A kind of construction method suitable for urban elevated two-layer steel truss rod composite beam

Abstract

This invention discloses a construction method for a two-layer steel truss web-supported composite beam suitable for urban elevated highways, solving the problem of complex stress distribution in existing technologies where large-span truss beams are converted into prestressed concrete structures with upper and lower chords and bridge decks. The invention includes an upper deck and a lower deck, connected by several evenly spaced web members. The upper deck has a crash barrier at its top, and an upper chord for fixing the upper web members is located within the upper deck. The lower deck has a lower chord for fixing the web members, and a pier is located at the bottom of the lower deck. A foundation is located below the pier, and cast-in-place piles are located below the foundation. This invention offers structural stability, rapid construction efficiency, low steel consumption in the steel truss web members (saving materials), minimal construction land area, low material consumption for the disc-buckle scaffolding, and a fast construction period.

Description

Technical Field

[0001] This invention relates to the field of urban railway co-construction technology, and in particular to a construction method applicable to composite beams with upper and lower steel truss web members on elevated structures in urban areas. Background Technology

[0002] The development of road and bridge engineering technology in my country is accelerating. New bridge deck design methods are being adopted, enabling composite bridge structures with double-deck steel trusses and prestressed concrete webs. This design improves the overall safety and stability of the bridge and has garnered widespread attention in recent years. However, the spatial position of the bridge structure changes continuously with the construction progress. The deformation coordination issues arising from the installation temperature and stress magnitude at different construction stages of the steel-concrete structure are extremely complex. Furthermore, considering the structural self-weight, construction loads, the instability of concrete materials, and changes in ambient temperature, all these factors cause the internal forces and stresses of the bridge structure to constantly change at each construction stage, making construction extremely difficult. Traditional truss beams with concrete-filled upper chords still have shortcomings. First, because concrete is only filled into the upper chord, the overall integrity of the truss beam is poor, and the structural strength and stiffness of the lower chord and web are still relatively weak. To ensure the reliability of the web, it is necessary to increase or thicken the web, or to install more webs, which further increases construction costs. On the other hand, on-site construction efficiency is low, mainly due to the foundation type. Foundation treatment takes a long time to complete, and the inadequate design of the bridge deck reinforcement binding and concrete pouring construction platform further reduces the overall construction efficiency.

[0003] Existing technologies, such as the Chinese invention patent with publication number CN 115928608 A, disclose a reverse construction method for a continuous steel truss web-plate truss double-layer composite rotating bridge. This method involves first erecting a support platform parallel to the railway direction to assemble the entire steel structure, then sequentially pouring and tensioning the steel strands of the concrete beam segments, followed by dismantling the support and installing temporary steel supports for the rotation construction. While this patent achieves safe and efficient hoisting and installation of the upper giant steel truss web-plate truss composite structure, thus successfully realizing the construction of the entire continuous steel truss web-plate truss double-layer composite rotating bridge spanning the railway, the construction process is complex due to the use of cast-in-place support formwork to connect with the upper steel truss structure, resulting in the upper steel truss acting as a counter-beam support during the pouring of the lower concrete beams. This also leads to poor overall integrity of the truss beams. Summary of the Invention

[0004] To address the shortcomings of the aforementioned background technology, this invention proposes a construction method for composite beams with upper and lower steel trusses and web members suitable for elevated roads in urban areas. This method solves the problems of low construction efficiency and poor overall integrity of the truss beams in the prior art.

[0005] The technical solution of this invention is implemented as follows: A composite beam with steel truss web members suitable for upper and lower layers of elevated roads in urban areas includes an upper panel and a lower panel. The upper panel and the lower panel are connected by a number of evenly arranged web members. The upper part of the upper panel is provided with a crash guardrail. The upper panel is provided with an upper chord for fixing the upper part of the web members. The lower panel is provided with a lower chord for fixing the web members. The lower part of the lower panel is provided with a pier. The lower part of the pier is provided with a foundation. The lower part of the foundation is provided with a cast-in-place pile.

[0006] Furthermore, the upper part of the upper panel is provided with a crash barrier, and an outer concrete covering is connected to the upper panel, which is set on the web bar.

[0007] Furthermore, a support and seismic blocks are provided between the lower panel and the pier, and a steel railing post and a power cable trough are provided on the upper part of the lower panel.

[0008] A construction method for composite beams with steel trusses and web members on two upper and lower levels of elevated roads in urban areas includes the following steps:

[0009] S1: Traffic control and site preparation at the intersection: First, construct the piers and cap beams. After completion, conduct an investigation and analysis of the intersection. Set up an assembly area on one side of the steel truss. The assembly area is divided into a pole and material storage area and a temporary assembly area.

[0010] S2: Temporary support construction condition: erection of steel pipe columns, distribution beams and pads;

[0011] S3: Install longitudinal and transverse movement devices: Arrange longitudinal and transverse limiting devices on the top of the pier column;

[0012] S4: Establish steel truss hoisting construction: Divide the steel truss into N (N>2) segments, and weld N-1 segments on site. The welded segments are the lower temporary horizontal bracing and the upper temporary horizontal bracing.

[0013] S5: Install the support: Install the support between the pier and the distribution beam. The support is located between the longitudinal limiting device and the transverse limiting device. The upper plate of the support is connected to the distribution beam, and the lower plate of the support is connected to the pier.

[0014] S6: Remove longitudinal limiting device: Remove the pad and the distribution beam on the pad, and remove the longitudinal limiting device;

[0015] S7: Remove the lower temporary horizontal bracing and pour the lower panel: Divide the welded segments into three segments: A, B, and C. First, remove segments A and C of the lower temporary horizontal bracing in stages. After removal, erect a pouring platform and pour the concrete. Then, remove segment B of the lower temporary horizontal bracing, erect the formwork, and pour the concrete for segment B. After tensioning and preloading, remove the formwork to form the lower panel.

[0016] S8: Remove the lateral limiting device;

[0017] S9: Dismantle the upper temporary horizontal bracing and pour the upper panel: Divide the upper temporary horizontal bracing into three segments: A, B, and C. First, dismantle segments A and C of the upper temporary horizontal bracing in stages. After dismantling, erect a pouring platform and pour the concrete. Then, dismantle segment B of the upper temporary horizontal bracing, erect the formwork, and pour the concrete. After tensioning and preloading, remove the formwork to form the upper panel.

[0018] S10: Construction of upper columns, upper cover beams and removal of temporary supports: Construct columns between the lower and upper panels, install upper cover beams on the columns to connect with the upper panels, and finally remove the steel pipe columns from step S2 to complete the construction.

[0019] Furthermore, in step S2, the steel pipe column includes a steel column and a pier-side steel pipe column. A steel plate is pre-embedded at the base of the steel column, and the pier-side steel pipe column is connected to the pre-embedded steel plate set in the pier cap. The steel column is connected by a steel pipe beam, and the pier-side steel pipe column is connected by a connecting system.

[0020] Furthermore, in step S2, the distribution beam includes distribution beam one, distribution beam two, and distribution beam three. Distribution beam three is a steel box and is erected on a steel pipe column. Distribution beam three is connected to distribution beam one through distribution beam two. Distribution beam two is a Bailey bridge sheet, and padding is placed on distribution beam one.

[0021] Furthermore, in step S4, the steel truss is divided into left and right sections. Each steel truss section includes an upper chord and a lower chord. Adjacent upper and lower chords are connected by nodes. The upper and lower chords are connected by web members. The left and right steel trusses are connected by temporary crossbeams to form a temporary horizontal bracing.

[0022] Furthermore, in step S4, the steel truss is divided into five segments in sequence. The steel truss is divided into segments two, one, four, five, and three in that order. The segment division should make the cantilever end form a closed triangular structure. In the temporary assembly area in step S1, the left truss segment is hoisted and temporarily fixed first, and then the right truss segment is hoisted and temporarily fixed. Then, the upper temporary horizontal bracing and the lower temporary horizontal bracing are formed by connecting them through temporary crossbeams, so that the upper chord and the lower chord are connected into a whole.

[0023] Furthermore, in step S7, segment A consists of two sections respectively set on the left and right piers, segment B consists of two sections each connected to the two middle piers, and segment C consists of one section connected between the two segments B. During construction, the construction sequence is segment A, segment C, segment A again, and finally segment B. The specific construction process is as follows:

[0024] 1) Based on the length of the panel segments, use a crane to dismantle the lower-level temporary horizontal bracing.

[0025] 2) After dismantling the temporary horizontal bracing, erect a pouring platform and tie the reinforcing bars. After tying, pour the lower panel. After pouring, dismantle the temporary support formed by the reinforcing bar tying. The construction methods for sections A, B, and C are the same. After the lower panel is poured, pour and cure the web members. After curing, dismantle the pouring platform.

[0026] Furthermore, in step S9, the construction is carried out in the order of segment A, segment C, and segment B. The specific construction process is as follows:

[0027] 1) Based on the length of the segment panel, use a crane to dismantle the lower temporary horizontal bracing;

[0028] 2) After dismantling the temporary flat joint, erect a pouring platform. The fourth distribution beam in the pouring platform is set on the lower layer panel and welded to the pre-embedded steel plate on the side of the lower panel through diagonal bracing. The fourth distribution beam is connected to the fifth distribution beam through a disc buckle diagonal brace. After the connection is completed, pour the upper layer formwork. After pouring, remove the temporary support formed by the disc buckle diagonal brace. The construction methods for sections A, B, and C are the same. After the upper layer panel is poured, it is cured. After curing, the pouring platform is dismantled.

[0029] The beneficial effects of the present invention are as follows: 1. The present invention has a stable structure, high construction efficiency, less steel used in the steel truss web members, saves materials, requires less construction space, uses less material in the disc buckle bracket, and has a fast construction period.

[0030] 2. The three working conditions in the construction method are both independent and interrelated, which ensures that the stress analysis of the temporary support is clear and ensures construction safety.

[0031] 3. By using a new type of support system that combines steel truss web members and lower panel for dual purposes, the connection between temporary steel pipe columns and distribution beams has been optimized, avoiding waste of turnover materials, saving costs, and improving the company's competitiveness.

[0032] 4. By establishing a novel structural model of a composite beam with upper and lower steel truss web members for an elevated urban railway, the upper and lower prestressed concrete panels are connected by steel truss web members, saving concrete materials and resulting in superior wind resistance. This structure offers advantages such as lower train vibration, reduced steel structure maintenance space, and lower cost. Attached Figure Description

[0033] To more clearly illustrate the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the structure of the present invention;

[0035] Figure 2 This is a schematic diagram of the site preparation structure during the construction process of this invention;

[0036] Figure 3 This is a schematic diagram of the temporary support structure during the construction process of this invention;

[0037] Figure 4 This is a cross-sectional view of the temporary flat connection of the steel truss in this invention;

[0038] Figure 5 This is a schematic diagram of segment allocation during the construction process of the present invention;

[0039] Figure 6 This is a schematic diagram of the construction of the upper panel of the present invention;

[0040] Figure 7 A schematic diagram showing the upper and lower panels supported by steel pipe columns;

[0041] Figure 8 This is a schematic diagram showing the construction positions of the upper column and upper cover beam after the steel pipe column has been removed.

[0042] In the diagram: 1. Cast-in-place pile, 2. Foundation, 3. Pier, 4. Seismic retaining block, 5. Lower chord, 6. Power cable trough, 7. Steel railing post, 8. Web member, 9. Concrete outer casing, 10. Upper chord, 11. Upper panel, 12. Crash guardrail, 13. Lower panel. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] like Figure 1As shown in Embodiment 1, a composite beam with upper and lower steel trusses and web members suitable for elevated urban railways includes an upper panel 11 and a lower panel 13. The upper panel 11 and the lower panel 13 are connected by several evenly arranged web members 8. The upper part of the upper panel 11 is equipped with a crash barrier 12, and the upper panel contains an upper chord member 10 for fixing the upper part of the web members 8. The lower panel 13 contains a lower chord member 5 for fixing the web members 8. A pier 3 is located at the bottom of the lower panel 13, and a foundation 2 is located at the bottom of the pier 3. A cast-in-place pile 1 is located at the bottom of the foundation 2. The upper panel 11 is a highway layer panel, and the lower panel 13 is a railway layer panel. By establishing a novel structural model of a composite beam with upper and lower steel trusses and web members for elevated urban railways, the connection of the upper and lower prestressed concrete panels through the steel truss web members 8 saves concrete materials, improves the structure's wind resistance, and offers advantages such as low train vibration, reduced steel structure maintenance space, and low cost. The upper and lower bridge decks are connected by steel web members to form a whole, forming a double-layer composite beam structure where the double-layer prestressed concrete bridge deck and steel truss share the load. In a large-span truss beam, the upper and lower chords and upper and lower bridge decks are converted into prestressed concrete structures, resulting in a novel structure with complex stress distribution.

[0045] In this embodiment, the upper part of the upper panel 11 is provided with a crash barrier 12, and an outer concrete cladding 9 is connected to the upper panel 11, which is set on the web member 8. A support and a seismic block 4 are provided between the lower panel 13 and the pier 3, and a steel railing post 7 and a high-voltage cable trough 6 are provided on the upper part of the lower panel 13. The outer concrete cladding 9 reinforces the connection between the single pole and the highway layer panel, and the seismic block 4 connects the railway layer panel and the pier 3, which can reduce the vibration of the railway layer during train operation and make the structure more stable.

[0046] Example 2: A construction method for a composite beam with steel truss web members on two upper and lower levels of an elevated road in an urban area, comprising the following steps:

[0047] S1: Traffic Management and Site Preparation at the Crossroads: First, construct Pier 3 and the cap beam. After completion, conduct a survey and analysis of the crossroads. Set up an assembly area on one side of the steel truss. The assembly area is divided into a component and material storage area and a temporary assembly area. For specific structural details, refer to [reference needed]. Figure 2 As shown, the assembly area is located next to the intersection, which reduces the construction site area. At the same time, the setting up of a storage area for poles and materials and a temporary assembly area can improve construction efficiency.

[0048] S2: Temporary support construction condition: Erect steel pipe columns, distribution beams, and pads. First, construct the steel truss, then the lower panel 13, and finally the upper panel 11. The specific construction process is as follows; please refer to the following for details. Figure 3As shown. In the temporary support, the steel pipe column is erected on the pier 3, and the pad is set on the raised pad stone of the pier 3. The upper part of the pad supports the distribution beam, and the steel truss is set on the distribution beam. The steel truss and the steel pipe column are temporary supports that run through the entire construction process.

[0049] S3: Installation of longitudinal and transverse displacement devices: Longitudinal and transverse limiting devices are installed at the top of pier 3; Adjustment of longitudinal displacement using the longitudinal and transverse displacement devices: Longitudinal displacement is adjusted using a longitudinal horizontal device. The longitudinal horizontal jacks of the longitudinal and transverse displacement devices are used to apply jacking force to the vertical jacks for adjustment. Stainless steel plates and MGE plates are added between the vertical jacks and the horizontal jacking reaction seats to reduce friction. Adjustment of transverse displacement using the longitudinal and transverse displacement devices: Longitudinal displacement is adjusted using a longitudinal horizontal device. The transverse horizontal jacks of the longitudinal and transverse displacement devices are used to apply jacking force to the vertical jacks for adjustment. Stainless steel plates and MGE plates are added between the vertical jacks and the horizontal jacking reaction seats to reduce friction.

[0050] S4: Establish steel truss hoisting construction: Divide the steel truss into N>2 segments, and weld N-1 segments on site. The welded segments are the lower temporary horizontal bracing and the upper temporary horizontal bracing.

[0051] S5: Install the support: Install the support between the pier 3 and the distribution beam. The support is located between the longitudinal limiting device and the transverse limiting device. The upper plate of the support is connected to the distribution beam, and the lower plate of the support is connected to the height adjustment pad on the pier 3 by anchor bolts.

[0052] S6: Remove longitudinal limiting device: Remove the pad and the distribution beam three on the pad, and remove the longitudinal limiting device;

[0053] S7: Dismantle the lower temporary horizontal bracing and pour the lower panel 13: Divide the welded segments into three segments: A, B, and C. First, dismantle segments A and C of the lower temporary horizontal bracing in stages. After dismantling, erect a pouring platform and pour the concrete. Then, dismantle segment B of the lower temporary horizontal bracing, erect formwork, and pour segment B. After tensioning and preloading, dismantle the pouring platform to form the lower panel 13. The specific construction method is as follows: dismantle temporary supports, erect a bottom formwork platform, tie reinforcing bars, erect side formwork, and finally pour concrete. The dismantling sequence of the pouring platform is: bottom formwork removal, bottom formwork distribution beam removal, crossbeam removal, and support removal.

[0054] S8: Remove the lateral limiting device;

[0055] S9: Remove the upper temporary horizontal bracing and pour the upper panel 11: Divide the upper temporary horizontal bracing into three segments: A, B, and C. First, dismantle segments A and C of the upper temporary horizontal bracing in stages. After dismantling, erect a pouring platform and pour the concrete. Then, dismantle segment B of the upper temporary horizontal bracing, erect the formwork, and pour the concrete. After tensioning and preloading, remove the pouring platform to form the upper panel 11. See details for further information. Figure 6 and Figure 7 As shown, the dismantling sequence of the pouring platform is as follows: bottom formwork removal, bottom formwork distribution beam removal, crossbeam removal, load-bearing beam removal, column clamp removal, column removal, and foundation removal.

[0056] S10: Construction of upper columns, upper cover beams, and removal of temporary supports: Construct columns between the lower panel 13 and the upper panel 11. Install upper cover beams on the columns to connect with the upper panel 11. Finally, remove the steel pipe columns from step S2 to complete the construction. (See details below.) Figure 8 As shown. The construction locations for the upper columns and upper cap beams are on the side piers on both sides.

[0057] Example 3: A construction method for a composite beam with steel truss web members on two upper and lower levels of an elevated road in an urban area. In step S2, the steel pipe column includes a steel column and a steel pipe column on the pier side. A steel plate is pre-embedded at the base of the steel column, and the steel pipe column on the pier side is connected to the pre-embedded steel plate in the pier cap. The steel pipe columns are connected by steel pipe beams, and the steel pipe columns on the pier side are connected by a connecting system.

[0058] In step S2, the distribution beam includes distribution beam one, distribution beam two and distribution beam three. Distribution beam three is a steel box and is erected on a steel pipe column. Distribution beam three is connected to distribution beam one through distribution beam two. Distribution beam two is a Bailey bridge sheet and pads are placed on distribution beam one.

[0059] Example 4: A construction method for a composite steel truss beam with web members on two upper and lower levels of an elevated road in an urban area. In step S4, the steel truss is divided into left and right sections. Each steel truss section includes an upper chord and a lower chord. Adjacent upper and lower chords are connected by nodes. The upper and lower chords are connected by web members. The left and right steel trusses are connected by temporary crossbeams and temporary horizontal bracing.

[0060] In step S4, the steel truss is divided into five segments in sequence. The steel truss is divided into segments two, one, four, five, and three in that order. The segment division should make the cantilever end form a closed triangular structure. In the temporary assembly area in step S1, the left truss segment is hoisted and temporarily fixed first, and then the right truss segment is hoisted and temporarily fixed. Then, the upper temporary horizontal bracing and the lower temporary horizontal bracing are formed by connecting them through temporary crossbeams, so that the upper chord and the lower chord are connected into a whole.

[0061] Example 5: A construction method for a two-layer steel truss web composite beam suitable for urban elevated highways. In step S7, segment A consists of two sections respectively set on the left and right piers; segment B consists of two sections each connected to the two middle piers; and segment C consists of one section connecting the two segments B. During construction, the construction sequence is segment A, segment C, segment A again, and finally segment B. The specific construction process is as follows:

[0062] 1) Based on the length of the panel segments, use a crane to dismantle the lower-level temporary horizontal bracing.

[0063] 2) After dismantling the temporary horizontal bracing, erect a pouring platform and tie the reinforcing bars. After tying, pour the lower panel. After pouring, dismantle the temporary support formed by the reinforcing bar tying. The construction methods for sections A, B, and C are the same. After the lower panel is poured, pour and cure the web members. After curing, dismantle the pouring platform.

[0064] Example 6: A construction method for a two-layer steel truss web composite beam suitable for elevated roads in urban areas. In step S9, the construction is carried out in the order of segment A, segment C, and segment B. The specific construction process is as follows:

[0065] 1) Based on the length of the segment panel, use a crane to dismantle the lower temporary horizontal bracing;

[0066] 2) After dismantling the temporary flat joint, erect a pouring platform. The fourth distribution beam in the pouring platform is set on the lower layer panel and welded to the pre-embedded steel plate on the side of the lower panel through diagonal bracing. The fourth distribution beam is connected to the fifth distribution beam through a disc buckle diagonal brace. After the connection is completed, pour the upper layer formwork. After pouring, remove the temporary support formed by the disc buckle diagonal brace. The construction methods for sections A, B, and C are the same. After the upper layer panel is poured, it is cured. After curing, the pouring platform is dismantled.

[0067] Example 7 describes a construction method for a two-layer steel truss web-supported composite beam suitable for elevated roads in urban areas. By establishing a structural model of the steel truss web-supported beam using Tekla, and comparing the hoisting scheme and the upper and lower panel schemes using 3D BIM simulation technology, a combined approach is achieved by using a shared support system for the steel truss beam and the lower panel. This method effectively utilizes the ground space at intersections, realizing a novel support combination that serves two purposes, saving materials, accelerating construction progress, and ensuring safe traffic flow. The process included: maintaining traffic flow at the intersection and preparing the site; erecting shared section steel pipe columns, distribution beam one and distribution beam two; erecting steel truss web distribution beam three and padding; installing longitudinal and transverse movement devices; building a steel truss web beam structure model using Tekla to simulate the hoisting construction of the steel truss web plate; installing supports; removing longitudinal limiting devices; dismantling temporary horizontal bracing in sequence according to segment divisions; pouring railway layer panels in sequence; removing transverse limiting devices; dismantling temporary horizontal bracing in sequence according to segment divisions; pouring highway layer panels in sequence; constructing upper columns; constructing upper cover beams; and dismantling supports.

[0068] Step 1: After the construction of some railway piers and cap beams is completed, the assembly site is located on the right side of the steel truss and is divided into two parts: one part is the stacking area for poles and materials, and the other part is the temporary assembly area. The middle part is used to maintain road traffic and ensure vehicle passage.

[0069] The steel truss assembly area is hardened, with unobstructed roads and a good drainage system. Temporary supports or fixed platforms in the storage area must be sturdy to prevent uneven settlement that could lead to member twisting and collapse. Members should be categorized and stacked sequentially on fixed platforms with wooden supports, ensuring a clearance of at least 30cm between the bottom of each member and the ground. Member supports should be located where their own weight will not cause permanent deformation. Based on the weight parameters of each member, similar members should not be stacked too high in multiple layers; the support blocks between layers should be on the same vertical line. Chords, web members, and temporary tie rods should not be stacked more than three layers high, and other members should not be stacked more than five layers high.

[0070] Step Two: The temporary support construction is divided into three phases. The first phase is the construction of the steel truss, with a total weight of 915.8t; the second phase is the construction of the railway bridge deck, with a total weight of 1733.2 x 2.6t / m³ = 4506.3t; the third phase is the construction of the highway bridge deck, with a weight of 2283.2m³ x 2.6t / m³ = 5936.3t. According to the design requirements, the maximum support reaction force at each temporary pier during construction is 800t. The temporary support structure from bottom to top consists of: a C30 reinforced concrete foundation (1.5m × 13.4m × 0.5m) as an enlarged foundation + D1000 × 10mm steel pipe piles as columns + three 321-type Bailey beams per column, totaling four rows + three sets of distribution beams.

[0071] Step 3: When the bridge deck is 27-30cm above the top, the pier top arrangement includes longitudinal and transverse movement devices and jacking devices. The longitudinal and transverse movement devices include horizontal jacks and horizontal jacking reaction seats. An MGE plate plus stainless steel plate friction pair is arranged between the vertical jacks and the horizontal jacking reaction seats to reduce friction during longitudinal and transverse movement. The jacking device includes a PLC synchronous jacking control system, vertical jacks, and distribution beams. Four 500t vertical jacks (longitudinal limiters) are set in the jacking device of the middle pier, and two 200t horizontal jacks (horizontal limiters) are set in the temporary steel pipe columns and the middle pier.

[0072] Step 4: Based on the structural characteristics of this bridge and taking into full consideration factors such as manufacturing and transportation, the steel truss is divided into left and right truss sections. Each section has 14 upper chord members and 13 lower chord members. The upper and lower chord members are connected longitudinally by nodes, vertically by web members, and temporarily connected by horizontal bracing. There are 15 upper nodes, 14 lower nodes, and 28 web members. The temporary crossbeams are arranged in an isosceles triangle, totaling 915.8 tons. The steel truss members are manufactured and pre-assembled in the factory, transported by land to the steel truss assembly yard, and assembled on-site. The steel truss is divided into 5 segments by hoisting, and 4 segments are welded on-site.

[0073] Step 5: The upper plate of the support is fixed to the bottom of the main beam with anchor bolts, and the lower plate is fixed to the pad stone with anchor bolts. The movement mode of the support is that the upper plate of the support moves on the lower plate to generate displacement. The spherical support is hoisted by a truck crane to install the middle pier first and then the side pier.

[0074] Step 6: Using the PTFE sliding plate of the pad, remove the pad and distribution beam three (steel box), and release the longitudinal limiting device on the top of the pier.

[0075] Step 7: The railway level bridge deck consists of 6 sections, each 14.5m wide, 20m or 40m long, and 26cm thick. Supports are spaced 4m apart, and the crossbeams are 1.5m thick. C50 reinforced prestressed concrete is used, and the 6 web sections are filled with C30 core concrete. Temporary supports are removed in stages according to sections A, C, and A of the railway level. The bottom formwork is then erected, reinforcement is tied, and concrete is poured in sections.

[0076] Step 8: Remove the lifting and fixing device by returning oil using the lateral limit jack.

[0077] Step 9: The highway bridge deck consists of 3 sections, each 24.7m wide, 44m or 57.5m long, and 26cm thick. The support beams are 1.6m thick, constructed with C50 reinforced prestressed concrete. The web members consist of 6 sections filled with C30 core concrete. After the tensioning and prestressing of sections A and C are completed in stages, section B will be constructed next.

[0078] Step 10: After tensioning the prestressed concrete, erect the columns and cap beams on the side piers, and finally dismantle the supports to complete the system conversion.

[0079] The second step, based on the design and traffic control requirements, involves upper and lower chords of 12m in length and 8m in width for traffic control. The longitudinal arrangement of the steel pipe columns at the steel truss nodes is 24m+48m+12m+48m, with 3 columns per row and a spacing of 1.5m. One row of columns is used on the side of the pier. Since the highway and railway layers in this section are on the same line, the bridge deck width of the highway layer is 25m, and that of the railway layer is 12.4m, with a total height of 28.8m above the ground and a support height of 14m. In conjunction with the traffic control plan, the transverse arrangement is 1.5m+10.9m+1.5m.

[0080] The independent foundation has plan dimensions of 5m × 13.4m × 0.5m, and is poured with C30 concrete. It contains two layers of Φ14@200 steel mesh. Embedded parts are pre-installed on the top surface for welding connection to the steel column base plate. A 1200×1200×20mm steel plate needs to be pre-embedded at the column base for later installation. The steel pipe columns on the pier side are directly connected to the pre-embedded steel plate in the foundation.

[0081] The temporary support structure's connecting members between columns are welded from D600×8mm steel pipe beams. Columns are connected to horizontal and diagonal connecting members using bolts. Column extensions are connected using flange bolts, and the piers are connected to the steel pipe columns via a connecting system.

[0082] Distribution beam one uses a steel box girder, and distribution beam two uses Bailey bridge panels (reinforcing chords) to jointly serve as temporary supports for the steel truss and the lower panel of the railway level. On this basis, the steel truss is supported by distribution beam three steel box girder + padding, and the lower panel of the railway level is supported by I20b I-beams @50cm + 10cm square timber @15cm.

[0083] Distribution Beam Construction: After the steel pipe column construction is completed, the crossbeams are installed. The top of the steel pipe piles is connected by bolts using cross flanges. Distribution beam one uses a steel box, and the crossbeams are installed at the center of the steel pipe piles. Steel plates are welded to the base to fix the position, reducing the eccentricity of the steel pipe piles. Bailey bridge panels are installed on distribution beam one, using Bailey beams (type 321) as the main beams. The Bailey beams are arranged in a single layer with 4 rows, 3 beams per row; the main Bailey beams are assembled on the ground (the Bailey beams serve as reinforcing chords). Before installation, surveying and layout must be carried out, and the installation positions of the main Bailey beams are marked on the lower crossbeams. Two 50t truck cranes are used to hoist the connected Bailey frames into place sequentially, first the middle and then the two sides. To enhance the stability of the Bailey frames, channel steel limiters are used to fix the Bailey beams and load-bearing beams to prevent slippage.

[0084] Feasibility analysis of hoisting: The design is for a maximum of 4 sets of Bailey bridges to be assembled. Two 50t truck cranes will be used for hoisting at the same time. The working radius is calculated as 12m. The hoisting height is 40m with a 40m main boom. The lifting weight of the two truck cranes is 15t. The hoisting operation is feasible.

[0085] Temporary support for steel truss: After the second distribution beam (Bailey section) is erected, the third distribution beam (steel box) is installed using a crane. After completion, the thickness of the support pad (steel plate combination) is controlled by elevation. The temporary support pad and the third distribution beam are installed and fixed with channel steel limiters. Longitudinal and transverse temporary limit devices are set at the central pier and transverse temporary limit devices are set on the temporary support to ensure the stability of the steel truss.

[0086] Temporary support for the railway level: After the steel truss is constructed, the steel truss is dismantled in batches, the distribution beams and pads are removed, horizontal I-beams and square timbers are erected, the bottom formwork is set up, and the construction of temporary support for the railway level is completed.

[0087] In the fourth step, the steel truss web composite beam is mainly composed of factory processing, transportation, hoisting and welding.

[0088] 1) After the steel truss members are manufactured, a comprehensive quality inspection and acceptance process is conducted. All inspection and acceptance documents are submitted, confirmed and signed by the supervising engineer, and random checks are performed. After obtaining the component certificate of conformity, the first batch of members are manufactured in the factory according to the manufacturing rules. A trial assembly is then carried out to verify the accuracy and reliability of the process and tooling, and a trial assembly review meeting is organized. After the review is passed, mass production of the steel truss girders is quickly commenced.

[0089] 2) Plan transportation routes in advance using land transportation, coordinate with relevant departments, and load steel truss components according to their weight to ensure that the steel truss components are transported from the factory to the designated assembly site.

[0090] 3) The steel truss beams are divided into segments in the order of segment two, segment one, segment four, segment five, and segment three. The segment division should form a closed triangular structure at the cantilever end. In the temporary assembly area on site, the left truss segment is hoisted and temporarily fixed first, followed by the right truss segment. The upper and lower chords are then connected into a whole through temporary cross bracing and temporary horizontal bracing. The largest segment four of the 24m truss weighs 175.79t. Based on a lifting height of 14m and an operating radius of 9m, two 300t truck cranes are used for overall hoisting. The crane station is located on the right side of the route, with one crane having four lifting points, one for each upper and lower chord node, which meets the requirements.

[0091] 4) Based on the on-site welding requirements, and considering the maximum weight of each member (8.03t), one 50t truck crane will be selected for hoisting. The steel truss construction will be completed in the following sequence: on-site welding segment one, on-site welding segment four, on-site welding segment two, or on-site welding segment three. Specifically, this will be done as follows: installation and welding of the lower chord → installation and welding of the upper chord → installation and welding of the web members → installation and welding of the horizontal and transverse bracing sections. The main beam structure is a steel truss girder with upper and lower chord stiffeners on both sides, resulting in high bridge rigidity and numerous closure members. Due to the various characteristics of the structure, the displacement of the steel truss girder at the closure end can be achieved through stress-free closure using measures such as counterweight, tension, and temperature changes. Beam installation will primarily utilize full penetration butt welds.

[0092] The seventh step mainly includes dismantling the horizontal bracing, erecting the platform, tying the reinforcing bars, and pouring concrete.

[0093] 1) Based on the length of the segment panels, use a crane to dismantle the temporary horizontal connection of the railway layer, hoisting and dismantling it in sections.

[0094] 2) The transverse distribution beams are I20a I-beams, arranged along the entire length of the transverse bridge, with a longitudinal spacing of 60cm and a transverse length approximately 120cm less than the width of one side of the top slab to support the outer supports. After the supports are installed, the bottom formwork uses new steel formwork, with 8cm×8m timber laid on top, and the back ribs are 10×10cm with a spacing of 30cm. The panels are supported by standard internal supports using ordinary supports, with the vertical poles spaced 60cm longitudinally and 90cm transversely according to the standard section, and the horizontal pole spacing is 90cm.

[0095] 3) All steel reinforcement mechanical properties must comply with the provisions of national standards GB1499 and GB13013. Steel reinforcement used in the structure should have a factory quality assurance certificate or inspection certificate. Each batch of steel reinforcement delivered to the construction site must be tested. Generally, longer pieces are cut first, followed by shorter pieces, to reduce short ends and waste. Avoid using short rulers to measure longer pieces to prevent cumulative errors; dimensions and graduations should be marked on the workbench, and baffles should be set up to control the cutting dimensions. Steel reinforcement bending and forming should be carried out using a bending machine; dimensions and graduations should be marked on the workbench, and baffles should be set up to control the bending dimensions. After the beam reinforcement cage is tied to the positioning bracket, the corrugated pipe is inserted into the designed position of the positioning bracket, ensuring accurate positioning, smooth pipe section connection, and the embedded plate at the anchoring end of the duct should be perpendicular to the center line of the duct.

[0096] 4) Vertical grooves 8 are installed on the outer side of the side formwork. The straps are locked together using Φ20 water-stop bolts as tie rods. The tie rods are arranged with a horizontal spacing of 0.6m and a vertical spacing of 0.9m, with at least 2 layers.

[0097] 5) Concrete mixing is centralized at a dedicated concrete batching plant. Concrete is transported to the site by mixer trucks. The minimum continuous mixing time for high-performance concrete with water in the mixer should be at least 30 seconds longer than that for ordinary concrete, generally exceeding 90 seconds. Avoid pouring concrete when the temperature is below 5℃ or above 32℃. After pouring, promptly level and finish the concrete with a screed, and roughen the surface with a wire brush to prevent cracking. The roughening width should be 5mm and the roughening depth 3-4mm. Concrete curing adopts the natural curing method, i.e., after the initial setting of the concrete, cover it with geotextile for heat and moisture retention. At normal temperature, concrete is cured by sprinkling water and should be kept moist for at least 10-14 days. When the temperature is high, the wet curing time can be appropriately shortened; when the temperature is low, the wet curing time should be appropriately extended.

[0098] 6) The web members are made of self-compacting concrete and compacted using a small vibrator.

[0099] The ninth step of the scaffolding erection is similar to the sixth step, with the main difference being that the fourth transverse distribution beam of the platform is made of I20a I-beams, arranged along the transverse bridge direction for 27m, with a longitudinal spacing of 90cm and a spacing of 60cm at the crossbeams. Its transverse length is approximately 100cm less than the width of one side of the top slab to support the outer scaffolding. One end of the diagonal brace is welded to the distribution beam, and the other end is welded to the pre-embedded steel plate on the side of the railway deck panel. The support portion uses a disc-lock scaffolding system, with a transverse spacing of 6×0.9+3×0.6+12×0.9+3×0.6+6×0.9, a longitudinal spacing of 90cm, and a spacing of 60cm at the crossbeams. The transverse distribution beams are I12 I-beams. The deck panel uses standardized internal supports, with a longitudinal spacing of 60cm for the uprights and a transverse spacing of 90cm according to the standard section, and a crossbar step distance of 90cm. After segments A and C meet the design requirements, the longitudinal prestressing of segments A and C is tensioned. After the concrete of segment B is poured, once the strength reaches 100% and the modulus of elasticity reaches 90%, the temporary transverse bracing members of the steel truss are removed, and the prestressed steel strands are tensioned (50% transverse → longitudinal → transverse).

[0100] This invention ensures clear stress analysis of temporary supports and guarantees construction safety through independent yet interrelated analysis of three working conditions. By employing a novel co-construction support method that utilizes both steel truss web members and railway floor panels, it optimizes materials such as temporary steel pipe columns, steel boxes, and Bailey beams, avoiding waste of reusable materials, saving costs, and enhancing enterprise competitiveness. Through the establishment of a novel structural model for a two-layer steel truss web member composite beam on an urban railway viaduct, the upper and lower layers of prestressed concrete panels are connected by the steel truss web members, saving concrete materials, resulting in superior wind resistance, and offering advantages such as lower train vibration, reduced steel structure maintenance space, and lower cost.

[0101] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A construction method for composite beams with upper and lower steel truss web members applicable to elevated roads in urban areas, characterized in that: The composite beam with steel truss web members for the upper and lower layers of elevated road in urban areas includes an upper panel (11) and a lower panel (13). The upper panel (11) and the lower panel (13) are connected by several evenly arranged web members (8). The upper part of the upper panel (11) is provided with a crash guardrail (12). The upper panel is provided with an upper chord (10) for fixing the upper part of the web members (8). The lower panel (13) is provided with a lower chord (5) for fixing the web members (8). The lower part of the lower panel (13) is provided with a pier (3). The lower part of the pier (3) is provided with a foundation (2). The lower part of the foundation (2) is provided with a cast-in-place pile (1). The construction method includes the following steps: S1: Crossroads traffic control and site preparation: First, carry out the construction of the piers (3). After completion, conduct an investigation and analysis of the crossroads. Set up an assembly site on one side of the steel truss. The assembly site is divided into a pole and material storage area and a temporary assembly area. S2: Temporary support construction condition: erection of steel pipe columns, distribution beams and pads; S3: Install longitudinal and transverse movement devices: Arrange longitudinal and transverse limiting devices on the top of the pier (3); S4: Establish steel truss hoisting construction: Divide the steel truss into N (N>2) segments and weld N-1 segments on site. The welded segments are the lower temporary horizontal bracing and the upper temporary horizontal bracing. The steel truss is divided into left and right pieces. Each steel truss piece includes an upper chord (10) and a lower chord (5). Adjacent upper chords (10) and lower chords (5) are connected by nodes. The upper chord (10) and lower chord (5) are connected by web members (8). The left and right steel trusses are connected by temporary crossbeams to form a temporary horizontal bracing. S5: Install the support: Install the support between the pier (3) and the distribution beam. The support is located between the longitudinal limiting device and the transverse limiting device. The upper plate of the support is connected to the distribution beam, and the lower plate of the support is connected to the pier (3). S6: Remove longitudinal limiting device: Remove the pad and the distribution beam on the pad, and remove the longitudinal limiting device; S7: Remove the lower temporary horizontal bracing and pour the lower panel (13): Divide the welded segments into three segments: A segment, B segment and C segment. First, remove the A segment and C segment of the lower temporary horizontal bracing in stages. After removal, set up a pouring platform and pour the material. Then, remove the B segment of the lower temporary horizontal bracing, set up the formwork and pour the material. After tensioning and preloading, remove the formwork to form the lower panel (13). S8: Remove the lateral limiting device; S9: Remove the upper temporary horizontal bracing and pour the upper panel (11): Divide the upper temporary horizontal bracing into three segments: A segment, B segment, and C segment. First, remove the A segment and C segment of the upper temporary horizontal bracing in stages. After removal, set up a pouring platform and pour the concrete. Then, remove the B segment of the upper temporary horizontal bracing, set up the formwork, and pour the concrete. After tensioning and preloading, remove the formwork to form the upper panel (11). S10: Construction of upper columns, upper cover beams and removal of temporary supports: Columns are constructed between the lower panel (13) and the upper panel (11). Upper cover beams are installed on the columns to connect with the upper panel (11). Finally, the steel pipe columns in step S2 are removed to complete the construction.

2. The construction method for composite beams with upper and lower steel truss web members applicable to elevated roads in urban areas, as described in claim 1, is characterized in that: The upper panel (11) is connected to an outer concrete (9), which is set on the web member (8).

3. The construction method for composite beams with upper and lower steel truss web members applicable to elevated roads in urban areas, as described in claim 1 or 2, is characterized in that: A support and a seismic block (4) are provided between the lower panel (13) and the pier (3). A steel railing post (7) and a power cable trough (6) are provided on the upper part of the lower panel (13).

4. The construction method for composite beams with upper and lower steel truss web members applicable to elevated roads in urban areas, as described in claim 3, is characterized in that... In step S2, the steel pipe column includes a steel column and a pier-side steel pipe column. A steel plate is embedded at the base of the steel column, and the pier-side steel pipe column is connected to the embedded steel plate in the pier cap (2). The steel column is connected by a steel pipe beam, and the pier-side steel pipe column is connected by a connecting system.

5. The construction method for composite beams with upper and lower steel truss web members applicable to elevated roads in urban areas, as described in claim 4, is characterized in that... In step S2, the distribution beam includes distribution beam one, distribution beam two and distribution beam three. Distribution beam three is a steel box and is erected on a steel pipe column. Distribution beam three is connected to distribution beam one through distribution beam two. Distribution beam two is a Bailey bridge sheet and pads are placed on distribution beam one.

6. The construction method for composite beams with upper and lower steel truss web members applicable to elevated roads in urban areas, as described in claim 5, is characterized in that... In step S4, the steel truss is divided into five segments in sequence. The steel truss is divided into segments two, one, four, five, and three in sequence. The segment division should make the cantilever end form a closed triangular structure. In the temporary assembly area in step S1, the left truss segment is hoisted and temporarily fixed first, and then the right truss segment is hoisted and temporarily fixed. Then, the upper temporary horizontal connection and the lower temporary horizontal connection are formed by connecting them through temporary crossbeams, so that the upper chord (10) and the lower chord (5) are connected into a whole.

7. The construction method for composite beams with upper and lower steel truss web members applicable to elevated roads in urban areas, as described in claim 6, is characterized in that... In step S7, segment A consists of two sections respectively set on the left and right piers (3), segment B consists of two sections respectively connected to the two middle piers (3), and segment C consists of one section connected between the two segments B. During construction, the construction sequence is segment A, segment C, segment A, and finally segment B. The specific construction process is as follows: 1) Based on the length of the panel segments, use a crane to dismantle the lower-level temporary horizontal bracing. 2) After removing the lower temporary flat joint, erect a pouring platform and tie the steel bars. After tying, pour the lower panel (13). After pouring, remove the temporary support formed by the steel bar tying. The construction methods of A section, B section and C section are the same. After the lower panel (13) is poured, pour and cure the web members (8). After curing, remove the pouring platform.

8. The construction method for composite beams with upper and lower steel truss web members applicable to elevated roads in urban areas, as described in claim 7, is characterized in that... In step S9, the construction is carried out in the order of segment A, segment C, and segment B. The specific construction process is as follows: 1) Based on the length of the segmental panels, use a crane to dismantle the upper temporary horizontal bracing; 2) After removing the upper temporary flat joint, a pouring platform is erected. The distribution beam four in the pouring platform is set on the lower panel (13) and welded to the pre-embedded steel plate on the side of the lower panel (13) through diagonal bracing. The distribution beam four is connected to the distribution beam five through the disc buckle diagonal brace. After the connection is completed, the upper template is poured. After the pouring is completed, the temporary support formed by the disc buckle diagonal brace is removed. The construction methods of A section, B section and C section are the same. After the upper panel (11) is poured, it is cured. After the curing is completed, the pouring platform is removed.

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