structure

Abstract

To provide a structure which includes a plurality of main girders supported by a bearing and a counter-tilt structure for joining the main girders to each other, has high corrosion resistance, and can be restored in an early stage even when level 2 earthquake motion or earthquake motion exceeding assumption occurs.SOLUTION: A structure 100 according to an embodiment is provided with a plurality of main girders 2, 2 supported by a bearing 1, and a counter-tilt structure 3 for joining the main girders 2, 2 to each other. The counter-tilt structure 3 has a bolt joint part 6 in which a gusset plate 4 is bolt-joined to both ends in an extending direction thereof. At least one of the counter-tilt structure 3 and the gusset plate 4 is composed of FRP. The bearing force of the counter-tilt structure 3, the bearing force of the gusset plate 4, and the bearing force of the bolt joint part 6 are larger than the load due to the level 1 earthquake motion. At least one of the bearing force of the counter-tilt structure 3, the bearing force of the gusset plate 4, and the bearing force of the bolt joint part 6 is less than the sliding bearing force of the bearing 1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a structure having a plurality of main girders supported by supports and counter-bracing structures that connect the main girders to each other. [Background technology]

[0002] Conventionally, counter-tilt structures are provided to join main girders together in order to prevent twisting of the main girders due to lateral loads such as earthquake loads and wind loads. For example, in Patent Document 1, the primary members for bearing the self-weight of the structure are divided, and friction dampers are provided between the divided primary members. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-124553 A Summary of the Invention [Problem to be solved by the invention]

[0004] Normally, the counter-tilt structure and the gusset plate are made of steel, and the girder end of a steel bridge is a part that is severely corroded and damaged by water leakage from the expansion device, so if the counter-tilt structure installed at the girder end is corroded and damaged, it is concerned that it will no longer be able to function as a counter-tilt structure. In addition, structures may be damaged by large earthquake motions such as level 2 earthquake motions. For this reason, even if level 2 earthquake motions or earthquake motions that exceed the expected level occur, it is required that the soundness of the structure is maintained as much as possible without falling from the supports, and that damaged structures can be restored quickly. However, the technology disclosed in Patent Document 1 requires the installation of heavy dampers, which makes the construction large-scale and increases the dead load. Therefore, the technology disclosed in Patent Document 1, which installs dampers, has concerns about the soundness of the structure in an emergency, and it is difficult to restore it quickly.

[0005] The present invention has been devised in consideration of the above-mentioned circumstances, and its objective is to provide a structure comprising a plurality of main girders supported by supports and counter-bracing structures that join the main girders together, which has high corrosion resistance and can be quickly restored even in the event of a level 2 earthquake motion or earthquake motion exceeding expectations. [Means for solving the problem]

[0006] The structure of the present invention is a structure comprising a plurality of main girders supported by supports and a counter-tilt structure which joins the main girders together, wherein the counter-tilt structure has bolted joints at both ends in its extension direction to which gusset plates are bolted, and at least one of the counter-tilt structure and the gusset plate are made of FRP, and the strength of the counter-tilt structure, the strength of the gusset plate and the strength of the bolted joint are greater than the load due to level 1 earthquake motion, and at least one of the strength of the counter-tilt structure, the strength of the gusset plate and the strength of the bolted joint are less than the sliding strength of the support. Effect of the Invention

[0007] The present invention has high corrosion resistance and allows for early restoration even in the event of a Level 2 earthquake or earthquake motion that exceeds expectations. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view showing an example of a structure according to an embodiment. [Diagram 2] FIG. 2 is a front view showing an example of a structure according to the embodiment. [Diagram 3] FIG. 3 is a photograph showing the test specimens after the tensile test, where FIG. 3(a) shows the test specimen of Comparative Example 1, FIG. 3(b) shows the test specimen of Example 1, and FIG. 3(c) shows the test specimen of Example 2. [Figure 4] FIG. 4 is a graph showing the relationship between load and displacement obtained by a tensile test. [Diagram 5] FIG. 5 is a photograph showing an overview of the test specimen in the compression test. [Figure 6] FIG. 6 is a graph showing the relationship between load and displacement in the compression test. [Figure 7] 7A and 7B are photographs showing the test specimens after the compression test, with FIG. 7A showing the test specimen of Example 4 and FIG. 7B showing the test specimen of Example 5. [Figure 8] FIG. 8 is a graph showing the relationship between strain and load in FEM analysis 1. [Figure 9] FIG. 9 is a diagram showing an outline of the analysis model used in the FEM analysis 2. [Figure 10] FIG. 10 is a graph showing the relationship between strain and load in Example 6. [Figure 11] FIG. 11 is a graph showing the relationship between strain and load in Example 7. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an example of a structure according to an embodiment of the present invention will be described with reference to the drawings.

[0010] 1 and 2, a structure 100 includes a plurality of main girders 2, 2 supported by supports 1, and a counter-bracing structure 3 that connects the main girders 2, 2 to each other. The structure 100 is, for example, a bridge.

[0011] The bearing 1 is placed on, for example, a bridge pier 81. The bearing 1 is a known bearing that supports a main girder 2.

[0012] The main girder 2 is a steel girder made of steel and formed with an I-shaped cross section. A deck 82 and the like are provided on the upper side of the main girder 2. The main girder 2 has a pair of flanges 21, 22, a web 23 connecting the pair of flanges 21, 22, and a vertical stiffener 24 provided between the pair of flanges 21, 22. A gusset plate 4 is joined to the vertical stiffener 24, for example, by bolts.

[0013] The counter-tilt structure 3 joins the main girders 2, 2 via gusset plates 4. The counter-tilt structure 3 has an end counter-tilt structure provided at the end of the main girder 2 in the extension direction, and an intermediate counter-tilt structure provided between the end of the main girders 2 in the extension direction. For example, angle iron is used for the counter-tilt structure 3. Square pipes, etc. may also be used for the counter-tilt structure 3. The counter-tilt structure 3 has bolt joints 6 at both ends in the extension direction to which the gusset plates 4 are bolted.

[0014] At least one of the counter-tilt structure 3 and the gusset plate 4 is made of FRP (Fiber Reinforced Plastics). FRP uses a thermosetting resin such as epoxy resin or vinyl ester resin as a matrix resin, and contains at least one of carbon fiber and glass fiber as reinforcing fibers. The carbon fiber may be either PAN-based carbon fiber or pitch-based carbon fiber. FRP is made by laminating two or more layers of fibers, and the fiber direction of FRP has a first fiber direction along the axial direction of the counter-tilt structure 3 and a second fiber direction different from the first fiber direction, and it is essential that the carbon fiber is arranged in the first fiber direction at least in the outermost layer of the FRP. Generally, carbon fiber reinforced plastic has high sliding properties, but wear of the matrix resin due to sliding suppresses excessive sliding, so it is presumed that by making the outermost layer of the FRP a carbon fiber layer in the first fiber direction, a smooth transition from a friction joint when a load due to normal operation or level 1 earthquake motion acts to a pressure bearing joint when a load due to level 2 earthquake motion acts is made.

[0015] Furthermore, when FRP is used for both the counter tilt structure 3 and the gusset plate 4, it is preferable that the angle between the fiber directions of both at the contact surface is 40° or less or 50° or more, from the viewpoint of reducing the friction coefficient.

[0016] The anti-tilt structure 3 has an upper chord 31 and a lower chord 32 extending along the horizontal direction, and two diagonal members 33 inclined with respect to the horizontal direction.

[0017] The upper chord 31 has bolted joints 6 at both ends in its extension direction where gusset plates 4 joined to the vertical stiffeners 24 are bolted. The upper chord 31 has the gusset plate 4 joined to the center of its extension direction by welding, bolts, etc.

[0018] The lower chord 32 has bolted joints 6 at both ends in its extension direction to which gusset plates 4 joined to vertical stiffeners 24 are bolted.

[0019] The diagonal members 33 have, at one end in the extension direction, a bolted joint 6 to which a gusset plate 4 joined to the vertical stiffener 24 is bolted, and at the other end in the extension direction, a bolted joint 6 to which a gusset plate 4 joined to the center of the upper chord member 31 is bolted. The gusset plate 4 joined to the center of the upper chord member 31 has a bolted joint 6 to which each diagonal member 33 is bolted.

[0020] 2, the gusset plate 4 to which the two diagonal members 33 are joined is joined to the center of the upper chord member 31, but in the present invention, the gusset plate 4 to which the two diagonal members 33 are joined may be joined to the center of the lower chord member 32. In this case, the end of the diagonal member 33 opposite to the end joined to the gusset plate 4 provided at the center of the lower chord member 32 is bolted to the gusset plate 4 joined to the upper chord member 31.

[0021] High-strength bolts are used for bolted joints. High-strength bolts are bolts for friction joints of steel structures that comply with JIS B 1186 or are certified by the Minister of Land, Infrastructure, Transport and Tourism. Examples of high-strength bolts include high-strength hexagonal bolts, hot-dip galvanized high-strength bolts, and torsion-type high-strength bolts. Any of these can be used in the present invention.

[0022] The sliding resistance of the bearing 1, the resistance of the counter-tilt structure 3, the resistance of the gusset plate 4, and the resistance of the bolted joint 6 are greater than the load caused by Level 1 earthquake motion. At least one of the resistance of the counter-tilt structure 3, the resistance of the gusset plate 4, and the resistance of the bolted joint 6 is less than the sliding resistance of the bearing 1.

[0023] The joining state of the bolted joint 6 is a frictional joint under normal conditions and when a load due to a level 1 earthquake motion acts, and is a bearing joint when a load due to a level 2 earthquake motion acts.

[0024] It is preferable that the sliding resistance of the bearing 1 is greater than the load due to the level 2 earthquake motion. In this case, it is possible to resist the level 2 earthquake motion and to further prevent the main girder 2 from falling off the bearing 1. The resistance of the counter-bracing structure 3, the resistance of the gusset plate 4, and the resistance of the bolt joint 6 may be less than the load due to the level 2 earthquake motion.

[0025] In this embodiment, at least one of the counter-tilt structure 3 and the gusset plate 4 is made of FRP. This improves corrosion resistance compared to when both the counter-tilt structure 3 and the gusset plate 4 are made of steel. In addition, since FRP is lighter than steel, the load on the support is reduced and earthquake resistance is improved. Furthermore, compared to when both the counter-tilt structure 3 and the gusset plate 4 are made of steel, the friction coefficient between the counter-tilt structure 3 and the gusset plate 4 can be reduced. Therefore, when a load caused by an earthquake motion exceeding a level 1 earthquake motion acts on the bolt joint 6, the joint state of the bolt joint 6 transitions from a friction joint to a bearing joint, exhibiting ductile behavior. As a result, the impact given to the structure 100 when transitioning from a friction joint to a bearing joint can be suppressed. In addition, since it exhibits ductile behavior, it is easy to predict the fracture load.

[0026] In this embodiment, the strength of the counter bracket 3, the strength of the gusset plate 4, and the strength of the bolt joint 6 are greater than the load caused by level 1 earthquake motion. This allows the structure 100 to resist level 1 earthquake motion.

[0027] In this embodiment, at least one of the strength of the counter-tilt structure 3, the strength of the gusset plate 4, and the strength of the bolted joint 6 is less than the slip resistance of the bearing 1. As a result, in the event of a Level 2 earthquake motion or an earthquake motion exceeding the expected level, at least one of the counter-tilt structure 3, the gusset plate 4, and the bolted joint 6 can be destroyed before slippage occurs in the main girder 2 supported by the bearing 1. For this reason, it is only necessary to replace the destroyed counter-tilt structure 3, the gusset plate 4, and the bolted joint 6, and there is no need to replace the bearing 1 or the main girder 2, so the structure 100 can be restored early.

[0028] In this embodiment, the FRP is configured by laminating two or more layers of fibers, and the fiber direction of the FRP has a first fiber direction along the axial direction of the counter tilt structure 3 and a second fiber direction different from the first fiber direction. This allows the stress transmitted by the bearing pressure in the bolt joint 6 to be smoothly transmitted in a direction intersecting the axial direction of the counter tilt structure 3. As a result, the shear fracture resistance of the bolt joint 6 can be improved.

[0029] In this embodiment, the joining state of the bolted joint 6 is a frictional joint under normal conditions and when a load due to a level 1 earthquake motion acts, and is a bearing joint when a load due to a level 2 earthquake motion acts. This makes it possible to more reliably improve the bearing strength of the bolted joint 6. EXAMPLES

[0030] In the following, tensile tests, compression tests, and FEM analysis were conducted to examine the load-bearing capacity when FRP is used for at least one of the counter beam structure and the gusset plate.

[0031] (Tensile test) In the tensile test, a 2000kN universal testing machine was used to perform the test under displacement control until fracture. An overview of the test specimens is shown in Table 1. Test specimens for the tensile test were prepared for Comparative Example 1, Example 1, and Example 2. In addition, the coefficient of friction between the angle bar and the gusset plate was calculated by dividing the slip resistance by the bolt axial force.

[0032] [Table 1]

[0033] The specimen for the tensile test was a gusset plate bolted to a 100 x 100 x 14 mm angle bar. The gusset plate was a flat plate measuring 375 mm long, 101 mm wide and 9 mm thick. F8T zinc-plated high-strength bolts were used. The friction surfaces of the SS400 gusset plate and angle bar were left black, while the FRP gusset plate and angle bar were left untreated. The members were joined using a friction joint, and the axial force was controlled to be 205 kN based on the value of the strain gauge attached to the bolt shaft.

[0034] In Comparative Example 1, bolt slippage occurred at a load of 239 kN, and the maximum load was 284 kN. As shown in Fig. 3(a), the failure mode in Comparative Example 1 was failure from the bolt hole of the steel gusset plate. The friction coefficient between the angle bar and the gusset plate was 0.52.

[0035] In Example 1, bolt slippage occurred at a load of 133 kN, and the maximum load was 268 kN. As shown in Fig. 3(b), the failure mode in Example 1 was a bearing failure from the FRP angle material. The friction coefficient between the angle material and the gusset plate was 0.35.

[0036] In Example 2, bolt slippage occurred at a load of 96 kN, and the maximum load was 233 kN. As shown in Fig. 3(c), the failure mode in Example 2 was a bearing failure from the FRP gusset plate. The friction coefficient between the angle bar and the gusset plate was 0.29.

[0037] FIG. 4 shows the relationship between the load and the displacement of the test specimen in the tensile test. In Comparative Example 1, the load significantly decreased when the bolt slipped, and the specimens exhibited brittle behavior, whereas in Examples 1 and 2, the load did not significantly decrease when the bolt slipped, and the specimens moved to bearing joints, exhibiting ductile behavior. The slip resistance of Example 1 was smaller than that of Comparative Example 1, but the slip resistance of Example 1 (133 kN) was 1.35 compared to the design value of the slip resistance of Comparative Example 1 (96 kN). The slip resistance of Example 2 (96 kN) was 1.00 compared to the design value of the slip resistance of Comparative Example 1 (96 kN). The maximum load of the test specimens of Examples 1 and 2 was not significantly different from the maximum load of Comparative Example 1.

[0038] From the above, by constructing at least one of the counter-tilt structure and the gusset plate from FRP, the coefficient of friction between the counter-tilt structure and the gusset plate can be reduced compared to when both the counter-tilt structure and the gusset plate are constructed from steel. Therefore, when a load caused by a level 2 earthquake motion or an earthquake motion exceeding the expected level acts on the bolted joint, the joint state of the bolted joint transitions from a friction joint to a bearing joint, exhibiting ductile behavior. As a result, the impact on the structure when transitioning from a friction joint to a bearing joint can be greatly suppressed. Furthermore, because it exhibits ductile behavior, it becomes easier to predict the fracture load.

[0039] (Compression test) The specimen for the compression test was designed assuming an end-to-end tilt structure, and was created by bolting a gusset plate and stiffener to both ends of the angle bar. The length of the angle bar of the test specimen was 1400 mm, and the slenderness ratio was about 50. The outline of the test specimen is shown in Table 2 and Figure 5. The FRP laminate structure of the angle bar with a mountain cross section (100 x 100 x 14 mm) used in the compression test is a hybrid laminate structure in which carbon fiber is laminated in the axial direction of the angle bar and glass fiber is laminated in the multi-axial direction. The treatment of the friction surfaces of the angle bar and the gusset plate was the same as that of the tensile test. The compression test was performed using a compression testing machine with a maximum load of 300 kN, and the loading method was displacement control.

[0040] [Table 2]

[0041] Figure 6 shows the relationship between load and displacement in the compression test. After the bolts slipped, each test specimen was destroyed at the maximum load (ultimate strength). Comparing the maximum loads, the maximum loads were 250 kN in Comparative Examples 2 and 3, 150 kN in Example 4, and 110 kN in Examples 3 and 5.

[0042] As shown in Fig. 7(a), the fracture mode in Example 4 was local fracture of the FRP angle due to plastic deformation of the steel gusset plate. As shown in Fig. 7(b), the fracture mode in Example 5 was delamination of the FRP gusset plate. Although not shown, the fracture mode in Example 3 was also delamination of the FRP gusset plate.

[0043] In addition, when the relationship between the load and strain in the compression test of Example 4 was measured, it was found that delamination began to occur at a strain of about 4700μ. Based on this, the breaking strain of the gusset plate was defined as 4700μ.

[0044] (FEM analysis 1) The compression test specimen was modeled using FEM analysis to evaluate the validity of the analytical model (FEM analysis 1). The analytical model of the compression test specimen was constructed using solid elements, and only Young's modulus was defined as the material property of the member. As shown in Figure 8, when the strain of the gusset plate in the analytical model was compared with the strain of the gusset plate in the compression test, they were roughly consistent, and therefore the analytical model was deemed valid. As the analysis was not able to reproduce the destruction up to the point, the ultimate state was defined. The ultimate state was defined by referring to the compression test, and was defined as the point when the strain of the gusset plate reached the fracture strain (when the strain was 4700μ).

[0045] (FEM analysis 2) Next, FEM analysis was used to evaluate the load-bearing capacity acting on the end brace structure that connects the bridge's main girders (FEM analysis 2). The analysis model was based on the end brace structure of a bridge with four main girders and a span length of 33m, described in the bridge design casebook "Examples and Commentary of Composite Girders" (published by the Japan Bridge Construction Association, pp. 68-78, 1995), and the load-bearing capacity of the end brace structure members against level 1 and level 2 earthquake motions was evaluated.

[0046] The outline of the analysis model used in FEM analysis 2 is shown in Fig. 9. The supports supporting the main girders of the analysis model were completely fixed. The end-to-end bracing structure in the analysis model has an upper chord, a lower chord, and a diagonal member, and gusset plates A to D are bolted to both ends of each. Concentrated loads were applied to the positions of the upper chord and the lower chord in the analysis model. In FEM analysis 2, the relationship between strain and load was obtained for gusset plate A at one end of the upper chord, gusset plate B bolted to the other end of the upper chord, gusset plate C at the center of the upper chord bolted to the diagonal member, and gusset plate D bolted to one end of the lower chord. Referring to FEM analysis 1, in FEM analysis 2, the ultimate state was determined when the strain reached 4700μ.

[0047] The outline of the analysis model used in FEM analysis 2 is shown in Table 3. The analysis model of Example 6 is an analysis model with a deck slab, simulating an actual structure. The analysis model of Example 7 is an analysis model without a deck slab, simulating a design model.

[0048] [Table 3]

[0049] The level 1 earthquake motion used in FEM analysis 2 is 137 kN, and the level 2 earthquake motion is 411 kN. As shown in Figs. 10 and 11, in Example 6 and Example 7, at the time of the level 1 earthquake motion, none of the gusset plates A to D reached their ultimate state, and the safety of the end-to-end bracing structure was ensured. In Example 6, at the time of the level 2 earthquake motion, none of the gusset plates A to D reached their ultimate state, and the safety of the end-to-end bracing structure was ensured. In Example 7, at the time of the level 2 earthquake motion, the gusset plates A and C reached their ultimate state. However, the bridge as a whole did not collapse, and the ultimate parts were only the gusset plates.

[0050] For this reason, by making the strength of the gusset plate less than the slip resistance of the support, it is possible to destroy the gusset plate before slip occurs in the main girder when a Level 2 earthquake motion or earthquake motion that exceeds the assumption occurs. Although the gusset plate was considered in this analysis, the same applies to the counter-tilt structure and bolted joints. In other words, if at least one of the strength of the counter-tilt structure, the strength of the gusset plate, and the strength of the bolted joints is designed to be less than the slip resistance of the support, it can be said that at least one of the counter-tilt structure, the gusset plate, and the bolted joints can be destroyed before slip occurs in the main girder.

[0051] In this way, if a level 2 earthquake or an earthquake beyond expectations (for example, equivalent to level 2 earthquake motion or above) occurs and at least one of the anti-tilt structure, gusset plate, or bolted joint is destroyed, it is sufficient to replace the destroyed anti-tilt structure, gusset plate, or bolted joint, and there is no need to replace the supports or main girders, allowing the structure to be restored quickly. [Explanation of symbols]

[0052] 100: Structure 1: Bearing 2: Main digit 21: Flange 22: Flange 23: Web 24: Vertical stiffener 3: Anti-tilt structure 31:Top chord material 32: Lower chord 33: Diagonal material 4: Gusset plate 6: Bolted joint 81: Bridge pier 82: Floor slab

Claims

1. A structure comprising a plurality of main girders supported by supports and a counter-tilt structure connecting the main girders, The counter tilt structure has a bolt joint portion to which a gusset plate is bolted at both ends in the extension direction, At least one of the counter tilt structure and the gusset plate is made of FRP, The strength of the counter-tilt structure, the strength of the gusset plate, and the strength of the bolt joint are greater than the load caused by a level 1 earthquake motion, At least one of the strength of the counter-tilt structure, the strength of the gusset plate, and the strength of the bolt joint is less than the slip strength of the support. A structure characterized by:

2. The FRP is constructed by laminating two or more layers of fibers, The fiber direction of the FRP has a first fiber direction along the axial direction of the counterweight structure and a second fiber direction different from the first fiber direction.

2. The structure of claim 1,

3. The FRP contains at least one of carbon fiber and glass fiber.

2. The structure of claim 1,

4. The connection state of the bolted joint is a frictional connection under normal conditions and when a load due to a level 1 earthquake motion is applied, and a bearing connection when a load due to a level 2 earthquake motion is applied.

2. The structure of claim 1,

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