CN219137409U

CN219137409U - Assembled cantilever bent cap support and modularized main truss girder thereof

Info

Publication number: CN219137409U
Application number: CN202221353413.4U
Authority: CN
Inventors: 王明达; 俞骥; 项志伟; 徐声亮
Original assignee: Ningbo City Ring Expressway Connection Line Construction Co ltd; Ningbo Municipal Engineering Construction Group Co Ltd
Current assignee: Ningbo City Ring Expressway Connection Line Construction Co ltd; Ningbo Municipal Engineering Construction Group Co Ltd
Priority date: 2022-05-31
Filing date: 2022-05-31
Publication date: 2023-06-06
Anticipated expiration: 2032-05-31

Abstract

The utility model discloses an assembled cantilever bent cap bracket and a modularized main truss girder thereof. The modularized main truss girder comprises a main truss girder body, wherein the main truss girder body comprises two main truss girder bodies which are arranged in parallel, and the two main truss girder bodies are connected into a whole through a supporting structure; each main truss girder body comprises a main truss upper chord, a main truss lower chord, a gusset plate, a main truss straight web member and a W-shaped bracket, wherein the main truss straight web member and the W-shaped bracket are arranged between the main truss upper chord and the main truss lower chord; the gusset plates comprise three gusset plates a which are welded and fixed on the upper chord of the main truss at intervals and two gusset plates b which are welded and fixed on the lower chord of the main truss at intervals. Therefore, the utility model provides necessary components for the field assembly of the assembled cantilever bent cap bracket, has reliable connection measures, low field assembly requirements, better universality and enough bearing capacity and rigidity.

Description

Assembled cantilever bent cap support and modularized main truss girder thereof

Technical Field

The utility model relates to an assembled cantilever bent cap bracket and a construction method thereof, belongs to the field of civil engineering construction, belongs to an industrialized large-scale temporary measure structure, can be used as a temporary support for construction of a large-volume concrete structure requiring high-altitude operation, and is particularly suitable for construction of an urban expressway bent cap.

Background

Expressway overhead has become an important means for solving traffic jam in cities, and main cities in China are built or are building urban overhead on a large scale.

At present, the urban expressway mainly comprises a double-column cantilever type bent cap, 8 prefabricated small box girders are configured to form a bidirectional 6-lane expressway driving route, the bridge deck width is about 25.5m, and the bent cap width is about 25-26.5 m, as shown; meanwhile, the upper structure of the width-changing section spliced with the ramp is widened to 10-12 prefabricated small box girders, the lower structure of the width-changing section is correspondingly adjusted to be a four-column continuous bent cap, the bridge deck width is equal to the bent cap length of 36-45 m, and the bent cap length is shown. In addition, the ramp of the urban expressway overhead is usually 7.5m wide, meets the requirement of unidirectional 2 lanes, and has a capping beam width of about 8.5m.

The different professional design institutes in China are slightly different about the structural form of the overhead bent cap of the urban expressway, wherein the two key parameters of the section structure (form and width) of the bent cap and the concrete square quantity (dead weight) have great influence on a bracket system. At present, the urban expressway mainly comprises a double-column cantilever type bent cap, wherein the maximum total length of the bent cap is 33.5m, and the minimum total length of the bent cap is 15.6m; maximum cantilever length 15m, minimum cantilever length 4.5m; the maximum column outer pitch is 12m and the minimum column outer pitch is 2.8m. The total length of the common bent cap is about 21.98-27.6 m, the cantilever length is 7-10 m, and the spacing between the outer sides of the columns is 6-10 m. The design standard difference is smaller, so that the prefabricated assembly feasibility of the bent cap bracket is higher, and the universality can be realized.

At present, the commonly used bracket system mainly comprises: a full framing system, a beret truss system, and a cantilever system. Wherein:

the full framing system can not adapt to urban overhead, and is mainly characterized in 2 aspects:

1) Occupation operation, extruding a temporary channel protection way and a construction operation channel space;

urban expressway construction is generally delayed from urban expansion and development, so that the range of project construction land is limited, and construction sites are very narrow. For a newly-built project, a conventional full framing system needs to occupy a construction site of a projection range of a bent cap, so that serious influence is caused on vehicle traffic in the site, and a channel is filled outside the projection range, so that repeated excavation and waste of ground materials are caused, the cost is increased, and the environment-friendly requirement is not met. For the rapid transformation project of the existing road, the more the space occupied by the capping beam bracket system is, the more the traffic guiding and modifying workload is, and particularly the occupation of the main road, the urban traffic is seriously influenced.

2) The new and old processes are alternated, and the cost is greatly increased

In the past, the conventional full framing system in China adopts bowl-buckle type framing, and the technology level and the cost control aspect reach the balance of all parties. In recent years, in order to match with the upgrading and transformation of the building industry, governments gradually push a disk buckle type bracket system to replace a bowl buckle type bracket. The dish knot type support is mainly used for upgrading and reforming a bowl knot type support system on the two sides of a vertical rod piece connecting node structure and a transverse rod piece node structure. Compared with the prior bowl-buckle type bracket system which is commonly adopted, the cost of the bowl-buckle type bracket system is greatly increased, which is about 1.8-2.0 times of that of the bowl-buckle type bracket.

The beret truss system is difficult to shoulder for temporary support of "cantilever, large span" structures because:

1) The bending bearing capacity and the shearing bearing capacity are not matched

Early bailey truss is used as military river-crossing equipment, and the requirement of the straddling under a certain load state is emphasized. Considering that the movable load (people, vehicles, tanks and the like) is mainly borne during the military river crossing period, and in order to avoid the vibration problem of the temporary structure, the beret truss adopts a diamond web system, so that the beret truss has high bending bearing capacity but poor shearing bearing capacity, as shown in table 2. As a temporary supporting structure, the shear capacity becomes a controlling factor, and is generally limited to a structure with a small unit density (concrete thickness is not more than 1 m).

2) The pin connection between the bailey trusses is not matched with the axial bearing capacity of the chord member

According to the highway steel structure bridge design specification (JTG D64-2015), the damage form of the pin connection mainly comprises 3 types of tensile damage, shearing damage, local bearing damage and the like.

In general, the bearing capacity of the cotter takes the minimum value of 420kN, which is only 60% of the axial bearing capacity of the chord member, which means that the connection bearing capacity between the bailey trusses is far lower than the bearing capacity of the bailey trusses, so that the deflection of the bailey truss system is greatly different from the classical structural mechanics, and the application of the bailey truss system in a large-span structure, a cantilever structure and a structure with larger load concentration is limited.

3) Beret truss gives way to structural performance with "universal performance" requirements

On the one hand, there is an upper load bearing limit for beret-based support structures. Taking the 321 type bailey truss which is absolutely dominant at present as an example, the beam height is 1.5m, the peak shear bearing capacity and the bending bearing capacity are determined, and the connection strength is lower than the member strength; on the other hand, the internal force distribution of the support system usually has peak-valley regions, and the structural specifications of the regions are the same, so that the stress state difference is very large. The components of each section have the same specification, so that about 40% of the section components have a stress state lower than an average state, and the utilization efficiency of materials is limited.

The existing cantilever bracket system mainly has 4 types, and corresponds to:

class 1 (cantilever bracket system assembled by a bailey truss with higher turnover capability and a large steel pipe system) still needs to occupy additional supporting space (the outermost supporting pile), and the temporary foundation cost in a soft soil area is higher (the steel pipe pile foundation needs to be put into a large amount of steel pipes, the mechanical cost for inserting and pulling out is high, the construction period is long, the RC concrete foundation needs additional foundation treatment, and the cost is not very good);

class 2 (a bent cap support system assembled by adopting a bailey truss, a steel truss positioned below the bailey truss and a large steel pipe system positioned below the steel truss), class 3 (a bent cap support system formed by welding rigid frames by adopting large-span steel), solves the problems of soft foundations and construction operation space, but has poor structural force transfer system (a rod piece bears the action of bending moment and axial force at the same time, and the stress distribution of the same rod piece is uneven), has higher steel index (the rod piece has overlarge cross section size to meet the stress state of the most unfavorable cross section because of the uneven stress distribution of the rod piece, so that the weight of a single support is not less than 45 tons), and has poor economic benefit;

class 4 cantilever capping beam type capping beam support system, as shown in fig. 1, achieves maximization of economic benefit on a single capping beam support system (on one hand, all the rods only bear axial force action, the stress of the rods is uniform, on the other hand, the truss is only provided with 1 field bolt splice joint, and other nodes are all connected by adopting welding seams, so that the weight of connecting materials is reduced), but 2 key problems still exist:

1) The integration of the components increases the difficulty of reuse, especially in multiple projects: (1) the single truss is oversized, the difficulty of short lightering transportation in a construction site is small, but the size requirement of highway transportation cannot be met; (2) the single truss is in a space state, has good bearing capacity and rigidity when bearing the vertical action, but the action of uncertain external load (such as collision, impact and the like) in other directions (non-vertical load directions) in the transportation process causes the single truss to be damaged and deformed, and influences the subsequent application functions thereof;

2) The double cantilever type bent cap is only suitable for double cantilever type bent caps, and is not suitable for a width-changing section of an urban expressway overhead, namely a four-column type continuous bent cap. The structural characteristics of truss systems determine that they are only suitable for cantilever systems in the span direction and cannot be lengthened into a continuous system.

In summary, the development of the industrial prefabricated cantilever bent cap bracket system which can be suitable for construction of most expressway overhead bent caps in China, has larger clearance, can reduce the influence of construction surrounding environment, has low cost and stronger economical efficiency, is a necessary trend of industry development, and is also a requirement of social progress on the building industry.

Disclosure of Invention

Aiming at the defects of the prior art, the utility model provides an assembled cantilever bent cap bracket.

In order to achieve the technical purpose, the utility model adopts the following technical scheme:

the modularized main truss girder comprises a main truss girder body, wherein the main truss girder body comprises two main truss girder bodies which are arranged in parallel, and the two main truss girder bodies are connected into a whole through a supporting structure; each main truss girder body comprises a main truss upper chord, a main truss lower chord, a gusset plate, a main truss straight web member and a W-shaped bracket, wherein the main truss straight web member and the W-shaped bracket are arranged between the main truss upper chord and the main truss lower chord;

the node plates comprise three node plates a which are welded and fixed on the upper chord of the main truss at intervals and two node plates b which are welded and fixed on the lower chord of the main truss at intervals;

the three node plates a are arranged at the middle position of the upper chord of the main truss, and the remaining two node plates a are symmetrically arranged and are closely arranged at the end part of the upper chord of the main truss;

the upper three endpoints of the W-shaped bracket are correspondingly arranged on the outer side plate surfaces of the three node plates a one by one, and the lower two endpoints are correspondingly arranged on the outer side plate surfaces of the two node plates b one by one;

the number of the main truss straight web members is 4, and the main truss straight web members are correspondingly from the first main truss straight web member to the fourth main truss straight web member; each main truss straight web member is vertically arranged between the main truss upper chord member and the main truss lower chord member; the lower ends of the first main truss straight web member and the third main truss straight web member are respectively fixed with the inner side plate surfaces of the two node plates b, and the upper ends of the first main truss straight web member and the third main truss straight web member are correspondingly connected and fixed with the upper chord member of the main truss; the second main truss straight web member and the fourth main truss straight web member are correspondingly arranged on the outer sides of the first main truss straight web member and the third main truss straight web member respectively, the upper ends of the second main truss straight web member and the fourth main truss straight web member are respectively connected with the inner side plate surface of a gusset plate a arranged close to the end part of the main truss upper chord member, and the lower ends of the gusset plate a are correspondingly connected and fixed with the main truss lower chord member.

Preferably, the three node plates a are respectively a first node plate a, a second node plate a and a third node plate a, the first node plate a is arranged at the middle position of the upper chord of the main truss, and the second node plate a and the third node plate a are symmetrically arranged at two sides of the first node plate a and are closely arranged at the end parts of the upper chord of the main truss;

the two node plates b are correspondingly a first node plate b and a second node plate b;

the lower end of the first main truss straight web member is fixed with the inner side plate surface of the second node plate b, and the upper end of the first main truss straight web member is fixedly connected with the corresponding position of the main truss upper chord member; the upper end of the second main truss straight web member is fixed with the inner side plate surface of the third node plate a, and the lower end of the second main truss straight web member is fixed with the inner side plate surface of the main truss lower chord member; the upper end of the third main truss straight web member is connected with the main truss upper chord member, and the lower end of the third main truss straight web member is fixed with the inner side plate surface of the first gusset plate b; the upper end of the fourth main truss straight web member is fixed with the inner side plate surface of the second gusset plate a, and the lower end of the fourth main truss straight web member is fixed with the inner side plate surface of the main truss lower chord member.

Preferably, the W-shaped bracket is formed by 4 main truss diagonal web members; the 4 main truss diagonal web members are correspondingly first to fourth main truss diagonal web members;

the upper ends of the second main truss diagonal web member and the third main truss diagonal web member are respectively fixed with the outer side plate surface of the first gusset plate a, the lower end of the second main truss diagonal web member is fixed with the outer side plate surface of the first gusset plate b, and the lower end of the third main truss diagonal web member is fixed with the outer side plate surface of the second gusset plate b; the upper end of the first main truss diagonal web member is fixed with the outer side plate surface of the second gusset plate a, and the lower end of the first main truss diagonal web member is fixed with the outer side plate surface of the first gusset plate b; the upper end of the fourth main truss diagonal web member is fixed with the outer side plate surface of the third gusset plate a, and the lower end of the fourth main truss diagonal web member is fixed with the outer side plate surface of the second gusset plate b.

Preferably, a first connecting plate B is arranged on one side of the main truss girder body, and a second connecting plate B is arranged on the other side of the main truss girder body;

the first connecting plate B is a straight plate, one end of the first connecting plate B is fixedly connected with the upper chord of the main truss through a bolt, and the other end of the first connecting plate B is provided with a connecting bolt a;

the second connecting plate B is a bending plate, one end of the second connecting plate B is fixedly connected with the lower chord member of the main truss girder through a bolt assembly, and the other end of the second connecting plate B is provided with a connecting bolt B.

Preferably, the bolts arranged on each side of the first and second connection plates B are arranged in a triangle.

An assembled cantilever bent cap bracket comprises an upper structure, a support cushion sand box and a lower structure; the upper structure comprises two truss type beam bodies which are arranged in parallel, and the truss type beam bodies are connected through a supporting frame; the lower structure comprises a middle supporting point and is characterized in that the truss type girder body comprises the main truss girder, and the main truss girder is supported above the middle supporting point.

Based on the technical objects, compared with the prior art, the utility model has the following advantages:

the truss type girder body of the upper structure of the single bracket system is formed by freely combining and assembling different module segments, so that various structural specifications are formed, and the construction requirements of capping girders with different length and size can be met. The modular segments are mainly divided into a main truss girder, a variable-height truss girder and two-specification auxiliary truss girders (the two-specification auxiliary truss girders are different in pin joints at the end parts only).

The supporting points are only arranged on the main truss beams, so that the beam bodies formed by splicing the two main trusses are used as foundation beam bodies in various working conditions, and then the variable-height truss beams, the auxiliary truss beams and the like are spliced on the foundation beam bodies formed by splicing the two main trusses according to the length structure of the cover beam so as to meet construction requirements.

Therefore, the utility model has the following advantages:

1) Better universality: the single component needs to adopt a planar structure similar to the beret truss instead of a three-dimensional structure, and meanwhile, the assembly type component has good specification modulus and can adapt to the requirements of various bent cap sizes;

2) Excellent bearing capacity and rigidity: the bracket system has enough bearing capacity and rigidity to meet the requirements of various specifications of weight capping beams, and has additional rod piece reinforcing measures to adapt to the requirements of individual large-volume concrete capping beams;

3) Reliable boundary connection measures: the connection between the main body components is matched with the main body components and is convenient to install;

4) Excellent economic benefit: the bracket system has lighter dead weight, lower manufacturing cost and good economy.

In addition, the stent system also needs to have the following functions:

1) The lower field assembly requirement is as follows: when the manual work required for one-time installation and dismantling is not more than 6 persons, the working time of a 70-ton automobile crane is not more than 2 working hours, the single installation time is not more than 8 hours, and the single dismantling and transferring time is not more than 8 hours;

2) The durability is better: the turnover capacity of more than 100 times of cyclic use is ensured.

Drawings

FIG. 1 is a schematic structural view of a prior art cantilever bent cap bracket system;

FIG. 2 is a schematic view of the structure of a first assembled cantilever bent cap holder (temporary support for a double cantilever bent cap of standard cross section) according to the present utility model;

FIG. 3 is a schematic structural view of a second assembled cantilever bent cap holder (temporary support for double cantilever bent caps of ramp sections) according to the present utility model;

FIG. 4 is a schematic structural view of a third assembled cantilever bent cap bracket (for temporary support of a three-pivot bent cap system) according to the present utility model;

FIG. 5 is a schematic structural view of a fourth fabricated cantilever bent cap bracket (for temporary support of a four-pivot bent cap system) according to the present utility model;

FIG. 6 is a schematic view of the structure of the secondary truss in the assembled cantilever bent cap bracket of the present utility model;

FIG. 7 is a schematic view of the structure of a heightened truss girder in an assembled cantilever bent cap bracket according to the present utility model;

FIG. 8 is a schematic view of the structure of a main truss girder in the assembled cantilever bent cap bracket according to the present utility model;

in fig. 2-8: 1-auxiliary truss girder; 2-heightening truss girders; 3-main truss girder;

101-a first secondary truss girder; 102-a second secondary truss girder; 103-a third sub truss girder;

201-a first heightened truss girder; 202-a second heightened truss girder; 203-a third variable height truss girder; 204-fourth variable high truss girder;

301-a first main truss girder; 302-a second main truss girder; 303-a third main truss girder; 304-fourth main truss girder.

1-1, an upper chord of the auxiliary truss; 1-2, lower chords of the auxiliary trusses; 1-3, auxiliary truss straight web members; 1-4, a first auxiliary truss diagonal web member; 1-5, a second auxiliary truss diagonal web member; 1-6, ear plates; 1-7, a pin joint;

2-1, a first height-changing truss upper chord; 2-2, a second height-changing truss upper chord; 2-3, a first connecting plate B;2-4, a first heightening truss straight web member; 2-5, a second connecting plate B;2-6, a first heightening truss diagonal web member; 2-7, a second height-changing truss straight web member; 2-8, a second heightening truss diagonal web member; 2-9, a third height-changing truss diagonal web member; 2-10, a third variable-height truss connecting joint; 2-11, third height-changing truss straight web members;

3-1, a main truss upper chord; 3-2, a first main truss straight web member; 3-3, connecting the plate A;3-4, a first main truss diagonal web member; 3-5, a main truss lower chord; 3-6, a second main truss diagonal web member; 3-7, a second main truss connecting joint; 3-8, a second main truss straight web member.

Detailed Description

The following description of the embodiments of the present utility model will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present utility model, but not all embodiments. The following description of at least one exemplary embodiment is merely exemplary in nature and is in no way intended to limit the utility model, its application, or uses. All other embodiments, which can be made by those skilled in the art based on the embodiments of the utility model without making any inventive effort, are intended to be within the scope of the utility model. The relative arrangement, expressions and numerical values of the components and steps set forth in these embodiments do not limit the scope of the present utility model unless it is specifically stated otherwise. Techniques, methods, and apparatus known to one of ordinary skill in the relevant art may not be discussed in detail, but should be considered part of the specification where appropriate. In all examples shown and discussed herein, any specific values should be construed as merely illustrative, and not a limitation. Thus, other examples of the exemplary embodiments may have different values.

The support of the present utility model, as shown in fig. 2-8, is mainly divided into an upper structure, a bolster flask and a lower structure.

The upper structure of a single bracket consists of two truss type beam bodies, and the two truss type beam bodies are connected and fixed by adopting a supporting frame so as to ensure the overall stability of the frame body.

In order to meet the requirement of bracket assembly construction, the single truss type girder body is assembled by freely combining modular segments, and the modular segments are mainly divided into a main truss girder (shown in fig. 8), a heightened truss girder (shown in fig. 7) and an auxiliary truss girder (shown in fig. 6). Wherein the length specification of the single main truss girder is set to 5.0m, the length specification of the single variable-height truss girder is set to 3.75m, and the length specification of the single auxiliary truss girder is set to 5.0m.

Note that: the maximum beam section is 5.0m, and the beam section is of a sheet structure, so that the transportation is convenient.

Main truss girder and main truss girder can assemble respectively, main truss girder and vice truss girder can assemble respectively through becoming high truss between the main truss girder and the vice truss girder. The multi-truss girder can be assembled and combined to meet the construction requirements of capping girders in different length sizes and various pier column forms.

The members constituting the truss girder include upper and lower chords, a straight web member and an inclined web member. The single rod piece is formed by symmetrically arranging two channel steels, the chord members are in a "] [" (limb-back opposite) form, and the straight web members are in a "[" (limb-back opposite) form. The diagonal web member is in the form of "[" (limb-back facing) in the main truss girder and the heightened truss girder, and in the form of "[" (limb-back facing) in the auxiliary truss girder.

Note that: the web members in the form of "[ ]" (opposite limbs and back) are welded at the flange ends to form a closed cylindrical structure which has greater stability in both the plane and the outside.

The upper chord and the lower chord of the single main truss girder are 25# channel steel, and the center distance between the upper chord and the lower chord is 3.0m. The web members are additionally arranged to form a strong rectangular frame structure, so that the load effect of the standard section of the bent cap can be resisted. Bolt holes with diameters of 33.0mm are formed at two ends of the chord member, and M30 bolts with diameters of 8.8 levels are matched for assembling and splicing the truss girders.

The single-piece main truss girder web member consists of 4 straight web members and 4 inclined web members, the straight web members adopt 10# channel steel, 1 straight web member is respectively arranged at two ends of the truss, and 2 straight web members in the middle are respectively arranged at the positions of 1/4 and 3/4 of the chord length. The 4 diagonal web members adopt 20# channel steel and are arranged on two sides of the middle 2 straight web members in a W shape. The intersection position of the diagonal web member and the chord member is welded and fixed by adopting a 2cm thick iron plate, the intersection position of the web member and the lower chord member is used as a node to be connected with a lower structure supporting point, the iron plate is welded and stiffened by adopting a 2cm thick rib plate, and a 4cm thick iron plate is additionally arranged below the node to be welded with the node plate and the stiffening plate for bearing stress. The rod piece arrangement and the node treatment are carried out in the mode, so that the bending action of the upper chord member can be effectively reduced, and the load can be effectively transmitted to the lower supporting structure.

The upper chord member and the lower chord member of the single auxiliary truss girder adopt 14# channel steel, the center distance between the upper chord member and the lower chord member is 1.5m, and a rectangular frame structure is formed after the web members are erected, so that the load effect of the cantilever end variable section of the capping girder can be resisted. The two ends of the chord member are provided with pin joints, the pin joints at the splicing ends of the excessive truss beams are in a 'male head' form, and the other end of the chord member is provided with a female head or a male head (the chord member is divided into two auxiliary truss beams, and only one pin joint at one end of each auxiliary truss beam is different from the female head or the male head, and the two truss beams can be bolted with the heightening truss beam).

The single-piece auxiliary truss girder web member consists of 3 straight web members and 4 inclined web members, wherein the straight web members and the inclined web members are respectively 10# channel steel, 1 straight web member is respectively arranged at two ends of the truss, and the other 1 straight web member is arranged at the position of 1/2 of the chord length. The 4 diagonal web members are arranged on two sides of the middle straight web member in an M shape, and are in a stress form of 5 nodes of the upper chord member and 3 nodes of the lower chord member. The intersection position of the web member and the chord member is fixed by welding, and the length of the web member extending into the chord member is consistent with the height of the chord member.

The center distances of the two ends of the upper chord member and the lower chord member of the single-piece variable-height truss girder are respectively 1.5m and 3.0m. The single channel steel of the upper chord member is welded and connected by a 14# channel steel and a 25# channel steel through a 2 cm-thick transfer steel plate, the node steel plate is arranged on the back of the channel steel, one third section close to the 1.5m end adopts the 14# channel steel, and two thirds section of the upper chord member close to the 3.0m end adopts the 25# channel steel. And a node steel plate with the thickness of 2cm is arranged on the outer side of the lower end of the adapter plate, and the adapter plate is welded and fixed with the node steel plate. The node plate is uniformly provided with 6 plug welding holes with the diameter of 2cm, the welding height of the plug welding holes is slightly higher than the thickness of the node plate, and the plug welding holes are polished to be flush with the outer surface of the node plate.

The lower chord member of the variable-height truss girder adopts a 20# channel steel, is in a trapezoid frame structure after being provided with web members, and can connect and assemble the main truss girder in the geometric form while resisting the load of the variable-section of the capping girder.

The single-piece height-variable truss girder web member consists of 3 straight web members and 3 inclined web members, the straight web members adopt 10# channel steel, 1 straight web member is respectively arranged at two ends of the truss, and the other 1 straight web member is arranged at the position of 1/3 of the chord member length and is close to the position of the long straight web member. The 1 diagonal web member that 3 diagonal web members are close to 1.5m end adopts 14# channel steel, and the 2 diagonal web members that are close to 3.0m end adopts 20# channel steel. The 3 diagonal web members are arranged in the frame in an N shape to form 4 nodes of the upper chord member and a stress form of 3 nodes of the lower chord member. And the intersecting position of the diagonal web member and the chord member is welded and fixed by adopting an iron plate with the thickness of 2 cm.

The joist steel is arranged along the bridge direction and coincides with the intersection point position of the web member and the upper chord member of the truss girder, and the joist steel and the iron plate are fixed by adopting a steel U-shaped clamp, so that the bottom die system also has assembly performance, and the stability of the joist steel is effectively ensured.

The two truss girders forming the bracket structure are connected and fixed by adopting a support frame form, the support frame is mainly made of 10# channel steel and 2cm iron plates, and the components are mainly divided into a cross rod, a vertical rod, an inclined rod, a small cross rod and a connecting plate.

The cross bars of the support frame are symmetrically arranged in a 'form' by 2 channel steels, and 1 bolt hole with the diameter of 22.0mm is arranged at the end part. A connecting plate with the thickness of 2.0cm is arranged near the end bolt and is welded with 2 cross bar channel steel. And a node plate with the thickness of 2.0cm is arranged in the middle of the cross rod and welded with 2 cross rod channel steel. The vertical rods of the support frame are symmetrically arranged in a 'form' by 2 channel steel, and are firmly welded with the connecting plate. And a node plate with the thickness of 2.0cm is arranged in the middle of the vertical rod and welded with 2 vertical rod channel steel. The diagonal rods are symmetrically arranged in a 'form' by 4 channel steel and are firmly welded with the gusset plates on the cross bars and the vertical bars respectively. The small cross bars are symmetrically arranged in a 'form' by 2 channel steel, and the connecting plates in the middle of the vertical bars are firmly welded.

And a connecting iron plate with a bolt hole is welded at the flange end of the truss girder straight web member at the connection position of the support frame, the connecting iron plate is vertical to the web plate of the straight web member, and a triangular stiffening iron plate is welded.

The support frame only provides lateral stabilization of the support superstructure and does not act as a primary load transfer structure.

The components of the support frame are matched with the corresponding main truss girder in height. The length of the support frame is set to 2.66m, so that the construction requirements of most upright post sizes and capping beam width sizes can be met.

The single support system has 4 support cushion sand boxes, and the support cushion sand boxes are arranged at the supporting point positions (below the main truss girder supporting iron plates) between the upper structure and the lower structure. The sand box is connected with the truss girder supporting point through bolts, and is connected with the lower structure through a flange, and the support cushion sand box can play roles in adjusting the elevation of the support and unloading the support.

The lower structure of the single support system consists of 4 steel pipe piles and 2-section steel beams, and longitudinal and transverse support frames are arranged between the steel pipe piles for connection and fixation, so that the overall stability of the lower structure is ensured.

The steel pipe piles are also of an assembled structure, the steel pipe piles are connected through flanges, the arrangement length of the steel pipe piles is 6.0m,5.0m,4.0m,3.0m and 0.5m, and the steel pipe piles are 5 specifications, so that corresponding combination can be carried out to meet the construction requirements of engineering sites.

2I-steel beams 60a are arranged at the bottom of the steel pipe pile, and a 2cm rear iron plate is attached to the I-steel beams at the supporting point of the steel pipe pile and can be connected with the first section of steel pipe pile at the bottom through bolts. The additional iron plate and the lower flange plate of the I-steel are provided with stiffening steel plates.

The steel pipe pile supporting frames and the truss girder supporting frames are identical in structural form, the height specification of the transverse supporting frames is set to be 3.78m and 2.78m, the height specification of the longitudinal supporting frames is set to be 1.78m and 2.78m, and the supporting frames with different specifications are used in combination, so that the connection requirements of steel pipe pile upright posts with different heights can be met.

In summary, the modular construction process ensures that the stent system has good versatility and meets the desired target requirements.

1.1 Combined assembled functions

1) Double cantilever bent cap of standard section

For a double cantilever capping beam of standard cross section, as shown in fig. 2, the bracket superstructure Liang Tixuan is spliced with "secondary truss girder + heightened truss girder + primary truss girder + heightened truss girder + secondary truss girder" sections.

2) Double cantilever bent cap of ramp section

For a double cantilever capping beam of the ramp section, as shown in fig. 3, the bracket superstructure Liang Tixuan is spliced with "tall truss beam + main truss beam + tall truss beam" sections.

Note that: when the length of the ramp bent cap is not more than 8.5m, the sections of the main truss girder and the main truss girder can be spliced to serve as an upper structure of the bracket.

3) Three-pivot bent cap system

For the three-pivot capping beam system, as shown in fig. 4, the bracket upper structure Liang Tixuan is spliced by the sections of the secondary truss beam, the variable-height truss beam, the main truss beam, the variable-height truss beam, the secondary truss beam, the variable-height truss beam and the main truss beam.

Note that: the actual number of two "secondary truss girder" sections of the continuous section is selected according to the specific span.

4) Four-pivot bent cap system

For the four-pivot bent cap system, as shown in fig. 5, the bracket upper structure Liang Tixuan is spliced by the sections of "main truss girder+heightened truss girder+sub truss girder+heightened truss girder+main truss girder+heightened truss girder+sub truss girder".

1.2 diversified node assembling system

The connection design between the units follows 2 principles: (1) the bearing capacity of the splicing joint is matched with the axial bearing capacity of the chord member; (2) the installation and the disassembly of the splicing joint are easy, convenient and quick.

(1) Pin joint

The 321-type bailey pieces which are widely used at present are combined, and the plane trusses are connected by adopting the pin joints, so that the installation and the dismantling of the planar trusses are remarkable. Meanwhile, the bearing capacity of the pin joint is obviously 'ceiling' due to the construction requirement, namely the sizes of lug plates of the pin joint are limited by the specification of connecting section steel, and the maximum matching pin joint lug plate construction of the 10# channel steel and the 20# channel steel is shown in fig. 6.

The bearing capacity was evaluated based on the maximum gauge pin joint ear plate, as shown in table 4.

Table 1 ear plate bearing capacity evaluation table with different specifications pin structure

Note that: when the specifications of chords at two ends of the splice joint are different, the smaller chords are used as references.

As can be seen from table 4, the pin connection still matches the channel No. 14, but is not applicable to the channel No. 20. It is used as a connection between the 1.5m truss (sub-truss girder) and the girder (girder).

(2) Node assembling system of connecting plate and bolt

When the chord member specification exceeds the 14# channel steel, the bearing capacity of the pin joint is obviously reduced, and the chord member bearing capacity of the 20# channel steel is higher than that of the pin joint by nearly 40%, so that the connection between the 3.0m truss and the variable-height truss is not selected by pin connection, and a 'connecting plate and bolt' structure is adopted.

The number of the bolts at the connecting joints is set according to the strength of the connected rod pieces, namely the total strength of the bolts and the strength of the connecting plate are larger than the strength of the connected rod pieces. Therefore, in order to meet the requirement of quick assembly disassembly, after the number of bolts meets the strength requirement, the strength and the diameter of the bolts are required to be improved to reduce the total number of the bolts, so that the bracket assembly and disassembly progress is quickened.

1) Winding up

The upper chord, the height-variable truss and the 3.0m truss (main truss girder) are respectively double-spliced 25# channel steel, and the axial bearing capacity of the chord member is as follows:

N＝f _y ·A＝190MPa×3490mm ² ＝663.1kN

the splicing area adopts 8.8-level common bolts, and the shear strength design value f of a single bolt is calculated according to the design Specification of highway Steel Structure bridge (JTG D64-2015) _vd ^b For 280MPa, 4M 30 bolts are selected, two rows of bolts are arranged, each row of bolts is provided with 1 shearing surface, and therefore the shearing bearing capacity of the bolts is as follows:

selecting a t=25mm connecting plate, wherein the bearing capacity of the node plate is as follows:

the tensile bearing capacity of the connecting plate is as follows:

N＝f _y ·(A ₀ -n·d·t _w )＝190MPa×3500mm ² ＝665kN

therefore, the upper chord adopts 4M 30 8.8-level bolts to meet the bearing capacity requirement of the node.

Similarly, 4M 30 class 8.8 bolts are used between the 3.0M truss (main truss beam) and the 3.0M truss (main truss beam) upper chord 25# channel steel.

2) Lower chord

The lower chord of the heightened truss girder adopts double-spliced 20# channel steel, the 3.0m truss (main truss girder) adopts double-spliced 25# channel steel, and the node bearing capacity is controlled according to smaller components. The axial bearing capacity of the double-spliced 20# channel steel is as follows:

N＝f _y ·A＝190MPa×2880mm ² ＝574.2kN

when the height-variable truss forms a certain included angle with the lower chord member of the 3.0m truss and is connected by adopting a connecting plate and a bolt, the core problem is that the connecting plate also forms an included angle, and the node design follows the following 2-point principle:

a) The center lines of chords of the heightening truss and the 3.0m truss are positioned at the same height at the joint, so as to provide a foundation for arranging the corner connecting plate, and the influence of additional bending moment of the node on the node plate is avoided;

note that: if top edge alignment or bottom edge alignment is adopted, the axis of the height-variable chord member and the axis of the main chord member intersect at the center of the connecting node, and a large additional bending moment is generated. The additional bending moment can lead the connecting plate of the node to bear larger concentrated stress, so that the node plate is unstable and is damaged by buckling.

B) The included angle of the connecting plate and the angle of the chord member connected with the connecting plate are arranged straight and smoothly, and the axial force of the lower chord member of the heightened truss is transmitted to the main truss.

The splicing area adopts 8.8-grade common bolts according to the design rule of highway steel structure bridgesRange (JTG D64-2015), design value f of shear strength of single bolt _vd ^b For 280MPa, 3M 30 pieces are selected, and 1 shearing surface is arranged on a single chord member, so that the shearing bearing capacity of the bolt is as follows:

selecting a t=30mm connecting plate, wherein the bearing capacity of the node plate is as follows:

the tensile bearing capacity of the connecting plate is as follows:

N＝f _y ·(A ₀ -n·d·t _w )＝190MPa×3600mm ² ＝684kN

therefore, the 8.8-level bolts of 3M 30 are adopted between the lower chord variable-height truss and the main truss to meet the node bearing capacity requirement.

The arrangement of bolt holes on the connecting plate with respect to the spacing requirement meets the requirements of the design Specification of highway Steel Structure bridge (JTG D64-2015): the minimum allowable distance between the centers of the bolts is 3d ₀ (d ₀ Is the bolt hole diameter); the minimum distance from the center of the bolt to the edge is 1.5d ₀ (d ₀ Is the bolt hole diameter). The two bolt holes on the connecting plate are arranged along the height direction of the connecting plate, so that the height of the connecting plate is at least (1.5+3+1.5) d ₀ =198 mm. And the height of the connecting plate meets the construction requirement, namely the height of the connecting plate is not more than the length of the inner flat section of the channel steel web, the length of the inner flat section of the No. 20 channel steel web is 156mm, and the height of the connecting plate is 150mm on the premise of ensuring the machining error.

Note that: the length of the inner flat section of the channel steel web=the height of the web-2× (flange thickness+arc section), and the height of the connecting plate exceeds the length of the inner flat section of the channel steel web, so that the connecting plate cannot be in effective contact with the channel steel web, and the connecting plate is seriously deformed in the bolt operation process to cause the failure of the bolt connection, as shown in the following figure.

Therefore, the maximum height of the connecting plate is 150mm, the bolt holes are required to be arranged singly in the height direction of the connecting plate, and the overall bolt holes are arranged in a delta mode.

In conclusion, the lower chord variable height truss and the main truss are arranged in a delta mode, so that the requirement of a section structure is met.

The connection between the 3.0M truss (main truss girder) and the 3.0M truss (main truss girder) lower chord 25# channel steel is the same as the upper chord 25# channel steel, and the requirement of bearing capacity can be met by adopting 4M 30 8.8-level bolts.

1.3 node splice area setup

The node area should pay attention to the "splice area arrangement" in addition to the bearing capacity of the connection members.

The chord members between the straight web members at the two sides of the node bear larger bending moment, the peak value is positioned at the intersection point of the chord members and the straight web members, the absolute value of the bending moment is obviously improved along with the increase of the spacing between the straight web members, and the maximum stress value of the whole chord member is correspondingly improved, so that the section becomes the most unfavorable section. To meet the stress conditions of the least favorable cross section, the cross section size of the rod piece needs to be increased, and the weight of a single bracket is greatly increased. Thus, the pitch of the web members on both sides of the node is reduced.

(1) Joint of connecting plate and bolt

The joint of the connecting plate and the bolt is arranged at the joint of the main truss girder and the joint of the main truss girder and the heightened truss girder. The edge of the straight web member at the joint of the connecting plate and the bolt is 2cm away from the end part of the chord member, and the straight web member is used as a welding fixing area of the straight web member and the chord member, so that the cantilever length of the chord member outside the intersection point of the web members is reduced. In order to avoid the welding area of the connection of the straight web member and the chord member, the bolt holes are arranged outside the axis of the straight web member.

(2) Pin joint

The pin bolt joints are arranged at the joints of the auxiliary truss girder and the joints of the auxiliary truss girder and the heightened truss girder. The edge of the straight web member at the joint of the pin bolt is 5cm away from the end part of the chord member, and the straight web member is used as a welding fixing area of the pin bolt male head and the chord member.

The two female head parts of the pin bolt are respectively welded and fixed with the inner sides (overhanging sides of the channel steel flanges) of the two channel steel webs of the chord member. The pin bolt female head and the chord member channel steel are fixed without collision with other rod pieces, and the pin bolt female head and the chord member channel steel can be provided with enough welding length to meet the strength requirement.

The male head part of the pin bolt is welded and fixed with the outer sides of two channel steel webs of the chord member respectively (the male head is fixed between the two channel steel webs of the chord member), and the thickness of the male head is always equal to the distance between the two channel steel webs of the chord member. The length of the overhanging end of the chord member channel steel, which can be welded and fixed with the male head of the pin bolt, is 5cm. And the contact area of the male head of the pin bolt and the chord member channel steel is provided with three plug welding holes with the diameter of 1cm uniformly on the channel steel web corresponding to the contact area. The welding height of the plug welding hole is slightly higher than the thickness of the channel steel web plate, and the plug welding hole is polished to be flush with the channel steel web plate. The plug welding holes can enhance the connection strength of the pin bolt male heads and chord member channel steel, and meet the strength requirement of joint splicing.

1.4 rod reinforcement in node area

The reinforced design of the node area mainly includes 2 aspects: 1) The straight web member is embedded between the two channel steels of the chord member; 2) And the diagonal web members of the variable-height truss girder and the main truss girder are welded and fixed with the chord members through the gusset plates.

Straight web member embedded arrangement

The straight web member is embedded between the two channel steels of the chord member and is welded and fixed. The two channel steels of the chord member are welded and fixed with the straight web member, so that the chord member is connected with the two channel steels into a whole, and the use of the batten plate for connecting the two channel steels of the chord member is greatly reduced. And the embedded welding of the straight web members and the chord members is used for strengthening the truss system.

For the variable-height truss girder and the main truss girder, after the straight web members are embedded in the chord members, the inclined web members and the straight web members can be arranged in a staggered manner, and the details are shown in the following figures. The inclined web members are arranged on the outer sides of the straight web members, the whole node structure is compact, and the load transmission path is obvious. The staggered arrangement of the inclined web members and the straight web members can obviously reduce the distance between the end parts of the inclined web members and the intersection point, and the rigidity of the gusset plate is enhanced.

Setting up the gusset plate

And the diagonal web members of the heightened truss girder and the main truss girder are welded and fixed with the chord members through node plates with the thickness of 2 cm. The gusset plate is welded on the chord member channel steel flange, and the outer edge of the gusset plate is flush with the outer side of the channel steel web plate. The welding length of the diagonal web member can be controlled by adjusting the size of the node plate, and the stability of the connecting node is improved. The diagonal web member is connected with the chord member through the gusset plate, so that fatigue resistance of a connecting node can be enhanced, and the using times of the truss are increased.

2 implementation method

a. When the bearing platform is constructed, the fixed iron plate is pre-buried according to the position of the cross beam of the bracket size;

b. after the construction of the bearing platform is finished, the 60a I-shaped steel beam is hung and installed after the concrete reaches the design strength;

c. according to the actual support height requirement, installing steel pipe piles and support frames on the ground section by section, hoisting the whole section, and installing flange bolts section by section;

d. measuring the pile top elevation of a section of steel pipe pile at the top, calculating the height of a support cushion sand box, and installing the sand box;

c. the truss girder is integrally installed on the ground, the main truss girder, the variable-height truss girder, the auxiliary truss girder and the supporting frame are all installed and then hoisted to the position of a supporting point of the support cushion sand box, and the truss installation checking and acceptance work is carried out before hoisting;

d. after the truss is installed, whether the truss position and elevation meet the design and construction requirements is confirmed again;

e. and installing a cover beam I-shaped steel bottom die cross beam on the truss girder, and fixing the I-shaped steel flange plate and the truss girder upper chord reinforcing iron plate by using a U-shaped clamp.

f. Installing a bent cap bottom die on the I-shaped steel beam, binding bent cap steel bars, pouring bent cap concrete, and closely monitoring a bracket in the construction process of the bent cap, wherein the deformation of the bracket is not more than 5mm.

g. After the capping beam is maintained to the design strength, the elevation of the support is reduced by utilizing a support cushion sand box, so that the truss beam is separated from the bottom of the capping beam, and the bottom die system is dismantled;

h. the truss is hung on the bent cap by utilizing the manual hoist, after splicing bolts between the truss beams are removed, the truss beams and the support frame are lifted out of one side of the bent cap together, and the support frame is removed after the truss beams are lifted to the ground. The truss girder hanging and removing sequence is that the auxiliary truss girder is firstly changed into the higher truss girder, and then the main truss girder is changed.

i. After the truss girder is dismantled, firstly dismantling the support cushion sand box from top to bottom, then removing flange connection among the steel pipe piles, and integrally hoisting the steel pipe pile system in sections.

j. And finally, the connection between the 60a I-steel and the embedded iron plate of the bearing platform is cut off, and the dismantling of all the components of the bracket is completed.

Claims

1. The modularized main truss girder comprises a main truss girder body and is characterized in that the main truss girder body comprises two main truss girder bodies which are arranged in parallel, and the two main truss girder bodies are connected into a whole through a supporting structure; each main truss girder body comprises a main truss upper chord, a main truss lower chord, a gusset plate, a main truss straight web member and a W-shaped bracket, wherein the main truss straight web member and the W-shaped bracket are arranged between the main truss upper chord and the main truss lower chord;

2. The modular main truss girder according to claim 1, wherein the three gusset plates a are first, second and third gusset plates a, respectively, the first gusset plate a is disposed at a middle position of the main truss upper chord, and the second and third gusset plates a are symmetrically disposed at both sides of the first gusset plate a and are disposed closely to the ends of the main truss upper chord;

3. The modular main truss girder of claim 2, wherein the W-shaped brackets are formed by 4 main truss diagonal web members; the 4 main truss diagonal web members are correspondingly first to fourth main truss diagonal web members;

4. A modular main girder according to claim 3, wherein a first connection plate B is arranged at one side of the main girder body and a second connection plate B is arranged at the other side;

5. A modular main truss girder according to claim 4, wherein the bolts arranged on each side of the first and second connection plates B are arranged in a triangle.

6. An assembled cantilever bent cap bracket comprises an upper structure, a support cushion sand box and a lower structure; the upper structure comprises two truss type beam bodies which are arranged in parallel, and the truss type beam bodies are connected through a supporting frame; the substructure includes a center point, wherein the truss girder body includes the main truss girder according to any one of claims 1 to 5, which is supported above the center point.