Construction method of cast-in-situ box girder in complex terrain

Abstract

The application discloses a kind of complex terrain cast-in-place box girder construction methods, belong to building construction field, comprising: with the through core rod that penetrates pier column as support, main cross beam is set on the through core rod, and bailey beam is set on cross beam, and scaffold is set on bailey beam and constructs support system, finally builds formwork and completes the pouring of box girder;The through core rod is provided with two upper and lower rods, and a support limiting device is arranged between the upper and lower through core rods for limiting support, and the support limiting device and the through core rod are fixed in a non-welding manner, and are fixed with the main cross beam in a welding manner.The method of the application uses the through core rod+bailey piece+disc type scaffold as the support system to replace the conventional full-frame support and steel pipe column scheme, without setting up full-frame support and steel pipe column support, saving time, speeding up construction progress, reducing the risk of support installation and removal, reducing material and personnel investment, and having strong practicality for cast-in-place box girder construction with a span of not more than 25m, especially in mountainous areas, with obvious cost reduction and efficiency improvement.

Description

Technical Field

[0001] This invention relates to the field of building construction technology, and more specifically, to a method for constructing cast-in-place box girders in complex terrain areas with small spans of no more than 25m, complex topography, and difficult foundation treatment. Background Technology

[0002] Currently, cast-in-place box girders are generally constructed using the full-span scaffolding method or the steel pipe column scaffolding method both domestically and internationally. This method is generally suitable for areas with flat terrain or high pier heights. Compared to mountainous areas, construction is more difficult and costly in complex terrain areas such as steep slopes, and there is a greater risk of scaffold collapse. On the other hand, the progress is slower, and more materials are used when the construction period is tight. At the same time, there is a greater safety risk when dismantling the scaffolding. Summary of the Invention

[0003] To address the aforementioned problems, this invention provides a method for constructing cast-in-place box girders in areas with small spans of no more than 25m, complex terrain, and difficult foundation treatment.

[0004] To achieve these objectives of the present invention, the present invention provides a method for constructing cast-in-place box girders in complex terrain, comprising:

[0005] The support system is constructed by using a through-bar that runs through the pier column as a support, setting the main crossbeam on the through-bar, setting Bailey beams on the crossbeams, setting scaffolding on the Bailey beams, and finally setting up the formwork to complete the casting of the box girder.

[0006] The core rod consists of two rods, upper and lower, with a support and limiting device between them for limiting and supporting. The support and limiting device is fixed to the core rod in a non-welding manner, but to the main crossbeam in a welding manner.

[0007] Preferably, in the construction method of cast-in-place box girder in complex terrain, the axes of the upper and lower core rods are vertically aligned.

[0008] Preferably, in the construction method of cast-in-place box girder in complex terrain, holes are pre-reserved on the piers, and the diameter of the holes is 0.1 to 10 mm larger than the diameter of the mandrel.

[0009] Preferably, in the construction method of cast-in-place box girder in complex terrain, a steel mesh is added around the pier hole to enhance the strength around the hole after the pier is poured.

[0010] Preferably, in the construction method of cast-in-place box girder in complex terrain, the support limiting device includes: a support body, a limiting groove, and a sleeve; the limiting groove is fixed on the top of the support body, the limiting groove has a groove portion for accommodating the through rod, the groove portion is tightly fitted with the through rod, the sleeve is fixed on the bottom of the support body, the sleeve has a clamping portion, the clamping portion is locked with the through rod by a locking bolt.

[0011] Preferably, in the construction method for cast-in-place box girders in complex terrain, the groove has a structure with a large opening and a small bottom.

[0012] Preferably, in the construction method of cast-in-place box girder in complex terrain, the support limiting device is fixed to the main crossbeam by welding with baffles, and the baffles are located on both sides of the through rod.

[0013] Preferably, in the construction method of cast-in-place box girder in complex terrain, the main crossbeam is set on the through rods on both sides of the pier and is close to the pier. Connecting channel steel is erected between the main crossbeams, and the connecting channel steel fixes the main crossbeam to form a stable structure.

[0014] Preferably, in the construction method of cast-in-place box girder in complex terrain, multiple connecting channel steels are provided, which are located on both sides of the pier to clamp the pier.

[0015] Preferably, the construction method for cast-in-place box girders in complex terrain specifically includes:

[0016] Foundation construction; installation of core beams; installation and reinforcement of main beams; installation of transverse distribution beams; erection of disc-type scaffolding; installation of bottom and side formwork; scaffolding protection erection; scaffolding pre-stressing; formwork installation, pouring and post-construction management.

[0017] The present invention has at least the following beneficial effects:

[0018] The construction method for cast-in-place box girders in complex terrain of the present invention does not require the erection of full-span scaffolding and steel pipe column supports. Therefore, it can save time and greatly accelerate the construction progress of cast-in-place box girders. It reduces the risks of scaffolding installation and dismantling, while reducing the input of materials and personnel. It also reduces the foundation treatment procedures and related costs required for erecting full-span scaffolding and steel pipe column supports. It is highly practical for the construction of cast-in-place box girders with a span of no more than 25m, and is particularly effective in reducing costs and increasing efficiency in mountainous areas.

[0019] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure constructed from the through-core bar, main crossbeam, and Bailey beam described in this invention.

[0021] Figure 2 This is a front structural diagram of the support and limiting device of the present invention supporting the crossbeam.

[0022] Figure 3 This is a side view of the support and limiting device of the present invention supporting the crossbeam.

[0023] Figure 4 This is a front structural diagram of the support and limiting device described in this invention;

[0024] Figure 5 This is a side view of the support and limiting device described in this invention.

[0025] Figure 6 This is a process flow diagram of the construction method for cast-in-place box girder in complex terrain as described in this invention;

[0026] Figure 7 This is a reference image of the actual object of the support and limiting device described in this invention when it is supported by the upper and lower through rods;

[0027] Figure 8 This is a physical reference drawing of the connecting channel steel as described in this invention being erected between the main crossbeams;

[0028] Figure 9 This is a reference image of the actual object after the through-core bar, main crossbeam, and Bailey beam described in this invention have been assembled. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to examples, so that those skilled in the art can implement it based on the description.

[0030] It should be noted that, unless otherwise specified, the experimental methods described in the following implementation plan are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified.

[0031] The technological principle of this invention is as follows: construction preparation → measurement and positioning → construction of strip foundation for side span support → installation of core rods for pier columns → erection of crossbeams → installation of Bailey bridge panels → installation of disc-lock scaffolding → installation of box girder bottom and side formwork → erection of support protection → pre-stressing of support → unloading of support → adjustment and installation of box girder bottom and side formwork → acceptance of box girder bottom and side formwork → processing and installation of bottom and web reinforcement → installation of inner formwork → pouring and curing of the first layer of concrete → binding of top reinforcement → pouring of the second layer of concrete → curing → removal of end formwork and loosening of inner formwork → dismantling of scaffolding → removal of bottom formwork → removal of Bailey bridge panels and steel bars → construction of the next section. Specifically, as follows... Figure 6 As shown.

[0032] The core components are: 1. Foundation construction; 2. Installation of the core beam; 3. Installation of the double I56b main crossbeams; 4. Installation and reinforcement of Bailey beams; 5. Installation of transverse distribution beams; 6. Erection of disc-type scaffolding; 7. Installation of bottom and side formwork; 8. Erection of scaffolding protection; 9. Pre-stressing of scaffolding; 10. Formwork installation, pouring, and post-construction management.

[0033] Conventional full-span scaffolding and steel pipe column scaffolding methods face challenges in complex terrain construction, including high construction difficulty, high cost, high risk, slow progress, tight schedule, large material input, and significant safety risks when dismantling scaffolding.

[0034] The core of this invention lies in providing a construction method using a support system of core rods, main beams, Bailey bridge panels, and disc-lock scaffolding to replace the conventional construction methods described above. Unlike conventional full-span scaffolding and steel pipe column scaffolding, the load-bearing terminal of this invention is the core rod. Ensuring sufficient support and safety for the core rod is paramount. This invention employs a non-welding connection method for the structure connecting to the core rod, while using welding or other methods to fix the structure to the main beam, ensuring structural stability without damaging the core rod. A support limiting device is also designed to limit the support of the core rod and fix its connection to the main beam, resulting in high construction efficiency and distributed upper pressure to the core rod.

[0035] Example 1

[0036] Taking the design of the cast-in-place box girder at the Dashuigou Interchange of the Menglu Expressway as an example, the construction method of the cast-in-place box girder in complex terrain according to the present invention includes:

[0037] I. Foundation Construction

[0038] (1) Foundation treatment. After the excavator has excavated to the required position, a foundation bearing capacity test shall be conducted. The foundation at the abutment must be built on a stable and reliable foundation. The bearing capacity of the natural foundation can be determined by a penetration test. The design bearing capacity is 220 kPa. If the bearing capacity of the foundation on site does not meet the requirements, special replacement treatment must be carried out on the foundation. Stone slag from the tunnel excavation shall be used for replacement. Only after the requirements are met can the foundation concrete be poured.

[0039] (2) Foundation construction. The strip foundation of the side span support adopts a reinforced concrete enlarged foundation of 1.5×0.8×n C30 reinforced concrete, ensuring that the foundation thickness is not less than 60cm (n is the beam width) as a load-bearing platform with the main crossbeam.

[0040] (3) After the foundation treatment is completed, a 40×30cm drainage ditch is set around the foundation. For the slope, a water interception ditch and a water diversion channel should be set up. Pay attention to keeping the drainage smooth to ensure that rainwater is discharged in time and avoid rainwater soaking the foundation, which will reduce the bearing capacity of the foundation and endanger the safety of the support. It is strictly forbidden to form water accumulation in the construction site, which will cause uneven settlement of the foundation, cause the support to become unstable, and lead to safety hazards and accidents.

[0041] II. Installation of the through rod

[0042] During pier construction, pre-drilled holes according to the design positions of the support structure. After the concrete reaches the design strength, a tower crane or crane is used to insert Φ130mm mandrels into the holes and lock them in place. Two mandrels are used for each pier. Preferably, mandrels of other diameters can be used instead, provided that the load-bearing and safety requirements are met. Preferably, the diameter of the pre-drilled hole is 0.1 to 10 mm larger than the diameter of the mandrel. This facilitates the insertion of the mandrel, prevents the mandrel from arching inside the pier due to an excessively large hole, and also facilitates the installation of the support and limiting device between the upper and lower mandrels. Preferably, the axes of the two mandrels for each pier are aligned vertically, meaning that the projections of the two mandrels in the vertical direction should overlap as much as possible, ensuring that the two mandrels bear the load. Preferably, steel bars are used for the mandrels.

[0043] Meanwhile, to ensure the impact of the through-hole rod on the concrete, steel mesh is added around the through-hole rod, especially at the top and bottom, to strengthen the structural strength around the pier hole. The steel mesh has a diameter of 20mm and a spacing of 20cm×20cm.

[0044] Preferably, a support and limiting device is provided between the upper and lower mandrels. The support and limiting device is connected to the upper and lower mandrels in a non-welding manner to avoid damage to the mandrels caused by welding.

[0045] like Figures 1-5 As shown, the support limiting device 10 includes: a support body 101, a limiting groove 102, and a sleeve 103; the limiting groove 102 is fixed to the top of the support body 101, and the limiting groove has a groove portion 104 for accommodating the through rod 40. Preferably, the groove portion has a larger opening and a smaller bottom structure, and the groove portion fits tightly with the through rod 40. The sleeve 103 is fixed to the bottom of the support body 101, and the sleeve has a clamping part 105. The clamping part 105 and the through rod 40 are locked together by a locking bolt 107. Figure 1 and 2 As shown, after the main crossbeam 30 is mounted on the through-bar, the support limiting device 10 is welded and fixed to the main crossbeam using the baffle 108. This ensures that all structures connected to the through-bar are connected in a non-welding manner, while all structures connected to the main crossbeam are fixed by welding. This not only meets the fixing requirements and strength requirements, but also effectively protects the through-bar and avoids damage to the through-bar caused by welding.

[0046] III. Installation of Double I56b Main Crossbeams

[0047] like Figures 1-5As shown, a main crossbeam 30 is installed at the top of the mandrel 40 of the pier column. The main crossbeam 30 is made of double-splittered I56b I-beams, placed opposite each other on both sides of the pier column 20. The main crossbeam 30 is placed directly on the upper mandrel 40. At the same time, 10cm connecting channel steel 60 is used to horizontally weld the main crossbeams 30 on both sides of the pier column 20 firmly to form a stable structure. Figure 3 As shown, the connecting channel steel 60 overlaps between the double-I-beam main crossbeams 30, and both ends are welded and fixed. On the one hand, it pulls the main crossbeams tightly against the pier column, and on the other hand, the connecting channel steel 60 can prevent the main crossbeams from moving, forming a stable structure. Preferably, multiple connecting channel steels 60 are provided.

[0048] like Figures 1-5 As shown, a baffle 108 is welded to each edge near the edge of the main crossbeam 30 of the I-beam. The baffle is welded and fixed to the support limiting device 10 to prevent the main crossbeam 30 of the I-beam from moving. The main crossbeam mainly distributes the upper load to the through rod 40 on the pier column and also bears the force. The main crossbeam 30 should be installed tightly against the pier column 20 without gaps.

[0049] As can be seen, in the installation of the aforementioned mandrels and main crossbeams, a support and limiting device 10 is used to support and limit the upper and lower mandrels. The pressure of the upper structure is borne by the upper and lower mandrels. The support and limiting device 10 is not fixed by welding, but by the limiting groove and sleeve in the support and limiting device 10. This allows for quick adjustment and installation, and avoids welding damage to the mandrels. The support and limiting device 10 is fixed to the main crossbeam by welding. For example, the baffle 108 welds the main crossbeam 30 to the support and limiting device 10. The double main crossbeams are fixed by welding the connecting channel steel, thereby ensuring structural stability. The combination of the above methods provides a stable and safe supporting foundation for the cast-in-place box girder.

[0050] in, Figure 7 Reference image showing the limiting device 10 supported by the upper and lower through rods; Figure 8 Reference image showing the connection of the 60mm channel steel between the main crossbeams.

[0051] IV. Bailey Beam Installation and Reinforcement

[0052] The Bailey bridge uses single-layer reinforced Bailey panels, with 12-26 rows arranged laterally, with row spacing of 90cm and 45cm. Each row is connected by standard connectors, and the longitudinal arrangement is based on the span of the box girder. The Bailey panels are connected laterally by matching support frames at 3m above and below the longitudinal direction, so that the Bailey panels are connected as a whole and the stress on each row of Bailey panels is relatively balanced.

[0053] Bailey panels are assembled on-site. Before assembly, the Bailey panels must be carefully inspected for any damage. Any damaged panels must not be used.

[0054] The Bailey beam is fixed to the main crossbeam using 10-type steel or U-shaped saddle-shaped retaining devices.

[0055] First, assemble the Bailey bridge panels on the ground according to the designed number of panels, and connect them in groups. Two vertical supports are installed between each group of Bailey beams to form a Bailey bridge frame. For example... Figure 1 As shown, the positions of each group of Bailey bridges 50mm apart are marked with paint on the main crossbeam of the I-beam according to the design spacing. The connected Bailey bridges are then hoisted into place by tower crane / crane in the order of the middle and then the two sides. After hoisting, their positions are checked and the elevation of the top surface of the Bailey bridge is measured.

[0056] Figure 9 Reference image showing the assembly of the core beam, main crossbeam, and Bailey beam.

[0057] V. Installation of transverse distribution beams

[0058] A transverse distribution beam is installed on the top of the Bailey bridge. After the Bailey bridge is installed, I18 I-beams are used as transverse distribution beams. The longitudinal spacing is 90cm in the standard section and 60cm in the transition section and the solid section on the pier top, which serve as the foundation for the adjustment support. The transverse distribution beams are fixed to the Bailey bridge with U-bolts to prevent slippage.

[0059] VI. Erection of Disc-lock Scaffolding

[0060] This example uses a variable cross-section box girder, with adjustable elevations for the flanges and transverse and longitudinal slopes achieved using disc-lock steel pipe scaffolding. Φ60×3.2mm disc-lock steel pipe scaffolding is erected on the I18 I-beam transverse distribution beams as a support structure, with adjustable top and bottom supports installed. The standard spacing of the scaffolding along the bridge direction is 0.9m / section, 0.6m / section for the transition sections of the box girder and the solid sections at the pier top, and 0.6m / section at the web in the transverse direction, and 0.9m elsewhere. The horizontal bar spacing is 1.2m / section. The top horizontal bar spacing should be one disc-lock distance less than the maximum spacing, and the free length at the top should not exceed 20cm. The bottom longitudinal and transverse horizontal bars serve as ground bracing, with a height of 30cm from the top surface of the transverse distribution beams. The longitudinal and transverse bars at both ends of the scaffolding are securely supported on the piers using wooden blocks. The crossbeams on the top supports are I12 I-beams. Considering the overall stability of the support structure, diagonal steel pipe shear bracing is arranged in both the longitudinal and transverse directions.

[0061] Using a position 1m from both ends of the I12 I-beam's top supporting beam as the centerline, lay 1m wide and 5cm thick wooden planks longitudinally to serve as the operating platform for guardrail installation and box girder formwork assembly. After the operators fasten their safety belts, install a row of steel pipe guardrails at the ends of the I-beams using φ48×3.5mm steel pipes, with a height of 120cm and a longitudinal spacing of 100cm.

[0062] VII. Installation of bottom and side molds

[0063] All formwork uses 15mm thick bamboo plywood with panel dimensions of 1.2m × 2.4m to accommodate the spacing of the uprights. I12 I-beams are used horizontally on the top support, with the spacing of the horizontal I-beams matching the spacing of the uprights along the bridge direction. Longitudinal beams are made of 10*10cm square timber spaced 30cm apart. Panels are nailed directly to the longitudinal square timber. When nailing the panels, each panel should be rolled from one end to the other to ensure a flat surface. The web beams use 6*8cm square timber spaced 20cm horizontally and 10*10cm square timber spaced 60cm vertically (same as the longitudinal step distance of the scaffolding).

[0064] After the timber is laid, the top elevation of the timber is measured and the scaffold supports are adjusted to ensure that the elevation of each point on the timber along the bridge direction matches the design value. Using a total station, the edge line of the box girder bottom formwork is marked on the timber along the bridge direction (considering the thickness of the side formwork). The bottom formwork is laid using bamboo plywood, the side formwork is erected, the planar position and bottom elevation of the wing plates are measured, and the side formwork frame is installed. The web and wing plate side formwork templates are fixed to 6cm×8cm square timber along the transverse bridge direction, with a spacing of 20cm between the timbers; then, they are fixed to 10cm×10cm square timber placed vertically and horizontally along the bridge direction, with a spacing of 60cm between the vertical and horizontal timbers.

[0065] All timber joints should be staggered and rest on the top support; suspended installation is strictly prohibited. If it is impossible to rest on the top support, place 15×15cm square timber shims at the joint locations for reinforcement. The formwork is fixed to the small square timber ribs with round nails. During installation, each base board is connected longitudinally and transversely with sponge strips and secured with screws. After the base formwork is laid, remove any exposed sponge strips from the base board surface. The formwork surface should be smooth and flat, with joints no larger than 1mm to ensure joint quality.

[0066] During formwork fabrication, the formwork can be divided into sections according to the box girder's alignment and width, thereby improving the efficiency of formwork use. After the bottom formwork of the support frame is laid, the center and corner positions of the bottom formwork of the box girder and the cross-sectional positioning of the beam are measured and marked. The bottom formwork elevation = design beam bottom elevation + support frame elastic deformation value + (± adjustment amount for previous construction errors) is used to control the erection of the bottom formwork. After the bottom formwork elevation and alignment adjustment are completed and approved by the supervisor, the side formwork and flange plate formwork are erected, and the plane position and bottom elevation of the flange plate are measured and marked (the calculation and determination method for the bottom formwork elevation of the flange plate is similar to that of the box girder bottom plate). Sponge strips are pasted at the joints between the side formwork and the bottom formwork to prevent grout leakage.

[0067] 8. Scaffolding and protective erection

[0068] To ensure civilized construction on site, safety protection measures are required on the scaffolding. These measures utilize a combined protective structure of safety netting and partitions, with a height of 1.2m. Partitions are installed on both sides of the roadside protective shed's scaffolding for isolation and protection against falling objects. All other adjacent edges are fully enclosed with dense mesh netting, the height of which increases accordingly with the scaffolding's erection height, and should be kept within 2m of the top of the scaffolding.

[0069] Combined staircases were installed at both ends of the bridge near the passageway to allow people to go up and down the bridge.

[0070] 9. Preloading of the support

[0071] To ensure construction safety and improve the quality of cast-in-place beams, preloading is applied to the support structure after the box girder support frame is erected and the bottom formwork is laid. The purpose of preloading is as follows:

[0072] First, it verifies whether the bearing capacity of the support and foundation meets the stress requirements and the overall stability of the support; second, it eliminates the inelastic deformation of the support and foundation; and third, it obtains the elastic deformation value of the support as one of the bases for the reserved arch during construction, while measuring the foundation settlement to provide empirical data.

[0073] 10. Formwork installation, pouring, and post-construction management

[0074] The process includes: unloading the support frame → adjusting and installing the bottom and side formwork of the box girder → accepting the bottom and side formwork of the box girder → processing and installing the bottom and web reinforcement → installing the inner formwork → pouring and curing the first layer of concrete → tying the top reinforcement → pouring the second layer of concrete → curing → removing the end formwork and loosening the inner formwork → dismantling the scaffolding → dismantling the bottom formwork → dismantling the Bailey bridge panels and steel bars. Among these:

[0075] (1) The coarse and fine aggregates, cement, and water-based admixtures used in the beam concrete must all meet the technical specifications.

[0076] (2) During concrete mixing, the moisture content of the aggregates should be measured periodically or at any time (especially on rainy days). When the moisture content changes significantly, the frequency of measurements should be increased, and the water and aggregate dosages should be adjusted promptly based on the test results. When mixing high-performance concrete, fine aggregates, cement, and mineral admixtures should be added to the mixer first, and after mixing evenly, water should be added and mixed into mortar. Then, admixtures should be added to the mixer, and after thorough mixing, coarse aggregates should be added and mixed evenly. The mixing time for each of the above feeding stages should not be less than 30 seconds, and the total mixing time should not be less than 3 minutes.

[0077] (3) The concrete transport equipment ensures continuous pouring operations, and its transport capacity is appropriately matched with the mixing capacity of the mixing equipment. Ensure the transport equipment is leak-proof and watertight. During concrete transport, maintain the uniformity of the concrete, preventing stratification, segregation, and leakage. Pumping construction ensures continuous and uniform material supply.

[0078] (4) Before pouring, carefully check the position, quantity, and tightness of the protective layer spacers. The size of the protective layer spacers ensures the accuracy of the reinforced concrete protective layer thickness, and their shape (I-shaped or conical) facilitates the positioning of the reinforcing bars. Mortar spacers are not used. The concrete pouring temperature should be adjusted according to the air temperature, generally not exceeding 25℃. For structures with a minimum cross-sectional dimension of 300mm or more, the concrete pouring temperature should be reduced as much as possible. When constructing under negative temperature conditions, the concrete pouring temperature should generally not be lower than 12℃. Control the temperature difference between the freshly poured concrete and the adjacent hardened concrete medium to not exceed 20℃.

[0079] (5) The prestressed concrete beams are cast in one go using a fast, stable, continuous and reliable casting method.

[0080] When using an immersion-type high-frequency vibrator, use vertical point vibration. The vibration time at each point should be based on whether the surface is covered with slurry or no large air bubbles appear, and should generally not exceed 30 seconds to avoid over-vibration.

[0081] (6) After the concrete is vibrated, the exposed concrete surface should be covered immediately, and appropriate heat preservation and moisture retention measures should be taken in a timely manner to cure the concrete.

[0082] (7) For concrete structures using formwork curing, ensure that the concrete at the formwork joints does not lose moisture and dries out. After the freshly poured concrete has been vibrated for 24–48 hours and its strength has developed to the point where it has no adverse effect on the structural safety, the formwork can be slightly loosened, and the concrete can be watered and cured for at least 7 days. For structures with large exposed surfaces, after vibration, the exposed concrete should be smoothed immediately, covered with geotextile, straw mats, etc., and then promptly treated with water spraying and other moisturizing measures for at least 14 days to reduce the exposure time of the concrete and prevent excessive evaporation of surface moisture. After the concrete is demolded, the exposed concrete should be quickly covered with geotextile, straw mats, etc., and effective measures should be taken to ensure that the concrete surface remains moist. Then, the geotextile, straw mats, and other moisturizing materials should be properly wrapped with plastic sheeting or canvas. The protective coverings should be intact, with good overlap, and have condensation on their inner surfaces. During concrete curing, select representative structures for temperature monitoring, regularly measure the core temperature and surface temperature of the concrete, as well as environmental parameters such as ambient air temperature, relative humidity, and wind speed, and adjust the curing regime in a timely manner according to changes in concrete temperature and environmental parameters, strictly controlling the temperature difference between the inside and outside of the concrete to meet the requirements of the specifications.

[0083] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Further modifications can be readily implemented by those skilled in the art.

Claims

1. Construction method for cast-in-place box girder in complex terrain, where complex terrain refers to steep slopes in mountainous areas with small spans not exceeding 25m, characterized by... include: The support system is constructed by using a through-bar that runs through the pier column as a support, setting the main crossbeam on the through-bar, setting Bailey beams on the crossbeams, setting scaffolding on the Bailey beams, and finally setting up the formwork to complete the casting of the box girder. The through rod is provided with two rods, upper and lower, and a support and limiting device is provided between the upper and lower through rods for limiting and supporting. The support and limiting device is fixed to the through rod in a non-welding manner, and fixed to the main crossbeam in a welding manner. The support limiting device includes: a support body, a limiting groove, and a sleeve; the limiting groove is fixed to the top of the support body, the limiting groove has a groove portion for accommodating the through rod, the groove portion is tightly fitted with the through rod, and the sleeve is fixed to the bottom of the support body, the sleeve has a clamping part, the clamping part is locked with the through rod by a locking bolt. The groove has a structure with a large opening and a small bottom; The support limiting device is fixed to the main crossbeam by welding with baffles, which are located on both sides of the through bar. The main crossbeams are correspondingly installed on the through bars on both sides of the pier and are close to the pier. Connecting channel steel is laid between the main crossbeams, and the connecting channel steel fixes the main crossbeams to form a stable structure. Multiple connecting channel steels are installed, located on both sides of the pier to clamp the pier.

2. The construction method for cast-in-place box girders in complex terrain as described in claim 1, characterized in that, The axes of the upper and lower mandrels are vertically aligned.

3. The construction method for cast-in-place box girder in complex terrain as described in claim 1, characterized in that, The pier has pre-drilled holes, the diameter of which is 0.1 to 10 mm larger than the diameter of the mandrel.

4. The construction method for cast-in-place box girders in complex terrain as described in claim 1, characterized in that, A steel mesh is added around the pier column hole to enhance the strength around the hole after the pier column is poured.

5. The construction method for cast-in-place box girders in complex terrain as described in claim 1, characterized in that, Specifically, it includes: Foundation construction; installation of core beams; installation and reinforcement of main beams; installation of transverse distribution beams; erection of disc-type scaffolding; installation of bottom and side formwork; scaffolding protection erection; scaffolding pre-stressing; formwork installation, pouring and post-construction management.

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