Lightweight precast small box girder structure with combined tensioning and construction method

Abstract

The present invention discloses a lightweight precast small box girder structure with hybrid tensioning and a construction method. The small box girder includes a top plate, webs, and a bottom plate; both the webs and the bottom plate adopt a constant thickness structure across the span; the bottom plate is provided with steel strands; the steel strands are arranged linearly and constructed by the pretensioning process; the webs are provided with multiple bundles of slow-bonding steel strands; each slow-bonding steel strand is arranged in a curve on the projection of the corresponding web in the vertical plane and is anchored at the beam end of the corresponding beam; the diameter of each slow-bonding steel strand is larger than that of the steel strand, and it is constructed by the post-tensioning process. The construction steps are as follows: 1. Prefabricate a single beam; 2. Erect a single beam; 3. Cast the transverse diaphragm between the beams in-situ; 4. Cast the wet joint of the bridge deck between the beams in-situ; 5. Cast the pavement in-situ. The present invention can reduce the structural weight of the small box girder by about 15% compared with the traditional structure, reduce the economy by about 10% compared with the original traditional small box girder, is more flexible in construction, has less impact on the site, and the weight reduction is also more conducive to the lightweight and prefabricated assembly of the lower structure.

Description

Technical Field

[0001] The present invention relates to the technical field of box girder construction, and particularly relates to a lightweight precast small box girder structure with hybrid tensioning and a construction method thereof. Background Art

[0002] Due to advantages such as mature technology, relatively economical cost, and convenient construction, precast small box girders have become a conventional precast bridge structure form commonly used in newly built elevated bridges in cities at present, which is constructed by the post-tensioning method.

[0003] At present, the side beams of precast small box girders are mostly precast and assembled together with anti-collision guardrails and installed integrally on site. Although problems such as the safety of anti-collision guardrail construction and on-site imaging are solved, due to the slightly larger self-weight of a single beam, and the overall precast together with the anti-collision guardrail, the weight increases, the construction flexibility is reduced, the requirements for mechanical equipment are increased, and the on-site impact is also correspondingly increased.

[0004] Therefore, how to reduce the weight of small box girders and improve construction flexibility and construction efficiency has become a technical problem that needs to be urgently solved by those skilled in the art. Summary of the Invention

[0005] In view of the above-mentioned defects of the prior art, the present invention provides a lightweight precast small box girder structure with hybrid tensioning and a construction method thereof, and the achieved purpose is to reduce the weight of small box girders and improve construction flexibility and construction efficiency.

[0006] To achieve the above purpose, the present invention discloses a lightweight precast small box girder structure with hybrid tensioning, and the small box girder includes a top plate, a web, and a bottom plate.

[0007] Wherein, both the web and the bottom plate adopt a medium-thickness structure across the span;

[0008] The bottom plate is provided with a plurality of steel strands; each steel strand is arranged in a straight line and constructed by the pretensioning method;

[0009] The web is provided with multiple bundles of slow-bonding steel strands; the projection of each slow-bonding steel strand on the vertical plane of the corresponding web is arranged in a curve and anchored at the beam end of the corresponding beam;

[0010] The diameter of each slow-bonding steel strand can be larger than the diameter of the pretensioning steel strand and is constructed by the post-tensioning method.

[0011] Preferably, the top plate, the web, and the bottom plate are all made of C60 to C80 self-compacting high-performance concrete.

[0012] Preferably, the diameter of the pretensioning steel strands is all 15.2.

[0013] Preferably, an anchorage block made of UHPC high-strength and tough concrete is adopted for the anchorage area where all the slow-bonded steel strands are anchored at the beam end.

[0014] More preferably, the anchorage block is a precast member, and connecting steel bars matching the bottom of the beam are reserved.

[0015] The present invention also provides a construction method for a lightweight precast small box girder structure with hybrid tensioning, and the steps are as follows:

[0016] Step 1: Precast single beam;

[0017] Step 2: Erect single beam;

[0018] Step 3: Cast in-situ transverse diaphragm between beams;

[0019] Step 4: Wet joint the in-situ bridge deck between beams;

[0020] Step 5: Cast in-situ pavement.

[0021] Preferably, in the step 1, the precast single beam includes constructing the steel strands on the bottom plate by the pretensioning process; then, constructing all the slow-bonded steel strands in the web by the post-tensioning process.

[0022] Advantages of the present invention:

[0023] The application of the present invention can reduce the structural weight of the small box girder by about 15% compared with the traditional structure, reduce the economy by about 10% compared with the original traditional small box girder, the construction is more flexible, the on-site impact is smaller, and the reduction of the upper structure weight of the small box girder is also more conducive to the lightweight and prefabrication of the bridge lower structure.

[0024] The following will further illustrate the concept, specific structure and technical effects generated by the present invention with reference to the drawings, so as to fully understand the purpose, features and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A structural schematic diagram showing an embodiment of the present invention.

[0026] Figure 2 Showing the present invention Figure 1 The sectional structure schematic diagram at AA in.

[0027] Figure 3 Showing the present invention Figure 1 The sectional structure schematic diagram at BB in. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0028] Embodiment

[0029] As Figures 1 to 3As shown, the structure of the lightweight precast small box girder with hybrid tensioning. The small box girder includes a top plate 7, a web 1, and a bottom plate 2. Both the web 1 and the bottom plate 2 adopt a medium-thickness structure across the span.

[0030] The bottom plate 2 is provided with a number of steel strands 3. Each steel strand 3 is arranged in a straight line and constructed by the pretensioning process.

[0031] The web 1 is provided with multiple bundles of slow-bonding steel strands 4. Each slow-bonding steel strand 4 is arranged in a curve on the projection of the corresponding web 1 in the elevation and is anchored at the beam end 6 of the corresponding beam.

[0032] The diameter of each slow-bonding steel strand 4 can be larger than that of the pretensioning steel strand 3 and is constructed by the post-tensioning process.

[0033] The principle of the present invention is that the steel strands 3 are set on the bottom plate 2 by the pretensioning process, and multiple slow-bonding steel strands 4 are set on the web 1 by the post-tensioning process. There is no need to reserve large-diameter ducts in the bottom plate 2 and the web 1, and the thickness reduction at the connection position of the bottom plate 2 and the web 1 to the beam end 6 can be cancelled.

[0034] In some embodiments, the top plate 7, the web 1, and the bottom plate 2 are all made of C60 to C80 self-compacting high-performance concrete.

[0035] In some embodiments, the diameter of the pretensioning steel strands is 15.2.

[0036] In some embodiments, an anchorage block 5 precast with UHPC high-strength and tough concrete is set in the anchorage area where all the slow-bonding steel strands 4 are anchored at the beam end 6.

[0037] In some embodiments, the anchorage block 5 is a precast member with connecting steel bars reserved to match the beam bottom of the beam.

[0038] Due to the relatively large local stress at the position under the anchor of the prestress tensioning end of the slow-bonding steel strand 4 to the beam end 6, an anchorage block 5 precast with UHPC high-strength and tough concrete is set in the anchorage area where all the slow-bonding steel strands 4 are anchored at the beam end 6 to improve the stress, simplify the anchorage structure, that is, there is no anchor plate and no grouting for sealing, and at the same time, it can also serve as the formwork for the web 1 at the beam end 6.

[0039] The present invention also provides a construction method for the structure of the lightweight precast small box girder with hybrid tensioning, and the steps are as follows:

[0040] Step 1: Single beam precasting;

[0041] Step 2: Single beam erection;

[0042] Step 3: Cast-in-place transverse diaphragms between beams;

[0043] Step 4: Cast-in-place wet connection of the bridge deck between beams;

[0044] Step 5, cast-in-place paving.

[0045] In some embodiments, single-beam prefabrication includes constructing steel strands 3 on the bottom plate 2 using the pretensioning process; afterwards, all the slow-bonding steel strands 4 are constructed in the web 1 using the post-tensioning process.

[0046] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning, or limited experiments based on the concept of the present invention on the basis of the prior art should fall within the protection scope determined by the claims.

Claims

1. Construction method of lightweight precast small box girder structure with combined tensioning. The small box girder includes a top plate (7), a web (1), and a bottom plate (2); it is characterized in that, Both the web (1) and the bottom plate (2) adopt a cross-medium-thickness structure; The bottom plate (2) is provided with a number of steel strands (3); each of the steel strands (3) is arranged in a straight line and constructed by the pretensioning method; The web (1) is provided with multiple bundles of slow-bonding steel strands (4); in the projection of each of the slow-bonding steel strands (4) on the vertical surface of the corresponding web (1), it is arranged in a curve and anchored at the beam end (6) of the corresponding beam; The diameter of each of the slow-bonding steel strands (4) can be larger than the diameter of the pretensioning steel strands (3) and is constructed by the post-tensioning method; The anchoring area for anchoring all the slow-bonding steel strands (4) at the beam end (6) is provided with an anchoring block (5) precast with UHPC high-strength and tough concrete; It includes the following construction steps: Step 1, single-beam prefabrication; Single-beam prefabrication includes constructing the steel strands (3) on the bottom plate (2) by the pretensioning method; afterwards, all the slow-bonding steel strands (4) are constructed in the web (1) by the post-tensioning method; Step 2, single-beam erection; Step 3, cast-in-place transverse diaphragm between beams; Step 4, cast-in-place wet connection of the bridge deck between beams; Step 5, cast-in-place paving.

2. The construction method of the lightweight precast small box girder structure with hybrid tensioning according to claim 1, characterized in that The top plate (7), the web (1) and the bottom plate (2) are all made of C60 to C80 self-compacting high-performance concrete.

3. The construction method of the lightweight precast small box girder structure with hybrid tensioning according to claim 1, characterized in that, The anchoring block (5) is a precast part and is reserved with connecting steel bars matching the bottom of the beam.

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