A construction method for the bridge deck structure of a through type basket steel box tied arch bridge

Abstract

The present invention provides a construction method for the deck structure of a through basket steel box tied arch bridge, including construction steps such as gantry crane installation, construction of main girder assembly supports and jacking supports, main girder assembly, erection of cross beam supports, cross beam hoisting, deck paving, and removal of cross beam supports. After the current segment is built, a structural system with load-bearing capacity is formed, and the self-weight of the cross beam and the deck no longer needs to be borne by the cross beam supports. Therefore, after the deck structure of one segment is assembled, the cross beam supports can be removed. The removed cross beam supports are dragged to the next segment for the installation of the cross beam of the next segment. The construction method in the present invention, according to the force change during the assembly process of the structure and based on the designed structural force transmission path, compared with the conventional method of erecting the beam body with full-span supports, greatly saves the cost of erecting the supports for the assembly of the arch bridge deck structure and also shortens the construction period.

Description

Technical Field

[0001] The invention belongs to the technical field of the construction technology of the deck structure of a through basket-shaped steel box tied arch bridge, and particularly relates to a construction method for the deck structure of a through basket-shaped steel box tied arch bridge. Background Art

[0002] The deck structure of a through basket-shaped steel box tied arch bridge generally consists of three parts: cross beams, longitudinal beams (side main beams / main beams) and deck plates. Among them, the deck plates are supported on the cross beams, and the cross beams are supported on the side main beams.

[0003] For the deck structure of a through basket-shaped steel box tied arch bridge, currently, the bracket method is generally adopted for assembly. First, brackets are erected, then the cross beams and longitudinal beams are assembled on the brackets, and finally the deck plates are installed on the cross beams. This traditional construction process requires a large number of brackets to be erected within the width and length ranges of the bridge deck for assembling the cross beams, and also requires brackets to be erected under the side main beams for assembling the longitudinal beams. The traditional method has problems such as a large number of brackets, a large amount of foundation pouring, and cumbersome erection and removal of brackets. Secondly, since the cross beams are supported on the side main beams, before the cross beams are welded to the deck plates, the cross beams need to bear their own weights and the weights of the upper deck plates. However, the special inverted T-shaped cross-section form of the cross beams determines that they are extremely prone to lateral instability problems. Usually, the way to deal with this is to add brackets under the cross beams to make the cross beams in a multi-point support state, thereby reducing the risk of lateral instability, which further increases the number of brackets. In addition, the main beam cross-section of a basket-shaped arch bridge is generally an inward-inclined inclined section, which has a tendency to rotate inward by itself. Moreover, the inward-inclined main beam also bears the torque applied by the cross beams, which will further cause the main beam to twist inward, making it difficult to position the main beam in space. Especially at the arch-beam connection section, the spatial attitude of the main beam will directly affect the inward-inclined angle of the arch rib, and the positioning is very difficult.

[0004] In summary, for the deck structure of a through basket-shaped steel box tied arch bridge, there are three major problems in the assembly process: a large number of brackets, easy instability of the cross beams, and difficult spatial positioning of the main beams. Summary of the Invention

[0005] Aiming at the above problems in the prior art, the present invention aims to provide a construction method for the deck structure of a through basket-shaped steel box tied arch bridge, which solves the problems of a large number of brackets used, easy instability of the cross beams, and difficult spatial positioning of the main beams existing in the prior art during the assembly of the deck structure of a through basket-shaped steel box tied arch bridge by the bracket method.

[0006] In order to achieve the above invention purpose, the technical solution adopted by the present invention is as follows:

[0007] A construction method for the deck structure of a through basket - type steel box tied - arch bridge is provided. The deck of the through basket - type steel box tied - arch bridge includes multiple segments spliced together. Each segment includes two main girders arranged at intervals, and multiple cross - beams are arranged between the two main girders. Multiple deck slabs are arranged on the multiple cross - beams; under each of the two main girders, there are a main girder assembly support and a jacking support, and the bottoms of the main girder assembly support and the jacking support are fixedly connected to the ground; the cross - section of each cross - beam is in an inverted "T" - shaped structure;

[0008] The construction method for the deck structure of the through basket - type steel box tied - arch bridge includes:

[0009] Step 1, installation of gantry crane. Install the two vertical supports of the gantry crane on both sides of the through basket - type steel box tied - arch bridge in the length direction; the horizontal support of the gantry crane is located at the top of the through basket - type steel box tied - arch bridge, and a winch is slidably arranged on the horizontal support of the gantry crane;

[0010] Step 2, construction of main girder assembly support and jacking support. A plurality of main girder assembly supports and jacking supports are arranged on both sides of the through basket - type steel box tied - arch bridge in the length direction;

[0011] Step 3, main girder assembly. Lift the two main girders in the current segment onto the main girder assembly supports and jacking supports on both sides of the through basket - type steel box tied - arch bridge in the length direction respectively by the winches on the gantry crane;

[0012] Step 4, erection of cross - beam support. Erect a cross - beam support between the two main girders in the current segment, and a first jack is arranged at the top of the cross - beam support;

[0013] Step 5, cross - beam hoisting. Hoist multiple cross - beams onto the two main girders and the cross - beam support by the gantry crane. After the cross - beams are positioned, fix the two ends of each cross - beam to the webs of the two main girders respectively, and the first jack extends upward and applies a jacking force to the middle of the cross - beam bottom plate;

[0014] Step 6, deck slab paving. Lift multiple deck slabs onto the tops of the cross - beams by the gantry crane. After the positions of the deck slabs on the cross - beams are confirmed to be correct, weld and fix the multiple deck slabs to the tops of the cross - beams; complete the assembly work of the current segment;

[0015] Step 7, removal of cross - beam support. After the construction of the current segment is completed, the deck slabs, cross - beams, and main girders in the current segment form a load - bearing whole. Remove the cross - beam support, and drag the cross - beam support to the cross - beam hoisting position of the next segment by the winch for cross - beam hoisting of the next segment;

[0016] Step 8, continue to assemble the next segment. Repeat steps 2 - 7 to complete the assembly work of the next segment, and fixedly connect the completed current segment to the next segment until the assembly construction of the entire deck structure of the through basket - type steel box tied - arch bridge is completed.

[0017] Furthermore, in step 2, supports are provided on the tops of the main beam assembly bracket and the jacking bracket.

[0018] Furthermore, in step 3, both main beams are steel box beams with a parallelogram cross section, and pre-bias angles are set between the bottoms of the two main beams and the supports.

[0019] Furthermore, in step 3, a pre-deflection angle is set when the main beam is hoisted, so that after the bracket is removed, the torsional deformation of the main beam caused by the deadweight of the crossbeam and the bridge deck and the set pre-deflection angle offset each other, thereby avoiding the main beam outer support from being emptied and preventing stress concentration on the inner side of the main beam bottom plate;

[0020] The bridge deck is set with a two-way cross slope, and the cross beam has a variable cross section. The cross-sectional geometric properties of the bridge deck and cross beam at different positions are slightly different. To facilitate calculation, the overall stiffness of the bridge deck and cross beam can be treated as equivalent. The deadweight of the cross beam and bridge deck is simplified into a rectangular uniformly distributed load. Since the two ends of the main beam are directly placed on the supports of the main beam assembly bracket, the two support reaction forces are represented by fa and fb respectively. The simplified mechanical model is obtained. According to the two-force equilibrium principle, two mechanical equilibrium equations are listed:

[0021]

[0022] The two formulas in equation 3.1 are combined to calculate the support reaction of the beam and the bridge deck: fa = fb = 1 / 2ql;

[0023] According to the moment balance of any section, the bending internal force at any section of the beam and bridge deck is calculated. The calculation formula is:

[0024]

[0025] Where, q is the unit deadweight of the beam and bridge deck, in N; l is the distance between the inner webs of the two main beams, in m; x is the distance from any section to the left endpoint, in m;

[0026] The pre-deflection angle of the main beam has an inverse relationship with the bending moment. Therefore, integrating Equation 3.2 and multiplying it by the inverse of the stiffness yields the formula for calculating the pre-deflection angle:

[0027]

[0028] Where θ is the pre-deflection angle of the main beam; EI is the equivalent stiffness of the bridge deck and beam.

[0029] Furthermore, in step 3, when hoisting the main beam, two second jacks are placed inside the main beam. The second jacks are used to lift the main beam to deflect it. The elevation of the lower edge of the web of the main beam is monitored by a total station at all times. The pre-deflection angle θ is calculated using a geometric relationship. The conversion formula for the pre-deflection angle θ is:

[0030]

[0031] Among them, h1 is the elevation of the lower edge of the side web of the main beam near the middle of the cross beam; h2 is the elevation of the lower edge of the side of the main beam far from the middle of the cross beam; b is the distance between the two webs of the main beam.

[0032] Furthermore, in step 4, a ground-connected cross beam is provided at the bottom of the cross beam support.

[0033] Furthermore, in step 5, the calculation method of the jacking force is as follows:

[0034] Step 5.1, establish a finite element model of the main beam and the cross beam in ANSYS, and apply position constraints to the finite element model of the main beam and the cross beam;

[0035] Step 5.2, apply different vertical loads to the mid-span of the bottom plate of the cross beam model to simulate the jacking force, and at the same time obtain the stress at the upper edge of the mid-span of the cross beam web under different vertical loads through ANSYS;

[0036] Step 5.3, fit the different vertical load data and the stress data at the upper edge of the mid-span of the cross beam web. The fitted function is:

[0037] y = 10.82 - 1.03F

[0038] Among them, y represents the stress at the upper edge of the mid-span of the cross beam web, and F represents the jacking force of the first jack.

[0039] Furthermore, in step 5, a construction ramp is provided between the two cross beams. The construction ramp includes ramp plates arranged on the wing plates of the two cross beams.

[0040] The beneficial effects of the present invention are as follows: First, in the construction method of the deck structure of the through-type basket-shaped steel box tied arch bridge in the present invention, after the current segment is erected, the main beam, the cross beam and the deck slab in the current segment form a load-bearing structural system. The self-weights of the cross beam and the deck slab no longer need to be borne by the cross beam support, but are transmitted from the cross beam and the deck slab to the two side main beams, and finally borne by the lower support of the main beam. Therefore, after the deck structure of a segment is assembled, the cross beam support can be removed. At this time, the removed cross beam support can be dragged to the next segment for the installation of the cross beam in the next segment. The construction method in the present invention saves the cost of scaffold erection for the assembly of the arch bridge deck structure and shortens the construction period compared with the conventional method of erecting the beam body with full paving scaffolds according to the force change during the assembly process of the structure and the designed structural force transmission path.

[0041] 2. In the construction method of the deck structure of a through-type basket-shaped steel box tied-arch bridge in the present invention, when hoisting the main girder, a pre-deviation angle is set for the main girder to resist the inward deflection of the main girder, so that after the cross-beam support is removed, the torsional deformation of the main girder caused by the self-weight of the cross-beam and the deck slab cancels out with the set pre-deviation angle, thereby avoiding the void of the outer support of the main girder and preventing stress concentration on the inner side of the bottom slab of the main girder.

[0042] 3. In the construction method of the deck structure of a through-type basket-shaped steel box tied-arch bridge in the present invention, by arranging a first jack on the cross-beam support, when hoisting the cross-beam, by controlling the extension of the extending end of the first jack, a vertically upward jacking force is applied to the mid-span position of the cross-beam. Under the action of the jacking force, the mid-span bending moment of the cross-beam is greatly reduced, so that the upper edge of the cross-beam web changes from being compressed to being in tension, fundamentally solving the problem of buckling of the cross-beam web under compression and ensuring the smooth progress of the construction.

[0043] 4. In the construction method of the deck structure of a through-type basket-shaped steel box tied-arch bridge in the present invention, by arranging a ground-connected cross-beam at the bottom of the cross-beam support, the ground-connected cross-beam is welded to the columns in the cross-beam support to serve as an enlarged foundation of the cross-beam support, so that the cross-beam support does not need to pour the foundation of the support, and only need to level the site to meet the requirements of the upper load-bearing. Brief Description of the Drawings

[0044] Figure 1 It is a process flow chart of a construction method for the deck structure of a through-type basket-shaped steel box tied-arch bridge.

[0045] Figure 2 It is a schematic cross-sectional structure diagram of the deck structure of a through-type basket-shaped steel box tied-arch bridge.

[0046] Figure 3 It is a schematic structure diagram of the deck structure of a through-type basket-shaped steel box tied-arch bridge in the length direction.

[0047] Figure 4 It is a schematic diagram of the deflection of the main girder arranged on the support.

[0048] Figure 5 It is a schematic structure diagram of the mechanical simplified model of the main girder arranged on the support.

[0049] Figure 6 It is a schematic diagram of calculating the pre-deviation angle of the main girder through a total station.

[0050] Figure 7 It is a schematic structure diagram of the cross-beam support.

[0051] Among them, 1. Main girder; 2. Cross-beam; 3. Deck slab; 4. Main girder assembly support; 5. Jacking support; 6. Cross-beam support; 7. First jack; 8. Support; 9. Ground-connected cross-beam. Detailed implementation manners

[0052] The following describes the detailed implementation manners of the present invention to facilitate the understanding of those skilled in the art of the present technology. However, it should be clear that the present invention is not limited to the scope of the detailed implementation manners. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

[0053] As Figures 1 to 3 shown, the present invention provides a construction method for the deck structure of a through basket-shaped steel box tied arch bridge. The deck of the through basket-shaped steel box tied arch bridge includes multiple segments spliced with each other. Each segment includes two main girders 1 arranged at intervals, and multiple cross beams 2 are arranged between the two main girders 1. Multiple deck plates 3 are arranged on the multiple cross beams 2; under each of the two main girders 1, a main girder assembly support 4 and a jacking support 5 are provided, and the bottoms of the main girder assembly support 4 and the jacking support 5 are fixedly connected to the ground; the cross section of each cross beam 2 is in an inverted "T" shape.

[0054] The construction method for the deck structure of the through basket-shaped steel box tied arch bridge includes:

[0055] Step 1: Installation of gantry crane. Install the two vertical supports of the gantry crane on both sides in the length direction of the through basket-shaped steel box tied arch bridge; the horizontal support of the gantry crane is located at the top of the through basket-shaped steel box tied arch bridge, and a winch is slidably arranged on the horizontal support of the gantry crane.

[0056] Specifically, the installation of the gantry crane includes steps such as track laying, leg assembly and erection, and trolley installation. The track laying step is as follows: Level the sites on both sides in the length direction of the through basket-shaped steel box tied arch bridge, and then set strip foundations on the leveled sites according to the requirements of the design drawings. The strip foundations are of reinforced concrete structure. After the strip foundations reach the design strength, install rail clamps on the strip foundations and lay the tracks at the same time. The elevation deviation of the track top surface does not exceed ±5 mm, and the flatness error within every two meters does not exceed 5 mm. On the track, settlement joints are set every 12 m.

[0057] The steps for assembling and erecting the outriggers are as follows: First, place the rigid and flexible outriggers flat on the ground and level them with sleepers at the bottom. Then, butt the flanges of the top crossbeam and the bottom crossbeam with the outrigger flanges, install bolts, install spring washers and nuts, and align and tighten the bolts. Next, place the bottom trolley flat and install it on both sides of the bottom crossbeam as required, align it and drive in the pin shafts, and install the safety retaining plates. Before erecting the outrigger, fasten a wire rope with a diameter of 24 mm at a suitable position on the outrigger, and then use an 80t truck crane to lift and erect the outrigger. Lower the trolley wheels onto the track and adjust the position of the wheels. The outer wheel rims of the wheels must be closely adjacent to the outer side of the track. Then, fasten the chain hoist to the wire rope and the ground anchor, one on each side, tighten it to adjust the verticality of the outrigger. After adjustment, lift the main girder 1.

[0058] The steps for installing the trolley are as follows: There are four lifting rings welded on both sides of the hoisting trolley. Before hoisting, wind the wire rope around it and hoist it with an 80t truck crane. Then, release the wire rope in the winch, wind it around the lower moving pulley and then around the fixed pulley in the upper hoisting trolley, pass through the first set of pulleys in sequence and wind it around to the last set of pulleys, lock the rope end on the load cell on the side of the fixed pulley of the overhead crane, connect the power supply, and conduct an overall no-load commissioning. It should be noted that the mechanism and installation method of the arch gantry crane equipment belong to the prior art, and the principle will not be elaborated here too much.

[0059] Step 2: Construction of the main girder assembly support 4 and the jacking support 5. A plurality of main girder assembly supports 4 and jacking supports 5 are arranged on both sides along the length direction of the through-type basket-shaped steel box tied arch bridge. Specifically, bearings 8 are provided at the tops of the main girder assembly support 4 and the jacking support 5, and the bearings 8 are used to support the two main girders 1. In this embodiment, the jacking support 5 also serves as the main girder assembly support 4, saving costs and shortening the construction period.

[0060] Step 3: Assembly of the main girder 1. Hoist the two main girders 1 in the current segment onto the main girder assembly support 4 and the jacking support 5 on both sides along the length direction of the through-type basket-shaped steel box tied arch bridge respectively through the winch on the gantry crane.

[0061] Specifically, the segmented main girders 1 are hoisted onto the main girder assembly support 4 and the jacking support 5 by the gantry crane. Before hoisting, fully consider the influence of the placement position of the steel beam on the construction sequence. During the hoisting process, it is commanded by a special person, and the position accuracy of the steel beam is checked synchronously with a total station.

[0062] Preferably, in this embodiment, each main girder 1 in the segment is a steel box girder with a parallelogram cross-section, and a pre-deviation angle is provided between the bottoms of the two main girders 1 and the bearing 8.

[0063] The reason for setting the pre-deviation angle for the main girder 1 is as Figure 4As shown in the figure, after the assembly and welding of the current segment are completed, the force transmission path becomes: bridge deck 3 → cross beam 2 → main beam 1. The main beam 1, cross beam 2, and bridge deck 3 form a load-bearing integral. At this time, the cross beam support 6 can be removed, but the deformation caused by the self-weight of the cross beam 2 and bridge deck 3 will generate a torque on the main beam 1, which will cause the side main beam 1 to twist inward and cause the outer support 8 of the main beam 1 to become disengaged, further leading to stress concentration on the inner bottom plate of the main beam 1.

[0064] By setting a pre-tilt angle for the main beam 1, after the support is removed, the torsional deformation of the main beam 1 caused by the self-weight of the cross beam 2 and bridge deck 3 cancels out with the set pre-tilt angle, thus avoiding the disengagement of the outer support 8 of the main beam 1 and preventing stress concentration on the inner side of the bottom plate of the main beam 1.

[0065] Specifically, the bridge deck 3 is provided with a two-way cross slope, and the cross beam 2 has a variable cross-section. The cross-sectional geometric properties of the bridge deck 3 and cross beam 2 are slightly different at different positions. For the convenience of calculation, the overall stiffness of the bridge deck 3 and cross beam 2 can be equivalently processed; the self-weight of the cross beam 2 and bridge deck 3 is simplified into a rectangular uniform load, as Figure 5 shown. Since the two ends of the main beam 1 are directly placed on the supports 8 of the main beam assembly support 4, the reaction forces of the two supports 8 are represented by fa and fb respectively, and a mechanical simplified model is obtained. According to the principle of two-force balance, two mechanical equilibrium equations are listed:

[0066]

[0067] By combining the two formulas in Equation 3.1, the reaction force magnitudes of the cross beam 2 and bridge deck 3 are calculated as: fa = fb = 1 / 2ql;

[0068] According to the moment balance of any cross-section, the bending internal force at any cross-section of the overall cross beam 2 and bridge deck 3 is calculated. The calculation formula is:

[0069]

[0070] In the formula, q is the unit self-weight of the cross beam 2 and bridge deck 3, with the unit of N; l is the distance between the inner webs of the two main beams 1, with the unit of m; x is the distance from any cross-section to the left end point, with the unit of m;

[0071] There is a reciprocal relationship between the pre-tilt angle of the main beam 1 and the bending moment. Therefore, by integrating Equation 3.2 and multiplying by the reciprocal of the stiffness, the pre-tilt angle calculation formula can be obtained:

[0072]

[0073] Among them, θ is the pre-tilt angle of the main beam 1; EI is the equivalent stiffness of the bridge deck 3 and cross beam 2.

[0074] As Figure 6As shown in the figure, when hoisting the main girder 1, two second jacks are placed inside the main girder 1. The main girder 1 is deflected by jacking with the second jacks. At the same time, the elevation of the lower edge of the web of the main girder 1 is monitored by a total station at all times. The pre-deviation angle θ is calculated by using geometric relations. The conversion formula for the pre-deviation angle θ is as follows:

[0075]

[0076] Among them, h1 is the elevation of the lower edge of the web on the side of the main girder 1 close to the middle of the cross beam 2; h2 is the elevation of the lower edge of the side of the main girder 1 far from the middle of the cross beam 2; b is the distance between the two webs of the main girder 1.

[0077] Because in the specific construction process, the pre-deviation angle of the main girder 1 is not easy to be directly measured. By controlling the elevation of the lower edge of the web of the main girder 1, during the construction control, based on the mechanical basis, the rotation angle formula of the cross beam 2 can be deduced, and further the rotation angle of the main girder 1 can be calculated. In the construction, the angle is difficult to control. By monitoring the elevation of the lower edge of the web of the main girder 1 and using geometric relations, the accurate control of the pre-deviation angle can be realized.

[0078] Step 4: Erect the cross beam support 6. As Figure 1 and Figure 7 shown, the cross beam support 6 is erected between the two main girders 1 in the current segment. A first jack 7 is arranged at the top of the cross beam support 6; preferably, a ground-connected cross beam 9 is arranged at the bottom of the cross beam support 6. The ground-connected cross beam 9 is welded to the columns in the cross beam support 6 to serve as an enlarged foundation of the cross beam support 6, so that the cross beam support 6 does not need to pour the foundation of the support. Only by leveling the site can the requirements of the upper load-bearing be met. Compared with the traditional construction method in which a concrete foundation is arranged at the bottom of the cross beam support 6, the construction method in the present invention not only saves the number of cross beam supports 6 in the assembly of the cross beam 2 and the bridge deck, but also saves 100% of the pouring volume of the support foundation, having obvious advantages.

[0079] Step 5: Hoist the cross beam 2. The cross beam 2 is hoisted onto the two main girders 1 and the cross beam support 6 by a gantry crane. After the cross beam 2 is positioned, the two ends of the cross beam 2 are fixedly connected to the webs of the two main girders 1 respectively. The first jack 7 extends upward and applies a jacking force to the middle of the bottom plate of the cross beam 2.

[0080] Preferably, the cross beam 2 is lifted by two lifting points, and the positions of the lifting points are 0.207L away from the endpoints of the cross beam 2, where L is the length of the cross beam 2. After the cross beam 2 is lifted to the predetermined position, use a total station to check whether the first jack 7 at the top of the cross beam support 6 is centered with the center of the bottom plate of the cross beam 2. If not centered, the position of the support needs to be finely adjusted. After the adjustment is completed, use high-strength bolts to reliably connect the cross beam 2 to the web of the main beam 1; after multiple cross beams 2 are connected, a construction ramp is provided between two cross beams 2. The construction ramp includes ramp plates provided on the wing plates of two cross beams 2, which facilitates the construction of workers.

[0081] Specifically, in this embodiment, the calculation method of the jacking force is as follows:

[0082] Step 5.1, establish the finite element models of the main beam 1 and the cross beam 2 in ANSYS, and apply position constraints to the finite element models of the main beam 1 and the cross beam 2; in actual construction, the main beam 1 is directly supported on the assembly support without anchoring. Therefore, in the finite element models of the main beam 1 and the cross beam 2, the translations in three directions of the bottom plates of the two main beams 1 are constrained, and the crosswise rotation is released; under the self-weight of the cross beam 2 and the bridge deck 3, the stability coefficient of the cross beam 2 is 0.99, showing out-of-plane buckling of the web surface at the mid-span. After the cross beam 2 is hoisted in place, it is connected to the web of the main beam 1 through high-strength bolts. Since the cross beam 2 has an inverted T-shaped cross section and there is no small longitudinal beam support on the upper edge of the web, under the self-weight, the web of the cross beam 2 is compressed and buckles out of plane.

[0083] On this basis, a cross beam support 6 is added below the cross beam 2 to improve the stability of the cross beam 2. To verify whether this scheme can achieve the expected effect, in the finite element model, a vertical constraint is applied to the mid-span position of the bottom plate of the cross beam 2 to simulate the cross beam support 6. Through the ANSYS software, the stability coefficient of the cross beam 2 is calculated to be 3.75, showing buckling of the upper edges of the webs at both ends of the cross beam 2. Compared with not setting the support, the improvement effect of the stability is obvious. The specification requires that during the construction process of the bridge structure, the linear buckling eigenvalue coefficient should be greater than 4.0. It can be seen that although adding only the cross beam support 6 can improve the stability of the cross beam 2, it still does not meet the construction requirements.

[0084] Step 5.2, apply different vertical loads to the mid-span of the bottom plate of the cross beam 2 model to simulate the jacking force, and at the same time obtain the stress at the upper edge of the web of the cross beam 2 under different vertical loads through ANSYS.

[0085] To prevent the cross beam 2 from buckling after installation and ensure construction safety, it is further proposed to apply an upward jacking force to the cross beam 2 through the jack at the top of the cross beam support 6, so as to reduce the mid-span moment of the cross beam 2 and thus improve the stability of the cross beam 2. The critical value of the jacking force is that the stress at the upper edge of the web of the cross beam 2 is 0, that is, it is not compressed.

[0086] To determine the reasonable value of the jacking force, in the finite element models of the main girder 1 and the cross beam 2, vertical loads are applied at the mid-span of the bottom plate of the cross beam 2 to simulate the jacking force, and the load values are 1 KN, 2 KN, 3 KN, 4 KN, 5 KN, and 6 KN respectively. The calculation target is the stress at the upper edge of the mid-span of the web of the cross beam 2, and the calculation results of the stress at the upper edge of the mid-span of the web of the cross beam 2 are shown in the following table:

[0087]

[0088] Step 5.3, fit the different vertical load data and the different stress data at the upper edge of the mid-span of the web of the cross beam 2. The fitted function is:

[0089] y = 10.82 - 1.03F

[0090] Where y represents the stress at the upper edge of the mid-span of the web of the cross beam 2, and F represents the jacking force of the first jack 7. Let y = 0 (the stress at the upper edge of the web of the cross beam 2 is 0). After calculation, it can be known that the jacking force of the first jack 7 is 10.50 KN. Therefore, when the cross beam 2 is hoisted, the designed jacking force of the first jack 7 is 1.05 t.

[0091] Step 6, paving the bridge deck 3. Use the gantry crane to lift multiple bridge decks 3 to the top of the cross beam 2. After the positions of the bridge decks 3 on the cross beam 2 are confirmed to be correct, weld and fix multiple bridge decks 3 to the top of the cross beam 2; complete the assembly work of the current segment.

[0092] Specifically, a 45° groove needs to be opened at the welding position of the bridge deck 3, and the groove is polished to ensure no rust and burrs. Use the gantry crane to lift the bridge deck 3. After the position of the bridge deck 3 is confirmed to be correct, position it with a code plate, and then carry out the first welding. After the welding is completed, cut off the code plate with a gas cutting torch, and polish the code plate and the weld, and then carry out the second welding. The welding method is submerged arc welding, and the welding flux is baked at 250 °C for 1 - 2 hours in advance. The position of the welding machine track is fixed after being confirmed to be correct to prevent the welding machine from running off during the moving process. The moving speed of the welding machine is controlled at 20 - 40 cm per minute, the welding current is 520 A, and the voltage is 34 v.

[0093] Step 7, remove the cross beam support 6. After the construction of the current segment is completed, the bridge deck 3, the cross beam 2, and the main girder 1 in the current segment form a load-bearing whole. Remove the cross beam support 6, and drag the cross beam support 6 to the hoisting position of the cross beam 2 in the next segment with a winch for hoisting the cross beam 2 in the next segment.

[0094] Step 8, continue to assemble the next segment, repeat steps 2 - 7, complete the assembly work of the next segment, and fixedly connect the completed current segment with the next segment until the assembly construction of the entire deck structure of the through-type basket-shaped steel box tied arch bridge is completed.

[0095] In summary, for the construction method of the deck structure of a through-type basket-shaped steel box tied arch bridge provided by the present invention, the jacking support 5 also serves as the main girder erection support 4, which saves costs and shortens the construction period; a pre-deflection angle is set on the main girder 1 to accurately preset torsional reverse deformation, solving the problem of spatial positioning caused by the torsion of the inward-tilting main girder 1; the cross beam 2 in the assembled segment of the moving cross beam support 6 is assembled, and the cross beam support 6 has its own foundation, realizing reuse and saving material and labor costs; by applying a jacking force to the mid-span of the cross beam 2 through the first jack 7, the force on the cross beam 2 is actively changed, and the problem of out-of-plane instability of the cross beam 2 is completely solved by "changing from compression to tension". The construction method of the deck structure of a through-type basket-shaped steel box tied arch bridge of the present invention can be applied to the construction of similar bridges for highways, railways and municipal works, and has broad application prospects and great economic value.

Claims

1. A construction method for the deck structure of a through-type basket-shaped steel box tied-arch bridge, characterized in that, The deck of a through basket - type steel box tied - arch bridge consists of multiple segments spliced together. Each segment includes two main girders arranged at intervals. Between the two main girders, there are multiple cross - beams, and multiple deck plates are arranged on the multiple cross - beams. Under each of the two main girders, there are main girder erection brackets and jacking brackets, and the bottoms of the main girder erection brackets and jacking brackets are fixedly connected to the ground. The cross - section of each cross - beam is in an inverted "T" - shaped structure. The construction method of the deck structure of a through basket - type steel box tied - arch bridge includes: Step 1: Erection of gantry crane. Install the two vertical brackets of the gantry crane on both sides in the length direction of the through basket - type steel box tied - arch bridge. The horizontal bracket of the gantry crane is located at the top of the through basket - type steel box tied - arch bridge, and a hoist is slidably arranged on the horizontal bracket of the gantry crane. Step 2: Construction of main girder erection brackets and jacking brackets. A plurality of main girder erection brackets and jacking brackets are arranged on both sides in the length direction of the through basket - type steel box tied - arch bridge. Step 3: Erection of main girders. Hoist the two main girders in the current segment respectively onto the main girder erection brackets and jacking brackets on both sides in the length direction of the through basket - type steel box tied - arch bridge by the hoists on the gantry crane. Both main girders are steel box girders with a parallelogram cross - section, and there is a pre - deflection angle between the bottoms of the two main girders and the bearings. Set the pre - deflection angle during the hoisting of the main girders so that after the removal of the brackets, the torsional deformation of the main girders caused by the self - weight of the cross - beams and deck plates cancels out with the set pre - deflection angle, thereby avoiding the disengagement of the outer bearings of the main girders and preventing stress concentration on the inner side of the bottom plate of the main girders. The bridge deck is provided with a two-way cross slope, and the cross beam has a variable cross section. The cross-sectional geometric properties of the bridge deck and the cross beam are slightly different at different positions. For the convenience of calculation, the overall stiffness of the bridge deck and the cross beam is equivalently processed; the self-weights of the cross beam and the bridge deck are simplified into rectangular uniformly distributed loads. Since the two ends of the main beam are directly placed on the supports of the main beam erection bracket, the two support reactions are respectively represented by fa and fb to obtain a mechanical simplified model. According to the principle of two-force balance, two mechanical balance equations are listed: By combining the two formulas in 3.1, the reaction forces of the cross beam and the deck are calculated as follows: fa = fb =1 / 2 ql ; According to the moment balance of any cross - section, calculate the bending internal force at any cross - section of the overall cross - beam and deck plate. The calculation formula is: In the formula, q is the unit self-weight of the cross beam and the bridge deck, with the unit of N ; l is the distance between the inner webs of the two main girders, with the unit of m ; x is the distance from any section to the left end point, with the unit of m ; There is a reciprocal relationship between the pre - deflection angle of the main girder and the bending moment. Therefore, integrate Equation 3.2 and multiply it by the reciprocal of the stiffness to obtain the pre - deflection angle calculation formula: Among them, θ is the pre - deflection angle of the main beam; EI is the equivalent stiffness of the bridge deck and the cross beam; Two second jacks are placed inside the main beam. The main beam is deflected by lifting it with the second jacks. The elevation of the lower edge of the web of the main beam is monitored by a total station at all times. The pre-deflection angle is calculated using a geometric relationship. θ , pre-bias angle θ The conversion formula is: Among them, h 1 is the elevation of the lower edge of the side web of the main beam near the middle of the cross beam; h 2 is the elevation of the lower edge of the side of the main beam far from the middle of the cross beam; b is the distance between the two webs of the main beam; Step 4: Erection of cross - beam brackets. Erect cross - beam brackets between the two main girders in the current segment. A first jack is arranged at the top of the cross - beam brackets. A ground - connected cross - beam is arranged at the bottom of the cross - beam brackets. Step 5: Hoisting of cross - beams. Hoist multiple cross - beams onto the two main girders and cross - beam brackets by the gantry crane. After the cross - beams are positioned, fix the two ends of the cross - beams to the webs of the two main girders respectively, and the first jack extends upward to apply a jacking force to the middle of the bottom plate of the cross - beam. Step 6: Paving of deck plates. Lift multiple deck plates to the top of the cross - beams by the gantry crane. After the positions of the deck plates on the cross - beams are confirmed to be correct, weld and fix the multiple deck plates to the tops of the cross - beams. Complete the assembly work of the current segment. Step 7: Removal of cross - beam brackets. After the construction of the current segment is completed, the deck plates, cross - beams, and main girders in the current segment form a load - bearing whole. Remove the cross - beam brackets, and drag the cross - beam brackets to the cross - beam hoisting position of the next segment by the hoist for the hoisting of the cross - beams in the next segment. Step 8: Continue to assemble the next segment. Repeat Steps 2 - 7 to complete the assembly work of the next segment, and fixedly connect the completed current segment and the next segment until the assembly construction of the entire deck structure of the through basket - type steel box tied - arch bridge is completed.

2. The construction method of a deck structure for a through-type basket-shaped steel box tied-arch bridge according to claim 1, characterized in that, In step 2, bearings are provided at the tops of both the main girder erection support and the jacking support.

3. The construction method of a deck structure for a through-type basket-shaped steel box tied arch bridge according to claim 1, characterized in that In step 5, the calculation method of the jacking force is as follows: Step 5.1, establish a finite element model of the main girder and the cross beam in ANSYS, and apply position constraints to the finite element model of the main girder and the cross beam; Step 5.2, apply different vertical loads to the mid-span of the bottom plate of the cross beam model to simulate the jacking force, and at the same time obtain the stress at the upper edge of the mid-span of the cross beam web under different vertical loads through ANSYS; Step 5.3, fit the different vertical load data and the different stress data at the upper edge of the cross beam web mid-span, and the fitted function is: y =10.82-1.03 F Among them, y represents the stress at the upper edge of the mid-span of the crossbeam web, F represents the jacking force of the first jack.

4. The construction method of a deck structure for a through-type basket-shaped steel box tied-arch bridge according to claim 1, characterized in that, In step 5, a construction ramp is provided between the two cross beams, and the construction ramp includes ramp plates provided on the flange plates of the two cross beams.

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