JP6589677B2 - Different diameter steel pipe pile - Google Patents
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本発明は、大径部から小径部に向けて縮径するテーパ部を有する異径鋼管杭に関するものである。 The present invention relates to a different-diameter steel pipe pile having a tapered portion that decreases in diameter from a large diameter portion toward a small diameter portion.
主に軟弱な地盤に構造物を建設する際、構造物を支持するために、一般に杭基礎が採用される。杭は、平常時において構造物の重量を支持することに加え、地震時には耐震性能を発揮することが重要である。 When constructing a structure mainly on soft ground, a pile foundation is generally employed to support the structure. In addition to supporting the weight of the structure during normal times, it is important that the piles exhibit seismic performance during an earthquake.
杭の耐震性能を向上させる一般的な方法としては、構造物から伝達される水平力に対し、杭材自体の水平耐力を高める方法と、周辺地盤の水平強度を増加させる方法とがある。杭材の水平耐力を高める方法としては、従来、杭頭部の拡径や杭頭のＣＦＴ（コンクリート充填鋼管構造）、あるいは二重管等にすること、等が提案されている。また、周辺地盤の水平強度を増加させる方法としては、地盤改良や置換等が提案されている。しかしながら、杭材の水平耐力の向上と周辺地盤の水平強度の増加とを両立させた方法は、未だ確立されていない。 As a general method for improving the seismic performance of the pile, there are a method for increasing the horizontal strength of the pile material itself with respect to a horizontal force transmitted from the structure and a method for increasing the horizontal strength of the surrounding ground. As methods for increasing the horizontal strength of pile members, conventionally, the diameter of the pile head, CFT (concrete-filled steel pipe structure) of the pile head, a double pipe, or the like has been proposed. Moreover, ground improvement, replacement, etc. are proposed as a method of increasing the horizontal strength of surrounding ground. However, a method that achieves both improvement of the horizontal strength of the pile material and increase of the horizontal strength of the surrounding ground has not yet been established.
特許文献１には、住宅等の小規模建築物の基礎等の摩擦杭として用いる鋼管杭において、外径を１００〜１４５ｍｍ、勾配を１／５０〜１／１００とする鋼管杭が開示されている。 Patent Document 1 discloses a steel pipe pile having an outer diameter of 100 to 145 mm and a gradient of 1/50 to 1/100 in a steel pipe pile used as a friction pile for a foundation of a small-scale building such as a house. .
また、特許文献２には、鉛直荷重の局部的な応力集中を防止し、鉛直荷重を確実に伝達することを目的として、テーパ部分の鋼管厚を外径に略反比例するように連続的に変化させるとともに、縮径率を０以上１／１０以下とする異径鋼管杭が開示されている。 In Patent Document 2, the steel pipe thickness of the tapered portion is continuously changed so as to be approximately inversely proportional to the outer diameter for the purpose of preventing local stress concentration of the vertical load and transmitting the vertical load with certainty. In addition, a different diameter steel pipe pile having a diameter reduction rate of 0 to 1/10 is disclosed.
しかしながら、上記特許文献１では、テーパ杭が周辺地盤の締固め効果を有することに言及しているものの、地盤改良のために最適な縮径率の範囲については言及されていない。特許文献１に開示されている鋼管杭の勾配は、縮径率が０．５／１００〜１／１００と小さく、締固め効果を発揮できるように十分に断面変化させるためには、必要長さが極めて長くなる。そのため、ストレート鋼管よりも高価なテーパ鋼管を多く用いる必要があり、コストの増大を招く。 However, in the said patent document 1, although it mentions that a taper pile has the compaction effect of a surrounding ground, it does not mention the range of the optimal diameter reduction rate for ground improvement. The gradient of the steel pipe pile disclosed in Patent Literature 1 is as small as 0.5 / 100 to 1/100 in diameter reduction, and is necessary to change the cross section sufficiently so that the compaction effect can be exhibited. Is extremely long. Therefore, it is necessary to use a taper steel pipe that is more expensive than a straight steel pipe, resulting in an increase in cost.
また、特許文献２では、鉛直荷重の応力集中を防止するために、大径部、テーパ部、および小径部の断面積を一定としている。一方で、地震時の水平荷重に対して曲げモーメントを確実に伝達することを目的とした場合、１／β以浅では杭の曲げ耐力を大きくする必要があるが、１／β以深では曲げ耐力はさほど必要ではない。ところが、特許文献２の異径鋼管杭の場合、地震荷重を想定して曲げ耐力を大きくした杭頭部に合わせて、杭全体の断面積を等しくしなければならないため、鋼材重量が増加する。また、特許文献２では、縮径率を０〜１０／１００と規定しているが、下限値の縮径率０を選択した場合には、周辺地盤を改良する効果は得にくい。 Moreover, in patent document 2, in order to prevent the stress concentration of a vertical load, the cross-sectional areas of a large diameter part, a taper part, and a small diameter part are made constant. On the other hand, for the purpose of reliably transmitting the bending moment to the horizontal load during an earthquake, it is necessary to increase the bending strength of the pile below 1 / β, but the bending strength below 1 / β Not very necessary. However, in the case of the different diameter steel pipe pile of Patent Document 2, the cross-sectional area of the entire pile has to be made equal in accordance with the pile head having an increased bending strength assuming an earthquake load, so that the steel weight increases. Moreover, in patent document 2, although the diameter reduction rate is prescribed | regulated as 0-10 / 100, when the diameter reduction rate 0 of the lower limit is selected, it is difficult to obtain the effect of improving the surrounding ground.
本発明は、かかる課題を解決し、地震時の水平荷重に対する水平耐力の向上と、周辺地盤の水平強度の増加とを両立させた鋼管杭を提供することを目的とする。 An object of the present invention is to solve this problem and to provide a steel pipe pile that achieves both an improvement in the horizontal strength against a horizontal load during an earthquake and an increase in the horizontal strength of the surrounding ground.
上記問題を解決するため、本発明は、上端側の大径部と、下端側の小径部と、前記大径部から前記小径部に向けて縮径するテーパ部とを有する異径鋼管杭であって、前記テーパ部は、板厚が一定であり、式（１）で求められる縮径率が１．５／１００〜１０／１００であり、前記大径部の板厚が、前記小径部の板厚以上であることを特徴とする、異径鋼管杭を提供する。
縮径率＝（Ｄ―ｄ）／２Ｌ ・・・（１）
Ｄ：大径部の外径（ｍｍ）
ｄ：小径部の外径（ｍｍ）
Ｌ：テーパ部の長さ（ｍｍ）
In order to solve the above problem, the present invention is a different diameter steel pipe pile having a large diameter portion on the upper end side, a small diameter portion on the lower end side, and a tapered portion that decreases in diameter from the large diameter portion toward the small diameter portion. there, the tapered portion is a plate thickness is constant, Ri radial contraction rate is 1.5 / 100-10 / 100 der obtained by the formula (1), the thickness of the large diameter portion, the small diameter Provided is a steel pipe pile with a different diameter characterized by being equal to or greater than the thickness of the part .
Reduction ratio = (D−d) / 2L (1)
D: Outer diameter of large diameter part (mm)
d: Outer diameter of the small diameter part (mm)
L: Length of taper part (mm)
前記テーパ部の上端が、前記大径部の外径Ｄに対して杭頭から２Ｄ〜８Ｄの高さに配置されていることが好ましい。なお、杭頭とは、杭と基礎スラブとの境界をさす。
It is preferable that the upper end of the tapered portion is disposed at a height of 2D to 8D from the pile head with respect to the outer diameter D of the large diameter portion. The pile head refers to the boundary between the pile and the foundation slab.
本発明によれば、地震時の水平荷重に対する水平耐力の向上と、周辺地盤の水平強度の増加とを両立させることができる。 ADVANTAGE OF THE INVENTION According to this invention, the improvement of the horizontal proof stress with respect to the horizontal load at the time of an earthquake and the increase in the horizontal strength of a surrounding ground can be made compatible.
以下、本発明の実施の形態を、図を参照して説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
図１は、本発明の実施形態にかかる異径鋼管杭１の形状を示す。異径鋼管杭１は、上部から順に、大径部１１、大径部１１の下端から小径部の上端に向けて縮径するテーパ部１２、および小径部１３を有している。テーパ部１２の板厚ｔ２は全長にわたって一定であり、本実施形態では、大径部１１の板厚ｔ１、テーパ部１２の板厚ｔ２、および小径部１３の板厚ｔ３は、略同一である。 FIG. 1 shows the shape of a different diameter steel pipe pile 1 according to an embodiment of the present invention. The different-diameter steel pipe pile 1 has a large-diameter portion 11, a tapered portion 12 that decreases in diameter from the lower end of the large-diameter portion 11 toward the upper end of the small-diameter portion, and a small-diameter portion 13 in order from the top. The plate thickness t2 of the taper portion 12 is constant over the entire length, and in this embodiment, the plate thickness t1 of the large diameter portion 11, the plate thickness t2 of the taper portion 12, and the plate thickness t3 of the small diameter portion 13 are substantially the same. .
そして、テーパ部１２は、下記式（１）で求められる縮径率が１．５／１００〜１０／１００である。
縮径率＝（Ｄ―ｄ）／２Ｌ ・・・（１）
Ｄ：大径部の外径（ｍｍ）
ｄ：小径部の外径（ｍｍ）
Ｌ：テーパ部の長さ（ｍｍ）
And the taper part 12 is 1.5 / 100-10/100 in the diameter reduction rate calculated | required by following formula (1).
Reduction ratio = (D−d) / 2L (1)
D: Outer diameter of large diameter part (mm)
d: Outer diameter of the small diameter part (mm)
L: Length of taper part (mm)
本発明者らは、三次元挙動の鋼管杭のマクロな応力分布を求めるため、異径鋼管杭の正面形状を模して、縮径率０／１００、１０／１００、２０／１００、３０／１００の平面形状を有する４種類の板状の試験体を製作し、長手方向の一辺を固定した片持ち梁として、自由端側を載荷する曲げ試験を行った。 In order to obtain a macroscopic stress distribution of a steel pipe pile having a three-dimensional behavior, the present inventors imitated the front shape of a different diameter steel pipe pile, and reduced diameter ratios of 0/100, 10/100, 20/100, 30 / Four types of plate-shaped test bodies having 100 planar shapes were manufactured, and a bending test was performed in which the free end side was loaded as a cantilever beam with one side in the longitudinal direction fixed.
図２〜図５は、各試験体の形状および応力分布を示す。図２〜図５において、（ａ）は試験体の形状および寸法を示し、（ｂ）は各試験体の平面上における等色線図であり、（ｃ）は縁応力分布図である。試験体の材料には、板厚が６ｍｍのジアリルフタレートプリポリマー（Diallyl phthalate polymer、 a≒0.7mm/kg, E=390kg/mm）を用いた。図２〜図５の（ｂ）の右端が固定端であり、左端付近の矢印位置に荷重Ｐを載荷した。実験精度を上げるため、暗視野、明視野法により（n÷1/2）Fringeで、最大Fringe order n≒7（n=0,0.5,1,1.5・・・7）になるような荷重で実験を行った。 2 to 5 show the shape and stress distribution of each specimen. 2-5, (a) shows the shape and dimension of a test body, (b) is a color map on the plane of each test body, (c) is an edge stress distribution map. As the material of the test body, diallyl phthalate prepolymer (Diallyl phthalate polymer, a≈0.7 mm / kg, E = 390 kg / mm) having a plate thickness of 6 mm was used. The right end of (b) in FIGS. 2 to 5 is a fixed end, and the load P is loaded at the arrow position near the left end. In order to increase the experimental accuracy, the dark field and bright field method (n ÷ 1/2) with a ringe, with a load such that the maximum fringe order n ≒ 7 (n = 0, 0.5, 1, 1.5 ... 7) An experiment was conducted.
図２は縮径率０／１００、すなわち一定幅の場合であり、局部的な応力集中は発生せず、固定端に向けて徐々に応力が増している。図３は縮径率１０／１００の場合であり、局部的な応力集中は見られない。これに対して、図４に示す縮径率２０／１００と、図５に示す縮径率３０／１００の場合には、小径部とテーパ部との境界およびテーパ部と大径部との境界に、主応力の流れが急変する特異点が発生している。この実験より、異径鋼管杭に地震による水平荷重が作用した場合の局部的な応力集中を防ぐために、テーパ部の縮径率の最大値を１０／１００以下とした。これにより、地震荷重により杭に曲げモーメントが作用する際、異径鋼管杭の板厚を変化させることなく応力集中を防ぐことができる。 FIG. 2 shows a case in which the diameter reduction ratio is 0/100, that is, a constant width, local stress concentration does not occur, and the stress gradually increases toward the fixed end. FIG. 3 shows a case where the diameter reduction ratio is 10/100, and no local stress concentration is observed. On the other hand, in the case of the diameter reduction ratio 20/100 shown in FIG. 4 and the diameter reduction ratio 30/100 shown in FIG. 5, the boundary between the small diameter portion and the taper portion and the boundary between the taper portion and the large diameter portion. In addition, there is a singular point where the flow of the main stress changes suddenly. From this experiment, in order to prevent local stress concentration when a horizontal load due to an earthquake acts on a different diameter steel pipe pile, the maximum value of the diameter reduction ratio of the tapered portion was set to 10/100 or less. Thereby, when a bending moment acts on a pile by an earthquake load, stress concentration can be prevented without changing the plate thickness of the different diameter steel pipe pile.
さらに、地盤改良に効果を発揮する縮径率の最小値を求めるため、縮径率０／１００、０．５／１００、１．５／１００、２．５／１００、３．５／１００の５種類の全長テーパ杭の残留水平土圧を実験により測定した。 Furthermore, in order to obtain the minimum value of the diameter reduction ratio that is effective for ground improvement, the diameter reduction ratio is 0/100, 0.5 / 100, 1.5 / 100, 2.5 / 100, 3.5 / 100. The residual horizontal earth pressure of five types of full-length taper piles was measured experimentally.
図６は試験装置２１を示す。土槽２２の中央に、試験杭２３をスクリュージャッキ２４により圧入する。試験用の地盤として、直径５２０ｍｍの円柱形土槽に、７００ｍｍの高さで、飯豊珪砂７号を目標の相対密度になるように振動締固めにより作製した。本試験での目標の相対密度は、地盤強度の違いが杭打設後の地盤締固め効果に与える影響を確認するため、３０％と５０％の２ケースとした。全ての試験杭２３で貫入速度（１０ｍｍ／ｍｉｎ）及び貫入量（６２０ｍｍ）を一定とした。 FIG. 6 shows the test apparatus 21. A test pile 23 is press-fitted into the center of the earth tub 22 with a screw jack 24. As a ground for the test, Iito Silica Sand No. 7 was prepared by vibration compaction in a cylindrical soil tank having a diameter of 520 mm so as to have a target relative density at a height of 700 mm. The target relative density in this test was set to two cases of 30% and 50% in order to confirm the influence of the difference in ground strength on the ground compaction effect after pile driving. The penetration speed (10 mm / min) and the penetration amount (620 mm) were constant in all the test piles 23.
試験杭２３は、土槽２２の側面境界の影響を受けない大きさとし、直径５２０ｍｍの土槽に対してストレート杭の直径を３４ｍｍとした。試験杭２３と砂粒子との比率に関しては、有効粒子径が杭径の１／２０以下となっている。図７は、試験杭２３の仕様の一覧を示す。既往の比較検討により、ＡＴ−５は、ストレート杭（Ｓ）に比べて大きな残留水平土圧が得られることを確認しているため、本試験では、ＡＴ−５を基準に、それよりも縮径率が大きいＡＴ−７、及び、縮径率が小さい２種類（ＡＴ−３、ＡＴ−１）を試験杭２３とし、形状による傾向を分析した。なお、全試験杭２３で、土中の排土量が一定となるように、土中杭体体積比をほぼ同一とした。 The test pile 23 was sized so as not to be affected by the side boundary of the soil tank 22, and the diameter of the straight pile was 34 mm with respect to the soil tank having a diameter of 520 mm. Regarding the ratio between the test pile 23 and the sand particles, the effective particle diameter is 1/20 or less of the pile diameter. FIG. 7 shows a list of specifications of the test pile 23. In past tests, it was confirmed that AT-5 was able to obtain a larger residual horizontal earth pressure than straight piles (S). Two types (AT-3, AT-1) having a small diameter ratio and AT-7 having a large diameter ratio were used as test piles 23, and the tendency due to the shape was analyzed. In all the test piles 23, the volume ratio of the piles in the soil was substantially the same so that the amount of soil discharged in the soil was constant.
本試験では、地盤の強度上昇と土圧の上昇との間に相互関係が存在することに着目し、地盤の改良効果を示す指標を、水平土圧の増分とした。地盤の締固め効果の逐次変化及び改良範囲を評価するため、鉛直方向には、図６（ａ）に示すように地表面から１３０ｍｍ、２３０ｍｍ、３３０ｍｍ、４３０ｍｍ、５３０ｍｍの５箇所、それぞれの鉛直方向位置において、水平方向には、図６（ｂ）に示すように試験杭２３の中心から北方向３０ｍｍ、東方向４８ｍｍ、南方向７０ｍｍ、西方向１００ｍｍの位置に土圧計を設置し、水平方向の土圧を測定した。 In this test, paying attention to the fact that there is a correlation between the increase in the strength of the ground and the increase in the earth pressure, the index indicating the improvement effect of the ground was taken as the increment of the horizontal earth pressure. In order to evaluate the sequential change and improvement range of the compaction effect of the ground, as shown in FIG. 6 (a), the vertical directions are 130mm, 230mm, 330mm, 430mm, and 530mm at five locations from the ground surface. In the horizontal direction, as shown in FIG. 6 (b), earth pressure gauges were installed at positions 30mm north, 48mm east, 70mm south, and 100mm west from the center of the test pile 23. Earth pressure was measured.
図８は、相対密度Ｄｒが３０、５０の２種類の地盤において、縮径率０／１００（ストレート杭）の場合を１としたときの残留水平土圧を示したグラフである。図８に示す実験結果より、全ての全長テーパ杭でストレート杭よりも顕著に残留水平土圧が大きくなることがわかる。また、縮径率１．５％までは縮径率に比例して水平土圧が大きくなるものの、それを越えるとほぼ横ばいになり、縮径率３．５％では、ピーク値よりも低下している。このことより、杭体体積一定の本実験条件であれば、縮径率が１．５〜２．５％程度の範囲に残留水平土圧を最大にできる最適縮径率が存在すると示唆される。したがって、本発明は、地盤改良に効果を発揮するために、テーパ部の縮径率の最小値を１．５／１００とした。 FIG. 8 is a graph showing the residual horizontal earth pressure when the relative density Dr is 30 and 50 and the ground diameter is 0/100 (straight pile). From the experimental results shown in FIG. 8, it can be seen that the residual horizontal earth pressure is remarkably increased in all the full length tapered piles than in the straight piles. In addition, the horizontal earth pressure increases in proportion to the diameter reduction ratio up to 1.5%, but when it exceeds that, it becomes almost flat, and at the diameter reduction ratio of 3.5%, it becomes lower than the peak value. ing. From this, it is suggested that there is an optimum diameter reduction ratio that can maximize the residual horizontal earth pressure in the range where the diameter reduction ratio is about 1.5 to 2.5% under the present experimental conditions where the pile body volume is constant. . Therefore, the present invention sets the minimum value of the diameter reduction ratio of the tapered portion to 1.5 / 100 in order to exert an effect on the ground improvement.
以上のように、本発明によれば、テーパ部の縮径率を１．５／１００〜１０／１００とすることにより、大径部、テーパ部、小径部を有する異径鋼管杭において、地盤改良効果が得られるとともに、地震荷重が作用しても応力集中を低減して曲げモーメントを確実に伝達できる。したがって、鉛直支持力、水平耐力の両方を向上させることができる。また、テーパ部の板厚が略一定でよいので、製造コストを低減できる。 As described above, according to the present invention, in the different diameter steel pipe pile having a large diameter portion, a tapered portion, and a small diameter portion by setting the diameter reduction ratio of the tapered portion to 1.5 / 100 to 10/100, the ground In addition to the improvement effect, the bending moment can be reliably transmitted by reducing the stress concentration even when an earthquake load is applied. Therefore, both the vertical support force and the horizontal proof stress can be improved. Moreover, since the plate | board thickness of a taper part may be substantially constant, manufacturing cost can be reduced.
なお、上記実施形態では、大径部１１の板厚ｔ１、テーパ部１２の板厚ｔ２、小径部１３の板厚ｔ３を全て略同一としたが、例えば、大径部１１の板厚ｔ１もしくは小径部１３の板厚ｔ３のいずれか一方とテーパ部１２の板厚ｔ２とを略同一としてもよい。すなわち、例えば地震による水平力に対する耐力を向上させるために、大径部１１の板厚ｔ１を最も厚くし、テーパ部１２の板厚ｔ２と小径部１３の板厚ｔ３を板厚ｔ１よりも薄くしてもよい。本発明では、杭頭部となる大径部１１の板厚ｔ１を大きくし、１／β（β：杭の特性値）よりも深い位置で曲げモーメントの影響を受けない範囲は、小径部１３として外径を小さくするとともに、小径部１３の板厚ｔ３を大径部１１やテーパ部１２と略同一かまたは小さくすることができるので、鋼材の総重量を削減し、コストを低減することができる。 In the above embodiment, the plate thickness t1 of the large diameter portion 11, the plate thickness t2 of the taper portion 12, and the plate thickness t3 of the small diameter portion 13 are all substantially the same, but for example, the plate thickness t1 of the large diameter portion 11 or One of the plate thicknesses t3 of the small diameter portion 13 and the plate thickness t2 of the tapered portion 12 may be substantially the same. That is, for example, in order to improve the proof strength against a horizontal force caused by an earthquake, the plate thickness t1 of the large diameter portion 11 is maximized, and the plate thickness t2 of the taper portion 12 and the plate thickness t3 of the small diameter portion 13 are thinner than the plate thickness t1. May be. In the present invention, the range in which the plate thickness t1 of the large-diameter portion 11 serving as the pile head is increased and is not affected by the bending moment at a position deeper than 1 / β (β: characteristic value of the pile) is the small-diameter portion 13. As described above, the outer diameter can be reduced and the thickness t3 of the small diameter portion 13 can be made substantially the same as or smaller than that of the large diameter portion 11 and the tapered portion 12, thereby reducing the total weight of the steel material and reducing the cost. it can.
なお、本発明において、各部の板厚は、例えばＪＩＳ Ａ ５５２５の表５に示される厚さｔの許容差の範囲の誤差であれば、「一定」あるいは「同一」と見なすことができる。 In the present invention, the plate thickness of each part can be regarded as “constant” or “same” as long as it is within the tolerance range of thickness t shown in Table 5 of JIS A 5525, for example.
また、杭頭に入力される水平荷重から杭体に発生する曲げモーメントを計算する場合、下記式により求められる杭の特性値βを算定し、深度１／βで断面変化させることが広く行われている。
ｋｈ０＝Ｅ０／０．３＝２８００Ｎ／０．３：水平方向地盤反力係数（ｋＮ／ｍ３）
Ｎ：地盤Ｎ値、表層では１〜１０程度と仮定
Ｄ：杭径（ｍｍ）
ＥＩ：杭の曲げ剛性（ｋＮ・ｍ２）
Also, when calculating the bending moment generated in the pile body from the horizontal load input to the pile head, it is widely performed to calculate the pile characteristic value β obtained by the following formula and change the cross section at a depth of 1 / β. ing.
k h0 = E 0 /0.3=2800 N / 0.3: Horizontal ground reaction force coefficient (kN / m 3 )
N: Ground N value, assumed to be about 1 to 10 on the surface layer D: Pile diameter (mm)
EI: Bending stiffness of pile (kN · m 2 )
鋼管杭で用いられる範囲は杭径Ｄ：４００〜１６００ｍｍ、板厚ｔ：６〜２５ｍｍ、かつ、杭径と板厚の比率を、杭径／板厚≦１００とする場合が多い。この範囲で杭径／板厚が最大値（１６００／１６）となる場合と、最小値（４００／２５）となる場合で、必要な根入れ長Ｌ＝１／βを計算し、ＬをＤを用いて表現すると、表１に示すように、２．５Ｄ＜Ｌ＜７．４Ｄとなる。したがって、異径鋼管杭１のテーパ部１２は、大径部の外径Ｄに対して、杭頭から２Ｄ〜８Ｄの範囲に配置されていることが好ましい。これにより、曲げモーメントを確実に伝達させつつ、鋼材重量を低減できる。 The ranges used for steel pipe piles are pile diameter D: 400 to 1600 mm, plate thickness t: 6 to 25 mm, and the ratio of pile diameter to plate thickness is often set to pile diameter / plate thickness ≦ 100. In this range, when the pile diameter / plate thickness becomes the maximum value (1600/16) and the minimum value (400/25), the necessary penetration length L = 1 / β is calculated, and L is D As shown in Table 1, 2.5D <L <7.4D. Therefore, it is preferable that the taper part 12 of the different diameter steel pipe pile 1 is arrange | positioned in the range of 2D-8D from a pile head with respect to the outer diameter D of a large diameter part. Thereby, steel material weight can be reduced, transmitting a bending moment reliably.
本発明が対象とする鋼管杭は、例えば全長１０〜８０ｍ、杭頭部側の大径部の外径４００〜１６００ｍｍ、板厚６〜２５ｍｍ程度であり、摩擦杭、支持杭の両方の用途に用いられる。このような異径鋼管杭は、例えばスパイラル、ロール、プレス等、従来公知の鋼管杭の製造方法により製造される。 The steel pipe pile targeted by the present invention has, for example, a total length of 10 to 80 m, an outer diameter of the large diameter part on the pile head side of 400 to 1600 mm, and a plate thickness of about 6 to 25 mm. Used. Such a different diameter steel pipe pile is manufactured by the conventionally well-known manufacturing method of a steel pipe pile, such as a spiral, a roll, and a press.
本発明の異径鋼管杭１は、単体で杭基礎として用いる場合もあるが、杭を構成する一部材として用いられる場合もある。この場合は、異形鋼管杭の上下に、それぞれ、異径鋼管杭と同種の鋼部材からなる大径の上杭材および小径の下杭材が、溶接または機械式継手で接合される。 Although the different diameter steel pipe pile 1 of this invention may be used alone as a pile foundation, it may be used as one member which comprises a pile. In this case, a large-diameter upper pile material and a small-diameter lower pile material made of a steel member of the same type as the different-diameter steel pipe pile are joined to each other by welding or mechanical joints above and below the irregular-shaped steel pipe pile.
以上、本発明の好適な実施形態について説明したが、本発明はかかる例に限定されない。当業者であれば、特許請求の範囲に記載された技術的思想の範疇内において、各種の変更例または修正例に想到しうることは明らかであり、それらについても当然に本発明の技術的範囲に属するものと了解される。 As mentioned above, although preferred embodiment of this invention was described, this invention is not limited to this example. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the technical idea described in the claims. It is understood that it belongs to.
本発明の異径鋼管杭と、従来例として上記特許文献２（図９中の先願特許）に記載された異径鋼管杭を、実構造物の杭として用いる場合の、それぞれの鋼材重量を算出した。本発明の実施例としては、地表面から１／β以下の曲げモーメントの影響を受けない範囲を小径部とし、大径部から小径部までの板厚を一定とした。従来例は、杭の断面積を一定にするため、小径部の板厚を大径部よりも大きくした。
Ｎ：地盤Ｎ値、表層では５と仮定
Ｄ：杭径（ｍｍ）
ＥＩ：杭の曲げ剛性（ｋＮ・ｍ２）
とし、板厚や杭径が異なる８通りについて設計した結果を図９に示す。いずれの規模の杭でも、本発明例の方が、従来例よりも１割程度鋼材重量が小さくなっていることがわかる。
The steel material weight in the case of using the different diameter steel pipe pile of this invention and the different diameter steel pipe pile described in the said patent document 2 (prior application patent in FIG. 9) as a prior art as a pile of a real structure is shown. Calculated. As an example of the present invention, the range not affected by the bending moment of 1 / β or less from the ground surface was set as the small diameter portion, and the plate thickness from the large diameter portion to the small diameter portion was made constant. In the conventional example, in order to make the cross-sectional area of the pile constant, the plate thickness of the small diameter portion is made larger than that of the large diameter portion.
N: Ground N value, assumed to be 5 on the surface layer D: Pile diameter (mm)
EI: Bending stiffness of pile (kN · m 2 )
FIG. 9 shows the results of designing for 8 different plate thicknesses and pile diameters. It can be seen that the weight of the steel material is smaller by about 10% in the example of the present invention than in the conventional example, regardless of the size of the pile.
本発明は、建築、土木分野における構造物の杭基礎に適用され、特に地震による水平応力を受ける場合の杭として有用である。 INDUSTRIAL APPLICABILITY The present invention is applied to a pile foundation of a structure in the construction and civil engineering fields, and is particularly useful as a pile when receiving horizontal stress due to an earthquake.
１ 異径鋼管杭
１１ 大径部
１２ テーパ部
１３ 小径部
1 Different diameter steel pipe pile 11 Large diameter part 12 Taper part 13 Small diameter part
Claims (2)
前記テーパ部は、板厚が一定であり、式（１）で求められる縮径率が１．５／１００〜１０／１００であり、
前記大径部の板厚が、前記小径部の板厚以上であることを特徴とする、異径鋼管杭。
縮径率＝（Ｄ―ｄ）／２Ｌ ・・・（１）
Ｄ：大径部の外径（ｍｍ）
ｄ：小径部の外径（ｍｍ）
Ｌ：テーパ部の長さ（ｍｍ） A different diameter steel pipe pile having a large diameter portion on the upper end side, a small diameter portion on the lower end side, and a tapered portion that reduces the diameter from the large diameter portion toward the small diameter portion,
The tapered portion is a plate thickness is constant, Ri radial contraction rate is 1.5 / 100-10 / 100 der obtained by the formula (1),
The steel pipe pile with different diameters , wherein the plate thickness of the large diameter portion is equal to or greater than the plate thickness of the small diameter portion .
Reduction ratio = (D−d) / 2L (1)
D: Outer diameter of large diameter part (mm)
d: Outer diameter of the small diameter part (mm)
L: Length of taper part (mm)
2. The different diameter steel pipe pile according to claim 1, wherein an upper end of the tapered portion is disposed at a height of 2D to 8D from a pile head with respect to an outer diameter D of the large diameter portion .
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