Double-layer steel truss arch bridge installation process

Abstract

The invention relates to a double-layer steel truss arch bridge mounting process. The double-layer steel truss arch bridge mounting process is characterized by comprising the following specific mounting processes: S1, field arrangement; s2, mounting on-shore and in-water temporary piers; s3, assembling the truss pieces and the bridge deck system; s4, mounting a main beam; s5, mounting an arch rib bracket; s6, assembling the arch ribs; s7, arch rib installation; and S8, the temporary structure is dismantled, and construction is completed. The construction sequence of mounting on-shore and in-water temporary piers, assembling truss pieces and a bridge deck system, mounting main beams and mounting arch ribs is sequentially carried out on the double-layer steel truss arch bridge, temporary support sets are adopted for auxiliary construction in the construction process of the main beams, and the laying sequence of the main beams is fully combined with the composition and erection positions of temporary supports; the main beam is laid in the side span direction by taking the revetment as a reference, so that the temporary support and the main beam are laid more scientifically; in addition, during installation of the arch rib sections, hoisting is carried out in the mode that the two ends are firstly arranged and then the middle is arranged, and safety and stability during installation of the arch rib sections are guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of double-layer steel truss arch bridge installation, and in particular to a double-layer steel truss arch bridge installation process. Background Art

[0002] Bridges are an important part of transportation infrastructure and provide important support for the development of the country's economy and society. China has been a major bridge construction country since ancient times, and the construction of bridges has greatly promoted the development of China's transportation industry.

[0003] Double-layer steel truss arch bridge is a common structural form of bridge; during the on-site assembly of double-layer steel truss arch bridge, the arch beam lifting structure is large in size, heavy in tonnage, high in lifting height, and high in requirements for lifting equipment, and the on-site assembly of the arch beam is difficult; the temporary piers are subjected to large forces, and the bridge line shape control and elevation control during the construction process are directly related to the quality of the main bridge construction; construction measurement, monitoring technology and installation sequence are key difficulties; therefore, a double-layer steel truss arch bridge installation process is needed to solve the above difficulties. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a double-layer steel truss arch bridge installation process, which can solve the safety hazards existing in the unscientific installation sequence in the installation of traditional double-layer steel truss arch bridges.

[0005] In order to solve the above technical problems, the technical solution of the present invention is: a double-layer steel truss arch bridge installation process, the innovation of which is: the specific installation process is as follows:

[0006] S1: On-site arrangement: Harden the construction site on both sides of the river, including the hoisting construction area, assembly area, beam storage area and internal roads, to ensure that the foundation for subsequent construction has sufficient bearing capacity;

[0007] S2: Installation of temporary piers on shore and in water: The temporary piers on shore and in water form an assembly platform, and the materials used are Q235 and Q345 steel. The temporary piers on shore are composed of C30 foundation, steel pipe piles, flat joints, and pile top beams. The temporary piers in water are composed of underwater steel pipe pile foundations, flat joints, and pile top beams. The structural connections are all welded;

[0008] S3: Assembling trusses and bridge deck systems: When installing temporary piers, trusses and bridge deck systems are assembled simultaneously at the main assembly site. Trusses are assembled in multiple sections in a continuous matching manner. The main cross beams of the bridge deck are lengthened by "three assemblies and one length". The bridge deck is widened and the secondary cross beams are welded to the bridge deck.

[0009] S4: Install the main beam: Use crawler crane to install the side span main truss and bridge deck system, assemble from the revetment to the side span, and the installation order is main truss → lower deck system → upper deck system; then use floating crane to install the main truss in the middle span area until closing, at this time, the temporary piers and main truss in the water are vacated for easy removal; transfer the crawler crane to the upper deck to install the middle span deck system, assemble from the revetment to the middle span until closing; install the cantilever unit after closing;

[0010] S5: Arch rib support installation: After the main beam is installed, the arch rib support is installed on the upper bridge deck using a crawler crane. The support consists of steel pipe columns, angle steel flat joints, and pile top steel beams, which are connected by welding;

[0011] S6: Arch rib assembly: When the main beam is constructed, the arch rib trusses are installed in bottles simultaneously, using a continuous matching assembly method;

[0012] S7: Arch rib installation: The side span arch ribs are hoisted synchronously and symmetrically from both sides to the middle of the bridge deck by crawler cranes, and the middle span arch ribs are installed by floating cranes until they are closed. The cross braces are installed synchronously during the arch rib installation process;

[0013] S8: Temporary structure removal and construction completion: After the arch rib installation is completed, the entire bridge installation is completed, the temporary structure is removed, and the hangers are tensioned.

[0014] Furthermore, temporary piers on shore and in water are installed in S2: the temporary piers on shore form installation platforms on the east and west banks, and the width in the transverse direction of the bridge is 32.5m; the foundation of the temporary pier on shore adopts a 4.5×4.5m C30 reinforced concrete foundation, with a pre-buried steel plate on the top for welding with the steel pipe, and φ478×8 steel pipe columns are set on the top, 4 in a group, 2×2 arrangement, column spacing of 2.5 meters, L100×10 angle steel is used to connect the columns, and double HN700×300 steel distribution beams are set on the top of the columns. Two groups of temporary piers on shore are arranged in the transverse direction of the bridge, respectively located below the lower chord of the main truss;

[0015] Two groups of temporary underwater piers are set up longitudinally on both sides of the river channel, with two piers set up transversely in each group, with a center spacing of 32.5m, a total of four, and a navigation hole reserved between the east and west sides with a net width of 76m; the temporary underwater piers all use steel pipe pile foundations with a longitudinal and transverse spacing of 4.8m, using φ820×10mm steel pipes; cross bars and diagonal bars use φ273×6.5mm steel pipes, and 2HN700 longitudinal and transverse beams are set on the pile tops.

[0016] Furthermore, the assembling of the truss and the bridge deck in S3: the truss assembly adopts a scheme of multi-segment continuous matching assembly, requiring that each round has no less than 3 segments, and after the previous round of assembly is completed, a segment is left as the mother segment of the next round to participate in the assembly, thereby ensuring the smooth connection between adjacent trusses; the assembly sequence is positioning the upper and lower chords → assembling the webs → welding the welds between the webs and the upper chord nodes → welding the welds between the webs and the lower chord nodes;

[0017] The main cross beam of the bridge deck is installed in a straight position. The assembly frame is arranged in a linear shape and reverse deformation is preset. Positioning tools are set at the end, mid-span and docking position. The main cross beam is positioned on the frame in turn, and the three main cross beams are connected in one. After the assembly is completed, the straightness and camber of the cross beam should be checked. The assembly sequence of the bridge deck is: bridge deck positioning → assembly of horizontal and longitudinal beams → welding of bridge deck.

[0018] Furthermore, in the installation of the main beam of S4, a 350t crawler crane is used to lift the first main truss lower chord at the revetment position and connect it to the support. Then, the node and the main pier are used as the installation reference of the whole bridge for positioning. After completion, the lower bridge deck system at the revetment position is installed. The lower bridge deck system is installed in the order of main crossbeam → longitudinal beam → secondary crossbeam + middle bridge deck → secondary crossbeam + side bridge deck to control the width of the lower chord girder;

[0019] Install the first truss at the revetment position, and then install the upper bridge deck system; the upper bridge deck is installed in the order of main crossbeam → longitudinal beam → secondary crossbeam + middle bridge deck → secondary crossbeam + side bridge deck; after the benchmark installation is completed, gradually install the side span until all the side spans are installed;

[0020] After the side span is installed, the floating crane is used to install the middle span trusses. The trusses on the inner side of the first main truss at the revetment position are installed first, and then the main trusses in the middle position are installed last. After the main trusses are closed, the underwater piers are removed, and the crawler crane is moved to the upper bridge deck. The bridge deck system is installed simultaneously on both sides toward the mid-span until the bridge deck system is closed. The installation sequence is to install each section at a time, first the lower bridge deck system and then the upper bridge deck system. After closing, the cantilever unit of the entire bridge is installed.

[0021] Furthermore, the S7 arch rib needs to be precisely controlled during the installation of the arch rib; before the arch rib segment is installed, the temporary bracket is made in place, including the plane position and vertical elevation; the contour edge of the arch rib segment is measured and laid out on the I-beam at the top of the temporary bracket with a total station, and the channel steel is vertically welded to the top surface of the I-beam to play a limiting role before the installation of the arch rib segment; when the arch rib segment is installed, the total station is used to track and measure the entire process of each measurement control point of the arch rib, and timely adjustments and corrections are made if any deviation is found; considering that the installation bracket is composed of a steel pipe lattice structure, there is a certain elastic and inelastic vertical deformation, and the installation elevation is 1 cm higher than the control elevation; after the component is installed in place, the hook is loosened to about 15%, but it is not unhooked. At this time, each measurement point is rechecked and measured, and the component is fully connected to the temporary pier after meeting the requirements before it can be unhooked;

[0022] After the component is installed and when the adjacent components are installed, pay attention to the protection of the installed components to ensure that they do not collide with the installed components; after the adjacent components are installed, observe the front components again;

[0023] After the installation of the arch rib segment is completed, the measurement and control points and the position of the hanger are promptly reviewed, and deviations are adjusted in time. The plane position adjustment of the arch rib segment installation also adopts the construction method of fine-tuning by manual hand winches and jacks, and the vertical height is fine-tuned by jacks.

[0024] Furthermore, during the installation of the S7 arch rib, the main arch trusses and cross braces were assembled in advance, the main arch supports were erected, and the components were transferred to the upper bridge deck; two crawler cranes synchronously and symmetrically lifted the side span arch ribs from both sides to the middle of the bridge deck, and installed them from both sides to the arch section; a floating crane was used to install the middle span arch ribs to the closure position, and the arch rib cross braces were installed in a timely and synchronous manner after the installation of each segment was completed; before the main arch was closed, the closure data was observed in advance, the closure section was cut in the factory, the arch rib closure section was installed, and finally the remaining cross braces were installed.

[0025] The advantages of the present invention are:

[0026] 1) In the installation construction of the double-deck steel truss arch bridge in the present invention, the construction sequence is as follows: installing temporary piers on the shore and in the water → assembling trusses and bridge deck systems → installing main beams → installing arch ribs. The main beams are assisted in construction by temporary support groups during construction, and the composition and erection positions of the temporary supports fully combine the laying sequence of the main beams. The main beams are laid in the direction of the side span with the revetment as the reference, so that the laying of temporary supports and main beams is more scientific. In addition, the arch rib segments are installed by hoisting at both ends first and then in the middle, which ensures the safety and stability of the arch rib segments during installation. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0028] Figure 1 The present invention is a process flow chart for installing a double-layer steel truss arch bridge.

[0029] Figure 2 This is a temporary pier layout diagram for the installation process of a double-layer steel truss arch bridge of the present invention.

[0030] Figure 3 The present invention is a schematic diagram of the first installation of the main beam of a double-layer steel truss arch bridge installation process.

[0031] Figure 4 This is a diagram showing the completion of the main beam installation in the onshore area of ​​a double-deck steel truss arch bridge installation process according to the present invention.

[0032] Figure 5 This is a diagram of the installation of the main truss in the middle span of a double-layer steel truss arch bridge installation process of the present invention.

[0033] Figure 6 This is a diagram of closing the main truss of the mid-span during the installation process of a double-layer steel truss arch bridge according to the present invention.

[0034] Figure 7 This is a diagram of the installation of the mid-span bridge deck system in the installation process of a double-deck steel truss arch bridge of the present invention.

[0035] Figure 8 This is an arch rib bracket installation diagram for a double-layer steel truss arch bridge installation process of the present invention.

[0036] Fig. 9 The invention discloses a side span arch rib installation diagram of a double-layer steel truss arch bridge installation process.

[0037] Fig.10 The present invention provides a mid-span arch rib installation diagram for a double-layer steel truss arch bridge installation process.

[0038] Fig.11 The present invention provides a double-layer steel truss arch bridge installation process for closing and installing the mid-span arch ribs.

[0039] Fig.12 This is a diagram of a double-layer steel truss arch bridge installation process of the present invention after the temporary structure is removed. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0041] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. 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.

[0042] like Figures 1 to 12 The installation process of a double-layer steel truss arch bridge shown in the figure is as follows:

[0043] S1: On-site arrangement: Harden the construction site on both sides of the river, including the hoisting construction area, assembly area, beam storage area and internal roads, to ensure that the foundation for subsequent construction has sufficient bearing capacity;

[0044] S2: Installation of temporary piers on shore and in water: The temporary piers on shore and in water form an assembly platform, and the materials used are Q235 and Q345 steel. The temporary piers on shore are composed of C30 foundation, steel pipe piles, flat joints, and pile top beams. The temporary piers in water are composed of underwater steel pipe pile foundations, flat joints, and pile top beams. The structural connections are all welded;

[0045] S3: Assembling trusses and bridge deck systems: When installing temporary piers, trusses and bridge deck systems are assembled simultaneously at the main assembly site. Trusses are assembled in multiple sections in a continuous matching manner. The main cross beams of the bridge deck are lengthened by "three assemblies and one length". The bridge deck is widened and the secondary cross beams are welded to the bridge deck.

[0046] S4: Install the main beam: Use crawler crane to install the side span main truss and bridge deck system, assemble from the revetment to the side span, and the installation order is main truss → lower deck system → upper deck system; then use floating crane to install the main truss in the middle span area until closing, at this time, the temporary piers and main truss in the water are vacated for easy removal; transfer the crawler crane to the upper deck to install the middle span deck system, assemble from the revetment to the middle span until closing; install the cantilever unit after closing;

[0047] S5: Arch rib support installation: After the main beam is installed, the arch rib support is installed on the upper bridge deck using a crawler crane. The support consists of steel pipe columns, angle steel flat joints, and pile top steel beams, which are connected by welding;

[0048] S6: Arch rib assembly: When the main beam is constructed, the arch rib trusses are installed in bottles simultaneously, using a continuous matching assembly method;

[0049] S7: Arch rib installation: The side span arch ribs are hoisted synchronously and symmetrically from both sides to the middle of the bridge deck by crawler cranes, and the middle span arch ribs are installed by floating cranes until they are closed. The cross braces are installed synchronously during the arch rib installation process;

[0050] S8: Temporary structure removal and construction completion: After the arch rib installation is completed, the entire bridge installation is completed, the temporary structure is removed, and the hangers are tensioned.

[0051] Temporary piers on shore and in water are installed in S2: The temporary piers on shore form installation platforms on the east and west banks, with a width of 32.5m in the transverse direction of the bridge; the foundation of the temporary pier on shore adopts a 4.5×4.5m C30 reinforced concrete foundation, with a pre-buried steel plate on the top for welding with steel pipes, and φ478×8 steel pipe columns are set on top, 4 in a group, arranged 2×2, with a column spacing of 2.5 meters, and L100×10 angle steel is used to connect the columns. Double HN700×300 steel distribution beams are set on the top of the columns. Two groups of temporary piers on shore are arranged in the transverse direction of the bridge, respectively located below the lower chord of the main truss;

[0052] Two groups of temporary underwater piers are set up longitudinally on both sides of the river channel, with two piers set up transversely in each group, with a center spacing of 32.5m, a total of four, and a navigation hole reserved between the east and west sides with a net width of 76m; the temporary underwater piers all use steel pipe pile foundations with a longitudinal and transverse spacing of 4.8m, using φ820×10mm steel pipes; cross bars and diagonal bars use φ273×6.5mm steel pipes, and 2HN700 longitudinal and transverse beams are set on the pile tops.

[0053] Furthermore, in S3, the truss and deck system are assembled: the truss assembly adopts a scheme of multi-segment continuous matching assembly, requiring no less than 3 segments in each round, and leaving one segment as the mother segment for the next round of assembly after the previous round of assembly is completed, thereby ensuring the smooth connection between adjacent trusses; the assembly sequence is positioning the upper and lower chords → assembling the webs → welding the welds between the webs and the upper chord nodes → welding the welds between the webs and the lower chord nodes;

[0054] The main cross beam of the bridge deck is installed in a straight position. The assembly frame is arranged in a linear shape and reverse deformation is preset. Positioning tools are set at the end, mid-span and docking position. The main cross beam is positioned on the frame in turn, and the three main cross beams are connected in one. After the assembly is completed, the straightness and camber of the cross beam should be checked. The assembly sequence of the bridge deck is: bridge deck positioning → assembly of horizontal and longitudinal beams → welding of bridge deck.

[0055] In the installation of the main beam of S4, a 350t crawler crane is used to lift the first main truss lower chord at the revetment position and connect it to the support. Then the node and the main pier are used as the installation reference for the whole bridge. After completion, the lower bridge deck system at the revetment position is installed. The lower bridge deck system is installed in the order of main crossbeam → longitudinal beam → secondary crossbeam + middle bridge deck → secondary crossbeam + side bridge deck to control the width of the lower chord girder;

[0056] Install the first truss at the revetment position, and then install the upper bridge deck system; the upper bridge deck is installed in the order of main crossbeam → longitudinal beam → secondary crossbeam + middle bridge deck → secondary crossbeam + side bridge deck; after the benchmark installation is completed, gradually install the side span until all the side spans are installed;

[0057] After the side span is installed, the floating crane is used to install the middle span trusses. The trusses on the inner side of the first main truss at the revetment position are installed first, and then the main trusses in the middle position are installed last. After the main trusses are closed, the underwater piers are removed, and the crawler crane is moved to the upper bridge deck. The bridge deck system is installed simultaneously on both sides toward the mid-span until the bridge deck system is closed. The installation sequence is to install each section at a time, first the lower bridge deck system and then the upper bridge deck system. After closing, the cantilever unit of the entire bridge is installed.

[0058] S7 Arch ribs require precision control during installation; Before the arch rib segments are installed, temporary supports are made in place, including the plane position and vertical elevation; the contour edge of the arch rib segments is measured and laid out on the I-beam at the top of the temporary support using a total station, and channel steel is vertically welded to the top surface of the I-beam to play a limiting role before the arch rib segments are installed;

[0059] When installing the arch rib segments, use a total station to track and measure all the measurement control points of the arch ribs throughout the process, and make timely adjustments and corrections if any deviation is found; considering that the installation bracket is composed of a steel pipe lattice structure, there is a certain elastic and inelastic vertical deformation, and the installation elevation is 1 cm higher than the control elevation; after the component is installed in place, the hook is loosened to about 15%, but it is not unhooked. At this time, each measurement point is rechecked and measured. After meeting the requirements, the component is fully connected to the temporary pier before it can be unhooked;

[0060] After the component is installed and when the adjacent components are installed, pay attention to the protection of the installed components to ensure that they do not collide with the installed components; after the adjacent components are installed, observe the front components again;

[0061] After the installation of the arch rib segment is completed, the measurement and control points and the position of the hanger are promptly reviewed, and deviations are adjusted in time. The plane position adjustment of the arch rib segment installation also adopts the construction method of fine-tuning by manual hand winches and jacks, and the vertical height is fine-tuned by jacks.

[0062] During the installation of S7 arch ribs, the main arch trusses and cross braces were assembled in advance, the main arch supports were erected, and the components were transferred to the upper bridge deck; two crawler cranes synchronously and symmetrically lifted the side span arch ribs from both sides to the middle of the bridge deck, and installed them from both sides to the arch section; a floating crane was used to install the middle span arch ribs to the closure position, and the arch rib cross braces were installed in a timely and synchronous manner after the installation of each segment was completed; before the main arch was closed, the closure data was observed in advance, the closure section was cut in the factory, the arch rib closure section was installed, and finally the remaining cross braces were installed.

[0063] Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A double-layer steel truss arch bridge installation process, characterized in that: The specific installation process is as follows: S1: On-site arrangement: Harden the construction site on both sides of the river, including the hoisting construction area, assembly area, beam storage area and internal roads, to ensure that the foundation for subsequent construction has sufficient bearing capacity; S2: Installation of temporary piers on shore and in water: The temporary piers on shore and in water form an assembly platform, and the materials used are Q235 and Q345 steel. The temporary piers on shore are composed of C30 foundation, steel pipe piles, flat joints, and pile top beams. The temporary piers in water are composed of underwater steel pipe pile foundations, flat joints, and pile top beams. The structural connections are all welded; S3: Assembling trusses and bridge deck systems: When installing temporary piers, trusses and bridge deck systems are assembled simultaneously at the main assembly site. Trusses are assembled in multiple sections in a continuous matching manner. The main cross beams of the bridge deck are lengthened by "three assemblies and one length". The bridge deck is widened and the secondary cross beams are welded to the bridge deck. S4: Install the main beam: Use crawler crane to install the side span main truss and bridge deck system, assemble from the revetment to the side span, and the installation order is main truss → lower deck system → upper deck system; then use floating crane to install the main truss in the middle span area until closing, at this time, the temporary piers and main truss in the water are vacated for easy removal; transfer the crawler crane to the upper deck to install the middle span deck system, assemble from the revetment to the middle span until closing; install the cantilever unit after closing; S5: Arch rib support installation: After the main beam is installed, the arch rib support is installed on the upper bridge deck using a crawler crane. The support consists of steel pipe columns, angle steel flat joints, and pile top steel beams, which are connected by welding; S6: Arch rib assembly: When the main beam is constructed, the arch rib trusses are installed in bottles simultaneously, using a continuous matching assembly method; S7: Arch rib installation: The side span arch ribs are hoisted synchronously and symmetrically from both sides to the middle of the bridge deck by crawler cranes, and the middle span arch ribs are installed by floating cranes until they are closed. The cross braces are installed synchronously during the arch rib installation process; S8: Temporary structure removal and construction completion: After the arch rib installation is completed, the entire bridge installation is completed, the temporary structure is removed, and the hangers are tensioned.

2. The installation process of a double-layer steel truss arch bridge according to claim 1 is characterized in that: In the said S2, temporary piers on shore and in water are installed: the temporary piers on shore form installation platforms on the east and west banks, and the width in the transverse direction of the bridge is 32.5m; the foundation of the temporary pier on shore adopts a 4.5×4.5m C30 reinforced concrete foundation, with a pre-buried steel plate on the top for welding with the steel pipe, and φ478×8 steel pipe columns are arranged on the top, 4 in a group, 2×2, with a column spacing of 2.5 meters, and L100×10 angle steel is used to connect the columns, and double HN700×300 steel distribution beams are set on the top of the columns. Two groups of temporary piers on shore are arranged in the transverse direction of the bridge, respectively located below the lower chord of the main truss; Two groups of temporary underwater piers are set up longitudinally on both sides of the river channel, with two piers set up transversely in each group, with a center spacing of 32.5m, a total of four, and a navigation hole reserved between the east and west sides with a net width of 76m; the temporary underwater piers all use steel pipe pile foundations with a longitudinal and transverse spacing of 4.8m, using φ820×10mm steel pipes; cross bars and diagonal bars use φ273×6.5mm steel pipes, and 2HN700 longitudinal and transverse beams are set on the pile tops.

3. The installation process of a double-layer steel truss arch bridge according to claim 1 is characterized in that: The truss and bridge deck assembly system in S3: the truss assembly adopts a scheme of multi-segment continuous matching assembly, requiring no less than 3 segments in each round, and leaving one segment as the mother segment of the next round for assembly after the previous round of assembly is completed, thereby ensuring the smooth connection between adjacent trusses; the assembly sequence is positioning the upper and lower chords → assembling the webs → welding the welds between the webs and the upper chord nodes → welding the welds between the webs and the lower chord nodes; The main beam of the bridge deck is installed upright, the assembly frame is arranged in a linear shape, and the reverse deformation is preset. Positioning tools are set at the end, mid-span and docking position; the main beam is positioned on the frame in turn, and the three main beams are connected in one. After the assembly is completed, pay attention to check the straightness and arch of the beam; the assembly order of the bridge deck is: bridge deck positioning → assembly of horizontal and longitudinal beams → welding of bridge deck.

4. The double-layer steel truss arch bridge installation process according to claim 1 is characterized in that: In the installation of the main beam of S4, a 350t crawler crane is used to lift the first main truss lower chord at the revetment position and connect it to the support. Then the node and the main pier are used as the installation reference of the whole bridge for positioning. After completion, the lower bridge deck system at the revetment position is installed. The lower bridge deck system is installed in the order of main crossbeam → longitudinal beam → secondary crossbeam + middle bridge deck → secondary crossbeam + side bridge deck to control the width of the lower chord girder; Install the first truss at the revetment position, and then install the upper bridge deck system; the upper bridge deck is installed in the order of main crossbeam → longitudinal beam → secondary crossbeam + middle bridge deck → secondary crossbeam + side bridge deck; after the benchmark installation is completed, gradually install the side span until all the side spans are installed; After the side span is installed, the floating crane is used to install the middle span trusses. The trusses on the inner side of the first main truss at the revetment position are installed first, and then the main trusses in the middle position are installed last. After the main trusses are closed, the underwater piers are removed, and the crawler crane is moved to the upper bridge deck. The bridge deck system is installed simultaneously on both sides toward the mid-span until the bridge deck system is closed. The installation sequence is to install each section at a time, first the lower bridge deck system and then the upper bridge deck system. After closing, the cantilever unit of the entire bridge is installed.

5. The double-layer steel truss arch bridge installation process according to claim 1 is characterized by: The S7 arch rib installation requires precision control of the arch rib; before the arch rib segment is installed, the temporary bracket is made in place, including the plane position and vertical elevation; the contour edge of the arch rib segment is measured and laid out on the I-beam at the top of the temporary bracket with a total station, and the channel steel is vertically welded to the top surface of the I-beam to play a limiting role before the installation of the arch rib segment; when the arch rib segment is installed, the total station is used to track and measure the entire process of each measurement control point of the arch rib, and timely adjustments and corrections are made if any deviation is found; considering that the installation bracket is composed of a steel pipe lattice structure, there is a certain elastic and inelastic vertical deformation, and the installation elevation is 1 cm higher than the control elevation; after the component is installed in place, the hook is loosened to about 15%, but it is not unhooked. At this time, each measurement point is rechecked and measured, and the component is fully connected to the temporary pier after meeting the requirements before it can be unhooked; After the component is installed and when the adjacent components are installed, pay attention to the protection of the installed components to ensure that they do not collide with the installed components; after the adjacent components are installed, observe the front components again; After the installation of the arch rib segment is completed, the measurement and control points and the position of the hanger are promptly reviewed, and deviations are adjusted in time. The plane position adjustment of the arch rib segment installation also adopts the construction method of fine-tuning by manual hand winches and jacks, and the vertical height is fine-tuned by jacks.

6. The installation process of a double-layer steel truss arch bridge according to claim 1 is characterized in that: During the installation of the S7 arch rib, the main arch trusses and cross braces are assembled in advance, the main arch supports are erected, and the components are transferred to the upper bridge deck; two crawler cranes synchronously and symmetrically lift the side span arch ribs from both sides to the middle of the bridge deck, and install them from both sides to the arch section; a floating crane is used to install the middle span arch rib to the closure position, and the arch rib cross braces are installed synchronously and promptly after each segment is installed; before the main arch is closed, the closure data is observed in advance, the closure section is cut and matched in the factory, the arch rib closure section is installed, and finally the remaining cross braces are installed.

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