Feb. 3rd, 2024
The precision of segmental bridge construction: How to turn prefabricated beams section by section into a fully completed bridge or road? This is a magic and mystery that you can’t imagine. Huadacrane will professionally reveal the secrets for you!
First, Segmental bridge construction requires assembling segmental beams together.
1. Precast beam splicing process:
① Prepare the concrete segmental beams corresponding to the type and size requirements. The bridge prefabricated parts designed by Huadacrane based on the actual conditions of the construction site have excellent stability and seismic performance.
②Transportation of segmental beams: After placing the precast beams in the beam yard to dry, a special straddle carrier that can match the beam shape, load-bearing capacity, and is friendly to the beams needs to be used to transport the precast beams to a suitable lifting point. Convenient for launching gantry and lifting beams.
③ Stacking of segmental beams: The stacking of segmental beams must follow the correct method to avoid damage to the beams. Segmental beams must be stacked in a manner that avoids warping and secondary stress. The floor can provide good support for the segments; the segments should be braced below and close to the webs, and the tops should be placed when stacking. The weight of the segment is directly transmitted by the web, avoiding bending of the top and bottom plates to transmit force.
④Adjust to the best bridge position:Due to the heavy weight of concrete precast beams, the precast site for concrete segmental beams is generally selected close to the bridge location, and a tire-type gantry crane, beam transport vehicle or beam transport rail car is used to transport it to the bridge location for assembly.
⑤ Segmental beam assembly: Different construction projects will use different assembly methods.
2. Here are six assembly methods for detailed introduction
a. Full-hall support method
A large number of formwork supports are required during construction. Bridge concrete is poured on the supports. The formwork and supports are removed after the concrete reaches strength. The biggest advantage of this method is that it does not require large-scale hoisting equipment. The disadvantage is that the support formwork used for construction is large in consumption and the construction period is long, which has great limitations for bridges and high piers in mountainous areas.
b. Less-support method
This method corresponds to the first method, but because the full-hall support method requires the treatment of the entire foundation under the bridge, it is more expensive and has a long construction period. Therefore, if conditions permit, the segments can generally be lengthened to reduce the use of formwork brackets and be assembled with fewer brackets.
c. Span-by-span assembly method
This method means that the bridge superstructure is erected in one direction and completed one span at a time. Before prestressing is applied, the prestressed segments are temporarily supported by lower or upper cantilever beams. The erected main beam can be simply supported on the piers, or several holes can be connected into a continuous structure through post-tensioning.
This method is suitable for prestressed concrete simply-supported girder bridges with small and medium spans, internal and external hybrids, and continuous girder bridges that are simply supported and become continuous span-by-span. The main equipment of the construction method is a steel truss guide beam with a length less than (or greater than) twice the standard span length, a lifting flat car, guide beam traveling and adjustment equipment, and other equipment.
If the segments are located under the guide beam and assembled by hanging, the bridge erecting machine is called an upper guide beam bridge erecting machine; if the segments are located above the guide beam and assembled by support, the bridge erecting machine is called a lower guide beam bridge erecting machine. machine; the guide beam will bear the weight of one span of prefabricated segments.
d. Balanced cantilever method
This method is to assemble segmental beams in a symmetrical sequence with a pier as the center. Each segment beam is integrated with the previously installed segment beam, balancing itself and serving as the assembly foundation for the next segment beam. For each construction step, the cantilever structure ensures its safety and stability by tensioning prestressed steel tendons set in the box girder segments. The segmental beams can be hoisted by bridge deck supporting cranes, guide beams or ground cranes. This method is suitable for cantilever construction, medium and large span internal and external mixed prestressed concrete bridges.
e. Cantilever assembly method
The general method is to use a simple device that moves on the cantilever of the assembled structure to ensure the lifting, translation and assembly of the segments; the lifting equipment is installed on a flat car, and the flat car runs on the bridge deck track. This method is suitable for cantilever construction of medium- and large-span bridges.
f. Cable hoisting method
A construction method that uses suspended cables to transport and install components. This method is generally suitable for the construction of arch ribs or beams of arch bridges and main beams of suspension bridges.
3. What is the installation method of prestressed steel bars?
Externally prestressed steel strand bundles usually use HDPE pipes as the outer casing. In order to arrange the steel strands neatly inside the outer casing and to make it possible to adjust and replace individual steel strands, the method of single-strand installation in sequence should be adopted.
4. How to adjust and replace prestressed tendons?
1) When the tension of the external prestressed tendons needs to be adjusted, the protective cover can be removed, the anti-corrosion grease can be removed, a special jack can be used to tension or loosen the steel strand, and then the protective cover can be reinstalled and filled with anti-corrosion grease;
2) When the external prestressed steel bars need to be replaced, use a special connector to connect the new and old steel strands, pull out the old steel strands, pull in the new steel strands, then tension, reinstall the protective cover, and fill with anti-corrosion grease .
5. There are three commonly used processing methods for expansion joints and segmental joint splicing methods:
1) Dry joints without treatment;
2) Glue joints coated with epoxy resin;
3) Wet joints poured with cement concrete.
Wet joints are mainly used to close segments or connecting sections; glue joints should be used for internal and external hybrid prestressed bridges and cyclic freeze-thaw areas. Sealing washers should be installed at the glue joints before the internal prestressed tendon pipe openings are assembled.
Second, details that should be paid attention to when assembling segments: such as the conditions and precautions for using adhesives.
1. When assembling the segments, the spatial position of the first stage should be temporarily positioned and fixed.
2. The segment matching surfaces should be pretreated in advance in the prefabrication site. After removing dust, grease and other contaminants as well as loose concrete and laitance, they should be rinsed and then dried.
3. A trial assembly should be carried out before the segments are assembled, and the quality of the segments assembled during the trial should meet the requirements of the field conditions.
4. Glued joints should meet the following requirements:
a. According to the annual temperature changes and usage environment of the construction area, appropriate adhesives should be selected through experiments and random inspections of mechanical properties and operating performance should be carried out.
b. The coating thickness of the adhesive should not exceed 3mm. Its effective working time should be determined according to the hole assembly requirements, and should be stirred evenly by machinery. Finally, it should be determined according to the product characteristics of the adhesive. In addition, it should be noted that insulation measures should be taken when using adhesives under low temperature conditions in winter.
c. The adhesive should be applied evenly and completely cover the matching surface. When applying temporary prestressing, the adhesive should be extruded across the entire cross-section of the beam, and the tunnel openings should be protected to prevent adhesive from entering the prestressed tunnel. After each segment is assembled, holes should be drilled in time.
d. The assembly of segments, temporary prestressing, fixing of segments, and removal of adhesive after shipment should be completed before the adhesive loses and changes properties.
e. When the area below the assembly and application operation is open to traffic, facilities must be installed above the driveway to prevent adhesive from dripping.
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Huadacrane's main products include
beam launcher、launching gantry、segment lifter、
straddle carrier、rubber tyred gantry crane、container straddle carrier 、travel lift、electric hoist、double/single girder gantry crane、Rail Mounted Container Gantry Craneand other products.
