, with oil gauge reading as the main factor and elongation value as the auxiliary factor.
(2) Tension of prestressed tendons: both tension and elongation are controlled, mainly tension, and the difference between actual elongation and calculated elongation is controlled within 6%. When tensioning, the concrete strength must reach 100% of the design strength.
(3) Grouting: Before grouting, fill the tunnel with water, check whether the tunnel is unblocked and wet the bellows. Pure cement slurry is used for tunnel grouting, and the cement grade is 52.5#. Before use, it must be screened and a certain amount of expansive agent is added to make the cement slurry expand without shrinking.
(4) Beam cutting and anchor sealing: After the steel strand bundle is grouted to strength, the beam cutting must be sawed by a grinder, and any prestressed steel bar cannot be cut by electric arc. Before sealing the anchor, the anchorage should be cleaned and roughened, and then the steel mesh should be arranged according to the drawing requirements, and the anchor sealing concrete should be poured.
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