CN114753265A - Midspan closure method of large-span composite beam cable-stayed bridge - Google Patents

Abstract

The invention discloses a mid-span closure method of a large-span composite beam cable-stayed bridge, which comprises the steps of manufacturing a mid-span closure section steel beam and a connecting piece thereof, moving a crane to the positions of a hoisting side-span closure section and a mid-span closure section, determining a matching cutting amount and an adjustment parameter, cutting and drilling according to the matching cutting amount and the adjustment parameter, temporarily constraining and converting into a pushing device, placing all steel members of the mid-span closure section at the cantilever end of the erected beam section in advance, welding a member for placing a beam on a side box beam, evaluating and adjusting the geometric posture of a mid-span closure opening, locking the pushing device after the pushing is in place, installing the side box beam, adjusting the closure posture again, locking the pushing device after the pushing is in place, splicing construction, installing a cross beam and a small longitudinal beam, and constructing a bridge deck, namely completing the mid-span closure operation. The construction precision problem is considered in all directions, adverse effects are eliminated as far as possible, and the closure speed and precision are improved.

Description

Midspan closure method of large-span composite beam cable-stayed bridge

Technical Field

The invention belongs to the technical field of bridge engineering, and particularly relates to a mid-span closure method of a large-span composite beam cable-stayed bridge.

Background

Compared with a pure steel beam cable-stayed bridge, the steel-concrete composite beam cable-stayed bridge has the advantages of less steel consumption, better economy, higher rigidity of the main beam and higher stability, and can effectively improve the durability of a pavement layer. In recent years, in the construction of bridges with 500-700 m span, a large number of composite beam cable-stayed bridges are used, wherein the maximum span reaches 720 m, and the number and the span are still continuously developed.

The composite beam cable-stayed bridge adopts a steel girder mode with smaller cross-sectional area to improve the crack resistance of the bridge deck, so that a double-side I-shaped cross section and a double-side box cross section are generally adopted. When the span of the composite beam cable-stayed bridge reaches more than 700 meters, the lower flange plate of the I-shaped section steel main beam cannot meet the stress requirement, and a double-side box type steel main beam is required.

No matter the steel girder of the composite beam cable-stayed bridge is a bilateral I-shaped section or a bilateral box section, the connection of webs between sections generally adopts a bolting mode. The diameter of the high-strength bolt is generally only 2-3 mm smaller than the diameter of the bolt hole, and one splicing surface is provided with hundreds of bolt holes. Due to the existence of manufacturing errors, the difficulty of completely installing the high-strength bolt into the bolt hole is high, and if the angle is adjusted through the joint between the sections, the adjustable amount is very small. And the splice face of bilateral case steel girder is more than bilateral I-steel girder, and the bulk rigidity is bigger, and angular adjustment maneuverability during midspan closure is lower, and the construction precision that requires is higher, and the closure degree of difficulty is also higher. Along with the increase of the span of the composite beam cable-stayed bridge, the precision requirement of the closure technology needing to be matched is higher.

Disclosure of Invention

The invention aims to provide a mid-span closure method of a large-span composite beam cable-stayed bridge, which aims to solve the problem that the requirement on the bolt connection precision of the closure section of the composite beam cable-stayed bridge in the form of double-side box steel girders is extremely high.

The invention solves the technical problems through the following technical scheme: a mid-span closure method of a large-span composite beam cable-stayed bridge comprises the following steps:

step 1: manufacturing a mid-span closure section steel beam and a connecting piece thereof, and reserving cutting quantities on two sides of the side box girder top plate and the bottom plate along the bridge direction respectively;

step 2: respectively moving the two mid-span cranes to the positions for hoisting the mid-span closure section;

and 3, step 3: carrying out continuous temperature effect monitoring on the beam sections erected on two sides of the mid-span closure opening during the side-span closure construction period to obtain the actually measured geometric attitude data of the mid-span closure opening, and analyzing the geometric attitude data of the mid-span closure opening to obtain the trimming amount of the mid-span closure opening and the adjustment parameters of the assembled plate drilling hole;

and 4, step 4: cutting the steel beam of the mid-span closure section according to the matched cutting amount, and drilling the splicing plate according to the adjustment parameters;

and 5: converting the temporary constraint of the tower area into a girder pushing device to perform midspan closure and performing a pushing test;

step 6: hoisting all steel members of the mid-span closure section, placing the steel members at the cantilever ends of the beam sections erected on the two sides of the mid-span closure opening, and welding the members for placing the beams on the top plate of the side box beam;

and 7: evaluating and adjusting the geometric attitude of the mid-span closure gap based on the state in the step 6;

and 8: when the side span closure construction is finished and a mid-span closure condition is met, pushing is carried out towards the side span direction, and a pushing device is locked after the pushing is in place;

and step 9: respectively and simultaneously hoisting one side box girder by using cranes at two sides of the midspan closure gap, moving the side box girder to the position right above the midspan closure gap, then slowly lowering the side box girder, embedding the two side box girders into the midspan closure gap, and placing the two side box girders on the erected girder sections at two sides by using members for placing the girders in the step 6;

step 10: adjusting the mid-span closure mouth posture and optimizing the relative geometric position;

step 11: unlocking the pushing device, carrying out back jacking towards the midspan direction, and locking the pushing device after the back jacking is in place;

step 12: splicing construction is carried out on the steel beam at the mid-span closure section and the erected beam sections at the two sides of the steel beam;

step 13: removing all temporary constraints among the tower beams;

step 14: and (4) installing a cross beam and a small longitudinal beam of the mid-span closure section, and completing the construction of the bridge deck, namely the mid-span closure operation.

Further, in the step 3, the specific operation of continuous temperature effect monitoring is as follows:

carrying out 24-hour continuous temperature effect monitoring on the beam sections erected on two sides of the mid-span closure gap during the side-span closure construction period, carrying out joint monitoring on the beam sections erected on two sides of the mid-span closure gap once every two hours, wherein the monitoring contents comprise the temperature field, tower deflection, elevation, mileage, shaft deflection, mileage of the front three sections of cantilever ends on two sides of the mid-span closure gap and the tension of a stay cable;

analyzing the monitoring data to obtain the inclination angle of the erected beam sections on the two sides of the midspan closure, the length of the midspan closure and the variation quantity of the midspan closure after the influence of the temperature;

and (4) performing heating and cooling simulation by using a calculation model, and rechecking the accuracy of the monitoring data.

Further, in the step 5, the concrete implementation process of converting the temporary constraint of the tower area into the main beam pushing device is as follows:

firstly installing a pushing device, applying a pre-jacking force obtained by calculation of a calculation model, and then removing longitudinal temporary constraint;

dismantling the transverse temporary constraint between the tower beams;

and (4) carrying out a closure pushing device test according to the pushing stroke and the pushing force required by the estimated closure temperature.

Further, in the step 6, the member for placing the beam is a steel vertical plate or a steel corbel.

Further, in the step 7, the specific implementation process of evaluating and adjusting the geometric posture of the mid-span closure gap is as follows:

measuring point elevations of a first section B and a second section A in front of the cantilever end of the beam section erected on two sides of the mid-span closure opening;

if the elevations of the measuring points of the first section B and the second section A are equal, or the elevation of the measuring point of the first section B is slightly higher than that of the second section A and the elevation of the upstream and the downstream are consistent, the adjustment of the geometric attitude of the mid-span closure opening is not carried out;

and if the elevation of the measuring point of the front first section B is lower than that of the measuring point of the front second section A, fine-tuning the cable force of the stay cable to lift the cantilever end beam section.

Further, in step 8, after the pushing is in place, D ═ L + D + S + Δ D, where D is the mid-span closure opening width, L is the actual length of the mid-span closure section side box girder, D is the seam width on both sides of the mid-span closure opening, S is the operating space at two seam surfaces, and Δ D is the change value of the mid-span closure opening width caused by temperature change.

Further, in the step 10, the specific implementation process of adjusting the mid-span closure gap posture is as follows: the relative elevation and the inclination angle of the erected beam sections on the two sides of the mid-span closure opening are finely adjusted through the cable force of the stay cables, and then the erected beam sections are diagonally and obliquely pulled through the opposite pulling device to finely adjust the axis.

Further, in the step 12, the concrete implementation process of the splicing construction is as follows: firstly, driving small punching nails into positioning bolt holes, then judging the alignment accuracy of the bolt holes of the steel beam and the splice plate through the evaluation holes, if the alignment accuracy meets the requirement of bolting of a hole group, driving the small punching nails and tool bolts into other bolt holes, then welding a temporary code plate to simultaneously lock joint surfaces on two sides of a mid-span closure gap, and then screwing high-strength bolts; if the alignment precision does not reach the requirement of bolting hole groups and small punching nails and tool bolts cannot be driven in, the geometric postures of the erected beam sections on the two sides of the midspan closure gap are adjusted again.

Further, the specific implementation process of driving the small punch nail into the positioning bolt hole is as follows: when the main beams on the two sides of the splicing surface incline upwards, small punching nails are punched into the middle two bolt holes of the bolt hole on the lowermost row, and then small punching nails are punched into one bolt hole on the outermost side of the bolt hole on the uppermost row;

when the main beams on the two sides of the splicing surface are declined, small punching nails are punched into the two middle bolt holes of the bolt holes on the uppermost row, and then the small punching nails are punched into the bolt holes on one outermost side of the bolt holes on the lowermost row.

Further, the method also comprises the step of swinging back the crane boom and transversely centering between the step 9 and the step 10.

Advantageous effects

Compared with the prior art, the invention has the advantages that:

the mid-span closure method of the large-span composite beam cable-stayed bridge provided by the invention fully considers and optimizes the aspects of manufacturing the closure section steel girder and the splice plate, adjusting the geometric attitude of the closure opening, hoisting and splicing the closure section, arranging the closure process and the like, comprehensively considers the construction precision problem, eliminates the adverse effect as much as possible and improves the closure speed and precision; the method has the advantages of less resource investment in the whole closure operation engineering, no need of balance weight, no need of welding a stiff framework, low construction cost, short closure operation duration, low risk intersection and higher operability, meets the splicing precision of the bolt hole groups of the steel beam at the closure section, further meets the high-precision requirement of the mid-span closure bolting of the combined beam cable-stayed bridge in the side box girder mode, and is suitable for the mid-span closure construction of various combined beam cable-stayed bridges.

Drawings

In order to more clearly illustrate the technical solution of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only one embodiment of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.

FIG. 1 is a mid-span layout elevation during pre-closure temperature monitoring in an embodiment of the present invention;

FIG. 2 is a mid-span elevational view of the front closure section of the closure of the embodiment of the present invention stored on a beam surface;

FIG. 3 is an elevation view of the closure section in a simply supported state after being lifted in an embodiment of the invention;

FIG. 4 is a detailed view of the closure opening of the closure section in a simply supported state according to an embodiment of the present invention;

FIG. 5 is a plan view of the crane boom as directed upstream and downstream in an embodiment of the present invention;

FIG. 6 is a plan view of the crane boom centered and the steel strand diagonally pulled in an embodiment of the present invention;

FIG. 7 is a diagram of the positions of the bolt evaluation holes with the inclination upward of the erected main beam during web splicing according to the embodiment of the invention;

FIG. 8 is a diagram of bolt evaluation hole positions for a down angle erected main beam during web splicing in an embodiment of the invention.

The method comprises the following steps of 1-erecting beam sections on two sides of a midspan closure opening, 2-stay cables, 3-side box beams, 4-cross beams, 5-beam-laying components, 6-side span direction, 7-cranes, 8-suspension arms, 9-counter-pulling devices, 10-positioning bolt holes and 11-evaluation holes.

Detailed Description

The technical solutions in the present invention are clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without inventive efforts based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.

The technical solution of the present application will be described in detail below with specific examples. The following several specific embodiments may be combined with each other, and details of the same or similar concepts or processes may not be repeated in some embodiments.

The mid-span closure method for the large-span composite beam cable-stayed bridge provided by the embodiment comprises the following steps:

step 1: manufacturing a midspan closure section steel beam and a connecting piece thereof, reserving 10cm cutting amount on two sides of the side box girder top plate and the bottom plate along the bridge direction respectively, and not drilling the splice plate temporarily.

And (3) monitoring the temperature effect of the erected beam sections 1 (namely main beams) on the two sides of the mid-span closure opening for multiple times and continuously, analyzing temperature effect monitoring data to determine the size of the steel beam of the mid-span closure section, manufacturing the steel beam of the mid-span closure section according to the size, and reserving allowance.

Step 2: and respectively moving the two cranes 7 in the midspan to the positions for hoisting the midspan closure section.

Fig. 1 shows a mid-span arrangement elevation, each crane 7 is respectively moved forward to the positions of a hoisting side-span closure section and a mid-span closure section, and the crane 7 is not moved as much as possible from the side-span closure to the completion of the mid-span closure, so that the problem of undefined load caused by the movement of the crane 7 in the whole closure process can be avoided, the irrational factor is reduced, and the accuracy and the high efficiency of closure construction are ensured.

And step 3: and during the side span closure construction period, monitoring the continuous temperature effect of the beam sections 1 erected on two sides of the mid-span closure to obtain the actually measured geometric attitude data of the mid-span closure, and analyzing the geometric attitude data of the mid-span closure to obtain the trimming amount of the mid-span closure and the adjustment parameters of the assembled plate drilling.

After the mid-span is moved forward to a position by using a crane 7 and the temporary load is cleaned, in the side-span closure construction period and in the state shown in fig. 1, carrying out 24-hour continuous temperature effect monitoring on the beam sections 1 erected on two sides of the mid-span closure, wherein the beam sections 1 erected on two sides of the mid-span closure are jointly monitored once every two hours, and the monitoring contents comprise a temperature field (the temperature of a stay cable 2, the temperature of a steel girder, the temperature of a bridge deck plate, the temperature of a main tower), tower deflection, the elevation, the mileage, the axial deflection and the tension of the stay cable 2 of three sections in front of the cantilever end on two sides of the mid-span closure; analyzing the monitoring data (namely the geometric attitude data) to obtain the inclination angle of the erected beam sections 1 on the two sides of the midspan closure, the length of the midspan closure and the variation of the midspan closure after the temperature influence; performing heating and cooling simulation by using a calculation model, and rechecking the accuracy of the monitoring data; and determining final manufacturing adjustment parameters of the steel member at the mid-span closure section according to the data analysis result (if the error is within an adjustable range, manufacturing according to the original size).

The continuous temperature effect monitoring is the prior art, and reference can be made to patent literature with publication number CN113106872A, entitled mid-span closure method for steel box girders of cable-stayed bridges.

And 4, step 4: and (3) cutting the mid-span closure section steel beam according to the trimming amount obtained in the step (3), drilling the splicing plate according to the adjustment parameters obtained in the step (3), and optimizing the manufacturing of the mid-span closure section steel beam and the splicing plate to improve closure precision.

And 5: and (4) converting the temporary constraint of the tower area into a main beam pushing device for mid-span closure, and performing a pushing test.

Determining whether two sides of a mid-span closure opening need to be provided with thrusters according to the thrusting stroke, in order to prevent the main beam from displacing when temporary constraint is removed, firstly installing the thrusters, applying pre-jacking force calculated by a model, locking the thrusters, then removing longitudinal temporary constraint, and then removing transverse temporary constraint between tower beams for preventing the horizontal plane of the main beam from rotating; and after the conversion is finished, carrying out a closure pushing device test according to the pushing stroke and the pushing force required by the estimated closure temperature.

Step 6: all steel members of the midspan closure section are lifted and placed at the cantilever ends of the beam sections 1 erected on the two sides of the midspan closure opening, and the beam placing members 5 are welded on the top plate of the side box beam 3.

Referring to fig. 2, all steel members for hoisting the mid-span closure section are placed at the cantilever ends of the erected beam sections 1 on two sides of the mid-span closure opening, and the steel beam loads (such as the side box beams 3, the cross beams 4 and the small longitudinal beams) of the mid-span closure section are all stored on the bridge floor in advance, and at the moment, the bridge floor load is consistent with the load during closure and only has difference in position; and simultaneously, the difference of the influences of the load of the side box girder 3 of the midspan closure section on the inclination angle of the girder on the current cantilever end and the middle of the midspan closure opening is simulated and analyzed by utilizing a calculation model, and the difference is considered when the attitude of the midspan closure opening is adjusted. The mid-span closure opening attitude is evaluated and adjusted in the state, the load arrangement in the state is closer to the final closure splicing state, the pre-control of the geometric attitude of the mid-span closure opening is more facilitated, and the rapidity and the accuracy of the follow-up formal mid-span closure construction can be ensured.

In this embodiment, the member 5 for a joist is a steel vertical plate or a steel corbel.

And 7: and (4) evaluating and adjusting the geometrical posture (mainly the dip angle) of the mid-span closure gap based on the state of the step 6.

Based on the state shown in fig. 2, evaluating the geometric attitude of the mid-span closure gap, and mainly measuring the measuring point elevations of a first section B and a second section A in front of the cantilever end of the beam section 1 erected on two sides of the mid-span closure gap; if the elevations of the measuring points of the front first section B and the front second section A are equal, the adjustment of the geometric posture of the mid-span closure gap is not carried out; if the elevation of the measuring point of the front first section B is slightly higher than that of the front second section A (the measuring point elevation difference of the front second section A of the front first section B is not more than 15mm) and the elevation of the upstream and the downstream are consistent, the adjustment of the geometric attitude of the mid-span closure opening is not carried out, and the cantilever end of the main beam is horizontal or slightly inclined, so that the bolting of the mid-span closure section is facilitated; and if the elevation of the measuring point of the front first section B is lower than that of the measuring point of the front second section A, the beam section of the cantilever end is lifted up by fine adjustment of the cable force of the groups of the stay cables 2 of the cantilever end 2-3.

And 8: when the side span closure construction is finished and the mid-span closure condition is met, pushing is carried out towards the side span direction 6, and the pushing device is locked after the pushing is in place.

After the side span closure construction is completed and the mid-span closure condition is met, the mid-span closure operation is started, firstly, pushing is carried out towards the side span direction 6, after the pushing is in place, a pushing device is locked, and after the pushing is in place, D is L + D + S + delta D, wherein D is the width of the mid-span closure opening, L is the actual length of the side box girder of the mid-span closure section, D is the width of the seam on two sides of the mid-span closure opening, S is the operating space of two seam surfaces, and delta D is the change value of the width of the mid-span closure opening caused by temperature change.

And step 9: the cranes 7 on the two sides of the mid-span closure opening respectively and simultaneously lift one side box girder 3, the side box girder 3 is slowly lowered after being moved to the position right above the mid-span closure opening, the two side box girders 3 are embedded into the mid-span closure opening and are placed on the two side erected girder sections 1 through the girder placing members 5 in the step 6, and the method is shown in reference to fig. 3-5.

Step 10: the suspension arm 8 of the crane 7 swings back and is centered transversely.

Referring to fig. 5, when two cranes 7 lower the side box girder 3 to be lifted up and down the midspan closure, the boom 8 of one crane 7 points downstream and the boom 8 of the other crane 7 points upstream, which may cause the main girder to twist, and swinging the boom 8 back and across the bridge may eliminate the effect. The two sides of the upstream and downstream of the bridge are in the transverse bridge direction, the two sides of the downstream bridge are in the north and south directions, namely the longitudinal bridge direction, and the two sides of the midspan closure opening are in the longitudinal bridge direction.

Referring to fig. 6, the boom 8 swings back and horizontally and is centered on the bridge, and the hook at this time is disengaged from the steel beam of the mid-span closure section, thereby reducing a safety measure of the closure section, also meaning that the steel vertical plate or the steel corbel for simply supporting the closure section must be firm enough and have a greater safety factor, and a device for preventing the closure section from sliding transversely must be provided.

The main beam torsion conditions of the suspension arm 8 in the middle and the deviation in the upstream and downstream can be respectively measured in advance under the no-load condition of the crane 7. If the suspension arm 8 is positioned at the upstream and downstream and does not twist or twists the main beam very little, the suspension arm 8 can not swing back to the transverse bridge to be centered, the crane 7 does not loosen the hook at the moment, the safety function is realized on the closure section, but the force is completely removed.

Step 11: and adjusting the mid-span closure opening posture to optimize the relative geometric position.

The specific implementation process for adjusting the mid-span closure attitude comprises the following steps: firstly, the relative elevation and the inclination angle of the erected beam section 1 at two sides of the mid-span closure opening are finely adjusted through the cable force of the stay cable 2, then the erected beam section 1 is diagonally and obliquely pulled through the steel strand counter-pulling device 9, and the axis is finely adjusted, as shown in fig. 6.

In step 7, the relative elevation and the inclination angle are adjusted to the proper position, so that the error of the relative elevation and the inclination angle in the state of step 11 is not very large, and the fine adjustment of the cable force of the stay cable 2 can be realized.

Step 12: and unlocking the pushing device, carrying out back jacking towards the midspan direction, and locking the pushing device after the back jacking is in place.

Step 13: and splicing the steel beam at the mid-span closure section and the erected beam sections 1 at the two sides of the steel beam.

The steel beam of the mid-span closure section is connected with the erected steel beams on the two sides through the splicing plates and then matched with the high-strength bolts, and the two joint surfaces operate simultaneously. Referring to fig. 7 and 8, the situation that the inclination angles of the erected beam sections 1 on two sides of the mid-span closure are upward and downward is respectively shown. Firstly, driving small punching nails into positioning bolt holes 10, and then evaluating and judging the bolt hole alignment precision of the steel beam and the splice plate through evaluation holes 11; and if the alignment precision meets the requirement of bolting of the hole group, immediately driving small punching nails and tool bolts into other bolt holes, welding temporary code plates to lock joint surfaces on two sides of the midspan closure opening simultaneously, and then screwing high-strength bolts (the sign that the initial screwing of the high-strength bolts of the splice plates is finished is the stress closure of the girder structure). And if the alignment precision does not meet the bolting requirement of the hole group and small punching nails and tool bolts cannot be driven, the geometric postures of the erected beam sections 1 on the two sides of the midspan closure opening are adjusted again. The other bolt holes are all bolt holes except the 3 positioning bolt holes 10, when the alignment precision meets the bolt connection requirement of the hole group, the bolt holes between the main beam and the splicing plate are aligned one by one, and the other bolt holes have the condition of driving small punching nails or tool bolts.

The positions of the positioning bolt holes 10 and the evaluation holes 11 are shown in fig. 7 and 8, when the main beams on two sides of the splicing surface incline upwards, 2 small punching nails are driven into the middle positions of the bolt holes in the lowest row (namely two positioning bolt holes 10 indicated by the reference number 10 in the lowest row in fig. 7), and then 1 small punching nail is driven into the outer side of the bolt holes in the highest row (namely 1 positioning bolt hole 10 indicated by the reference number 10 in the highest row in fig. 7); when the main beams on the two sides of the splicing surface are declined, 2 small punching nails are firstly driven into the middle positions of the bolt holes in the uppermost row (namely two positioning bolt holes 10 indicated by the reference numeral 10 in the uppermost row in fig. 8), and then 1 small punching nail is driven into the outer sides of the bolt holes in the lowermost row (namely 1 positioning bolt hole 10 indicated by the reference numeral 10 in the lowermost row in fig. 8). No matter the inclination is gone up or down, the pilot bolt hole 10 is 3.

Step 14: removing all temporary constraints among the tower beams;

step 15: and (3) installing a cross beam 4 and a small longitudinal beam of the mid-span closure section, and constructing the bridge deck (comprising a prefabricated bridge deck, a wet joint and a cast-in-place belt), namely completing the mid-span closure operation.

The construction precision problem is considered in all directions, the high-precision requirement of mid-span closure bolting of the combined beam cable-stayed bridge in the side box girder 3 mode can be met, the engineering resource investment is less, balance weight is not needed, a stiff framework is not needed to be welded, the closure operation duration is short, the risk is lower, the operability is higher, and the construction method can be suitable for mid-span closure construction of various combined beam cable-stayed bridges.

The above disclosure is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any changes or modifications within the technical scope of the present disclosure may be easily conceived by those skilled in the art and shall be covered by the scope of the present invention.

Claims (10)

1. A mid-span closure method of a large-span composite beam cable-stayed bridge is characterized by comprising the following steps:

step 1: manufacturing a mid-span closure section steel beam and a connecting piece thereof, and reserving cutting quantities on two sides of the side box girder top plate and the bottom plate along the bridge direction respectively;

and 2, step: respectively moving the two mid-span cranes to the positions for hoisting the mid-span closure section;

and 3, step 3: carrying out continuous temperature effect monitoring on the beam sections erected on two sides of the mid-span closure opening during the side-span closure construction period to obtain the actually measured geometric attitude data of the mid-span closure opening, and analyzing the geometric attitude data of the mid-span closure opening to obtain the trimming amount of the mid-span closure opening and the adjustment parameters of the assembled plate drilling hole;

and 4, step 4: cutting the steel beam of the mid-span closure section according to the matched cutting amount, and drilling the splicing plate according to the adjustment parameters;

and 5: converting the temporary constraint of the tower area into a girder pushing device to perform midspan closure and performing a pushing test;

step 6: hoisting all steel members of the mid-span closure section, placing the steel members at the cantilever ends of the beam sections erected on the two sides of the mid-span closure opening, and welding the members for placing the beams on the top plate of the side box beam;

and 7: evaluating and adjusting the geometric attitude of the mid-span closure gap based on the state in the step 6;

and 8: when the side span closure construction is finished and a mid-span closure condition is met, pushing is carried out towards the side span direction, and a pushing device is locked after the pushing is in place;

and step 9: respectively and simultaneously hoisting one side box girder by using cranes at two sides of the midspan closure gap, moving the side box girder to the position right above the midspan closure gap, then slowly lowering the side box girder, embedding the two side box girders into the midspan closure gap, and placing the two side box girders on the erected girder sections at two sides by using members for placing the girders in the step 6;

step 10: adjusting the posture of the mid-span closure opening and optimizing the relative geometric position;

step 11: unlocking the pushing device, carrying out back jacking towards the midspan direction, and locking the pushing device after the back jacking is in place;

step 12: splicing construction is carried out on the steel beam at the mid-span closure section and the erected beam sections at the two sides of the steel beam;

step 13: removing all temporary constraints between the tower beams;

step 14: and (4) installing a cross beam and a small longitudinal beam of the mid-span closure section, and completing the construction of the bridge deck, namely the mid-span closure operation.

2. The mid-span closure method of a large-span composite beam cable-stayed bridge according to claim 1, wherein the continuous temperature effect monitoring in the step 3 is performed by the following specific operations:

carrying out 24-hour continuous temperature effect monitoring on the beam sections erected on two sides of the mid-span closure gap during the side-span closure construction period, carrying out joint monitoring on the beam sections erected on two sides of the mid-span closure gap once every two hours, wherein the monitoring contents comprise the temperature field, tower deflection, elevation, mileage, shaft deflection, mileage of the front three sections of cantilever ends on two sides of the mid-span closure gap and the tension of a stay cable;

analyzing the monitoring data to obtain the inclination angle of the erected beam sections on the two sides of the midspan closure, the length of the midspan closure and the variation quantity of the midspan closure after the influence of the temperature;

and (5) performing heating and cooling simulation by using a calculation model, and rechecking the accuracy of the monitoring data.

3. The mid-span closure method of a large-span composite beam cable-stayed bridge according to claim 1, wherein in the step 5, the concrete implementation process of converting the temporary tower area constraint into the main beam pushing device comprises the following steps:

firstly installing a pushing device, applying a pre-jacking force obtained by calculation of a calculation model, and then removing longitudinal temporary constraint;

dismantling transverse temporary constraints between the tower beams;

and (4) carrying out a closure pushing device test according to the pushing stroke and the pushing force required by the estimated closure temperature.

4. The mid-span closure method for a cable-stayed bridge with a large-span composite beam according to claim 1, wherein in the step 6, the members for the joist are steel vertical plates or steel corbels.

5. The mid-span closure method of a large-span composite beam cable-stayed bridge according to claim 1, wherein in the step 7, the specific implementation process of evaluating and adjusting the geometric attitude of the mid-span closure opening comprises the following steps:

measuring point elevations of a first section B and a second section A in front of the cantilever end of the beam section erected on two sides of the mid-span closure opening;

if the elevations of the measuring points of the front first section B and the front second section A are equal, or the elevation of the measuring point of the front first section B is slightly higher than that of the front second section A and the elevation of the upstream and the downstream are consistent, the adjustment of the geometric attitude of the mid-span closure gap is not carried out;

and if the elevation of the measuring point of the front first section B is lower than that of the measuring point of the front second section A, finely adjusting the cable force of the stay cable to lift the cantilever end beam section.

6. The mid-span closure method of a large-span composite beam cable-stayed bridge according to claim 1, wherein in the step 8, after the pushing is in place, D is L + D + S + Δ D, where D is a mid-span closure width, L is an actual length of the box girder at the side of the mid-span closure section, D is a width of a seam at two sides of the mid-span closure, S is an operation space at two seam surfaces, and Δ D is a change value of the mid-span closure width caused by a temperature change.

7. The mid-span closure method of a cable-stayed bridge with a large-span composite beam according to claim 1, wherein in the step 10, the specific implementation process for adjusting the attitude of the mid-span closure opening is as follows: the relative elevation and the inclination angle of the erected beam sections on the two sides of the mid-span closure opening are finely adjusted through the cable force of the stay cables, and then the erected beam sections are diagonally and obliquely pulled through the opposite pulling device to finely adjust the axis.

8. The mid-span closure method of a cable-stayed bridge of a long-span composite beam according to any one of claims 1 to 7, wherein in the step 12, the splicing construction is implemented by the following specific steps: firstly, driving small punching nails into positioning bolt holes, then judging the alignment accuracy of the bolt holes of the steel beam and the splice plate through the evaluation holes, if the alignment accuracy meets the requirement of bolting of a hole group, driving the small punching nails and tool bolts into other bolt holes, then welding a temporary code plate to simultaneously lock joint surfaces on two sides of a mid-span closure gap, and then screwing high-strength bolts; and if the alignment precision does not meet the bolting requirement of the hole group and small punching nails and tool bolts cannot be driven, the geometric postures of the erected beam sections on the two sides of the midspan closure opening are adjusted again.

9. The mid-span closure method of a cable-stayed bridge with a large-span composite beam according to claim 8, wherein the specific implementation process of driving small punch nails into the positioning bolt holes comprises the following steps: when the main beams on the two sides of the splicing surface incline upwards, small punching nails are punched into the middle two bolt holes of the bolt hole on the lowermost row, and then small punching nails are punched into one bolt hole on the outermost side of the bolt hole on the uppermost row;

when the main beams on the two sides of the splicing surface are declined, small punching nails are punched into the two middle bolt holes of the bolt holes on the uppermost row, and then the small punching nails are punched into the bolt holes on one outermost side of the bolt holes on the lowermost row.

10. The mid-span closure method of a cable-stayed bridge with a large-span composite beam as claimed in claim 1, further comprising the step of swinging back the crane boom and centering the crane boom transversely between the step 9 and the step 10.

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