JP7719680B2 - Reinforced concrete steel structure - Google Patents

Description

The present invention relates to reinforced concrete structures used for gap lap joints and rebar anchorage.

In conventional reinforced concrete structures, lap joints are widely used to connect the rebars embedded in the concrete.

A lap splice overlaps the rebars being joined by the required length (joint length), allowing the tensile force between the rebars to be transmitted to each rebar via their adhesion to the concrete.

With this type of lap joint, the joint length is generally set to approximately 30 to 35 times the diameter of the rebar, which means that the larger the diameter of the rebar, the longer the joint length becomes, which creates the problem of significantly reducing workability.

Therefore, when the diameter of the rebar is large, mechanical joints, gas pressure welding joints, enclosed welding, etc. have often been used to connect the rebars.

Another type of lap joint is known as a gap lap joint, in which a gap is provided between the rebars so that they do not come into contact with each other.

This gap lap joint can be treated as equivalent to a lap joint if it meets certain criteria, namely, the gap is 0.2L1 and 150mm or less for the joint length L1.

Meanwhile, in the construction of decks, in addition to the typical method using loop joints, a method is currently being used in which the ends of the rebars protruding from the opposing end faces of precast deck components placed abutting each other at a specified distance are overlapped, and concrete is poured into these areas to connect the precast deck components.

In this type of construction method, a joint structure has been developed in which the ends of the rebars protruding from the end faces of the precast deck members are provided with heads with a larger diameter than the diameter of the rebars, and the combined action of the adhesion force with the concrete and the bearing resistance force acting on the heads shortens the length of the overlapping portion (joint length) compared to conventional methods (see, for example, Patent Document 1).

Furthermore, at the joints between structural components that make up a structure, such as the joint between a concrete beam and a concrete column, in order to ensure sufficient joint strength between the two structures, it is necessary to anchor the ends of the rebar embedded in one structure to the other structure. In such cases, the rebar anchored to the concrete column is bent into an L-shape to ensure sufficient anchorage length.

However, there are cases where it is difficult to secure enough space to bend the rebar at the anchor point. In such cases, a head with a larger diameter than the rebar is provided at the end of the rebar that is to be anchored to the other structure, and the bearing resistance acting on the head is used to shorten the anchorage length.

Japanese Patent Application Laid-Open No. 2001-11940

However, with the conventional technologies described above, joint structures such as mechanical joints, gas pressure welding joints, and enclosed welding, which are used when the rebar diameter is large, have the problem of being large-scale in structure and construction, which increases costs, and also has the problem of being less easy to construct than lap joints.

On the other hand, gap lap joint structures, which have heads attached to the ends of the rebar used in deck construction, allow for shorter joint lengths compared to standard lap joint structures. However, installing such heads at the construction site is difficult, and the heads are fixed to the ends of the rebar in advance at the factory by crimping or welding, etc. This means that the position of the head cannot be freely set at the construction site, posing the problem of not being able to adjust the joint length during construction.

Similar problems may also occur when attaching heads to reinforcing bars at anchor points when joining structures.

In light of these conventional problems, the present invention aims to provide a reinforced concrete structure that uses a simple structure to increase the anchorage strength between the reinforcing bars and concrete and the joint strength of gap lap joints.

The feature of the invention described in claim 1 for solving the above-mentioned conventional problems is that in a reinforced concrete structure in which the ends of reinforcing bars connected longitudinally in concrete, or in mortar filled between concrete members, or in concrete are overlapped by a predetermined length to form a lap joint, and the reinforcing bars are provided with expanded diameter support sections with a diameter larger than the diameter of the reinforcing bars, the overlapping ends of the reinforcing bars are provided with a plurality of expanded diameter support sections spaced apart in the longitudinal direction of the reinforcing bars, and at least one of the plurality of expanded diameter support sections is constituted by a movable expanded diameter support body consisting of a plurality of nut-shaped members screwed onto threaded portions formed on the reinforcing bars, and at least one of the plurality of nut-shaped members is tightened to another adjacent nut-shaped member so that the movable expanded diameter support body is fixed at a desired position on the reinforcing bars.

The invention described in claim 2 is characterized in that in a reinforced concrete structure in which concrete, or mortar filled between concrete members, or reinforcing bars embedded in concrete are provided with expanded diameter support sections with a diameter larger than the diameter of the reinforcing bars, at the joints between structures that make up the reinforced concrete structure, the reinforcing bars supported by one structure are provided at the part where they are fixed into another structure with a plurality of expanded diameter support sections spaced apart in the longitudinal direction of the reinforcing bars, and at least one of the plurality of expanded diameter support sections is formed by a movable expanded diameter support body consisting of a plurality of nut-shaped members screwed onto threaded portions formed on the reinforcing bars, and at least one of the plurality of nut-shaped members is tightened to another adjacent nut-shaped member so that the movable expanded diameter support body is fixed at the desired position of the reinforcing bars.

The invention as set forth in claim 3 is characterized in that, in addition to the configuration of claim 1 or 2 , all of the plurality of expanded diameter support portions are formed by the movable expanded diameter support bodies.

The invention described in claim 4 is characterized in that, in addition to the configuration of any one of claims 1 to 3 , the spacing between the expanded diameter support sections is greater than or equal to the maximum aggregate size of the concrete.

The invention as set forth in claim 5 is characterized in that, in addition to the configuration of claim 4 , the spacing between the plurality of expanded diameter support portions is 1 to 3 times the diameter of the reinforcing bar.

The feature of the invention described in claim 6 is that, in addition to the configuration of any one of claims 1 to 5 , the torque strength of the movable expansion support body when tightening the nut-shaped member is 20 Nm or more and 180 Nm or less.

The invention described in claim 7 is characterized in that, in addition to the configuration of any one of claims 1 to 6 , the reinforcing bar is a threaded reinforcing bar having a threaded portion formed all over it.

The reinforced concrete structure of the present invention, having the configuration of claim 1, can enhance anchorage to the concrete through the combined action of the adhesion force acting on the straight sections of the reinforcing bars and the bearing resistance force acting on the enlarged bearing sections, and can also improve workability by allowing the positions of the enlarged bearing sections to be determined arbitrarily at the construction site. Furthermore, the bearing resistance force of multiple enlarged bearing sections can further enhance anchorage to the concrete. Furthermore, because the enlarged bearing sections of adjacent reinforcing bars support each other through the bearing resistance force, the joint length can be shorter than conventional lap joints.

Furthermore, in the present invention, by providing the configuration of claim 2 , the anchorage length of the reinforcing bars can be reduced compared to the conventional case when joining the structures that make up a reinforced concrete structure.

Furthermore, in the present invention, by incorporating the configuration of claim 3 , when design changes or fine adjustments are required at the construction site, the position of the expanded diameter support section can be freely set to an effective position for exerting support resistance force.

Furthermore, in the present invention, by providing the configurations of claims 4 and 5 , concrete can be suitably filled.

Furthermore, in the present invention, by providing the configuration of claim 6 , it is possible to introduce a tightening force into the movable expansion bearing body so that a resistance force greater than the bond stress between the concrete and the reinforcing bar can be obtained by human power.

Furthermore, in the present invention, by providing the configuration of claim 7 , the bearing area coefficient of the threaded reinforcing bars, i.e., the protruding area of the reinforcing bar surface per unit area, is large, thereby achieving higher adhesion performance to concrete than deformed reinforcing bars, etc.

1 is a longitudinal cross-sectional view showing an example of a reinforced concrete structure according to the present invention. FIG. 2 is a cross-sectional view taken along the line AA of the same. This is a schematic diagram of steel bar arrangement to explain the effect of the bearing resistance force by the expanded diameter bearing section of the same. 1A is a schematic diagram of the rebar arrangement showing the state where the expansion support section of the same has shifted in position, and FIG. 1B is a schematic diagram of the rebar arrangement showing the state where the movable expansion support body has been aligned. 1A is a graph showing the results of a pull-out strength experiment of the movable diameter expansion bearing body of the same, and FIG. 1B is a front view showing an outline of the same experimental device. 4A is a plan view showing an example of a nut-shaped member constituting the movable diameter expansion support body of the same, and FIG. 4B is a side view of the same. 10 is a graph showing the results of an adhesion performance test between the reinforced concrete structure according to the present invention and concrete. 10 is a graph showing the load sharing between the adhesive force of the reinforcing bar and the support pressure by the movable expansion support body. FIG. 2 is a vertical cross-sectional view showing another example of a reinforced concrete structure according to the present invention. FIG. 2 is a cross-sectional view taken along the line AA of the same. 1A is a longitudinal sectional view showing another example of a reinforced concrete structure according to the present invention, and FIG. 1B is a longitudinal sectional view showing a conventional reinforced concrete structure.

Next, a first embodiment of a reinforced concrete structure according to the present invention will be described based on the example shown in Figures 1 to 4. In the figures, reference numeral 1 denotes a reinforced concrete structure.

This reinforced concrete structure 1 has reinforcing bars 3, 3 embedded in concrete 2, with the reinforcing bars 3, 3 connected longitudinally by open lap joints, so that the axial force acting on each reinforcing bar 3, 3 is transmitted via the concrete 2. Note that the reference symbol 4 in the figure denotes horizontal reinforcement arranged in a direction that intersects with the reinforcing bars 3.

A gap lap joint is a structure in which the ends of reinforcing bars 3, 3 connected in the longitudinal direction are arranged with a predetermined gap (gap) between them and overlapped by a predetermined length in the longitudinal direction (joint length = L1), so that the axial force acting on each reinforcing bar 3, 3 is transmitted via the concrete 2.

Furthermore, this lap joint can be treated the same as a general lap joint, as the spacing between the reinforcing bars 3, 3 meets specified standards (a spacing of 0.2L1 and 150 mm or less for the joint length L1).

The reinforcing bars 3, 3 have multiple enlarged bearing sections 5, 5 spaced apart along their length, each with a diameter larger than the diameter of the reinforcing bar, and are structured so that the bearing resistance force of the enlarged bearing sections 5, 5 of adjacent reinforcing bars 3, 3 supports each other.

It is desirable that the reinforcing bar 3 be a threaded reinforcing bar with a male thread formed at least at the end and a male thread formed throughout. Note that the reinforcing bar 3 is not limited to a threaded reinforcing bar, and may be a general reinforcing bar, such as an epoxy resin-coated reinforcing bar, with a male thread formed thereon.

The expanded diameter support sections 5, 5 are composed of movable expanded diameter support bodies consisting of multiple (a pair in this embodiment) nut-type members 6, 7 threaded onto the threaded portions, and at least one of the multiple nut-type members 6, 7 (nut-type member 7 in this embodiment) can be fastened to an adjacent nut-type member 6 to fix it in a predetermined position on the reinforcing bar 3.

The positions of the expanded diameter support sections 5, 5 of adjacent reinforcing bars 3 are adjusted so that they are positioned in a direction (forming an angle of approximately 45 degrees with the reinforcing bars 3) in which the compressive stress transfer areas (compression struts) are formed, and in a position where the compressive stress transfer areas overlap, allowing the expanded diameter support sections 5, 5 of adjacent reinforcing bars 3, 3 to support each other.

In this embodiment, we will explain the case where there are two expanded diameter support sections 5, 5, but up to three expanded diameter support sections 5 can be set.

In addition, in this embodiment, all of the expanded diameter support sections 5, 5 are constructed as movable expanded diameter support bodies, allowing all of the expanded diameter support sections 5, 5 to be set at any position relative to the reinforcing bars 3, 3.

The nut-type members 6, 7 are constructed using commonly used hexagonal nuts or similar, and are threaded onto the reinforcing bars 3 so that they are tightened in different directions. Both nut-type members 6, 7 are threaded forward to move them to the desired position on the reinforcing bars 3, 3. By tightening one nut-type member 6 to the other nut-type member 7 with a predetermined torque (tightening strength), the nut-type members 6, 7 engage with the male threads and are fixed in place. The shape of the nut-type members 6, 7 is not limited to hexagonal nuts, and other shapes such as discs, ovals, and rectangles can also be used.

The nut-type members 6 and 7 may be tightened in different directions to introduce torque into both nut-type members 6 and 7.

The tightening strength of the nut-shaped members 6, 7 is set to 20 Nm or more and 180 Nm or less. By applying a torque of 20 Nm or more, it is possible to obtain nut slippage resistance greater than the bond stress between the reinforcing bar 3 and the concrete 2, and by setting it to 180 Nm or less, it is possible to prevent damage to the threads formed in the reinforcing bar 3.

Figure 5(a) shows the results of an experiment verifying the relationship between the slip resistance force between the movable expansion bearing body and the threaded rebar.

In this experiment, a torque wrench was used to apply torques of 20, 120, and 180 Nm between the nut-shaped members 6 and 7, and the device shown in Figure 5(b) was used to measure the displacement (nut displacement) δ of the nut member 6 relative to the reinforcing bar 3 when a static pull-out load P was applied to the reinforcing bar 3.

In the figure, the symbol 8 denotes a displacement meter. When a pull-out load P is applied to the reinforcing bar 3 and a misalignment occurs between the reinforcing bar 3 and the nut-shaped member 6, the displacement meter 8 is pushed in and the displacement due to this push-in is measured as the nut misalignment δ.

For the nut-type components 6 and 7, hexagonal nuts with a nominal diameter d = 19 mm, a width across flats s = 31 mm, and a diagonal distance e = 32.6 mm were used, as shown in Figure 6.

The pull-out load P varies depending on the applied torque. For example, the bond stress equivalent when the free end slip shown by the vertical dotted line on the left side of Figure 5(a) is 0.2% of the rebar diameter is converted as shown.

Here, the bond stress between the reinforcing bars and concrete is designed using the formula below, so the bond stress between normal concrete and reinforcing bars is generally 2.1 to 3.8 N/ ^mm2 .

Therefore, from Figure 5(a), it can be seen that a torque of 20 Nm or more must be introduced into the movable expansion bearing body.

In addition, the spacing between the expanded bearing sections 5, 5 should be equal to or greater than the maximum aggregate size of the concrete 2, and should preferably be 1 to 3 times the diameter of the rebar.

In a reinforced concrete structure 1 constructed in this manner, multiple expanded bearing sections 5, 5 are provided in the overlapping portions of the reinforcing bars 3, 3 of the gap lap joint. This not only improves the bond strength between the reinforcing bars 3, 3 themselves (straight sections) and the concrete 2, but also, as shown in Figure 3, creates a compressive stress transfer area (compression strut) X in a specified direction (at an angle of approximately 45 degrees to the reinforcing bars) in the expanded bearing sections 5, 5 attached to adjacent reinforcing bars 3, 3. Since the expanded bearing sections 5, 5 support each other, the joint length can be reduced to approximately one-third of that of a typical lap joint, without using a mechanical joint.

In addition, in this reinforced concrete structure 1, the expanded diameter bearing sections 5, 5 are constructed from movable expanded diameter bearing bodies consisting of multiple nut-shaped members 6, 7, so that the expanded diameter bearing sections 5, 5 are not completely integrated with the reinforcing bars 3, 3, and tightening of the nut-shaped members 6, 7 can provide nut slippage resistance greater than the bond stress between the reinforcing bars 3, 3 and the concrete 2.

As a result, the position of the expanded bearing sections 5, 5 relative to the reinforcing bars 3, 3 can be set as desired at the construction site, allowing for flexible response to changes caused by malfunctions or design changes, such as misalignment of the reinforcing bars 3, 3 in the axial direction or changes in the width between adjacent reinforcing bars 3, 3.

For example, as shown in Figure 4(a), if the rebars 3, 3 are misaligned in the axial direction of the rebars due to a change in the specifications for the rebar placement, as compared to the arrangement of the rebars 3, 3 shown in Figure 3, the corresponding expanded diameter support sections 5, 5 of adjacent rebars 3, 3 may move out of the compressive stress transmission area (compression strut) X, and an effective support effect may not be achieved.

However, with the present invention, as shown in Figure 4(b), the position can be easily adjusted by moving and tightening the nut-shaped members 6 and 7 at the construction site, so the bearing effect of the expanded diameter bearing portion 5 can always be effectively exerted.

Next, we will describe the results of bond performance tests on reinforcing bars in reinforced concrete structures related to the present invention.

In this performance test, a rebar structure was embedded in normal concrete (50N) and a pull-out load P was applied to the free end of the test specimen, and the relationship between the load and the free end slippage _S0 was measured. Note that when the free end slippage is the same, a larger pull-out load indicates a higher pull-out resistance (adhesion performance).

This test was conducted using five test specimens: one containing only deformed rebar; one containing only threaded rebar; one containing a single movable expansion bearing body consisting of a pair of nut-shaped members attached to the threaded rebar (hereafter referred to as threaded rebar + nut 1); one containing two movable expansion bearing bodies consisting of a pair of nut-shaped members attached to the threaded rebar (hereafter referred to as threaded rebar + nut 2); and one containing two movable expansion bearing bodies spaced far apart (hereafter referred to as threaded rebar + nut 2').

In addition, in this performance test, the support pressure of the movable expansion bearing body was estimated by comparing the pull-out load P at a specified free end slippage _S0 in the cases of threaded rebar + nut 1, threaded rebar + nut 2, and threaded rebar + nut 2' with the case of threaded rebar alone, and the load sharing between the adhesion force of the rebar and the support pressure by the movable expansion bearing body was also examined.

As shown in Figure 7, as is clear from an index called the bearing area coefficient BA (the protruding area of the rebar surface per unit area), threaded rebars have a larger protruding area than deformed rebars, making them easier to fill between the nodes, and therefore the pull-out load of threaded rebars is greater than that of deformed rebars.

Next, when comparing deformed rebar with threaded rebar + nut 1, the threaded rebar + nut 1 exhibits a pull-out load 1 that is 1.4 times greater when the free end slip is 0.02 mm (equivalent to 0.1% of the rebar diameter), confirming the improved pull-out resistance achieved by the movable expansion bearing body.

Furthermore, when there are two movable expansion bearing bodies, such as in the case of threaded rebar + nut 2 and threaded rebar + nut 2', the pull-out load is 1.6 times greater than that of a deformed rebar.

However, the pull-out load was greater for the threaded rebar + nut 2 than for the threaded rebar + nut 2', and the pull-out performance was better when the distance between the movable expansion bearing bodies was narrow.

On the other hand, with regard to the load sharing between the adhesive force of the rebar and the bearing pressure of the movable expansion bearing body, in the case of the threaded rebar + nut 1, as shown in Figure 8, in the initial step, the adhesive force is the cause of the pull-out load, but as the displacement step progresses, the effect of the bearing pressure begins to be exerted. This is because the adhesive force is exerted from the loaded end of the rebar to the free end, so in the initial step, the load is not transmitted to the movable expansion bearing body.

On the other hand, with the threaded rebar + nut 2 (2'), the bearing pressure accounts for 30% of the total tensile load from the initial step, indicating that the effect of the movable expanding bearing body is being demonstrated from the beginning.

In other words, it was confirmed that when two movable expanding bearing bodies are installed, the initial gradient of the load-displacement relationship is large and there is little initial rebar slippage.

As shown in Figures 9 and 10, this gap lap joint can also be used when reinforced concrete members 20, 20 with embedded reinforcing bars 3 are placed at a distance from each other and a filler material 21 made of concrete or mortar is filled between the two concrete members 20, 20. Components similar to those in the above-mentioned embodiment are designated by the same reference numerals and will not be described again.

In this embodiment, the ends of the reinforcing bars 3 protrude from the end faces of the concrete members 20, 20 to be connected, with the protruding portions spaced a predetermined distance apart between the reinforcing bars 3, 3 and overlapping by a predetermined length in the longitudinal direction (joint length = L1). The axial force acting on each reinforcing bar 3, 3 is transmitted via filler material 21, made of concrete or mortar, filled between the concrete members 20, 20.

When the filler 21 is concrete, it is preferable that the spacing between the radial support sections 5, 5 be equal to or greater than the maximum aggregate size of the concrete 2. However, when mortar is used for the filler 21, there are no particular restrictions on the spacing between the radial support sections 5, 5.

Next, a second embodiment of a reinforced concrete structure according to the present invention will be described with reference to Figure 9. In the figure, reference numeral 10 denotes a reinforced concrete structure.

This reinforced concrete structure 10 has a concrete beam 12 (one structural element) joined to the side of a reinforced concrete column 11 (another structural element), and the ends of reinforcing bars 13, 13 embedded in the concrete beam 12 are fixed within the concrete column 11. Note that the reference numeral 14 in the figure denotes the longitudinal main reinforcement of the concrete column 11.

The reinforcing bars 13, 13 embedded in the concrete beam 12 have multiple expanded bearing sections 15, 15 at their ends, spaced longitudinally, with diameters larger than the diameter of the reinforcing bars, and the ends of the reinforcing bars 13, including the multiple expanded bearing sections 15, 15, are fixed to the concrete column 11.

It is desirable that the reinforcing bars 13, 13 be threaded reinforcing bars with male threads formed at least at the ends and with male threads formed throughout.

The expanded diameter support sections 15, 15 are composed of movable expanded diameter support bodies consisting of multiple nut-shaped members 16, 17 threaded onto threaded sections, and can be fixed in a predetermined position on the reinforcing bars 13, 13 by tightening at least one of the multiple nut-shaped members 16, 17 against the adjacent nut-shaped member 16.

As a result, in this reinforced concrete structure 10, a high anchorage force can be obtained due to the bearing resistance force acting on the expanded bearing sections 15, 15, and the anchorage length of the reinforcing bars 13, 13 can be significantly reduced compared to conventional reinforcing bars 18, 18, which are bent into an L-shape as shown in Figure 9(b) to ensure the anchorage length.

In this case, the positions of the expanded diameter support sections 15, 15 can be set at any position on the reinforcing bars 13, 13, so when assembling the reinforcing bars 13, 13, the positions of the expanded diameter support sections 15, 15 can be flexibly adjusted at the construction site to match the positions of the reinforcing bars 14, 14 embedded in the concrete pillar 11.

Note that the aspects of the present invention are not limited to the above-described examples, and may also be applied to, for example, joints between precast concrete members.

1. Reinforced concrete structure 2. Concrete 3. Reinforcement 4. Reinforcement (horizontal reinforcement)
5 Expanded bearing portions 6, 7 Nut-shaped members 10 Reinforced concrete structure 11 Concrete column 12 Concrete beam 13 Reinforcement bar 14 Reinforcement bar 15 Expanded bearing portions 16, 17 Nut-shaped members 18 Reinforcement bar 20 Concrete member 21 Filler material

Claims (7)

In a reinforced concrete structure, the ends of reinforcing bars connected longitudinally in concrete, or in mortar filled between concrete members, or in concrete are overlapped by a predetermined length to form a lap joint, and the reinforcing bars are provided with enlarged bearing parts with a diameter larger than the diameter of the reinforcing bars.
A reinforced concrete reinforcing bar structure characterized in that the ends of the overlapping reinforcing bars are provided with a plurality of expanded diameter support sections spaced apart in the longitudinal direction of the reinforcing bars, at least one of the plurality of expanded diameter support sections is constituted by a movable expanded diameter support body consisting of a plurality of nut-shaped members screwed onto threaded portions formed on the reinforcing bars, and at least one of the plurality of nut-shaped members is tightened to another adjacent nut-shaped member so that the movable expanded diameter support body is fixed at a desired position on the reinforcing bars. In a reinforced concrete structure, the reinforced concrete is provided with an expanded bearing section with a diameter larger than the diameter of the reinforcing bar, in concrete, or in mortar filled between concrete members, or in concrete.
A reinforced concrete reinforcing structure characterized in that at the joints between structures that make up a reinforced concrete structure, a plurality of expansion bearing sections are provided at intervals in the longitudinal direction of the reinforcing bar at the portion where the reinforcing bar supported by one structure is fixed into another structure , and at least one of the plurality of expansion bearing sections is constituted by a movable expansion bearing body consisting of a plurality of nut-shaped members screwed onto threaded portions formed on the reinforcing bar, and at least one of the plurality of nut-shaped members is tightened to another adjacent nut-shaped member so that the movable expansion bearing body is fixed at a desired position on the reinforcing bar. 3. A reinforced concrete structure according to claim 1 , wherein all of the plurality of expansion bearing sections are constituted by the movable expansion bearing bodies. 4. A reinforced concrete structure according to claim 1 , wherein the spacing between the expanded bearing sections is equal to or greater than the maximum aggregate size of the concrete. 5. The reinforced concrete structure according to claim 4 , wherein the spacing between the plurality of expanded diameter bearing sections is 1 to 3 times the diameter of the reinforcing bar. The reinforced concrete structure according to any one of claims 1 to 5 , wherein the movable expansion support body has a torque strength of 20 Nm or more and 180 Nm or less when tightening the nut-shaped member. 7. A reinforced concrete structure according to claim 1 , wherein the reinforcing bar is a threaded reinforcing bar having a threaded portion formed throughout the entire structure.