JP2005256368A - Pile head joint structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pile head joint structure that is inexpensive, can easily absorb construction errors, and can reduce a pile head bending moment.
SOLUTION: It is a joint structure of a pile 1 and a column 2 in which a steel foundation beam 3 is joined to a column base, and a central part of a concrete section constituting a pile head of the pile 1 and a column base of the column 2 In the concrete 7 which comprises a part, the rod-shaped metal object 6 extended in the axial direction of the pile 1 and the pillar 2 is arrange | positioned. When a bending moment exceeding a predetermined level is applied, the pile head joint becomes semi-fixed by pulling out the rod-shaped hardware 6, reducing the bending moment of the pile head, and making the pile head joint an inexpensive and simple structure. Can do. Further, it is possible to install the bar-shaped hardware 6 in the pillar 2 even for a certain degree of construction error of the pile 1, and it is easy to absorb the construction error in the horizontal direction. The base plate 4 at the lower end of the column 2 also serves as a diaphragm for foundation beam joining, so that the number of joining processes can be reduced, and the amount of excavated soil can be reduced by reducing the height of the foundation beam 3 portion.
[Selection] Figure 1

Description

  The present invention relates to a structure of a pile head joint that connects a pile and a column to which a steel foundation beam is joined.

  Conventionally, for pile head joints, it has been the mainstream to rigidly join the foundation beam and the pile head using RC foundation beams.

  For example, in order to join the steel pipe pile and footing joint more than the bending strength of the pile body, reinforcing bars are welded to the outer periphery of the pile and fixed to the foundation beam. Similarly, in the case of cast-in-place piles, the reinforcing bars of the pile body are extended and fixed to the foundation beam.

  However, the conventional rigid joint causes over-pile arrangement of pile head reinforcing bars, large cross-section of the foundation beam, and the like, leading to an increase in cost.

  On the other hand, in recent years, techniques for pin-joining or semi-rigidly joining pile heads are spreading to reduce pile head stress and solve the above problems.

  For example, Patent Document 1 describes a pile head structure that reduces the pile head moment by making the pile head spherical.

  In Patent Literature 2, the pile head and the foundation concrete slab are connected to each other through a column having a non-slip bar and having a smaller cross-sectional area than the pile head. Is made smaller than the pile body.

In the case of using a steel foundation beam, for example, in Patent Document 3, a pile head is inserted inside a reinforced concrete column or a filled steel pipe concrete column, and the steel foundation beam and the column are welded to the foundation beam via a diaphragm. What is being described is described.
JP 2001-73387 A Utility Model Registration No. 3058823 JP 2001-248167 A JP 2002-115323 A

  In the case of the invention described in Patent Literature 1, although the pile head has an uneven surface, it is effective in reducing the moment.

  The invention described in Patent Document 2 is an invention that targets a foundation concrete slab that is not easily affected by horizontal construction errors of piles as a superstructure, and is provided with a column with a closed cross section at the top of the pile In some cases, it is not possible to place a stiffening bar inside the column due to construction errors in the horizontal direction of the pile.

  The invention described in Patent Document 3 inserts a pile head inside a filled steel pipe concrete column, and since the gap between the column and the pile inside the column is small, error absorption in the direction of the water level of the pile accompanying placement Is difficult, and is also disadvantageous in terms of simplifying the pile head joint.

  The present invention has been made to solve the problems in the prior art as described above, and aims to provide a pile head joint structure that is inexpensive, can easily absorb construction errors, and can reduce the pile head bending moment. It is what.

  In the pile head joint structure according to claim 1 of the present application, a steel foundation beam is joined to a column base portion of the column at a joint portion of the pile and the column, and a concrete cross section constituting the pile head portion of the pile. A rod-shaped hardware extending in the axial direction of the pile and the column is arranged in the center and the concrete constituting the column base of the column, and the base plate provided at the lower end of the column is the steel foundation beam It also serves as a diaphragm for joining.

  When a bending moment exceeding a specified level is applied, the pile head joint becomes semi-fixed due to the removal of the rod-shaped hardware placed over the pile head and column base, reducing the bending moment of the pile head. The pile head joint can be made an inexpensive and simple structure.

  Since the steel foundation beam is used, the bending moment of the pile head can be reduced and the effect is further improved as compared with the case of the RC foundation beam.

  In addition, since it has a structure in which a rod-shaped hardware is arranged in the center of the cross section of the pile, it is possible to install the rod-shaped hardware in the column even for a certain amount of construction error of the pile, and it is easy to absorb the construction error in the horizontal direction. is there.

  In addition, the structure of the present invention that reflects the joint deformation positively in the design can be said to be a semi-rigid joint structure compared to the conventional case where the pile head is considered as a rigid joint and the deformation of the pile head joint is not considered in the design. .

  In addition to round bars such as steel bars and deformed bars, rods, square bars, polygonal bars with a cross section perpendicular to the longitudinal direction, round steel pipes, square steel pipes, very thick reinforcing bars, cross-shaped cross sections, cross H There is no particular limitation as long as it has a cross section and rigidity sufficient to bear the shearing force at the joint, such as a cross-sectional material. Further, the bar-shaped hardware is not limited to one, but may be a rebar rod or a bundle of a plurality of bars.

  The bar-shaped hardware is sized so that it can be installed in the pillar even if the construction error of the pile is taken into account. When installing a plurality of bar-shaped hardware, considering the overall diameter, the inner diameter of the pillar, and the construction error of the pile, the number of bar-shaped hardware to be bundled and the specifications such as the reinforcing bar can be determined. .

  Further, in the present invention, a base plate made of a steel plate or the like is provided at the lower end of the column for the purpose of smoothly distributing and transmitting axial force between the column and the pile. By combining this diaphragm, the man-hours for joining can be reduced, and the height of the foundation beam portion can be reduced, so that the amount of excavated soil can be reduced.

  The pile head joint structure according to claim 1 is characterized in that the rod-shaped hardware is provided with means for increasing the fixing force to the concrete or the adhesion force with the concrete. .

  Tensile force is generated in the rod-shaped hardware, but by providing means for increasing the fixing force to the concrete or the adhesion force with the concrete, it is possible to effectively prevent the rod-shaped hardware from coming out.

  As a means for increasing the fixing power to concrete, for example, a fixing plate attached to both ends or an intermediate portion of a rod-shaped hardware, which can obtain a large supporting pressure to concrete, means for increasing the adhesion to concrete Examples include studs, joints (including deformed steel bar joints), protrusions, holes, etc. provided on the outer periphery of the shaft part of a rod-shaped hardware, but it is necessary to clearly distinguish both functions of fixing force and adhesion force. There is no.

  According to a third aspect of the present invention, in the pile head joint structure according to the first or second aspect, the pile has a structure in which at least the pile head has a steel shell filled with concrete.

  The piles to which the present invention is applied include on-site RC piles, steel pipe piles, and various other prefabricated piles, but since rod-shaped hardware must be embedded in concrete, for example, at least piles in the case of steel pipe piles The head is filled with concrete so that, for example, the lower half of the rod-shaped hardware is embedded in the concrete of the pile head.

  In this case, steel pipe piles as steel shells or steel pipes of SC piles, or steel pipes provided only on pile heads such as RC piles, RC piles as existing piles, PC piles, etc., restrain the concrete inside. Therefore, an increase in the fixing force or adhesion force of the rod-shaped hardware can be expected.

  A fourth aspect of the present invention is the pile head joint structure according to the first, second, or third aspect, wherein the column has a structure in which at least a column base is filled with concrete in a steel shell. is there.

  As for the pillars, the pillars to which the present invention is applied can be various types of pillars such as steel pipe pillars, concrete-filled steel pipe pillars, as well as on-site RC structures and SRC pillars. Similarly, since the rod-shaped hardware must be embedded in the concrete, for example, in the case of a steel pipe column, at least the column base is filled with concrete, and for example, the upper half of the rod-shaped hardware is approximately half the length of the column base. Be buried in concrete.

  Further, a steel shell may be provided on the outer periphery of the column base portion of the RC structure or SRC structure. In that case, as in the pile side, the fixing force of the rod-shaped hardware by the steel shell portion restraining the inner concrete or An increase in adhesion can be expected.

  In the present invention, the rod-shaped hardware placed in the concrete in the center of the pile and the column base bears a shearing force, and when a bending moment exceeding a predetermined level is applied, the semi-rigid connection is caused by the axial strain of the rod-shaped hardware. Since the bending moment of the pile head joint can be reduced by the shape, the pile head joint can be made an inexpensive and simple structure.

  In addition, because it has a structure in which a rod-shaped hardware is placed in the center of the cross section of the pile, it is possible to install a column even for a certain degree of construction error, it is easy to absorb horizontal construction error, and the pile head joint There is little influence on the function due to construction errors.

  Furthermore, since the base plate at the bottom of the column also serves as a diaphragm for joining steel foundation beams, the number of man-hours for joining can be reduced, and the amount of excavated soil can be reduced by reducing the height of the foundation beam portion.

  FIG. 1 shows an embodiment of a pile head joint structure of the present invention.

  In this embodiment, the superstructure is a steel structure, the column 2 is a square steel pipe column, the foundation beam 3 is an H-shaped steel beam, and the pile 1 is a cast-in-place RC pile.

  The steel foundation beam 3 and the column 2 are welded together via a base plate 4 that also serves as a diaphragm and a diaphragm 22 thereabove. A hole 4 a is provided in the base plate 4, and a metal round bar as a rod-shaped hardware 5 passes through the hole 4 a from the pile 1 to the inside of the column 2.

  The lower part of the bar-shaped hardware 5 is buried in the concrete of the pile 1, and concrete 7 is placed in the vicinity of the joint portion of the pillar 2 with the foundation beam 3, and the upper part of the bar-shaped hardware 5 is placed in the concrete 7. Buried. A large number of studs 6 are welded to the rod-shaped hardware 5 over substantially the entire length located at the joint surface between the pile 1 and the column 2.

  In the present invention, the cross section of the pillar 2 may be circular, square, polygonal, etc., and is not limited to that shown in FIG. Further, the cross section of the foundation beam 3 may be a square, a circle, a double web H or the like in addition to the H shape of FIG.

  2 (a) to 2 (h) show modified examples of the rod-shaped hardware. FIG. 2 (a) shows a round bar 5a (round steel), and FIG. 2 (b) shows a polygonal bar 5b (square steel). 2 (c) shows a case of a small diameter steel pipe 5c, FIG. 2 (d) shows a case of a small diameter square steel pipe 5d, FIG. 2 (e) shows a case of a cross-shaped cross section 5e, FIG. Is the case of the cross H-shaped cross-section material 5f. In addition, a plurality of reinforcing bars 5g as shown in Fig. 2 (g), or a plurality of bars, round bars, polygonal bars, etc., which are bundled densely with some gaps, or a reinforcing bar 5h as shown in Fig. 2 (h) May be used.

  Any of studs, nodes, fixing plates, steel plates with protrusions, and holes may be used to attach and fix the metal rod-like member 5 and the concrete 7. As shown in FIG. 3, the pillar 2 and the concrete 7 may be adhered and fixed by providing a plurality of protrusions 8 inside the pillar 2.

  Further, the joining of the steel foundation beam 3 and the column may be any of an outer diaphragm type, an inner diaphragm type, and a through diaphragm type. The column structure can be applied to concrete-filled steel pipe structures and steel structures. As the pile 1, it is applicable also to the earthquake-resistant cast-in-place pile and steel pipe pile of steel pipe winding reinforcement.

  FIG. 4 shows a case where a taper 1a is provided on the head of the pile 1 as a modification of the embodiment of FIG. When the gap between the steel foundation beam 3 and the pile 1 is small and there is a possibility that the steel foundation beam 3 and the pile 1 are in contact with each other at the time of an earthquake, this can be dealt with in this way.

  The invention described in Patent Document 4 listed in the section of the background art assumes a direct foundation, and does not assume a pile foundation as in the present invention, but has rotational rigidity due to withdrawal of the metal rod-like member 5 or the like. Reduction of pile head bending moment as a decreasing effect is not considered.

  Moreover, in the structure of invention of patent document 4, since only the shear resistance of a concrete part can be expected substantially with respect to a shearing force, it cannot respond when the shearing force which becomes a problem in a pile head junction part is large.

  Below, the dimension example of a junction part at the time of examining the dimension shape of the pile head junction part by this invention is demonstrated about the pile head of a 10-story steel-frame building.

  The pile head joint is assumed to have the dimensions shown in FIG. The steel foundation beams are H-shaped steel, and the foundation beams and columns are sufficiently stiffened.

As shown in Fig. 6, the pile head moment / rotation angle is infinitely rigid up to the proof stress M _cr when the compressive stress of the outermost edge concrete part is 0, and after that, the metal round bar in the center is It is assumed that rotation is caused by pulling out.

Rotational stiffness after the M _cr is determined and the tensile at yield strength M _y of round bar of the central portion than the rotation angle θ _y. M _y is calculated base plate as an RC section. θ _y is a value obtained by integrating the axial strain distribution in the axial direction of the round bar at the yield of the round bar shown in FIG. 7 and dividing the deformation of the protruding portion by the distance x _n to the neutral axis of the cross section.

  FIG. 8 shows the relationship between the pile head moment M calculated in this way and the rotation angle. In the figure, the case where the horizontal construction error e is 100 mm is also shown.

  As shown in FIG. 9, the analysis model is assumed to be an infinite uniform frame, and is calculated for the upper and lower parts integrally. The rotation deformation of the pile head is evaluated by providing a rotation spring on the pile head.

  The ground conditions are a clay layer with N value = 5 from GL to −12 m, a fine sand layer with N value = 20 from −12 m to −16 m, and a gravel layer with N value = 50 from the depth.

Apply horizontal force during an earthquake (short term) to such a model. In this case, the shear force applied to the pile head is 7.03 × 10 ⁵ N.

  FIG. 10 shows the pile moment distribution during the earthquake (short term) as a result of using the analysis model. Compared with the case where the pile head is rigidly connected, the pile head moment when the pile head is semi-fixed is reduced to about 60%.

  FIG. 11 shows the relationship between the short-term allowable axial force N of the pile head and the bending moment M, and the generated moment is within the short-term tolerance, and it can be seen that there is no structural problem.

At this time, the axial stress generated in the round bar is 7.64 × 10 ³ N / cm ² . Assuming that the round bar bears all the pile head shear force, the shear stress generated in the round bar is: pile head shear force / round bar cross-sectional area = (7.03 × 10 ⁵ N) / (78.5 cm ² ) = It becomes 8.92 × 10 ³ N / cm ² .

  Consider the following as yield conditions for round bars.

(Κ · τ _mean / τ _y ) ² + (σ / σ _y ) ²
here,
κ: Shape factor (since it is circular, 1.3)
τ _mean : Average shear stress τ _y : Yield shear stress (= σ _y / √3)
σ: axial stress σ _y : yield stress (2.35 × 10 ⁴ N / cm ² )
Substituting the specifications into the above equation gives the following, and the round bar does not yield even if it bears axial and shear forces.

(Κ · τ _mean / τ _y ) ² + (σ / σ _y ) ² = 0.83 <1.0
Considering that there is no round bar and that the shear force is borne only by the concrete part inside the column, it is assumed that concrete F _c = 2.35 × 10 ³ N / cm ² and the short-term allowable shear force is 2.94 × 10 ^5. It is clear that there is only about half of the required value 7.03 × 10 ³ N / cm ² , and it is obvious that it is difficult to bear with only the shear resistance of the concrete part.

  Thus, in the present invention, the pile head moment can be reduced, and there is sufficient resistance against the moment and the shearing force.

  Next, consider the case where horizontal construction errors occur.

  FIG. 12 is a pile moment distribution at the time of earthquake (short term) when the relationship between the moment M of the pile head and the rotation angle with e = 100 mm in FIG. 8 is used. As shown in the figure, the pile head moment hardly changes between e = 0 mm and e = 100 mm.

  FIG. 13 shows the relationship between the short-term allowable axial force N and bending moment M of the pile head in consideration of the construction error. Even in the case of a construction error of 100 mm, it is within the short-term tolerance, and the horizontal error is It can be seen that there is no structural problem even if it occurs.

  FIG. 14 shows an embodiment in which the column is an H-shaped steel column as another embodiment of the pile head joint structure of the present invention. The superstructure is steel, the column 12 is an H-shaped steel column, and the foundation beam 3 is an H-shaped steel. Pile 1 is a cast-in-place pile.

  The cross-sectional shape of the steel foundation beam 3 may be either a square steel pipe or a double web H in addition to the H-shaped steel. The pile 1 can be applied not only to cast-in-place piles but also to earthquake-resistant cast-in-place piles and steel pipe piles for reinforcing steel pipe winding.

  A cover plate 14 is welded to the column leg portion of the H-shaped steel column 12 at the tip of the flange 12b. The cover plate 14 is installed over the entire joint between the base beam 3 and the column base of the H-shaped steel column 12, and the upper flange of the base beam 3 attached in the weak axis direction of the H-shaped steel column 12 is directly attached to the cover plate 14. It is welded.

  The column base web 12 a of the H-shaped steel column 12 has an opening 13 through which the rod-shaped hardware 5 is passed. A perforated base plate 4 is welded and joined to the lower part of the H-shaped steel column 12, and a metal round bar as a bar-shaped metal object 5 penetrates the center of the hole 4 a from the pile 1 to the inside of the column base. .

  Concrete 7 is placed in a portion surrounded by the cover plate 14 and the H-shaped steel column 12 of the column base, and the concrete 7 and the rod-shaped metal rod 5 are integrated. In order to improve adhesion / fixation between the column base of the H-shaped steel column 12 and the filling concrete 7, a plurality of protrusions may be provided on the inner surface of the flange 12b or the web 12a of the H-shaped steel or the inner surface of the cover plate 14. .

  The lower flange of the steel foundation beam 3 and the column base are welded together via a base plate 4 that also serves as a diaphragm. On the other hand, the upper flange of the steel foundation beam 3 is welded directly to the column base in a non-diaphragm form in this figure.

  By using the base plate 4 also as the diaphragm for the lower beam flange, it is possible to reduce the number of man-hours for joining. At the same time, by installing the foundation beam 3 at the lowest position of the column base, the height from the top surface of the pile to the upper flange of the foundation beam 3 can be kept small. Can be expected.

  FIG. 15 is a horizontal cross-sectional view of another embodiment when the column is an H-shaped steel column. Unlike the example of FIG. 14, in this case, an opening is not provided in the web 12 a of the column base portion of the H-shaped steel column 12. Therefore, it is necessary to install at least one rod-shaped hardware 5 in each of two spaces formed by sandwiching the web 12a, surrounded by the cover plate 14, the flange 12b and the web 12a.

  FIG. 16 is a vertical cross-sectional view showing another example of the cover plate for the embodiment of FIG. In the example of FIG. 14, the cover plate 14 is composed of one plate per one surface of the column base portion over the entire joint portion to which the foundation beam 3 is attached. However, as shown in this example, the cover plates 15 a and 15 b are attached to the cover plate 15. Multiple sheets may be installed.

  However, when the steel foundation beam 3 is attached in the weak axis direction as shown in FIG. 16, the cover plate 15 a is always installed at the position where the upper flange of the foundation beam 3 is attached.

  In the case of the embodiment of FIG. 16, when filling the column base with the concrete 7, it is necessary to devise a way to prevent the concrete 7 from flowing out by installing a formwork in the portion where the cover plate is missing. It becomes.

  FIG. 17 shows a variation when the upper flange of the steel foundation beam is attached to the diaphragm with respect to the embodiment of FIG.

  Besides the non-diaphragm as shown in FIG. 14, the outer diaphragm type shown in FIG. 14 (a) and the through-diaphragm type shown in FIG. 14 (b) are used for the purpose of improving the rigidity against local deformation of the upper flange of the steel foundation beam 3. Any of the inner diaphragm types shown in FIG. 14 (c) may be used.

The procedure for diaphragm welding is, for example, as follows.
(1) In the outer diaphragm type, after attaching the cover plate to the H-shaped steel column 12 in advance, the diaphragm 21 is installed on the column base part having the box cross section, and the H-shaped steel column 12, the cover plate, the diaphragm 21 and the like Welded together.
(2) In the through-diaphragm type, the H-shaped steel column 12 is temporarily cut at the position of the diaphragm 22 so that the H-shaped steel column at the column base portion and the H-shaped steel column above it are sandwiched by the diaphragm 22. After welding, the cover plate is welded to the H-shaped steel column 12 and the diaphragm 22.
(3) In the inner diaphragm type, after the diaphragm 23 is welded and fixed to the inner wall of the H-shaped steel column 12, the cover plate is welded to the H-shaped steel column 12 and the diaphragm 23.

It is a vertical sectional view showing one embodiment of a pile head junction structure of the present invention. (a)-(h) is sectional drawing orthogonal to the axial direction which shows the deformation | transformation form of the rod-shaped metal object with respect to embodiment of FIG. 1, respectively. It is a vertical sectional view which shows the deformation | transformation form regarding adhesion with the steel pipe and concrete which comprise a column. It is a vertical sectional view which shows the deformation | transformation form which provided the taper in the pile head. The design model for demonstrating the pile head junction structure of this invention is shown, (a) is a vertical sectional view, (b) is a horizontal sectional view. It is a graph for demonstrating the relationship between the moment of a pile head in a design model, and a rotation angle. It is a figure for demonstrating the relationship between the bending moment and axial force in a design model, the rotation angle, and the distortion | strain of the axial direction of a rod-shaped metal fitting. It is the graph which showed the relationship between the calculated moment M of the pile head, and a rotation angle. It is explanatory drawing of the analysis model supposing the infinite uniform frame. It is a graph which shows the pile moment distribution at the time of an earthquake at the time of using the analysis model of FIG. It is a graph which shows the relationship between the short-term allowable axial force N and the bending moment M of a pile head. It is the graph which compared and showed the pile moment distribution when the construction error e of a horizontal direction is 0 (solid line) and 100 mm (dotted line). (a) is a graph showing the relationship between the short-term allowable axial force N and bending moment of the pile head considering the construction error, and (b) is an explanatory diagram of the construction error in the study. As another embodiment of the pile head joint structure of the present invention, an embodiment in which the column is an H-shaped steel column is shown, (a) is a vertical sectional view, (b) is a horizontal sectional view, (c ) Is a side view. It is a horizontal sectional view in other embodiments in case a pillar is a H-shaped steel pillar. FIG. 15 is a vertical cross-sectional view showing another example of the cover plate for the embodiment of FIG. 14. 14 shows a modified example in which the upper flange of the steel foundation beam is attached to the diaphragm with respect to the embodiment of FIG. 14, (a) is a vertical sectional view in the case of the outer diaphragm type, and (b) is a through diaphragm type. (C) is a vertical sectional view in the case of the inner diaphragm type.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Pile, 1a ... Taper, 2 ... Column, 3 ... Foundation beam, 4 ... Base plate, 4a ... Hole, 5 ... Bar-shaped metal, 6 ... Stud, 7 ... Concrete, 8 ... Projection,
12 ... H-shaped steel column, 12a ... Web, 12b ... Flange, 13 ... Web opening, 14 ... Fuzzer plate, 15a, 15b ... Fuzzer plate,
21 ... Outer diaphragm, 22 ... Through diaphragm, 23 ... Inner diaphragm,
w ... Welding point

Claims (4)

  In the joint between the pile and the column, a steel foundation beam is joined to the column base of the column, and the central part of the concrete section constituting the pile head of the pile and the column base of the column are configured. In the concrete, rod-shaped hardware extending in the axial direction of the pile and the column is arranged, and the base plate provided at the lower end of the column also serves as a diaphragm for joining the steel foundation beam Pile head joint structure.   The pile head joint structure according to claim 1, wherein means for increasing the fixing force to the concrete or the adhesion force to the concrete is provided on the bar-shaped hardware.   The pile head joint structure according to claim 1, wherein the pile has a structure in which at least a pile head has a steel shell filled with concrete. The pile head joint structure according to claim 1, 2 or 3, wherein the column has a structure in which at least a column base is filled with concrete in a steel shell.

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