Steel bracket fixing structure for external cable reinforcement method

Abstract

To make it possible to stably fix steel brackets to existing bridge girders while improving workability of steel brackets.SOLUTION: In a steel bracket fixing structure for an external cable reinforcement method, which fixes steel brackets to concrete girders for the external cable reinforcement method, there are a fastening hole provided on the side of the steel bracket for inserting a fastening material and a fastening tool for fastening one end of the fastening material to the fastening hole of the steel bracket, the surface in contact with the inner peripheral surface of the fastening hole of the steel bracket of the fastening tool has a convex spherical shape, and the inner circumferential surface of the fastening hole of the steel bracket is in close contact with the convex spherical surface of the fastening tool and has a concave spherical shape to accommodate this.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a steel bracket fixing structure for an external cable reinforcement method of a concrete girder.

Background Art

[0002] In recent years, in addition to the progress of aging of road structures, due to the increase in the size of automobiles and the increase in traffic volume, road bridges are in an extremely harsh usage situation. Under such circumstances, large-scale repair work associated with the maintenance management such as the grasp of the aging status of structures and preventive maintenance is actively carried out.

[0003] For example, there is an external cable reinforcement method in which an external cable is used to additionally introduce prestress to an existing concrete bridge girder to improve the load-bearing capacity of the existing bridge girder.

[0004] In the external cable reinforcement method, it is necessary to fix the external cable to the existing bridge girder. The fixing method is a method of fixing the external cable to the existing bridge girder by using a post-installed fixing body provided on the existing bridge girder.

[0005] The fixing body refers to a steel or concrete structural member attached to the existing bridge girder to fix the external cable fixing tool.

[0006] For the concrete fixing body, there is a method of adding concrete blocks to both side surfaces of the existing bridge girder to form a bracket fixing body (Patent Document 1). In this bracket fixing body, concrete brackets are constructed on both side surfaces of the existing bridge girder, and prestress is introduced and fixed by tensioning a fastening material penetrating the existing bridge girder and the concrete brackets constructed on both side surfaces of the existing bridge girder.

[0007] In addition, there is a method of installing steel brackets on both side surfaces of the existing bridge girder (Patent Document 2). The steel brackets are fixed to both side surfaces of the existing bridge girder by post-construction anchors, bolts penetrating the existing bridge girder, or tensioned fastening materials.

[0008] Furthermore, there is also a method of bonding and attaching the existing bridge girder and the bracket by interposing an adhesive member between the bracket mounting surface of the existing concrete bridge girder and the bracket (Patent Document 3). [Prior art documents] [Non-patent literature]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 8-158315 [Patent Document 2] Japanese Patent Publication No. 2003-176506 [Patent Document 3] Japanese Patent Publication No. 2013-007250 [Overview of the project] [Problems that the invention aims to solve]

[0010] Conventionally, steel and concrete brackets are fixed to existing bridge girders by introducing tension into fasteners inserted through holes drilled in the existing bridge girders and fastening holes provided in the steel or concrete brackets, in order to integrate them with the existing bridge girders. The prestress force introduced by tensioning the fasteners resists the tension of the external cables through in-plane frictional force on the mounting surface of the steel or concrete bracket. However, tensioning the fasteners frequently involves carrying heavy tensioning equipment such as jacks, and this work is difficult in the narrow scaffolding space beneath the existing bridge girders. Therefore, there is a need for a fixing method that does not involve tensioning the fasteners. In this case, the structure relies on the shear strength of the fasteners to withstand the tension of the external cables.

[0011] In particular, with steel brackets, if the fasteners are not tensioned, the tension of the external cables causes the steel brackets to shift due to the gap between the fastening holes and the fasteners. This reduces the amount of prestress on the existing bridge girders caused by the external cables, and the sliding of the steel brackets during tensioning work could endanger the safety of on-site workers.

[0012] In conventional steel brackets, the gap between the fastening hole and the fastener is the gap between the fastening hole 13' and the fastener 12', as shown in Figure 7. This gap occurs because the inner diameter of the fastening hole 13' is made larger than the outer diameter of the fastener 12' in order to absorb installation errors of the steel bracket 10. When this gap exists, non-shrink mortar 18 fills the gap between the fastening hole 13' and the fastener 12'. When non-shrink mortar 18 is present in the gap between the fastening hole 13' and the fastener 12', the tension force of the external cable 21 is transmitted to each member in the following order. Steel bracket 10 (side wall 11) → non-shrink mortar 18 in the gap between fastening hole 13' and fastening material 12' → fastening material 12' → non-shrink mortar 18 outside the gap between fastening hole 13' and fastening material 12' → existing bridge girder 1.

[0013] As described above, shear force is transmitted from the steel bracket 10 (side wall 11) to the fastener 12' via the non-shrink mortar 18 in the gap between the fastening hole 13' and the fastener 12'. This causes locally excessive stress to act on the non-shrink mortar 18 in the gap between the fastening hole 13' and the fastener 12'. The bearing pressure from the fastening hole 13' and the fastener 12' of the steel bracket 10 (side wall 11) causes the non-shrink mortar 18 in the gap between the fastening hole 13' and the fastener 12' to pulverize, which can result in displacement such as rotation of the steel bracket 10.

[0014] If each of the above components satisfies the required strength, the steel bracket 10 will be stably fixed to the existing bridge girder 1 against the tension of the outer cable 21. However, if the non-shrink mortar 18 in the gap between the fastening hole 13' and the fastener 12' is crushed due to insufficient strength of the above components or bearing pressure, or if a void is created due to poor filling of the non-shrink mortar 18 in the gap between the fastening hole 13' and the fastener 12', bending may occur in the fastener 12', causing the steel bracket 10 to shift and potentially reducing the tension of the outer cable 21.

[0015] The method described in Patent Document 3, which involves interposing an adhesive member between the concrete mounting surface of an existing bridge girder and a steel bracket, does not disclose specific numerical values ​​for the strength of the adhesive, making it impossible to confirm whether the bracket and the existing bridge girder are sufficiently integrated by the tension of the external cable.

[0016] The present invention was made to solve these problems, and its objective is to provide a steel bracket fixing structure for an external cable reinforcement method that can stably fix a steel bracket to an existing bridge girder without using heavy tensioning equipment, prevents a reduction in the amount of prestress on the existing bridge girder due to external cables caused by displacement of the steel bracket, and further enables safety maintenance during external cable tensioning work. [Means for solving the problem]

[0017] The steel bracket fixing structure for external cable reinforcement method according to the present invention, in order to achieve the above objective, is a structure for fixing a steel bracket for external cable reinforcement method to a concrete girder, comprising: a fastening material for fastening the concrete girder and the steel bracket; a fastening hole provided on the side surface of the steel bracket for inserting the fastening material; and a fastener for fastening one end of the fastening material to the fastening hole of the steel bracket, wherein the surface of the fastener that contacts the inner circumferential surface of the fastening hole of the steel bracket is convex spherical, and the inner circumferential surface of the fastening hole of the steel bracket is concave spherical, which is in close contact with and receives the convex spherical surface of the fastener. [Brief explanation of the drawing]

[0018] [Figure 1] This is a side view showing an external cable reinforcement method for concrete girders according to one embodiment of the present invention. [Figure 2] Figure 1 is a plan view of the external cable reinforcement method. [Figure 3] This is a side view showing details of a steel bracket fixed to a concrete girder as an external cable anchoring body for the external cable reinforcement method of the concrete girder according to this embodiment. [Figure 4] Figure 3 is a cross-sectional view showing details of the steel bracket. [Figure 5] This figure shows the relationship between the fastening hole 13, the fastening material 12, and the fastener 17 in the steel bracket shown in Figure 3. [Figure 6]It is a diagram showing the procedure for fastening the fastener 17 and the fastening hole 13 of the steel bracket 10. [Figure 7] It is a diagram showing the gap between the fastening hole 13' and the fastening material 12' in the prior art.

Embodiment for Carrying out the Invention

[0019] Hereinafter, embodiments of the present invention will be described based on the drawings.

[0020] FIG. 1 is a side view showing an external cable reinforcement method for a concrete girder according to an embodiment of the present invention, FIG. 2 is a plan view of FIG. 1, FIG. 3 is a side view showing details of a steel bracket fixed as an external cable fixing body to a concrete girder for the external cable reinforcement method of the present embodiment, and FIG. 4 is a cross-sectional view showing the structure of the steel bracket of FIG. 3 from the girder longitudinal direction.

[0021] In these figures, 10 is a steel bracket as an external cable fixing body. The steel bracket 10 is fixed to the side surface of the existing bridge girder 1 of a T-girder having a lower flange shape.

[0022] The steel bracket 10 has a U-shaped cross-sectional shape so as to sandwich the lower flange 1a of the existing bridge girder 1 from the lower surface side. As shown in FIG. 4, a fastening hole 13 (FIG. 5) through which a fastening material 12 is inserted is drilled in a side wall 11 of the steel bracket 10 corresponding to the web portion 1b (the thinnest part of the member) of the existing bridge girder 1. The fastening holes 13 are provided in the side walls 11 on both sides of the steel bracket 10 fixed to both side surfaces of the existing bridge girder 1. The fastening material 12 is inserted into the insertion hole 1d drilled in the web portion 1b of the existing bridge girder 1 and the fastening holes 13 provided in both side walls 11 of the steel bracket 10, and is tightly fastened to the steel bracket 10 from both sides by fastening tools 17 fitted from the outside of both side walls 11, whereby the steel bracket 10 is fixed to the existing bridge girder 1.

[0023] A cable support portion 15 for supporting one end portion of the external cable 21 is provided at the lower part of the steel bracket 10.

[0024] Furthermore, the steel bracket 10 is not limited to having a U-shaped cross-section so as to be able to clamp the lower flange 1a of the existing bridge girder 1 from below. It may also be a structure that is installed only on the lower side of the lower flange 1a of the existing bridge girder 1, or it may be an independent structure on both sides of the existing bridge girder 1. In addition, the concrete girder to which the steel bracket 10 is fixed is not limited to a T-shaped bridge girder with a lower flange shape, but can be applied to any concrete girder, such as a box girder, a hollow slab bridge, or a slab girder.

[0025] Next, the procedure for attaching the steel bracket 10 to the existing bridge girder 1 will be explained. First, prior to attaching the steel bracket 10 to the existing bridge girder 1, through holes 1d are drilled in the web portion 1b of the existing bridge girder 1 for inserting fasteners 12. Next, reinforcing bars 16 are assembled to be placed in the gap between the web portion 1b of the existing bridge girder 1 and the side wall 11 of the steel bracket 10. The reinforcing bars 16 are assembled by installing anchor bars (not shown in the drawing) on ​​both sides of the existing bridge girder and using the anchor bars to assemble the reinforcing bars 16, thereby holding the reinforcing bars 16 in the predetermined position.

[0026] Next, the steel bracket 10 is positioned and installed on the existing bridge girder 1 so that the fastener 12 can be inserted through the insertion hole 1d in the web portion 1b of the existing bridge girder 1 and the fastening hole 13 of the steel bracket 10. The fastener 12 is then inserted through the fastening hole 13 of the steel bracket 10 and the insertion hole 1d in the web portion 1b of the existing bridge girder 1, and the existing bridge girder 1 is temporarily fastened from both sides with the fastener 17. After this, the concrete cover over the reinforcing bars 16 is adjusted. When installing the steel bracket 10 on the existing bridge girder 1, the unevenness of the lower surface 1e of the lower flange 1e of the existing bridge girder 1 is leveled using resin putty or the like to ensure a tight fit between the lower surface 1e of the lower flange 1e of the existing bridge girder 1 and the steel bracket 10.

[0027] Next, formwork is installed on both end faces of the steel bracket 10 in the cross-sectional direction of the existing bridge girder 1. Then, non-shrink mortar 18 is filled into the gap between the existing bridge girder 1 and the steel bracket 10. After confirming that the non-shrink mortar 18 has reached a predetermined strength, the fasteners 17 are tightened to a predetermined torque. By filling the gap between the existing bridge girder 1 and the steel bracket 10 with non-shrink mortar 18, the non-shrink mortar 18 also flows into the gap between the insertion hole 1d of the web portion 1b of the existing bridge girder 1 and the fastener 12.

[0028] Furthermore, the steel brackets 10 are fixed to the existing bridge girder 1 not by frictional force from the fastening of the fasteners 12, but by the shear strength of the fasteners 12. In other words, as shown in Figures 1 and 2, the external cable reinforcement method involves arranging the external cable 21 between two external cable anchoring bodies (steel brackets 10) and applying tension to the external cable 21. After the construction of the steel brackets 10 at the two predetermined locations is completed, the external cable 21 is stretched between the two steel brackets 10 and tension is applied to the external cable 21. The tension of the external cable 21 causes a shear force to act on the fasteners 12. When a shear force acts on the fasteners 12, the force is transmitted from the non-shrink mortar 18 around the fasteners 12 to the existing bridge girder 1, and the external cable reinforcement is achieved. This shear force is transmitted from the steel bracket 10 to the fastener 12, but in order for external cable reinforcement to be achieved by transmitting the force from the non-shrink mortar 18 around the fastener 12 to the existing bridge girder 1, the strength of each component constituting the steel bracket 10 must be ensured.

[0029] The steel bracket fixing structure of this embodiment is a structure that can transmit shear force from the steel bracket 10 to the fastening material 12 without the need for non-shrink mortar 18 in the gap between the fastening hole 13 of the steel bracket 10 and the fastening material 12.

[0030] In order to transmit shear force from the steel bracket 10 to the fastener 12 without passing through the non-shrink mortar 18 in the gap between the fastening hole 13 of the steel bracket 10 and the fastener 12, in this embodiment, as shown in Figure 5, the tip portion of the fastener 17 is made into a convex spherical shape, and the inner circumferential surface of the fastening hole 13 through which the fastener 12 is inserted in the steel bracket 10 is made into a concave spherical shape that is in close contact with and receives the convex spherical surface of the fastener 17.

[0031] Figure 6 shows the procedure for fastening the fastener 17 to the fastening hole 13 of the steel bracket 10. First, the fastener 12 is inserted into the fastening hole 13 of the steel bracket 10 (A), and the fastener 17 is fitted into the fastening hole 13 of the steel bracket 10, with the convex spherical surface of the fastener 17 facing the fastening hole 13 of the steel bracket 10 (B). The circumferential surface of the end region of the fastener 12 is provided with screw threads, and the inner circumferential surface of the hole in the fastener 17 is provided with screw grooves corresponding to the screw threads on the circumferential surface of the fastener 12. As the fastener 17 is fitted further in, the convex spherical surface of the tip of the fastener 17 is accommodated in the concave spherical surface of the inner circumference of the fastening hole 13, and by tightening the fastener with a predetermined torque, they become tightly fitted together, completing the fixing of the steel bracket 10 (C).

[0032] By adopting this structure, the gap between the fastening hole 13 of the steel bracket 10 and the surface of the fastener 12 is eliminated, and the shear force transmitted to the steel bracket 10 by the tension of the external cable 21 is transmitted from the steel bracket 10 to the fastener 12 without going through the non-shrink mortar 18. As a result, displacement of the steel bracket 10 due to insufficient filling of the non-shrink mortar 18 in the gap between the fastening hole 13 and the fastener 12 or crushing of the non-shrink mortar 18 due to bearing pressure is prevented, the introduction of prestress to the existing bridge girder by the external cable is stabilized, and the reinforcement effect of the external cable is maximized.

[0033] Furthermore, by making the tip of the fastener 17 a convex spherical shape, and making the inner circumferential surface of the fastening hole 13 of the steel bracket 10 a concave spherical shape so that it can closely contact and receive the convex spherical surface of the fastener 17, even if the position of the fastening hole 13 of the steel bracket 10 is misaligned, the convex spherical surface of the fastener 17 can rotate freely along the concave spherical surface of the inner circumferential surface of the fastening hole 13, thereby enabling the steel bracket 10 to be fixed to the existing bridge girder.

[0034] The fastening material 12 can be made of any material that has sufficient strength to resist the shear force caused by the tension of the external cable, for example, PC steel bars or SS material.

[0035] In this embodiment, reinforcement is carried out with one external cable on one existing bridge girder 1, but the present invention can be similarly applied to a configuration in which external cables are arranged on both sides of the web portion of the existing bridge girder 1. [Explanation of Symbols]

[0036] 1…Existing bridge girder 1a... Lower flange 1b...Web Department 1d... Through hole 1e... Lower flange bottom surface 10…Steel bracket 11…Side wall 12… Fasteners 13…Fastening hole 15…Cable support section 16…Reinforcement bars 17… Fasteners 18…Non-shrink mortar 21…External cable

Claims

1. In a structure for fixing steel brackets for external cable reinforcement to a concrete girder, A fastening material for fastening the concrete girder and the steel bracket, A fastening hole provided on the side surface of the steel bracket for inserting the fastening material, The steel bracket has a fastener for fastening one end of the fastening material to the fastening hole, The surface of the fastener that contacts the inner circumferential surface of the fastening hole of the steel bracket is convex spherical in shape. The inner circumferential surface of the fastening hole of the steel bracket is in a concave spherical shape that is in close contact with and receives the convex spherical surface of the fastener. A shear force acts on the fastening material due to the tension of the external cable. Steel bracket fixing structure for external cable reinforcement construction methods.

2. A steel bracket fixing structure for the external cable reinforcement method described in Claim 1, The present invention further comprises non-shrink mortar filled in the gap between the concrete girder and the steel bracket. Steel bracket fixing structure for external cable reinforcement construction methods.

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