JP2013057207A - Exposure type column base structure of iron frame column - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure type column base structure of an iron frame column that can secure large elastic rotational rigidity against flexural moment operating on a column base structure, and exhibit energy absorption performance of good efficiency on both an extension side and a compression side.SOLUTION: The exposure type column base structure includes: a square steel pipe column 1 installed on an upper surface 3a of base concrete across a base plate 2 joined to a lower end; a plurality of anchor bolts 7 fixed to the base concrete in an array surrounding an outer periphery of the base plate; and an energy absorption member 8 which is provided having an inner end 8a fitted to a corner part 1b of the square steel pipe column at an interval C above the base plate and also having an outer end 8b fitted to the anchor bolts, and absorbs energy over shearing deformation with flexural moment operating on the square steel pipe column.

Description

  The present invention is an exposed type of a steel column that can secure a large elastic rotational rigidity with respect to a bending moment acting on a column base, and can exhibit efficient energy absorption performance on both the tension side and the compression side. It relates to the column base structure.

  In the conventional exposed column base structure of a steel column, there are one that absorbs energy such as an earthquake by plastically deforming an anchor bolt or a base plate, and one that absorbs energy by plastically deforming a steel column.

  In the case of absorbing the energy by bearing with the former anchor bolts etc., if the anchor bolts etc. are plastically deformed, the base plate may be lifted from the foundation concrete, resulting in a state where almost no load can be transmitted to the foundation concrete. Yes, energy absorption capacity is poor. If the bolt diameter is increased or the base plate is made thicker in order to delay the plasticization of the anchor bolt or the base plate, the steel column will be plastically deformed, which is limited. Also, increasing the bolt diameter will increase costs.

  On the other hand, if the latter steel column is loaded with energy absorption, it is necessary to replace the plastically deformed steel column, and the repair work becomes large.

  Based on the above, on the premise of the former configuration, Patent Literature 1 and Patent Literature 2 disclose a technique that includes an energy absorption portion instead of an anchor bolt or the like. Patent Literature 1 discloses a “base-damping structure for column base” which is a column-base section that can easily secure the safety of a structure during an earthquake by giving a seismic control function to the column base. An object of the present invention is to provide a seismic control structure, and the leg of the column is provided so that it can be displaced in the vertical direction in a state in which the displacement in the horizontal direction is constrained on the guide column fixed to the foundation. A base plate damper that absorbs the tensile force by bending yield or shear yield when a tensile force is applied to the column is interposed between the portion and the portion.

  More specifically, in the first embodiment, the tensile force is absorbed in a state where the steel column is arranged so as to surround the steel column and in contact with the foundation portion between the column base of the steel column and the mounting plate fixed to the foundation portion. A bending panel is provided. In the second embodiment, as in the first embodiment, the steel plate is disposed so as to be in contact with the support plate between the column base of the steel column and the support plate fixed to the support plate on the foundation portion. In the state, a shear panel is provided.

  Patent document 2 “Steel column fixing structure” eliminates the need for butt welding to thick plate base plate and steel column, and absorbs seismic energy by yielding deformation of vertical ribs or anchor bolts. An object is to provide a structure for fixing a column base of a steel column, and a plurality of vertical ribs having anchor bolt insertion portions are arranged at intervals in the circumferential direction of the steel column on the peripheral side surface of the leg portion of the steel column. In addition, the end of each vertical rib is fixed to the steel column, the anchor bolt fixed to the foundation concrete is inserted into the anchor bolt insertion portion in the vertical rib, and the vertical rib is fixed by the nut, thereby the steel column The column base is fixed to the foundation concrete through the vertical ribs fixed to it and the anchor bolts fixed to the foundation concrete, and the tensile stress acting on the steel column is And so as to be transmitted to the foundation concrete through the longitudinal ribs and the anchor bolts without passing through the plate.

  Specifically, in the first to third embodiments, the horizontal displacement of the steel column is constrained by the short core material, and the vertical rib is brought into contact with the base plate between the leg of the steel column and the anchor bolt. It is provided in the state. In the fourth embodiment, a steel column whose horizontal displacement is constrained by a short core material is supported by vertical ribs and anchor bolts spaced apart from the foundation concrete.

JP 2004-92096 A JP 2009-24367 A

  Each patent document is an energy absorption structure for absorbing the vertical force of pulling out a steel column, and restrains the horizontal displacement of the steel column with a guide column or a short core material. For the bending moment acting on the column, the guide struts and the like resist the bending moment, and the base plate dampers and vertical ribs in these patent documents are not capable of efficiently absorbing energy against the bending moment. It was.

  Even if the bending panel or the shearing panel, which is a base plate damper, is deformed by bearing a bending moment in Patent Document 1, there are the following problems.

  In order to reduce the damage to the building by absorbing energy for the bending moment at the column base of the steel column, it is necessary to absorb energy from the stage of small rotational deformation as much as possible, that is, the elastic rotational rigidity of the column base. It is desirable to set as large as possible. If the elastic rotational rigidity is small, the bending moment cannot be absorbed efficiently.

  The bending panel of Patent Document 1 can exhibit an energy absorbing effect on the bending moment by out-of-plane bending yield, but large elastic rotational rigidity cannot be ensured by out-of-plane bending yield. In order to obtain a large elastic rotational rigidity, it is necessary to use a bent panel having a large thickness, which increases the cost.

  In addition, when viewed from the left and right of the steel column, the bending panel can exert energy absorbing action on the tension side due to the bending moment, but on the compression side, the bending panel hits the foundation part. It cannot function and cannot absorb energy on both the tension side and the compression side.

  Even if it is a shear panel, one end of the shear panel is fixed to the support plate via the support plate. Therefore, like the bending panel, out-of-plane deformation is likely to occur, and the elastic rotational rigidity is small. The bending moment cannot be absorbed effectively, and the energy cannot be absorbed on both the tension side and the compression side.

  About patent document 2, in the structure of the 1st-3rd embodiment, although a large elastic rotation rigidity can be ensured by a vertical rib, since a vertical rib exists in a contact state with a base plate, like patent document 1, On the compression side, the bending moment cannot be absorbed efficiently.

  In the configuration of the fourth embodiment, the vertical rib bears the vertical load of the building acting on the steel column in a static state. In this state, when a bending moment acts on the steel column, a compressive load acts on the compression-side longitudinal rib, and a tensile load acts on the tension-side longitudinal rib, the compression-side longitudinal rib applies a compressive load in addition to the vertical load. On the other hand, the vertical rib on the tension side is subjected to a force that reduces the tensile load from the vertical load, and there is a large difference in energy absorption between the tension side and the compression side of the steel column against the bending moment. Efficient energy absorption performance cannot be secured on both the left and right sides of the steel column.

  The present invention was devised in view of the above-described conventional problems, and can secure a large elastic rotational rigidity with respect to a bending moment acting on a column base, and is efficient energy on both the tension side and the compression side. An object of the present invention is to provide an exposed column base structure of a steel column capable of exhibiting absorption performance.

  The exposed column base structure of a steel column according to the present invention is fixed to a steel column installed on an upper surface of a foundation concrete through a base plate joined to a lower end, and to the foundation concrete in an arrangement surrounding an outer periphery of the base plate. A plurality of anchor bolts are provided with an inner end attached to a side portion of the steel column with an interval upward from the base plate and an outer end attached to the anchor bolt, and with respect to a bending moment acting on the steel column, An energy absorbing member that absorbs energy while being sheared and deformed is provided.

  The base plate is formed with an outer dimension that can be joined to a lower end of the steel column in order to reduce a moment arm from a column core of the steel column to an outer peripheral edge thereof.

  The lower surface of the base plate facing the upper surface of the foundation concrete is formed with a three-dimensional curved surface.

  The energy absorbing member includes a bolt-side attachment portion attached to the anchor bolt, a column-side attachment portion attached to a side portion of the steel column, and a steel column between the bolt-side attachment portion and the column-side attachment portion. It is provided in a longitudinal direction along the column axis direction, and is composed of a deformation absorbing portion that absorbs energy while being sheared and deformed.

  The deformation absorbing portion is formed with a deficient portion that adjusts energy absorbing ability.

  The bolt side mounting portion is formed in a hollow cylindrical shape through which the anchor bolt is inserted.

  In the exposed column base structure of a steel column according to the present invention, it is possible to secure a large elastic rotational rigidity with respect to a bending moment acting on the column base, and efficient energy absorption performance on both the tension side and the compression side Can be demonstrated.

1 is a partially broken side view showing a preferred embodiment of an exposed column base structure for a steel column according to the present invention. It is a perspective view which abbreviate | omits foundation concrete and shows the exposed type column base structure shown in FIG. It is a side view which illustrates typically the effect | action of the exposed type column base structure shown in FIG. It is a side view which shows the modification of the exposed type column base structure of the steel column which concerns on this invention. It is a side view explaining the effect | action of the modification shown in FIG. It is explanatory drawing explaining the other modification of the exposed type column base structure of the steel column which concerns on this invention.

  Hereinafter, a preferred embodiment of an exposed column base structure for a steel column according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a partially broken side view of an exposed-type column base structure of a steel column according to the present embodiment, and FIG. 2 is a perspective view showing the exposed-type column base structure shown in FIG. FIG. 3 is a side view for explaining the operation of the exposed column base structure shown in FIG.

  In the present embodiment, a rectangular steel pipe column 1 having a hollow cylindrical shape having a rectangular shape in a flat cross section and having opened upper and lower ends is illustrated as a steel column. The lower end of the column base 1a of the square steel pipe column 1 is closed, and the base plate 2 made of steel plate is joined by welding or the like. A bolt insertion hole 2 a is formed in the base plate 2 at the column core position of the square steel tube column 1.

  The steel column is not limited to the rectangular steel tube column 1 having a rectangular cross section, and may be a steel tube column having a polygonal or circular cross section, or an H-shaped steel column. In the case of an H-shaped steel column, a pair of bolt insertion holes 2a formed in the base plate 2 are formed at positions where the web is sandwiched.

  On the other hand, the main anchor bolt 4 is fixed to the foundation concrete 3 on which the square steel pipe column 1 is installed, protruding from the foundation concrete upper surface 3a. On the grout G constructed on the upper surface 3a of the concrete foundation, the main anchor bolt 4 is inserted into the bolt insertion hole 2a of the base plate 2 and the square steel pipe column 1 is installed through the base plate 2, and then the square steel pipe column 1 is attached. The square steel pipe column 1 is provided on the upper surface 3 a of the foundation concrete 3 by fastening a nut 6 via a washer 5 to an upper end thread portion of the main anchor bolt 4 from the provided work hole (not shown).

  The main anchor bolt 4 resists the force acting upward in the vertical direction and prevents the rectangular steel pipe column 1 from being pulled out. At the same time, the square steel pipe column 1 is allowed to tilt in the front-rear and left-right directions due to the bending moment M (see FIG. 3) acting on the column base 1a by the pin connection to the foundation concrete 3 by the main anchor bolt 4. . In addition, about the main anchor bolt 4, it does not need to provide especially, and the square steel pipe column 1 and the foundation concrete 3 may be joined only by the anchor bolt 7 mentioned later.

  Further, in a static state where no external force acts, all the vertical loads of the building transmitted by the square steel pipe column 1 are transmitted to the base concrete 3 via the base plate 2 and are supported and supported by the base concrete 3. It has become.

  When the column base 1a of the square steel pipe column 1 is slightly tilted back and forth and left and right by the bending moment M, the base plate 2 is a large moment arm from the column core, and its lower peripheral edge interferes with the upper surface 3a of the foundation concrete and the grout G. Therefore, in order to reduce the moment arm, that is, in order to reduce the moment arm, it is formed with a planar outer dimension slightly larger than the planar outer dimension of the square steel pipe column 1. Preferably, the base plate 2 is set to a minimum planar external dimension that can be joined to the lower end of the square steel pipe column 1 by welding or the like.

  A plurality of anchor bolts 7 are fixed to the foundation concrete 3 at an appropriate interval from each other so as to protrude from the upper surface 3 a of the foundation concrete and surround the outer periphery of the base plate 2. Accordingly, the anchor bolt 7 is disposed on the side of the square steel pipe column 1. In the illustrated example, four anchor bolts 7 are provided outside the corner portion 1b of the square steel pipe column 1 having a square cross section (see FIG. 2).

  Four anchor bolts 7 may be provided so as to face the four side surfaces 1c of the square steel pipe column 1, or eight anchor bolts 7 may be provided so as to face both the side surface portion 1c and the corner portion 1b. The number may be set as appropriate. Of course, even if the steel column is a steel pipe column having a polygonal or circular cross section, or an H-shaped steel column, the number of columns may be provided at an appropriate position. Preferably, the anchor bolts 7 are evenly arranged with respect to the front, rear, left and right of the steel column. As the anchor bolt 7, any conventionally known one such as a deformed reinforcing bar or a round steel bar may be used.

  An energy absorbing member 8 is provided between the square steel pipe column 1 and each anchor bolt 7 positioned on the side of the square steel pipe column 1. In the planar arrangement of the square steel pipe column 1 and the anchor bolt 7 on the basic concrete upper surface 3a, the energy absorbing member 8 has an inner end 8a attached and fixed to a side portion (corner portion 1b) of the square steel pipe column 1, and an outer end 8b. Is fixed to the anchor bolt 7 and provided between the square steel pipe column 1 and the anchor bolt 7.

  Specifically, the energy absorbing member 8 is made of a steel plate, and is configured mainly with a deformation absorbing portion 8c that is vertically oriented with respect to the foundation concrete 3 along the column axis direction of the square steel pipe column 1. The outer end 8b is configured as a bolt side mounting portion that is fixed to the anchor bolt 7, and the inner end 8a is configured as a column side mounting portion that is fixed to the side portion of the square steel pipe column 1, and these column side mounting portions and the bolt side A deformation absorbing portion 8c is provided between the mounting portion.

  In the present embodiment, the column-side mounting portion faces the corner portion 1b of the square steel pipe column 1 and has a longitudinal end edge (inner side) of the deformation absorbing portion 8c that is butt welded to the corner portion 1b. The energy absorbing member 8 is attached and fixed to the square steel pipe column 1 by the welding connection.

  The column-side mounting portion may be configured by joining an L-shaped or flat plate-shaped bracket along the corner portion 1b or the side surface portion 1c of the square steel pipe column 1 to the end edge of the deformation absorbing portion 8c. . When attaching with a bracket, it is good also as bolt joining by a high strength bolt instead of welding joining.

  The bolt-side attachment portion is formed of a hollow cylindrical sleeve 9 that is vertically joined to the outer end 8b of the deformation absorbing portion 8c and through which the anchor bolt 7 is inserted. A pair of nuts 10 and 11 are fastened to the anchor bolt 7 inserted through the sleeve 9 so as to sandwich the sleeve 9 from above and below. The lower nut 11 is screwed into the anchor bolt 7 in advance, and the sleeve 9 is inserted into the anchor bolt 7, and then the lower nut 11 is abutted against the sleeve 9 while the upper nut 10 is fastened to the anchor bolt 7. The energy absorbing member 8 is attached and fixed to the anchor bolt 7.

  The sleeve 9 may be formed integrally with the deformation absorbing portion 8c by bending the deformation absorbing portion 8c. The bolt-side attachment portion may be directly welded to the anchor bolt 7 in the same manner as the column-side attachment portion, instead of being attached by the sleeve 9.

  Further, the entire energy absorbing member 8 is provided at an interval C upward from the base plate 2. The distance C between the lower end of the energy absorbing member 8 and the upper surface of the base plate 2 is such that when the deformation absorbing portion 8c is deformed as described later, the deformation absorbing portion 8c interferes with the foundation concrete 3 and the grout G. It is set so that the deformation is not hindered.

  The yield strength of the deformation absorbing portion 8c of the energy absorbing member 8 is set to be smaller than any of the yield strengths of the square steel pipe column 1, the anchor bolt 7 and the sleeve 9, and the deformation absorbing portion 8c is deformed in the exposed column base structure. Set to concentrate. The yield strength of the deformation absorbing portion 8c is appropriately set according to the plate thickness, height dimension, and width dimension.

  In the static state, all the vertical loads of the building are borne by the foundation concrete 3 via the base plate 2, and the energy absorbing member 8 is set so as to be almost unloaded.

  Next, the operation of the exposed column base structure for a steel column according to this embodiment will be described. At the time of construction, the base plate 2 and the energy absorbing member 8 are attached to the square steel pipe column 1 in advance. Further, anchor bolts 7 to which main anchor bolts 4 and energy absorbing members 8 are attached are fixed to the foundation concrete 3.

  Next, the square steel pipe column 1 is suspended on the foundation concrete 3, the main anchor bolt 4 is inserted into the bolt insertion hole 2 a of the base plate 2, and the anchor bolt 7 is inserted into the sleeve 9 of the energy absorbing member 8. The square steel pipe column 1 is installed on the foundation concrete 3 through the level mortar provided in 3a.

  Next, nuts 6, 10, and 11 are fastened to the main anchor bolt 4 and the anchor bolt 7, a gap between the base plate 2 and the foundation concrete upper surface 3 a is filled with grout G, and the square concrete is formed on the foundation concrete 3 through the base plate 2. The steel pipe column 1 is fixedly supported. Thus, the installation work of the square steel pipe column 1 is completed.

  In a static state where no external force acts, the foundation concrete 2 bears the vertical load of the building acting along the column axis direction of the square steel pipe column 1.

  When an external force is applied to the building and a bending moment M is generated in the column base 1a of the square steel pipe column 1, the energy absorbing member 8 is mainly subjected to shear deformation with respect to the bending moment M as shown in FIG. In some cases, energy is absorbed with bending deformation.

  Specifically, the deformation absorbing portion 8c of the energy absorbing member 8 is pulled up by the pulling side (indicated by an arrow t in the drawing) of the column base portion 1a of the square steel pipe column 1 that can be tilted by the bending moment M. On the compression side (indicated by an arrow c in the figure), shear deformation is performed by a relative push-down action, and energy is absorbed by this deformation action. At this time, since the energy absorbing member 8 is provided at a distance C upward from the base plate 2, the deformation absorbing portion 8 c is brought into contact with the foundation concrete 3 and the base plate 2, and the energy absorbing action due to deformation is inhibited. There is no such thing.

  When an upward pulling load acts on the square steel pipe column 1, the main anchor bolt 4 prevents this, and all the energy absorbing members 8 are supplementarily accompanied by the deformation action of the deformation absorbing portion 8c. Resist.

  In the exposed column base structure of a steel column according to the present embodiment described above, the inner end 8a is attached to the corner portion 1b and the side portion 1c of the square steel pipe column 1, and the outer end 8b is attached to the anchor bolt 7. Since the energy absorbing member 8 that absorbs energy while being sheared is provided for the bending moment M that acts on the square steel pipe column 1, a large elastic rotational rigidity is provided by the energy absorbing member 8 that absorbs energy by shearing deformation. It can be ensured, energy can be absorbed from the stage of small rotational deformation in the column base 1a of the square steel pipe column 1, and damage to the building can be reduced appropriately.

  Since the energy absorbing member 8 is provided above the base plate 2 with a gap C therebetween, that is, since they are not in contact with each other, when absorbing the energy of the bending moment M by the deformation action, Even on the compression side, the energy absorbing member 8 does not interfere with the base plate 2 or the foundation concrete 3 and the deformation thereof is not hindered, and the bending moment M is efficiently absorbed on both the tension side and the compression side. The action can be secured.

  Since the base plate 2 is formed with an external dimension that can be joined to the lower end of the square steel pipe column 1, the moment arm in the base plate 2 can be reduced, and the base plate 2 is changed to the basic concrete 3 along with the bending moment M. The force that can be transmitted can be reduced as much as possible, and thereby the resistance force that acts on the square steel pipe column 1 from the basic concrete 3 can be reduced. Moreover, cost reduction can be achieved by making the base plate 2 compact.

  The energy absorbing member 8 includes a bolt side attachment portion (outer end 8b side) attached to the anchor bolt 7, a column side attachment portion (inner end 8a side) attached to the corner portion 1b of the square steel pipe column 1, and the like. Since it is provided between the bolt side mounting portion and the column side mounting portion and is composed of the deformation absorbing portion 8c that absorbs energy while being sheared, it can be easily attached to the square steel pipe column 1 and the anchor bolt 7 with a simple configuration. Can do.

  Since the deformation absorbing portion 8c is provided vertically along the column axis direction of the square steel pipe column 1, the deformation absorbing portion 8c can be easily and surely deformed by a shear deformation main body to absorb energy.

  Since the bolt side mounting portion is constituted by a hollow cylindrical sleeve 9 through which the anchor bolt 7 is inserted, the energy absorbing member 8 is fixed to the anchor bolt in parallel with the work of installing the square steel pipe column 1 on the foundation concrete 3. 7 can be attached and workability can be improved.

  4 and 5 show a modification of the above embodiment. This modification is different from the above embodiment in that the lower surface 2b of the base plate 2 facing the basic concrete upper surface 3a is formed by a three-dimensional curved surface. In the present modification, a concave portion 12 having a three-dimensional curved surface shape is formed along the three-dimensional curved surface of the base plate 2 on the upper surface of the grout G to be constructed on the foundation concrete 3.

  The three-dimensional curved surface of the base plate lower surface 2b is, for example, a spherical surface, but is not limited to a spherical surface having a constant curvature radius, and may be a three-dimensional curved surface in which the curvature radius gradually increases from the center of the base plate 2 toward the periphery. .

  When the lower surface 2b of the base plate 2 is formed with a three-dimensional curved surface, when a bending moment M acts on the column base 1a of the square steel pipe column 1, the displacement (shown by u in the figure) is pushed up in the column axis direction on the tension side. At the same time, there is a clear subsidence displacement (indicated by d in the figure) on the compression side, which can cause sufficient deformation in the deformation absorbing portion 8c on the compression side. The energy absorbing members 8 on both sides can exhibit an almost uniform energy absorbing action, and efficient energy absorbing performance can be ensured.

  In addition, since the base plate 2 rolls almost on the foundation concrete upper surface 3a, load transmission from the base plate 2 to the foundation concrete 3 can be further reliably suppressed.

  FIG. 6 shows another modification of the above embodiment. This modified example is different from the above embodiment in that a defect portion is formed in the deformation absorbing portion 8c in order to adjust the energy absorption capability.

  FIG. 6A shows a plurality of horizontal slits 13a formed at intervals in the column axis direction, and FIG. 6B shows a configuration in which vertical slits 13b are arranged along the column axis direction. 6 (c) is the one in which the cutout portion 13c is formed in a curved shape at the upper end and the lower end. By these deficient portions, it is possible to easily adjust the energy absorption capacity by setting the deformation performance or yield strength of the deformation absorbing portion 8c made of steel plate.

  Even in the above modification, it is needless to say that the same effect as that of the above embodiment can be obtained.

  In the above embodiment, the energy absorbing member 8 is attached to the anchor bolt 7 by the sleeve 9, but a coupler having an internal thread formed on the inner peripheral surface may be used instead of the sleeve 9. . In this case, an additional bolt to be screwed to the coupler may be prepared and connected to the upper end of the anchor bolt 7 via an additional nut.

DESCRIPTION OF SYMBOLS 1 Square steel pipe pillar 2 Base plate 2b Bottom surface of base plate 3 Foundation concrete 3a Top surface of foundation concrete 7 Anchor bolt 8 Energy absorption member 8a Inner end of energy absorption member 8b Outer end of energy absorption member 8c Deformation absorption part 9 Sleeve 13a Lateral slit 13b Vertical Orientation slit 13c Notch C Interval

Claims (6)

A steel column installed on the upper surface of the foundation concrete via a base plate joined to the lower end;
A plurality of anchor bolts fixed to the foundation concrete in an arrangement surrounding the outer periphery of the base plate;
An inner end is attached to a side portion of the steel column and an outer end is attached to the anchor bolt with a space upward from the base plate, and energy is absorbed while being subjected to shear deformation with respect to a bending moment acting on the steel column. An exposed-type column base structure for a steel column, comprising:   The said base plate is formed in the external dimension which can be joined to the lower end of this steel column, in order to make the moment arm from the column core of the said steel column to the outer periphery part small. Exposed type column base structure of steel column.   The exposed column base structure of a steel column according to claim 1 or 2, wherein the lower surface of the base plate facing the upper surface of the foundation concrete is formed with a three-dimensional curved surface.   The energy absorbing member includes a bolt-side attachment portion attached to the anchor bolt, a column-side attachment portion attached to a side portion of the steel column, and a steel column between the bolt-side attachment portion and the column-side attachment portion. The exposed column of a steel column according to any one of claims 1 to 3, wherein the exposed column is provided in a longitudinal direction along a column axis direction and includes a deformation absorbing portion that absorbs energy while being sheared. Leg structure.   5. The exposed column base structure for a steel column according to claim 4, wherein the deformation absorbing portion is formed with a deficient portion that adjusts energy absorbing ability.   6. The exposed column base structure for a steel column according to claim 4, wherein the bolt-side attachment portion is formed in a hollow cylindrical shape through which the anchor bolt is inserted.

Images