Method for cast-in-place platform of concrete box girder

Abstract

The invention discloses a method of a concrete box girder cast-in-place platform, and belongs to the field of building formworks and supports. The method for erecting the cast-in-place platform for manufacturing the concrete box girder comprises the steps that the assembled truss units are erected and temporarily supported; the truss units are connected through the cross beams to form a truss set, and the temporary supports are dismantled; and welding the main truss upper chord link beam to the tops of the plurality of truss groups. The cast-in-place platform formed through the method has a good supporting effect and can support the large-mass concrete box girder.

Description

Technical Field

[0001] The present application belongs to the field of building formwork and supports, and in particular, relates to a method for casting a concrete box beam platform. Background Art

[0002] At present, large concrete box girder bridges are being used more and more.

[0003] Large concrete box girders are widely used in highways, high-speed railways, national and provincial road network construction, and urban overpasses. Concrete box girders are typically simply supported on concrete bridge columns. Columns are typically cast on-site using formwork, while concrete box girders are typically manufactured using either precast or cast-in-place methods.

[0004] After the precast concrete boxes are manufactured in the precast plant, they are transported to the construction site by a beam transporter and then hoisted by a bridge crane. There are several questions here:

[0005] First, a large prefabrication site covering a vast area is required;

[0006] Secondly, large equipment such as beam transport vehicles, beam lifting machines and bridge erection machines are needed.

[0007] The above conditions are generally only available to large construction companies, and the cost is very high. Especially when the on-site construction environment is limited, the bridge erection machine is not suitable and cast-in-place production is the only option. This raises other problems:

[0008] Concrete box girders are typically placed at higher column tops, making cast-in-place platforms difficult to fabricate at such heights. Furthermore, the weight of a concrete box girder is typically around 1,000 tons, making cast-in-place platforms unable to withstand such a high beam weight. Summary of the Invention

[0009] The example of this application provides a method for a cast-in-place platform of a concrete box beam to solve the problems of the existing cast-in-place platform with low load-bearing capacity and inconvenience in use.

[0010] The solution of this application example is implemented through the following content.

[0011] A method for setting up a cast-in-place platform for making a concrete box beam comprises:

[0012] Erect the assembled truss units and provide temporary support;

[0013] Connect the truss units with beams to form truss groups and remove temporary supports;

[0014] And, welding the main truss upper chord connecting beam to the top of the plurality of truss groups.

[0015] A method for manufacturing a concrete box girder, comprising:

[0016] A cast-in-place platform is built on the top of the bridge column through the main truss of the CB450 steel bridge. The cast-in-place platform is formed by the cast-in-place platform method used to make concrete box girders.

[0017] Erection of scaffolding and formwork support; and

[0018] Concrete box beams are cast with formwork support.

[0019] The present invention has the following advantages:

[0020] First, it significantly reduces the amount of steel used in cast-in-place concrete box girder platforms, offering promising economic benefits and widespread application prospects. Previously, cast-in-place box girder platforms typically used domestically produced 321-type Bailey plates, which had a low load-bearing capacity, required a large number of Bailey plates, and required numerous supports, resulting in high labor intensity. By fully leveraging the high load-bearing capacity of CB450 steel bridges, this has significantly reduced steel usage and generated significant economic benefits for the company.

[0021] Second, the overall structure is simple and beautiful. The cast-in-place platforms previously constructed with 321-type Bailey plates were densely packed, practically impenetrable. Now, using CB450 steel bridge main trusses, the structure is simple and beautiful, with rows and rows clearly visible. This significantly reduces labor intensity and promotes safe and civilized production for construction companies.

[0022] Third, the foundation pedestals of the surrounding completed bridge columns were fully utilized as the load-bearing points for the main trusses of the CB450 steel bridge. This was a very smart and cost-effective move. Previously, the platform built with 321-type Bailey plates required additional hard ground as a support point, which was not cost-effective and was prone to additional settlement, affecting the casting quality of the upper box girder.

[0023] Fourth, a PTFE plate is installed at the bottom of the CB450 main truss support, which makes it easier for the machine to pull the entire platform through special steel rails to enter the next work station, realizing assembly line operation and eliminating the time-consuming, labor-intensive, repetitive and ineffective work of disassembly and reassembly. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] For a clearer explanation, the following briefly introduces the drawings required for the description.

[0025] Figure 1 This is an elevation view of the large concrete box girder scheme for CB450 in the present invention;

[0026] Figure 2 A plan view of the large concrete box girder for CB450 in the present invention;

[0027] Figure 3 This is a cross-sectional view of the scheme for erecting a large concrete box girder for CB450 in the present invention.

[0028] Figure 4Schematic diagram of the structure of the 9m upper chord in the present invention;

[0029] Figure 5 Schematic diagram of the structure of the 9m lower chord in the present invention;

[0030] Figure 6 This is a schematic structural diagram of the 6.75m upper chord in the present invention;

[0031] Figure 7 This is a schematic structural diagram of the 6.75m lower chord in the present invention;

[0032] Figure 8 Schematic diagram of the structure of the end upper chord in the present invention;

[0033] Figure 9 It is a structural schematic diagram of the end column end lower chord in the present invention;

[0034] Figure 10 Schematic diagram of the structure of the end lower chord in the present invention;

[0035] Figure 11 Schematic diagram of the structure of the triangular web in the present invention;

[0036] Figure 12 Schematic diagram of the structure of the high shear web member in the present invention;

[0037] Figure 13 This is a schematic structural diagram of the end high shear web member of the present invention;

[0038] Figure 14 It is a structural schematic diagram of the double-row end columns in the present invention;

[0039] Figure 15 Schematic diagram of the structure of the connecting beam in the present invention;

[0040] Figure 16 The upper chord connecting plate of the present invention;

[0041] Figure 17 The lower chord outer connecting plate of the present invention;

[0042] Figure 18 The lower chord inner connecting plate of the present invention;

[0043] Figure 19 It is the lower chord connecting mesh plate in the present invention;

[0044] Figure 20 The upper chord span end bracket of the present invention;

[0045] Figure 21 The traction seat of the present invention;

[0046] Figure 22For the installation of the traction seat in the present invention;

[0047] Figure 23 For the installation of the PTFE plate in the present invention;

[0048] Figure 24 The upper chord of the CB450 main truss and the connecting beam of the upper platform in the present invention;

[0049] Figure 25 A schematic structural diagram of step one in the process of setting up a cast-in-place platform in the present invention;

[0050] Figure 26 A schematic diagram of the structure of step 2 in the process of setting up a cast-in-place platform in the present invention;

[0051] Figure 27 A schematic diagram of the structure of step three in the process of setting up a cast-in-place platform in the present invention;

[0052] Figure 28 A schematic structural diagram of step four in the process of setting up a cast-in-place platform in the present invention;

[0053] Figure 29 A schematic structural diagram of step five in the process of setting up a cast-in-place platform in the present invention. DETAILED DESCRIPTION

[0054] Casting concrete box girders at the top of the columns is quite difficult. Previously, domestically produced 321-type Bailey plates were generally used to construct cast-in-place box girder platforms.

[0055] However, the 321-type Bailey plates have a low load-bearing capacity. Furthermore, the large number of 321-type Bailey plates required to construct the cast-in-place platform for concrete box girders is labor-intensive. Furthermore, platforms constructed with 321-type Bailey plates typically require additional hard ground support points, which is uneconomical and prone to excessive settlement, affecting the quality of the upper box girder casting. Furthermore, after pouring a section of the box girder, the existing 321-type Bailey plates must be disassembled and reassembled at the next workstation, making their operation inconvenient and time-consuming.

[0056] To address the above shortcomings, the present invention uses CB450 steel bridge main trusses to construct a large cast-in-place concrete box girder platform. This invention fully utilizes the high load-bearing capacity of CB450 steel bridges, greatly saving steel consumption and achieving significant economic and social benefits for the enterprise.

[0057] Furthermore, the use of CB450 steel bridge main trusses offers a simple and aesthetically pleasing structure. This scheme, with the main trusses arranged in rows, provides a clear and intuitive view, significantly reducing labor intensity and significantly improving safe and civilized production.

[0058] Furthermore, the present invention makes full use of the foundation pedestals of the surrounding completed bridge columns as the load-bearing points of the CB450 steel bridge main trusses, without the need for additional hard ground. At the same time, the foundation has almost no settlement, which ensures the casting quality of the upper box girder to the greatest extent.

[0059] Furthermore, the present invention eliminates the need for disassembly before proceeding to the next workstation. This is achieved by installing a PTFE plate at the bottom of the CB450 main truss. This facilitates mechanically pulling the entire platform along specialized rails to the next workstation, enabling streamlined operations and eliminating the time-consuming, labor-intensive, and repetitive labor of disassembly and reassembly.

[0060] Before discussing the specific solutions of the present invention, some terms are explained:

[0061] CB450 Steel Bridge:

[0062] This is a prefabricated highway steel bridge developed in 2008. CB450 steel bridges are primarily used as semi-permanent (with a service life of up to 25 years) prefabricated highway steel bridges. The main components of a CB450 steel bridge include upper and lower chords, triangular webs, high shear webs, end columns, upper and lower chord connection plates, crossbeams, and bridge decks. CB450 steel is primarily used. Based on carbon content, these steels can be categorized as follows: 1. High-carbon medium-carbon steel. This is primarily used in the manufacture of high-pressure, wear-resistant parent materials such as general machinery casings. 2. Low-carbon medium-carbon steel. This is primarily used in stainless steel casting. 3. Low-carbon steel. Low-carbon steel has a carbon content of 0.02% to 0.3%. Low-carbon steel is a carbon steel with a short tempering time. It is soft, stamping-resistant, and ductile. It is primarily used in the manufacture of rebar, stamping-resistant mechanical parts, and special steels.

[0063] CB450 steel bridge main truss:

[0064] Except for the bridge deck components such as the bridge deck and crossbeams, the system composed of the remaining components of the CB450 steel bridge is called the main truss of the CB450 steel bridge, presenting a linear, row-like structural form.

[0065] During actual construction, first of all, technicians need to determine the on-site environmental conditions.

[0066] Environmental conditions such as: box girder bottom elevation, box girder length, width and height dimensions, box girder deadweight, box girder outer contour shape, foundation pedestal surface elevation, foundation pedestal plane geometry and dimensions.

[0067] Under the above environmental conditions, the span of the CB450 main truss and the height dimension from the top of the main truss to the bottom plane of the box girder can be determined. At the same time, the specific values ​​of the linear load generated by the deadweight of the box girder in the span direction, the deadweight load of the scaffolding and formwork, and the live loads such as construction machinery and personnel can also be determined.

[0068] Afterward, structural calculations were performed to determine the structural layout of the CB450 main trusses. For example, the specific number of rows required, the spacing between rows, the layout of the tie beams at the top of the CB450 main trusses, which primarily bear the deadweight of the upper box girder and construction loads, and their cross-sectional dimensions were determined. Before determining the specific dimensions of the main trusses, the bridge span should be determined. Truss bridge design should be based on minimizing the combined construction costs of the upper and lower structures to determine the most economical span. Key dimensions of the main truss of a steel truss bridge include truss height, span length, diagonal bar inclination, and the center-to-center distance between the two main trusses.

[0069] It should be pointed out that the solution of the present invention is mainly implemented with CB450 steel bridge main truss components. The upper formwork and scaffolding used in the actual casting process can use solutions in the existing technology, and the present invention does not impose specific restrictions on this.

[0070] The CB450 steel bridge main truss is the main truss of the CB450 type prefabricated highway steel bridge. The relevant background knowledge of the CB450 type prefabricated highway steel bridge can be obtained from the Chinese patent publication number CN111809500A.

[0071] The method of setting up a cast-in-place platform for making concrete box girders in the present invention includes: erecting assembled truss units (made of CB450 steel, provided with skids; and a polytetrafluoroethylene plate is also provided at the bottom) and providing temporary support; connecting the truss units through crossbeams to form truss groups (each truss group has two truss units), and removing the temporary support; and welding the main truss upper chord connecting beam to the top of multiple truss groups.

[0072] The temporary support truss units are for example channel steels.

[0073] The distance between two adjacent beams is 4.5m.

[0074] More specifically, the steps for setting up a cast-in-place platform are as follows:

[0075] The CB450 main truss is assembled with a cast-in-place box girder platform using a crane-assisted, on-site assembly method. The specific steps are as follows:

[0076] Step 1: Assemble the first main truss unit on the horizontal ground ( Figure 25 );

[0077] Step 2: Erect the first main truss unit and use 20# channel steel as temporary support ( Figure 26 );

[0078] Step 3: Assemble the first section of the second row of main trusses according to the methods of steps 1 and 2, and then firmly connect the first and second rows with connecting beams and M24 high-strength bolts, with one beam installed every 4.5m. After the connecting beams are firmly installed, remove the temporary support ( Figure 27 ).

[0079] Step 4: Use the above method to assemble the third and fourth rows in sequence, and connect them firmly with connecting beams; then assemble the fifth and sixth rows, and connect them firmly with connecting beams ( Figure 28 ).

[0080] Step 5: On-site welding of the main truss upper chord connecting beam ( Figure 29 ).

[0081] Step 6: Assemble the second, third, fourth, and other units in the upper rows in sequence. Each time a unit is installed, it is connected with a connecting beam, and the upper chord connecting beam is welded on site.

[0082] A certain amount of skids were required for the installation of the first, second, third, and subsequent sections. Thus, the cast-in-place box girder platform constructed with the CB450 main truss was completed.

[0083] On this basis, the present invention also proposes a method for manufacturing a concrete box beam, comprising:

[0084] A cast-in-place platform is set up at the top of the bridge column through the main truss of the CB450 steel bridge. The cast-in-place platform is formed by setting up a cast-in-place platform for making concrete box beams; wherein the cast-in-place platform is supported by the bridge through the foundation pedestal on the top of the bridge column.

[0085] Scaffolding and formwork support are then erected; and the concrete box beams are then poured through the formwork support.

[0086] To cast multiple concrete box girders, after the concrete box girders are cast on top with formwork support, the cast-in-place platform is moved to the next station and formwork support is set up for pouring. This process is repeated to complete the casting of multiple concrete box girders.

[0087] Figure 1 、 Figure 2 and Figure 3 This is a schematic diagram of the overall structure of the cast-in-place platform.

[0088] The specific structure of the cast-in-place platform formed based on the main truss is explained below.

[0089] The entire platform has a large number of parts, excluding the upper scaffolding system, and the platform's own weight is generally around 300 tons.

[0090] According to the functions of each component, the platform components can be divided into 6 parts:

[0091] Upper chord, lower chord, triangular web members, double rows of end columns, connection system and auxiliary structures.

[0092] The upper chord and the lower chord bear the bending moment generated by the upper load, and the upper chord is under compression and the lower chord is under tension.

[0093] The webs bear the shear force generated by the upper load. Based on the distribution characteristics of the shear force generated by the upper load, three structural types are produced: triangular webs, high shear webs, and end high shear webs.

[0094] Double rows of end columns and high shear web members at the ends bear the support reaction forces.

[0095] The connecting beam ensures the stability of the lower part of the main truss.

[0096] The upper chord connecting beam ensures the stability of the upper chord plane of the main truss and bears the upper load of the platform.

[0097] The upper chords are tightened against each other by the end sealing plates at both ends, and the end sealing plates are connected by 22-M24 high-strength bolts. Figure 16 ) is connected to the two upper chord wing plates. Each upper chord connecting plate ( Figure 16 ) are distributed with 32-φ26 bolt holes.

[0098] The lower chords are connected by two t22mm lower chord outer connecting plates ( Figure 17 ), four t22mm lower chord inner connecting plates ( Figure 18 ) and two t14mm lower chord connecting mesh panels ( Figure 19 ) connection, and the connecting bolts are all 10.9 grade M24 high-strength bolts. The upper chord span end brackets are added on both sides of the upper chord rods at both ends of the main truss.

[0099] The triangular web members are connected by three high-strength pins (30CrMnSi) with a diameter of φ65mm and 2-M24 high-strength bolts. The upper and lower ends of the triangular web members are connected to the upper and lower chords respectively by four high-strength pins (30CrMnSi) with a diameter of φ36mm and 4-M24 high-strength bolts. Figure 13 ) and double row end posts ( Figure 14 ) is connected to the upper and lower chords respectively through eight high-strength pins (material 30CrMnSi) with a diameter of φ36mm and 8-M24 high-strength bolts.

[0100] Next, we will explain each component separately.

[0101] 1. Upper chord

[0102] The upper chord includes a 9m upper chord ( Figure 4 )、6.75m upper chord ( Figure 6 ), end chord ( Figure 8 ) three types.

[0103] The combination of the 9m upper chord and the 6.75m upper chord can create different span sizes, making the overall platform more applicable. The two have similar structures.

[0104] The upper chord at the end needs to be connected with the high shear web at the end ( Figure 13 ) or double row end posts ( Figure 14 ) connection, so the structure is different. The left and right upper chords can be used interchangeably.

[0105] 2. Lower chord

[0106] The lower chord includes a 9m lower chord ( Figure 5 )、6.75m lower chord ( Figure 7 ), end lower chord ( Figure 10 ), end column end lower chord ( Figure 9 ) Four types.

[0107] The lower chord at the end ( Figure 10 ) is used for the left end, the lower chord at the end column ( Figure 9 ) is used on the right side and cannot be interchanged.

[0108] 3. Triangular belly bar

[0109] Triangular web members include triangular web members ( Figure 11 )、High shear bar ( Figure 12 ), end high shear web ( Figure 13 ) three types.

[0110] The triangular belly bar ( Figure 11 ) and high shear web ( Figure 12 ) The appearance is exactly the same. High shear bar ( Figure 12 ) The diagonal rods in the bracket are thicker and made of DB685, while the triangular web members are made of Q355. Pay attention to the identification marks in actual use.

[0111] The cross section of the diagonal rod in the end high shear web member is the same as that in the high shear web member, except that there are two vertical rods in the end high shear web member, while the high shear web member ( Figure 12 ) has only one vertical pole.

[0112] 4. Double row end columns

[0113] See also Figure 14 , on the right end.

[0114] 5. Connection system

[0115] The connection system includes connecting beams ( Figure 15 ), and upper chord connecting beam and load-bearing beam ( Figure 24 ).

[0116] 6. Auxiliary structure

[0117] Auxiliary structure includes traction seat ( Figure 21), PTFE plate ( Figure 22 )、Upper chord span end bracket ( Figure 20 ). The additional PTFE plate ( Figure 22 ) is installed at the support.

[0118] Some of the above components are connected as follows.

[0119] The upper chords of each row of main trusses are connected by double-jointed H600×200×11×17 steel plates welded on site to the upper chords.

[0120] This beam is the main load-bearing beam that bears the load of the upper platform, and also plays a role in maintaining the stability of the upper chord plane of the CB450 main truss.

[0121] The center-to-center spacing of the beam in the span direction is approximately 4.2m.

[0122] Then lay the platform longitudinal beam H400×200×8×13 on the beam, with the center-to-center spacing of the platform longitudinal beams being 0.6m.

[0123] The detailed structure of the upper chord of the CB450 main truss and the connecting beam of the upper platform is shown in Figure 24 .

[0124] Add polytetrafluoroethylene plate at the support Figure 23 ), so that after the construction of the concrete box girder section is completed, the entire platform can be mechanically pulled along the special steel rails to the next workstation if the site permits. This avoids the time-consuming and labor-intensive repetitive work of disassembling and reassembling the entire platform.

[0125] The above describes in detail the structure, features and effects of the present application based on the embodiments shown in the drawings. The above are only preferred embodiments of the present application, but the scope of implementation of the present application is not limited to what is shown in the drawings. Any changes made in accordance with the concept of the present application, or modifications to equivalent embodiments with equivalent changes, which do not exceed the spirit covered by the description and drawings, should be within the scope of protection of the present application.

Claims

1. A method for setting up a cast-in-place platform for making concrete box beams, characterized in that: The method comprises: Erect the assembled truss units and provide temporary support; Connect the truss units with beams to form truss groups and remove temporary supports; And, welding the main truss upper chord connecting beam to the top of the plurality of truss groups.

2. The method for constructing a cast-in-place platform for manufacturing a concrete box beam according to claim 1, characterized in that: Channel steel is used to temporarily support the truss units.

3. The method for constructing a cast-in-place platform for manufacturing a concrete box beam according to claim 1 or 2, characterized in that: The distance between two adjacent beams is 4.5m.

4. The method for constructing a cast-in-place platform for manufacturing a concrete box beam according to claim 1, characterized in that: The truss unit is made of CB450 steel.

5. The method for constructing a cast-in-place platform for manufacturing a concrete box beam according to claim 1, characterized in that: The truss unit is provided with skids.

6. The method for constructing a cast-in-place platform for manufacturing a concrete box beam according to claim 1, characterized in that: A polytetrafluoroethylene plate is also provided at the bottom of the truss unit.

7. The method for constructing a cast-in-place platform for manufacturing a concrete box beam according to claim 1, characterized in that: Each truss group has two truss units.

8. A method for manufacturing a concrete box beam, characterized in that: include: A cast-in-place platform is erected at the top of the bridge column through the main truss of the CB450 steel bridge, wherein the cast-in-place platform is formed by the method for erecting a cast-in-place platform for manufacturing a concrete box girder according to any one of claims 1 to 7; Erection of scaffolding and formwork support; and Concrete box beams are cast with formwork support.

9. The method for manufacturing a concrete box beam according to claim 8, characterized in that: The cast-in-place platform is supported by the bridge through the foundation cap on top of the bridge columns.

10. The method for manufacturing a concrete box beam according to claim 8, characterized in that: The manufacturing method further comprises: After pouring the concrete box girder with formwork support, pull the cast-in-place platform to the next work station and set up formwork support for pouring.

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