A method for pouring ultra-large steel box concrete structure

Abstract

This invention relates to the field of bridge tower steel-concrete structure design technology, and particularly to a super-massive steel box concrete structure and its pouring method. The steel box concrete structure is installed in the lower bridge tower structure, located at the bottom of the lower tower. No cooling water pipes are installed inside the steel box shell. The concrete formula includes the following raw materials per cubic meter by weight: cement 200±5kg, fly ash 200±5kg, expansion agent 30±5kg, sand 822±5kg, aggregate 1047±5kg, and water 151±5kg. Active cooling of the super-massive steel box concrete is achieved by optimizing the concrete mix proportions. Utilizing the concrete formula's inherent low shrinkage, low temperature rise, and self-compacting properties, the super-massive steel box concrete structure achieves high density and low shrinkage within the steel box structure even without cooling water pipes. It can work collaboratively with the steel box to bear loads, and the adhesion between the steel box and concrete is strong and does not detach, resulting in good overall load-bearing capacity for the lower bridge tower.

Description

Technical Field

[0001] This invention relates to the field of bridge tower steel-concrete structure design technology, and in particular to a super-large steel box concrete structure and its pouring method. Background Technology

[0002] With the development of composite structure technology, steel box concrete structures are increasingly used for the towers of cable-stayed bridges. Their cross-sections can be designed in various shapes such as square, rectangular or polygonal, and they have advantages in load-bearing capacity, high stiffness, toughness and good seismic performance. As the span of bridges continues to increase, steel box concrete bridge towers are also developing towards larger scales. At present, components with a maximum geometric dimension of not less than 7m in each direction of the cross-section are defined as super-mass steel box concrete components.

[0003] The excessive volume of concrete inside the box leads to a rise in thermal insulation temperature, while the surface steel box formwork has a high thermal conductivity and dissipates heat quickly, resulting in a large temperature difference between the inside and outside of the concrete, poor crack resistance, and susceptibility to temperature stress caused by hydration heat and early cracking. A common temperature control measure in engineering is to pre-embed numerous cooling water pipes inside the large-volume concrete, using circulating water to carry away internal heat and achieve internal cooling. However, extensive engineering investigations and tests have shown that: ① The cooling effect of the cooling water pipes is not significant, only a 2-8°C reduction. Furthermore, the low temperature of the cooling water and the high temperature of the concrete create a large local temperature difference, easily generating numerous micro-cracks around the cooling water pipes, affecting the structural load-bearing performance. ② Grouting of the cooling water pipes in the later stages of construction is difficult to achieve 80% compaction, becoming a weak point affecting the durability of the concrete. ③ The installation of multi-layer cooling water pipes is complex, the water flow control procedure is complicated, and the labor intensity for workers is high. Compared to the passive cooling mode of cooling water pipes, a more scientific and reasonable technical approach is to reduce the heat of hydration through the performance regulation of concrete materials, achieve active cooling, and eliminate the need for cooling water pipes.

[0004] Unlike conventional large-volume concrete structures, steel-concrete composite structures are composite structures, and the density of the concrete within the steel box is crucial to their coordinated load-bearing capacity. When the concrete is not densely poured or shrinkage is excessive, debonding and voids between the steel box and the concrete not only reduce the confinement effect of the steel box concrete, affecting the coordinated load-bearing behavior of the composite section, but also cause the concrete to become an external load on the steel structure, losing its supporting function for the external steel box and further reducing the load-bearing capacity of the steel-concrete composite structure. This further increases the requirements for the concrete: it must be fluid and dense enough to completely fill the external steel box; at the same time, shrinkage must be controllable, and the bonding performance with the steel wall interface must be good, ensuring that the steel box and concrete remain tightly bound throughout the construction and operation phases.

[0005] To control the temperature stress of the super-large steel box concrete and ensure the coordinated stress distribution between the steel box and the concrete, the concrete material needs to possess multiple performance objectives, including self-compacting, low shrinkage, low temperature rise, and high crack resistance, in addition to ensuring basic mechanical and workability properties. However, the concrete volume inside the steel box is enormous, and it is characterized by high cementitious material consumption, susceptibility to shrinkage cracking, high heat of hydration, and poor crack resistance. These characteristics create a stark contradiction with the multiple performance objectives, posing a pressing technical challenge that needs to be overcome. Summary of the Invention

[0006] The purpose of this invention is to overcome the technical defects of existing technologies, such as large amount of adhesive material used in ultra-large steel box concrete, easy shrinkage, high heat of hydration, poor crack resistance, poor cooling effect, many micro-cracks around the pipe, and incomplete grouting inside the pipe, which affect the durability of the structure. The invention proposes an ultra-large steel box concrete structure and grouting method.

[0007] In a first aspect, the present invention provides a super-massive steel box concrete structure, wherein the steel box concrete structure is disposed in the lower bridge tower structure of a bridge, the steel box concrete structure is located at the bottom of the lower bridge tower, the steel box concrete structure includes a steel box shell and concrete poured into the inner cavity of the shell, the steel box shell is not provided with cooling water pipes for cooling the poured concrete, and the concrete formula includes the following raw materials per cubic meter by weight: cement 200±5kg, fly ash 200±5kg, expansion agent 30±5kg, sand 822±5kg, stone 1047±5kg, and water 151±5kg.

[0008] In order to overcome the technical defects of passive cooling of concrete by setting up cooling water pipes in the existing technology of super-massive steel box concrete structures, such as poor cooling effect, many micro-cracks around the pipes, incomplete grouting inside the pipes, and poor structural durability, the present invention proposes to eliminate the external cooling water pipes and actively cool the super-massive steel box concrete structure during the pouring process by optimizing the concrete mix ratio. The above-mentioned technical defects are overcome by the comprehensive performance characteristics of the concrete formula itself, such as low shrinkage, low temperature rise, and self-compacting properties. This allows the super-massive steel box concrete structure to achieve high density of concrete in the steel box structure and low shrinkage without the setting of cooling water pipes. The concrete can work together with the steel box to bear the load, and the adhesion between the steel box and the concrete is strong and does not debond, so that the lower bridge tower has good overall load-bearing capacity.

[0009] Preferably, the steel box concrete structure is embedded in the tower base, the steel box concrete structure is trapezoidal in shape, the transverse length of the steel box concrete structure is 7-9m, the longitudinal length of the steel box concrete structure is 10-18m, and the height of the steel box concrete structure is 18-20m.

[0010] In the technical solution of this invention, the steel box concrete structure is located at the bottom of the bridge tower and is the main load-bearing part of the bridge tower. In order to improve the load-bearing capacity, concrete is poured into the steel box to form a steel box concrete composite structure. The amount of concrete used exceeds 3,000 cubic meters, showing the characteristics of "super volume".

[0011] Preferably, the steel box shell is provided with a plurality of first partitions at intervals from bottom to top. The first partitions divide the inner cavity of the steel box shell into a plurality of first chambers. Each first chamber is provided with a plurality of second partitions along the transverse bridge direction. The second partitions divide the first chamber into three chamber units along the transverse bridge direction. The chamber unit located in the middle is the middle chamber, and the chamber units located on both sides of the middle chamber are the side chambers.

[0012] If the chamber volume is too large and no cooling water pipes are provided, there is still a risk of exceeding the temperature limit, even with the optimal mix proportion. If the chamber volume is too small, the mix proportion can easily meet the low temperature rise target, but too many chambers increase the amount of steel structure used, increase the difficulty of steel structure processing and manufacturing, and increase the number of concrete pours, thus lengthening the construction period. Therefore, the number of chambers should be determined based on the performance of the optimal mix proportion. Preferably, in the technical solution of this application, the volume range of each chamber unit is preferably 200m³. 3 -400m 3 .

[0013] According to the structural features of the steel box shell of the present invention, concrete is poured in layers from bottom to top.

[0014] In a second aspect, the present invention provides a method for pouring concrete into a super-large steel box, wherein the concrete is used to pour into the steel box shell structure, comprising the following steps:

[0015] Step 1: Preparation before concrete pouring: Verify and adjust the mix proportions of each raw material in the concrete for the steel box shell structure to obtain a concrete slurry formula that meets the requirements.

[0016] Step 2: Layered construction and pouring of concrete for the steel shell. In each layer of the steel shell structure, the concrete is poured in separate chambers. The pouring sequence for each chamber is as follows: first, the concrete is poured in the two side chambers, and then the concrete is poured in the middle chamber. Within the same chamber, the concrete is further poured in sections: the steel shell is provided with multiple pouring ports at intervals along the bridge direction. First, the pouring port located in the middle is poured, and then the pouring ports located at both ends are poured. The pump pipe pours concrete slurry into the interior of the steel shell structure through the pouring ports.

[0017] Step 3: After the concrete pouring of the first layer of the steel box shell is completed, it is cured and reaches the target strength and age, and then the construction of the next layer of the steel box shell and the pouring of concrete inside the steel box shell are carried out.

[0018] Step 4: Repeat steps 2-3 to obtain the steel box concrete structure.

[0019] The core improvement of the grouting method of the present invention lies in the optimized design of the concrete mix proportion, thereby eliminating the need for a cooling water pipe temperature control system to cool the poured concrete in the steel box concrete structure. The optimized concrete mix proportion replaces the purpose of cooling the concrete by setting cooling water pipes in the steel shell structure in the prior art.

[0020] Preferably, in step 1, the optimal mix proportion of the concrete is obtained according to the following steps:

[0021] Step 11: Determine the initial mix proportion D0 = (W) based on the concrete performance parameters. 10 W 20 W 30 W 40 W 50 W 60 ) T ;

[0022] W 10 W indicates the quality of cement. 20 W represents the mass of fly ash. 30 W represents the mass of the expanding agent. 40 W represents the mass of sand. 50 W represents the mass of the stone. 60 Indicates the mass of water;

[0023] Step 12: Based on the initial mix proportion, adjust the design range of each component of the concrete to form a set of candidate mix proportions D;

[0024] Step 13: Mix concrete for all candidate mix proportions and conduct adiabatic temperature rise calculation, shrinkage test, compressive strength test, and self-compacting performance test.

[0025] Step 14: Use the optimal mix proportion decision model to select the optimal mix proportion D. * .

[0026] In the technical solution of this invention, the mathematical model for determining the optimal mix ratio in step 4 is as follows:

[0027]

[0028] In formula (1) above, D is the set of all candidate mix proportions, W1 to W6 are the masses of cement, fly ash, expansion agent, sand, aggregate and water per cubic meter of concrete, respectively; target f1 is the self-compacting performance target, T L K represents the slump. z For scalability, T 500The time required to achieve an expansion of 500mm, where U is the filling height of the U-shaped box; target f2 is the target low-temperature rise performance, T max Δ represents the peak adiabatic temperature rise; target f3 is the low shrinkage performance target, where Δ is the concrete shrinkage rate; target f4 is the comprehensive performance target of self-compacting, low shrinkage, and low temperature rise; g1 is the constraint to ensure the mechanical properties of concrete, requiring the measured concrete strength f to stably reach the design strength. c Greater than 1.1 times the standard value of compressive strength f cu,k .

[0029] In the technical solution of this application, the workability of concrete is expressed by slump H, spread SF, and spread time T. 500 The evaluation was conducted using the 28-day cube compressive strength test. For the service environment of the steel-frame concrete structure, concrete shrinkage deformation was assessed using a closed-environment shrinkage rate test. The density of the concrete components was determined using ultrasonic non-destructive testing.

[0030] Slump, spread, T 500 The units and magnitudes of indicators such as U-shaped box filling height differ significantly, making direct comparison impossible. Max-min normalization is employed to linearly map the data to a specified range (usually [0,1]) to eliminate dimensional differences. Dimensional expressions are transformed into dimensionless expressions, becoming scalars, which facilitates mathematical operations between various performance indicators.

[0031] The specific steps are as follows:

[0032] 1) Calculate extreme values: Calculate x separately for each feature. min and x max ,

[0033] 2) Transform all data points according to the following formula:

[0034]

[0035] x min and x max These are the minimum and maximum values ​​of the original data, respectively.

[0036] Preferably, for the optimal mix design decision model, a reasonable initial mix design can avoid large-scale adjustments to the mix design and related calculations and experiments, thus accelerating the discovery of the optimal mix design. Furthermore, determining a reasonable initial mix design can prevent the optimal mix design decision model from getting stuck in local optima during execution, and can help find the globally optimal mix design.

[0037] Among all the candidate mix proportions that meet the strength constraint conditions, the one with the smallest f4 is selected as the optimal low-temperature rise, low-shrinkage, and self-compacting concrete mix proportion D. * .

[0038] Preferably, in step 1, before on-site concrete pouring, the concrete mix proportions need to be verified by testing slump, spread, and T0. 500 Only when both compressive strength and compressive strength meet the design requirements can we proceed to step 2. If there are properties that do not meet the design requirements, the mix proportion of the concrete is fine-tuned until all properties meet the requirements.

[0039] Preferably, in step 2, each layer of the steel shell has multiple 40-50cm openings as injection ports and grout outlets, and the concrete is injected vertically from the top of each layer of the steel shell into the interior of the steel shell.

[0040] Preferably, in step 3, after each layer of the steel shell is filled, the opening is sealed with a hole sealing plate, water storage and curing are set up, and external heat preservation is carried out for at least 3 days. After the concrete strength reaches 80% of the design strength, the process proceeds to step 4.

[0041] Preferably, step 1 also includes initial temperature control of the concrete slurry. The initial temperature is the benchmark value for the temperature development of the super-mass concrete. The temperature of the concrete raw materials is reduced by using aggregate shading treatment, increasing the heat dissipation time of the cementitious materials, and by adding insulation materials to the tank truck during transportation and setting up sunshades on site.

[0042] Preferably, step 3 also includes external insulation measures: after the concrete is poured, about 5cm of water is placed on the top surface of the concrete for curing, and wooden formwork with low thermal conductivity is used on the sides of the steel box shell. If steel formwork is used, insulation material with low thermal conductivity is covered on the outer surface of the steel formwork.

[0043] Preferably, in step 1, after the optimized concrete mix proportion passes the density test, the subsequent concrete pouring operation is carried out.

[0044] Specifically, the concrete density test of the steel box is conducted in the following manner:

[0045] Multiple steel box specimens were fabricated, each with a rectangular cross-section of 130×330mm and a height of 1m. After concrete pouring, the specimens were cured under natural conditions for 28 days. Ultrasonic non-destructive testing was used to test the density of the steel box concrete, with measurements taken at a cross-shaped pattern along both the long and short sides of the steel box. Only when all steel box specimens met the density test requirements could the final optimized formula be used for pouring.

[0046] If there is a gap between the steel box and the concrete, compared to the through path in a dense state, the pulse wave will bypass the gap and take a diffraction path when there is a gap defect, resulting in a longer propagation path and a lower sound speed.

[0047] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0048] 1. This invention provides a super-massive steel-concrete composite structure that eliminates the passive cooling mode of installing cooling water pipes inside the bridge tower. It reduces the heat of hydration and achieves active cooling by controlling the performance of concrete materials. Furthermore, to ensure the coordinated stress distribution between the steel box and the concrete, an optimal mix design is used to obtain a concrete mix proportion that achieves flow and compaction by its own weight, completely filling the steel structure without vibration. At the same time, it has low shrinkage during the hardening process and good bonding performance with the steel structure interface. This ensures that the steel box and concrete are always tightly bound together during construction and operation, thereby improving the structural bearing capacity and stability.

[0049] 2. The technical solution of the present invention overcomes the problems of large amount of concrete adhesive used in super-large steel box concrete, easy shrinkage and cracking, high heat of hydration and poor crack resistance in the prior art, and simplifies the construction process, saving construction time and cost. Attached Figure Description

[0050] Figure 1 This is a structural diagram of the super-volume steel box concrete of the present invention.

[0051] Figure 2 This is a diagram showing the location of the pump pipe in the first layer of steel box in the injection method of the present invention.

[0052] Figure 3 This is a diagram showing the location of the pump pipe in the second layer of the steel box in the injection method of the present invention.

[0053] Figure 4 This is a diagram showing the location of the pump pipe in the third layer of the steel box in the injection method of the present invention.

[0054] Figure 5 This is a diagram showing the location of the pump pipe in the fourth layer of the steel box in the injection method of the present invention.

[0055] Figure 6 This is a schematic diagram of the block-by-block casting sequence in the grouting method of the present invention.

[0056] Figure 7 This is the hydration heat analysis model for steel box concrete of the present invention.

[0057] Figure 8 This is the temperature change curve of the steel box concrete over time according to the present invention.

[0058] Figure 9 This is a curve showing the temperature difference between the inner and outer surfaces of the steel box concrete according to the present invention.

[0059] Figure 10 This is the temperature field distribution of the steel box concrete according to the present invention.

[0060] Figure 11(a) shows the steel box concrete σ of the present invention. z Stress field distribution diagram.

[0061] Figure 11(b) shows the steel box concrete σ of the present invention. x Stress field distribution diagram.

[0062] Figure 11(c) shows the steel box concrete σ of the present invention. y Stress field distribution diagram.

[0063] Figure 12 This is a diagram showing the arrangement of temperature sensor measuring points in the steel-concrete structure of the present invention.

[0064] Figure 13 This is a measured temperature change curve over time in the steel-concrete composite structure of the present invention.

[0065] Marked in the image:

[0066] 1-Lower bridge tower, 2-Tower base, 3-Steel box concrete structure, 4-First diaphragm, 6-Second diaphragm, 7-Middle chamber, 8-Side chamber, 9-Pump pipe, 10-First injection port, 11-Second injection port, 12-Middle injection port, 13-Side injection port, 14-Side injection port. Detailed Implementation

[0067] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0068] Unless otherwise specified, the use of terms such as "upper," "lower," "left," "right," "center," "inner," and "outer" to indicate orientation or positional relationships in the description of specific embodiments of the present invention is based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the product / equipment / device is typically placed during use. These terms are merely for the purpose of facilitating the description of the present invention or simplifying the description in specific embodiments, enabling those skilled in the art to quickly understand the solution, and do not indicate or imply that a particular device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship. Therefore, they should not be construed as limitations on the present invention.

[0069] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," and "parallel" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, or parallel, but rather that it can be slightly tilted or have a deviation. For example, "horizontal" merely means that its direction is more horizontal relative to "vertical," not that the structure must be completely horizontal, but that it can be slightly tilted. Alternatively, it can be simplified to mean that the corresponding device / component / element, when set in a "horizontal," "vertical," "suspended," or "parallel" direction, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the present invention.

[0070] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing descriptions of identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0071] Furthermore, in the description of the embodiments of the present invention, "several", "more than", and "a number of" represent at least two. The number can be any number, such as 2, 3, 4, 5, 6, 7, 8, or 9, and can even exceed nine.

[0072] Furthermore, in the description of the technical solution of this invention, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "provided with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to common connection methods in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0073] Example 1

[0074] This embodiment discloses a large-scale steel-box concrete structure, which has been implemented in the steel-box concrete project at the base of a bridge tower. Through mechanical property tests, workability tests, adiabatic temperature rise calculations, shrinkage rate tests, and density tests, multiple performance indicators of the experimental mix proportions were obtained. With strength as the basic constraint and self-compacting, low shrinkage, low temperature rise, and high crack resistance as the optimization objectives, an optimal mix proportion decision model was proposed, yielding the recommended mix proportion for the steel-box concrete of the bridge.

[0075] Project Overview:

[0076] like Figure 1 The diagram shows the structural layout of the bridge's tower base. The steel-concrete box girder at the base is divided into four layers on the elevation, and each layer is further divided into three chambers in cross-section, totaling twelve chambers across the four layers. The bridge is a single-tower, double-cable-stayed bridge with a span arrangement of 45m + 185m + 238m + 45m. The bridge tower is a spatially irregularly shaped, twisted steel tower with a total height of 173.3m, which will become the world's tallest inclined bridge tower upon completion. The "V-leg" section at the base is the main load-bearing part of the tower. To improve its load-bearing capacity, C40 concrete is poured into the "V-leg" section, forming a steel-concrete box girder composite structure. The cross-sectional dimensions of the steel-concrete box girder at the base are 8.5 × 20.0m, with a concrete volume of 3055 cubic meters per single "V-leg," exhibiting a "super-massive" characteristic. Based on the cross-sectional chamber structure, the concrete pouring within the box girder is carried out in four layers.

[0077] The steel box concrete structure 3 is installed in the lower bridge tower 1 structure of the bridge. The steel box concrete structure 3 is located at the bottom of the lower bridge tower. The steel box concrete structure 3 includes a steel box shell and concrete poured into the inner cavity of the shell. No cooling water pipes are installed in the steel box shell. The concrete formula includes the following raw materials per cubic meter by weight: cement 200±5kg, fly ash 200±5kg, expansion agent 30±5kg, sand 822±5kg, stone 1047±5kg, and water 151±5kg.

[0078] The steel box concrete structure 3 is embedded in the tower base 2. The steel box concrete structure 3 is trapezoidal in shape. The transverse length of the steel box concrete structure is 7-9m, the longitudinal length of the steel box concrete structure 3 is 10-18m, and the height of the steel box concrete structure 3 is 18-20m.

[0079] The steel box shell is provided with multiple first partitions 4 at intervals from bottom to top. The first partitions 4 divide the inner cavity of the steel box shell into multiple first chambers. Each first chamber is provided with multiple second partitions 6 along the transverse bridge direction. The second partitions 6 divide the first chamber into three chamber units along the transverse bridge direction. The chamber unit located in the middle is the middle chamber 7, and the chamber units located on both sides of the middle chamber 7 are the side chambers 8.

[0080] Example 2

[0081] This embodiment provides a method for pouring concrete into a super-large steel box girder structure, including the following steps:

[0082] Step 1, Preparation before concrete pouring: Verify and adjust the mix proportions of each concrete ingredient for the steel box shell structure to obtain a concrete slurry formula that meets the requirements; in Step 1, the optimal mix proportion of the concrete is obtained according to the following steps:

[0083] Step 11: Determine the initial mix proportion D0 = (W) based on the concrete performance parameters. 10 W 20 W 30 W 40 W 50 W 60 ) T W 10 W indicates the quality of cement. 20 W represents the mass of fly ash. 30 W represents the mass of the expanding agent. 40 W represents the mass of sand. 50 W represents the mass of the stone. 60 Indicates the quality of water; based on low-temperature rise performance, first determine the type of cement and the range of fly ash content: W 20 / (W 10+ W 20 );

[0084] The water-cement ratio range is determined based on low shrinkage properties, where the water-cement ratio refers to: W 60 / (W 10+ W 20 Water consumption range and expansion agent dosage range;

[0085] Based on self-compacting properties, determine the stone particle size range and sand ratio range: W 40 / (W 40+ W 50 );

[0086] Based on the performance guidelines in step 11, conduct trial mixing of 3-5 different concrete mix proportions. Perform the following performance tests on the concrete slurry from these 3-5 different mix proportions: slump, spread, and 7-day compressive strength. The concrete must meet the requirement of 7-day cubic compressive strength > 0.80f. cu,k (f cu,k Under the premise of the standard value of concrete design strength, the mix proportion with the largest slump and spread is selected as the initial mix proportion. The optimal mix proportion is: 200 kg cement, 200 kg fly ash, 20 kg expansion agent, 752 kg sand, 1127 kg aggregate, and 151 kg water.

[0087] Step 12: Based on the initial mix proportion, adjust the design range of each component of the concrete to form a set of candidate mix proportions D; each component of the concrete is designed as follows:

[0088] Cement: based on the standard dosage W 10 Based on this, the amount of cement is increased or decreased by 5 kg / grade to form W 10 -20, W 10 -15, W 10 -10, W10 -5、W 10 W 10 +5, W 10 +10, W 10 +15, W 10 +20 units to be selected;

[0089] Fly ash: Based on the proportion of fly ash in the benchmark mix proportion, the fly ash dosage is varied in 3-4 steps with a fly ash content of ±3% / grade.

[0090] Water: Keep the baseline water-cement ratio constant, and adjust the amount of cementitious material (W) according to the selected mix proportion. 10+ W 20 Determine the water usage;

[0091] Expanding agent: Based on the amount of expanding agent in the standard mix proportion, the amount of expanding agent is varied in 3-4 steps with ±10kg / grade;

[0092] Sand and stone: Keeping the design density of concrete constant, the total weight of sand and stone is obtained by subtracting the mass of cement, fly ash, water, and expansion agent from the design density. Based on the initial mix proportion sand ratio, the sand ratio is varied in 3-4 steps at ±2% / grade to obtain the mass of sand and stone respectively.

[0093] Based on the above raw material design values, several sets of candidate mix proportions D are formed.

[0094] Step 13: Mix concrete for all the selected mix proportions D, and perform adiabatic temperature rise calculation, shrinkage test, compressive strength test, and self-compacting performance test.

[0095] Step 14: Use the optimal mix proportion decision model to select the optimal mix proportion D. * Based on the optimal mix proportion decision-making approach of this invention, the comprehensive performance of each group was obtained. Under the premise of satisfying the strength constraint, the mix proportion with the smallest f4 is: 200kg cement, 200kg fly ash, 30kg expansion agent, 822kg sand, 1047kg stone, and 151kg water. It exhibits comprehensive performance advantages of self-compacting, low shrinkage, and low temperature rise, and is selected as the optimal mix proportion.

[0096] Before pouring concrete on site, it is also necessary to determine the optimal mix proportion D. * Verification is required. Only if the slump, spread, T500 and compressive strength properties all meet the design requirements can we proceed to step 2. If any properties do not meet the design requirements, the concrete mix proportions are fine-tuned until all properties are satisfied.

[0097] Step 2: Layered construction and pouring of concrete for the steel box. In each layer of the steel shell structure, the concrete is poured in separate chambers. The pouring sequence for each chamber is as follows: first, pour the concrete in the two side chambers, and then pour the concrete in the middle chamber. In the same chamber, the concrete is further poured in sections: the steel box shell is provided with multiple pouring ports at intervals along the bridge direction. First, pour the concrete into the pouring port located in the middle position, and then pour the concrete into the pouring ports located at both ends.

[0098] Each layer of the steel shell has multiple 40-50cm openings as injection ports and grout outlets, and the concrete is poured vertically from the top of each layer of the steel shell into the interior of the steel shell.

[0099] After the pump pipes are installed on-site, the concrete is poured in layers, cavities, and sections after the concrete condition is adjusted. This maximizes the time-based heat dissipation of the concrete and avoids the continuous retention and accumulation of internal heat. After the concrete pouring is completed, any remaining concrete on the surface of the steel box is promptly cleaned, and the grout outlets are sealed with formwork. Water retention curing and external insulation measures are implemented. The next layer of steel box and stiffening ribs can only be installed after at least 3 days of curing and until the concrete strength reaches 80% of the design strength.

[0100] The entire construction process of the super-large steel box concrete eliminates the need for cooling water pipes, saving cumbersome procedures such as cooling water pipe installation, water circulation control, and pipe grouting, thus saving time, manpower, and costs.

[0101] Specifically, the construction of the super-large steel box concrete at the bottom of a bridge tower of a certain bridge adopted the pumping pouring process, using a combination of two truck pumps and trailer pumps to complete the pumping pouring process.

[0102] To ensure the compactness of the concrete pouring for the large-volume steel box, the horizontal pouring distance of the concrete within the steel box should be minimized. In this invention, concrete is poured vertically from the top of each steel box, filling all parts of the steel box using its own weight and excellent workability. For example... Figure 2-5 The diagram shows the pump pipe locations for each layer. A 40-50cm opening is made on the top plate of each steel box at the bottom of the tower. This opening serves several purposes: it acts as a concrete pouring port for continuous filling of self-compacting concrete into the steel box; it also serves as a concrete grout outlet to identify whether the concrete is full and to determine when to stop pouring; and it can be used as a manhole for welding workers to move between layers of the steel box. The first layer includes five pouring ports per row along the bridge direction, totaling three rows, arranged according to the positions of the central and side chambers. These pouring ports are divided into two types: one located on the top partition plate, marked as the second pouring port 11, and the other located on the vertical partition plate, marked as the first pouring port 10.

[0103] Layered pouring process: The overall concrete pouring sequence for the steel box is a layered pouring process from the bottom (first layer) to the top (fourth layer). After each layer of concrete is poured, cured, and reaches the target strength and age, a steel box wall panel and stiffening ribs are installed. Layered pouring avoids concentrated heat release during concrete hydration, reducing adiabatic temperature rise. Furthermore, when installing the upper steel box, the concrete already poured in the lower layer can participate in the combined stress, jointly resisting the dead load of the upper steel box, and can also provide support for the lower steel box wall panels, improving stability.

[0104] Figure 2 The middle layer is the first pouring layer. Figure 3 For the second pouring layer, three second pouring ports 11 are set at intervals along the bridge direction in each row. Figure 4 For the third injection layer, three second injection ports 11 are set at intervals along the bridge direction in each row. Figure 5 This is the fourth injection layer, and the injection port for the fourth layer is located on the vertical partition.

[0105] The process involves pouring concrete into three separate chambers within the same steel box layer, based on the cross-sectional characteristics. The pouring sequence is to first pour the two side chambers, followed by the middle chamber. The side chambers, poured first, are closer to the atmosphere, facilitating direct heat transfer and dissipation, thus preventing excessively high temperatures when the core concrete of the middle chamber is poured.

[0106] Segmented process: Concrete pouring within the same chamber is carried out in stages, segmented according to the pouring process. For example... Figure 6 As shown, the cavity space is divided into three pouring blocks according to the location of the pouring inlets. The top surface of the concrete in pouring block ① is flush with the top surface of the central pouring inlet 12; the top surface of the concrete in pouring block ② is flush with the top surface of the side pouring inlet 13; and the highest area is the last pouring block ③. In the initial stage, the pump pipe can evenly distribute concrete at multiple points—the central pouring inlet 12, the side pouring inlet 13, and the edge pouring inlet 14—to quickly fill pouring block ①. During this stage, the amount of concrete poured inside the steel box is relatively small, with few air bubbles, and the concrete flow rate is fast with excellent filling performance, allowing most of the internal volume of the steel box to be filled quickly in a short time. After the top surface of the concrete rises to be flush with the pouring inlet, and fresh concrete continues to emerge from the central pouring inlet 12 for 5 minutes, the central pouring inlet 12 is sealed using a hole-sealing template. Afterward, filler blocks No. 2 are poured into the chamber through the two side pouring ports 14. During pouring, the depth of the pump pipe is adjusted to ensure that the concrete pouring height does not exceed 2m. After grout continues to emerge from the two side pouring ports 13, the two side pouring ports 13 are sealed. Finally, filler blocks No. 3 are poured until the chamber is full.

[0107] Step 3: After the concrete pouring of the first layer of the steel box shell is completed, it is cured until it reaches the target strength and age, and the construction of the next layer of the steel box shell and the pouring of concrete inside the steel box shell are continued; In Step 3, after the pouring of each layer of the steel box shell is completed, the opening is sealed with a hole sealing plate, water storage curing and external heat preservation are set up, and the curing is carried out for at least 3 days. After the concrete strength reaches 80% of the design strength, the process proceeds to Step 4.

[0108] Step 4: Repeat steps 2-3 to obtain the steel box concrete structure.

[0109] The large cross-section steel box wall panels have a significant width-to-thickness ratio, making them prone to deformation under the pressure of the liquid side formwork during concrete pouring. The proposed layered, cavity-based, and block-based pouring process effectively reduces the deformation of the steel box wall panels caused by the concrete.

[0110] In the technical solution of this application, it is also necessary to control the concrete temperature and performance before it is poured into the formwork:

[0111] To minimize the initial temperature of the concrete before it is poured into the formwork, the commercial concrete plant employs measures such as shading the aggregates, increasing the heat dissipation time of the cementitious materials, and pouring concrete at night at low temperatures before mixing. Through strict control, the temperature of the mixed concrete before pouring into the formwork is controlled at 25℃, meeting the 5℃~30℃ temperature control requirement for pouring into the formwork as specified in the "Standard for Construction of Mass Concrete" (GB 50496-2018).

[0112] The transportation time between the ready-mix concrete plant and the construction site is 1 hour. Considering the waiting time for the concrete mixer trucks on site, the concrete must have sufficient slump retention to ensure its workability upon arrival at the bridge site and to ensure that the concrete can be densely poured into the steel box. Furthermore, during the layered pouring process, to prevent the first-poured concrete from failing to withstand the weight of the later-poured concrete and prematurely developing stress cracks, the initial setting time of the concrete must be greater than the interval between pours.

[0113] During the concrete mix design process, admixture compounding technology was used to introduce retarding and slump-retaining functions. Tests showed that the initial setting time of the concrete was 9 hours and 40 minutes, and the final setting time was 13 hours and 20 minutes. The initial setting time was longer than the 6-7 hour pouring time for a single layer of steel box concrete. Two hours after the concrete was mixed and molded, the on-site measured slump was 230 mm, and the spread was 600 mm. The concrete exhibited good encapsulation, no bleeding, and minimal loss of workability, meeting the requirements for pumping construction.

[0114] Heat of hydration analysis of concrete

[0115] The heat of hydration of the concrete in the steel box at the base of a bridge tower was analyzed using the FEANX finite element method. The concrete in the steel box was poured in four layers with timed cooling, without cooling water pipes; the second layer had the largest volume, with a single pour of 984 m³. 3 Therefore, the case of pouring the second layer of concrete was chosen as the analysis object.

[0116] The mechanical and thermal parameters of concrete are set as shown in Table 1, where E, α, and λ are the elastic modulus, linear expansion coefficient, and thermal conductivity of concrete, respectively.

[0117] Table 1 Concrete Material Properties

[0118]

[0119] like Figure 7 The diagram shows the hydration heat analysis model of the steel-concrete composite box girder. The concrete was constructed using 3D solid elements. The mechanical boundary was a consolidated constraint on the bottom surface of the first concrete layer, and the temperature boundary was a fixed temperature of 32℃ on the bottom surface of the first concrete layer. Based on actual bridge testing, the concrete pouring temperature was 25℃, and the average ambient temperature was also 25℃. The calculated adiabatic temperature rise based on material composition was 35.4℃, and m = 1.45 was obtained according to specifications. The convection coefficient β reflects the heat exchange properties between the concrete and the environment, and is related to the wind speed at the bridge site, surface smoothness, and the type and thickness of the formwork and insulation materials. A higher value indicates faster heat dissipation. The top surface of the second concrete layer used a 5cm steel formwork and 2cm of water, with β = 14.5kJ / (m²). 2 ·h·℃); Due to structural design and on-site construction conditions, no insulation measures were installed on the long sides, only 5cm steel formwork was used, β=29.2kJ / (m 2 (·h·℃); The short side is the concrete pouring inlet, and after pouring, it is covered with 1cm geotextile for insulation, β=5.0kJ / (m 2 ·h·℃).

[0120] like Figure 8 The figure shows the temperature variation curve of the steel box concrete over time. The highest temperature at the center of the second layer of concrete is 59.0℃, with a temperature rise of 34℃ after placement. The highest surface temperature is 41.4℃, with a temperature rise of 16.4℃ after placement. Both adiabatic temperature rises are less than the allowable value of 50℃ specified in the standard. After reaching the highest temperature, the cooling rate of the center concrete is 0.2℃ / d, and the cooling rate of the surface concrete is 0.5℃ / d, both less than the allowable value of 2℃ / d specified in the standard.

[0121] like Figure 9 The figure shows the temperature difference curve between the inner and outer surfaces of the steel-concrete box. During the hydration heat release process of the super-large steel-concrete box, the temperature difference between the inner and outer surfaces is consistently less than the allowable value of 25℃ specified in the standard, indicating that the internal cooling and external insulation measures are well controlled, which helps to reduce the temperature stress of the concrete. Figure 10 The diagram shows the temperature field distribution when the center temperature of the second layer of concrete reaches its maximum. The temperature of the second layer of concrete is transferred downwards to the first layer, and the temperature gradient distribution transitions smoothly. The maximum temperature occurs in the central region of the second layer of concrete, while the minimum temperature occurs at the corners of the structural surface.

[0122] The crack resistance of super-large steel box concrete is calculated according to the "Standard for Construction of Mass Concrete" (GB50496-2018): σ≤f tk (1-e -γt ) / K

[0123] In the formula: σ represents the normal stress in each direction of the concrete; f tk The standard value for the tensile strength of concrete is 2.40 MPa for C40 concrete; γ is the coefficient for the increase of tensile strength of concrete with age, taken as 0.3; K is the safety factor for crack prevention, taken as 1.15; therefore, the stress control value for crack prevention of concrete can be calculated to be 1.55 MPa. Figure 11 shows the stress field distribution at the moment of highest internal temperature of concrete. The maximum tensile stress of concrete is concentrated on the surface of the structure. In Figure 11(a), the maximum σ z =1.21MPa, Figure 11(b) shows the maximum σ. x =1.48MPa, Figure 11(c) Maximum σ y =0.92MPa, which is less than the concrete crack-resistant stress control value of 1.55MPa, indicating that the concrete crack resistance meets the specification requirements under the temperature control strategy without cooling water pipes.

[0124] Furthermore, to further verify the effectiveness of the cooling water pipe-free temperature control strategy, actual bridge temperature monitoring was conducted during the concrete pouring process of the second-layer steel box girder of a bridge tower. Based on the temperature field distribution calculated using finite element analysis, temperature measuring points were deployed in the areas of maximum and minimum temperature distribution. For example... Figure 12 The diagram shows the arrangement of temperature sensor measuring points.

[0125] The temperature control targets for steel box concrete are as follows: ① The temperature rise of the concrete pouring body based on the pouring temperature should not exceed 50℃; ② The temperature difference between the inner and outer surfaces of the concrete pouring body should not exceed 25℃; ③ The cooling rate of the concrete pouring body should not exceed 2.0℃ / d; ④ The temperature difference between the surface concrete and the ambient temperature should not exceed 20℃.

[0126] like Figure 13 The figure shows the temperature curves of various parts of the steel box concrete over time. The highest temperature, 56.8℃, was reached at the center point after 45 hours. The temperature rise after placement was 31.8℃, and the subsequent cooling rate was 1.53℃ / day, meeting the temperature control target requirements. The measured maximum temperature difference between the inner and outer surfaces was 22.9℃, and the maximum temperature difference between the surface concrete and the environment was 19.9℃, both meeting the temperature control target requirements.

[0127] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A super-large steel-concrete composite structure, characterized in that, The steel box concrete structure (3) is installed in the lower bridge tower (1) structure of the bridge. The steel box concrete structure (3) is located at the bottom of the lower bridge tower (1). The steel box concrete structure (3) includes a steel box shell and concrete poured into the inner cavity of the shell. The steel box shell does not have a cooling water pipe for cooling the poured concrete. The concrete formula includes the following raw materials per cubic meter by weight: cement 200±5kg, fly ash 200±5kg, expansion agent 30±5kg, sand 822±5kg, stone 1047±5kg, and water 151±5kg.

2. The super-mass steel-concrete composite structure according to claim 1, characterized in that, The steel box concrete structure (3) is embedded in the tower base (2). The steel box concrete structure (3) is trapezoidal in shape. The transverse length of the steel box concrete structure (3) is 7-9m, the longitudinal length of the steel box concrete structure (3) is 10-18m, and the height of the steel box concrete structure (3) is 18-20m.

3. The super-mass steel-concrete composite structure according to claim 2, characterized in that, The steel box shell is provided with multiple first partitions (4) at intervals from bottom to top. The first partitions (4) divide the inner cavity of the steel box shell into multiple first chambers. In each first chamber, multiple second partitions (6) are arranged longitudinally along the transverse bridge direction. The second partitions (6) divide the first chamber into three chamber units along the transverse bridge direction. The chamber unit located in the middle is the middle chamber (7), and the chamber units located on both sides of the middle chamber (7) are the side chambers (8).

4. A method for pouring concrete into an ultra-large steel box, characterized in that, The grouting method is applied to the super-mass steel-concrete composite structure as described in any one of claims 1-3, and specifically includes the following steps: Step 1: Preparation before concrete pouring: Verify and adjust the mix proportions of each raw material in the concrete for the steel box shell to obtain a concrete slurry formula that meets the requirements. Step 2: Layered construction and pouring of concrete for the steel box. In each layer of the steel box shell, the concrete is poured in separate chambers. The pouring sequence of the chambers is as follows: first pour the concrete in the two side chambers, and then pour the concrete in the middle chamber. In the same chamber, the concrete is further poured in sections: the steel box shell is provided with multiple pouring ports at intervals along the bridge direction. First pour the concrete into the pouring port located in the middle position, and then pour the concrete into the pouring ports located at both ends. Step 3: After the concrete pouring of the first layer of the steel box shell is completed, it is cured and reaches the target strength and age, and then the construction of the next layer of the steel box shell and the pouring of concrete inside the steel box shell are carried out. Step 4: Repeat steps 2-3 to obtain the steel box concrete structure.

5. The method for pouring concrete into a super-large steel box according to claim 4, characterized in that, In step 1, the optimal mix proportion of the concrete is obtained according to the following steps: Step 1: Determine the initial mix proportion D0 = (W...) based on the concrete performance parameters. 10， W 20， W 30， W 40， W 50， W 60 ) T ; W 10 W indicates the quality of cement. 20 W represents the mass of fly ash. 30 W represents the mass of the expanding agent. 40 W represents the mass of sand. 50 W represents the mass of the stone. 60 Indicates the mass of water; Step 2: Based on the initial mix proportion, adjust the design range of each component of the concrete to form a set of candidate mix proportions. D ; Step 3: For all the aforementioned candidate mix proportion sets D Concrete mixing is carried out, and adiabatic temperature rise calculation, shrinkage test, compressive strength test and self-compacting performance test are performed. Step 4: Use the optimal mix design decision model to select the optimal mix design. D .

6. The method for pouring super-large steel box concrete according to claim 5, characterized in that, In step 1, before pouring concrete on site, the concrete mix proportions need to be verified by testing slump, spread, and T. 500 Only when both compressive strength and compressive strength meet the design requirements can we proceed to step 2. If there are properties that do not meet the design requirements, the mix proportion of the concrete is fine-tuned until all properties meet the requirements.

7. The method for pouring concrete into a super-large steel box according to claim 4, characterized in that, In step 2, multiple 40-50cm openings are made in each layer of the steel shell as injection ports and grout outlets, and the concrete is poured vertically from the top of each layer of the steel shell into the interior of the steel shell.

8. The method for pouring concrete into a super-large steel box according to claim 7, characterized in that, In step 3, after each layer of the steel shell is filled, the opening is sealed with a hole sealing plate, water storage and curing are set up, and external heat preservation is carried out for at least 3 days. After the concrete strength reaches 80% of the design strength, the process proceeds to step 4.

9. The method for pouring concrete into a super-large steel box according to claim 8, characterized in that, Step 1 also includes initial temperature control of the concrete slurry. The initial temperature is the benchmark value for the temperature development of super-volume concrete. The temperature of the concrete raw materials is reduced by using aggregate shading treatment, increasing the heat dissipation time of cementitious materials, and by adding insulation materials to the tank trucks during transportation and setting up sunshades on site.

10. The method for pouring concrete into a super-large steel box according to claim 8, characterized in that, Step 3 also includes external insulation measures: after the concrete is poured, about 5cm of water is placed on the top surface of the concrete for curing, and the sides of the steel box shell are covered with wooden formwork with low thermal conductivity as an insulation layer. If steel formwork is used as the side formwork, then a thermal insulation material with low thermal conductivity should be covered on the outer surface of the steel formwork.

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