Method of prestressing a composite beam

Abstract

The present application relates to a kind of methods for prestressing of composite beam, comprising the following steps: by the multiple jacking devices along the longitudinal arrangement of steel beam jacking, the linear shape of whole steel beam after jacking is generally circular arc curve;Concrete is covered on the steel beam after jacking, and composite beam is formed;Cancel the jacking device of steel beam jacking, and make composite beam drop to design state, to apply continuous pre-compressive stress to composite beam.Because by the multiple jacking devices along the longitudinal arrangement of steel beam jacking, the linear shape of whole steel beam after jacking is generally circular arc curve, in the case where the jacking linear shape of steel beam is circular arc curve, the bending moment of each point on steel beam is also equal, after concrete is covered on steel beam and drops to design state, it can apply continuous uniform pre-compressive stress to composite beam, and the continuous uniform pre-compressive stress applied to composite beam can offset the continuous change influence of temperature change and shrinkage creep to composite beam, to limit crack of composite beam.

Description

Technical Field

[0001] This invention relates to the field of bridge construction, and in particular to a method for applying prestress to composite beams. Background Technology

[0002] Currently, steel-concrete composite beams are being used more and more widely in my country. They combine the excellent tensile properties of steel with the excellent compressive properties of concrete. Compared with traditional reinforced concrete beams, composite beams reduce the structural self-weight and cross-sectional dimensions, increase the ductility of the beam, and shorten the construction period. Compared with steel beams, they reduce the amount of steel used, improve the stiffness of the bridge, increase the stability and integrity of the bridge, and at the same time improve the fire resistance and durability of the structure.

[0003] The application of steel-concrete composite beams in bridges also presents some design challenges, especially since concrete slabs are prone to cracking, and the methods for controlling crack width are quite complex.

[0004] Concrete slabs are prone to cracking, primarily due to the excellent compressive strength but poor tensile strength of concrete. When a concrete slab is subjected to tensile stress, cracks easily form. The tensile stress in a concrete slab is mainly caused by the following factors: ① negative bending moment caused by the structure's self-weight and live load, which has a localized effect; ② temperature changes, which have a continuous effect; ③ shrinkage and creep, which have a continuous effect. Among these, temperature changes and shrinkage and creep have the greatest impact on composite beams.

[0005] In related technologies, the crack width of concrete is usually controlled by methods such as the top-and-drop beam method or by incorporating prestressing into the concrete slab. The top-and-drop beam method involves lifting a steel beam, covering it with a concrete slab, and then lowering the steel beam to apply prestress to the concrete, thereby reducing the damage to the concrete caused by subsequent tensile stress.

[0006] However, the current top-drop beam method can only apply prestress to local points or sections, and can only adapt to the local effects of negative bending moments caused by the self-weight and live load of the composite beam structure. It cannot adapt to the continuous changes in temperature and shrinkage creep on the composite beam, which will still cause cracks in the composite beam. Summary of the Invention

[0007] This invention provides a method for applying prestress to composite beams to solve the problem in related technologies that cannot adapt to the continuous changes in temperature and shrinkage / creep of composite beams, thus causing cracks in the composite beams.

[0008] In a first aspect, a method for applying prestress to a composite beam is provided, comprising the following steps:

[0009] The steel beams are lifted by multiple lifting devices arranged along the longitudinal direction of the bridge, so that the overall shape of the steel beams after lifting is roughly an arc curve.

[0010] Concrete is then poured over the lifted steel beams to form a composite beam.

[0011] The lifting device is removed from the steel beam, allowing the composite beam to descend to its design state so that continuous prestress can be applied to the composite beam.

[0012] In some embodiments, before the step of lifting the steel beam using multiple lifting devices arranged along the longitudinal direction of the bridge to make the overall shape of the lifted steel beam generally an arc curve, the following steps are included:

[0013] Calculate the tensile stress generated by the composite beam during construction and use based on the design parameters and working conditions of the composite beam;

[0014] The target preload stresses, which are equal in magnitude but opposite in direction, are obtained based on the calculated tensile stress.

[0015] The arc-shaped curve after the steel beam is lifted is calculated based on the target prestress.

[0016] In some embodiments, calculating the arc-shaped curve of the steel beam after jacking based on the target preload stress includes the following steps:

[0017] A steel beam model was created in finite element software based on the design parameters of the composite beam.

[0018] The steel beam model is simulated to be lifted so that the shape of the steel beam model is an arc curve with an opening downward and a radius of R.

[0019] A composite beam model is established based on the steel beam model after jacking;

[0020] The estimated prestressing stress of the concrete above the composite beam model after it has been laid back, calculated using finite element software;

[0021] Determine whether the estimated prestress value is within the range of the target prestress and the allowable compressive strength of the concrete. If so, use R as the radius of the arc curve after the steel beam is lifted.

[0022] Otherwise, adjust the value of radius R, recalculate the estimated prestress obtained by the concrete above the composite beam model after it falls back, and continue to judge the estimated prestress.

[0023] In some embodiments, the design parameters include the structural dimensions of the composite beam and the material properties of the concrete. The operating condition information includes the loading age of the concrete, ambient temperature, and ambient humidity. The calculation of the tensile stress generated in the concrete of the composite beam during construction and use based on the design parameters and operating condition information includes the following steps:

[0024] The creep coefficient of concrete is obtained based on the material properties of concrete, ambient humidity, and the loading age of concrete.

[0025] The time curve of concrete creep stress was obtained based on the creep coefficient and the structural dimensions of the composite beam.

[0026] The time curve of concrete shrinkage stress was obtained based on the material properties of concrete, ambient temperature, ambient humidity, and the structural dimensions of the composite beam.

[0027] The tensile stress generated in concrete during construction and use is obtained from the time curves of shrinkage stress and creep stress in concrete.

[0028] In some embodiments, the process of lifting the steel beam using multiple lifting devices arranged along the longitudinal direction of the bridge, so that the overall shape of the lifted steel beam is generally an arc curve, includes the following steps:

[0029] The lifting amount of each lifting device is calculated based on the pre-calculated arc curve of the steel beam after lifting and the position of each lifting device.

[0030] The steel beams are lifted simultaneously according to the lifting capacity of each lifting device.

[0031] In some embodiments, before calculating the lifting amount of each lifting device based on the pre-calculated arc curve of the steel beam after lifting and the position of each lifting device, the following steps are included:

[0032] Calculate the spacing between two adjacent jacking devices based on the total length and inter-section length of the steel beam, so that the spacing between two adjacent jacking devices is less than five times the inter-section length of the steel beam or less than five times the beam height of the steel beam.

[0033] The lifting devices are arranged at equal intervals below the steel beams.

[0034] In some embodiments, covering the jacked steel beam with concrete to form a composite beam includes the following steps:

[0035] Multiple precast concrete slabs were placed over the lifted steel beams;

[0036] Wet joint concrete is poured into the gaps between two adjacent concrete slabs and between the concrete slab and the steel beam.

[0037] In some embodiments, covering the jacked steel beam with concrete to form a composite beam includes the following steps:

[0038] Install shear studs above the steel beam, so that the shear studs protrude from the upper surface of the steel beam;

[0039] Concrete is poured on top of the steel beam to form a composite beam, and the concrete covers the shear studs.

[0040] In some embodiments, before the step of lifting the steel beam using multiple lifting devices arranged along the longitudinal direction of the bridge to make the overall shape of the lifted steel beam generally an arc curve, the following steps are included:

[0041] The lifting device is installed on a support or temporary pier below the steel beam.

[0042] In some embodiments, before canceling the lifting device's jacking of the steel beam and lowering the composite beam to its design state to apply continuous prestress to the composite beam, the following steps are included:

[0043] The concrete should be cured for at least 28 days until the concrete above the steel beam reaches 90% of its design strength.

[0044] The beneficial effects of the technical solution provided by this invention include:

[0045] This invention provides a method for applying prestress to a composite beam. By using multiple lifting devices arranged along the longitudinal direction of the bridge to lift the steel beam, the overall shape of the lifted steel beam is roughly an arc curve. When the lifting shape of the steel beam is an arc curve, the bending moment at each point on the steel beam is also equal. After the concrete covers the steel beam and lowers it to the design state, a continuous and uniform prestress can be applied to the composite beam. The continuous and uniform prestress applied to the composite beam can offset the effects of temperature changes and shrinkage and creep on the continuous changes of the composite beam, thereby limiting the formation of cracks in the composite beam. Attached Figure Description

[0046] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0047] Figure 1 A flowchart illustrating a method for applying prestress to a composite beam, as provided in an embodiment of the present invention;

[0048] Figure 2 for Figure 1 Flowchart prior to step S1;

[0049] Figure 3 for Figure 2 Flowchart of step S03;

[0050] Figure 4 This is a schematic diagram of the structure after the steel beam is erected, as provided in an embodiment of the present invention.

[0051] Figure 5This is a schematic diagram of the steel beam after it has been lifted by the lifting device, according to an embodiment of the present invention.

[0052] Figure 6 This is a schematic diagram of the structure after concrete has been covered on the lifted steel beam, as provided in an embodiment of the present invention.

[0053] Figure 7 A schematic diagram of the composite beam whose jacking is cancelled after the concrete strength reaches the required level, provided in an embodiment of the present invention.

[0054] Figure 8 This is a cross-sectional schematic diagram of a composite beam provided in an embodiment of the present invention. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] This invention provides a method for applying prestress to composite beams, which can solve the problem in related technologies that cannot adapt to the continuous changes in temperature and shrinkage / creep of composite beams, thus causing cracks in the composite beams.

[0057] See Figure 1 and Figures 4 to 6 As shown in the figure, a method for applying prestress to a composite beam provided by an embodiment of the present invention may include: S1: lifting the steel beam using multiple lifting devices arranged along the longitudinal direction of the bridge, so that the overall shape of the lifted steel beam is generally an arc curve; S2: covering the lifted steel beam with concrete to form a composite beam; S3: canceling the lifting of the steel beam by the lifting devices, allowing the composite beam to be lowered to the design state, so as to apply continuous prestress to the composite beam. That is, first lifting the steel beam to an arc shape, then constructing and installing concrete slabs or pouring concrete on top of the steel beam to form a composite beam, and finally lowering the composite beam to achieve the application of prestress in the concrete.

[0058] To apply a continuous and equal prestress to the composite beam, the elongation of each small segment of the beam must be equal. Therefore, the bending moment on each section of the composite beam must be equal. In the principles of mechanics of materials, when the bending moment of a beam is equal, the deflection curve is a circular arc. In this embodiment, because the steel beam is lifted by multiple lifting devices arranged along the longitudinal direction of the bridge, the overall shape of the lifted steel beam is roughly a circular arc. According to the conversion principle of displacement and internal force, when the lifting shape of the steel beam is a circular arc, the bending moment at each point on the steel beam is also equal. After the concrete covers the steel beam and lowers it to the design state, a continuous and uniform prestress can be applied to the composite beam. The continuous and uniform prestress applied to the composite beam can offset the effects of temperature changes and shrinkage and creep on the continuous changes of the composite beam, thereby limiting the formation of cracks in the composite beam.

[0059] Compared to jacking up a section of steel beam and then pouring a section of concrete, this scheme uses a single jacking followed by unified concrete construction. This not only reduces the number of jacking operations but also simplifies the stress distribution of the steel beam compared to staged jacking, making the jacking amount easier to calculate. Furthermore, constructing the concrete above the steel beam after jacking improves efficiency and ensures consistent construction time and conditions across different areas, reducing inconsistencies in stress conditions due to varying construction times and improving the consistency of the composite beam concrete. In this embodiment, jacking the steel beam into a circular arc further simplifies the calculation of the jacking amount. The arc shape also ensures equal elongation across all parts of the composite beam, allowing for uniform prestressing of the concrete above the beam after its descent. This prevents uneven prestressing across areas, which could reduce the quality of the composite beam and achieves a uniform distribution of prestress, thus better controlling crack width.

[0060] See Figure 1 As shown, in some optional embodiments, before step S1, i.e., before the step of lifting the steel beam using multiple lifting devices arranged along the longitudinal direction of the bridge to make the overall shape of the lifted steel beam generally an arc curve, the following steps may be included: S01: Calculate the tensile stress generated by the composite beam during construction and use based on the design parameters and working conditions of the composite beam; S02: Obtain the target preload stress of equal magnitude and opposite direction based on the calculated tensile stress; S03: Calculate the arc curve of the steel beam after lifting based on the target preload stress. In other words, the tensile stress that the composite beam needs to overcome is first calculated based on the actual working conditions and the design parameters of the composite beam. The target preload stress that needs to be applied to the concrete of the composite beam is then deduced from the tensile stress that may be generated during construction. The tensile stress that may be generated during construction is offset by the preload stress of equal magnitude and opposite direction, so that the concrete is mainly subjected to compression rather than tension during use, thereby improving the service life of the concrete and the construction quality of the composite beam.

[0061] See Figures 1 to 3 As shown, in some optional embodiments, step S03, namely calculating the arc-shaped curve of the steel beam after lifting based on the target prestress, includes the following steps: establishing a steel beam model in finite element software based on the design parameters of the composite beam; simulating the lifting of the steel beam model so that the line shape of the steel beam model is an arc-shaped curve with an opening downward and a radius of R; establishing a composite beam model based on the lifted steel beam model; calculating the estimated prestress obtained by the concrete above the composite beam model after it falls back using finite element software; determining whether the estimated prestress value is within the range of the target prestress and the allowable compressive strength of the concrete; if so, using R as the radius of the arc-shaped curve of the steel beam after lifting; otherwise, adjusting the value of the radius R, recalculating the estimated prestress obtained by the concrete above the composite beam model after it falls back, and continuing to judge the estimated prestress. In other words, a composite beam model is built using finite element method (FEM) software. An initial radius R of the circular arc is pre-defined based on experience. The FEM software simulates the lifting of the steel beam, causing it to form an arc with radius R during the lifting process. Based on the estimated prestress of the concrete after the fall, calculated by the FEM software, this estimated prestress is compared with the target prestress and the allowable compressive strength of the concrete. R is repeatedly adjusted until the final estimated prestress falls between the target prestress and the allowable compressive strength of the concrete. Using this final R as the radius of the circular arc after the steel beam is lifted ensures that the concrete prestress exceeds the potential tensile stress, thus compressing the concrete, while simultaneously ensuring that the prestress remains within the allowable compressive strength, preventing excessive prestress. FEM simulation simplifies the calculation process for the circular arc, allowing for a satisfactory result after a few trials. Furthermore, FEM software can simulate the actual stress on the composite beam, providing a more intuitive and error-free simulation compared to manual calculations, thus reducing the computational difficulty.

[0062] The radius R can also be calculated using the following method:

[0063] According to the formulas for curvature and bending moment in mechanics of materials:

[0064] In the above formula, ρ is the curvature; M is the bending moment; E is the elastic modulus of concrete; and I is the bending moment of inertia of the combined beam (converted according to the concrete material).

[0065] According to the formula for calculating stress in mechanics of materials:

[0066] In the above formula, σ is the required prestress of the concrete slab; y0 is the distance from the upper edge of the concrete to the neutral axis of the bonding beam (converted according to the concrete material).

[0067] Conversion formula between radius of curvature and curvature:

[0068] Substituting equations (1) and (2) into equation (3), we obtain the radius R as:

[0069]

[0070] Therefore, as long as the required prestress σ of the concrete and the distance y0 from the upper edge of the concrete to the neutral axis of the bonding beam are known, the jacking radius R can be derived.

[0071] When calculating the distance y0 from the top edge of the concrete to the neutral axis of the composite beam, first calculate the area As and centroidal axis height ys of the steel beam, and the area Ac and centroidal axis height yc of the concrete. Here, ys is the distance from the centroidal axis of the steel beam to the top of the composite beam, and yc is the distance from the centroidal axis of the concrete to the top of the composite beam (see details). Figure 8 (As shown).

[0072] Convert the steel to concrete and calculate the elastic modulus ratio n:

[0073] Among them, E S E represents the elastic modulus of the steel beam. C This refers to the elastic modulus of concrete.

[0074] Calculate the converted combined area A0:

[0075] Based on equations (4) and (5) above, the converted neutral axis position y0 can be calculated:

[0076]

[0077] See Figure 1 and Figure 2As shown, in some optional embodiments, the design parameters include the structural dimensions of the composite beam and the material properties of the concrete. The working condition information includes the loading age of the concrete, ambient temperature, and ambient humidity. Step S01, which calculates the tensile stress generated in the concrete of the composite beam during construction and use based on the design parameters and working condition information of the composite beam, includes the following steps: obtaining the creep coefficient of the concrete based on the material properties of the concrete, ambient humidity, and the loading age of the concrete; obtaining the time curve of the creep stress of the concrete based on the creep coefficient and the structural dimensions of the composite beam; obtaining the time curve of the shrinkage stress of the concrete based on the material properties of the concrete, ambient temperature, ambient humidity, and the structural dimensions of the composite beam; and obtaining the tensile stress generated in the concrete during construction and use based on the time curves of the shrinkage stress and creep stress. In other words, in addition to the load of the composite beam, the creep and shrinkage of the concrete itself also need to be considered. The creep stress is mainly affected by the concrete mix ratio and ambient humidity. Over time, the creep of the concrete will gradually increase until it stabilizes. The creep stress of the concrete at various time periods can be roughly obtained through the time curve of the creep stress. In addition to the influence of concrete mix proportions and ambient humidity, the shrinkage stress of concrete is also affected by ambient temperature. By combining creep stress and shrinkage stress, the tensile stress that the composite beam concrete may generate can be roughly calculated. In this embodiment, the creep stress is approximately 1.5 MPa, and the total tensile stress is approximately 2 MPa.

[0078] See Figure 1 , Figure 4 and Figure 5 As shown, in some optional embodiments, step S1, which involves lifting the steel beam using multiple lifting devices arranged along the longitudinal direction of the bridge to achieve a roughly circular arc shape after lifting, includes the following steps: calculating the lifting amount of each lifting device based on the pre-calculated circular arc shape of the lifted steel beam and the position of each lifting device; and simultaneously lifting the steel beam according to the lifting amount of each lifting device. In other words, lifting the steel beam simultaneously using multiple lifting devices shortens the lifting time and distributes the weight of the steel beam across different lifting devices, preventing excessive load on a single lifting device and reducing its service life. Furthermore, lifting allows for better control of the steel beam's curve, ensuring consistent elongation across all areas of the steel beam within the same time period and equal tensile stress throughout the beam, preventing damage to the steel beam during lifting and improving the construction quality of the composite beam.

[0079] See Figure 1 , Figure 4 and Figure 5As shown, in some optional embodiments, before calculating the lifting amount of each lifting device based on the pre-calculated arc curve of the steel beam after lifting and the position of each lifting device, the following steps are included: calculating the spacing between two adjacent lifting devices based on the total length and segment length of the steel beam, such that the spacing between two adjacent lifting devices is less than five times the segment length of the steel beam or less than five times the beam height of the steel beam; and arranging the lifting devices at equal intervals below the steel beam. That is, the lifting devices are arranged at equal intervals below the steel beam to ensure that the force on each lifting device is approximately equal. At the same time, when the steel beam is a steel truss beam, the spacing between two adjacent lifting devices is less than five times the segment length of the steel beam, which reduces the spacing between each apex, making the curve of the steel beam after lifting closer to an arc curve, so that the compression rate of the concrete at each position after falling back is approximately equal, and the prestress applied to the concrete is approximately consistent. In this embodiment, the span length W of the steel beam is 12m, the total length of the steel beam is 432m, and the distance L1 between the two lifting devices is 48m < 5 * W = 60m. In other embodiments, the appropriate distance between the lifting devices can be determined based on the total length and span length of the steel beam. When the steel beam is a steel box girder, the distance between two adjacent lifting devices is less than five times the beam height; when the steel beam is a steel plate girder, the distance between two adjacent lifting devices is less than five times the beam height.

[0080] See Figure 1 and Figure 6 As shown, in some optional embodiments, step S2, which involves covering the lifted steel beam with concrete to form a composite beam, includes the following steps: covering the lifted steel beam with multiple precast concrete slabs; and pouring wet joint concrete to fill the gaps between adjacent concrete slabs and the gaps between the concrete slabs and the steel beam. In other words, by precasting the concrete slabs beforehand and then installing them on top of the lifted steel beam, the construction time is shortened, and concrete creep and shrinkage are released in advance, reducing creep or shrinkage during use and lowering the tensile stress generated by the concrete. The gaps between the concrete slabs are connected by the wet joint concrete, and the concrete slabs are also connected to the steel beam by the wet joint concrete.

[0081] See Figure 1 and Figure 6 As shown, in some optional embodiments, step S2, which involves covering the jacked steel beam with concrete to form a composite beam, includes the following steps: installing shear studs above the steel beam, making the shear studs protrude from the upper surface of the steel beam; pouring concrete on top of the steel beam to form a composite beam, and covering the shear studs with concrete. By installing shear studs above the steel beam and connecting the shear studs to the upper concrete slab through concrete pouring, the connection strength between the steel beam and the concrete slab is further improved, thus enhancing the construction quality of the composite beam.

[0082] See Figure 1 and Figure 4 As shown, in some optional embodiments, before step S1, i.e., before the step of lifting the steel beam using multiple lifting devices arranged along the longitudinal direction of the bridge to make the overall shape of the lifted steel beam generally an arc curve, the following steps are included: installing the lifting devices on supports or temporary piers below the steel beam. That is, the lifting devices are installed above the supports or temporary piers. In this embodiment, the lifting devices are installed above the temporary piers. Since steel beams are generally installed using the support method, temporary supports or temporary piers are built below the steel beam during the construction process. Compared to arranging the lifting devices on the ground using other devices, arranging the lifting devices above the temporary piers reduces the amount of equipment used during construction. At the same time, the temporary piers have a strong load-bearing capacity and can meet the support requirements of the lifting devices during the lifting process.

[0083] See Figure 1 As shown, in some optional embodiments, before step S3, i.e., before canceling the lifting device's jacking of the steel beam and lowering the composite beam to its design state to apply continuous prestress to the composite beam, the following steps are included: curing the concrete for at least 28 days until the concrete above the steel beam reaches 90% of its design strength. That is, curing the concrete to 90% of its design strength first, and then lowering the jacking device after the concrete has reached its design strength, can prevent significant deformation of the concrete due to compression after lowering, which could lead to damage to the bridge deck above the composite beam. This ensures the construction quality of the composite beam concrete.

[0084] In the description of this invention, it should be noted that the terms "upper," "lower," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Unless otherwise expressly specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication between two elements. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0085] It should be noted that in this invention, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0086] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for applying prestress to a composite beam, characterized in that, It includes the following steps: The creep coefficient of concrete is obtained based on the material properties of concrete, ambient humidity, and the loading age of concrete. The time curve of concrete creep stress was obtained based on the creep coefficient and the structural dimensions of the composite beam. The time curve of concrete shrinkage stress was obtained based on the material properties of concrete, ambient temperature, ambient humidity, and the structural dimensions of the composite beam. The tensile stress generated in concrete during construction and use is obtained from the time curves of shrinkage stress and creep stress in concrete. The target preload stresses, which are equal in magnitude but opposite in direction, are obtained based on the calculated tensile stress. Calculate the arc-shaped curve of the steel beam after jacking up based on the target prestress; The steel beams are lifted by multiple lifting devices arranged along the longitudinal direction of the bridge, so that the overall shape of the steel beams after lifting is roughly an arc curve. Concrete is then poured over the lifted steel beams to form a composite beam. The lifting device is removed from the steel beam, allowing the composite beam to descend to its design state in order to apply continuous prestress to the composite beam; The calculation of the arc-shaped curve of the steel beam after jacking based on the target preload stress includes the following steps: A steel beam model was created in finite element software based on the design parameters of the composite beam. The steel beam model is simulated to be lifted, so that the shape of the steel beam model is an arc curve with an opening downward and a radius of R; A composite beam model is established based on the steel beam model after jacking; The estimated prestressing stress of the concrete above the composite beam model after it has been laid back, calculated using finite element software, is based on the calculation of the composite beam model. Determine whether the estimated prestress value is within the range of the target prestress and the allowable compressive strength of the concrete. If so, use R as the radius of the arc curve after the steel beam is lifted. Otherwise, adjust the value of radius R, recalculate the estimated prestress obtained by the concrete above the composite beam model after it falls back, and continue to judge the estimated prestress.

2. The method for applying prestress to a composite beam as described in claim 1, characterized in that, The steel beam is lifted using multiple lifting devices arranged along the longitudinal direction of the bridge, so that the overall shape of the lifted steel beam is roughly an arc curve. The process includes the following steps: The lifting amount of each lifting device is calculated based on the pre-calculated arc curve of the steel beam after lifting and the position of each lifting device. The steel beams are lifted simultaneously according to the lifting capacity of each lifting device.

3. The method for applying prestress to a composite beam as described in claim 2, characterized in that, Before calculating the lifting amount of each lifting device based on the pre-calculated arc curve of the steel beam after lifting and the position of each lifting device, the following steps are included: Calculate the spacing between two adjacent jacking devices based on the total length and inter-section length of the steel beam, so that the spacing between two adjacent jacking devices is less than five times the inter-section length of the steel beam or less than five times the beam height of the steel beam. The lifting devices are arranged at equal intervals below the steel beams.

4. The method for applying prestress to a composite beam as described in claim 1, characterized in that, The concrete is then poured over the jacked steel beams to form a composite beam, comprising the following steps: Multiple precast concrete slabs were placed over the lifted steel beams; Wet joint concrete is poured into the gaps between two adjacent concrete slabs and between the concrete slab and the steel beam.

5. The method for applying prestress to a composite beam as described in claim 1, characterized in that, The concrete is then poured over the jacked steel beams to form a composite beam, comprising the following steps: Install shear studs above the steel beam, so that the shear studs protrude from the upper surface of the steel beam; Concrete is poured on top of the steel beam to form a composite beam, and the concrete covers the shear studs.

6. The method for applying prestress to a composite beam as described in claim 1, characterized in that, Before the step of lifting the steel beam using multiple lifting devices arranged along the longitudinal direction of the bridge, so that the overall shape of the lifted steel beam is roughly an arc curve, the following steps are included: The lifting device is installed on a support or temporary pier below the steel beam.

7. The method for applying prestress to a composite beam as described in claim 1, characterized in that, Before removing the jacking device from the steel beam and lowering the composite beam to its design state to apply continuous prestress to the composite beam, the following steps are included: The concrete should be cured for at least 28 days until the concrete above the steel beam reaches 90% of its design strength.

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