DOUBLE-DECK MULTI-SPAN BRIDGE CONSTRUCTION METHOD

Abstract

Disclosed in the present disclosure is a double-deck multi-span bridge construction method. According to the double-deck bridge construction method of the present disclosure, construction is carried out by using a method of disassembling a support jig frame in a graded and span-separated mode, an upper chord jig frame and a lower chord jig frame can be used in a recycle manner, and construction costs are reduced. In addition, a construction period of building the support jig frame is shortened, and other construction operations can be synchronously carried out on a span in which the jig frame is disassembled, for example, fire retardant coating construction can be carried out on a mounted bridge deck after the jig frame is disassembled, and the construction period of a double-deck multi-span bridge is effectively shortened. Additionally, according to the double-deck multi-span bridge construction method in embodiments of the present disclosure, the upper chord jig frame and the lower chord jig frame are disassembled in a graded manner, thereby ensuring that a bridge structure can be smoothly and safely transitioned to a designed stress state.

Description

TECHNICAL FIELD

The present disclosure relates to the field of construction, in particular to a double-deck multi-span bridge construction method.

BACKGROUND

Currently, nationwide steel structures are strongly developed, and multi-span double-deck steel structure bridges are constantly increasing. A construction method of the multi-span double-deck steel structure bridge currently adopts a support method. The support method is to lay jig frames before the construction of a double-deck multi-span bridge to support the construction of the double-deck multi-span bridge, and to disassemble the jig frames after the construction of the double-deck multi-span bridge. But the number of jig frames required to support the double-deck multi-span bridge is large, the construction cost is high, and the construction period is long.

SUMMARY

The present disclosure aims to solve at least one of the technical problems existing in the prior art. To this end, the present disclosure proposes a double-deck multi-span bridge construction method, which can shorten the construction period of a double-deck multi-span bridge and reduce the construction cost of the double-deck multi-span bridge.

A double-deck multi-span bridge construction method according to an embodiment in a first aspect of the present disclosure includes:

• • construction of a first span: mounting a lower chord jig frame of the first span, and mounting a lower-deck bridge structure of the first span by using the lower chord jig frame of the first span as a support; and
  • mounting an upper chord jig frame of the first span, and mounting an upper-deck bridge structure of the first span by using the upper chord jig frame of the first span as a support;
  • construction of a second span: mounting a lower chord jig frame of the second span, and mounting a lower-deck bridge structure of the second span by using the lower chord jig frame of the second span as a support; and
  • mounting an upper chord jig frame of the second span, and mounting an upper-deck bridge structure of the second span by using the upper chord jig frame of the second span as a support;
  • demounting the upper chord jig frame of the first span;
  • performing construction of the remaining spans of the bridge in sequence by adopting a construction manner of demounting a jig frame in a span-separated mode, and after construction of all spans of the double-deck multi-span bridge is completed, disassembling the remaining upper chord jig frames and lower chord jig frames;
  • wherein the construction manner of demounting a jig frame in a span-separated mode includes the following steps of:
  • mounting an upper chord jig frame of the currently constructed span, and mounting an upper-deck bridge structure of the currently constructed span by using the upper chord jig frame of the currently constructed span as a support; and
  • demounting an upper chord jig frame of a span adjacent to the currently constructed span, and demounting a lower chord jig frame of a span which is separated from the currently constructed span by one span.

The double-deck multi-span bridge construction method according to the embodiments of the present disclosure has at least the following beneficial effects: according to the double-deck multi-span bridge construction method in the embodiments of the present disclosure, by demounting the upper chord jig frames and the lower chord jig frames of constructed spans in a graded manner during construction, the upper chord jig frame and the lower chord jig frame can be used in a recycle manner, and the construction cost is reduced. In addition, the construction period of building the upper chord jig frame and the lower chord jig frame is short, and other construction operations can be simultaneously carried out on a span in which the jig frame is disassembled, for example, fire retardant coating construction can be carried out on a mounted bridge deck after the jig frame is disassembled, and the construction period of the double-deck multi-span bridge is effectively shortened. Additionally, a bridge structure of a double-layer continuous steel truss structure does not have an expansion joint, by disassembling all the support jig frames at one time, the bridge structure cannot digest its internal deformation, which may result in the warping of the free end of mounting, and according to the double-deck multi-span bridge construction method in the embodiments of the present disclosure, the upper chord jig frame and the lower chord jig frame are disassembled in a graded manner, thereby ensuring that a bridge structure can be smoothly and safely transitioned to a designed stress state.

The double-deck multi-span bridge is constructed from both ends to the middle, and joined at any span in the middle, spans at both ends of the double-deck multi-span bridge adopt the construction manner of the first span, spans adjacent to the spans at both ends of the double-deck multi-span bridge adopt the construction manner of the second span, and the remaining spans of the double-deck multi-span bridge adopt the construction manner of demounting a jig frame in a span-separated mode. According to some embodiments of the present disclosure, a process of mounting a lower-deck bridge structure by using the lower chord jig frame as a support includes: mounting a lower chord at the top of the lower chord jig frame, and mounting the lower-deck bridge structure on the lower chord.

According to some embodiments of the present disclosure, a process of mounting an upper-deck bridge structure by using the upper chord jig frame as a support includes: mounting a portal frame on the lower-deck bridge structure, mounting a support distribution beam between the top of the portal frame and the top of the upper chord jig frame, mounting an upper chord upon the support distribution beam, and mounting the upper-deck bridge structure on the upper chord.

According to some embodiments of the present disclosure, a process of mounting the upper chord upon the support distribution beam includes: mounting a positioning stopper on the support distribution beam, and positioning and mounting the upper chord by using the positioning stopper.

According to some embodiments of the present disclosure, the lower-deck bridge structure of one or more spans of the double-deck multi-span bridge is made to have an arched structure.

According to some embodiments of the present disclosure, before mounting the upper chord jig frames and the lower chord jig frames, jig frame abutments are constructed at mounting positions of the upper chord jig frames and the lower chord jig frames.

According to some embodiments of the present disclosure, before mounting the upper chord jig frames and the lower chord jig frames, the jig frame abutments are pre-compressed.

Additional aspects and advantages of the present disclosure will be given in part in the following description, and in part will be obvious from the following description, or will be understood by the practice of the present disclosure.

BRIEF DESCRIPTION OF FIGURES

The present disclosure will be further described with reference to the accompanying drawings and embodiments, wherein:

FIG. 1 is a structural schematic diagram of a double-deck multi-span bridge according to an embodiment of the present disclosure;

FIG. 2 is a schematic diagram of construction of a first span of the double-deck multi-span bridge according to an embodiment of the present disclosure;

FIG. 3 is a schematic diagram of construction of a second span of the double-deck multi-span bridge in FIG. 2;

FIG. 4 is a schematic diagram of construction of a third span of the double-deck multi-span bridge in FIG. 2;

FIG. 5 is a schematic diagram of construction of a fourth span and a sixth span of the double-deck multi-span bridge in FIG. 2; and

FIG. 6 is a schematic diagram of construction of a fifth span of the double-deck multi-span bridge in FIG. 2.

REFERENCE NUMERALS

• • Bridge pier 100, upper chord jig frame 110, upper-deck bridge structure 120, web member 121, lower chord jig frame 130, lower-deck bridge structure 140, lower chord 150, portal frame 161, support distribution beam 162, upper chord 163, first span 200, second span 300, third span 400, fourth span 500, fifth span 600, and sixth span 700.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described in detail below, and examples of the embodiments are shown in the drawings, wherein the same or similar numerals throughout represent same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the drawings are exemplary, and are only used for explaining the present disclosure, and are not to be understood as limiting the present disclosure.

In the description of the present disclosure, it should be understood that when orientation descriptions are involved, orientation or positional relationships indicated by, e.g., upper, lower, front, back, left, right, etc., are based on the orientation or positional relationships shown in the drawings, and are merely for ease of description of the present disclosure and for simplicity of description, and are not intended to indicate or imply that the device or element referred to must have a particular orientation, and be constructed and operated in a particular orientation, and therefore cannot to be construed as limiting the present disclosure.

In the description of the present disclosure, “a number of” means one or more, “a plurality of” means two or more, greater than, less than, more than, and the like are understood to be exclusive of the number itself, and above, below, within, and the like are understood to be inclusive of the number itself. In the description of the present disclosure, unless otherwise explicitly defined, the words such as arranged, mounted, connected, etc., should be understood in a broad sense, and the specific meanings of the words in the present disclosure can be reasonably determined by those skilled in the art in conjunction with the specific contents of the technical solution.

In the description of the present disclosure, descriptions with reference to the terms “one embodiment”, “some embodiments”, “illustrative embodiments”, “examples”, “specific examples”, or “some examples” or the like mean that specific features, structures, materials, or characteristics described in combination with the embodiments or examples are included in at least one embodiment or example of the present disclosure. In this specification, schematic descriptions of the aforementioned terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

Referring to FIGS. 1-4, an embodiment of the present disclosure provides a double-deck multi-span bridge construction method, including: construction of a first span 200, construction of a second span 300, and demounting a jig frame in a span-separated mode, wherein

• • the construction of the first span includes: mounting a lower chord jig frame 130 of the first span 200, and mounting a lower-deck bridge structure 140 of the first span 200 by using the lower chord jig frame 130 of the first span 200 as a support; and
  • mounting an upper chord jig frame 110 of the first span 200, and mounting an upper-deck bridge structure 120 of the first span 200 by using the upper chord jig frame 110 of the first span 200 as a support.

The construction of the second span includes: mounting a lower chord jig frame 130 of the second span 300, and mounting a lower-deck bridge structure 140 of the second span 300 by using the lower chord jig frame 130 of the second span 300 as a support; and

• • mounting an upper chord jig frame 110 of the second span 300, and mounting an upper-deck bridge structure 120 of the second span 300 by using the upper chord jig frame 110 of the second span 300 as a support; and
  • demounting the upper chord jig frame 110 of the first span 200.

Construction of the remaining spans of the bridge is performed in sequence by adopting a construction manner of demounting a jig frame in a span-separated mode, and after construction of all spans of the double-deck multi-span bridge is completed, the remaining upper chord jig frames 110 and lower chord jig frames 130 are disassembled;

Wherein the construction manner of demounting a jig frame in a span-separated mode includes the following steps of:

• • mounting an upper chord jig frame 110 of a currently constructed span, and mounting an upper-deck bridge structure 120 of the currently constructed span by using the upper chord jig frame 110 of the currently constructed span as a support; and
  • demounting an upper chord jig frame 110 of a span adjacent to the currently constructed span, and demounting a lower chord jig frame 130 of a span which is separated from the currently constructed span by one span.

Wherein a span refers to a bridge structure between two adjacent bridge piers 100. The span adjacent to the currently constructed span refers to a span of which a bridge structure is already installed that is adjacent to the currently constructed span, for example, when the currently constructed span is a third span 400, the span adjacent to the currently constructed span is the second span 300 of which a bridge structure is already installed. The span which is separated from the currently constructed span by one span is a span separated from the currently constructed span by the span adjacent to the currently constructed span and of which a bridge structure is already installed, for example, when the currently constructed span is a sixth span 700, the span which is separated from the currently constructed span by one span is a fourth span 500. Both the lower chord jig frames 130 and the upper chord jig frames 110 can be assembled by stepwise assembly of standard sections, and the height and load of the lower chord jig frames 130 and the upper chord jig frames 110 are set according to the bridge structures. In the construction of the bridge, after the upper-deck bridge structures 120 are mounted, the upper-deck bridge structures 120 and the lower-deck bridge structures 140 are integrally connected by web members 121. The upper-deck bridge structures 120 and the lower-deck bridge structures 140 may be bridge decks formed by casting concrete on a reinforcing bar template, segmented traffic lane plates, or integral bridge deck steel plates, wherein the bridge deck steel plates and the traffic lane plates may be assembled by welding.

The upper chord jig frame 110 is disassembled after the upper-deck bridge structure 120 is mounted, and the upper-deck bridge structure 120 is supported by the lower-deck bridge structure 140 and the lower chord jig frame 130 at the lower part, without affecting the stability of the upper-deck bridge structure 120. Both ends of the lower-deck bridge structures 140 of the bridge are mounted on the bridge piers 100, the bridge piers 100 can support the bridge as a whole, and according to the double-deck multi-span bridge construction method in the embodiments of the present disclosure, after mounting of the currently constructed span is completed, the lower chord jig frame 130 of a span of which both ends are connected with the bridge piers 100 and separated from the currently constructed span by one span is disassembled, so that load bearing of the bridge can be safely transitioned to the bridge piers 100, and the double-deck multi-span bridge can be prevented from collapsing.

The following is an example of applying the double-deck bridge construction method in the embodiment of the present disclosure to a 5-span double-deck bridge:

• • a lower chord jig frame 130 and an upper chord jig frame 110 of a first span 200 are mounted, and an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the first span 200 are mounted, and
  • a lower chord jig frame 130 and an upper chord jig frame 110 of a second span 300 are mounted, and the upper chord jig frame 110 of the first span 200 is disassembled after an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the second span 300 are mounted;
  • a lower chord jig frame 130 and an upper chord jig frame 110 of a third span 400 are mounted, and the upper chord jig frame 110 of the second span 300 and the lower chord jig frame 130 of the first span 200 are disassembled after the upper-deck bridge structure 120 and the lower-deck bridge structure 140 of the third span 400 are mounted;
  • a lower chord jig frame 130 and an upper chord jig frame 110 of a fourth span 500 are mounted, and the upper chord jig frame 110 of the third span 400 and the lower chord jig frame 130 of the second span 300 are disassembled after an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the fourth span 500 are mounted; and
  • a lower chord jig frame 130 and an upper chord jig frame 110 of a fifth span 600 are mounted, and after an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the fifth span 600 are mounted, the construction of the bridge structures is completed, and the remaining upper chord jig frames 110 and lower chord jig frames 130 are disassembled.

In the double-deck multi-span bridge construction method in the prior art, all jig frames are laid before the bridge construction to support the bridge construction, and after completion of the double-deck multi-span bridge, all the jig frames are disassembled. In this method, jig frames of a jig frame support system are large in one-time input, which requires a large area of temporary storage yards, and the construction period is long.

According to the double-deck multi-span bridge construction method in the embodiment of the present disclosure, the upper chord jig frame 110 and the lower chord jig frame 130 of the already constructed span are properly demounted during construction, so that the upper chord jig frame 110 and the lower chord jig frame 130 can be used in a recycle manner, and the construction cost is reduced. In addition, the construction period of building the upper chord jig frame 110 and the lower chord jig frame 130 is short, and other construction operations can be simultaneously carried out on a span in which the jig frame is disassembled, for example, fire retardant coating construction can be carried out on a mounted bridge deck after the jig frame is disassembled, and the construction period of the double-deck multi-span bridge is effectively shortened. Additionally, a bridge structure of a double-layer continuous steel truss structure does not have an expansion joint, by disassembling all the support jig frames at one time, the bridge structure cannot digest its internal deformation, which may result in the warping of the free end of mounting, and according to the double-deck multi-span bridge construction method in the embodiments of the present disclosure, the upper chord jig frame 110 and the lower chord jig frame 130 are disassembled in a graded manner, thereby ensuring that a bridge structure can be smoothly and safely transitioned to a designed stress state.

In other embodiments of the present disclosure, the double-deck multi-span bridge is constructed from both ends to the middle, and joined at any span in the middle, spans at both ends of the double-deck multi-span bridge adopt the construction manner of the first span, spans adjacent to the spans at both ends of the double-deck multi-span bridge adopt the construction manner of the second span, and the remaining spans of the double-deck multi-span bridge adopt the construction manner of demounting a jig frame in a span-separated mode. The bridge is constructed in one direction, and the construction span is large, which makes the construction difficult, and the bidirectional construction of the bridge can reduce the currently constructed span of the bridge in one direction, reduce the construction difficulty, and shorten the construction period of the bridge.

The double-deck multi-span bridge is constructed from both ends to the middle, the both ends are constructed in the same manner, and a process of properly disassembling the upper chord jig frame 110 and the lower chord jig frame 130 of the already constructed span is used, so that the upper chord jig frame 110 and the lower chord jig frame 130 can be used in a recycle manner, the construction cost is reduced, and the construction period is shortened. The selection of the location of the span where the bridge is joined may be set according to the structure of the double-deck multi-span bridge and the terrain where the bridge is located. Construction of both ends of the double-deck multi-span bridge can be started at the same time, or can be performed one after another according to construction requirements. For example, a 8-span double-deck bridge can be constructed at both ends at the same time; and can also be constructed from one end of the double-deck multi-span bridge, and can then be started to be constructed at the other end of the double-deck multi-span bridge after the construction is completed to the part or all of the span at a position where the bridge is joined.

Referring to FIGS. 2 to 6, a 6-span double-deck bridge is constructed from both ends to the middle by applying the double-deck multi-span bridge construction method in this embodiment, and is joined at a fifth span 600, and the steps are as follows:

• • a lower chord jig frame 130 and an upper chord jig frame 110 of a first span 200 are mounted, and an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the first span 200 are mounted, and
  • a lower chord jig frame 130 and an upper chord jig frame 110 of a second span 300 are mounted, and the upper chord jig frame 110 of the first span 200 is disassembled after an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the second span 300 are mounted;
  • a lower chord jig frame 130 and an upper chord jig frame 110 of a third span 400 are mounted, and the upper chord jig frame 110 of the second span 300 and the lower chord jig frame 130 of the first span 200 are disassembled after the upper-deck bridge structure 120 and the lower-deck bridge structure 140 of the third span 400 are mounted;
  • a lower chord jig frame 130 and an upper chord jig frame 110 of a fourth span 500 are mounted, and the upper chord jig frame 110 of the third span 400 and the lower chord jig frame 130 of the second span 300 are disassembled after an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the fourth span 500 are mounted;
  • a lower chord jig frame 130 and an upper chord jig frame 110 of a sixth span 700 are mounted, and an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the sixth span 700 are mounted; and
  • a lower chord jig frame 130 and an upper chord jig frame 110 of the fifth span 600 are mounted, and after an upper-deck bridge structure 120 and a lower-deck bridge structure 140 of the fifth span 600 are mounted, the fourth span 500 and the fifth span 600 are joined, and the remaining upper chord jig frames 110 and lower chord jig frames 130 are disassembled.

In some embodiments of the present disclosure, a process of mounting a lower-deck bridge structure 140 by using the lower chord jig frame 130 as a support includes: mounting a lower chord 150 at the top of the lower chord jig frame 130, and mounting the lower-deck bridge structure 140 on the lower chord 150. Specifically, the lower chord 150 is hoisted to the top of the lower chord jig frame 130, the lower chord jig frame 130 supports the lower chord 150, and then the lower-deck bridge structure 140 is hoisted to the operating surface of the lower chord 150, and the lower-deck bridge structure 140 and the lower chord 150 are mounted and fixed. The lower-deck bridge structures 140 may be bridge decks formed by casting concrete on a reinforcing bar template, segmented traffic lane plates, or integral bridge deck steel plates, wherein the bridge deck steel plates and the traffic lane plates may be assembled by welding, and then are be in combination with and fixed to the lower chords 150.

In some embodiments of the present disclosure, a process of mounting an upper-deck bridge structure 120 by using the upper chord jig frame 110 as a support includes: mounting a portal frame 161 on the lower-deck bridge structure 140, mounting a support distribution beam 162 between the top of the portal frame 161 and the top of the upper chord jig frame 110, mounting an upper chord 163 upon the support distribution beam 162, and mounting the upper-deck bridge structure 120 on the upper chord 163. The portal frame 161 is a door-type structure consisting of a crossbar and a plurality of upright posts. The upper chord 163 is connected to the support distribution beam 162. The support distribution beam 162 is connected to the portal frame 161. The upper chord jig frame 110 can support the upper-deck bridge structure 120. By changing the structure of the portal frame 161, the upper chord jig frame 110 can be adapted to different bridge structures. For example, the portal frame 161 passes through the web members 121 of the upper-deck bridge structure 120 and the lower-deck bridge structure 140, and the upper chord jig frame 110 is connected to the portal frame 161 to prevent interference between the upper chord jig frames 110 and the web members 121. The portal frame 161, the support distribution beam 162 and the upper chord 163 may be mounted by welding or fixed by bolts.

In some embodiments of the present disclosure, a process of mounting the upper chord 163 upon the support distribution beam 162 includes: mounting a positioning stopper on the support distribution beam 162, and positioning and mounting the upper chord 163 by using the positioning stopper. The chords in bridge steel structures are generally rigid bar members with parallelogram sections, which are difficult to mount accurately in a set position when being directly mounted. The positioning stopper is set at a mounting position of the upper chord 163, and can abut against the upper chord 163 at a set position, thereby positioning the upper chord 163 at the set position, reducing manual adjustment difficulty and improving the construction efficiency. The positioning stopper may be mounted on the support distribution beam 162 by welding, bolting, or the like.

Referring to FIG. 3, in some embodiments of the present disclosure, the lower-deck bridge structure 140 of one or more spans of the double-deck multi-span bridge is made to have an arched structure. The arched bridge structure has large spanning capacity, and uniform surface stress, and is suitable for use in a large bridge span. The arched bridge structure may be formed by making the lower chord 150 change in a parabola with a downward opening.

In some embodiments of the present disclosure, before mounting the upper chord jig frames 110 and the lower chord jig frames 130, jig frame abutments are constructed at mounting positions of the upper chord jig frames 110 and the lower chord jig frames 130. The mounting positions of the upper chord jig frames 110 or the lower chord jig frames 130 are on a land surface, a process of constructing the jig frame abutment may include pouring concrete at the mounting positions of the upper chord jig frames 110 or the lower chord jig frames 130 to form a concrete abutment; and may also include mounting a steel base plate at the mounting positions of the upper chord jig frames 110 or the lower chord jig frames 130 to support the upper chord jig frames 110 or the lower chord jig frames 130 with the steel base plate. The concrete abutment or the steel base plate has better stiffness relative to soil to prevent the soil from being depressed and deformed, resulting in a change in the height of the upper chord jig frames 110 or the lower chord jig frames 130. The mounting positions of the upper chord jig frames 110 or the lower chord jig frames 130 are at a river-crossing section, and a process of constructing the jig frame abutment may include providing a pipe pile at the mounting positions of the upper chord jig frames 110 or the lower chord jig frames 130 to support the upper chord jig frames 110 and the lower-chord carcass 130 by the pipe pile.

In some embodiments of the present disclosure, the jig frame abutments are pre-compressed before mounting the upper chord jig frames 110 and the lower chord jig frames 130. After the jig frame abutments are constructed, and the upper chord jig frames 110 or the lower chord jig frames 130 of the jig frame abutments are stressed, the jig frame abutments may have changes such as being partially depressed, and the jig frame abutments are pre-compressed in advance to stabilize the positions of the jig frame abutments. A process for pre-compressing the jig frame abutments may be carried out by placing concrete briquettes or other heavy objects on the jig frame abutments.

Although the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings, the present disclosure is not limited to the above embodiments, and various changes can be made without departing from the spirit of the present disclosure within the scope of knowledge of those of ordinary skill in the art. Furthermore, the embodiments of the present disclosure and the features in the embodiments may be combined with each other without conflict.

Claims

1. A double-deck multi-span bridge construction method, comprising:

construction of a first span: mounting a lower chord jig frame of the first span, and mounting a lower-deck bridge structure of the first span by using the lower chord jig frame of the first span as a support; and mounting an upper chord jig frame of the first span, and mounting an upper-deck bridge structure of the first span by using the upper chord jig frame of the first span as a support;

construction of a second span: mounting a lower chord jig frame of the second span, and mounting a lower-deck bridge structure of the second span by using the lower chord jig frame of the second span as a support; and mounting an upper chord jig frame of the second span, and mounting an upper-deck bridge structure of the second span by using the upper chord jig frame of the second span as a support; demounting the upper chord jig frame of the first span;

performing construction of the remaining spans of the bridge in sequence by adopting a construction manner of demounting a jig frame in a span-separated mode, and after construction of all spans of the double-deck multi-span bridge is completed, disassembling the remaining upper chord jig frames and lower chord jig frames;

wherein the construction manner of demounting a jig frame in a span-separated mode comprises the following steps of: mounting an upper chord jig frame of a currently constructed span, and mounting an upper-deck bridge structure of the currently constructed span by using the upper chord jig frame of the currently constructed span as a support; and demounting an upper chord jig frame of a span adjacent to the currently constructed span, and demounting a lower chord jig frame of a span which is separated from the currently constructed span by one span.

2. The double-deck multi-span bridge construction method according to claim 1, wherein the double-deck multi-span bridge is constructed from both ends to the middle, and joined at any span in the middle, spans at both ends of the double-deck multi-span bridge adopt the construction manner of the first span, spans adjacent to spans at both ends of the double-deck multi-span bridge adopt the construction manner of the second span, and the remaining spans of the double-deck multi-span bridge adopt the construction manner of demounting a jig frame in a span-separated mode.

3. The double-deck multi-span bridge construction method according to claim 1, wherein a process of mounting a lower-deck bridge structure by using the lower chord jig frame as a support comprises: mounting a lower chord at the top of the lower chord jig frame, and mounting the lower-deck bridge structure on the lower chord.

4. The double-deck multi-span bridge construction method according to claim 3, wherein a process of mounting an upper-deck bridge structure by using the upper chord jig frame as a support comprises: mounting a portal frame on the lower-deck bridge structure, mounting a support distribution beam between the top of the portal frame and the top of the upper chord jig frame, mounting an upper chord upon the support distribution beam, and mounting the upper-deck bridge structure on the upper chord.

5. The double-deck multi-span bridge construction method according to claim 4, wherein a process of mounting the upper chord upon the support distribution beam comprises: mounting a positioning stopper on the support distribution beam, and positioning and mounting the upper chord by using the positioning stopper.

6. The double-deck multi-span bridge construction method according to claim 5, wherein the lower-deck bridge structure of one or more spans of the double-deck multi-span bridge is made to have an arched structure.

7. The double-deck multi-span bridge construction method according to claim 1, wherein, before mounting the upper chord jig frames and the lower chord jig frames, jig frame abutments are constructed at mounting positions of the upper chord jig frames and the lower chord jig frames.

8. The double-deck multi-span bridge construction method according to claim 7, wherein, before mounting the upper chord jig frames and the lower chord jig frames, the jig frame abutments are pre-compressed.