CN107984610B - A prestressed small box girder manufacturing method - Google Patents

Abstract

The invention discloses a method for manufacturing a prestressed small box girder. The prestressed small box girder is divided into an open channel section in the middle and anchor sections located at both ends. Reserve the open slots for arranging the prestressed tendons, and preset two tension holes for tensioning the prestressed tendons at the bottom of the open slots at a certain distance; The prestressed tendons after beam penetration are fixedly connected to the reinforcement cages of the anchorage sections at both ends, and the anchorage sections at both ends are poured. After the anchorage sections are poured and solidified, they are drawn by tensioning equipment through the two transverse tension holes at the bottom of the open groove. The prestressed tendons are stretched downward, and the tension and elongation values of the prestressed tendons are checked to meet the requirements; the open grooves in the open groove section are poured, and the third pouring is completed. After curing, the tensioning equipment is removed to complete the entire prestressed tendons. Fabrication of stressed small box girders. The invention makes the grout more compact in the prestressed stretching of the small box girder, and improves the utilization rate of the prestressed tendons at the same time.

Description

A prestressed small box girder manufacturing method

technical field

The invention relates to the field of bridge construction, and relates to a method for manufacturing a small box girder, in particular to a method for manufacturing a prestressed small box girder.

Background technique

Prefabricated continuous small box girders are widely used in small and medium-span bridges in my country because of their simple structure, convenient construction, low cost, and time-saving construction. In this type of prefabricated beams, prestressed tendons are an essential component. The relatively mature tensioning methods in prestressed construction at this stage are post-tensioning and pre-tensioning. According to whether the prestressed tendon is in contact with concrete, it can be divided into bonded prestressed concrete and unbonded prestressed concrete. In the prefabrication of continuous small box girders, the post-tensioning method is adopted for the prestressed tendons, and the bonded form is bonded. But adopt the post-tensioning method, the following problems will occur with the existing construction technology: (1) the tension force at the end of the prestressed tendon is relatively large, while the tension force at the mid-span is often small; (2) after the prestressed tendon is stretched , there is a situation where the channel grouting is not dense, which affects the quality of the beam.

Contents of the invention

Aiming at the existing prestressed prefabricated small box girder construction technology, the purpose of the present invention is to avoid the adverse effects brought by the tensioning method of the prior art, and integrate pre-tensioning and post-tensioning, external beam and internal beam, and bonding Based on the respective advantages of unbonded prestressed concrete, a new type of prestressed tensioning technology—transverse tension method prestressed construction is proposed.

Another object of the present invention is to provide a method for constructing a prestressed small box girder with a simple structure and safe construction.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A method for manufacturing a prestressed small box girder, characterized in that: the prestressed small box girder is divided into an open channel section in the middle and anchor sections located at both ends of the open channel section, and the entire prestressed small box girder is poured in three times to complete, specifically as follows:

Step 1. First pour the open channel section, reserve an open channel for arranging prestressed tendons on the prestressed small box girder web of the open channel section, and preset two at the bottom of the open channel for tensioning Tension holes for prestressed tendons;

Step 2. Thread the prestressed tendons in the open grooves reserved in the open groove section, connect the prestressed tendons after the bundles with the reinforcement cages of the anchorage sections at both ends, and pour the anchorage sections at both ends to complete the second secondary pouring;

Step 3. After the second pouring and solidification, stretch the prestressed tendons downward with tensioning equipment through the two transverse stretching holes at the bottom of the open groove, and check that the tension and elongation values of the prestressed tendons meet the requirements;

Step 4: Concrete the open channel in the open channel section, complete the third pouring, remove the tensioning equipment after solidification, and complete the production of the entire prestressed small box girder.

As an improvement, the pouring process of the open channel section is as follows: first bind the bottom plate and web steel bars of the open channel section, hang the steel cage into the outer formwork, and put it into the air bag reserved for the open channel, after the air bag is inflated to the required air pressure, Install the inner formwork, tie the roof steel bars, and set reserved holes with pipes at intervals between the roof steel bars for the third pouring of the open channel and the installation of tensioning equipment, and reserve two holes at the bottom plate of the open channel In the tension hole where the prestressed tendon is stretched horizontally, after checking that the steel formwork is correct, the first concrete is poured to complete the pouring of the open channel section.

As an improvement, in step 2, a positioning steel plate for positioning the prestressed tendon is provided at the anchorage section at the junction with the open groove section, specifically, according to the design requirements of the prestressed tendon, a plurality of corresponding positioning holes are provided on the positioning steel plate , each prestressed tendon passes through one of the positioning holes, and the positioning steel plate and the reinforcement cage of the anchorage section are welded together.

As an improvement, in step 2, locate the steel bars from the top of the beam in the anchorage section to hook the prestressed tendons, keep the prestressed tendons in the anchorage section in a straight state, and tie the prestressed tendons to the reinforcement cage of the anchorage section. Section pouring, complete the second pouring.

As an improvement, the bottom plate and the web around the tension hole on the open channel section are respectively provided with reinforcing steel mesh.

As an improvement, when binding the reinforcement cage of the open channel section, the distance between the holes reserved by pipes on the roof reinforcement of the open channel section is 1.5-3m, and the two reserved holes correspond to the two tension holes on the bottom plate.

As an improvement, before the anchoring section is poured, after the prestressed tendons pass through, the prestressed tendons are supported by temporary positioning steel bars at intervals in the open groove, and the temporary positioning steel bars are removed after the anchoring section is poured and solidified.

As an improvement, after the prestressed tendon is stretched horizontally, the prestressed tendon is divided into an inclined section and a straight section in the open groove, and the ratio of the descending distance of the prestressed tendon to the length of the inclined section is in the range of 1:4.5~1 :6.

As an improvement, the concrete for the third pouring of the open channel is micro-expansion fine stone concrete with a grade higher than the strength of the concrete for the first two pouring of the open channel section and the anchor section.

As an improvement, the tensioning equipment includes a tensioning rod, a pressure bearing plate, an anchor and a jack. First, the top of the tensioning rod is fixedly connected to the pressure bearing plate, and then the tensioning rod is lowered from the top of the open groove. There are at least two tensioning rods. And symmetrically distributed on both sides of the prestressed tendons, the lower end of the tension rod protrudes from the tension hole at the bottom of the open groove, and then a steel gasket is placed between the pressure bearing plate and the prestressed tendon, and the bottom of the tension rod and the jack are installed. A wedge-shaped pressure bearing plate is set between the jack and the bottom plate of the open groove section. The upper surface of the wedge-shaped pressure bearing plate is parallel to the bottom plate of the open groove section, and the lower surface is perpendicular to the tension rod. After the tension meets the requirements, pour the open groove, remove the jack and wedge-shaped pressure bearing plate after the open groove is poured and solidified, cut off the tension rod protruding from the bottom plate, and close the tension hole.

The beneficial effects of the present invention are:

(1) The biggest defect of post-tensioning construction is that the pipeline grouting is prone to non-compacting, which affects the quality of the beam. Therefore, the horizontal tension method is changed to pipe grouting to reserve open grooves to pour concrete, so that the quality of the beams can be better controlled.

(2) When the post-tensioning method is used, the prestressed tendons are uneven in tension and the utilization rate of the central prestressed tendons is low when the prestressed tendons are long, while the transverse tension method is used to stretch the prestressed tendons in the middle of the beam span. Tensile effect, it has been proved by experiments that the utilization rate of prestressed tendons can be as high as 80% to 90%.

(3) The post-tensioning method requires anchors to fix the prestressed tendons, while the transverse-tensioning method uses the bonded self-anchor of the pre-tensioning method to save anchors; at the same time, the tension required by the transverse-tensioning method is much smaller than that of post-tensioning Jacks with a smaller tonnage can be used for the tensile force of the method; the horizontal tension method is used to stretch from the lower part of the box girder, and the prestressed beams at both ends do not need to extend out of the beam body to obtain a tensioning operation space, saving a certain amount of prestressed tendons.

(3) The present invention solves the problem of insufficient grouting in the prestressed stretching of the existing small box girder, reduces the stress loss of the prestressed tendons, improves the utilization rate of the prestressed tendons, and effectively reduces the tension force. The invention has simple structure and safe construction, and is mainly used for the construction of prestressed small box girders with prestressed tension at the bottom of the beams.

Description of drawings

Figure 1 is a top view of the prestressed small box girder.

Fig. 2 is a sectional view of the prestressed small box girder in Fig. 1;

Among them, A-A is the cross-sectional view of the anchoring section in Figure 1, and B-B is the cross-sectional view of the open groove section in Figure 1.

Fig. 3 is a schematic diagram of the prestressed tendons of the prestressed small box girder passing through and stretched.

Figure 4 is a schematic diagram of the distribution of reinforcing steel mesh in the open channel section of a prestressed small box girder.

Figure 5 is a schematic diagram of the use of tensioning equipment.

Fig. 6 is a schematic top view of the reserved holes on the left half of the prestressed small box.

Fig. 7 is a bottom view schematic diagram of the setting of the tension holes on the left half of the prestressed small box.

1-open channel section, 2-anchor section, 3-prestressed tendons, 4-top plate of open channel section, 5-web plate of open channel section, 6-bottom plate of open channel section, 7-top plate of anchor section, 8-bottom plate of anchor section , 9-web plate of anchor section, 10-positioning steel plate, 11-web reinforcement mesh, 12-bottom plate reinforcement mesh, 13-open groove, 14-tension hole, 15-hole, 16-P anchor extrusion sleeve , 17-pressure bearing plate, 18-steel gasket, 19-tension rod, 20-wedge bearing plate, 21-anchor, 22-jack, 23-reinforcing steel bar for anchorage section.

Detailed ways

The present invention will be further described below by non-limiting embodiment:

A kind of prestressed small box girder manufacturing method, as shown in Figure 1, this prestressed small box girder is divided into the open groove section 1 in the middle and the anchorage section 2 that is positioned at the open groove section 1 two ends, and the whole prestressed small box girder is divided into The pouring was completed three times, as follows:

Step 1. First pour the open channel section 1, reserve the open channel 13 for arranging the prestressed ribs 3 on the prestressed small box girder web of the open channel section 1, and preset two holes at the bottom of the open channel 13 at a distance. A tension hole 14 for tensioning the prestressed tendons 3;

Step 2, thread the prestressed tendons 3 in the open groove 13 reserved in the open groove section 1, connect the threaded prestressed tendons 3 with the reinforcement cages of the anchorage sections 2 at both ends, and pour the anchorage bars at both ends. Section 2, complete the second pouring;

Step 3. After the second pouring and solidification, stretch the prestressed tendons 3 downward through the two horizontal stretching holes at the bottom of the open groove 13, and check that the tension and elongation values of the prestressed tendons 3 meet the requirements. ;

Step 4: Concrete the open channel 13 in the open channel section 1, complete the third pouring, remove the tensioning equipment after curing, and complete the production of the entire prestressed small box girder.

The pouring process of the open channel section 1 is as follows: first bind the bottom plate and web steel bars of the open channel section 1, hoist the reinforcement cage into the outer formwork, and put the air bag reserved for the open channel 13 into it, and after the air bag is inflated to the required air pressure, Install the inner formwork, bind the steel bars of the roof, and set reserved holes 15 with PVC pipes at intervals of 2m at the steel bars of the roof for the third pouring of the open channel 13 and the installation of tensioning equipment, at the bottom plate of the open channel 13 Two tension holes 14 are reserved for the transverse tension of the prestressed tendons 3. After checking that the steel formwork is correct, the first concrete is poured, and the pouring of the open channel section 1 is completed. After pouring, the air bag is deflated and taken out to form the open channel 13.

In step 2, a positioning steel plate 10 for positioning the prestressed tendons 3 is provided at the anchorage section 2 at the junction with the open channel section 1, specifically, according to the design requirements of the prestressed tendons 3, multiple corresponding Each prestressed tendon 3 passes through one of the positioning holes to ensure accurate positioning of the prestressed tendons 3. The positioning steel plate 10 is welded or tied together with the web steel cage of the anchorage section 2, and the positioning steel plate 10. The thickness is about 30 mm, and the distance between adjacent prestressed tendons 3 meets the specification requirements.

In step 2, locate the steel bars under the beam top in the anchorage section 2 to hook the prestressed tendons 3, keep the prestressed tendons 3 in the anchorage section 2 in a straight state, and bind the prestressed tendons 3 to the reinforcement cage of the anchorage section 2, After that, the anchorage section 2 is poured to complete the second pouring.

The bottom plate and the web around the tension hole 14 on the open channel section 1 are respectively provided with a bottom plate reinforcing steel mesh 12 and a web strengthening steel mesh 11, so as to ensure that the concrete surface of the bottom plate and the web when the prestressed tendons 3 are stretched transversely Cracks do not appear.

When binding the open channel section 1 reinforcement cage, on the open channel section top plate 4 steel bars, the hole 15 spacing reserved with the pipeline is 1.5-3m, and the present embodiment is 2m, wherein two of the reserved holes 15 are connected with the two holes on the bottom plate. Tension holes 14 correspond.

Before the anchorage section 2 is poured, after the prestressed tendons 3 are threaded, use temporary positioning steel bars to support the prestressed tendons 3 at intervals of 4m in the open groove 13, so as to ensure that the prestressed tendons 3 meet the straight line required by the design before tensioning position, after the anchor section 2 is poured and solidified, the temporary positioning reinforcement is removed, and the two ends of the prestressed tendon 3 are tied to the reinforcement cage of the anchor section web 9 .

After the prestressed tendon 3 is stretched transversely, the prestressed tendon 3 is divided into an inclined section and a straight section in the open groove 13, wherein the ratio of the descending distance of the prestressed tendon 3 transversely stretched to the length of the inclined section ranges from 1:4.5 to 1:6.

The concrete for the third pouring of the open channel 13 is micro-expansion fine stone concrete one level higher than the strength of the concrete for the first two pouring of the open channel section 1 and the anchor section 2 .

The tensioning equipment used in the above-mentioned transverse tension method prestressed small box girder manufacturing method includes a tension rod 19, a pressure bearing plate 17, an anchor 21 and a jack 22. First, the top of the tension rod 19 and the pressure bearing plate 17 are passed through the P anchor extrusion sleeve 16 are fixedly connected, and then the tension rod 19 is lowered from the top of the open groove 13. There are at least two tension rods 19, and they are symmetrically distributed on both sides of the prestressed tendon 3. The lower end of the tension rod 19 extends from the tension hole 14 at the bottom of the open groove 13. Afterwards, a steel gasket 18 is placed between the pressure-bearing plate 17 and the prestressed tendon 3, the bottom of the tension rod 19 and the jack 22 are installed, and a wedge-shaped pressure-bearing plate 20 is set between the jack 22 and the bottom plate 6 of the open groove section. The upper surface of the wedge-shaped pressure bearing plate 20 is parallel to the bottom plate 6 of the open groove section, and the lower surface is perpendicular to the tension rod 19. Finally, the jack 22 is started to stretch the prestressed tendons 3 transversely. After the groove 13 and the open groove 13 are poured and solidified, the jack 22 and the wedge-shaped pressure bearing plate 20 are removed, the tension rods 19 protruding from the bottom plate 6 of the open groove section are cut off, and the tension holes 14 are closed.

The length of the anchoring section 2 should meet the minimum length required for the bonding and anchoring of the prestressed tendon 3. The specific size is determined according to the structure of the beam body. The length of the open groove section 1 is the remaining length after subtracting the anchoring sections 2 at both ends of the beam. Real-time supervision of the construction quality before and after the box girder construction is completed. Other parts of this embodiment adopt the prior art.

Claims (6)

1. A prestressed small box girder manufacturing method, characterized in that: the prestressed small box girder is divided into an open channel section in the middle and an anchor section positioned at the two ends of the open channel section, and the whole prestressed small box girder is poured in three times and completed ,details as follows: Step 1. First pour the open channel section, reserve an open channel for arranging prestressed tendons on the prestressed small box girder web of the open channel section, and preset two at the bottom of the open channel for tensioning Tension holes for prestressed tendons; Step 2. Thread the prestressed tendons in the open grooves reserved in the open groove section, connect the prestressed tendons after the bundles with the reinforcement cages of the anchorage sections at both ends, and pour the anchorage sections at both ends to complete the second secondary pouring; Step 3. After the second pouring and solidification, stretch the prestressed tendons downward with tensioning equipment through the two transverse stretching holes at the bottom of the open groove, and check that the tension and elongation values of the prestressed tendons meet the requirements; Step 4, pouring the open channel in the open channel section, completing the third pouring, removing the tensioning equipment after solidification, and completing the production of the entire prestressed small box girder; The pouring process of the open channel section is as follows: first bind the bottom plate and web steel bars of the open channel section, hoist the reinforcement cage into the outer formwork, and put it into the air bag reserved for the open channel, and install the inner formwork after the air bag is inflated to the required air pressure , tie the top plate reinforcement, and at the same time, set reserved holes with pipes at intervals at the roof reinforcement for the third pouring of the open channel and installation of tensioning equipment, and reserve two at the bottom of the open channel for prestressing For the tension hole where the reinforcement is stretched horizontally, after checking that the reinforcement template is correct, pour the first concrete and complete the pouring of the open channel section; In step 2, a positioning steel plate for positioning the prestressed tendon is provided at the anchorage section at the junction with the open groove section, specifically, according to the design requirements of the prestressed tendon, a plurality of corresponding positioning holes are set on the positioning steel plate, each The prestressed tendon passes through one of the positioning holes, and the positioning steel plate is welded together with the reinforcement cage of the anchorage section; In step 2, locate the steel bars from the top of the beam at the anchorage section to hook the prestressed tendons, keep the prestressed tendons in the anchorage section in a straight state, bind the prestressed tendons to the reinforcement cage of the anchorage section, and then pour the anchorage section , complete the second pouring; Before the anchoring section is poured, after the prestressed tendons have passed through the beam, the prestressed tendons are supported by temporary positioning steel bars at intervals in the open groove, and the temporary positioning steel bars are removed after the anchoring section is poured and solidified. 2. The manufacturing method of a prestressed small box girder according to claim 1, characterized in that: the bottom plate and the web around the tension hole on the open channel section are respectively provided with reinforcing steel mesh. 3. a kind of prestressed small box girder manufacturing method as claimed in claim 1 is characterized in that: when tying open channel section reinforcement cage, on the open channel section top plate reinforcing bar, the hole spacing reserved with pipeline is 1.5-3m, Two of the reserved holes correspond to the two tension holes on the bottom plate. 4. A kind of prestressed small box girder manufacturing method as claimed in claim 1, is characterized in that: after the prestressed tendon is stretched transversely, the prestressed tendon is divided into an inclined section and a straight section in the open groove, wherein the prestressed tendon The ratio of the descending distance of the transverse stretching of the rib to the length of the inclined section ranges from 1:4.5 to 1:6. 5. The manufacturing method of a kind of prestressed small box girder as claimed in claim 1, characterized in that: the concrete for the third pouring of the open channel is a slightly higher grade concrete than the strength of the concrete for the first two pouring of the open channel section and the anchorage section. Expanded fine stone concrete. 6. The manufacturing method of a prestressed small box girder as claimed in any one of claims 1 to 5, wherein the tensioning equipment includes a tensioning rod, a pressure bearing plate, an anchor and a jack, and the tensioning rod is first The top is fixedly connected with the pressure bearing plate, and then the tension rods are lowered from the top of the open groove. There are at least two tension rods, which are symmetrically distributed on both sides of the prestressed tendons. The lower ends of the tension rods protrude from the tension holes at the bottom of the open groove. Place a steel gasket between the pressure bearing plate and the prestressed tendon, install the bottom of the tension rod and the jack, set a wedge-shaped pressure bearing plate between the jack and the bottom plate of the open groove section, and the upper surface of the wedge-shaped pressure bearing plate and the bottom plate of the open groove section Parallel, the lower surface is perpendicular to the tension rod, and finally the jack is started to stretch the prestressed tendon laterally. After the prestressed tendon is stretched to meet the requirements, the open groove is poured. The tension rod outside the bottom plate is cut off, and the tension hole is closed.