Energy absorbing member and pretreatment method thereof

Abstract

This avoids cost increases for the main body of the braking system into which the energy-absorbing component is incorporated, as well as for the devices to which the system is applied. [Solution] An energy absorbing member made of steel is attached at both ends between two mounting parts spaced apart from each other, and a tensile force is applied to increase the distance between the mounting parts. A pre-deformation is given where the strain exceeds the elastic range by applying a tensile force in advance. The energy absorbing member is a component that is incorporated into a braking device installed between a seismic isolation building and its foundation.

Description

Technical Field

[0001] This invention relates to an energy absorption member, and more particularly to an energy absorption member made of a steel material such as low yield point steel incorporated in a braking device installed between a seismic isolation building and a foundation, and a pretreatment method thereof.

Background Art

[0002] As a braking device incorporating an energy absorption member made of a steel material such as low yield point steel, the applicant of this application proposed the one described in Patent Document 1. This braking device (in Patent Document 1, the invention name is "displacement limiting device") is installed between a building and a foundation in a building equipped with a seismic isolation device, thereby suppressing excessive deformation of the seismic isolation device, avoiding the collision between the building and the retaining wall, preventing large swaying and damage of the building, and having a function of greatly attenuating vibration energy.

[0003] This braking device includes a cylindrical body and a rod that moves inside the cylindrical body, and movable end plates that move by the heads at the rod tips are provided at both ends of the cylindrical body. The energy absorption member has both ends attached between the movable end plate and the outer periphery of the axial intermediate part of the cylindrical body, and by the action of tensile force due to the movement of the movable end plate, excessive deformation of the seismic isolation device is suppressed, and vibration energy is absorbed by plastic deformation.

[0004] Regarding the energy absorption member incorporated in the braking device described in Patent Document 1, the inventors of this invention conducted a loading test by variously changing the tensile speed (strain rate) (1 cm / s to 80 cm / s). As a result, in the load-displacement relationship, as shown in FIG. 5, it was confirmed that the upper yield point (indicated by the symbol P) that appears at the rising of the load protrudes in a spike shape.

[0005] The load indicated by the upper yield point is less than the tensile strength of the material due to velocity dependence when the tensile speed of the steel is low (static or low-speed loading), so it does not need to be considered as the maximum reaction force during design. On the other hand, when the tensile speed of the steel is high (e.g., 10 cm / s or more), the upper yield point rises in a spike-like manner due to velocity dependence and becomes greater than the tensile strength of the material, and the load indicated by the upper yield point can become the maximum reaction force in design.

[0006] The design strength of the braking device and the structural strength of the building-side mounting section to which the braking device is attached must take into account the maximum reaction force of the energy-absorbing member. However, in the case of energy-absorbing members where high-speed loading is expected, it is necessary to anticipate the spike-shaped upper yield point load. However, anticipating this requires increasing the cross-sectional shape of the braking device body and the mounting section structure, or increasing the material strength, which leads to increased costs for the device's manufacture and its application. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-030727 [Overview of the project] [Problems that the invention aims to solve]

[0008] This invention was made based on the technical background described above, and aims to achieve the following objectives. The objective of this invention is to avoid cost increases for the main body of the braking device into which the energy-absorbing member is incorporated, and for the devices to which the device is applied. [Means for solving the problem]

[0009] The inventors of this invention conducted extensive research to solve the above-mentioned problems and discovered the following phenomenon: When repeated loading using seismic response waves was applied to an energy-absorbing member made of low-yield-point steel, as shown in Figure 1, the spike-like load that occurred during the first loading (load 1) was not observed in the second and subsequent loadings (load 2 and load 3) after the energy-absorbing member had yielded once.

[0010] As a result of discovering this phenomenon, we realized that if the energy-absorbing member is deformed in advance, the spike-like load will no longer appear when it experiences subsequent load applications and is put into practical use. Therefore, it is not necessary to account for this spike-like load as the maximum reaction force during the design phase.

[0011] This invention is based on the above-described background and is defined as follows: This invention is an energy absorbing member made of steel, which has both ends attached between two spaced-apart mounting parts, and is subjected to a tensile force such that the distance between the mounting parts increases. The energy absorbing member is characterized by being pre-deformed to a point where the strain exceeds the elastic range due to the application of a tensile force beforehand.

[0012] More specifically, the energy absorbing member is a component that is incorporated into a braking device installed between the seismically isolated building and its foundation.

[0013] Furthermore, this invention relates to a pretreatment method for an energy absorbing member made of steel, in which both ends are attached between two mounting parts spaced apart from each other, and a tensile force is applied such that the distance between the mounting parts becomes large. The present invention relates to a pretreatment method for an energy-absorbing member, characterized by applying a tensile force in advance to induce pre-deformation that exceeds the elastic range.

[0014] More specifically, the energy absorbing member is a component that is incorporated into a braking device installed between the seismically isolated building and its foundation. Pre-deformation is applied by operating the braking device either before or after its installation. [Effects of the Invention]

[0015] According to this invention, it is possible to avoid cost increases for the device body, such as a braking device into which the energy absorbing member is incorporated, and for the device to which it is applied. [Brief explanation of the drawing]

[0016] [Figure 1] This graph shows the load (tensile stress)-displacement (elongation) relationship when repeated loads (loads 1-3) are applied to an energy-absorbing member made of low-yield-point steel. [Figure 2] An example of a braking device incorporating an energy-absorbing member is shown, with (a) being a plan view and (b) being an axial cross-sectional view. [Figure 3] This is a perspective view showing an energy-absorbing component. [Figure 4] An example of a jig used to pre-deform an energy-absorbing member is shown, with (a) being a plan view and (b) being a cross-sectional view. [Figure 5] This graph shows the load-displacement relationship when a loading test is performed with various tensile speeds (strain rates). [Modes for carrying out the invention]

[0017] Embodiments of this invention will be described below with reference to the drawings. First, the configuration of the braking device described in Patent Document 1 (as previously mentioned, referred to in that document as a "displacement limiting device"), to which the energy absorbing member according to this invention is assembled, will be briefly described.

[0018] The braking device 10 is arranged between a building having a seismic isolation device and a foundation, and as shown in FIG. 2, includes a cylindrical body 11 and a rod 12 that is movable within the cylindrical body 11. One end of the cylindrical body 11 is connected to the building (or the foundation) via a clevis 13, and the rod 12 protruding from the other end of the cylindrical body 11 is connected to the foundation (or the building) via a clevis 14.

[0019] Notch grooves 15 are formed at both ends of the cylindrical body 11, and movable end plates 16a, 16b that are guided by the notch grooves 15 and are movable in the axial direction are provided. A head 17 that is slidable along the inner circumference of the cylindrical body 11 is provided at the tip of the rod 12, and a plurality of disc springs are incorporated in this head to mitigate impact when it collides with the movable end plates 16a, 16b.

[0020] Energy absorption members 20 made of steel materials such as low yield point steel are attached at both ends between the movable end plate 16a and the outer circumference of the intermediate portion in the axial direction of the cylindrical body 11, and between the movable end plate 16b and the outer circumference of the intermediate portion in the axial direction of the cylindrical body 11. The attachment portions of the energy absorption members 20 provided on the movable end plates 16a, 16b and the cylindrical body 11 respectively correspond to the "two spaced-apart attachment portions" defined in the claims. A plurality of energy absorption members 20 are provided at intervals in the circumferential direction of the cylindrical body 11.

[0021] In the braking device 10 as described above, if the displacement of the seismic isolation device accompanying the displacement of the building due to an earthquake or the like is within a distance S, the head 17 moves within the cylindrical body 11 and the braking device 10 expands and contracts, but no tensile force acts on the energy absorption member 20. On the other hand, when the displacement of the seismic isolation device exceeds the distance S, the head 17 collides with the movable end plates 16a, 16b, and the movable end plates 16a, 16b are moved in the axial direction so that the separation distance between the attachment portions of the energy absorption member 20 increases. As a result, a tensile force acts on the energy absorption member 20 to restrain the displacement of the seismic isolation device. Further, when the energy absorption member 20 is strained beyond the elastic range by tension, it absorbs and attenuates vibration energy.

[0022] The energy absorbing member 20, made of steel such as low yield strength steel, has a predetermined length, width, and thickness, and as shown in Figure 3, widened portions 21 are provided at both ends. One of the widened portions 21 is attached to the movable end plates 16a and 16b, and the other is attached to the cylindrical body 11.

[0023] The energy absorbing member 20 is pre-treated as follows. The widened portions 21 at both ends of the energy absorbing member 20 are fixed to a pair of jigs 30, 30, as shown in Figure 4. The jigs 30 are equipped with inter-jig displacement gauges 31 and jig sliding displacement gauges 32, and strain gauges 33 are attached to the energy absorbing member 20. These jigs 30, 30 are then set in a uniaxial loading device (not shown), and the energy absorbing member 20 is subjected to tensile load by the operation of the device, thereby pre-deforming it. After pre-deformation, the energy absorbing member 20 is unloaded and assembled into the braking device 10.

[0024] The pre-deformation of the energy absorbing member 20 may be performed not only before assembly to the braking device 10, but also after assembly. That is, after assembling the energy absorbing member 20 to the braking device 10, the clevis 13 on the cylindrical member 11 side and the clevis 14 on the rod 12 side of the braking device 10 are connected to a uniaxial load-bearing device. Then, the braking device 10 is operated via the operation of the uniaxial load-bearing device to apply a tensile load to the energy absorbing member 20, pre-deform it, and then the load is removed.

[0025] Here, the amount of pre-deformation applied should be limited to approximately 3% of the tensile strain (elongation). In the load-displacement relationship, after the strain exceeds the elastic range and the upper yield point is reached, the initial strain in the strain region called the yield shelf (indicated by symbol A in Load 1 of Figure 1) is the optimal amount.

[0026] Furthermore, the loading can be either dynamic (high-speed) loading or static (low-speed) loading, but in order to accurately pre-deform, a strain rate of about 0.3% / min is preferable. In addition, it is preferable that the multiple energy absorbing members 20 arranged on the same movable end plates 16a and 16b side in the braking device 10 are subjected to the same pre-deformation.

[0027] As described above, when the pre-deformed energy absorbing member is put into practical use, that is, when the braking device 10 is installed in the seismically isolated building, it will not exhibit the load (tensile stress)-displacement (elongation) relationship shown in Load 1 in Figure 1, but will exhibit relationships like Loads 2 and 3, in which spike-like loads do not occur.

[0028] Therefore, it becomes unnecessary to anticipate spike-like loads in the design of the device itself or the building mounting structure, allowing for a slimmer design of the device and mounting structure. This enables the manufacturing and operation of the device at a lower cost. Furthermore, by applying the aforementioned pre-deformation, it becomes possible to perform quality checks and manufacturing processes simultaneously.

[0029] The braking device shown in the above embodiment is merely illustrative, and the energy absorbing member according to this invention can be applied to various types of devices that exhibit an energy absorbing function when a tensile load is applied. Furthermore, the energy absorbing member covered by this invention is not limited to low yield strength steel, but also includes general steel.

[0030] As can be understood from the above explanation, this invention is preferably applied to energy absorbing members where the tensile speed (strain rate) is high. Here, a high tensile speed (strain rate) can be defined as "a speed range in which the initial load that shows the upper yield point in the load-displacement relationship exceeds the tensile strength of the material (steel)." However, no problems arise when it is applied to energy absorbing members where the strain rate is low or static. [Explanation of symbols]

[0031] 10: Braking device 11: Cylindrical body 12: Rod 13, 14: Clevis 16a, 16b: Movable end plate 17: Head 20: Energy absorbing member 30: Jig

Claims

1. An energy absorbing member made of steel, which has both ends attached between two mounting parts spaced apart from each other, and on which a tensile force is applied so as to increase the distance between the mounting parts, An energy-absorbing member characterized by being pre-deformed to a state where the strain exceeds the elastic range by being subjected to a tensile force beforehand.

2. The energy absorbing member according to claim 1 is characterized in that the energy absorbing member is a member that is incorporated into a braking device installed between a seismically isolated building and its foundation.

3. A pretreatment method for an energy absorbing member made of steel, in which both ends are attached between two mounting parts spaced apart from each other, and a tensile force is applied such that the distance between the mounting parts becomes large, A pretreatment method for an energy-absorbing member, characterized by applying a tensile force in advance to induce pre-deformation that exceeds the elastic range.

4. The pretreatment method for an energy absorbing member according to claim 3, characterized in that the energy absorbing member is a member that is assembled to a braking device installed between a seismically isolated building and its foundation.

5. The pretreatment method for an energy absorbing member according to claim 4, characterized in that pre-deformation is applied by operating the braking device before or after assembly to the braking device.

Images