Large-span door type bent cap construction technology

Abstract

The invention belongs to the technical field of capping beam construction, and particularly discloses a large-span door type capping beam construction technology which is used for a capping beam with the span larger than 50 m and comprises the steps that a vertical foundation support is assembled on an existing structure; a support is erected on the periphery of the existing structure, a supporting mechanism is arranged at the bottom of the support and forms a stress face, and when the supporting mechanism is stressed to rotate, bending moment force generated by concentrated stress in the supporting mechanism is released; integrally hoisting the pre-assembled steel truss to a preset bent cap; and layered pouring is conducted on the steel truss hoisted to the preset bent cap, so that bent cap construction is completed. The vertical support is directly arranged on the existing structure, so that the reliable transmission of the load of the upper structure is realized; through the arrangement of the supporting mechanism, flexible adjustment of the elevation of the support is achieved, and the construction efficiency is remarkably improved; through the free rotation effect of the stress surface, the bending moment is prevented from being transmitted to the foundation, the stress performance of the support is effectively improved, and the overall design of the steel support is further optimized.

Description

Technical Field

[0001] This invention relates to the technical field of portal girder construction, and more particularly to the construction process of large-span portal girder construction. Background Technology

[0002] In existing technologies, the construction of ultra-long span portal girder (typically 50m in diameter) crossing existing drainage channels and main traffic arteries presents significant challenges. Specifically, during construction, the existing methods for splicing the steel structure within the girder typically involve assembling individual members into a steel support frame in mid-air. This process is cumbersome, time-consuming, and carries substantial risks associated with working at height. Furthermore, ensuring the safe passage of existing roads below during construction places high demands on construction organization and safety measures, making implementation difficult.

[0003] During construction, the entire cap beam concrete was approximately 900m³. 3 However, the concrete pouring window is only 4 hours. In current construction, when the volume of concrete is large and the pouring time window is limited, if a one-time overall pour is adopted, it not only places high demands on the concrete supply capacity, but is also limited by the site conditions, making construction organization more difficult. Summary of the Invention

[0004] The purpose of this invention is to provide a construction process for large-span portal girder bridges to solve the above-mentioned technical problems.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions.

[0006] Construction technology for large-span portal girder cap beams, used for cap beams with spans exceeding 50m, including... The vertical foundation supports the assembly of the existing structure; A support frame is erected around the existing structure. The bottom of the support frame is equipped with a support mechanism, which forms a force-bearing surface. When the support mechanism rotates under force, it releases the bending moment force generated by the concentrated stress in the support mechanism. The pre-assembled steel truss is hoisted as a whole to the pre-set cap beam; The steel truss, which is hoisted at the pre-set cap beam, is poured in layers to complete the cap beam construction.

[0007] Furthermore, the vertical foundation support includes a support foundation constructed by inserting reinforcing bars pre-embedded in the pile cap.

[0008] Furthermore, the support foundation is constructed along the height direction of the pier cap, forming a foundation support surface higher than the ground elevation.

[0009] Furthermore, the support mechanism is a screw jack, and at least two screw jacks are provided at the bottom of the support mechanism, with the two screw jacks symmetrically arranged on the vertical foundation support.

[0010] Furthermore, from top to bottom, the screw jack includes an upper nut, an adjusting nut, and a lower nut in sequence. The upper nut, adjusting nut, and lower nut are connected by a screw. It also includes a base connected to the lower nut by a bolt. A curved surface structure forming the force-bearing surface is provided between the lower nut and the base.

[0011] Furthermore, the curved surface structure is an arc-shaped structure, which forms a symmetrical structure with the bolt as the axis of symmetry, and the bottom of the arc-shaped structure abuts against the base.

[0012] Furthermore, the construction of supports around the existing structure specifically includes frame assembly and support assembly, wherein the supports form assembly grooves along the outer side of the frame for assembling and overlapping the cap beam frame.

[0013] Furthermore, the frame assembly includes a lower frame assembly and an upper frame assembly, wherein the upper frame overlaps the lower frame and extends to form an upper support.

[0014] Furthermore, during the bracket assembly, the lower bracket is inserted through the slot formed by the upper bracket and then assembled with the lower frame, so that the upper and lower brackets and the upper and lower frames form an integrated structure.

[0015] Furthermore, the layered pouring specifically includes at least three pours, and the pouring thickness of the second pour is less than the pouring thickness of the first and third pours.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: In this invention, for the construction of steel supports that cross roads, the scattered steel components are assembled into an integral steel truss in advance on the ground, and then the steel truss is hoisted into place in one go using a double-machine lifting method, so as to reduce high-altitude assembly operations and the occupation of existing road traffic.

[0017] This invention effectively solves the problems of difficulty and complexity in pouring large volumes of concrete in a limited time by using layered pouring. It ensures both concrete pouring quality and construction safety while simplifying on-site construction organization and improving construction efficiency. The layered concrete pouring method in this invention uses the concrete poured in the first stage as a support system for subsequent pours, further reducing the amount of steel structure support needed and lowering project costs. Furthermore, it avoids the construction difficulties associated with large-volume pouring in one go, simplifying on-site operations and improving construction efficiency.

[0018] In this invention, a spiral jack is installed at the bottom of the support to enable rapid adjustment of the support elevation; the jack has a curved structure that allows it to rotate freely under load, thereby effectively releasing bending moment and preventing bending moment from being transmitted to the foundation. Attached Figure Description

[0019] Figure 1 A flowchart of the construction process for large-span portal girder provided by the present invention; Figure 2 An assembly diagram of the bracket and cap beam provided by the present invention; Figure 3 A schematic diagram of the frame assembly provided by the present invention; Figure 4 This is a schematic diagram of the steel truss series structure provided by the present invention; Figure 5 This is a schematic diagram of the steel truss series lifting structure provided by the present invention; Figure 6 Assembly diagram of the vertical foundation support and support mechanism provided for this invention; Figure 7 The vertical foundation support and the cross-sectional view of the assembled support mechanism provided by the present invention; Figure 8 A schematic diagram of the support mechanism provided by the present invention; Figure 9 A plan view of the steel truss hoisting provided by the present invention; Figure 10 An elevation view of the steel truss hoisting system provided by this invention; In the picture: 100. Vertical foundation support; 110. Existing structure; 120. High-strength bolt; 200. Bracket; 210. Frame; 300. Support mechanism; 310. Load-bearing surface; 320. Upper nut; 330. Adjusting nut; 340. Lower nut; 350. Screw; 360. Bolt; 370. Base; 400. Steel truss. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, it should be noted that these embodiments are not intended to limit the present invention. Equivalent changes or substitutions in function, method, or structure made by those skilled in the art based on these embodiments are all within the scope of protection of the present invention.

[0021] Existing construction techniques typically require the addition of temporary vertical support units to support the load of the superstructure. However, this method is not only complex to construct but also necessitates the construction of additional temporary support foundations, leading to extended construction periods and increased costs. The large-span portal girder construction technique of this invention utilizes a permanent structural foundation, directly placing vertical supports on the foundation to achieve reliable load transfer from the superstructure. By fully utilizing the permanent structural foundation as the support base, this invention avoids the construction of temporary vertical support foundations, significantly saving construction time and costs while improving construction efficiency.

[0022] See attached document Figure 1-10 As shown, the construction process for large-span portal girder in this embodiment is used for girder spans exceeding 50m, and specifically includes the following construction steps: 1) Assembly of vertical foundation support 100 on existing structure 110; 2) A support 200 is erected on the outer periphery of the existing structure 110. The support 200 has a support mechanism 300 at its bottom. The support mechanism 300 forms a force-bearing surface 310. When the support mechanism 300 is rotated under force, the bending moment force generated by the concentrated stress in the support mechanism 300 is released. The pre-assembled steel truss 400 is hoisted to the pre-set cap beam. At this time, the support mechanism 300 will be subjected to downward pressure, which will cause stress concentration. However, the generation of the stress-bearing surface 310 reduces stress concentration and other problems.

[0023] Finally, the steel truss 400, which is hoisted at the pre-set cap beam, is poured in layers to complete the cap beam construction.

[0024] Specifically, in this embodiment, the specific vertical foundation support 100 is a support foundation constructed by inserting reinforcing bars pre-embedded in the foundation. At this time, it is connected with the structure pre-embedded in the existing structure 110 to form a permanent structure, which can reliably transmit force in the future.

[0025] The entire support foundation is constructed from a position below the ground elevation, and then a foundation support surface above the ground elevation is formed along the height direction of the pier cap. This type of support foundation has sufficient height to ensure support.

[0026] Preferably, the support mechanism 300 is a screw jack, and at least two screw jacks are provided at the bottom of the support mechanism, with the two screw jacks symmetrically arranged on the vertical foundation support 100.

[0027] See attached document Figure 8 As shown, from top to bottom, the screw jack includes an upper nut 320, an adjusting nut 330, and a lower nut 340. The upper nut 320, adjusting nut 330, and lower nut 340 are connected by a screw 350. It also includes a base 370 connected to the lower nut 340 by a bolt 360. A curved surface structure forming the force-bearing surface 310 is provided between the lower nut 340 and the base 370.

[0028] In the specific design, the curved surface structure is an arc-shaped structure, which forms a symmetrical structure with the bolt as the axis of symmetry, and the bottom of the arc-shaped structure abuts against the base 370. At this time, since it is a helical jack, it will rotate under force, and drive the curved surface to rotate, so as to relieve the excessively concentrated stress.

[0029] A support frame 200 is erected around the existing structure, specifically including the assembly of the frame 210 and the support frame 200. The support frame 200 forms an assembly groove along the outer side of the frame 210 for the assembly and overlapping of the cap beam frame. The subsequent assembly is then completed through the assembly groove.

[0030] Because the entire support frame is quite long (200mm), it is divided into upper and lower frames. The assembly process includes the assembly of the lower frame and the assembly of the upper frame. The upper frame is attached to the lower frame and extends to form an upper support. The extended upper support provides space and support for the subsequent assembly of the steel truss.

[0031] Furthermore, during the bracket assembly, the lower bracket is inserted through the slot formed by the upper bracket and then assembled with the lower frame, so that the upper and lower brackets and the upper and lower frames form an integrated structure.

[0032] To avoid temperature control and shrinkage cracking problems caused by pouring a large volume of concrete at once, the layered pouring specifically includes at least three pours, and the thickness of the second pour is less than the thickness of the first and third pours.

[0033] For the pouring of cap beams, if a large volume of concrete is poured in one go (such as a total height of 5m), a large amount of steel structure is often required as temporary support, which leads to a significant increase in steel consumption. This not only increases construction costs but also brings great difficulty to the design and construction of temporary structures.

[0034] The layered casting method in this invention employs a 2m+1m+2m layered casting approach. By using the 2m of concrete structure already cast in the first layer as the supporting structure for the second and third layers, the reliance on steel structure supports is reduced. This invention significantly reduces the amount of temporary steel structure supports while ensuring structural safety and stability, thus lowering project costs. Simultaneously, it avoids the construction difficulties associated with large-volume single-casting, simplifying on-site operations and improving construction efficiency.

[0035] For the support mechanism, the existing process mainly involves setting up a sand cylinder to adjust the elevation of the support. When the support is dismantled, sand is released to reduce the height of the support and to achieve demolding. (In actual operation, the sand inside the sand cylinder is squeezed and becomes extremely dense, which makes it difficult to release the sand smoothly, thus making it impossible to achieve the purpose of dismantling the support and demolding.)

[0036] This invention addresses the problems of inconvenient elevation adjustment and easy transfer of bending moment to the foundation under stress in existing support structures, resulting in insufficient structural load-bearing capacity. It proposes an improved support structure. This invention incorporates a screw jack at the bottom of the support for convenient and rapid elevation adjustment. The jack has a curved surface structure that allows free rotation under stress, effectively releasing bending moment. Through the screw jack, this invention achieves flexible elevation adjustment, significantly improving construction efficiency. The free rotation of the curved surface structure prevents the transfer of bending moment to the foundation, effectively improving the load-bearing capacity of the support and further optimizing the overall design of the steel support.

[0037] Existing construction methods typically involve assembling individual steel supports piece by piece in the air, a cumbersome and time-consuming process with significant risks associated with working at heights and substantial disruption to existing traffic. In contrast, the steel truss in this invention employs a single-span structure to minimize traffic disruption caused by intermediate supports. Furthermore, steel components are pre-assembled into a single steel truss structure on the ground, and then hoisted into place entirely using a dual-crane lifting system. In actual construction, the ground-based assembly and dual-crane hoisting significantly reduce aerial work time and construction risks; it also avoids the prolonged traffic congestion caused by traditional segmented assembly, effectively improving construction efficiency and minimizing traffic impact. This invention reduces road impact by pre-assembling individual steel components into a steel truss on the ground, and then hoists the entire truss into place entirely using a dual-crane lifting system. Through optimization, aerial work time is significantly shortened, construction risks are reduced, and the overall hoisting avoids the prolonged traffic congestion caused by traditional segmented assembly, effectively improving construction efficiency and minimizing traffic impact. Existing layered pouring techniques primarily focus on construction organization considerations such as temperature control and concrete supply for large-volume concrete, without fully utilizing the existing concrete structure formed during the layered pouring process as a load-bearing system for subsequent construction. This invention employs a 2m+1m+2m layered pouring method. After the first 2m thick layer of concrete is poured and reaches its design strength, the embedded permanent prestressed tendons are tensioned. Simultaneously, by rotating jacks at the bottom of the support frame, the frame is lowered and separated from the bottom surface of the first poured concrete. This ensures that during the second concrete pour, the load is no longer transferred to the support frame but is directly borne by the already formed concrete structure. The same principle applies to the third pour. Compared to existing technologies, this invention significantly reduces reliance on temporary steel structure supports by using the first poured concrete as the support system for subsequent pours. Furthermore, the combination of tensioning the permanent prestressed tendons and separating the support frame by the jacks avoids additional loads on the support frame, improves the rationality of structural stress, reduces construction risks, and effectively saves on steel structure usage and construction costs.

[0038] The existing layered pouring process is mainly based on construction organization considerations such as temperature control and concrete supply for large-volume concrete, and does not make full use of the concrete structure formed during the layered pouring process as a load-bearing system for subsequent construction.

[0039] The bracket elevation adjustment and bending moment release in this invention are achieved by setting a spiral jack at the bottom of the bracket to enable rapid adjustment of the bracket elevation; the jack has a curved surface structure that allows it to rotate freely when under force, thereby effectively releasing the bending moment and preventing the bending moment from being transmitted to the foundation.

[0040] The permanent structural support platform of this invention places the vertical support directly on the permanent structural support platform, and uses the platform to reliably transfer the load of the superstructure to the foundation, thereby avoiding the need to set up an additional temporary vertical support foundation.

[0041] The layered pouring process in this invention adopts a 2m+1m+2m layered pouring method. After the first 2m of concrete is poured and reaches the design strength, the pre-embedded permanent prestressed tendons are tensioned; at the same time, by rotating the screw jack, the support is lowered and separated from the bottom of the concrete, thereby ensuring that the subsequent concrete load is completely borne by the poured concrete structure, reducing the need for temporary support of the steel structure.

[0042] In this embodiment, the entire construction process is as follows: Assembly of support frames located on the outside of supporting piers or columns; Several steel trusses that form the cap beam frame are lifted from the processing area and moved to the area below the cap beam to be constructed. Several of the aforementioned steel trusses were hoisted in series to the location of the steel beam to be constructed; Layered pouring.

[0043] The construction process in this invention is as follows: The installation of the supporting steel frame near the bridge piers should be carried out on a stable ground surface and in a safe working area. Ensure that work access and lifting areas are obstructed, and keep away from the hoisting area when installing the supporting steel frame near the bridge piers. Perform boom lifting operations on stable ground conditions and in a safe working area to avoid mechanical collisions during operation.

[0044] Before further lifting operations, conduct a pre-inspection of the fixed steel frame section. Use a boom lift to perform a proper assembly check. Always adhere to safe practices for working at heights.

[0045] All steel truss sections should be placed near the assembly operation area. Maintain the stability of the crane. Maintain close supervision and conduct a pre-inspection of the steel truss sections before lifting operations. Use safe passageways for appropriate lifting operations. A pre-inspection of the steel truss sections was conducted before the lifting operation. The lifting team conducts a pre-lifting operation summary, and the LS and WSHC / QPS conduct a post-lifting operation check, closely monitoring and coordinating the placement of the steel truss. In this embodiment, the boom is used to continue securing the steel truss to the steel frame. A final check of the safety platform is performed before releasing the LG. The boom is used to continue securing the balance bolts and check that these bolts secure the steel truss to the steel frame. No loose items should be left on the steel truss.

[0046] In this invention, a cofferdam or frame structure is first fitted onto the outside of the column, and then the upper frame structure of the column is fitted on top, with a support frame installed at the top of the frame structure. The support frame is then inserted through the upper frame structure and into the lower support frame, forming an integral unit with the upper support frame. The cap beam frame is then lifted and hoisted to the ground, and the two frames of the cap beam are spliced ​​together. The cap beam frame is then lifted again and placed on the support frame, and then adjusted so that its top is aligned. Finally, it is lowered from top to bottom until aligned, completing the assembly.

[0047] In this invention, the ultra-long span portal-type cap beam (span exceeding 50m) crosses an existing drainage channel and a main traffic artery, making construction organization quite difficult. The countermeasures include: optimizing the construction process by using layered pouring to reduce the amount of steel used in the cast-in-place supports; and actively communicating with road management departments to close roads during support installation and concrete pouring to minimize disruption to public transportation.

[0048] Results: Risk assessment was conducted in advance, and optimization measures were proposed; smooth construction was ensured through 3D technology briefing; structural safety was ensured through PE design and design acceptance; I09 and I13 have been successfully completed.

[0049] In this embodiment, it is applied to a project in Singapore, and the details are as follows: In highway reconstruction and expansion projects and urban rail transit construction, large-span portal girder bridges spanning existing roads are widely used due to their reasonable structural stress distribution and good clearance conditions. For this type of structure, various mature construction technologies have been developed both domestically and internationally, such as full-span scaffolding cast-in-place construction, steel pipe column support systems, and segmented cantilever construction, and related research results are also quite abundant.

[0050] However, in urban built-up areas with high traffic levels, dense underground pipelines, and the need to maintain 24-hour road access, the aforementioned traditional techniques often fail to meet actual needs in terms of road occupation, construction window, and safety risk control. This is especially true in regions like Singapore, where the requirements for traffic impact, construction safety, and local compliance are extremely strict, further limiting their applicability.

[0051] In this project, the portal girder of pier I13 in the elevated subway structure crosses the main road of the industrial zone. The road is busy with traffic and has a dense network of underground municipal pipelines, and temporary supports in the middle of the road are not allowed during construction. How to safely and efficiently complete the construction of the large-span portal girder while ensuring that the permanent structure participates in the load-bearing capacity is a key technical problem that urgently needs to be solved in this project.

[0052] This subway project is a municipal project independently undertaken by the applicant in Singapore, using a design-build contracting model. Throughout the design, construction, and acceptance processes, European standards and the relevant local construction standards of the Singapore Land Transport Authority (LTA) were strictly adhered to.

[0053] The elevated section of this project comprises 39 cap beams, mainly of three structural types: I-type, T-type, and portal type. The cross-sectional width is 3.4m or 4m, and the cross-sectional height varies from 2.4m to 6m. Due to limitations imposed by the subway track layout and ground road conditions, pier I13 utilizes a prestressed concrete portal cap beam. This portal cap beam is approximately 17m above ground, 58.434m long, 3m wide, and 5m high, spanning the existing main road of the industrial area. The structural type is as follows... Figure 1 As shown. Due to limitations imposed by surface traffic and underground pipeline conditions, conventional ground-supported scaffolding cannot be used for construction.

[0054] First, an analysis of the project's characteristics and challenges.

[0055] Pier I13's portal-type cap beam spans a busy main road in an industrial zone. This section has a dense network of municipal utility pipelines beneath it (including water supply, drainage, electricity, gas, and communication lines), creating a complex underground space. Furthermore, ensuring uninterrupted road traffic during construction was crucial. Due to these limitations, traditional monolithic cast-in-place support systems were not feasible.

[0056] The cap beam is designed to be 5.0m high. If a one-time integral cast-in-place solution is adopted, the temporary steel structure support system will be huge. Not only will the installation and dismantling of the supports be difficult and the construction space be limited, but it will also significantly extend the road occupation construction time, increase the disturbance to existing pipelines and the risk of damage to their protection, and greatly increase the difficulty of construction safety and organization.

[0057] Meanwhile, during road crossing construction (such as scaffold installation and dismantling, concrete pouring, etc.), traffic control or even full road closures are required. To ensure traffic safety during operations, it is often necessary to apply for 24-hour road closures, which will have a significant impact on the operation of main roads, resulting in extremely high pressure on construction coordination and traffic management.

[0058] Second, process selection.

[0059] Before finalizing the construction plan, the project team comprehensively considered the structural characteristics of the portal girder, existing road traffic conditions, and local management requirements, and systematically compared and analyzed the feasibility of various common construction plans.

[0060] (1) Option 1: Full-span scaffolding integral cast-in-place scheme The proposed solution involves deploying dense ground-supported scaffolding within the road area to complete the overall concrete pouring of the cap beam in one go. This method is mature, the structural stress path is clear, and construction control is relatively simple. However, this project is situated beneath a busy industrial zone's main road with numerous underground municipal pipelines, making ground-supported foundation implementation difficult. Furthermore, the construction period would require prolonged full-width road closures, significantly impacting traffic flow and posing substantial safety and social risks, thus failing to meet local approval and implementation requirements.

[0061] (2) Option 2: Steel structure support scheme with temporary piers at mid-span This proposed solution shortens the calculated span of the support structure by setting temporary steel supports at the mid-span of the portal girder, which can reduce the amount of steel used and improve construction efficiency and safety to some extent. However, the construction conditions for the foundations of the temporary supports are limited due to the intersecting layout of various underground pipelines such as gas, electricity, and communications, resulting in high implementation risks. Furthermore, the temporary supports occupy the roadway for extended periods, significantly impacting traffic flow, increasing the difficulty of construction coordination and the pressure on safety management, thus rendering the overall feasibility insufficient.

[0062] (3) Option 3: Single-span steel structure support system + layered casting scheme (adopted scheme) Considering factors such as safety, feasibility, and traffic impact control, a single-span steel structure support system combined with a layered pouring construction scheme was ultimately adopted. This scheme places the support system foundation directly on a permanent abutment, avoiding the need for temporary supports within the road area, and achieves a gradual transition of the structural load-bearing system through layered pouring and staged prestressing tensioning. While ensuring structural safety and construction quality, it minimizes the impact on existing road traffic and underground pipelines, offers flexible construction organization, high feasibility for local approval, and demonstrates good engineering applicability and technical rationality. For details of the support system, please refer to [link to details]. Figure 2 .

[0063] Main process principle: (1) Single-span steel structure support system A single-span steel structure support system is adopted to avoid interference with road traffic and underground pipelines caused by intermediate piers. The support system foundation is directly arranged on the permanent abutment, allowing the load of the superstructure to be reliably transferred through the permanent structure. This scheme makes full use of the bearing capacity of the abutment, eliminates the construction of temporary vertical support foundations, significantly shortens the construction period, reduces construction costs, minimizes disturbance to roads and underground spaces, and makes the construction organization simpler and more efficient.

[0064] (2) Layered pouring construction process The cap beam has a total height of 5m and is constructed using a layered pouring method of "2m+1m+2m". After the first 2m of concrete is poured, prestressing is applied to form an independently load-bearing structural unit, which serves as the load-bearing support for the subsequent two layers. This process effectively distributes the structure's self-weight and construction load, reduces reliance on temporary steel supports, and lowers the amount of steel used and the project cost. Simultaneously, it avoids the temperature control and shrinkage cracking problems associated with large-volume concrete pouring in one go, making the construction process more controllable and flexible, significantly improving overall construction efficiency and safety.

[0065] (3) Adjustment of support elevation and optimization of stress design.

[0066] A spiral jack is installed at the bottom of the 200mm support frame for convenient and quick adjustment of the frame's elevation. The jack features a curved surface design, allowing free rotation under load, thus effectively releasing bending moments. The spiral jack enables flexible adjustment of the support frame's elevation, significantly improving construction efficiency; simultaneously, it prevents the transfer of bending moments to the foundation, effectively improving the support frame's load-bearing capacity and further optimizing the overall design of the steel support.

[0067] (4) Overall hoisting construction process.

[0068] The main truss spanning the road (i.e., steel truss 400) was installed using a dual-crane hoisting process. By assembling the entire structure on the ground and then hoisting it in one go, the high-altitude assembly time can be significantly shortened, reducing the risks associated with high-altitude construction. Compared to traditional segmented assembly methods, this process minimizes traffic closure time, reduces the impact on existing roads, and improves construction safety and organizational efficiency.

[0069] Third, construction techniques.

[0070] First, key technologies.

[0071] 1. Key technologies for foundation construction.

[0072] The I13 portal girder is 58.4m long, with a single concrete pour volume of approximately 350m³ and a weight of approximately 870t. To ensure effective load transfer from the superstructure and reduce the adverse impact of the support foundation on roads and underground pipelines, the support system foundation is arranged on a permanent pile cap.

[0073] During the substructure construction phase, reinforcing bars are pre-installed in the foundation and the support base is constructed simultaneously, serving as the support node for the subsequent steel structure support system. To ensure the adjustable elevation and stable stress of the support system, 120 M30 8.8 grade high-strength bolts are pre-embedded in the top of the temporary supports (i.e., vertical foundation support 100) to fix the screw jacks. The screw jacks, as important adjustment components of the support system, can achieve rapid and precise elevation adjustments. Simultaneously, a curved structure (i.e., load-bearing surface 310) is installed between the jack nut and the base. When the superstructure (i.e., the entire support 200) transmits vertical loads accompanied by bending moments, the curved structure can adaptively rotate, effectively releasing the bending moment and preventing it from being directly transmitted to the jack body and the lower foundation.

[0074] This structural design can effectively reduce the adverse effects of localized stress concentration on the jack, significantly reduce the risk of deformation or damage under bending conditions, further ensure the overall stability and construction safety of the support system, improve the stress adaptability and durability of the jack, and extend its service life.

[0075] Key technologies for scaffold installation and construction: Adjust the adjusting nut 330 in the rotating jack (i.e., support mechanism 300) to adjust the screw jack to the design elevation. With the assistance of the crane, assemble the individual components of the steel support into small units and install them sequentially around the pier to form the entire support 200. At this point, all nodes of the steel support (i.e., support 200) are connected by bolts for easy installation.

[0076] Due to road traffic constraints, the main truss spanning the road could not be assembled piece by piece in the air to form a whole. To ensure construction safety and work efficiency, a construction process of "ground assembly + dual-machine lifting and installation" was adopted. The main truss spanning the road was pre-assembled into a whole on the ground and then lifted into place in one go by a large-tonnage truck crane.

[0077] To reduce the risk of component misalignment caused by uneven foundation settlement, a 300mm thick crushed stone cushion layer was laid and compacted in the assembly area, followed by a 100mm concrete cushion layer and precise leveling, providing a stable operating surface for the overall assembly of the truss.

[0078] The truss assembly proceeds in the order of "lower chord → web members → upper chord," and is completed piece by piece with the assistance of cranes and aerial work platforms. During assembly, the node bolts are tightened to the specified torque as required by the design to ensure reliable node connections and initial structural stability.

[0079] Due to site constraints, the main truss, after being assembled on the ground, was lifted and installed using a combination of a 750t and a 900t heavy-duty truck crane. Before lifting, the foundation of the lifting operation area was replaced and compacted in layers according to the design and relevant specifications to form a support platform that meets the requirements for operation of ultra-heavy-tonnage lifting equipment.

[0080] The hoisting operation adopted a "single command, unified command" organizational model, with the general commander coordinating all operations. Each of the two cranes was equipped with a dedicated driver and signalman. During the hoisting process, the difference in lifting speed and displacement between the two cranes was strictly controlled to ensure balanced stress and stable posture of the truss. After the truss was in place, the two cranes simultaneously lowered their hooks at low speeds to achieve precise docking between the truss and the steel structure of the piers on both sides. Fine adjustments were made to the spatial posture to align the bolt holes at the nodes and meet the design tolerances. Subsequently, the bolts were pre-tightened to create a stable temporary fixed state for the structure.

[0081] After confirming that all node connections are reliable and the structure is stable, the crane lifting force is gradually reduced and the rigging is removed. Then, all node bolts are tightened to the final tightening torque value according to the design specifications to ensure connection quality.

[0082] After the support system is installed and its planar position, elevation, and stability are verified, the bottom formwork system is installed on top of it. During the bottom formwork installation, the design drawings are strictly followed to ensure sufficient rigidity, integrity, and resistance to deformation. After acceptance, the subsequent structural construction procedures begin.

[0083] Key technologies for layered pouring construction.

[0084] To reduce the amount of steel structure support and lower the construction difficulty, the cap beam adopts a construction process that combines layered casting (i.e., the top, middle, and bottom layers are 2m + 1m + 2m thick) with staged prestressing tensioning. After the first layer of concrete is poured and prestressed, it forms a structural unit with independent load-bearing capacity, serving as the main force system for the subsequent two layers of concrete construction, thus achieving reasonable transfer of construction loads and structural system transformation.

[0085] After the bottom formwork is laid out and accepted, the structural boundary lines are laid out according to the design drawings. The coordinates of the axis, boundary lines, and key control points are strictly controlled to provide accurate control benchmarks for the installation of reinforcing steel and the prestressed system. Subsequently, the steel reinforcement binding, prestressed duct laying, and embedded part installation are carried out sequentially. During the steel reinforcement binding process, the spacing between steel bars and the thickness of the protective layer are carefully controlled. The prestressed ducts are laid out strictly according to the designed curve, with a focus on checking their smoothness, the position of the limiting bars, and the sealing of the joints to prevent leakage or displacement of the ducts during concrete pouring. All types of embedded parts are positioned, reinforced, and verified as required to ensure construction stability.

[0086] After the above procedures are completed and passed inspection, the side formwork system is installed. The flatness, verticality, and overall alignment of the formwork are strictly controlled, and supports, tie rods, and back braces are installed according to calculation requirements to ensure that the formwork system has sufficient rigidity, strength, and overall stability during the concrete pouring stage. After the formwork passes inspection, the first layer of concrete is poured. During the pouring process, the principle of layered mortar application and layered vibration is followed to ensure the concrete is compacted. Deformation monitoring of the steel support system is conducted throughout the process to prevent excessive deformation.

[0087] After the first layer of concrete reaches the designed tensile strength, prestressing tensioning is carried out. Before tensioning, a comprehensive inspection is conducted on the concrete strength, component alignment, prestressing duct unobstructedness, and the condition of tensioning equipment such as anchors, jacks, and pressure gauges to ensure that all conditions meet design and specification requirements. During tensioning, the principles of "symmetry, gradation, and phased application" are strictly followed, with loading performed according to the designed tension force and sequence. A dual control method using tension force and strand elongation is employed to ensure the accuracy and consistency of prestressing application. Once the tension stress reaches the design control value and the measured elongation meets the allowable deviation range specified in the specification, the anchoring is completed, and the condition of the anchors and exposed strands is verified.

[0088] To ensure that the loads from the subsequent second and third floor concrete construction are effectively transferred to the already load-bearing first floor structure, screw jacks installed at the bottom of the steel support system are used to lower the entire support system, gradually unloading the steel support and completing the load transfer from the temporary support to the already tensioned concrete structure. Subsequently, following the construction process of the first floor, the second and third floor concrete structures are constructed sequentially until the overall cap beam structure is formed.

[0089] Key technologies for scaffold removal: Due to space constraints imposed by the existing cap beams and the influence of existing road traffic, the conventional reverse construction method could not be used during the support dismantling phase of the cross-road steel truss, i.e., the entire truss could not be moved and withdrawn to the construction site using a dual-crane lifting system. To achieve safe and efficient transfer of the steel truss under confined space conditions, this project adopted a comprehensive construction process of "dual-crane lifting + self-propelled modular transport vehicle (SPMT) transfer" to move the main cross-road truss as a whole to a designated area within the site.

[0090] During the truss lowering phase, a 750t and a 700t heavy-duty truck crane were used for joint lifting. After the two cranes completed hooking and assuming load, the connection points between the steel truss and the original support system were sequentially released to ensure complete separation of the steel truss from the support system. Under the unified command of the general manager, the two cranes lowered the steel truss synchronously, smoothly detaching it vertically from the original support system. Under strict control of its posture and the balance of force at the lifting points, it was precisely placed onto the pre-arranged and leveled self-propelled modular transport vehicle (SPMT) platform.

[0091] After the steel truss is positioned, it is locked in place using specialized connection structures and temporary fixing devices to ensure the overall stability of the structure and transportation equipment during transport. After verifying the connection status, component posture, and transportation system operating parameters, the SPMT (Special Purpose Transporter) is manipulated to transfer the entire steel truss to the construction site along a predetermined path. Using the SPMT's built-in hydraulic jacking system, the steel truss is then smoothly lowered onto pre-arranged temporary supports, achieving a transition from transport to temporary support. This process, combining heavy-duty lifting operations with modular transportation technology, effectively solves the challenges of dismantling and transporting steel trusses crossing roads in confined spaces, while simultaneously ensuring the safety of existing road traffic.

[0092] After the steel truss was stabilized on the temporary supports, the truss members were dismantled in the order of "upper chord → web members → lower chord" using cranes and aerial work platforms. The dismantling process strictly adhered to the principle of symmetrical operation to prevent overall instability. The steel supports around the pier were also gradually dismantled using the same process until the support system was completely removed.

[0093] Construction effect: The large-span portal girder of Pier I13 adopted a comprehensive construction technology of "single-span steel structure support system + layered casting + overall hoisting and modular transportation". The construction was successfully completed under complex traffic and confined space conditions, achieving good technical and social results.

[0094] (1) Construction safety has been significantly improved No temporary supports were installed in the middle of the road during the entire construction process, avoiding disturbance to the existing road structure and underground municipal pipelines, and effectively reducing the safety risks of construction across the road. In key processes such as steel support installation, layered concrete pouring, and support removal, the structural stress path was clear and the stress system transformation was controllable. No abnormal structural deformation or safety accidents occurred during construction, ensuring the safety of traffic on the road below.

[0095] (2) Minimize the impact on existing traffic By employing SPMT (Special Material Handling) technology for the overall ground assembly of the main truss across the road, simultaneous installation using dual-machine lifting, and dismantling of the scaffolding, the time spent on high-altitude operations and traffic closures was significantly reduced. During construction, road traffic control was only implemented for short periods during two key hoisting phases, with each closure lasting less than 6 hours. Compared to traditional full-span scaffolding solutions, this is expected to reduce road occupancy time by approximately 70%, effectively ensuring the smooth operation of the main roads in the industrial zone.

[0096] (3) Construction efficiency and economy are significantly improved. By using layered casting and changing the load-bearing system, the amount of temporary steel structure used is reduced by about 35% compared to the overall cast-in-place scheme; the amount of high-altitude assembly work is reduced by about 60%; and the overall construction period is shortened by about 45 days, resulting in significant comprehensive economic benefits.

[0097] (4) Good structural quality and molding effect During the layered pouring of the cap beam, deformation monitoring throughout the process and dual-controlled prestressing tensioning ensured that the structural alignment and stress state met design and specification requirements. The concrete appearance quality was good, with no obvious cracks or defects, the prestressing system functioned normally, and the overall structural load-bearing performance was reliable.

[0098] Engineering practice has shown that the construction technology system proposed in this paper effectively solves the key engineering problems of "how to construct safely, how to reduce traffic impact, and how to control the scale of temporary structures" for large-span portal girder under complex traffic conditions, and achieves comprehensive optimization of safety, quality, schedule and social benefits.

[0099] In this embodiment, in response to the engineering challenges such as crossing existing busy roads, limited construction space, and high safety requirements, a construction technology system of "single-span steel structure support system + layered pouring and staged prestressing tensioning + overall hoisting and SPMT transportation" was systematically summarized and applied.

[0100] Engineering practice results show that by using permanent foundations as the basis for temporary support systems and adopting a construction approach of layered pouring and gradual conversion of the load-bearing system, the scale of temporary supports can be effectively reduced, and the impact on existing roads and underground pipelines can be minimized. By combining overall hoisting with modular transportation, the installation and dismantling of cross-road steel trusses can be completed safely and efficiently under confined space conditions, significantly improving construction safety and organizational efficiency.

[0101] This construction technology system has not only achieved good results in engineering implementation, but also provided a replicable and scalable technical path for the construction of large-span portal girder bridges under complex traffic conditions, and has high engineering application and research value.

[0102] The detailed descriptions listed above are merely specific descriptions of feasible embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. All equivalent embodiments or modifications made without departing from the spirit of the present invention should be included within the scope of protection of the present invention.

[0103] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0104] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A construction process of a large-span portal roof beam, used for a roof beam with a span of more than 50 m, characterized in that, The utility model relates to a vertical foundation support assembly on the existing structure, The support is arranged on the periphery of the existing structure, and the bottom of the support is provided with a support mechanism forming a stress surface. The steel truss is hoisted and assembled to the preset cap beam. The steel truss hoisted on the preset cap beam is poured in layers to complete the cap beam construction. The vertical foundation support comprises a support foundation constructed by a reinforcing bar embedded in the pile cap.

2. The long-span portal roof beam construction process of claim 1, wherein, The support foundation is constructed along the height direction of the pile cap to form a foundation support surface higher than the ground level.

3. The long-span portal roof beam construction process of claim 2, wherein, The support mechanism is a screw jack, and the bottom of the support mechanism is provided with at least two screw jacks symmetrically arranged on the vertical foundation support.

4. The long-span portal roof beam construction process of claim 1, wherein, From top to bottom, the screw jack comprises an upper nut, an adjusting nut and a lower nut connected by a screw rod, and further comprises a base connected to the lower nut by a bolt.

5. The long-span portal roof beam construction process of claim 4, wherein, The curved surface structure is an arc structure, and the arc structure forms a symmetrical structure with the bolt as the symmetrical axis.

6. The long-span portal roof beam construction process of claim 5, wherein, The arc structure bottom abuts against the base.

7. The long-span portal roof beam construction process of claim 1, wherein, The support arranged on the periphery of the existing structure comprises a frame assembly and a support assembly.

8. The long-span portal roof beam construction process of claim 7, wherein, The frame assembly comprises a lower frame assembly and an upper frame assembly, and the upper frame is arranged on the lower frame and extends to form an upper support.

9. The long-span portal roof beam construction process of claim 8, wherein, In the support assembly, the lower support is inserted into the through slot formed by the upper support and is combined with the lower frame assembly, so that the upper and lower supports and the upper and lower frames form an integrated structure.

10. The long-span portal roof beam construction process of claim 1, wherein, The pouring in layers comprises at least three times of pouring, and the pouring thickness of the second time of pouring is less than that of the first and third times of pouring.

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