Construction method of bridge deck portal crane

Abstract

The construction method comprises the following steps that S1, a beam lifting station area is constructed, I-shaped beams are installed on a bridge floor through a truck crane, and the I-shaped beams are located on the left part and the right part of a main bridge respectively; s2, an installation site is arranged, brick slag is replaced and filled in an uncured area of the site, prefabricated concrete planks are laid, a track foundation of the left side of the main bridge is poured firstly to serve as the elevation of the track foundation, and then a track foundation of the right side is poured, so that the two sides are located on the same plane; (S3); a crane track is laid, the two sides of the track are fixed through pressing plates, and a concrete expanded foundation is adopted as a temporary anchor point; (S4); firstly, supporting legs and main beam components are assembled, then the supporting legs are assembled and erected on a bridge floor, a main beam and a trolley are installed, and finally an electrical accessory device and a safety protection device are installed. Compared with a traditional construction method, most splicing work is carried out on the ground, supporting legs and main beam components are integrally hoisted, the installation efficiency is improved, and the hoisting pressure is relieved.

Description

Technical Field

[0001] The present invention relates to the technical field of gantry cranes, and in particular to a construction method of a bridge deck gantry crane. Background Art

[0002] Gantry crane is one of the common equipment in bridge construction, also known as gantry crane. By laying tracks on the bridge deck and installing the outriggers on both sides into the tracks, it provides functions such as suspension and transportation. It has the characteristics of high site utilization, large operating range, wide adaptability, and strong versatility. Gantry crane consists of main beam, outriggers, trolley travel mechanism, lifting trolley, electrical auxiliary structure, etc. In the bridge construction scene, the outriggers on both sides are respectively placed on the left and right sides, the main beam is erected above the outriggers on both sides, and the lifting trolley is installed above the main beam to realize the installation of the gantry crane. At present, the construction methods of most gantry cranes are relatively complicated, resulting in a large workload for lifting and low construction efficiency. In addition to increasing the labor time cost, it will delay the construction period of the overall bridge. Summary of the invention

[0003] The purpose of the present invention is to solve the shortcomings in the prior art and to propose a construction method for a bridge deck gantry crane.

[0004] To achieve the above object, the present invention adopts the following technical solution:

[0005] A construction method for a bridge deck gantry crane, characterized in that it comprises the following steps:

[0006] S1: Construct the beam lifting station area, use a truck crane to install the I-beam on the bridge deck. The I-beam is located on the left and right sides of the main line bridge to support the two side legs of the gantry crane;

[0007] S2: Arrange the installation site, replace the uncured area with brick slag, lay precast concrete slabs, first cast the track foundation of the left side of the main line bridge as the track foundation elevation, and then cast the track foundation of the right side to make both sides on the same plane;

[0008] S3: Lay the crane track, fix the two sides of the track with pressure plates, use the concrete expanded foundation as a temporary anchor point, and hoist the expanded foundation to the designated position on the bridge deck in advance with a truck crane;

[0009] S4; first assemble the outriggers and main beam components, then assemble the outriggers on the bridge deck, install the main beam and the trolley, and finally install the electrical auxiliary devices and safety protection devices;

[0010] S5: After the installation of the gantry crane is completed, carry out no-load test, load test and dynamic load test.

[0011] Preferably, the step S2 of replacing the uncured area of ​​the site with brick slag specifically includes:

[0012] Brick slag is used to fill and compact the working area, and soft soil, drill slag pool, mud pool and other locations are replaced as required. In order to ensure that the bearing capacity and flatness of the foundation meet the requirements of outrigger walking, 50cm brick slag is used for site treatment, and the paved site is repeatedly compacted.

[0013] Preferably, the step S3 of laying the crane track specifically includes:

[0014] The longitudinal slope of the bridge deck meets the climbing ability of the gantry crane, and the rails are laid directly on the bridge deck; the transverse slope of the bridge deck is bidirectionally offset, and rubber pads or steel plates are used for fine-tuning according to the track elevation; the transverse slope of the bridge deck is unidirectionally offset, and the unidirectional transverse slope of the bridge deck is leveled. First, the track position is roughened, and the threaded steel bars are arranged at equal intervals according to the protective layer of 5cm, and then the wooden formwork is installed. The arm is extended from the beam lifting station to the bridge deck with a sky pump, and concrete is poured to form the track foundation. The track foundation and the crane track are guaranteed to be straight and do not follow the slope of the bridge deck.

[0015] Preferably, assembling the legs in step S4 specifically includes:

[0016] Determine the outrigger assembly positioning points on site, place the truck crane at a suitable position on the ground, assemble the outriggers first, then assemble the traveling trolley, upper connecting beam, and lower connecting beam in sequence, use a spirit level to level the four corner points, assemble the outrigger connecting frame, and finally install the outrigger ladder, back cage, and fall arrester.

[0017] Preferably, assembling the main beam components in step S4 specifically includes:

[0018] According to the site requirements, choose to assemble on the ground, or assemble into sections and then hoist to the bridge deck for assembly; select the area outside the connecting beam under the legs as the main beam assembly position, avoiding the leg installation position; find out the main beam single section number, assemble the main beam section by section, and finally assemble guardrail walkways, stop plates and other accessories.

[0019] Preferably, assembling the legs in step S4 specifically includes:

[0020] The legs are hoisted by a truck crane, and the legs on both sides are connected to the top in advance; a plumb line is set when the legs are installed, and the length can reach the lower crossbeam, which is used to observe the verticality after erection; the guy ropes are reliably fixed to their respective anchors, and the hand winch is adjusted to make the main leg in a vertical state; the guy ropes on both sides should be pre-tightened as synchronously as possible, and the legs are ensured to be in a vertical state by observing the plumb line suspended from the midpoint of the top of the leg in advance; the verticality and straightness of the legs are adjusted, and the crane is loosened after the hand winch is pulled, and the stability of the legs is observed. The hook can be completely released after confirmation, and channel steel is set horizontally under the legs to fix the legs.

[0021] Preferably, the step S4 of installing the main beam and the trolley specifically includes:

[0022] The lifting points at both ends of the main beam are connected with slings, and two truck cranes are used to lift the beam at the same time. First, they are suspended for observation for 3 minutes, and then they are lifted synchronously after stabilization. The lifting is stopped when the lower surface of the main beam exceeds the top of the outrigger by about 1m. After observing that the main beam does not sway, the two truck cranes swing their arms in the direction of the outriggers at the same time until they are directly above the outriggers. After the main beam is stable and does not sway, it is slowly lowered until the load sensor shows that it has contacted the outriggers, and then it is lifted a small amount. A crowbar is used to guide the main beam to align accurately with the outriggers, and the alignment is assisted by fine-tuning the hand winch, and the bolts are tightened one by one. Referring to the above steps, another main beam and the lifting trolley are installed, and all guy ropes are removed after completion.

[0023] Preferably, the load test is performed in step S5, specifically including:

[0024] According to the weight of the I-beam, the rated lifting capacity is loaded at 80% of the rated crane capacity, and the movements of the gantry crane, trolley running mechanism and lifting mechanism in various directions are completed one by one. Each movement is performed at least 3 times; first, the empty trolley is parked at the extreme position, and the midpoint of the main beam span is taken as the deflection measurement reference point, and the elevation of the reference point in the no-load state is measured; then, the trolley lifting mechanism is parked in the middle of the main beam span, and loaded according to the rated lifting capacity, with the load 100mm~200mm off the ground and maintained for 10min; the downward deflection value of the reference point is measured, and then unloaded, and the downward deflection value of the main beam base point is divided by the span of the gantry crane, which is the static rigidity in the span of the gantry crane.

[0025] The present invention has the following beneficial effects:

[0026] Compared with the traditional construction method, the bridge deck gantry crane construction method provided by the present invention installs most of the assembly work on the ground, hoists the legs and main beam components as a whole, improves the installation efficiency and relieves the hoisting pressure. At the same time, through the installation site layout, bridge deck cross slope adjustment and other methods, the straightness of the crane track is ensured, and the plumb line, cable wind rope, hand winch and other devices are used to ensure the verticality of the legs, effectively improving the overall installation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the structure of the main line bridge of the present invention.

[0028] Figure 2 The schematic diagram of the structure of the gantry crane of the present invention is

[0029] Figure 3 The schematic diagram of the structure of the track foundation of the present invention is

[0030] Figure 4 Schematic diagram of the state of the assembled legs of the present invention

[0031] Figure 5 Schematic diagram of the state of the load test according to the present invention

[0032] Figure 6 A schematic diagram of the state of the typhoon prevention measures according to the present invention

[0033] Description of the drawings: main line bridge 1, I-beam 2, track foundation 3, crane track 4, pressure plate 5, concrete enlarged foundation 6, outrigger 7, cable wind rope 8, hand hoist 9, channel steel 10, main beam 11, trolley 12, anchor bolt 13. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Reference Figures 1 to 6 , an embodiment provided by the present invention:

[0036] A construction method for a bridge deck gantry crane comprises the following steps:

[0037] S1: construct the beam lifting station area, use a truck crane to install an I-beam 2 on the bridge deck, the I-beam 2 is located on the left and right sides of the main line bridge 1, and is used to support the two side legs 7 of the gantry crane;

[0038] S2: Arrange the installation site, replace the brick slag in the uncured area of ​​the site, lay the precast concrete slab, first cast the track foundation 3 of the left side of the main line bridge 1 as the track foundation 3 elevation, and then cast the track foundation 3 of the right side to make both sides in the same plane;

[0039] S3: Lay the crane track 4, fix the two sides of the track with pressure plates 5, use the concrete expansion foundation 6 as a temporary anchor point, and hoist the expansion foundation to the designated position on the bridge deck in advance by the truck crane;

[0040] S4; first assemble the legs 7, the main beam components, and then assemble the legs 7 on the bridge deck, install the main beam 11 and the trolley 12, and finally install the electrical accessories and safety protection devices;

[0041] S5: After the installation of the gantry crane is completed, carry out no-load test, load test and dynamic load test.

[0042] Compared with the traditional construction method, the bridge deck gantry crane construction method provided by the present invention installs most of the assembly work on the ground, hoists the legs 7 and the main beam components as a whole, improves the installation efficiency and relieves the hoisting pressure. At the same time, through the installation site layout, bridge deck cross slope adjustment and other methods, the straightness of the crane track 4 is ensured, and the plumb line, cable wind rope 8, hand winch 9 and other devices are used to ensure the verticality of the legs 7, effectively improving the overall installation accuracy.

[0043] In this embodiment, as a preference, in step S1, a truck crane is used to install the I-beam 2 on the bridge deck, which specifically includes:

[0044] The I-beam 2 of the main line bridge 1 is hoisted in two times by two truck cranes. After the truck crane lifts the I-beam 2, it is adjusted horizontally to ensure that the beam can be lifted vertically above the bridge deck. After the I-beam 2 is lifted vertically above the bridge deck, it is adjusted horizontally for the second time and moved horizontally into place and lowered.

[0045] In this embodiment, as a preference, the uncured area of ​​the site is replaced with brick slag in step S2, specifically comprising:

[0046] Brick slag is used to fill and compact the working area, and soft soil, drilling slag pool, mud pool and other locations are replaced as required. In order to ensure that the bearing capacity and flatness of the foundation meet the requirements of leg 7 walking, 50cm brick slag is used for site treatment, and the paved site is repeatedly compacted.

[0047] In this embodiment, as a preference, laying the crane track 4 in step S3 specifically includes:

[0048] The longitudinal slope of the bridge deck meets the climbing ability of the gantry crane, and the rails are laid directly on the bridge deck; the transverse slope of the bridge deck is bidirectionally offset, and rubber pads or steel plates are used for fine-tuning according to the track elevation; the transverse slope of the bridge deck is unidirectionally offset, and the unidirectional transverse slope of the bridge deck is leveled. First, the track position is roughened, and the threaded steel bars are arranged at equal intervals according to the protective layer of 5 cm, and then the wooden formwork is installed. The arm is extended from the beam lifting station to the bridge deck with a sky pump, and concrete is poured to form the track foundation 3. The track foundation 3 and the crane track 4 are guaranteed to be straight and do not follow the slope of the bridge deck.

[0049] In this embodiment, as a preference, assembling the legs 7 in step S4 specifically includes:

[0050] Determine the assembly positioning points of the outrigger 7 on site, place the truck crane at a suitable position on the ground, assemble the outrigger 7 first, and then assemble the traveling trolley, upper connecting beam, and lower connecting beam in sequence. After leveling the four corner points with a spirit level, assemble the outrigger connecting frame, and finally install the outrigger ladder, back cage, and fall arrester.

[0051] Note: After the main limbs and upper and lower connecting beams are assembled, they must be checked for leveling to avoid subsequent assembly in a twisted state. The rods must be assembled according to the joint numbers to avoid twisting caused by forced docking. After assembly, check the bolts, pins, cotter pins and other connection parts.

[0052] In this embodiment, as a preference, assembling the main beam components in step S4 specifically includes:

[0053] According to the site requirements, choose to assemble on the ground, or assemble into segments and then hoist to the bridge deck for assembly; select the area outside the connecting beam under the leg 7 as the assembly position of the main beam 11, avoiding the installation position of the leg 7; find out the single section number of the main beam 11, assemble the main beam 11 section by section, and finally assemble the guardrail walkway, stop plate and other accessories.

[0054] Note: Ensure that the span, pre-arch, lateral bend, and track joint misalignment of the main beam are within the allowable range. The rods should be assembled according to the joint numbers to avoid distortion caused by forced docking. The main beam joint pins are firmly connected and the cotter pins are correctly installed. The walkway guardrails are firmly connected and there is no obvious deformation of the walkway. Since there is a central dividing strip on the left and right sides of the bridge deck, the assemblers must use the cross-width channel and are prohibited from walking in the middle of the gantry crane truss.

[0055] In this embodiment, preferably, assembling the legs 7 in step S4 specifically includes:

[0056] The outrigger 7 is hoisted by a truck crane, and the outriggers 7 on both sides are connected to the top in advance; a plumb line is set when installing the outrigger 7, and the length can reach the lower beam, so as to observe the verticality after erection; the guy rope 8 is reliably fixed to each anchor, and the hand winch 9 is adjusted to make the main outrigger 7 in a vertical state; the guy ropes 8 on both sides should be pre-tightened as synchronously as possible, and the outrigger 7 is ensured to be in a vertical state by observing the plumb line suspended from the midpoint of the top of the outrigger 7 in advance; the verticality and straightness of the outrigger 7 are adjusted, and the crane is loosened after the hand winch 9 is pulled, and the stability of the outrigger 7 is observed. The hook can be completely released after confirmation, and a channel steel 10 is set on the lower beam to fix the outrigger 7.

[0057] Note: When lifting, be careful not to touch the already pulled cable wind rope 8. The lifting process requires unified command and close cooperation. Be careful not to hook the cable wind rope 8 and hemp rope on other parts; during the lifting process, the driver should always pay attention to the load and torque state, and predict possible situations in advance. Only after the fixing measures are in place can the hook be unhooked.

[0058] In this embodiment, as a preference, the main beam 11 and the trolley 12 are installed in step S4, specifically including:

[0059] The lifting points at both ends of the main beam 11 are connected by slings, and two automobile cranes are used to lift them simultaneously. First, they are suspended for observation for 3 minutes, and then they are lifted synchronously continuously after they are stable. When the lower surface of the main beam 11 is lifted to about 1m above the top of the leg 7, the lifting is stopped. After observing that the main beam 11 is not swaying, the two automobile cranes swing their arms in the direction of the leg 7 at the same time, until they are directly above the position where they are aligned with the leg 7. After the main beam 11 is stable and not swaying, it is slowly lowered until the load sensor shows that it has contacted the leg 7, and then it is lifted a small amount. A crowbar is used to guide the main beam 11 to accurately align with the leg 7, and the alignment is assisted by fine-tuning the hand winch 9, and the bolts are tightened one by one. Referring to the above steps, another main beam 11 and the lifting trolley 12 are installed, and all the guy ropes 8 are removed after completion.

[0060] Note: Before hoisting the main beam 11, check again whether all connecting pins are installed in place and whether all platform guardrails are reliably connected. In addition, check whether there are any small items left behind and not cleaned up to avoid falling objects from high altitude during the hoisting process. The process of lifting the swing arm requires unified command and close cooperation. During the lifting process, attention should be paid to keeping a sufficient distance from the outrigger 7 and the cable wind rope 8; when hoisting the trolley 12, personnel working on the main beam 11 should avoid human power to restrict the shaking of the trolley 12 before the trolley 12 is suspended in the air and has not stopped steadily. Pay attention to the installation direction of the main beam 11 and the trolley 12. Workers working at high altitudes must apply force when they are standing firmly and with reliable protection from the safety belt. Deconstruction can only be carried out after confirming that the bolts are tightened.

[0061] In this embodiment, preferably, the electrical auxiliary device is installed in step S4, specifically including:

[0062] Connect the lines of each motor, safety limiter, control system, etc., and require that all wiring is neat and the positioning is consistent; install the lifting height limiter, weight limiter, travel limiter, rail clamp and other devices of the gantry crane one by one.

[0063] In this embodiment, preferably, installing a safety protection device in step S4 specifically includes:

[0064] Install according to the usage requirements of each part, including lifting height limiter, weight limiter, trolley 12-stroke limit switch, limit ruler, track clamp, track sweeper, and cable wind rope 8; the upper end of the cable wind rope 8 is fixed with a rope clamp, and the lower end of the cable wind rope 8 is connected with a galvanized basket bolt with a rope clamp, and the excess length is coiled in the non-anchored state.

[0065] In this embodiment, preferably, after step S4, the following steps are further included:

[0066] Anti-typhoon measures are taken. For coastal areas prone to typhoons, gantry cranes are subject to large wind loads and overturning moments. To ensure the safe use of gantry cranes, cable wind anchor points are embedded in the bridge deck in advance. The anchor points use anchor bolts 13 and are set next to the track foundation 3. After the typhoon warning takes effect, the track clamps are locked and cable wind ropes 8 are pulled in front and behind the gantry crane.

[0067] In this embodiment, preferably, a load test is performed in step S5, specifically including:

[0068] According to the weight of I-beam 2, the rated lifting capacity is loaded at 80% of the rated crane capacity, and the movements of the gantry crane, trolley running mechanism and lifting mechanism in various directions are completed one by one, and each movement is performed at least 3 times; first, the empty trolley 12 is parked at the extreme position, and the midpoint of the span of the main beam 11 is taken as the deflection measurement reference point, and the elevation of the reference point in the no-load state is measured; then, the trolley 12 lifting mechanism is parked in the middle of the span of the main beam 11, and loaded according to the rated lifting capacity, with the load 100mm~200mm off the ground and maintained for 10min; the downward deflection value of the reference point is measured, and then unloaded, and the downward deflection value of the base point of the main beam 11 is divided by the span of the gantry crane, which is the static rigidity in the span of the gantry crane.

[0069] Result requirements: The speeds of lifting, lowering, trolley travel, and trolley 12 operation meet the requirements of the design documents and are within the error range. The synchronous speed of each working mechanism meets the design requirements. The brake action is flexible and reliable. The vertical static deflection of the main beam 11 in the span meets the requirements. There is no visible damage to the main components.

[0070] In this embodiment, preferably, a no-load test is performed in step S5, specifically including:

[0071] First, use a 500V megohmmeter to measure the insulation resistance of each mechanism's main circuit, control circuit, and ground; turn on the power to start each mechanism, so that the trolley 12 runs along the entire length of the main beam 11 and the gantry crane runs back and forth along the track for no less than 3 times. There should be no jamming. Check whether the limit switches and buffers are working properly, and check whether the control system, safety devices, and lifting range meet the requirements; during the idling test, start each mechanism separately and run it in the forward and reverse directions for a cumulative time of no less than 5 minutes.

[0072] In this embodiment, as a preference, a dynamic load test is performed in step S5, specifically including:

[0073] Each action of each mechanism shall be started and braked repeatedly within its travel range; according to the power-on duration rate of the motor, leave an interval between operations and control according to the operating procedures, and must pay attention to limiting the acceleration, deceleration and speed within the normal operating range of the gantry crane; according to the power-on duration rate and its working cycle, the total test time should last at least 0.5h.

[0074] Result requirements: During the test, all mechanisms operate normally, work smoothly, and have no abnormal noise. During the test, the brake is effective and reliable during the braking process, and there is no reverse action or sliding phenomenon during air starting. After the test, all mechanisms and components are not damaged, the connections are not loose or damaged, the motor reducer, etc. have no abnormal temperature rise, and the hydraulic system has no leakage, oil seepage, or oil dripping.

[0075] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A construction method for a bridge deck gantry crane, characterized in that: The steps include: S1: Construct the beam lifting station area, use a truck crane to install the I-beam on the bridge deck. The I-beam is located on the left and right sides of the main line bridge to support the two side legs of the gantry crane; S2: Arrange the installation site, replace the uncured area with brick slag, lay precast concrete slabs, first cast the track foundation of the left side of the main line bridge as the track foundation elevation, and then cast the track foundation of the right side to make both sides on the same plane; S3: Lay the crane track, fix the two sides of the track with pressure plates, use the concrete expanded foundation as a temporary anchor point, and hoist the expanded foundation to the designated position on the bridge deck in advance with a truck crane; S4; first assemble the outriggers and main beam components, then assemble the outriggers on the bridge deck, install the main beam and the trolley, and finally install the electrical auxiliary devices and safety protection devices; S5: After the installation of the gantry crane is completed, carry out no-load test, load test and dynamic load test.

2. A bridge deck gantry crane construction method according to claim 1, characterized in that: In step S2, the uncured area of ​​the site is filled with brick slag, specifically comprising: Brick slag is used to fill and compact the working area, and soft soil, drill slag pool, mud pool and other locations are replaced as required. In order to ensure that the bearing capacity and flatness of the foundation meet the requirements of outrigger walking, 50cm brick slag is used for site treatment, and the paved site is repeatedly compacted.

3. A bridge deck gantry crane construction method according to claim 1, characterized in that: The step S3 of laying the crane track specifically includes: The longitudinal slope of the bridge deck meets the climbing ability of the gantry crane, and the rails are laid directly on the bridge deck; the transverse slope of the bridge deck is bidirectionally offset, and rubber pads or steel plates are used for fine-tuning according to the track elevation; the transverse slope of the bridge deck is unidirectionally offset, and the unidirectional transverse slope of the bridge deck is leveled. First, the track position is roughened, and the threaded steel bars are arranged at equal intervals according to the protective layer of 5cm, and then the wooden formwork is installed. The arm is extended from the beam lifting station to the bridge deck with a sky pump, and concrete is poured to form the track foundation. The track foundation and the crane track are guaranteed to be straight and do not follow the slope of the bridge deck.

4. A bridge deck gantry crane construction method according to claim 1, characterized in that: The step S4 of assembling the legs specifically includes: Determine the outrigger assembly positioning points on site, place the truck crane at a suitable position on the ground, assemble the outriggers first, then assemble the traveling trolley, upper connecting beam, and lower connecting beam in sequence, use a spirit level to level the four corner points, assemble the outrigger connecting frame, and finally install the outrigger ladder, back cage, and fall arrester.

5. The method for constructing a bridge deck gantry crane according to claim 1, characterized in that: The step S4 of assembling the main beam components specifically includes: According to the site requirements, choose to assemble on the ground, or assemble into sections and then hoist to the bridge deck for assembly; select the area outside the connecting beam under the legs as the main beam assembly position, avoiding the leg installation position; find out the main beam single section number, assemble the main beam section by section, and finally assemble guardrail walkways, stop plates and other accessories.

6. The method for constructing a bridge deck gantry crane according to claim 1, characterized in that: The step S4 of assembling the legs specifically includes: The legs are hoisted by a truck crane, and the legs on both sides are connected to the top in advance; a plumb line is set when the legs are installed, and the length can reach the lower crossbeam, which is used to observe the verticality after erection; the guy ropes are reliably fixed to their respective anchors, and the hand winch is adjusted to make the main leg in a vertical state; the guy ropes on both sides should be pre-tightened as synchronously as possible, and the legs are ensured to be in a vertical state by observing the plumb line suspended from the midpoint of the top of the leg in advance; the verticality and straightness of the legs are adjusted, and the crane is loosened after the hand winch is pulled, and the stability of the legs is observed. The hook can be completely released after confirmation, and channel steel is set horizontally under the legs to fix the legs.

7. The method for constructing a bridge deck gantry crane according to claim 1, characterized in that: The step S4 of installing the main beam and the trolley specifically includes: The lifting points at both ends of the main beam are connected with slings, and two truck cranes are used to lift the beam at the same time. First, they are suspended for observation for 3 minutes, and then they are lifted synchronously after stabilization. The lifting is stopped when the lower surface of the main beam exceeds the top of the outrigger by about 1m. After observing that the main beam does not sway, the two truck cranes swing their arms in the direction of the outriggers at the same time until they are directly above the outriggers. After the main beam is stable and does not sway, it is slowly lowered until the load sensor shows that it has contacted the outriggers, and then it is lifted a small amount. A crowbar is used to guide the main beam to align accurately with the outriggers, and the alignment is assisted by fine-tuning the hand winch, and the bolts are tightened one by one. Referring to the above steps, another main beam and the lifting trolley are installed, and all guy ropes are removed after completion.

8. The method for constructing a bridge deck gantry crane according to claim 1, characterized in that: The load test is performed in step S5, specifically including: According to the weight of the I-beam, the rated lifting capacity is loaded at 80% of the rated crane capacity, and the movements of the gantry crane, trolley running mechanism and lifting mechanism in various directions are completed one by one. Each movement is performed at least 3 times; first, the empty trolley is parked at the extreme position, and the midpoint of the main beam span is taken as the deflection measurement reference point, and the elevation of the reference point in the no-load state is measured; then, the trolley lifting mechanism is parked in the middle of the main beam span, and loaded according to the rated lifting capacity, with the load 100mm~200mm off the ground and maintained for 10min; the downward deflection value of the reference point is measured, and then unloaded, and the downward deflection value of the main beam base point is divided by the span of the gantry crane, which is the static rigidity in the span of the gantry crane.

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