Construction method of bridge tower concrete solid section

Abstract

The application discloses a construction method of a solid section of a bridge tower concrete, and belongs to the technical field of bridge construction engineering. The technical scheme aims to solve the technical problems of a complex formwork system, difficult vertical transportation of materials and cracks in mass concrete pouring in the construction of a traditional solid section of a bridge tower. The technical scheme is characterized in that: I-beams with two ends anchored to the tower wall are embedded at the top of a completed hollow section of the bridge tower as a bearing structure, a hole is reserved in the middle of the I-beam and a reinforcing treatment is performed, and then square wood and multiple layers of boards are laid on the I-beam to form a closed bottom formwork system; a three-time pouring process of concrete is adopted during construction, a thin layer is poured for the first time to form an initial bearing layer, and after the strength of the initial bearing layer reaches a standard, a second and a third thicker layer are poured, and anti-cracking and fine maintenance measures are taken during the last pouring. The method is mainly used for the construction of a solid section of a bridge tower of a large-span bridge, and can effectively guarantee the safety of the structure, simplify the construction process and improve the work efficiency.

Description

Technical Field

[0001] This invention relates to the field of bridge construction engineering technology. More specifically, this invention relates to a construction method for solid concrete sections of bridge towers. Background Technology

[0002] As the main load-bearing structure of cable-stayed bridges, the construction quality of bridge towers directly affects the overall safety and durability of the bridge. During the construction of the solid sections of bridge towers, where the cross-section transitions from hollow to solid, several long-standing technical challenges have arisen that have plagued engineering practice.

[0003] First, the bottom formwork support structure for solid concrete sections faces installation difficulties and unclear stress distribution issues. Since the solid section is typically beneath a hollow section of the bridge tower, the traditional method of direct support from below, as used in ground construction or lower sections, is not feasible. The conventional approach is to pre-embed support components at the top of the hollow section; however, overly simple designs may pose safety hazards due to the immense weight of the concrete itself, while overly complex designs significantly increase construction time and costs. More critically, reserving a vertical material transport channel for subsequent sections within this support system presents a dilemma. A separate transport channel would compromise the temporary or permanent integrity of the tower structure, and its installation and removal would be extremely inconvenient; without a channel, the efficient transport of formwork, steel, and other materials required for subsequent sections would be impossible, becoming a bottleneck restricting the construction schedule. Therefore, designing a support system that can safely bear the load of the solid section while naturally forming a passage for subsequent construction is a pressing problem to be solved.

[0004] Secondly, the issue of controlling the heat of hydration in large-volume concrete is particularly prominent in the construction of solid sections of bridge towers. Solid sections contain a large volume of concrete, falling into the typical category of large-volume concrete. The hydration process of cement releases a significant amount of heat, causing a rapid increase in the internal temperature of the concrete, while the surface dissipates heat more quickly, resulting in a significant temperature difference between the interior and surface. When this temperature difference is too large, thermal stress is generated. Once this stress exceeds the early tensile strength of the concrete, thermal cracks will occur. These cracks not only affect the durability of the structure but may even endanger its safety. Traditional curing methods focus primarily on surface insulation and moisture retention, representing passive curing with limited effectiveness in dissipating internal high temperatures. Although pre-embedded cooling water pipes are a known technical method, dynamically and precisely controlling the cooling process based on the actual development of the internal temperature of the concrete, keeping the internal and external temperature difference and cooling rate within the allowable range specified in the standards, and avoiding improper control that could lead to new shrinkage cracks, presents significant challenges in practice. This requires real-time monitoring of the concrete temperature field and the establishment of an effective feedback control mechanism.

[0005] Third, both one-time and layered pouring of solid concrete sections have inherent drawbacks. While one-time, monolithic pouring simplifies the process, the concrete's fluidity, slump loss, and the immense impact of pouring place extremely high demands on the formwork system and support structure. Furthermore, the concentrated heat of hydration from large volumes of concrete becomes more severe, making temperature control extremely difficult. Layered pouring alleviates some of these problems, but the treatment of the interfaces between layers becomes crucial. Improper interface treatment can easily create weak points, affecting the overall structural integrity. In addition, during layered pouring, the lower layer of concrete must reach a certain strength before the upper layer is poured. This involves reasonable strength assessment standards and control of the interval time. Too short a strength waiting time may damage the lower layer; too long a waiting time will affect the construction schedule, and the bonding quality between the old and new concrete may deteriorate. Therefore, determining a safe, reasonable, and efficient standard for layer thickness, interval time, and strength control is a vital step in ensuring construction quality and progress.

[0006] The aforementioned challenges are interconnected. The design of the support system affects the formation of construction access channels and load transfer paths; the selection of the pouring scheme directly relates to the hydration heat effect and construction efficiency; and the effectiveness of temperature control measures is crucial to ensuring the quality of large-volume concrete pouring. Therefore, a comprehensive construction method is needed to systematically solve these intertwined technical problems. Summary of the Invention

[0007] One objective of this invention is to provide a construction method for solid concrete sections of bridge towers, primarily used for the construction of solid sections of bridge towers in long-span bridges, which can effectively ensure structural safety, simplify the construction process, and improve work efficiency.

[0008] To achieve these objectives and other advantages of the present invention, according to one aspect of the present invention, a method for preparing a solid concrete section for a bridge tower is provided, comprising the following steps: Step 1: During the concrete construction stage of the top segment of the hollow section of the completed bridge tower, multiple I-beams are pre-embedded at the top of the segment as load-bearing structures. The two ends of the I-beams are anchored in the tower wall of the hollow section. Holes with a width of 600-700mm are reserved in the middle area of ​​the I-beams and the holes are reinforced. Horizontal square timbers are laid on top of the I-beams, with the extension direction of the square timbers perpendicular to the extension direction of the I-beams. The square timbers are fixedly connected to the I-beams using connectors. Multi-layer boards are laid on top of the square timbers to form a closed bottom formwork system. Step 2: The first pouring of solid concrete for the bridge tower is carried out on the bottom formwork system. The thickness of the first pouring of concrete is controlled to be 0.2~0.3m. The poured concrete covers the entire bottom formwork system and forms the initial load-bearing layer. Step 3: After the initial load-bearing layer concrete strength reaches 10~20MPa, set up side formwork on the initial load-bearing layer and pour the second concrete for the solid section of the bridge tower. Control the thickness of the second concrete pour to be 1.5~2.0m. The second concrete pour should be vibrated in layers, with the thickness of each layer controlled at 25~35cm, and vibrated symmetrically. Step 4: After the concrete strength of the second pour reaches 10~20MPa, the third pour of solid concrete for the bridge tower is carried out. The thickness of the third pour of concrete is controlled to be 1.8~2.2m. Anti-crack steel mesh is set on the top of the third pour of concrete. The second finishing and grouting is completed before the concrete sets. After the second finishing, the concrete is continuously cured by drip irrigation. Step 5: After the solid section is completed, the formwork and timber are hoisted to the upper working face of the bridge tower through the pre-reserved holes in the middle of the I-beam, and the subsequent bridge tower segments located above the solid section are then constructed.

[0009] Preferably, in step one, the length of the anchoring end of a single I-beam embedded in the concrete of the tower wall is 1.5~1.8m, multiple I-beams are arranged along the transverse direction of the bridge tower, the center-to-center distance between adjacent I-beams is 0.8~1.2m, and the flatness deviation of the top surface of the upper flange of the pre-embedded I-beam is controlled within 3mm.

[0010] Preferably, the specific steps for reinforcing the hole in step one are as follows: The holes are made in the middle web and lower flange of the I-beam using CNC cutting in the factory. After the holes are made, circumferentially welded closed annular stiffening ribs are used to reinforce the inner surfaces of the web and flanges around the holes. The thickness of the annular stiffening ribs is 10-12mm, and their outer contour is larger than the contour of the holes and 80-100mm wider on each side. After multiple I-beams are installed in place, the holes on all the I-beams form a continuous vertical transport channel in the transverse direction of the bridge tower. This transport channel is kept unobstructed during the first and second concrete pours of the solid section and is used to transport small materials and tools. Before the third concrete pour of the solid section, a steel cover plate is used to cover and fix the transport channel, and a crack-resistant steel mesh is laid on the cover plate to form an integral whole with the third concrete pour.

[0011] Preferably, all corners of the holes made on the I-beam are smoothly transitioned with rounded arcs, with a radius of not less than 50mm; the welds between the annular stiffening ribs and the web and flanges of the I-beams are continuous, full-penetration welds; when welding the annular stiffening ribs, the base material is preheated and a multi-layer, multi-pass welding process is used to control the interpass temperature.

[0012] Preferably, the specific steps of the multi-layer, multi-pass welding process include: The welding current for the first layer is 180~200A, the welding voltage is 22~24V, and the wire extension length is 15~20mm. Subsequent weld layers are applied using a segmented back-welding method, with each weld segment being 100~150mm long and overlapping adjacent segments by 10~15mm. After each weld layer is completed, the weld surface is ground smooth. The interpass temperature is controlled within the range of 100~200℃. The reinforcement height of the outermost weld surface is controlled within the range of 0~2mm, and the weld transitions smoothly with the base material.

[0013] Preferably, during the second and third concrete pours, a cyclic cooling curing method based on real-time temperature difference feedback is implemented, specifically including the following steps: A cooling water pipe network is embedded in the concrete casting body. The horizontal spacing of the cooling water pipes is 0.8~1.2m, the vertical spacing is 0.8~1.2m, and the inner diameter of the cooling water pipes is 25~30mm. Temperature sensor groups are embedded at different depths inside the concrete. The temperature sensor placement depths are 0.1m, 0.5m, and 1.0m from the surface of the concrete casting body, respectively. After the concrete is poured, water circulation begins to cool it. The internal temperature of the concrete is monitored in real time by temperature sensors. When the difference between the highest internal temperature and the lowest surface temperature of the concrete reaches the threshold of 20~25℃, the flow rate and velocity of the cooling water are adjusted to control the internal and external temperature difference within the range of 25℃. Cover the concrete surface with insulation material, the thermal conductivity of which should not exceed 0.05 W / (m•K), and keep the surface moist by continuously sprinkling water during the curing period.

[0014] Preferably, the circulating water cooling is divided into two continuous stages: The first stage begins after the concrete pouring is completed and ends when the highest internal temperature of the concrete reaches its peak and begins to decline. During this stage, the difference between the inlet temperature of the cooling water and the highest internal temperature of the concrete is controlled within 15℃, and the flow velocity of the cooling water in the pipe is controlled between 0.6 and 0.8 m / s. The second stage begins after the first stage ends and continues until the difference between the highest internal temperature and the surface temperature of the concrete stabilizes below 20℃. During this stage, the daily cooling rate of the highest internal temperature of the concrete is controlled within 2.0℃ / d.

[0015] Preferably, the method for controlling the daily cooling rate of the highest internal temperature of the concrete is as follows: Establish a feedback regulation logic with the highest internal temperature of concrete, the surface temperature of concrete, and the daily cooling rate as control parameters. When it is necessary to reduce the daily cooling rate, the cooling water inlet temperature is increased first according to the first preset strategy, and the adjustment range of the inlet water temperature is 2~5℃. If the daily cooling rate is still higher than 2.0℃ / d after increasing the inlet water temperature, the second preset strategy is activated to reduce the flow rate of cooling water in the pipe, with the flow rate adjustment range being 0.1~0.3 m / s; When it is necessary to increase the daily cooling rate, the cooling water inlet temperature will be reduced first according to the third preset strategy, and the adjustment range of the inlet water temperature is 2~5℃. When the daily cooling rate is still below 1.5℃ / d after lowering the inlet water temperature, the fourth preset strategy is activated to increase the flow rate of cooling water in the pipe, with the flow rate adjustment range being 0.1~0.3 m / s; After each adjustment operation, maintain the adjusted parameters for at least 6 hours until the temperature field stabilizes, then collect data again and evaluate the daily cooling rate.

[0016] Preferably, the specific process of collecting data again and evaluating the daily cooling rate after the temperature field has stabilized is as follows: After each adjustment of the cooling water inlet temperature or flow rate, a continuous monitoring program is started to record the highest internal temperature Tcmax of the concrete at 1-hour intervals. Calculate the instantaneous cooling rate Vi reflected by three consecutive monitoring data, and calculate the standard deviation σ of these three consecutive instantaneous cooling rate values; When the standard deviation σ drops below 0.1℃ / d, it is determined that the temperature field has reached a stable state, and then a formal assessment and subsequent decision-making of the daily cooling rate Vc are carried out. If the standard deviation σ still does not drop below 0.1℃ / d after 12 hours of continuous monitoring, the daily cooling rate Vc will be evaluated, and the next adjustment operation will be carried out based on the evaluation results. The instantaneous cooling rate Vi is calculated using the formula: Vi = (Tcmax(t) - Tcmax(t + Δt)) / Δt, where Δt is the time interval between two adjacent monitoring sessions.

[0017] This invention offers at least the following beneficial effects: The construction method for solid concrete sections of bridge towers described in this invention utilizes pre-embedded H-beams with reinforcing holes as an integrated load-bearing and transportation foundation. Combined with layered pouring and intelligent temperature control, this forms a safe and efficient comprehensive construction method for solid concrete sections of bridge towers. Firstly, by precisely controlling the anchorage length, spacing, and top surface flatness of the H-beams, the reliability and stability of the load-bearing system are ensured, providing a solid foundation for the superstructure construction. The holes in the middle of the H-beams are reinforced with annular stiffening ribs, and a circular transition and strict welding process are specified, effectively eliminating stress concentration and ensuring the structural integrity of the components after the holes are opened. This allows the channel to be safely used for material transportation in the early stages of construction and to be reliably closed to participate in overall load bearing in the later stages. The three-layered pouring process first forms a thin initial load-bearing layer, and then the pouring thickness is gradually increased, achieving safe and progressive load transfer. Furthermore, by controlling the layered material placement and symmetrical vibration, the density and uniformity of the concrete are ensured. To address the heat of hydration in large-volume concrete, a circulating cooling and curing system based on real-time temperature difference feedback was introduced. By precisely controlling the cooling water parameters and concrete cooling rate in stages, the internal and external temperature differences and shrinkage stress were kept within safe limits, fundamentally suppressing the formation of temperature cracks. Furthermore, by establishing a feedback regulation logic based on temperature stability and cooling rate, the temperature control process was automated and refined, ensuring the reliability of the curing effect. Finally, the materials were hoisted using a reserved vertical transport channel, significantly improving the construction efficiency of subsequent bridge tower segments. This method systematically solved key challenges in the construction of solid bridge tower segments, including support, transportation, and crack control, effectively guaranteeing project quality and construction safety.

[0018] 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. Detailed Implementation

[0019] The present invention will now be described in further detail with reference to specific embodiments, so that those skilled in the art can implement it based on the description.

[0020] It should be understood that terms such as “having,” “comprising,” and “including” as used herein do not exclude the presence or addition of one or more other elements or combinations thereof.

[0021] This invention provides a construction method for a solid concrete section of a bridge tower, comprising the following steps: Step 1: During the concrete construction stage of the top segment of the hollow section of the completed bridge tower, multiple I-beams are pre-embedded at the top of the segment as load-bearing structures. The two ends of the I-beams are anchored in the tower wall of the hollow section. Holes with a width of 600-700mm are reserved in the middle area of ​​the I-beams and the holes are reinforced. Horizontal square timbers are laid on top of the I-beams, with the extension direction of the square timbers perpendicular to the extension direction of the I-beams. The square timbers are fixedly connected to the I-beams using connectors. Multi-layer boards are laid on top of the square timbers to form a closed bottom formwork system. Step 2: The first pouring of solid concrete for the bridge tower is carried out on the bottom formwork system. The thickness of the first pouring of concrete is controlled to be 0.2~0.3m. The poured concrete covers the entire bottom formwork system and forms the initial load-bearing layer. Step 3: After the initial load-bearing layer concrete strength reaches 10~20MPa, set up side formwork on the initial load-bearing layer and pour the second concrete for the solid section of the bridge tower. Control the thickness of the second concrete pour to be 1.5~2.0m. The second concrete pour should be vibrated in layers, with the thickness of each layer controlled at 25~35cm, and vibrated symmetrically. Step 4: After the concrete strength of the second pour reaches 10~20MPa, the third pour of solid concrete for the bridge tower is carried out. The thickness of the third pour of concrete is controlled to be 1.8~2.2m. Anti-crack steel mesh is set on the top of the third pour of concrete. The second finishing and grouting is completed before the concrete sets. After the second finishing, the concrete is continuously cured by drip irrigation. Step 5: After the solid section is completed, the formwork and timber are hoisted to the upper working face of the bridge tower through the pre-reserved holes in the middle of the I-beam, and the subsequent bridge tower segments located above the solid section are then constructed.

[0022] In the above technical solution, the pre-embedded load-bearing structure can be made of hot-rolled I-beams, specifically I32b or I36a. The width of the pre-reserved hole in the middle of the I-beam can be 600 mm, 650 mm, or 700 mm. For reinforcement of the hole, it can be opened in the factory using CNC flame cutting, and stiffening ribs made of 10 mm thick Q235B steel plates can be welded circumferentially around the hole. The I-beam is assembled by anchoring both ends to the concrete wall of the top segment of the hollow section of the bridge tower, with an anchorage length of 1.5 meters. After the I-beam is installed, 100 mm × 100 mm pine square timbers are laid on the top surface of its upper flange as transverse distribution beams, with a center-to-center spacing of 0.3 meters. The square timbers and the I-beam can be fixed together using U-shaped clamps or welded short steel bars. Finally, a 18 mm thick laminated plywood panel is laid on top of the square timber as a face panel, together forming a closed bottom mold system.

[0023] The first pour of concrete can be 0.2 meters thick, using C50 micro-expansion concrete, and must cover the entire bottom formwork system. This layer of concrete must reach a strength of 10 MPa before proceeding to the next stage. The second pour of concrete can be 1.8 meters thick, poured in layers with a single layer thickness controlled at 0.3 meters, and symmetrically vibrated using an immersion vibrator to prevent formwork displacement. Once the concrete strength again reaches the 15 MPa threshold, a third pour can be made, with a thickness of 2.0 meters. The top surface of this third pour must be covered with a layer of HRB400 welded steel mesh with a diameter of 8 mm and a spacing of 100 mm × 100 mm to prevent cracking. After initial setting and before final setting, a secondary finishing process is performed using a power trowel. Immediately after finishing, cover with geotextile and use a drip irrigation curing system to keep the concrete surface continuously moist for at least 7 days. The concrete strength threshold can be determined by casting test blocks cured under the same conditions on-site and conducting pressure tests.

[0024] Once the concrete strength of the solid sections of the bridge towers reaches the design value, material hoisting can begin. The vertical transport channel is formed by the pre-drilled holes in the middle of all the I-beams running transversely through the bridge. A small winch with a rated lifting capacity of 1 ton can be used for hoisting operations, with wire ropes passing through this channel. The materials hoisted are mainly steel formwork, timber, and scaffolding used for the construction of the upper bridge tower segments. The process involves securing the materials firmly at the bottom of the solid section, then lifting them with the winch and transporting them through the channel to the working surface on top of the solid section. This process requires dedicated personnel to direct and ensure safety.

[0025] Regarding construction safety, the core of this method lies in constructing a safe and reliable load-bearing and force-transfer system. By pre-embedding I-beams anchored at both ends at the top of the hollow section of the bridge tower, and controlling the thickness of the initial concrete pour to 0.2 to 0.3 meters, this thin layer of concrete, after reaching a strength of 10 to 20 MPa, can effectively transfer the larger loads poured later (1.5 to 2.0 meters for the second pour, and 1.8 to 2.2 meters for the third) to the I-beam load-bearing structure below, and ultimately distribute them to the completed bridge tower wall. This process of pouring in three stages, allowing the lower layer to gain strength before constructing the upper layer, achieves a gradual increase and safe transfer of load, significantly reducing the instantaneous impact on the bottom support system and avoiding structural risks caused by excessive one-time loading. Simultaneously, opening holes in the middle of the I-beams and implementing rigorous reinforcement treatment, while ensuring structural integrity, provides access for subsequent construction, eliminating potential safety hazards associated with alternative access methods.

[0026] In terms of quality control, this method employs multiple control measures to address the challenges of constructing large-volume concrete. Layered pouring, combined with 25-35 cm layers of material and symmetrical vibration, effectively reduces the accumulation of shrinkage and temperature stresses in the concrete, lowering the probability of crack formation. In particular, the installation of anti-crack steel mesh at the top of the third pour and the secondary finishing before the concrete's final set further enhance the surface's crack resistance. The subsequent drip curing method keeps the concrete surface continuously moist, promoting thorough cement hydration and contributing to the long-term stable increase in concrete strength. These meticulous process requirements work together to effectively ensure the density, uniformity, and overall durability of the solid concrete sections.

[0027] In terms of operational efficiency, this method demonstrates the rationality of process transitions. The pre-reserved holes in the middle of the I-beams can be used to lift small tools in the early stages of construction. After the solid section is fully constructed, they serve as crucial vertical transport channels for directly hoisting large quantities of formwork, timber, and other reusable materials to the upper working face. This design avoids the cumbersome procedures of traditional methods, which may require the construction of external lifting equipment or repeated disassembly and reassembly of internal channels. This allows for the rapid commencement of subsequent bridge tower segment construction, shortens process transition time, and thus improves overall construction efficiency.

[0028] In other technical solutions, in step one, the length of the anchoring end of a single I-beam embedded in the concrete of the tower wall is 1.5~1.8m. Multiple I-beams are arranged along the transverse direction of the bridge tower, and the center-to-center distance between adjacent I-beams is 0.8~1.2m. After pre-embedding, the flatness deviation of the top surface of the upper flange of the I-beam is controlled within 3mm.

[0029] In the above technical solution, the length of the anchoring end of a single H-beam embedded in the tower wall concrete can be selected as 1.5 meters, 1.65 meters, or 1.8 meters. This length is mainly based on calculations of the H-beam's pull-out resistance and anchoring safety, ensuring that the H-beam will not be pulled out of the concrete when bearing the load of the upper solid concrete section. Available H-beam models include I32b or I40a, and their material can be Q235B or Q355B steel. These H-beams are prefabricated in the factory and transported to the site. Their assembly position is pre-embedded in the concrete of the topmost segment of the hollow section of the bridge tower, ensuring that the anchoring section is completely encased in concrete during installation. During construction, before pouring the concrete for this segment, the H-beams must be fixed to the reinforcing steel frame according to the design position, and then the concrete is poured together.

[0030] Multiple I-beams are evenly arranged along the transverse direction of the bridge tower. The center-to-center spacing between adjacent I-beams can be 0.8 meters, 1.0 meter, or 1.2 meters. This spacing is determined to ensure uniform stress on the upper supporting beams and bottom formwork system, avoiding excessive local stress. I-beams of the same specification can be arranged in parallel. These I-beams are laid horizontally in the transverse direction of the bridge tower section, with both ends anchored to the left and right tower walls respectively. The arrangement process requires precise positioning using a total station to ensure that the axial position and spacing of each I-beam meet the design requirements, and then they are firmly welded to the main reinforcing steel.

[0031] After pre-embedding, the flatness deviation of the top surface of the upper flange of the I-beam needs to be controlled within a threshold of 3 mm. Controlling this indicator is to provide a flat reference surface for the square timber laid above, ensuring the flatness of the bottom formwork system. During construction, a laser level with a spirit level or a long aluminum alloy ruler with a feeler gauge can be used for inspection. Leveling methods include adding steel shims to the bottom of the I-beam or making fine adjustments using adjustable supports during installation. The final assembly position must ensure that the top surfaces of the upper flanges of all I-beams are at the same design elevation, and that local height differences meet the requirements. The process involves preliminary leveling and fixing of the I-beams before concrete pouring, real-time monitoring of elevation changes during concrete pouring, and final adjustments before the initial setting of the concrete if any deviations are found.

[0032] This technical solution provides specific technical guidance for the installation of load-bearing I-beams by clearly defining three key parameters: anchorage length, spacing, and flatness. This ensures that the embedded load-bearing structure itself has sufficient anchorage safety, can evenly transfer the load to the tower wall, and creates favorable conditions for the installation of the upper bottom formwork system, thus laying a reliable foundation for the safe construction of the entire solid section.

[0033] In other technical solutions, the specific steps for reinforcing the hole in step one are as follows: The holes are made in the middle web and lower flange of the I-beam using CNC cutting in the factory. After the holes are made, circumferentially welded closed annular stiffening ribs are used to reinforce the inner surfaces of the web and flanges around the holes. The thickness of the annular stiffening ribs is 10-12mm, and their outer contour is larger than the contour of the holes and 80-100mm wider on each side. After multiple I-beams are installed in place, the holes on all the I-beams form a continuous vertical transport channel in the transverse direction of the bridge tower. This transport channel is kept unobstructed during the first and second concrete pours of the solid section and is used to transport small materials and tools. Before the third concrete pour of the solid section, a steel cover plate is used to cover and fix the transport channel, and a crack-resistant steel mesh is laid on the cover plate to form an integral whole with the third concrete pour.

[0034] In the above technical solution, the holes can be precisely cut using a CNC plasma cutting machine or a laser cutting machine in the factory, and the corners of the holes can be rounded with a radius of 50 mm. The thickness of the annular stiffening rib can be 10 mm, 11 mm, or 12 mm, and its material can be Q235B steel plate. The dimension of each side extending beyond the hole outline can be 80 mm, 90 mm, or 100 mm. A carbon dioxide gas shielded welding machine can be used for welding, and the welding wire type can be matched with the base material, ER50-6. The stiffening rib is assembled close to the inner surface of the web and lower flange of the I-beam around the hole, and is fully welded circumferentially. The working process is as follows: first, the edges of the cut hole are ground; then, the prefabricated annular stiffening rib is positioned inside the hole, and welding is performed using a segmented symmetrical welding sequence to control welding deformation.

[0035] After multiple H-beams are installed in place on site, their individual holes are aligned transversely with the bridge tower, forming a continuous vertical channel. The width of this channel is the width of a single hole, for example, 650 mm, and its length is consistent with the transverse direction of the bridge tower. During the first and second concrete pouring stages of the solid section, this channel remains unobstructed and can be used to lift bolts, small hand tools, and other construction materials using small winches or manually. The channel's assembly position extends throughout the bottom support system of the entire solid section. The process involves protecting the shape of the holes during the initial concrete pouring using pre-embedded sleeves or temporary supports to ensure the channel is not blocked by concrete, allowing for easy access during subsequent construction.

[0036] Before the third concrete pour in the solid section, the passage needs to be permanently sealed. A 20mm thick Q235B steel plate can be used as the cover plate, with each side extending 50mm beyond the opening outline for overlapping and fixing. Fixing methods include welding shear reinforcement bars to the upper flange of the I-beam or using high-strength bolts. The crack-resistant steel mesh can be made of 8mm diameter HRB400 steel mesh with a spacing of 100mm x 100mm. The mesh is laid on top of the cover plate. The process involves first hoisting and securely fixing the steel cover plate, ensuring it fits tightly against the upper flange of the I-beam. Then, the steel mesh is laid on the cover plate and surrounding I-beams. Finally, the third concrete pour is performed, forming an integral load-bearing structure with the cover plate, mesh, and concrete.

[0037] The above technical solutions ensure the structural safety of the I-beams after the opening is made through precise prefabrication and reinforcement in the factory; achieve rational use of resources by planning the use of the passage at different construction stages; and ensure the integrity of the solid concrete section and the uniform stress of the superstructure through the final reliable sealing treatment.

[0038] In other technical solutions, all corners of the holes made on the I-beam are smoothly transitioned with rounded arcs, with a radius of not less than 50mm; the welds between the annular stiffening ribs and the web and flanges of the I-beams are continuous, full-penetration welds; when welding the annular stiffening ribs, the base material is preheated and a multi-layer, multi-pass welding process is used to control the interpass temperature.

[0039] In the above technical solution, all corners of the holes drilled in the I-beams must be rounded. The specific dimensions of the radius of the rounded area can be 50 mm, 75 mm, or 100 mm, all meeting the requirement of not less than 50 mm. This rounding process can be completed in the factory using the beveling function of a CNC cutting machine or a dedicated portable chamfering machine. Suitable processing tools include CNC plasma cutting machines or flame cutting machines, achieved by pre-setting the fillet parameters in the cutting path. The assembly positions for the rounded transitions are located at the four inner corners of the hole. The process involves, after completing the straight-line cutting of the hole's main body, automatically or manually cutting along the corners using a rounded trajectory, and then grinding the rounded edges to eliminate gaps and burrs.

[0040] The weld between the annular stiffening rib and the web and flanges of the I-beam must be a continuous, full-penetration weld. This means the weld must ensure complete penetration of the base metal, achieving complete fusion between the weld metal and the base metal. Suitable welding methods include CO2 gas shielded welding or manual arc welding. The welding consumables must be compatible with the base metal; for example, for Q235B I-beams and ribs, ER50-6 welding wire or E4303 welding rods can be used. The weld should be positioned along all edges where the annular stiffening rib contacts the web and lower flange of the I-beam. The welding process requires continuous, uninterrupted welding to ensure a weld without interruptions, undercut, or lack of fusion, and the penetration effect should be verified using methods such as ultrasonic testing.

[0041] When welding annular stiffening ribs, the base material needs to be preheated, and a multi-layer, multi-pass welding process should be adopted, while controlling the interpass temperature. The preheating temperature range can be controlled between 80 and 120 degrees Celsius, and a flame torch or electric heating element can be used for preheating. Multi-layer, multi-pass welding refers to dividing a weld into several layers, each of which is then welded in several passes sequentially. Suitable welding parameters are: 180 amps for the root pass and 200 amps for subsequent filler passes. The interpass temperature needs to be controlled between 100 and 200 degrees Celsius, which can be monitored using an infrared thermometer. The process involves first uniformly preheating the welding area to the specified temperature, then performing the root pass welding. After completing one layer, the weld slag is cleaned, and the temperature is measured to ensure it is within the required interpass temperature range before proceeding to the next pass or layer. This cycle continues until the weld is complete.

[0042] The aforementioned technical solution provides clear and operable quality standards for the reinforcement of I-beam holes by specifying concrete geometric structures and welding process parameters. The circular arc transition effectively reduces the stress concentration factor, the full penetration weld ensures an equal-strength connection between the reinforced structure and the base material, and the multi-layer, multi-pass welding process with preheating and controlled interpass temperature effectively reduces welding stress and deformation, collectively ensuring the long-term structural reliability and fatigue durability of the reinforced area.

[0043] In other technical solutions, the specific steps of the multi-layer, multi-pass welding process include: The welding current for the first layer is 180~200A, the welding voltage is 22~24V, and the wire extension length is 15~20mm. Subsequent weld layers are applied using a segmented back-welding method, with each weld segment being 100~150mm long and overlapping adjacent segments by 10~15mm. After each weld layer is completed, the weld surface is ground smooth. The interpass temperature is controlled within the range of 100~200℃. The reinforcement height of the outermost weld surface is controlled within the range of 0~2mm, and the weld transitions smoothly with the base material.

[0044] In the above technical solution, the welding current for the first layer of welding, i.e., the root pass, can be selected as 180 amps, 190 amps, or 200 amps. The welding voltage can be selected as 22 volts, 23 volts, or 24 volts. The wire extension length, i.e., the distance from the tip of the welding torch to the workpiece, can be selected as 15 mm, 17 mm, or 20 mm. A carbon dioxide gas shielded welding machine can be used. The welding wire type can be ER50-6 with a diameter of 1.2 mm. These parameters are applied to the root weld between the annular stiffening rib and the I-beam base material. The working process involves the welder adjusting the welding machine parameters on the preheated workpiece to perform the root pass welding, aiming to achieve good penetration and root formation, laying the foundation for subsequent welding.

[0045] Subsequent filler and cover layers are welded using a segmented back-and-forth welding method. The length of each weld segment can be 100 mm, 120 mm, or 150 mm. The overlap between adjacent segments can be 10 mm, 12 mm, or 15 mm. A possible operating method is for the welder to divide a long weld into several smaller segments and weld them in a segmented, skip-and-go manner, either from the middle to both ends or from one end to the other. After each weld layer is completed, the weld surface needs to be ground smooth. An angle grinder with resin-bonded grinding wheels can be used for this purpose. The process involves welding one segment and allowing it to cool to the specified interpass temperature before welding the next adjacent segment, thus reducing heat accumulation and deformation. After each layer is welded, the slag is immediately cleaned and the surface oxides and protrusions are ground away to ensure the quality of the next weld layer.

[0046] Interpass temperature needs to be controlled within the range of 100°C to 200°C, which can be monitored using a handheld infrared thermometer. The surface reinforcement of the outermost weld, i.e., the capping weld, needs to be controlled within the range of 0 to 2 mm, which can be measured using a welding inspection ruler. A smooth transition between the weld and the base material is required, without obvious undercut or protrusions. A possible final treatment method is to use a grinding wheel to finely grind the weld reinforcement. The process involves measuring the temperature of the current weld area before welding the next layer, ensuring it is above 100°C and below 200°C; after completing the capping weld, the weld contour is finally inspected and trimmed to meet the requirements for a smooth transition.

[0047] The aforementioned technical solution provides a repeatable and verifiable guarantee for the welding quality of the annular stiffening ribs by specifying highly detailed welding process parameters and operating procedures. Precisely controlled root pass welding parameters ensure root quality, while the segmented back pass welding method effectively disperses welding heat input to reduce stress and deformation. Strict interpass temperature and forming control guarantee the internal density of the weld and the external geometric accuracy, ultimately resulting in a high-performance reinforced welded joint.

[0048] In other technical solutions, a cyclic cooling curing method based on real-time temperature difference feedback is implemented during the second and third concrete pours, specifically including the following steps: A cooling water pipe network is embedded in the concrete casting body. The horizontal spacing of the cooling water pipes is 0.8~1.2m, the vertical spacing is 0.8~1.2m, and the inner diameter of the cooling water pipes is 25~30mm. Temperature sensor groups are embedded at different depths inside the concrete. The temperature sensor placement depths are 0.1m, 0.5m, and 1.0m from the surface of the concrete casting body, respectively. After the concrete is poured, water circulation begins to cool it. The internal temperature of the concrete is monitored in real time by temperature sensors. When the difference between the highest internal temperature and the lowest surface temperature of the concrete reaches the threshold of 20~25℃, the flow rate and velocity of the cooling water are adjusted to control the internal and external temperature difference within the range of 25℃. Cover the concrete surface with insulation material, the thermal conductivity of which should not exceed 0.05 W / (m•K), and keep the surface moist by continuously sprinkling water during the curing period.

[0049] In the above technical solution, the horizontal spacing of the cooling water pipe network embedded in the concrete casting can be selected as 0.8 meters, 1.0 meters, or 1.2 meters, and the vertical spacing can also be selected as 0.8 meters, 1.0 meters, or 1.2 meters. The inner diameter of the cooling water pipes can be selected as 25 mm, 28 mm, or 30 mm, and black iron pipes or HDPE plastic pipes can be used. The temperature sensor group can be a platinum resistance temperature sensor, and its placement depth is 0.1 meters, 0.5 meters, and 1.0 meters from the surface of the concrete casting, respectively. The cooling water pipes are fixed to the steel reinforcement cage according to the pre-designed grid layout, and the temperature sensors are positioned by binding them to the steel reinforcement or by using a special bracket to ensure that they do not shift during the pouring process. The working process is as follows: after the steel reinforcement of the solid section of the bridge tower is tied, the cooling water pipes and temperature sensors are installed simultaneously. All pipelines and sensor wires must be led out of the concrete body and marked for subsequent connection and monitoring.

[0050] After the concrete is poured, circulating water cooling begins, using a centrifugal water pump as the power source. Temperature sensors collect data and can be connected to an automatic data acquisition system for real-time monitoring. Adjustments are required when the temperature difference between the highest internal temperature and the lowest surface temperature of the concrete reaches thresholds of 20°C, 22°C, or 25°C. The flow rate and velocity of the cooling water can be adjusted by regulating the pump frequency or valve opening, with the goal of consistently controlling the internal and external temperature difference within the upper limit of 25°C. The process involves initially using a smaller flow rate; as the temperature difference approaches the threshold, a feedback control system or manual intervention increases or decreases the water flow rate and velocity, dynamically responding to changes in the internal temperature field of the concrete to achieve active temperature control.

[0051] The thermal conductivity of the insulation material covering the concrete surface should not exceed 0.05 W / m / Kelvin. Flame-retardant polyethylene foam rolls or rock wool felt can be used. During curing, continuous watering is required to keep the surface moist; this can be achieved by installing an automatic sprinkler system or assigning personnel to water the surface at regular intervals. The insulation material should be tightly fitted over the exposed concrete surface, with tight overlaps at the joints. The process involves immediately covering the concrete after pouring and finishing, and then continuously watering to keep the insulation material moist and prevent excessive evaporation from the concrete surface. The curing period should be at least 7 days.

[0052] The aforementioned technical solution, through the deployment of an internal cooling system and temperature monitoring network, combined with surface insulation and moisture retention, forms a coordinated active temperature control system. This system can dynamically adjust cooling parameters based on the actual temperature development of the concrete, effectively suppressing excessive internal temperature rise and large internal-external temperature differences, thereby significantly reducing the risk of concrete cracking due to temperature stress and ensuring the construction quality of large-volume concrete.

[0053] In other technical solutions, circulating water cooling is divided into two continuous stages: The first stage begins after the concrete pouring is completed and ends when the highest internal temperature of the concrete reaches its peak and begins to decline. During this stage, the difference between the inlet temperature of the cooling water and the highest internal temperature of the concrete is controlled within 15℃, and the flow velocity of the cooling water in the pipe is controlled between 0.6 and 0.8 m / s. The second stage begins after the first stage ends and continues until the difference between the highest internal temperature and the surface temperature of the concrete stabilizes below 20℃. During this stage, the daily cooling rate of the highest internal temperature of the concrete is controlled within 2.0℃ / d.

[0054] In the above technical solution, the first stage begins with water flow calculations after concrete pouring. During this stage, the difference between the inlet temperature of the cooling water and the highest internal temperature of the concrete needs to be controlled within an upper limit of 15 degrees Celsius. The specific inlet temperature needs to be adjusted based on real-time monitoring of the highest internal temperature. The flow rate of the cooling water in the pipeline can be selected as 0.6 m / s, 0.7 m / s, or 0.8 m / s, and can be controlled by adjusting the water pump valve or using a flow meter. The termination condition for this stage is that the highest internal temperature of the concrete reaches its peak and begins to decline continuously. This needs to be identified through temperature sensor data curves, which is usually manifested as the rate of temperature rise approaching zero and then turning negative.

[0055] The second stage begins immediately after the first stage, without any interval. The core control objective in this stage is the daily cooling rate of the highest internal temperature of the concrete, which must be controlled within the upper limit of 2.0 degrees Celsius per day. The daily cooling rate is calculated based on the decrease in the highest internal temperature over a continuous 24-hour period. This rate can be monitored using an automatic temperature control system or by manually recording and calculating temperature data daily. When the daily cooling rate is detected to be too rapid, approaching or exceeding the control value, intervention is required by adjusting the water temperature or flow rate.

[0056] The second stage does not end at a fixed time, but rather depends on the stabilization of the temperature field. The termination condition is that the difference between the highest internal temperature and the surface temperature of the concrete remains consistently below 20 degrees Celsius. "Stable" here means that the temperature difference fluctuates very little over 24 consecutive hours and remains consistently below 20 degrees Celsius. A data acquisition system can be used to record the trend of temperature difference changes for judgment. Once this condition is met, it indicates that the internal heat of the concrete has been fully dissipated, the risk of temperature stress has been significantly reduced, and active water cooling operations can be stopped, transitioning to routine curing.

[0057] The aforementioned technical solution scientifically divides the cooling process into two stages: heating and cooling, and sets clear and different control targets and parameters for each stage, thus achieving refined control over the temperature development of concrete. This staged control method is more in line with the objective laws of temperature field development in large-volume concrete, effectively suppressing the maximum temperature rise and preventing shrinkage cracks caused by excessively rapid cooling in the later stages, thereby improving the pertinence and reliability of temperature control measures.

[0058] In other technical solutions, the method for controlling the daily cooling rate of the highest internal temperature of concrete is as follows: Establish a feedback regulation logic with the highest internal temperature of concrete, the surface temperature of concrete, and the daily cooling rate as control parameters. When it is necessary to reduce the daily cooling rate, the cooling water inlet temperature is increased first according to the first preset strategy, and the adjustment range of the inlet water temperature is 2~5℃. If the daily cooling rate is still higher than 2.0℃ / d after increasing the inlet water temperature, the second preset strategy is activated to reduce the flow rate of cooling water in the pipe, with the flow rate adjustment range being 0.1~0.3 m / s; When it is necessary to increase the daily cooling rate, the cooling water inlet temperature will be reduced first according to the third preset strategy, and the adjustment range of the inlet water temperature is 2~5℃. When the daily cooling rate is still below 1.5℃ / d after lowering the inlet water temperature, the fourth preset strategy is activated to increase the flow rate of cooling water in the pipe, with the flow rate adjustment range being 0.1~0.3 m / s; After each adjustment operation, maintain the adjusted parameters for at least 6 hours until the temperature field stabilizes, then collect data again and evaluate the daily cooling rate.

[0059] In the above technical solution, the core of the control method is to establish a closed-loop feedback system. This system uses the real-time monitored maximum internal temperature of the concrete, the concrete surface temperature, and the calculated daily cooling rate as basic control parameters. A programmable logic controller (PLC) or an industrial computer can be used as the control core, and corresponding control algorithms can be written. These parameters are located at the input port of the control system, continuously receiving data from field sensors. The system works by periodically collecting temperature data, calculating the current daily cooling rate, and comparing this rate with a preset target range to automatically determine whether a control strategy needs to be activated and which strategy to select.

[0060] When the system detects an excessively high daily cooling rate that needs to be reduced, it first executes the first preset strategy, which prioritizes increasing the cooling water inlet temperature. The adjustment range for the inlet temperature can be selected as an increase of 2, 3, or 5 degrees Celsius. Electric heating devices or mixing valves can be used to precisely regulate the water temperature. If, after increasing the inlet temperature, the daily cooling rate still exceeds the daily upper limit of 2.0 degrees Celsius, the system automatically activates the second preset strategy, which reduces the cooling water flow rate in the pipes. The flow rate can be reduced by 0.1, 0.2, or 0.3 meters per second, achieved by adjusting the pump frequency or valve opening. Conversely, when an excessively low daily cooling rate needs to be increased, the third and fourth preset strategies are executed in reverse: first, the inlet temperature is reduced, and if this is insufficient, the flow rate is increased.

[0061] After each adjustment operation, whether changing the water temperature or flow rate, the control system enters a stable observation period. During this period, the adjusted parameters will remain unchanged for at least 6 hours. This hold-up period can be achieved using a timer function. The purpose is to allow the internal temperature field of the concrete to reach a new dynamic equilibrium under the new cooling conditions, avoiding system oscillations caused by frequent adjustments. Once the temperature field stabilizes, the system will collect a new round of data and reassess the daily cooling rate to determine the next step. This "assessment-adjustment-hold-reassessment" cycle continues until the daily cooling rate stabilizes within the ideal range.

[0062] The aforementioned technical solution provides a clear, orderly, and automated decision-making process to precisely control the daily cooling rate of concrete. By setting clear priorities and adjustment ranges, and combining adjustment with stable observation, this method avoids blind operation and systematically guides and stabilizes the cooling rate within the target range, thereby effectively preventing the formation of temperature cracks.

[0063] In other technical solutions, the specific process of collecting data again and evaluating the daily cooling rate after the temperature field has stabilized is as follows: After each adjustment of the cooling water inlet temperature or flow rate, a continuous monitoring program is started to record the highest internal temperature Tcmax of the concrete at 1-hour intervals. Calculate the instantaneous cooling rate Vi reflected by three consecutive monitoring data, and calculate the standard deviation σ of these three consecutive instantaneous cooling rate values; When the standard deviation σ drops below 0.1℃ / d, it is determined that the temperature field has reached a stable state, and then a formal assessment and subsequent decision-making of the daily cooling rate Vc are carried out. If the standard deviation σ still does not drop below 0.1℃ / d after 12 hours of continuous monitoring, the daily cooling rate Vc will be evaluated, and the next adjustment operation will be carried out based on the evaluation results. The instantaneous cooling rate Vi is calculated using the formula: Vi = (Tcmax(t) - Tcmax(t + Δt)) / Δt, where Δt is the time interval between two adjacent monitoring sessions.

[0064] In the above technical solution, a continuous monitoring program is initiated after each adjustment of cooling parameters. This program automatically records the maximum internal temperature Tcmax of the concrete at fixed time intervals of 1 hour. This high-frequency recording can be achieved by using a multi-channel automatic data acquisition instrument connected to a platinum resistance temperature sensor. The instantaneous cooling rate Vi is calculated as follows: Vi equals the Tcmax value at time t minus the Tcmax value at time t plus Δt, divided by the time interval Δt. Here, Δt is 1 hour, and the calculated Vi is in degrees Celsius per day. The system works by immediately substituting the new Tcmax data point with the previous data point into the formula to calculate an instantaneous Vi value, used to track the trend and fluctuation of temperature changes in real time.

[0065] The system continuously calculates the three most recent consecutive instantaneous cooling rate values ​​Vi and determines the standard deviation σ of these three values. The standard deviation σ is a statistic that measures the dispersion of data and can be directly calculated by the algorithm built into the data acquisition system. When the calculated standard deviation σ falls below the threshold of 0.1 degrees Celsius per day, the system considers the temperature field inside the concrete to have reached a stable state. This criterion means that the three consecutive instantaneous cooling rate values ​​are very close, and the temperature change tends to be stable. Subsequently, the system will conduct a formal evaluation of the daily cooling rate Vc based on data from a longer time period (usually the past 24 hours) and make subsequent decisions accordingly, such as maintaining the current parameters or making new adjustments.

[0066] As a safeguard against abnormal situations, this process has a maximum waiting time. If, after parameter adjustment, continuous monitoring continues for 12 hours, but the calculated standard deviation σ consistently fails to fall below the daily threshold of 0.1 degrees Celsius, the system will no longer wait but will forcibly initiate an assessment of the daily cooling rate Vc. This forced operation can be triggered using a timer function. The process is as follows: when the timer reaches 12 hours, regardless of the value of σ, the system will collect currently available data, calculate Vc, and execute the next adjustment operation based on the assessment result. This ensures that the control process does not fall into indefinite waiting due to continuous slight fluctuations in the temperature field, maintaining the efficiency of temperature control management.

[0067] The above technical solution provides a quantitative and operable criterion for judging the fuzzy concept of "temperature field stability". By introducing the instantaneous cooling rate and its standard deviation as the judgment basis and setting a timeout mechanism, the control system can intelligently and automatically determine the intervention time, which avoids misjudgment when the temperature field is not stable and prevents control lag caused by long-term non-convergence, thereby improving the automation and reliability of the entire temperature control process.

[0068] Example 1 Before pouring concrete for the topmost segment (assuming it's the nth segment) of the completed hollow section of the bridge tower, the pre-embedded load-bearing structure is constructed. Q235B I36a hot-rolled I-beams are selected as the load-bearing structure, with a designed anchorage length of 1.6 meters embedded in the tower wall concrete. Twelve of these I-beams are evenly spaced along the transverse direction of the bridge tower, with a center-to-center distance of 1.0 meter between adjacent I-beams. In the factory, a rectangular hole with a width of 650 mm is cut in the middle of the web and lower flange of each I-beam using a CNC plasma cutting machine. All corners are smoothly transitioned with a 60 mm radius rounded arc. Immediately after cutting the hole, closed-ring stiffening ribs made of 10 mm thick Q235B steel plates are welded circumferentially to the inner surface of the web and flange around the hole for reinforcement. The outer edge of these ribs extends 90 mm beyond the hole outline on each side. During welding, the base material is preheated to 100℃, and multi-layer, multi-pass welding is performed using carbon dioxide gas shielded welding: the first layer uses a welding current of 190A and a voltage of 23V, with a welding wire extension length of 18mm; subsequent weld layers are welded using a segmented back-and-forth welding method, with each weld segment being 120mm long and adjacent segments overlapping by 12mm; the interpass temperature is strictly controlled at around 150℃, ultimately ensuring a continuous, full-penetration weld, with the outermost weld reinforcement height controlled within 1mm. During pre-embedding, a total station is used for precise positioning to ensure that the flatness deviation of the top surface of the upper flange of the I-beam is less than 2mm, and then it is firmly welded to the tower wall reinforcement skeleton, and the hollow segment concrete is poured.

[0069] After the hollow section concrete reaches its design strength, transverse square timber is laid on the top surface of the upper flange of the pre-embedded I-beams. The timber is 100mm x 100mm pine wood, with a center-to-center spacing of 0.3 meters, and its extension direction is perpendicular to the extension direction of the I-beams. U-shaped clamps are used to secure the square timber to the upper flange of the I-beams. A 18mm thick high-quality film-coated plywood panel is laid on top of the square timber as a face sheet, forming a closed bottom formwork system. Subsequently, the first pour of solid concrete for the bridge tower is carried out, using C50 micro-expansion concrete. The pouring thickness is strictly controlled to 0.25 meters to ensure that the concrete covers the entire bottom formwork system, forming the initial load-bearing layer. During the pouring process, all holes on the I-beams are kept clear for the hoisting of a small number of emergency tools.

[0070] After the initial load-bearing layer concrete strength reaches 15MPa as tested by test blocks cured under the same conditions, steel side formwork is erected on top for the second concrete pour, with a thickness of 1.8 meters. Cooling water pipes and temperature sensors are simultaneously installed while tying the reinforcing steel for this pour. The cooling water pipes are 28mm inner diameter HDPE pipes, laid out in a mesh pattern with horizontal and vertical spacing of 1.0 meter each. Temperature sensor arrays are embedded at depths of 0.1 meters, 0.5 meters, and 1.0 meter from the surface of the poured concrete in typical cross-sections. The concrete is poured in layers, with each layer controlled to a thickness of 0.3 meters, and symmetrically and uniformly vibrated using an immersion vibrator. Immediately after pouring, circulating water cooling is initiated, and the concrete is covered with insulation and moisture-retaining materials.

[0071] Water cooling is precisely controlled in two stages. In the first stage, starting after pouring, the temperature difference between the cooling water inlet temperature and the highest internal temperature of the concrete is controlled within 12℃, and the flow velocity in the pipes is controlled at 0.7m / s. Temperature sensors monitor this in real time until the highest internal temperature of the concrete reaches its peak of 68℃ and begins to decrease. The second stage then begins, with the core control objective being to ensure that the daily cooling rate of the highest internal temperature of the concrete does not exceed 2.0℃ / d. To this end, an automatic feedback adjustment system is established: when the monitored daily cooling rate Vc is 2.5℃ / d (above the upper limit), the system activates the first preset strategy, increasing the inlet water temperature by 3℃; after adjustment, the parameters are maintained for 8 hours, and the highest internal temperature Tcmax is recorded at 1-hour intervals. The three consecutive instantaneous cooling rates Vi (formula: Vi=[Tcmax(t)-Tcmax(t+1h)] / 1h×24) are calculated, and their standard deviation σ is determined. When the σ value drops to 0.08℃ / d (below the threshold of 0.1℃ / d), the temperature field is considered stable, and Vc is reassessed at 1.8℃ / d, which meets the requirements. If Vc is still too high after adjustment, the second preset strategy is activated to reduce the flow rate by 0.2 m / s. Conversely, if it is necessary to increase the excessively low Vc, the preset strategy is followed to first reduce the inlet water temperature, and if the effect is insufficient, the flow rate is increased. At the same time, a polyethylene foam insulation roll with a thermal conductivity of 0.04 W / (m·K) is covered on the concrete surface, and water is continuously sprayed to keep it moist, successfully controlling the internal and external temperature difference within 25℃.

[0072] After the concrete from the second pour reaches a strength of 15 MPa, a third pour, 2.0 meters thick, is carried out. Before pouring, all holes and channels on the I-beams are covered with 20 mm thick Q235B steel cover plates, which are then welded and fixed to the upper flanges of the I-beams. A layer of HRB400 crack-resistant steel mesh with a diameter of 8 mm and a spacing of 100 mm × 100 mm is laid on the cover plates and the entire top surface of the third pour layer. After the concrete is poured, a second finishing process is completed before final setting, and a drip irrigation curing system is immediately used for continuous moisturizing for 14 days.

[0073] After the solid section was completed and the concrete strength met the design requirements, a small winch was used to hoist materials such as formwork and timber to the top of the solid section through a vertical channel formed by the holes reserved in the middle of the I-beam, and construction of the upper bridge tower segment began smoothly.

[0074] Comparative Example 1 The difference from Example 1 lies in the use of traditional construction methods for the solid section of the bridge tower. First, simple embedded parts are pre-embedded in the top of the lower hollow section, followed by the erection of a full-span steel pipe scaffold as the load-bearing support system. This scaffold system is independent of the bridge tower structure, requiring construction from the bottom up, consuming a large amount of steel pipes and fasteners, and its stability is highly dependent on the foundation treatment and the quality of the member connections. To meet the vertical transportation requirements of materials, a separate wall-mounted construction elevator needs to be installed on the outside of the tower or a separate shaft needs to be set up inside the tower. The solid section concrete is poured in two stages: the first pour is 0.8 meters thick, and after reaching the required strength, the second pour is made to the design elevation. In this method, the support system and the transportation system are completely separated; the support system is large and complex, and installation and dismantling are time-consuming and labor-intensive; the separately set transportation channel increases additional costs and construction time; and the thicker first pour layer places high initial load requirements on the support system, posing significant safety risks. The construction period is long, and the overall economic benefits are poor.

[0075] Comparative Example 2 The difference from Example 1 lies in the use of a single, integral casting to complete the solid section of the bridge tower. While the bottom formwork system is also supported by embedded parts, no pre-drilled holes are provided. The concrete is poured continuously in one go, reaching a total thickness of over 4 meters. To cope with the high heat of hydration, cooling water pipes are embedded only inside the concrete, but a fixed flow rate and temperature are used, lacking real-time temperature feedback control. The concrete surface is cured using conventional methods of covering with geotextile and sprinkling water. As a result, the highest internal temperature of the concrete reached 75°C, and the temperature difference between the inside and outside exceeded 35°C at one point. Although no obvious visible cracks were found, subsequent non-destructive testing revealed multiple micro-cracks in the central area of ​​the solid section. Furthermore, due to the lack of pre-drilled access, materials required for subsequent construction could only be transported from the outside using a tower crane, resulting in low efficiency and severely hindering the construction progress of the upper segments. This method offers fast construction speed but carries high quality control risks and inconveniences for subsequent construction.

[0076] Comparative Example 3 The difference from Example 1 lies in the absence of any active temperature control measures. After concrete pouring, curing relied solely on natural heat dissipation through covering the surface with insulation material and sprinkling water. Monitoring by embedded temperature sensors revealed that after the second and third thick-layer pours, the highest internal temperature of the concrete exceeded 70°C, and the temperature difference between the inside and outside remained above 30°C for several days. Ultimately, several visible temperature cracks approximately 0.2 mm wide appeared on the surface of the solid section, requiring subsequent chemical grouting. While this method reduced some of the cracking risk through layered pouring, the lack of effective internal heat dissipation means it could not fundamentally control temperature cracks in large-volume concrete, posing a potential risk to project quality.

[0077] Temperature control performance comparison test Test Method: A chain of temperature sensors was embedded in a representative cross-section (e.g., the center) inside the second pour of concrete (1.8 meters thick, falling under the category of large-volume concrete). Temperatures were monitored at depths of 0.1 m, 0.5 m, 1.0 m from the surface, and at the center (approximately 0.9 m). Monitoring continued until the temperature dropped to near ambient temperature. The highest internal temperature (Tmax) and the maximum temperature difference between the core and surface (ΔTmax) were recorded throughout the process. The results are shown in Table 1.

[0078] Table 1 Example 1 employs a "circulatory cooling curing method based on real-time temperature difference feedback," where the cooling system dynamically adjusts according to monitoring data. Data shows that the highest internal temperature, Tmax, is controlled at 68℃. By actively introducing cooling water into the concrete to remove heat, the maximum internal and external temperature difference, ΔTmax, is successfully limited to the allowable range of 25℃. The temperature curve exhibits a steady upward and slow downward trend, without drastic fluctuations.

[0079] Although Comparative Example 2 (one-time casting) also had cooling water pipes installed, it used fixed parameters for water flow, which could not respond to the actual temperature rise of the concrete. This resulted in a large accumulation of cement hydration heat, with Tmax reaching as high as 75℃. Fixed cooling was insufficient to offset the central heat, causing ΔTmax to reach 35℃, far exceeding the standard limit (usually required to be ≤25℃), generating enormous temperature stress.

[0080] Comparative Example 3 (layered without active temperature control) relies entirely on natural heat dissipation, resulting in low heat dissipation efficiency. Tmax reached 72℃, and ΔTmax was 32℃, both significantly exceeding the limits. This indicates that for a 1.8-meter-thick cast-in-place layer, surface insulation and moisture retention alone cannot effectively solve the internal temperature rise problem.

[0081] Comparative Example 1 (traditional method) has a first pour thickness of only 0.8 meters, which is not considered large-volume concrete, so the heat of hydration problem is not prominent, and the temperature control data is acceptable. However, this precisely illustrates that the solution avoids the problem by sacrificing the thickness of a single pour (increasing construction joints), rather than fundamentally solving the temperature control problem of thick-layer pouring.

[0082] Crack control comparison test Test method: Appearance observation: After 28 days of concrete curing, experienced engineers conducted a general survey of all outer surfaces of the solid section under sufficient light using the naked eye and a crack observation instrument, and recorded the location, number and maximum width of all visible cracks (width ≥ 0.05 mm).

[0083] Non-destructive testing: An ultrasonic testing instrument was used to scan the interior of the concrete. When ultrasonic waves encounter defects such as cracks, they diffract, causing changes in parameters such as sound duration and amplitude. This allows for the determination of the presence and approximate distribution of micro-cracks (width < 0.05 mm) within the concrete. The results are shown in Table 2.

[0084] Table 2 Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Visual observation (cracks are visible) none none none There are (several, maximum 0.2mm) Non-destructive testing (microscopic cracks) none none (Multiple locations in central China) It is connected to the visible crack. As shown in Table 2, the apparent observation result of Example 1 is "no visible cracks". Ultrasonic testing showed that the internal acoustic parameters were uniform and no obvious micro-crack defects were found. This is due to its excellent temperature control effect (keeping ΔTmax below 25℃), which ensures that the temperature stress is always lower than the early tensile strength of concrete, thus fundamentally avoiding the formation of cracks.

[0085] Comparative Example 2 (one-time casting) may appear to have "no visible cracks," but ultrasonic testing revealed multiple discontinuous microcracks in the central region of the solid section. These cracks were caused by tensile stress exceeding the ultimate tensile strength of the concrete due to excessive ΔTmax (35℃). These microcracks pose a potential durability risk and may propagate under long-term loads and environmental influences.

[0086] Comparative Example 3 (layered without active temperature control): Visual inspection revealed several visible cracks, with a maximum width of approximately 0.2 mm. These cracks typically appear on the surface and are a typical manifestation of surface tensile cracking caused by excessive ΔTmax (32℃). Ultrasonic testing further confirms the depth and extension of these cracks. Such cracks require pressure grouting, increasing both cost and time.

[0087] Comparative Example 1 (traditional method) achieves better crack control due to its smaller pouring thickness and lower temperature stress. However, this also comes at the cost of increasing construction joints (potential weak points).

[0088] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and embodiments shown and described herein.

Claims

1. A construction method for solid concrete sections of bridge towers, characterized in that, Includes the following steps: Step 1: During the concrete construction stage of the top segment of the hollow section of the completed bridge tower, multiple I-beams are pre-embedded at the top of the segment as load-bearing structures. The two ends of the I-beams are anchored in the tower wall of the hollow section. Holes with a width of 600-700mm are reserved in the middle area of ​​the I-beams and the holes are reinforced. Horizontal square timbers are laid on top of the I-beams, with the extension direction of the square timbers perpendicular to the extension direction of the I-beams. The square timbers are fixedly connected to the I-beams using connectors. Multi-layer boards are laid on top of the square timbers to form a closed bottom formwork system. The steps for reinforcing the holes are as follows: Holes are cut in the middle web and lower flange of the I-beam using CNC cutting in the factory; after the holes are cut, circumferentially welded closed annular stiffening ribs are used to reinforce the inner surfaces of the web and flanges around the holes. The thickness of the annular stiffening ribs is 10-12mm, and their outer contour is larger than the contour of the holes, with each side being 80-100mm wider; after multiple I-beams are installed, all the holes on the I-beams form a continuous vertical transport channel in the transverse direction of the bridge tower. This transport channel remains unobstructed during the first and second concrete pours of the solid section, used for transporting small materials and tools; before the third concrete pour of the solid section, a steel cover plate is used to cover and fix the transport channel, and anti-crack steel mesh is laid on the cover plate to form an integral whole with the third concrete pour; All corners of the holes made in the I-beam are smoothly transitioned with rounded arcs, with a radius of not less than 50mm; the welds between the annular stiffening ribs and the web and flanges of the I-beam are all continuous, full-penetration welds. When welding the annular stiffening ribs, the base material is preheated and a multi-layer, multi-pass welding process is used to control the interpass temperature. Step 2: The first pouring of solid concrete for the bridge tower is carried out on the bottom formwork system. The thickness of the first pouring of concrete is controlled to be 0.2~0.3m. The poured concrete covers the entire bottom formwork system and forms the initial load-bearing layer. Step 3: After the initial load-bearing layer concrete strength reaches 10~20MPa, set up side formwork on the initial load-bearing layer and pour the second concrete for the solid section of the bridge tower. Control the thickness of the second concrete pour to be 1.5~2.0m. The second concrete pour should be vibrated in layers, with the thickness of each layer controlled at 25~35cm, and vibrated symmetrically. Step 4: After the concrete strength of the second pour reaches 10~20MPa, the third pour of solid concrete for the bridge tower is carried out. The thickness of the third pour of concrete is controlled to be 1.8~2.2m. Anti-crack steel mesh is set on the top of the third pour of concrete. The second finishing and grouting is completed before the concrete sets. After the second finishing, the concrete is continuously cured by drip irrigation. Step 5: After the solid section is completed, the formwork and timber are hoisted to the upper working face of the bridge tower through the pre-reserved holes in the middle of the I-beam, and the subsequent bridge tower segments located above the solid section are then constructed.

2. The construction method for the solid concrete section of the bridge tower as described in claim 1, characterized in that, In step one, the length of the anchoring end of a single H-beam embedded in the concrete of the tower wall is 1.5~1.8m. Multiple H-beams are arranged along the transverse direction of the bridge tower, and the center-to-center distance between adjacent H-beams is 0.8~1.2m. After pre-embedding, the flatness deviation of the top surface of the upper flange of the H-beam is controlled within 3mm.

3. The construction method for the solid concrete section of the bridge tower as described in claim 1, characterized in that, The specific steps of multi-layer, multi-pass welding process include: The welding current for the first layer is 180~200A, the welding voltage is 22~24V, and the wire extension length is 15~20mm. Subsequent weld layers are applied using a segmented back-welding method, with each weld segment being 100~150mm long and overlapping adjacent segments by 10~15mm. After each weld layer is completed, the weld surface is ground smooth. The interpass temperature is controlled within the range of 100~200℃. The reinforcement height of the outermost weld surface is controlled within the range of 0~2mm, and the weld transitions smoothly with the base material.

4. The construction method for the solid concrete section of the bridge tower as described in claim 1, characterized in that, During the second and third concrete pours, a cyclic cooling curing method based on real-time temperature difference feedback is implemented, specifically including the following steps: A cooling water pipe network is embedded in the concrete casting body. The horizontal spacing of the cooling water pipes is 0.8~1.2m, the vertical spacing is 0.8~1.2m, and the inner diameter of the cooling water pipes is 25~30mm. Temperature sensor groups are embedded at different depths inside the concrete. The temperature sensor placement depths are 0.1m, 0.5m, and 1.0m from the surface of the concrete casting body, respectively. After the concrete is poured, water circulation begins to cool it. The internal temperature of the concrete is monitored in real time by temperature sensors. When the difference between the highest internal temperature and the lowest surface temperature of the concrete reaches the threshold of 20~25℃, the flow rate and velocity of the cooling water are adjusted to control the internal and external temperature difference within the range of 25℃. Cover the concrete surface with insulation material, the thermal conductivity of which should not exceed 0.05 W / (m•K), and keep the surface moist by continuously sprinkling water during the curing period.

5. The construction method for the solid concrete section of the bridge tower as described in claim 4, characterized in that, The circulating water cooling system is divided into two continuous stages: The first stage begins after the concrete pouring is completed and ends when the highest internal temperature of the concrete reaches its peak and begins to decline. During this stage, the difference between the inlet temperature of the cooling water and the highest internal temperature of the concrete is controlled within 15℃, and the flow velocity of the cooling water in the pipe is controlled between 0.6 and 0.8 m / s. The second stage begins after the first stage ends and continues until the difference between the highest internal temperature and the surface temperature of the concrete stabilizes below 20℃. During this stage, the daily cooling rate of the highest internal temperature of the concrete is controlled within 2.0℃ / d.

6. The construction method for the solid concrete section of the bridge tower as described in claim 5, characterized in that, The method for controlling the daily cooling rate of the highest internal temperature of concrete is as follows: Establish a feedback regulation logic with the highest internal temperature of concrete, the surface temperature of concrete, and the daily cooling rate as control parameters. When it is necessary to reduce the daily cooling rate, the cooling water inlet temperature is increased first according to the first preset strategy, and the adjustment range of the inlet water temperature is 2~5℃. If the daily cooling rate is still higher than 2.0℃ / d after increasing the inlet water temperature, the second preset strategy is activated to reduce the flow rate of cooling water in the pipe, with the flow rate adjustment range being 0.1~0.3 m / s; When it is necessary to increase the daily cooling rate, the cooling water inlet temperature will be reduced first according to the third preset strategy, and the adjustment range of the inlet water temperature is 2~5℃. When the daily cooling rate is still below 1.5℃ / d after lowering the inlet water temperature, the fourth preset strategy is activated to increase the flow rate of cooling water in the pipe, with the flow rate adjustment range being 0.1~0.3 m / s; After each adjustment operation, maintain the adjusted parameters for at least 6 hours until the temperature field stabilizes, then collect data again and evaluate the daily cooling rate.

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