JP7629387B2 - Joining structure and joining method - Google Patents

Description

The present invention relates to a joining structure and joining method for joining a steel girder to a precast deck installed on the upper flange of the steel girder.

Conventionally, the joining structure and joining method disclosed in Patent Document 1 below join a steel girder to a precast deck installed on the upper flange of the steel girder. In this joining structure and joining method, a stud dowel is provided on the upper surface of the flange of the steel girder. An insert nut is embedded in the underside of the precast deck, and a bolt is attached to this insert nut so that it protrudes downward. When joining the precast deck to the steel girder, the precast deck is installed on the upper surface of the flange in a positional relationship such that the lower end of the bolt is located below the upper end of the stud dowel, and a filler is filled between the upper surface of the upper flange and the underside of the precast deck so as to embed the stud dowel and bolt.

Patent Publication No. 2021-1457

However, the above-mentioned joint structure had to be designed so that the bolts and stud dowels did not interfere with each other, which resulted in many design constraints. In addition, when constructing the above-mentioned joint structure, the precast deck had to be installed on the flange while adjusting its position so that the bolts did not interfere with the stud dowels, which resulted in poor workability. The present invention aims to provide a joint structure and a joint method that improves design freedom and workability in the joint structure between a precast deck and a steel girder.

The joining structure of the present invention is a joining structure for joining a steel girder and a precast deck installed on the upper flange of the steel girder, and is equipped with a slip prevention part having a protrusion provided on the upper surface of the upper flange and protruding upward, an insert nut embedded in the underside of the precast deck, a bolt attached to the insert nut and protruding downward from the underside of the precast deck, and a filler filled between the upper surface of the upper flange and the underside of the precast deck so as to embed the protrusion and the bolt, and the upper end of the protrusion of the slip prevention part is located closer to the upper surface of the upper flange than the lower end of the bolt.

The joint structure of the present invention is a joint structure for a precast deck constructed by replacing the deck on the upper flange of a steel girder, and the projection of the slip stopper may have remnants of the projection that was included in the slip stopper of the deck before replacement. Also, the filler may be an ultra-high performance fiber-reinforced cement-based composite material.

The joining method of the present invention is a joining method for joining a steel girder and a precast deck installed on the upper flange of the steel girder, and includes a deck installation step in which a precast deck having an insert nut embedded on its underside and a bolt attached to the insert nut is installed on the upper surface of an upper flange provided with a slip prevention part having a protrusion protruding upward, and a filling step in which a filler is filled between the upper surface of the upper flange and the lower surface of the precast deck so as to embed the protrusion and the bolt. In the deck installation step, the precast deck is installed so that the upper end of the protrusion of the slip prevention part is closer to the upper surface of the upper flange than the lower end of the bolt.

The present invention provides a joint structure and method for connecting a precast deck and a steel girder that improves design freedom and ease of construction.

1 is an exploded perspective view of a road bridge to which the joint structure and joining method of the present embodiment are applied. 1A, 1B, and 1D are enlarged side views of the upper part of the steel girder, and 1C is an enlarged side view of the lower part of the precast deck. A cross-sectional view of a precast deck. 4A and 4B are cross-sectional views showing a precast deck and steel girders. 1A and 1B are cross-sectional views showing the precast deck installed on the steel girder. 1A and 1B are cross-sectional views showing the state in which filler material has been filled between the precast deck and the steel girder.

The following describes in detail an embodiment of the joining structure and joining method according to the present invention with reference to the drawings.

Figure 1 is an exploded perspective view of a road bridge 101 to which the joint structure and joining method according to this embodiment are applied. The precast deck 3 is made of a concrete-based material and may be used when constructing a road bridge or may be used to replace the deck of an existing road bridge. The precast deck 3 has a rectangular shape in plan view, measuring, for example, about 2 m in the bridge axis direction and about 11 m in the direction perpendicular to the bridge axis.

The road bridge 101 has multiple steel girders 103 (three in the example shown in the figure) extending in the bridge axis direction. The precast deck 3 is spanned over the three steel girders 103 and joined at three points at the joints 107 of the upper flanges 105 of each steel girder 103. The road structure is constructed by arranging and installing multiple precast decks 3 in the bridge axis direction. The precast decks 3 are connected to each other in the bridge axis direction by a specified joint structure. The road bridge 101 is a composite girder, and it is important to have a slip stop between the precast deck 3 and the steel girders 103 so that the steel girders 103 and the precast deck 3 are integrated to resist loads.

The joining structure and joining method for joining the steel girder 103 and the precast deck 3 in this road bridge 101 will be described. The joining structure and joining method described below are applied when replacing the old deck of the road bridge 101 with a new precast deck 3.

Figures 2 to 6 are cross-sectional views sequentially showing each step of the joining method of one precast deck 3, and show cross-sectional views at a position corresponding to the joint 107. Figures 2(a), (b), and (d) are side views showing an enlarged view of the upper part of the steel girder 103. Figure 2(c) is a side view showing an enlarged view of the lower part of the precast deck 3. Figure 3 is a cross-sectional view of the precast deck 3 taken in a vertical section extending in the bridge axis direction. In each of Figures 4 to 6, (a) is a cross-sectional view of the precast deck 3 and the steel girder 103 taken in a vertical section extending in the bridge axis direction, and (b) is a cross-sectional view of the precast deck 3 and the steel girder 103 taken in a vertical section extending perpendicular to the bridge axis.

In the road bridge 101 before the deck replacement, a stud dowel is provided on the upper surface 105a (hereinafter referred to as the "flange upper surface 105a") of the upper flange 105 of the steel girder 103, and the deck is made of concrete so that the stud dowel is embedded in the underside. This stud dowel functions as a slip prevention device for the deck before replacement. When replacing the deck, a cutting tool is inserted between the underside of the old deck and the flange upper surface 105a to cut off the head of the stud dowel, and the old deck is removed. After the old deck is removed, as shown in FIG. 2(a), the remnants 10 of many cut stud dowels remain on the flange upper surface 105a. The remnants 10 are in a state where the heads of the stud dowels have been cut off and only the round bar-shaped body remains, and protrude upward from the flange upper surface 105a.

(Steel girder processing process)
In the steel girder processing step, as shown in Fig. 2(b), some of the debris 10 on the flange upper surface 105a is further cut and removed, and the removed area is polished and smoothed. Meanwhile, the other debris 10 remaining on the flange upper surface 105a is left as it is. Here, the number of debris 10 left is, for example, about 1/4 to 1/3 of the total debris 10. The arrangement of the debris 10 left may be irregular or may follow a predetermined rule.

(Precast floor slab preparation process)
As shown in Fig. 3, a precast deck 3 is prepared. The precast deck 3 has a plate-shaped structural part 5 made of a concrete-based material and a plurality of insert nuts 7 embedded in the structural part 5. The insert nuts 7 are embedded in the lower surface 3a of the precast deck 3 and exposed on the lower surface of the structural part 5. The "lower surface" refers to the surface that forms the lower surface when the precast deck 3 is finally installed on the road bridge 101. The lower end surface of the insert nuts 7 is located at a position that is approximately flush with the lower surface 3a of the precast deck 3.

In a plan view, the insert nuts 7 are arranged two-dimensionally in an area corresponding to the joint 107 with the upper flange 105. For example, about a hundred insert nuts 7 are arranged for one joint 107. The number and arrangement of the insert nuts 7 as described above are just an example, and the actual number and arrangement are appropriately set according to the slip prevention performance required between the precast deck 3 and the steel girder 103. Such a precast deck 3 is fabricated in advance in a factory or the like and transported to the construction site of the road bridge 101.

(Bolt installation process)
Next, as shown in FIG. 4, the bolts 9 are screwed into each insert nut 7 of the precast floor slab 3. At this time, as shown in an enlarged view in FIG. 2(c), at least some of the bolts 9k among the bolts 9 have a threaded portion longer than the threaded portion of the insert nut 7, and are screwed in until the tip of the threaded portion abuts against the female thread bottom of the insert nut 7, and protrude downward from the lower surface 3a of the precast floor slab 3. A vertical gap is formed between the head of the bolt 9 and the lower surface 3a of the precast floor slab 3. The head side of each of these bolts 9k protrudes downward from the lower surface 3a of the precast floor slab 3 by approximately the same length. The remaining bolts 9j among the bolts 9 have a threaded portion shorter than the threaded portion of the insert nut 7, and are screwed in until the head abuts against the lower surface 3a, and protrude downward from the lower surface 3a by the thickness of the head. In this way, the arrangement of two types of bolts 9k, 9j having different protruding amounts may be irregular or may follow a predetermined rule. This bolt installation process may be carried out in advance at a factory or the like before the precast deck 3 is transported to the construction site.

(Stud dowel installation process)
As shown in FIG. 4, a plurality of stud dowels 11 protruding upward are installed on the flange upper surface 105a of the steel girder 103. As shown in an enlarged view in FIG. 2(d), the stud dowels 11 have a round bar-shaped body 11b extending upward from the flange upper surface 105a, and a head 11a provided at the upper end of the body 11b and formed with a larger diameter than the body 11b. Each stud dowel 11 protrudes vertically upward from the flange upper surface 105a by approximately the same length. Each stud dowel 11 is melt-planted on the flange upper surface 105a by a known method so as not to overlap with the installation position of the remnant 10 left on the flange upper surface 105a as described above. For example, the stud dowel 11 may be melt-planted at the position of the removal trace of the polished remnant 10. The stud dowel 11 melt-planted here may be the same as the old stud dowel of the deck before replacement, or may be different.

Hereinafter, the stud dowels 11 fused to the flange top surface 105a and the remnants 10 left on the flange top surface 105a are collectively referred to as "protrusions 21." A large number of such protrusions 21 form a slip prevention portion 23 on the flange top surface 105a. The protrusions 21 are arranged two-dimensionally in an area corresponding to the joint portion 107 in a plan view, and the same number of protrusions 21 as the bolts 9 described above are provided. In the example of Figures 4 to 6, each protrusion 21 and each bolt 9 are provided in a position facing each other vertically, but this arrangement is not limited to this, and each protrusion 21 and each bolt 9 may be arranged in a position offset from each other in a plan view.

Note that the number and arrangement of the debris 10 left on the flange top surface 105a, the stud dowels 11 melted into the flange top surface 105a, and the bolts 9k and 9j of the precast deck 3 shown in each figure are examples, and the actual number and arrangement are set appropriately depending on the anti-slip performance required between the precast deck 3 and the steel girder 103.

(Deck installation process)
Next, as shown in FIG. 5, the precast deck 3 is installed on the steel girder 103. In the installed state, the lower surface 3a of the precast deck 3 and the flange upper surface 105a of the steel girder 103 face each other with a predetermined gap. In order to form a gap between the lower surface 3a and the flange upper surface 105a as described above, a spacer (not shown) or the like is sandwiched between them. In addition, in this installed state, the upper end of the projection 21 of the slip prevention part 23 is closer to the flange upper surface 105a (i.e., lower) than the lower end of the bolt 9. That is, the upper end of the one (stud dowel 11) that protrudes most upward among the projections 21 is closer to the flange upper surface 105a than the lower end of the bolt 9k that protrudes most downward among the bolts 9. In other words, the gap between the lower surface 3a of the precast deck 3 and the flange upper surface 105a is larger than the sum of the protrusion amount of the bolt 9k and the protrusion amount of the stud dowel 11. With this positional relationship, a vertical gap exists between the projection 21 and the bolt 9, and no interference occurs between the projection 21 and the bolt 9.

(Filling process)
6, the formwork material 13 is inserted between the lower surface 3a and the flange upper surface 105a, and a hardening filler 15 is introduced into the space between the lower surface 3a and the flange upper surface 105a. In order to properly fill the above-mentioned space with the filler 15, a filler introduction hole (not shown) that penetrates the precast deck 3 in the vertical direction may be provided. The filled filler 15 hardens with the protruding parts of the bolts 9 and the protrusions 21 embedded in it. As the above-mentioned filler 15, for example, a hydraulic material, such as non-shrink mortar, is used.

The filler 15 may be a high-strength fiber-reinforced mortar. The high-strength fiber-reinforced mortar is a short-fiber-reinforced mortar having a compressive strength of 120 N/mm2 ^or more and a tensile strength of 1 N/mm2 ^or more borne by the short fibers.

Filler 15 may also be ultra high performance fiber reinforced cement-based composites. Ultra high performance fiber reinforced cement-based composites are sometimes commonly referred to as "UHPFRC."

UHPFRC is a mixture containing, for example, cement, inorganic powder, aggregate, mixing water, chemical admixtures for concrete, and reinforcing fibers. The cement may be, for example, ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, or low-heat Portland cement. The inorganic powder may be, for example, silica fume, ground granulated blast furnace slag, fly ash, fine silica powder, wollastonite, or an expanding agent.

As an example, the above-mentioned aggregate has a particle size of 5.0 mm or less, an oven-dry density of 2.5 g/cm3 ^or more, a water absorption rate of 3.0% or less, a clay mass amount of 1.0% or less, a fine powder amount of 2.0% or less, and a NaCl content of 0.02% or less. This aggregate is one for which the organic impurity test result for fine aggregate specified in JIS (Japanese Industrial Standards) A 1105 is "light". In addition, this aggregate is one for which the stability of sodium sulfate specified in JIS A 1122 is 10% or less according to the aggregate stability test method, and further, which is classified as Class A in terms of alkali-silica reactivity specified in JIS A 5308 Appendix 1.

The mixing water is, for example, mixing water other than recycled water specified in JSCE-B 101-2013. The chemical admixture for concrete is a high-performance water reducing agent specified in JIS A 6204. The reinforcing fiber is a fiber having a diameter of 0.1 to 0.25 mm, a length of 10 to 24 mm, and a tensile strength of 2×10 N ³ /mm ² or more. The reinforcing fiber may be, for example, steel fiber, high-strength aramid fiber, or carbon fiber.

The UHPFRC constituting the filler 15 is, for example, a matrix composed of Portland cement, a binding material containing inorganic powder such as a pozzolana material and an ettrin-guide generating material, aggregate having a particle size of 2.5 mm or less, water, and a water reducing agent. The mix of the filler 15 is standard formula mix. The reinforcing fiber may be a mixture of steel fiber having a diameter of 0.2 mm, a length of 15 mm (manufacturing error less than ±2 mm), and a tensile strength of 2×10 ³ N/mm ² or more, mixed at 1.75 vol. %. The characteristic values of each strength of the UHPFRC after hardening are preferably a compressive strength of 150 N/mm ² or more, a crack initiation strength of 4 N/mm ² , and a tensile strength of 5 N/mm ² .

The standard designated mix ratio of the UHPFRC constituting the filler 15 can be as follows: flow value 250±20 mm, mixing water to binder ratio 15%, air content 2.0%, mixing water 195 kg/ ^m3 , high-performance water reducer 32.2 kg/ ^m3 , and reinforcing fiber 137.4 kg/ ^m3 (1.75 vol.%).

The above-mentioned joining method constructs the joining structure 1 between the steel girder 103 and the precast deck 3, and joins the steel girder 103 and the precast deck 3. In this joining structure 1, the bolt 9 and the protrusion 21 connected via the filler 15 function as a horizontal stopper between the precast deck 3 and the steel girder 103. The head of the bolt 9k included in the bolt 9 engages with the filler 15, and similarly, the head 11a of the stud dowel 11 included in the protrusion 21 engages with the filler 15. Therefore, in the joining structure 1, the bolt 9k and the stud dowel 11 can resist a force that tries to pull the precast deck 3 upward away from the steel girder 103 due to the presence of the bolt 9k and the stud dowel 11.

The effects of the above-mentioned joint structure 1 and joining method are explained below. In the above-mentioned joint structure 1 and joining method, the bolt 9 on the underside 3a of the precast deck 3 and the protrusion 21 of the steel girder 103 are connected via the filler material 15, and horizontal displacement between the precast deck 3 and the steel girder 103 is prevented.

As described above, in the deck installation process, the precast deck 3 is installed on the steel girder 103 so that the upper end of the projection 21 of the anti-slip portion 23 is closer to the flange upper surface 105a (i.e., lower) than the lower end of the bolt 9. This positional relationship results in a vertical gap between the projection 21 and the bolt 9, and no interference between the projection 21 and the bolt 9 occurs. This reduces the constraint of avoiding interference between the projection 21 and the bolt 9 in the design of the joint structure 1. In addition, when installing the precast deck 3 on the flange upper surface 105a in the deck installation process, it is not necessary to adjust the position of the precast deck 3 to avoid interference between the projection 21 and the bolt 9. In addition, there is no need to increase the accuracy of the installation position of the projection 21 on the flange upper surface 105a, and the workload of melting the stud dowel 11 in the stud dowel installation process is also reduced. Therefore, in the joint structure 1 between the precast deck 3 and the steel girder 103, the design freedom is improved and the workability is also improved.

As described above, the joint structure 1 has a structure in which the protrusions 21 and the bolts 9 do not overlap vertically within the filler 15, and therefore is considered to have a slightly inferior slip-stop function compared to a structure in which the protrusions 21 and the bolts 9 overlap vertically (e.g., the connection structure described in Patent Document 1). However, particularly when a high-strength material (e.g., high-strength fiber-reinforced mortar, UHPFRC) is used as the filler 15 material, horizontal shear forces are sufficiently transmitted between the precast deck 3 and the steel girders 103 via the filler 15, which has high shear resistance, so that sufficient slip-stopping between the precast deck 3 and the steel girders 103 can be achieved.

In addition, the anti-slip portion 23 on the flange upper surface 105a reuses not only the stud dowels 11 but also the debris 10 remaining on the flange upper surface 105a as protrusions 21. With this configuration, in the steel girder processing process after the old deck is removed, it is not necessary to remove all of the debris 10 on the flange upper surface 105a, and as a result, the burden of cutting and removing the debris 10 and polishing the removed area is reduced.

The present invention can be implemented in various forms, including the above-described embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. It is also possible to construct modified versions by utilizing the technical matters described in the above-described embodiment. The configurations of each embodiment may be used in appropriate combination.

For example, in the embodiment, the joint structure 1 and the above-mentioned joining method are applied to the road bridge 101, which is a composite girder, but the joint structure 1 and the above-mentioned joining method can also be applied to bridges that use a non-composite girder system. Also, in the embodiment, the joint structure 1 and the above-mentioned joining method are applied to the road bridge 101 that uses a steel girder system, but the joint structure 1 and the above-mentioned joining method can also be applied to bridges that use a box girder system.

In addition, instead of the stud dowels 11 on the flange upper surface 105a in the embodiment, bolts and nuts may be installed by drilling holes in the upper flange 105. The protrusions 21 on the flange upper surface 105a may be composed of newly installed stud dowels 11 without including the debris 10. In other words, in the above-mentioned steel girder processing process, all of the debris 10 on the flange upper surface 105a may be removed. In addition, it is not essential that the bolts 9 of the precast deck 3 include bolts 9j with a small protrusion amount, and all of the bolts 9 may be composed of bolts 9k.

The joining structure 1 and joining method in the embodiment are applied when replacing the old deck of the road bridge 101 with a new precast deck 3, but the present invention can be applied not only when replacing the deck, but also when constructing a new road bridge 101. In this case, the protrusions 21 on the flange upper surface 105a are all composed of newly installed stud dowels 11, and no remnants 10 exist.

1... Joint structure, 3... Precast deck, 3a... Underside, 7... Insert nut, 9... Bolt, 10... Debris, 15... Filler, 21... Protrusion, 23... Anti-slip part, 103... Steel girder, 105... Upper flange, 105a... Upper surface of flange.

Claims (4)

A joint structure for joining a steel girder and a precast deck installed on the upper flange of the steel girder,
A slip prevention portion having a protrusion provided on an upper surface of the upper flange and protruding upward;
An insert nut embedded in the underside of the precast deck;
A bolt attached to the insert nut and protruding downward from the underside of the precast deck;
A filler is filled between the upper surface of the upper flange and the lower surface of the precast floor slab so as to embed the protrusion and the bolt,
A joining structure, wherein the upper end of the protrusion of the anti-slip portion is located closer to the upper surface of the upper flange than the lower end of the bolt. A joint structure of a precast deck constructed by replacing the deck on the upper flange of the steel girder,
The projection of the anti-slip portion is
The joint structure according to claim 1 , comprising remnants of a protrusion that was included in the deck slab's shear stop before it was replaced. The joint structure according to any one of claims 1 to 2, wherein the filler is an ultra-high performance fiber-reinforced cement-based composite material. A joining method for joining a steel girder and a precast deck installed on an upper flange of the steel girder, comprising:
A deck installation process in which the precast deck having an insert nut embedded in the underside and a bolt attached to the insert nut is installed on the upper surface of the upper flange provided with a slip prevention portion having a protrusion protruding upward;
and a filling step of filling a filler between the upper surface of the upper flange and the lower surface of the precast floor slab so as to embed the protrusion and the bolt.
In the deck installation process,
A joining method in which the precast deck is installed so that the upper end of the protrusion of the anti-slip portion is located closer to the upper surface of the upper flange than the lower end of the bolt.

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