CN113512932A - Prestressed steel beam connected prefabricated small box girder type hidden cover beam and construction method thereof - Google Patents

Prestressed steel beam connected prefabricated small box girder type hidden cover beam and construction method thereof Download PDF

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CN113512932A
CN113512932A CN202110297475.1A CN202110297475A CN113512932A CN 113512932 A CN113512932 A CN 113512932A CN 202110297475 A CN202110297475 A CN 202110297475A CN 113512932 A CN113512932 A CN 113512932A
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box girder
small box
steel
plate
prefabricated
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CN113512932B (en
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徐声亮
陈巨峰
奚康
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Ningbo Municipal Engineering Construction Group Co Ltd
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Ningbo Municipal Engineering Construction Group Co Ltd
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    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01D—CONSTRUCTION OF BRIDGES, ELEVATED ROADWAYS OR VIADUCTS; ASSEMBLY OF BRIDGES
    • E01D19/00—Structural or constructional details of bridges
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01D—CONSTRUCTION OF BRIDGES, ELEVATED ROADWAYS OR VIADUCTS; ASSEMBLY OF BRIDGES
    • E01D2/00—Bridges characterised by the cross-section of their bearing spanning structure
    • E01D2/04—Bridges characterised by the cross-section of their bearing spanning structure of the box-girder type
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01D—CONSTRUCTION OF BRIDGES, ELEVATED ROADWAYS OR VIADUCTS; ASSEMBLY OF BRIDGES
    • E01D21/00—Methods or apparatus specially adapted for erecting or assembling bridges
    • E—FIXED CONSTRUCTIONS
    • E01—CONSTRUCTION OF ROADS, RAILWAYS, OR BRIDGES
    • E01D—CONSTRUCTION OF BRIDGES, ELEVATED ROADWAYS OR VIADUCTS; ASSEMBLY OF BRIDGES
    • E01D2101/00—Material constitution of bridges
    • E01D2101/20—Concrete, stone or stone-like material
    • E01D2101/24—Concrete
    • E01D2101/26—Concrete reinforced
    • E01D2101/28—Concrete reinforced prestressed

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  • Engineering & Computer Science (AREA)
  • Architecture (AREA)
  • Civil Engineering (AREA)
  • Structural Engineering (AREA)
  • Bridges Or Land Bridges (AREA)

Abstract

The invention discloses a precast small box girder type hidden cover beam connected by prestressed steel beams and a construction method thereof. The prefabricated small box girder type hidden cover beam comprises a prefabricated small box girder, a cast-in-place hidden cover beam and a prestress system, wherein a prefabricated-cast-in-place interface in multi-protrusion tooth block engagement is arranged between the end head of the prefabricated small box girder and the cast-in-place hidden cover beam, and the prestress system comprises an in-vivo prestress system and an in-vitro prestress system; the in-vivo prestressed system comprises a plurality of in-vivo prestressed steel bundles, and the anchoring points of the in-vivo prestressed steel bundles are arranged at the end part of the web plate of the prefabricated small box girder and distributed along the height direction of the web plate of the prefabricated small box girder; the external prestress system comprises a plurality of external prestress steel beams; an inclination angle alpha exists between each external prestress steel beam and the web plate of the prefabricated small box girder. Therefore, the invention can improve the overall height of the lifting frame, meets the requirement of insufficient local clearance of the bridge, and effectively solves the problems of bearing capacity, deformation and durability between the prefabricated small box girder and the cast-in-situ hidden cover girder.

Description

Prestressed steel beam connected prefabricated small box girder type hidden cover beam and construction method thereof
Technical Field
The invention discloses a prefabricated small box girder type hidden cover beam connected by prestressed steel beams and a construction method thereof, belonging to the field of civil engineering design.
Background
Under the promotion of national strategic guidance and the requirements of society and industry development, the bridge construction technology is developing towards the direction of assembly, industrialization and standardization. In the overhead construction of urban expressways, prefabricated structures gradually replace cast-in-place structures. On one hand, under the same span, the concrete consumption of the prefabricated small box girder is only 50% of that of the cast-in-place box girder; in soft soil areas, the construction cost of the scheme of the prefabricated small box girder is less than 75 percent (the lower structure engineering amount is reduced, the field foundation treatment cost is eliminated) (the general calculation index per square meter of the urban overhead of the prefabricated small box girder is about 4439 yuan/m 2, and the general calculation index per square meter of the cast-in-place box girder is about 5944 yuan/m 2), the prefabricated small box girder or the prefabricated hollow plate girder is adopted for 75 percent of the upper structure (taking Ningbo city as an example, the cast-in-place box girder structure is adopted for 2011 completed airport road upper structure, the south ring and the north ring overhead are adopted for 2015 completed airport road upper structure, the prefabricated small box girder structure or the prefabricated hollow plate girder is adopted for 75 percent of the upper structure, only the curve section, the width-changing section and the ramp connecting section, the south extension of the airport road started in 2017, the west-large bridge connection engineering started in 2018 and the west extension of the south-line of the city road are adopted for 95 percent of the prefabricated small box girder (the curve section, the width-changing section and the ramp connecting section are all prefabricated structures), only the passage clearance limited section adopts a cast-in-place box girder); on the other hand, the prefabricated box girder adopts a mode of factory manufacturing and field installation, and has remarkable advantages in construction period and quality control (factory manufacturing can be synchronous with construction of other structures on the field, the construction period is saved, and the quality is easier to control by adopting assembly line and standardized operation in a factory than field operation).
However, the prefabricated box girders have a significant disadvantage in terms of passage clearance because conventional prefabricated concrete girders (prefabricated box girders) are erected on the capping beams, the specific construction of which is shown in fig. 1. When the bridge deck elevation is fixed, the occupied clearance (the height of the prefabricated small box girder and the height of the cover girder) required by the scheme of the prefabricated concrete girder is larger than that of a cast-in-place box girder, so that when the line type of the bridge deck road is determined and the clearance of the bridge is limited, a prefabricated concrete girder type system cannot be adopted (except for the unadjusted bridge deck elevation, the line type of the whole engineering road can be influenced).
In a conventional precast concrete beam structure, 1 wet joint of 25cm width is provided between precast box girders, see fig. 2. Although the wet joint is not effectively connected with the prefabricated small box girder, the wet joint is positioned in the range of the support, most of the counter-force diffusion area is positioned in the area of the prefabricated small box girder when the counter-force of the support is diffused by 45 degrees, and therefore, the wet joint is not used for bearing load for the conventional prefabricated concrete girder structure. On the contrary, for the conventional precast concrete beam structure, the bridge span part and the beam part are formed by one-time casting, and it is shown according to a large amount of destructive test data that when the structure is designed according to the specification requirement, the shearing failure near the fulcrum is an oblique section, so that the crack development needs to be inhibited by densely distributed stirrups, see fig. 3.
A prefabricated small box girder type hidden cover girder structure system is reported in the Key technology research on the design of hidden cover girders in prefabricated small box girders (urban road bridges and flood control, 10 th 2020), and finite element analysis and calculation show that the system has 0.42MPa of tensile stress under various load working conditions, so the structure system needs to be designed according to A-type prestressed concrete components. According to investigation, at present, domestic urban viaducts are usually designed according to 'fully prestressed concrete members', and when an implicit bent cap system is adopted to replace a cast-in-place box girder system, the safety state of the structural system should not be adjusted. In addition, during construction of the Ningbo north-loop viaduct, a hidden cover beam system based on prefabricated hollow plate beams is adopted in part of ramp ways, a design method similar to that adopted in the above document is adopted, and after the viaduct is operated for 5 years, common vertical cracks appear in the joint area of the hidden cover beams. In other words, how to enhance the bearing capacity of the joint area of the hidden canopy beam and improve the durability of the joint area of the hidden canopy beam is a problem that needs to be solved in the design stage of the current hidden canopy beam structure.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the precast small box girder type hidden cover girder connected by the prestressed steel bundles so as to improve the overall height of an overhead, meet the defect of insufficient local clearance of a bridge and effectively solve the problems of bearing capacity, deformation and durability between the precast small box girder and the cast-in-situ hidden cover girder.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
a precast small box girder type hidden bent cap connected with prestressed steel bundles comprises precast small box girders arranged along the bridge direction, cast-in-place hidden bent caps arranged along the transverse bridge direction and a prestressed system configured along the precast small box girder web direction, wherein a precast-cast-in-place interface in multi-protrusion tooth block engagement is arranged between the end head of each precast small box girder and each cast-in-place hidden bent cap, and each prestressed system comprises an in-vivo prestressed system and an in-vitro prestressed system;
the in-vivo prestressed system comprises a plurality of in-vivo prestressed steel bundles, wherein the anchoring points of the in-vivo prestressed steel bundles are arranged at the end part of the web plate of the prefabricated small box girder and are distributed along the height direction of the web plate of the prefabricated small box girder;
the in-vitro prestressed system comprises a plurality of in-vitro prestressed steel bundles; an inclination angle alpha exists between each external prestressed steel beam and the web plate of the prefabricated small box girder;
when the prefabricated small box girder type hidden cover beam is positioned in a continuous section, the middle area of each external prestressed steel bundle is horizontally buried in the cast-in-place hidden cover beam and distributed along the height direction of the cast-in-place hidden cover beam, one end of each external prestressed steel bundle is anchored on the bottom plate of the prefabricated small box girder on one side of the cast-in-place hidden cover beam, and the other end of each external prestressed steel bundle is anchored on the bottom plate of the prefabricated small box girder on the other side of the cast-in-place hidden cover beam;
when the small box girder type hidden cover girder is in the simply supported section, one end of each external prestressed steel bundle is anchored on the top plate of the small box girder, and the other end of each external prestressed steel bundle is anchored in the cast-in-place hidden cover girder.
Preferably, when the prefabricated small box girder type hidden cover girder is positioned in a continuous section, the prefabricated small box girders, namely a prefabricated small box girder a and a prefabricated small box girder b, are arranged on two sides of the cast-in-place hidden cover girder; the prefabricated-cast-in-place interface between the end of the prefabricated small box girder a and the cast-in-place hidden cover girder is a prefabricated-cast-in-place interface a, and the prefabricated-cast-in-place interface between the end of the prefabricated small box girder b and the cast-in-place hidden cover girder is a prefabricated-cast-in-place interface b;
the middle area of each external prestressed steel beam is horizontally buried in the cast-in-place hidden cover beam and distributed along the height direction of the cast-in-place hidden cover beam, one end of each external prestressed steel beam penetrates through the prefabrication-cast-in-place interface a and then turns through the corresponding turning block a, and is finally anchored on the bottom plate of the prefabricated small box beam a, and the other end of each external prestressed steel beam penetrates through the prefabrication-cast-in-place interface b and turns through the corresponding turning block b, and is finally anchored on the bottom plate of the prefabricated small box beam b; the steering block a is installed on the web plate of the prefabricated small box girder a, and the steering block b is installed on the web plate of the prefabricated small box girder b.
Preferably, the steering block a and the steering block b respectively comprise a web plate outer side steel plate, a web plate inner side steel plate, an anchor bolt steel bar and a tensioning base plate; the web outside steel sheet is installed at the web inboard of prefabricated little case roof beam, and the inboard steel sheet of web passes through the crab-bolt reinforcing bar and is connected with web outside steel sheet, and the tensioning backing plate is connected with the inboard steel sheet of web, and external prestressing steel bundle passes the through-hole setting of seting up on the tensioning backing plate.
Preferably, when the prefabricated small box girder type hidden cover beam is positioned in the simply supported section, one end of each external prestressed steel beam sequentially penetrates through the prefabricated-cast-in-place interface and the anchor sealing plate, and then is steered by the steering block and finally anchored on the top plate of the prefabricated small box girder;
the steering block comprises a web plate outer side steel plate, a web plate inner side steel plate, an anchor bolt steel bar and a tensioning base plate; the web outside steel sheet is installed at the web inboard of prefabricated little case roof beam, and the inboard steel sheet of web passes through the crab-bolt reinforcing bar and is connected with web outside steel sheet, and the tensioning backing plate is connected with the inboard steel sheet of web, and external prestressing steel bundle passes the through-hole setting of seting up on the tensioning backing plate.
Preferably, the number of the anchor reinforcing steel bars is 4-6.
Preferably, the prefabricated-cast-in-place interface comprises an end head of a prefabricated small box girder and a cast-in-place concrete joint meshed with the end head of the prefabricated small box girder; wherein:
the end of the small prefabricated box girder comprises a box girder bottom plate end, a box girder top plate end and two box girder web plate ends positioned between the box girder bottom plate end and the box girder top plate end; the outer side surface of the end of the box girder bottom plate and the outer side surface of the end of the box girder top plate are positioned in the same plane; a plurality of web raised teeth are arranged on the outer sides of the ends of the web plates of the two box girders; the web convex teeth are arranged on the top of the web convex teeth, the upper end of the web convex teeth starts from the outer side surface of the end of the box girder top plate, the lower end of the web convex teeth crosses the connecting limit of the end of the box girder top plate and the end of the box girder web plate and ends at the outer side surface of the end of the box girder web plate, and the rest web convex teeth are arranged on the outer side surface of the end of the box girder web plate.
Preferably, the number of web lobes matches the number of in vitro prestressed steel strands.
Preferably, the number of the web convex teeth arranged at the end of the web of the single-side box girder is 3, and the number of the external prestressed steel bundles on the single side is 3.
Preferably, 4 in-vivo prestressed steel bundles are arranged in the prefabricated small box girder; correspondingly, 4 individual internal prestressed steel strand anchoring points are arranged at the end part of the prefabricated small box girder web plate along the height direction.
The invention also aims to provide a construction method of the precast small box girder type hidden cover beam connected by the prestressed steel beams, which comprises the following construction steps:
step one, factory manufacturing of prefabricated small box girder
I, construction forming of conventional section of prefabricated small box girder
1.1 preparation of the bench
Respectively arranging corresponding notch templates according to the beam bottom tensioning notch position and the operation manhole position of the prefabricated small box girder, so that after the conventional section of the prefabricated small box girder is constructed and molded, a beam bottom tensioning notch is formed on a bottom plate of the conventional section of the prefabricated small box girder, and an operation manhole is formed on a top plate of the conventional section of the prefabricated small box girder; an end die is arranged at the end part of the conventional section of the prefabricated small box girder so as to obtain a multi-protrusion type tooth block end structure meeting the design requirement after the conventional section of the prefabricated small box girder is cast and molded;
1.2 binding the steel bars of the conventional section of the prefabricated small box girder
Binding top, bottom and web steel bars of the conventional section of the prefabricated small box girder, and then installing a prestressed corrugated pipe at the preset position of the prestressed corrugated pipe;
the longitudinal main ribs at the top and the bottom of the bound conventional section of the prefabricated small box girder can extend out of the end part of the prefabricated small box girder after the conventional section of the prefabricated small box girder is cast and molded;
1.3 Embedded steering Block Embedded parts
Arranging a steering block embedded part at a preset position of the conventional section of the prefabricated small box girder, and welding and fixing the steering block embedded part and the common steel bars of the conventional section of the prefabricated small box girder in a spot welding manner; the steering block embedded part is an assembly part consisting of a steering block embedded plate and anchor bolt reinforcing steel bars, the number of the steering block embedded plate is two, the two steering block embedded plates are respectively corresponding to a web plate outer side steel plate and a web plate inner side steel plate, and the anchor bolt reinforcing steel bars are connected between the web plate outer side steel plate and the web plate inner side steel plate;
the width of a web plate of the conventional section of the prefabricated small box girder at the embedded position of the steering block embedded part is the same as the length of the steering block embedded plate, and the steering block embedded plate close to the inner web plate side is closely attached to the prefabricated small box girder inner film;
adjusting the distribution of stirrups at the positions of the steering block embedded parts to adjust the stirrups at the positions of the steering block embedded parts to the two sides of the steering block embedded plate;
II, welding the steel plate with the outside leakage of the steering block
In the step I, after the conventional section of the prefabricated small box girder is constructed and molded, a core mold of the conventional section of the prefabricated small box girder is dismantled, and then a steel plate with an outward leakage of a steering block is welded at a preset position on a steel plate on the inner side of a web plate on the outer side of the embedding position of an embedded part of the steering block, wherein the steel plate with the outward leakage of the steering block is vertical to the steel plate on the inner side of the web plate, and the steel plate with the outward leakage of the steering block is a tensioning base plate;
III, constructing the solid cast-in-place section of the beam end
After the tensioning and grouting of the prestressed steel beams of the conventional section of the prefabricated small box girder are completed, the construction of the solid cast-in-place section of the girder end is carried out, and the construction requirements are met:
3.1, welding and fixing the steel bars of the solid cast-in-place section at the beam end with the outer leakage main bars of the conventional section of the prefabricated small box girder;
3.2, arranging a plugging plate used for an inner membrane of the solid cast-in-place section at the beam end on the outer side of the outer leakage steel plate;
3.2, combining the design requirement and the actual position of the steering block, and pre-burying a steel pipe used as a reserved hole position of the external beam;
step two: hidden cover beam temporary support system installation
Mounting a temporary supporting system of the hidden cover beam on a construction site;
step three: prefabricated small box girder hoisting
In a construction site, a hidden cover beam temporary supporting system is matched, and the prefabricated small box beam obtained in the step one is hoisted in place;
step four: hidden cover beam bottom/end mould laying and reinforcing steel bar binding
Laying a hidden cover beam bottom/end mould and binding steel bars according to design requirements on a construction site;
step five: hidden cover beam prestress corrugated pipe burying and external beam reserved hole channel arrangement
Burying a pre-stressed corrugated pipe and an external beam reserved hole channel of the hidden cover beam according to design requirements; wherein: the external bundle reserved hole channel in the hidden cover beam is a straight bundle, is connected with the steel pipe embedded in the step 3.2, and is fixed on the hidden cover beam steel bar by adopting a hanging bar;
step six: hidden cover beam side form support
Step seven: concrete pouring of hidden cover beam
Step eight: stretching of prestressed first steel bundle of hidden cover beam
Stretching a first batch of prestressed steel bundles of the hidden cover beam to resist the action of bending moment generated by the self weight of the prefabricated small box girder and the self weight of the hidden cover beam;
step nine: temporary support system frame of hidden cover beam
Disassembling the temporary supporting system of the hidden cover beam;
step ten: stretching of prestressed second steel bundle of hidden cover beam
Tensioning the hidden cover beam to prestress the second steel bundle so as to resist bending moment generated by second-stage dead load and automobile live load; the second-stage constant load comprises the dead weight of bridge deck pavement and an anti-collision railing;
step eleven: small box girder hogging moment steel bundle tensioning
Step twelve: small box girder external beam construction and notch sealing
Inserting external prestress steel beams and tensioning; then closing the tensioning slot;
step thirteen: small box girder body operation manhole closure
And closing the operation manhole on the top plate of the prefabricated small box girder.
According to the technical scheme, compared with the prior art, the invention has the following advantages:
according to the invention, at the splicing position between the prefabricated small box girder and the cast-in-place hidden cover girder, the cast-in-place shear interface is converted into the pressure-bearing interface by arranging the prefabricated-cast-in-place interface in multi-protrusion tooth block occlusion, the pressure-bearing interface is transmitted through the cast-in-place shear interface, the bearing capacity improving effect is obvious, and the prestress system is configured along the web plate direction of the prefabricated small box girder, so that the positive pressure of the interface is increased, the tooth block type shear key is tightly occluded, the effectiveness of the interface is ensured, and the transmission state can fully exert the effect.
Drawings
Fig. 1 is a schematic structural view of a conventional precast concrete beam;
FIG. 2 is a schematic force-bearing diagram of a conventional precast concrete beam structure;
fig. 3 is a schematic view of a shear structure of a conventional precast concrete beam structure;
FIG. 4 is a schematic structural view of a prefabricated small box girder type hidden cover beam (a connection structure between the prefabricated small box girder and the hidden cover beam without a prestressed steel beam);
FIG. 5 is a schematic illustration of the prefabricated mini-box girder canopy beam of FIG. 4 having a torsional effect;
FIG. 6 is a shear analysis diagram of the prefabricated mini-box girder hidden cover beam of FIG. 4;
FIG. 7 is a schematic structural view of a prefabricated mini-box girder type hidden canopy beam with an interlocking precast-cast in place interface (with shear analysis);
FIG. 8 is a schematic structural view of a prestressed steel beam-connected prefabricated small box girder type hidden cover beam (continuous section) according to the present invention;
FIG. 9 is a schematic structural diagram of a prestressed steel beam-connected prefabricated small box girder type hidden cover beam (simply supported section) according to the present invention;
FIG. 10 is a schematic structural view of a prefabricated box girder end according to the present invention;
FIG. 11 is a schematic view of a steering block according to the present invention;
in FIGS. 1-6: 1-prefabricating a small box girder; 2-cast-in-place hidden bent cap; 2' -capping beam; 3' -a support; 4' -wet seaming; 5' -support reaction force diffusion line; 6' -longitudinal steel bars; 7' -encrypted stirrup;
h1, net height of the original cast-in-place box girder; h2, net height of conventional precast concrete beam; h3, height of a cast-in-place box girder; h4, hidden bent cap net height;
in fig. 7 to 11: 1. prefabricating a small box girder; 1-1, a small box girder bottom plate; 1-2, a small box girder web plate; 1-3, a small box girder top plate; 1-4, web convex teeth; 2. casting a hidden bent cap in situ; 3. sealing the anchor plate; 4. prefabricating a cast-in-place interface; 5. an in-vivo prestressed tendon; 6. a turning block; 6-1, a steel plate outside the web plate; 6-2, a steel plate on the inner side of the web plate; 6-3, anchor bolt reinforcing steel bars; 6-4, tensioning the base plate; 7. an anchoring groove; 8. and (3) externally prestressing tendons.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. The relative arrangement of the components and steps, expressions and numerical values set forth in these embodiments do not limit the scope of the present invention unless specifically stated otherwise. Meanwhile, it should be understood that the sizes of the respective portions shown in the drawings are not drawn in an actual proportional relationship for the convenience of description. Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate. In all examples shown and discussed herein, any particular value should be construed as merely illustrative, and not limiting. Thus, other examples of the exemplary embodiments may have different values.
Spatially relative terms, such as "above … …," "above … …," "above … …," "above," and the like, may be used herein for ease of description to describe one device or feature's spatial relationship to another device or feature as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if a device in the figures is turned over, devices described as "above" or "on" other devices or configurations would then be oriented "below" or "under" the other devices or configurations. Thus, the exemplary term "above … …" can include both an orientation of "above … …" and "below … …". The device may also be oriented in other different ways (rotated 90 degrees or at other orientations).
In order to increase the overall height of the lifting frame due to insufficient local clearance, it is necessary to develop a hidden beam structure system based on prefabricated small box girder type, which can effectively break through the existing bottleneck of the prefabricated structure, and its structural diagram can be seen in fig. 4.
The concept design of the prefabricated small box girder + cast-in-place hidden type capping beam structure system is relatively easy, the function is taken as the target, and the core difficulty of the design is that the prefabricated structure (the prefabricated small box girder) is connected with the cast-in-place structure (the cast-in-place hidden type capping beam), namely the bearing capacity, the rigidity and the durability are all 3 core design elements.
Urban elevations usually adopt a bidirectional 6-lane design and are composed of 8 prefabricated small box girders. When the lanes are not full, the loads borne by different prefabricated box girders are different, and besides the conventional bending and shearing, the prefabricated box girders also generate torsional deformation, and refer to fig. 5. According to the traditional prefabricated small box girder structure, because the end part is located in the range of the support, the prefabricated small box girder forms a couple through the vertical counter force difference of 2 plate type rubber supports, and resists the torque action of uneven load, namely when a prefabricated small box girder and cast-in-situ hidden cover girder structure system is adopted, the end part of the prefabricated small box girder and the combined section of the cast-in-situ hidden cover girder are in fixed end constraint, which means that the prefabricated small box girder needs to rely on self torsional rigidity to resist the effect, namely the nature of the torsional rigidity, and has the performance of bearing and resisting the circumferential shear stress flow.
The end of the prefabricated box girder is a shear peak area. The shear force peak value of the prefabricated small box girder type hidden cover beam system can not be transmitted through a support diffusion area of the traditional prefabricated small box girder, and can not be a continuous structure like a cast-in-place box girder (see figure 6, a construction wet joint exists between new concrete and old concrete, the shear force forms stress concentration in the area, the interface can form association through longitudinal steel bars, but vertical stirrups are discretely distributed and can not effectively influence the interface), the crack development can be restrained through the area encrypted stirrups, the interface area is a concrete surface, if the shear force peak value excessively extends into the cast-in-place hidden cover beam area, the rigidity of the cast-in-place hidden cover beam can be weakened, a weak surface is formed at the prefabricated small box girder, the shear force is of nature, and the shear force peak value is vertical shear stress flow.
In addition, when the prefabricated box girder is simply supported and then constructed continuously, the tearing of the interface area is aggravated by the top surface tensile stress caused by the hogging moment effect of the prefabricated small box girder in the continuous section (the tensile stress and the shear stress act synchronously). Therefore, the core and key of the development of the prefabricated small box girder hidden cover girder system lies in the development of new and old concrete contact surfaces, and the essence of the development lies in how to ensure that the contact surfaces resist shear stress. The existing method cannot meet the requirements of the bearing capacity, deformation and durability of the structural system.
The prefabricated small box girder greatly increases the difficulty of interface treatment due to the structural characteristics of the prefabricated small box girder, namely the end part of a web plate of the prefabricated small box girder is an anchoring area of a prestressed steel beam of the prefabricated small box girder, and the web plate is a key part for transferring shearing force and bearing torque, so that the shearing structural measures of the prefabricated small box girder are interrupted at the end part of the web plate, and a continuous shearing structure cannot be formed, which is the greatest difficulty in the research and development of a prefabricated small box girder type hidden cover girder system.
As shown in fig. 7 to 11, the precast small box girder type hidden bent cap connected by prestressed steel bundles according to the present invention includes precast small box girders arranged along a bridge direction, cast-in-place hidden bent caps arranged along a transverse bridge direction, and a prestressed system configured along a precast small box girder web direction, wherein the prestressed system includes an in-vivo prestressed system and an in-vitro prestressed system;
the anchoring points of the steel bundles of the in-vivo prestressed system and the in-vitro prestressed system are arranged at the web plate end of the prefabricated small box girder, and a protrusion is arranged corresponding to each steel bundle anchoring point, so that when the cast-in-place hidden cover girder is poured, a prefabricated-cast-in-place interface in multi-protrusion tooth block engagement is formed between the end of the prefabricated small box girder and the cast-in-place hidden cover girder, and the shearing resistance of the interface is improved. Specifically, the prefabricated-cast-in-place interface comprises an end head of a prefabricated small box girder and a cast-in-place concrete joint meshed with the end head of the prefabricated small box girder; wherein: the end of the small prefabricated box girder comprises a box girder bottom plate end, a box girder top plate end and two box girder web plate ends positioned between the box girder bottom plate end and the box girder top plate end as shown in fig. 10; the outer side surface of the end of the box girder bottom plate and the outer side surface of the end of the box girder top plate are positioned in the same plane; a plurality of web raised teeth are arranged on the outer sides of the ends of the web plates of the two box girders; the web convex teeth are arranged on the top of the web convex teeth, the upper end of the web convex teeth starts from the outer side surface of the end of the box girder top plate, the lower end of the web convex teeth crosses the connecting limit of the end of the box girder top plate and the end of the box girder web plate and ends at the outer side surface of the end of the box girder web plate, and the rest web convex teeth are arranged on the outer side surface of the end of the box girder web plate. And the web convex tooth at the lowest part starts at the position of 20cm from the top surface of the bottom plate, and the depth of the web convex tooth is not less than 25cm of the section plane of the end part of the bottom plate of the box girder. The number of the web convex teeth is matched with the number of the in-vitro prestressed steel bundles. In this embodiment, the number of web convex teeth arranged at the end of the web of the single-side box girder is 3, and the number of the external prestressed steel bundles on the single side is 3. 4 in-vivo prestressed steel bundles are arranged in the small prefabricated box girder; correspondingly, 4 individual internal prestressed steel strand anchoring points are arranged at the end part of the prefabricated small box girder web plate along the height direction.
As shown in fig. 7, although the prefabricated-cast-in-place interface area can not be configured with steel bars, the prefabricated small box girder type hidden cover girder system is divided into 2 independent individuals despite the existence of construction joints, and the two individuals are only communicated through the bonding force of new concrete and old concrete, when the interface state is poor, the interface bearing capacity is not optimistic; when the interface state is good, the interface bearing capacity is not worse than that of a cast-in-place structure, namely, a multi-tooth block protrusion (a multi-tooth block meshed prefabricated-cast-in-place interface) of a shear key type is adopted, the cast-in-place shear interface is converted into a bearing interface and is transmitted through the cast-in-place shear interface, and the bearing capacity lifting effect is obvious; the arrangement of the prestress system increases the positive pressure of the interface, so that the engagement of the tooth block type shear key is tight, the effectiveness of the interface is ensured, and the effect of the transmission state is fully exerted.
The biggest difficulty of the precast small box girder type hidden cover beam system connected by the prestressed steel bundles lies in how to arrange the prestressed steel bundles at the interface, namely 4 individual prestressed steel bundle anchoring points are configured at the end part of a precast small box girder web plate along the height direction, and the steel bars and the steel bundles in the web plate are dense, so the external prestressed steel bundle anchoring points are arranged at the precast-cast-in-place interface.
Specifically, as shown in fig. 7-9, the in-vivo prestressed system includes a plurality of (4 in the drawing) in-vivo prestressed steel bundles, and the anchoring points of the in-vivo prestressed steel bundles are all arranged at the end of the web of the prefabricated small box girder and distributed along the height direction of the web of the prefabricated small box girder; the in vitro prestressed system comprises a plurality of in vitro prestressed steel bundles (3 on one side and 6 on two sides in the drawing); an inclination angle alpha exists between each external prestress steel beam and the web plate of the prefabricated small box girder. In other words, the invention arranges prestress (internal and external prestress steel beams) perpendicular to the contact surface along the direction of the prefabricated small box girder web, and improves the shear-resisting bearing capacity of the interface by improving the normal stress sigma of the section.
As shown in fig. 8, when the precast mini-box girder hidden cover beam is in a continuous section, the outer bundle of the prestressed body adopts a floor anchoring mode. On one hand, the hogging moment effect of the continuous beam pivot area is considered, if the continuous beam pivot area is anchored at the top, the function of the hogging moment beam of the top plate is counteracted, the beam distribution quantity of the hogging moment beam is increased, and the hogging moment beam is unreasonable and uneconomical; the bottom is anchored, so that the effect of the negative bending moment of a fulcrum can be counteracted, and the positive stress effect can be exerted on the whole cross section of the prefabricated small box girder and the cast-in-place hidden cover girder.
3 external prestressed steel beams are arranged along the height direction, and the external prestressed steel beams are arranged near each web plate of the prefabricated small box girder, namely 6 external prestressed steel beams with single section are arranged, and the external prestressed steel beams with the single section have small diameter and large quantity, so that the positive pressure balance of the section is ensured as much as possible;
the direction of the external prestressed steel beam is adjusted through the steering block, the steering block needs to be embedded in the prefabricated small box girder web plate and is usually positioned on the rear side of the end sealing plate, namely the external prestressed steel beam completely passes through a cast-in-place concrete area and then turns, at the moment, the anchor sealing plate of the prefabricated small box girder is consistent with a conventional product and does not need to move backwards.
The steering block consists of 2 embedded plates (web plate outer side steel plates and web plate inner side steel plates), 4-6 connecting steel bars (anchor bolt steel bars) and 1 steering plate (tensioning base plate). Different from the anchoring steel plate of the PBL key, the steering block is anchored by adopting a double-layer steel plate, on one hand, because the concentrated force effect of the prestressed steel beam is obvious; on the other hand, the double-layer steel plate is beneficial to positioning (namely, installation accuracy) in the small box girder prefabricating stage.
Wherein web outside steel sheet passes through crab-bolt reinforcing bar and the inboard steel sheet welded connection of web, and web outside steel sheet outside interval is the stretch-draw end position web thickness, and stretch-draw backing plate and the inboard steel sheet welding of web simultaneously, welding seam intensity accords with the design requirement.
In order to ensure the anchoring strength of the tensioning end, the size of the steel plates at the inner side and the outer side of the web plate is not less than 150mmx150mm, the thickness of the steel plate is not less than 20mm, the diameter of the anchor bolt steel bar is not less than 20mm, and round steel is adopted.
The size of the tensioning cushion plate is determined according to the design tensioning load, the width of the lower opening is not less than 100mm, and the thickness is not less than 20 mm. Groove welding seams are preferably adopted between the tensioning backing plate and the steel plate on the inner side of the web plate, the quality of the welding seams is designed to the end and meets the standard requirements, 100% detection is carried out by adopting ultrasonic and magnetic powder, and the tensioning backing plate can be used when the design requirements are met.
A beam bottom tensioning notch is formed in a bottom plate of the prefabricated small box beam, and the position of the beam bottom tensioning notch is based on the condition that the external beam inclination angle is 15 +/-1 degrees. Near the anchoring section of the beam bottom tensioning slot, besides a stiffening spiral rib (ensuring that the anchoring section is not damaged under local stress), a rigid metal corrugated pipe with a small diameter is required to be configured as a reserved channel of an external prestressed steel beam, wherein the diameter of the metal corrugated pipe is small, so that the influence of an opening on the prefabricated small box beam is reduced; the metal corrugated pipe is used for bonding the small prefabricated box girder after external prestress pore canal grouting.
Arranging metal corrugated pipes (installed in the stage of binding the cast-in-place hidden cover beam steel bars) between anchor sealing plates (tensioning backing plates) of the continuous sections; between the anchor sealing plate and the beam bottom tensioning notch, a plastic pipeline (before the anchor sealing plate is installed) needs to be pre-embedded in advance, namely, in an installation site, a steel beam only needs to penetrate through a reserved external prestress steel beam hole, if the pipeline does not exist, the site installation of the external prestress steel beam cannot be executed, the external prestress steel beam is installed and tensioned after the hidden cover beam is cast in place, and otherwise, the prestress cannot take effect on a prefabricated-cast-in-place concrete interface.
In short, for the prefabricated small box girder type hidden capping beam with a continuous section, the middle area of each external prestressed steel bundle correspondingly penetrates through a horizontally-buried metal corrugated pipe in the cast-in-place hidden capping beam and is distributed along the height direction of the cast-in-place hidden capping beam, one end of each external prestressed steel bundle is anchored on a bottom plate of the prefabricated small box girder on one side of the cast-in-place hidden capping beam, and the other end of each external prestressed steel bundle is anchored on a bottom plate of the prefabricated small box girder on the other side of the cast-in-place hidden capping beam; specifically, two sides of a cast-in-place hidden cover beam are respectively provided with a prefabricated small box beam a and a prefabricated small box beam b; the prefabricated-cast-in-place interface between the end of the prefabricated small box girder a and the cast-in-place hidden cover girder is a prefabricated-cast-in-place interface a, and the prefabricated-cast-in-place interface between the end of the prefabricated small box girder b and the cast-in-place hidden cover girder is a prefabricated-cast-in-place interface b; the middle area of each external prestressed steel beam penetrates through a horizontally-buried metal corrugated pipe in the cast-in-place hidden cover beam and is distributed along the height direction of the cast-in-place hidden cover beam, one end of each external prestressed steel beam penetrates through a prefabrication-cast-in-place interface a and then turns through a turning block a corresponding to the external prestressed steel beam to be finally anchored on the bottom plate of the prefabricated small box beam a, and the other end of each external prestressed steel beam penetrates through a prefabrication-cast-in-place interface b and then turns through a turning block b corresponding to the external prestressed steel beam to be finally anchored on the bottom plate of the prefabricated small box beam b; the steering block a is installed on the web plate of the prefabricated small box girder a, and the steering block b is installed on the web plate of the prefabricated small box girder b. The structures of the steering block a and the steering block b are consistent, and as shown in fig. 11, the steering block a and the steering block b respectively comprise a web plate outer side steel plate, a web plate inner side steel plate, an anchor bolt steel bar and a tensioning base plate; the web outside steel plate is installed at the web inboard of prefabricated little box girder, the inboard steel plate of web passes through the crab-bolt reinforcing bar and is connected with web outside steel plate, the inboard steel sheet of stretch-draw backing plate is connected, external prestressing steel bundle passes behind the through-hole of seting up on the stretch-draw backing plate, can turn to the setting, make the part that external prestressing steel bundle is in prefabricated little box girder can alternate obliquely in the steel pipe of presetting in prefabricated little box girder and stretch-draw targets in place, and be in the part of cast-in-place implicit expression bent cap, then be the level form and alternate in the steel pipe of pre-buried in the cast-in-place implicit expression bent cap and stretch-draw targets in place.
When the precast box girder type hidden cover girder is in the simply supported section, as shown in fig. 9, the biggest difference between the simply supported section and the continuous section is that no fulcrum bending moment acts, so the external prestressed steel beam is allowed to be anchored on the precast box girder top plate, which is lower than the bottom plate in operation difficulty. Note: the continuous section has limited clearance of the hidden cover beam, so the stretching stage can be operated by a climbing vehicle, and the difficulty of stretching the prestressed steel beam on the bottom plate is not particularly high.
The simply supported section has no tension operation space at the side of the cast-in-place hidden cover beam (the beam body at the other side of the telescopic layer is constructed), so that an embedded P anchor is adopted as an anchoring section.
In other words, for the prefabricated small box girder type hidden capping beam of the simply supported section, one end of each external prestressed steel beam is anchored on the top plate of the prefabricated small box girder, and the other end is anchored in the cast-in-place hidden capping beam. Specifically, one end of each external prestressed steel beam sequentially penetrates through a prefabrication-cast-in-place interface and an anchor sealing plate, and is finally anchored on a bottom plate of the prefabricated small box girder after being turned by a turning block; the structure of the steering block, as shown in fig. 11, includes a web outer steel plate, a web inner steel plate, an anchor bolt steel bar and a tension pad; the web outside steel sheet is installed at the web inboard of prefabricated little case roof beam, and the inboard steel sheet of web passes through the crab-bolt reinforcing bar and is connected with web outside steel sheet, and the tensioning backing plate is connected with the inboard steel sheet of web, and external prestressing steel bundle passes the through-hole setting of seting up on the tensioning backing plate. The number of the anchor bolt reinforcing steel bars is 4-6.
The general diagram of the public road bridge in the traffic industry of the people's republic of China is as follows: the shear force of the end part of a precast beam with the maximum span (40 m) and the maximum load (highway-I level) in the upper structure of the assembled prestressed concrete box-shaped continuous beam bridge is taken as a reference, and the shear bearing capacity of the end part of the hidden cover beam structure system is checked. The design value of the end peak shearing force borne by the single-piece precast beam is shown in the table 1.
Table 140 m span prefabricated small box girder end peak shear design value statistical table
Figure 465507DEST_PATH_IMAGE001
As can be seen from Table 1, the design value of the peak shear bearing capacity of the end part of the small box girder prefabricated by the single piece is not lower than 3200 kN.
Although the small prefabricated box girder and the hidden cover girder are formed by pouring concrete, the contact surface of the new concrete and the old concrete is closer to the prefabricated splicing seam of the sections, namely the shearing damage of the structure is not damaged along the shearing and pressing inclined crack of the traditional concrete structure, but is damaged along the pouring seam of the new concrete and the old concrete.
According to the domestic scientific research achievement, by combining with the local standard 'segment precast assembled concrete bridge design and construction specification' of Jiangsu province (DB 32/T3564-2019), the shearing resistance and bearing capacity of the new and old concrete joints are executed according to the shearing resistance and bearing capacity of the glued joint type key tooth shearing key joint, as follows:
Figure 84707DEST_PATH_IMAGE002
γ 0 : taking a structural importance coefficient as 1.1;
V d : a peak shear design value;
α: the reduction coefficient of the shearing resistance of the glued joint key teeth is 0.85;
σ pc，m : and the effective prestress generated at the centroid of the section of the member after the prestress loss is deducted in the using stage is used for generating the concrete prestress. The total cross-sectional area of the prefabricated small box girder is 2.663m2And assembling 6 bundles of 15.2-3 steel stranded wires on the assembled section, controlling the tension stress 1395MPa, wherein the effective prestress is 75 percent, and the effective concrete prestress of the section is as follows:
Figure 882899DEST_PATH_IMAGE003
A w : the area of the web section of the joint surface is 0.825m, which is taken as the sum of the web areas2；
f cu，k : the cubic compressive strength standard value of the concrete, the hidden cover beam adopts C40 concrete, and 40 is selected.
Therefore, shear resistance design valueV d Comprises the following steps:
Figure 612957DEST_PATH_IMAGE004
and the standard requirement is met.
The core element of the construction period of the precast small box girder type hidden cover beam structure system connected by the prestressed steel bundles is the construction quality control of the external prestressed steel bundle structure and the components. The construction process and the considerations of the overall structure are as follows:
the method comprises the following steps: factory fabrication of prefabricated box girders
The most key technical key points of the precast small box girder type hidden cover girder structure system connected by the prestressed steel bundles are mostly concentrated on the precast small box girder part, and the precast small box girder is cast and molded in two steps, wherein the conventional section of the precast small box girder is cast and molded in the first step, and the solid cast-in-place section at the end part of the precast small box girder is cast and molded in the second step.
1) Conventional section of prefabricated small box girder
The conventional section of the prefabricated small box girder is basically manufactured by a conventional process, which comprises the steps of preparing a pedestal, binding reinforcing steel bars (binding top, bottom and web plates together) and installing prestressed corrugated pipes, installing inner and outer templates, pouring concrete, demoulding, implementing concrete curing and tensioning prestressed steel bundles.
Preparation of a pedestal
A notch template is arranged according to the beam bottom tensioning notch position of the external prestressed steel beam, the notch template adopts a customized steel die, and the notch steel die is connected with a pedestal bottom steel plate through bolts.
Note 1: if the wood mold is adopted, the wood mold is not only not convenient to be fixed with the pedestal steel bottom plate, but also inconvenient to be connected with the prestressed pipeline and the grouting hole pipeline;
note 2: the length of the prefabricated small box girder is usually between 26m and 35m, and the length of the pedestal is usually between 40m and 45 m. The distance between the bottom tensioning notch of the prefabricated small box girder and the girder end is relatively fixed, so that a connecting bolt hole site can be reserved on one side of the steel plate of the pedestal, a connecting bolt hole site is reserved on the other side of the steel plate of the pedestal according to modulization, and the influence on the anchoring of the external prestressed steel beam is small by slightly adjusting the length of the prefabricated small box girder.
② embedding steering block embedded part
The steering block is divided into an embedded part (a steering block embedded part) and a welding part, wherein the steering block embedded part refers to the web inner side steel plate, the web outer side steel plate and a connecting anchor bolt between the web inner side steel plate and the web outer side steel plate, the outer leakage steel plate refers to the steering plate, and later-stage welding is adopted. The prestressed body outer beam is provided with a steering block behind the plugging plate, the hidden bent cap beam section is bent to the beam bottom tensioning notch through the steering block, so that the steering block bears a large load, the processing quality of the steering block directly influences the later-stage outer beam tensioning effect, and the steering block embedded part is positioned in the web plate transition section of the prefabricated small box girder, so that the following matters need to be taken into consideration when the steering block embedded part is installed:
a) the steering block embedded part is accurately positioned, and the steering block embedded plate and the common steel bars of the prefabricated small box girder are fixed by spot welding;
note: the length of the overall dimension of the steering block embedded plate (a web plate on the inner side or a web plate on the outer side) is the same as the width of the web plate at the position of the prefabricated small box girder, the side, close to the inner web plate, of the steering block embedded plate needs to be closely attached to the inner membrane of the prefabricated small box girder, and after the inner membrane of the prefabricated small box girder is removed, the steering block welded steel plate can be welded.
b) The steering block embedded part is welded in advance according to a design drawing (2 steel plates and 4 steel columns), and the welding quality meets the design requirement;
c) the steering block embedded part needs to be installed after the prefabricated small box girder web plate reinforcing steel bars are bound and the prestressed corrugated pipes are positioned and installed.
Note 1: if the steering block embedded part is installed before the prefabricated small box girder web steel bars, the web steel bar binding efficiency can be greatly reduced (the accurate positioning cannot be realized, the assembly line work cannot be realized), the corrugated pipe line is avoided in the position of the steering block embedded part in principle, and the steering block embedded part is installed after the prestressed corrugated pipe is installed in a positioning mode to ensure that the prestressed corrugated pipe is installed smoothly.
Note 2: the accuracy requirement of the steering block embedded part is relatively small, and the positioning tolerance error is acceptable within 10mm, so the installation difficulty is small.
d) The steering block embedded part positions occupy the prefabricated small box girder web stirrup arrangement space, so that the steering block embedded part position stirrups are distributed to two sides of the steel plate on the premise that the original stirrups are kept unchanged in quantity and spacing according to the steering block embedded part position adjustment stirrup arrangement principle, and the rest distributed reinforcements of the prefabricated small box girder web remain unchanged.
When the end die of the prefabricated small box girder is designed and used, a tensioning notch sawtooth block at the end of the prefabricated small box girder is required to be arranged according to the design drawing requirements while the influence of the external prestress beam corner is considered;
fourthly, a reserved operation manhole is required to be arranged on a prefabricated small box girder top plate and is used for a post-period external beam penetrating operation channel;
prefabricating conventional sections of the small box girders, wherein longitudinal main ribs of the top plate and the bottom plate should leak a certain length (the length is consistent with the length of the cast-in-place sections at the beam ends).
2) Welding a steel plate of the steering block;
the welding of the external beam steering block of the prefabricated small box girder can be finished after the core mould of the small box girder is dismantled, and the following points need to be noticed during the welding:
firstly, cleaning cement paste on the surface of a steel plate on the inner side of a web plate before welding a steering block outer leakage steel plate, and carrying out preparation work such as rust removal before welding;
the welding surface of the steel plate leaking outside the steering block is subjected to groove processing only by mounting steel structure design specifications and drawing requirements;
welding seams between the outer leakage steel plates of the steering blocks and the embedded parts of the steering blocks meet the design requirements, 100% ultrasonic detection is carried out, and the design strength of the outer beam steering blocks is ensured;
the steering block outer leakage steel plate is perpendicular to the web plate, and can be used as an inner membrane support of a solid cast-in-place section at the end part of the prefabricated small box girder while providing an outer beam steering function.
3) Construction of solid cast-in-place section at end part of prefabricated small box girder
The construction of the beam end solid cast-in-place section is carried out after the prestressed steel beam tensioning and grouting are finished in the conventional section of the prefabricated small box beam, and the following points are noted in the construction stage of the beam end solid cast-in-place section:
firstly, the steel bar of the cast-in-place section and the outer leakage main bar of the conventional section form a whole, namely the steel bar of the cast-in-place section is welded to form a complete multi-layer reinforcing mesh and is welded with the outer leakage main bar of the conventional section to form a whole, so that the strength of the beam body of the cast-in-place section is ensured;
secondly, prefabricating a 20cm thick plugging plate in advance to be used as a solid cast-in-place section box chamber inner membrane, wherein the box chamber inner membrane is supported on an external beam steering block;
and thirdly, pre-embedding the outer beam reserved hole positions of the solid cast-in-place section according to the position of a design drawing and the actual position of the outer beam steering block of the combination, adopting a steel pipe with the diameter of 20mm as an embedded part, and enabling the embedded part to leak at least 5cm outwards, so as to ensure that the embedded hole positions are not deformed and not blocked.
4) Construction of beam bottom body external beam tensioning notch
And beam bottom tensioning notches of the prefabricated small box girder type hidden cover beam system connected by the prestressed steel beams are arranged at the beam bottom of the prefabricated small box girder, and the depth of the beam bottom tensioning notches is smaller than the thick bottom of the bottom plate of the prefabricated small box girder. The tooth block bottom die is arranged on the base according to the position of the beam bottom tensioning notch during the construction of the conventional section of the prefabricated small box girder, and the beam bottom tensioning notch can pay attention to the following points during construction:
firstly, pre-burying a steel pipe (along the external beam forming direction) with the inner diameter of 20mm as an external beam pre-buried duct before mounting a prefabricated small box girder core mould, wherein the steel pipe needs to leak the core mould;
reserving a plurality of reserved holes with the diameter not less than 10mm in the range of the beam bottom tensioning notch, and filling the reserved holes as the beam bottom tensioning notch in the later period;
and reserving a grouting pipe in the range of the beam bottom stretching notch, and completing grouting (filling high-strength grouting material) of the beam bottom stretching notch after the external prestressed beam stretching is completed.
Step two: installation of on-site temporary supporting system for hidden cover beam
The design of the hidden beam temporary supporting system refers to Chinese patent CN 201911001747.8.
Step three: prefabricated small box girder hoisting
Different from the conventional prefabricated small box girder, the hidden capping beam system prefabricated small box girder is constructed by erecting a temporary supporting system to support the load of the prefabricated small box girder, the temporary supporting system occupies a large space, and most of the hidden capping beam structure has limited clearance, so that the 'girder lifting in a crossing mode' process of a bridge girder erection machine cannot be adopted.
Therefore, either a lateral lifting installation process of an automobile crane or a span-rear beam feeding process of a bridge girder erection machine is adopted, or a temporary beam lifting support of the bridge girder erection machine is additionally arranged at the side section of the hidden cover beam support system.
Step four: hidden cover beam bottom (end) mould laying and reinforcing steel bar binding
After the preset small box girder is erected, bottom (end) mould laying and reinforcement binding construction of the hidden cover girder are carried out, and the concrete construction steps are as follows:
firstly, designing a bottom die system according to a construction scheme, and paving a bottom die of a hidden cover beam;
roughening treatment (finishing before binding reinforcing steel bars) of the contact surface of the end part of the prefabricated small box girder and the hidden cover girder is finished after the bottom mould is paved, and the bonding property of the interface of new and old concrete is enhanced;
installing an end mould of the hidden cover beam after the hidden cover beam bottom mould is laid, wherein the end mould is provided with two main functions, namely determining the plane position of the corrugated pipe and limiting the length of a main reinforcement framework of the hidden cover beam;
fourthly, welding the hidden cover beam steel reinforcement framework sheets on the ground, and sequentially hanging the hidden cover beam steel reinforcement framework sheets to a specified position for installation;
note 1: the hidden cover beam longitudinal main rib framework pieces are in scattered states during hoisting, so that the framework pieces are particularly important for temporary support, each framework must be stably supported, and support materials can be processed by main rib waste materials.
Note 2: when the hidden cover beam framework piece is installed, a corrugated steel plane space needs to be avoided, and meanwhile, the ingot rib of the framework piece needs to be avoided from the position of a reserved hole channel of the external beam of the small box beam.
Installing hidden-cover beam stirrups which are large closed hoops, dividing the stirrups according to the relevant requirements of highway bridge and culvert construction technical specifications according to the construction conditions during actual construction, wherein the stirrups are required to be closed according to the specification requirements, and avoiding the positions of small box girder body outer beam reserved channels at the same time;
and sixthly, finishing the construction of transversely distributing the steel bars on the surface of the hidden cover beam and distributing the steel bars in the anchor notch of the hidden cover beam after binding the stirrups.
Note: and enough concrete pouring space should be reserved during construction of the anchor notch distribution steel bars.
Step five: hidden cover beam prestress corrugated pipe burying and external beam reserved hole channel arrangement
The hidden cover beam prestress corrugated pipes are arranged according to the design drawing requirements and are consistent with the cover beam process of the conventional prefabricated small box beam.
The hidden cover beam small box girder is characterized in that a reserved hole is formed in an external beam, a part of steel pipe with the inner diameter of 20mm is reserved during small box girder construction, the hidden cover beam section straight beam area steel pipe is connected with the small box girder reserved steel pipe (is wrapped) and is fixed on hidden cover beam steel bars through hanging bars.
Step six: hidden cover beam side form support
The side templates of the hidden cover beam are made of wood templates, and are installed through a climbing vehicle, and the process is consistent with the beam process of the conventional prefabricated small box beam.
Step seven: concrete pouring of hidden cover beam
The construction process of the concrete in the hidden capping beam area is consistent with that of the conventional capping beam, and the vibration effect of the concrete at the notch position of the hidden capping beam anchor needs to be paid special attention.
Step eight: stretching of prestressed first steel bundle of hidden cover beam
Note: the hidden cover beam prestress first steel bundle is mainly used for resisting the bending moment generated by the dead weight of the prefabricated small box beam and the dead weight of the hidden cover beam.
Step nine: temporary support system frame of hidden cover beam
The hidden cover beam area bracket system can be dropped according to the Chinese patent CN 201911002531.3.
Step ten: stretching of prestressed second steel bundle of hidden cover beam
Note 1: the second batch of prestressed steel bundles of the hidden cover beam are mainly used for resisting the bending moment effect generated by the second-stage dead load (bridge deck pavement, anti-collision railings and the like) and the live load of the automobile.
Note 2: the second batch of hidden cover beam prestressed steel bundles must be implemented after the hidden cover beam support system is relieved, otherwise, the prestress action generated by the first batch of hidden cover beam prestressed steel bundles can be combined with the second batch of hidden cover beam prestressed steel bundles under the condition of no dead load offset, so that the hidden cover beam structure system is damaged reversely.
Step eleven: small box girder hogging moment steel bundle tensioning
And the tensioning process of the steel beam in the hogging moment area of the small box girder is consistent with the conventional process for prefabricating the small box girder.
Step twelve: small box girder external beam construction and notch sealing
And after the construction of the hidden cover beam is finished, inserting the steel bundles outside the small box beam body, tensioning, and conveying tensioning equipment (single-hole top) and personnel to a beam bottom tensioning notch by using a climbing vehicle for operation during tensioning.
And after the external beam tensioning is finished, installing a notch suspended formwork by using a preformed hole in the early small box girder prefabricating stage, injecting high-strength grouting material by using a preformed grouting hole, and removing the suspended formwork after the high-strength grouting material reaches the strength.
Step twelve: small box girder body operation manhole closure
And closing the reserved manhole at the top of the small box girder after the construction of the prefabricated small box girder type hidden cover girder connected with the prestressed steel bundles is completed.
In general, the invention comprises 3 parts of construction of a tensioning end, corrugated pipe (providing a prestressed tendon penetration channel), steel strand installation, steel strand tensioning and grouting and the like during construction.
1.1 stretch-draw end construction
1.1.1 continuous end tension anchoring construction
The continuous end tensioning anchoring component is manufactured according to the requirement of a design drawing, the web plate inner steel plate, the web plate outer steel plate and the anchor bolt steel bar are welded to form a tensioning end anchoring structure, the tensioning backing plate and the web plate inner steel plate are welded to form a tensioning end integral structure, a welding seam between the web plate inner steel plate and the tensioning backing plate needs to be subjected to 100% detection of ultrasonic and magnetic powder, and the continuous end tensioning anchoring component can be used after the continuous end tensioning anchoring component is qualified.
Because the whole structure of the steel structure at the tensioning end is in contact with the air, the steel structure needs to be subjected to corrosion prevention measures such as galvanizing and the like after being welded and formed, and the durability of the steel structure is improved.
After the prefabricated small box girder bottom web plate steel bars are bound, a small box girder core mould is installed, then a tensioning end steel member is installed according to the designed position, and the core mould needs to be provided with holes at the position of the steel member. The web plate steel plate of the tensioning end steel component, particularly the inner web plate steel plate, must be parallel to the core die so as to ensure that the tensioning base plate is perpendicular to the web plate.
1.1.2 construction of simply supported end tensioning notch
The prefabricated small box girder structure simple support end longitudinal prestress structure stretching end based on the hidden bent cap is arranged at the position of a small box girder top plate to form a top plate stretching notch, the top plate stretching notch is provided with a pre-buried steel plate and a threaded steel bar according to design drawing construction stretching end, a part of corrugated pipes are pre-buried in a box chamber, and the later-stage corrugated pipes are connected with the residual corrugated pipes.
1.2 corrugated pipe and Steel Strand installation
After the small box girder is installed, firstly, the hidden type bent cap transverse main reinforcement construction is carried out, a stirrup space is reserved in the position of the corrugated pipe, then, the corrugated pipe and the steel beam are installed, and the small box girder installation method mainly comprises the following two steps:
1) and the plug plate of the small box girder at the continuous end is perforated in advance according to the design position, the linear corrugated pipe is installed to the tensioning base plates at the two ends, and the corrugated pipe is temporarily fixed on the hidden cover girder and the tenon constructional steel bar for ensuring the corrugated pipe line type.
2) The simple support end adopts a single-end tensioning P anchor structure, the corrugated pipes are arranged according to a design drawing and are connected with the pre-reserved corrugated pipes at the tensioning end, and the corrugated pipe joints are connected by adopting hot melting and are provided with prestressed steel beams.
1.3 stretch-draw grouting of steel bundle
And (3) after the hidden capping beam steel bar and the template project are finished, carrying out hidden capping beam and beam end tenon structural concrete pouring, and stretching prestress and grouting after the concrete strength reaches the design strength. And extra longitudinal prestress between the prefabricated box girders is provided, and the tightness of the male and female tooth structures of the hidden cover girder and the small box girder is provided, so that the shear-resistant bearing capacity of the longitudinal connecting structure is improved.

Claims (10)

1. The prefabricated small box girder type hidden bent cap connected with the prestressed steel bundles is characterized by comprising prefabricated small box girders arranged along a bridge direction, a cast-in-place hidden bent cap arranged along a transverse bridge direction and a prestressed system configured along the web direction of the prefabricated small box girders, wherein a prefabricated-cast-in-place interface in multi-projection tooth block engagement is arranged between the end head of each prefabricated small box girder and the cast-in-place hidden bent cap, and the prestressed system comprises an in-vivo prestressed system and an in-vitro prestressed system;
the in-vivo prestressed system comprises a plurality of in-vivo prestressed steel bundles, wherein the anchoring points of the in-vivo prestressed steel bundles are arranged at the end part of the web plate of the prefabricated small box girder and are distributed along the height direction of the web plate of the prefabricated small box girder;
the in-vitro prestressed system comprises a plurality of in-vitro prestressed steel bundles; an inclination angle alpha exists between each external prestressed steel beam and the web plate of the prefabricated small box girder;
when the prefabricated small box girder type hidden cover beam is positioned in a continuous section, the middle area of each external prestressed steel bundle is horizontally buried in the cast-in-place hidden cover beam and distributed along the height direction of the cast-in-place hidden cover beam, one end of each external prestressed steel bundle is anchored on the bottom plate of the prefabricated small box girder on one side of the cast-in-place hidden cover beam, and the other end of each external prestressed steel bundle is anchored on the bottom plate of the prefabricated small box girder on the other side of the cast-in-place hidden cover beam;
when the small box girder type hidden cover girder is in the simply supported section, one end of each external prestressed steel bundle is anchored on the top plate of the small box girder, and the other end of each external prestressed steel bundle is anchored in the cast-in-place hidden cover girder.
2. The precast small box girder hidden cover beam connected with prestressed steel beams as recited in claim 1, wherein when the precast small box girder hidden cover beam is in a continuous section, precast small box girders, namely a precast small box girder a and a precast small box girder b, are respectively arranged on two sides of the cast-in-place hidden cover beam; the prefabricated-cast-in-place interface between the end of the prefabricated small box girder a and the cast-in-place hidden cover girder is a prefabricated-cast-in-place interface a, and the prefabricated-cast-in-place interface between the end of the prefabricated small box girder b and the cast-in-place hidden cover girder is a prefabricated-cast-in-place interface b;
the middle area of each external prestressed steel beam is horizontally buried in the cast-in-place hidden cover beam and distributed along the height direction of the cast-in-place hidden cover beam, one end of each external prestressed steel beam penetrates through the prefabrication-cast-in-place interface a and then turns through the corresponding turning block a, and is finally anchored on the bottom plate of the prefabricated small box beam a, and the other end of each external prestressed steel beam penetrates through the prefabrication-cast-in-place interface b and turns through the corresponding turning block b, and is finally anchored on the bottom plate of the prefabricated small box beam b; the steering block a is installed on the web plate of the prefabricated small box girder a, and the steering block b is installed on the web plate of the prefabricated small box girder b.
3. The prestressed steel beam-connected precast small box girder hidden cover beam as claimed in claim 2, wherein the turning blocks a and b each comprise a web outer steel plate, a web inner steel plate, an anchor bolt steel bar and a tension pad plate; the web outside steel sheet is installed at the web inboard of prefabricated little case roof beam, and the inboard steel sheet of web passes through the crab-bolt reinforcing bar and is connected with web outside steel sheet, and the tensioning backing plate is connected with the inboard steel sheet of web, and external prestressing steel bundle passes the through-hole setting of seting up on the tensioning backing plate.
4. The precast small box girder type hidden cover beam connected with prestressed steel bundles according to claim 1, wherein when the precast small box girder type hidden cover beam is in a simply supported section, one end of each external prestressed steel bundle passes through a precast-cast-in-place interface and an anchor sealing plate in sequence, then is turned by a turning block and finally is anchored on a top plate of the precast small box girder;
the steering block comprises a web plate outer side steel plate, a web plate inner side steel plate, an anchor bolt steel bar and a tensioning base plate; the web outside steel sheet is installed at the web inboard of prefabricated little case roof beam, and the inboard steel sheet of web passes through the crab-bolt reinforcing bar and is connected with web outside steel sheet, and the tensioning backing plate is connected with the inboard steel sheet of web, and external prestressing steel bundle passes the through-hole setting of seting up on the tensioning backing plate.
5. The prestressed steel-beam-connected precast mini-box girder hidden cover beam as claimed in claim 3 or 4, wherein the number of the anchor bars is 4-6.
6. The precast small box girder type hidden cover beam connected with the prestressed steel bundles according to claim 1, wherein the precast-cast-in-place interface comprises an end head of the precast small box girder and a cast-in-place concrete joint meshed with the end head of the precast small box girder; wherein:
the end of the small prefabricated box girder comprises a box girder bottom plate end, a box girder top plate end and two box girder web plate ends positioned between the box girder bottom plate end and the box girder top plate end; the outer side surface of the end of the box girder bottom plate and the outer side surface of the end of the box girder top plate are positioned in the same plane; a plurality of web raised teeth are arranged on the outer sides of the ends of the web plates of the two box girders; the web convex teeth are arranged on the top of the web convex teeth, the upper end of the web convex teeth starts from the outer side surface of the end of the box girder top plate, the lower end of the web convex teeth crosses the connecting limit of the end of the box girder top plate and the end of the box girder web plate and ends at the outer side surface of the end of the box girder web plate, and the rest web convex teeth are arranged on the outer side surface of the end of the box girder web plate.
7. The prestressed tendon-joined precast trabecular hidden canopy beam of claim 6, wherein the number of web lobes matches the number of in vitro prestressed tendons.
8. The prestressed steel-beam-connected precast mini-box girder hidden cover beam as claimed in claim 7, wherein the number of web convex teeth provided at the end of the web of the single-sided box girder is 3, and the number of the external prestressed steel beams on the single side is 3.
9. The prestressed steel-strand-connected precast small box girder hidden cover girder according to claim 7, wherein the number of the in-body prestressed steel strands provided in the precast small box girder is 4; correspondingly, 4 individual internal prestressed steel strand anchoring points are arranged at the end part of the prefabricated small box girder web plate along the height direction.
10. The construction method of the precast mini box girder type hidden cover beam connected by the prestressed steel bundles according to claim 1 is characterized by comprising the following construction steps:
step one, factory manufacturing of prefabricated small box girder
I, construction forming of conventional section of prefabricated small box girder
1.1 preparation of the bench
Respectively arranging corresponding notch templates according to the beam bottom tensioning notch position and the operation manhole position of the prefabricated small box girder, so that after the conventional section of the prefabricated small box girder is constructed and molded, a beam bottom tensioning notch is formed on a bottom plate of the conventional section of the prefabricated small box girder, and an operation manhole is formed on a top plate of the conventional section of the prefabricated small box girder; an end die is arranged at the end part of the conventional section of the prefabricated small box girder so as to obtain a multi-protrusion type tooth block end structure meeting the design requirement after the conventional section of the prefabricated small box girder is cast and molded;
1.2 binding the steel bars of the conventional section of the prefabricated small box girder
Binding top, bottom and web steel bars of the conventional section of the prefabricated small box girder, and then installing a prestressed corrugated pipe at the preset position of the prestressed corrugated pipe;
the longitudinal main ribs at the top and the bottom of the bound conventional section of the prefabricated small box girder can extend out of the end part of the prefabricated small box girder after the conventional section of the prefabricated small box girder is cast and molded;
1.3 Embedded steering Block Embedded parts
Arranging a steering block embedded part at a preset position of the conventional section of the prefabricated small box girder, and welding and fixing the steering block embedded part and the common steel bars of the conventional section of the prefabricated small box girder in a spot welding manner; the steering block embedded part is an assembly part consisting of a steering block embedded plate and anchor bolt reinforcing steel bars, the number of the steering block embedded plate is two, the two steering block embedded plates are respectively corresponding to a web plate outer side steel plate and a web plate inner side steel plate, and the anchor bolt reinforcing steel bars are connected between the web plate outer side steel plate and the web plate inner side steel plate;
the width of a web plate of the conventional section of the prefabricated small box girder at the embedded position of the steering block embedded part is the same as the length of the steering block embedded plate, and the steering block embedded plate close to the inner web plate side is closely attached to the prefabricated small box girder inner film;
adjusting the distribution of stirrups at the positions of the steering block embedded parts to adjust the stirrups at the positions of the steering block embedded parts to the two sides of the steering block embedded plate;
II, welding the steel plate with the outside leakage of the steering block
In the step I, after the conventional section of the prefabricated small box girder is constructed and molded, a core mold of the conventional section of the prefabricated small box girder is dismantled, and then a steel plate with an outward leakage of a steering block is welded at a preset position on a steel plate on the inner side of a web plate on the outer side of the embedding position of an embedded part of the steering block, wherein the steel plate with the outward leakage of the steering block is vertical to the steel plate on the inner side of the web plate, and the steel plate with the outward leakage of the steering block is a tensioning base plate;
III, constructing the solid cast-in-place section of the beam end
After the tensioning and grouting of the prestressed steel beams of the conventional section of the prefabricated small box girder are completed, the construction of the solid cast-in-place section of the girder end is carried out, and the construction requirements are met:
3.1, welding and fixing the steel bars of the solid cast-in-place section at the beam end with the outer leakage main bars of the conventional section of the prefabricated small box girder;
3.2, arranging a plugging plate used for an inner membrane of the solid cast-in-place section at the beam end on the outer side of the outer leakage steel plate;
3.2, combining the design requirement and the actual position of the steering block, and pre-burying a steel pipe used as a reserved hole position of the external beam;
step two: hidden cover beam temporary support system installation
Mounting a temporary supporting system of the hidden cover beam on a construction site;
step three: prefabricated small box girder hoisting
In a construction site, a hidden cover beam temporary supporting system is matched, and the prefabricated small box beam obtained in the step one is hoisted in place;
step four: hidden cover beam bottom/end mould laying and reinforcing steel bar binding
Laying a hidden cover beam bottom/end mould and binding steel bars according to design requirements on a construction site;
step five: hidden cover beam prestress corrugated pipe burying and external beam reserved hole channel arrangement
Burying a pre-stressed corrugated pipe and an external beam reserved hole channel of the hidden cover beam according to design requirements; wherein: the external bundle reserved hole channel in the hidden cover beam is a straight bundle, is connected with the steel pipe embedded in the step 3.2, and is fixed on the hidden cover beam steel bar by adopting a hanging bar;
step six: hidden cover beam side form support
Step seven: concrete pouring of hidden cover beam
Step eight: stretching of prestressed first steel bundle of hidden cover beam
Stretching a first batch of prestressed steel bundles of the hidden cover beam to resist the action of bending moment generated by the self weight of the prefabricated small box girder and the self weight of the hidden cover beam;
step nine: temporary support system frame of hidden cover beam
Disassembling the temporary supporting system of the hidden cover beam;
step ten: stretching of prestressed second steel bundle of hidden cover beam
Tensioning the hidden cover beam to prestress the second steel bundle so as to resist bending moment generated by second-stage dead load and automobile live load; the second-stage constant load comprises the dead weight of bridge deck pavement and an anti-collision railing;
step eleven: small box girder hogging moment steel bundle tensioning
Step twelve: small box girder external beam construction and notch sealing
Inserting external prestress steel beams and tensioning; then closing the tensioning slot;
step thirteen: small box girder body operation manhole closure
And closing the operation manhole on the top plate of the prefabricated small box girder.
CN202110297475.1A 2021-03-19 2021-03-19 Prestressed steel beam connected prefabricated small box girder type hidden cover beam and construction method thereof Active CN113512932B (en)

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