JP4929331B2 - Steel frame exposed column base construction method - Google Patents

Description

The present invention relates to a method for constructing , for example, an exposed steel column base .

  The Great Hanshin Earthquake caused damage to many steel structures such as collapses and wrecking, some of which were due to damage to the exposed steel column bases. These damages have been reported to be due to anchor bolt products such as breakage of anchor bolts in steel-frame exposed column bases, slipping out of foundation concrete, and related design and construction defects. In response to this damage, the Ministry of Land, Infrastructure, Transport and Tourism (former Ministry of Construction) issued a notification in December 1995 regarding the design of column bases for steel structures (see Non-Patent Document 1). It is described in “Structural Rules for Buildings” published by the Japan Architecture Center. Against this background, basic research has been advanced on the stress transferability and strength of steel exposed column base structures.

  In such a steel frame exposed column base structure, since anchor bolts are an important factor that affects the plastic deformation capacity of the column base, SS400, SS490, etc. of JIS standard rolled steel for general structure having plastic deformation capacity are used. in use. Furthermore, a method has been adopted in which high strength steel such as a high strength PC steel bar is used, the strength of the column base is increased, and a large tension is introduced to form a tension joint type to improve the fixing degree (Non-patent Document 2). See).

And after installing an anchor bolt, the column main reinforcement of the same performance as anchor bolt yield strength is arranged around the anchor bolt.
In addition, a fixing plate is provided at the lower end of the anchor bolt to prevent removal. Further, in the case where a fixing plate is provided at the lower end portion of the anchor bolt, the fixing length is set to be 20 times or more the anchor bolt diameter in order to prevent cone-like destruction (see Non-Patent Document 2).

  When installing the anchor bolts, first, the nuts for fixing the lower part of the anchor bolts, which are positioned by inserting them through the insertion holes of the upper and lower templates of the anchor bolt mounting base on the foundation bottom (discard) concrete The upper part of the anchor bolt is temporarily fixed to the upper template with a washer and nut. After that, the anchor bolt installation base is fixed to the foundation bottom (discard) concrete with the anchor bolt for installation (see Patent Document 1).

  In addition, the clearance of the insertion hole in the base plate is determined to be 5 mm or less due to performance problems, but in order to evenly bear the shearing force on all anchor bolts, compared to the diameter of the anchor bolts, A washer having a very small hole diameter is used and welded to the base plate to prevent the base plate from moving (see Non-Patent Document 2).

  The spring constant (rotational rigidity) related to the bending moment and rotation angle at the base plate position is affected by the elongation of the anchor bolt, local deformation of the anchor bolt screw, deformation of the base plate, and compressive deformation of the concrete on the bottom surface of the base plate. Is difficult.

  By the way, when the base plate does not yield on the side where the anchor bolt is received before the anchor bolt yields, rough prediction is possible. It is possible to calculate the theoretical value of the spring constant, assuming that this rotational rigidity is due only to the extension deformation of the tension side anchor bolt and assuming the compression reaction force position and the rotation center as the column compression side flange outer edge. Actually, there are a decrease in Young's modulus due to the influence of the thread, bending deformation of the base plate, deformation of the concrete on the compression side, etc., and a value that is approximately ½ times the theoretical value is experimentally derived and used as a design value ( (Refer nonpatent literature 2).

JP 2000-273951 A

1456 Article 1456 related to the Building Standards Act Explanation of steel pipe structure design and construction guidelines, Architectural Institute of Japan

  However, in the conventional steel-exposed type column base structure, when the general structural rolled steel SS400, SS490, etc. are used, there are two types of threading methods, rolling and cutting. The flow of the metal structure is not cut, and the strength of the screw part is almost the same as that of the shaft part because the flow of the metal structure is compressed especially at the screw bottom, but the flow of the metal structure is cut in the cutting screw. Since the thread shape is made, the thread valley is not strengthened, and the thread portion has a smaller cross-sectional area than the shaft portion, so that the strength is weak and the thread portion may break. Therefore, in the case of using a screw, it is necessary to purchase a rolled screw, but there is a problem that the availability is poor.

  In addition, when using anchor bolts of high-strength steel, there are types with small plastic deformation capacity, so it is necessary to calculate the strength again when changing from general structural rolled steel to high-strength steel. There was a problem that it took.

  In the case where both the anchor bolt and the column main reinforcement are arranged, there is a problem in that it requires cost and construction work because a bar arrangement work is required.

  In the case where the fixing plate is provided at the lower end portion of the anchor bolt, there is no standard for the fixing plate, and there is a problem in that the material, thickness, and size are different depending on the contractor and the reliability is lacking.

  Also, if the anchor bolt is too long, when the tensile force acts on the column and the force to pull out the anchor bolt acts, the anchor bolt grows larger and the tightening nut part loosens, resulting in a steel column There was a problem that the degree of leg fixation was low.

  Furthermore, in the case where the anchor bolt installation base is erected and fixed to the foundation bottom (discard) concrete, the cost and construction work are required for the production and installation of the anchor bolt installation base. There was a point.

  If the clearance of the insertion hole in the base plate is 5 mm or less, there is a problem that construction on site is difficult. In addition, when the washer is welded to the base plate, there is a problem in that welding work and incidental work accompanying welding occur, and it takes time for construction. There has been a problem that heat deformation strain may occur in the base plate itself due to the thermal effect of welding.

  In addition, when the spring constant (rotational rigidity) of 1/2 of the theoretical value is used as the design value, the strength of the steel column base becomes over-spec, which is uneconomical. was there.

Therefore, the present invention has been made in view of the above problems, and in the construction method of the steel exposed column base, the seismic performance of the column base is improved, the construction is simplified, the construction period is shortened, and the cost is reduced. Reduce.

The construction method of the steel-frame-exposed-type column base of the present invention that solves the above-mentioned problem is that a plate nut serving as a fixing plate is screwed into a screw joint, and the lower surface level of the plate nut is fixed from the top level of the foundation concrete. Move to a long position, screw the lower end side of the screw rebar into a nut fixed to the end of the lower positioning guide, and fix the upper end side of the screw bar to the insertion hole of the upper positioning guide Insert and pass through and temporarily fix with a washer and nut, check and adjust the verticality and horizontality of the screw joint reinforcing bar, set the screw joint reinforcing bar at the column installation position on the foundation bottom concrete, the lower part After fixing the positioning guides with anchor bolts and nuts and fixing the threaded reinforcing bars on the foundation bottom concrete, the lower surface level of the plate nut is changed from the top end level of the foundation concrete. After confirming that it is in the position of the contact length, fill the non-shrinkable grout material between the plate nut and the threaded reinforcing bar, fix the plate nut, and cast the concrete to a predetermined level to make the foundation concrete When the concrete is hardened, the upper positioning guide is removed, and a horizontal level is taken out with the mortar. After the mortar is hardened, the column material to which the base plate is connected is inserted into the insertion hole of the base plate and the screw reinforcing bar. It is characterized by being inserted and standing up .

ADVANTAGE OF THE INVENTION According to this invention, in the construction method of a steel frame exposure type column base part, it becomes possible to improve the earthquake resistance performance of a column base, to simplify construction, and to reduce a construction period and cost.

  In the present invention, by using a threaded reinforcing bar as an anchor bolt, the threaded reinforcing bar has a cross-sectional area larger than that of a screw conventionally used as an anchor bolt and has a strength equal to or greater than that of a reinforcing bar used for a column main reinforcing bar. Therefore, it can be used as an anchor bolt that also serves as a column main reinforcement.

  In addition, by placing the lower end of the screw joint reinforcing bar directly or indirectly in contact with the foundation bottom concrete, it becomes a substitute for the column main reinforcement, eliminating the complicated reinforcement that was done in the conventional column base, The work is labor-saving, the amount of reinforcing bars to be used can be reduced, the construction time can be shortened, the concrete can be easily filled, and the quality can be increased.

  Further, the screw joint reinforcing bar is easily available and economical because it has a low unit price, and has the advantage that it is easy to manage because it does not mix with other materials.

  Furthermore, since a solid object such as an anchor bolt installation base used conventionally is not used and only a simple screw joint reinforcing bar positioning guide is used, the material cost can be reduced and the construction time can be shortened.

  If there is no fixing metal fitting with a flange, such as a plate nut (trade name of Tokyo Steel Co., Ltd., obtained a general rating from the Japan Architecture Center), so that it can be screwed onto the threaded reinforcing bar on the upper part of the foundation concrete. Resistance to such compressive stress is borne only by the concrete of the support. In the present invention, when a plate nut is provided at the upper part of the foundation concrete so as to be screwed into the screw joint reinforcing bar, the compressive stress applied to the base plate is also transmitted to the screw joint reinforcing bar. Therefore, a compressive load is applied to the cross section of the concrete of the support and the threaded joint. Therefore, the resistance to the compressive stress can be increased by the cross-sectional integral of the screw joint reinforcing bar, compared with the case where the plate nut is not provided so as to be screwed into the screw joint reinforcing bar on the foundation concrete.

  In the present invention, a plate nut is used for the fixing plate, and the fixing length is set to 15 times the diameter of the screw joint reinforcing bar, so that the plate nut has been evaluated as a fixing plate, thereby ensuring a reliable fixing strength. It is possible to reduce the thickness of the foundation concrete by shortening the fixing length.

  In the present invention, in order to fill the non-shrinkable grout material from between the base plate and the foundation concrete to between the insertion hole of the base plate and the screw joint, there is a clearance between the insertion hole of the base plate and the screw joint. However, the shear stress applied to the base plate can be reliably transmitted to the anchor bolt.

  Therefore, by implementing all of the present invention, a decrease in Young's modulus due to the influence of the thread portion, which has been the reason for using a half of the theoretical value as a design value when calculating the spring constant (rotational rigidity), the base plate Since it is possible to reduce the influence of bending deformation, deformation of the compression side concrete, etc., it becomes possible to design according to the theoretical value of the spring constant calculated based on the above-mentioned assumptions.

  Therefore, it is necessary to change the specification and review the construction method. As a result, the cost is reduced and the construction period is shortened, which is economical.

It is a whole side view of the fixation structure of the exposure type fixed column base which concerns on the Example of this invention. It is a side view of the fixed structure part of the exposure type fixed column base which concerns on the Example of this invention. It is an enlarged view of the principal part of the fixation structure of the exposure type fixed column base which concerns on the Example of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an overall side view of a fixing structure of an exposed fixed column base according to an embodiment of the present invention. As shown in FIG. 1, the fixing structure of this embodiment has a foundation beam 1 with a bottom beam 2, a foundation beam 3, and a stirrup 4 embedded therein, and screw joints 5 are arranged vertically as anchor bolts. The upper end of the threaded joint reinforcing bar 5 is inserted into the insertion hole 8 of the base plate 7 connected to the column 6, nuts 9 and 10 are attached to the upper part of the threaded joint reinforcing bar 5, and both nuts 9 and 10 are tightened. Initial tension is introduced into the threaded reinforcing bar 5, thereby fixing the base plate 7 to the foundation concrete 1. A non-shrinkable grout material 11 is filled between the base plate 7 and the foundation concrete 1.

  Further, plate nuts 12 and 13 are screwed to the threaded reinforcing bar 5. In this embodiment, as the anchor bolt, for example, the threaded reinforcing bar 5 made of the material SD490 is used. According to the "2001 Structure-Related Technical Standards for Buildings", the anchor bolt's elongation capacity is as follows: "If the effective cross-sectional area of the screw part is equal to or greater than that of the shaft part, Some anchor bolts are described as (hereinafter abbreviated). Therefore, the screw joint reinforcing bar has an elongation capability because the cross-sectional areas of the screw portion and the shaft portion are substantially equal, and is effective as an anchor bolt.

  In order to transmit the compressive stress applied to the base plate 7 to the screw joint reinforcing bar 5, a plate nut 13 for compressive stress resistance is screwed onto the upper portion of the foundation concrete 1. At this time, the position of the compression stress strength plate nut 13 is adjusted so that the upper surface level of the compression stress strength plate nut 13 is the same as the top level of the foundation concrete 1. The top concrete level of the foundation concrete 1 can be adjusted by placing the concrete up to the upper surface level of the compression stress proof plate nut 13 screwed into the screw joint reinforcing bar 5. In this way, if the concrete is placed up to the upper surface level of the compression stress proof plate nut 13 screwed into the screw joint reinforcing bar 5, the top end level adjustment of the foundation concrete can be performed, so that other level adjustments are possible. Work is easy without using any means.

When a plurality of compression stress proof plate nuts are provided, a steel plate such as a long plate or an angle can be installed between the upper surfaces of the plurality of compression stress proof plate nuts (not shown). Thereby, it is possible to easily level the top end surface of the basic concrete by placing concrete to the lower end surface of a steel material such as a long plate or an angle.
Note that the compressive stress proof plate nut 13 is not essential for the construction structure of the present invention, and it is possible to select to use a general nut as in the past or not to use the nut itself. .

FIG. 2 is a side view of the fixing structure portion of the exposed fixed column base according to the embodiment of the present invention.
At the time of construction, as shown in FIG. 2, a plate nut 12 serving as a fixing plate is screwed into the screw joint reinforcing bar 5, and the lower surface level of the plate nut 12 is 15 times the diameter of the screw joint reinforcing bar from the top end level of the foundation concrete. Move to a position where the fixing length is doubled.

  The lower end side of the screw rebar 5 is screwed and fixed to a nut 21 fixed by welding to the end portion of the lower positioning guide 20, and then the upper end side of the screw rebar 5 is connected to an upper positioning guide (not shown). Pass through the insertion hole and temporarily fix it with a washer and nut, and check and adjust the verticality and horizontality of the screw rebar.

  Then, the screw rebar is set at the column installation position on the foundation bottom (discard) concrete, and the lower positioning guide 20 is fixed by the anchor bolt 22 and the nut 23. After fixing the screw rebar 5 on the foundation bottom (throw away) concrete, confirm that the bottom surface level of the plate nut 12 is at a fixed length 15 times the diameter of the screw rebar 5 from the top level of the foundation concrete. Then, the plate nut 12 is fixed by filling a non-shrinkable grout material between the plate nut 12 and the screw joint reinforcing bar 5.

  After that, concrete is cast to a predetermined level to form foundation concrete. When the concrete is hardened, the upper positioning guide is removed, and a horizontal level is obtained with a mortar (commonly known as a wharf). After the mortar (commonly known as the wharf) has hardened, the pillar material 6 is built.

FIG. 3 is an enlarged view of a main part of the fixing structure of the exposed fixed column base according to the embodiment of the present invention.
As shown in FIG. 3, the column material 6 to which the base plate 7 is connected is carried in, and the insertion hole 8 of the base plate 7 is inserted into the screw rebar 5 to stand.
The column 6 is, for example, a square steel pipe, a round steel pipe, an H-shaped steel, and the like, and the base plate 7 is made of cast steel, forged steel, steel plate, or the like.

  After the column material 6 is erected, the non-shrinkable grout material 11 is filled between the base plate 7 and the foundation concrete 1. Further, the non-shrinkable grout material 11 is filled in the gap between the screw rebar 5 and the insertion hole 8 of the base plate 7 and the gap between the base plate 7 and the nut 10.

  Then, the base plate 7 is tightened by the nuts 9 and 10, and the filler overflows from the gap between the base plate 7 and the nut 10. After confirming that the gap between the base plate 7 and the nut 10 is sufficiently filled, initial tension is introduced into the threaded reinforcing bar 5 to fix the base plate 7 to the foundation concrete 1.

  Therefore, according to the structure of the embodiment of the present invention, it is not necessary to be so sophisticated that a specialized column base construction company starts up the threaded joint. In addition, there is no need to meet and rework by a specialized column base construction company to ensure accuracy when laying the foundation and placing concrete. This eliminates the need for technicians for each type of work and simplifies process management.

DESCRIPTION OF SYMBOLS 1 Basic concrete 5 Threaded joint 6 Column material 7 Base plate 8 Insertion hole 11 Non-shrinkable grout material 12 Plate nut 13 for compressive stress strength Plate nut 20 Lower positioning guide 22 Anchor bolt

Claims (1)

It is a construction method for steel exposed column bases,
The plate nut that becomes the fixing plate is screwed into the threaded reinforcing bar, and the lower surface level of the plate nut is moved to the position where the fixing length becomes the fixing length from the top end level of the basic concrete,
The lower end side of the threaded reinforcing bar is screwed and fixed to a nut fixed to the end of the lower positioning guide,
The upper end side of the threaded reinforcing bar is inserted into the insertion hole of the upper positioning guide and temporarily fixed with a washer and a nut, and the verticality and levelness of the threaded reinforcing bar is confirmed and adjusted,
Set the threaded reinforcing bar at the column installation position on the foundation bottom concrete, and fix the lower positioning guide with anchor bolts and nuts,
After fixing the screw joint reinforcing bar on the foundation bottom concrete, confirm that the lower surface level of the plate nut is at the fixing length from the top end level of the foundation concrete,
Filling the non-shrinkable grout material between the plate nut and the threaded reinforcing bar to fix the plate nut,
Placing concrete to a predetermined level to form foundation concrete,
When the concrete is hardened, remove the upper positioning guide and put out a horizontal level with mortar,
After the mortar has hardened, a column material to which a base plate is connected is erected by inserting an insertion hole of the base plate into the screw joint reinforcing bar.