JP4438637B2 - Structure design method of diagonal lattice braces and oblique lattice braces designed by the structure design method - Google Patents

Description

  The present invention relates to a structure design method for a steel-structured diagonal lattice brace incorporated in a structural frame and used for seismic reinforcement and the like, and an oblique lattice brace obtained by this design method.

  Conventionally, in various structures such as steel structures, reinforced concrete structures, and reinforced steel concrete structures, diagonal lattice braces are incorporated as structural elements for earthquake resistance and wind resistance. In addition, this type of diagonal lattice brace is also used as a steel frame for seismic reinforcement of existing structures.

Here, as shown in FIG. 3, the oblique lattice brace generally has a rectangular peripheral frame steel frame 1 incorporated in a column beam frame of a structure and is inclined with respect to the horizontal in the peripheral frame steel frame 1. The brace members 2 are arranged in a lattice shape in the state, and these brace members 2 are rigidly joined at the intersections, and both ends thereof are rigidly joined to the peripheral frame steel frame 1. Yes. Incidentally, an oblique lattice brace having such a configuration is also disclosed in, for example, Patent Document 1 below.
JP-A-11-152908

  By the way, when an earthquake occurs, a horizontal force acts on the diagonal lattice braces incorporated in the frame of the structure via columns and beams. As a result, a compressive force acts on one inclined brace member in the peripheral frame steel frame 1, and a tensile force acts on the other inclined brace member intersecting with the brace member. And the compressive yield strength in the brace member to which the compressive force acts is determined by the buckling length.

  However, for example, when the brace member is arranged in the out-of-plane weak axis direction, the buckling occurs in the out-of-plane direction, but the brace member receiving the compressive force receives tensile force at a plurality of intermediate positions. Because the brace member is rigidly connected, its buckling length is affected by out-of-plane restraint by the brace member that receives tensile force. For this reason, the buckling length of the brace member that receives the compressive force is expected to be shorter than the case where there is no brace member that intersects the brace member, but the quantitative evaluation method is not clear at present.

  For this reason, conventionally, when designing the above diagonal lattice brace, for example, the brace member is disposed on an out-of-plane strong shaft capable of obtaining a high buckling strength, and the designed buckling length is assumed to be an expected length. By setting the length longer than this, a method of ensuring a sufficient strength as the entire diagonal lattice brace is adopted.

  For this reason, the obtained diagonal lattice brace has an excessive strength with respect to the originally required strength, and is inferior in economic efficiency and has a problem of increasing weight.

  In particular, when a general-purpose H-section steel is used as the brace member and it is placed on the out-of-plane strong shaft, the fitting at the intersection of the brace member becomes poor, and a large number of additional gusset plates are required. As a result, the structure becomes complicated, and there is a problem that a lot of labor is required for the joining work.

Therefore, in order to design a diagonal lattice brace having the necessary and sufficient strength, it may be possible to conduct a detailed strength simulation separately using the finite element method etc., but the design itself requires excessive labor and cost. Is not realistic.
For this reason, development of a simple design method capable of determining a reasonable brace member size and the like of the above oblique lattice braces is desired.

On the other hand, the Japan Architectural Institute “Steel Structure Buckling Design Guidelines” (1980) describes a member AB that receives a compressive force N ₁ as shown in FIG. And the member CD receiving the tensile force N ₂ cross in an X shape, the buckling length L _κ of the member AB outside the surface is determined by the axial force and dimension of the intersecting member CD, etc. (1952 edition) describes that the buckling length L _κ is expressed by the following equation.

ここで、Ｅはヤング率、Ｉ₂は部材ＣＤの断面二次モーメント、Ｌ₁、Ｌ₂はそれぞれ部材ＡＢ、部材阿ＣＤの長さである。

Here, E is the Young's modulus, I ₂ is the cross-sectional secondary moment of the member CD, and L ₁ and L ₂ are the lengths of the member AB and the member CD, respectively.

  Incidentally, although the above equation is rarely applied to the design of bridges of continuous girders, it is not used for the design of brace members in actual structures.

Therefore, as a result of intensive studies on whether or not the above formula can be used for the design of the diagonal lattice braces, the present inventors have determined that the buckling length L _κ is the lattice spacing (L _{1) of the} brace member that receives the compressive force. / 2) Buckling stiffening due to the fact that there are multiple buckling stiffening points in the middle of the brace member (= rigid joint points with the member subjected to the tensile force) By introducing the additional factor κ of the sexuality and further evaluating this additional factor κ according to the number of divisions of the brace member, the inventors have obtained the knowledge that it can be applied to the design of the oblique lattice braces.

  The present invention has been made on the basis of such knowledge, and it is possible to appropriately evaluate the buckling strength of a brace member that receives a compressive force by a simple method, and therefore to design a rational oblique lattice brace. It is an object of the present invention to provide a structure design method for a slanted lattice brace and a slanted lattice brace designed by the structure design method.

で定めるσ_c以下になるように設計することを特徴とするものである。 In order to solve the above-mentioned problem, the invention according to claim 1 is arranged in a rectangular peripheral frame steel frame built in along the columns and beams constituting the column beam frame, and in the peripheral frame steel frame. A plurality of brace members made of the same material and having the same cross-sectional area, and the plurality of brace members are arranged in a grid pattern with the central axis positioned in the same plane and inclined with respect to the horizontal. It is a structure design method of an obliquely inclined brace in which the intersecting portions are rigidly joined and both ends are rigidly joined to the peripheral frame steel frame, and the following specifications of the brace member that receives a compressive force,
E: Young's modulus of the material constituting the brace member λ: Elongation ratio in which the lattice spacing of the brace member is a buckling length, and λ = L / i
L: lattice spacing of the braces i: secondary radius of cross section of the brace member in the out-of-plane direction, i = (I / A) ^1/2
I: Cross-sectional secondary moment in the out-of-plane direction of the brace member A: Cross-sectional area of the brace member m: Maximum number of divisions of one brace member by the intersecting brace members γ: Buckling of the entire length of the brace member Length coefficient, 0.5 ≦ γ ≦ 1
κ: Additional coefficient of buckling stiffening rigidity of the brace member, 1 ≦ κ ≦ 2
n: The ratio of the absolute values of the tensile force acting on one of the brace members and the compressive force acting on the other brace member, and the compression stress σ acting on the brace member is

It is designed to be less than or equal to σ _c defined by

  The buckling length coefficient γ of the entire length of the brace member is a value determined by the rigidity ratio between the brace member and the peripheral frame steel frame and the torsional rigidity of the peripheral frame steel frame, and is fixed in the out-of-plane direction at the end of the brace member. When the degree is high, γ is close to 0.5, and when both ends are free to rotate, γ = 1.

  Further, the additional coefficient κ of the buckling stiffening rigidity of the brace member is a value in the range of 1 ≦ κ ≦ 2, specifically, according to the above knowledge, the maximum division number m of one brace member. It is optimal that κ = 1 when = 2, κ = 1.5 when m = 3, and κ = 2 when m = 4.

  Further, the absolute value ratio n between the tensile force acting on the one brace member and the compressive force acting on the other brace member depends on the degree of integration of the joints between the peripheral frame steel frame and the columns and beams. In the case where the peripheral frame steel frame and the column and beam are integrated so that there is no slip between them, and therefore a horizontal force acts equally on the peripheral frame steel frame, n = 1.

  On the other hand, when the horizontal force acts by the compressive force main body as in the case of the joint configuration in which slippage may occur between the peripheral frame steel frame and the beam, n <1, and conversely by the tensile force main body. When it acts, n> 1. For example, when a steel frame surrounding a diagonal grid brace is inserted without installing sufficient anchors in an existing column beam structure for seismic reinforcement of the existing frame, horizontal force is transmitted by the support pressure from the existing column. By doing so, it acts on the peripheral frame steel frame mainly by the compressive force. Incidentally, when a general construction method of fixing the peripheral frame steel frame to the columns and beams with anchor bolts is adopted, 0.5 ≦ n ≦ 1.

  The invention according to claim 2 is characterized in that the brace member according to claim 1 is arranged with its weak axis direction facing out of the surface of the column beam frame. is there.

  Next, an oblique lattice brace according to the invention described in claim 3 is arranged in a rectangular peripheral frame steel frame incorporated along the columns and beams constituting the column beam frame, and in the peripheral frame steel frame. A plurality of brace members made of the same material and having the same cross-sectional area, and the plurality of brace members are arranged in a lattice shape with the central axis in the same plane and inclined with respect to the horizontal. The structure design method of the diagonal lattice brace according to claim 1 or 2, wherein the brace member is rigidly joined to each other and both ends are rigidly joined to the peripheral frame steel frame and receives a compressive force. It is characterized by being designed by.

According to the invention described in claim 1 or 2 and the invention described in claim 3 using the same, the specifications obtained uniquely from the brace member and the peripheral frame steel frame itself, and the above obtained from the degree of fixation of both. From the buckling length coefficient γ of the entire length of the brace member and the ratio n of the absolute values of the tensile force and the compressive force obtained from the engagement between the surrounding frame steel frame and the column beam frame, the compressive stress σ acting on the brace member is It can be designed to be σ _c or less obtained by the equation.

Therefore, it is possible to appropriately evaluate the buckling strength of the brace member that receives a compressive force by a simple method, and therefore, it is possible to design a rational oblique lattice brace.
The invention according to claim 1 can be similarly applied to the case where the brace member is disposed on the out-of-plane weak shaft and the case where the brace member is disposed on the out-of-plane strong shaft. When arranged on the out-of-plane weak shaft as in the second aspect of the invention, when the H-shaped steel which is a general-purpose material is used as the brace member, the fitting fits well at the intersection of the brace member. Therefore, the effect that the construction is facilitated can be obtained.

  In the present embodiment, the diagonal lattice brace symmetric is the rectangular peripheral frame steel frame 1 incorporated in the column beam frame of the structure, and the peripheral frame steel frame 1 in the same manner as shown in FIG. It consists of a plurality of brace members 2 arranged in a grid in a state inclined with respect to the horizontal. The brace members 2 are all made of H-section steel having the same cross section, and are arranged in the out-of-plane weak axis direction.

  Further, these brace members 2 are rigidly joined to each other by welding one brace member 2 at an intersection and welding the web of the other brace member 2 and a flange. The brace member 2 is rigidly joined to the peripheral frame steel frame 1 at both ends.

  Further, the peripheral frame steel frame 1 is configured by joining and integrating a plurality of intermediate members 1a and 1b (two on the column side and four on the beam side) on both the column side and the beam side, A joint joint portion 3 to which the end portion of the brace member 2 is joined is formed at the joint portion between these intermediate members 1a and 1b.

On the other hand, first, in the equation of [Equation 1], an additional coefficient κ of stiffening rigidity due to the fact that there are a plurality of intermediate buckling stiffening points of the brace member 2 that receives the compressive force is Get the formula.

Furthermore, each variable of the above formula is replaced and modified as follows based on FIG.
L _κ = 0.5 L ₁ , N ₂ / N ₁ = n, N ₁ = Aσ _c , I ₂ = Ai ² ,
L ₁ = 2λi, L ₂ = mγλi

Thereby, the following equation can be derived.

here,
E: Young's modulus of the material constituting the brace member λ: Elongation ratio in which the lattice spacing of the brace member is a buckling length, and λ = L / i
L: lattice spacing of the braces i: secondary radius of cross section of the brace member in the out-of-plane direction, i = (I / A) ^1/2
I: Cross-sectional secondary moment in the out-of-plane direction of the brace member A: Cross-sectional area of the brace member m: Maximum number of divisions of one brace member by the intersecting brace members γ: Buckling of the entire length of the brace member Length coefficient, 0.5 ≦ γ ≦ 1
κ: Additional coefficient of buckling stiffening rigidity of the brace member, 1 ≦ κ ≦ 2
n: Ratio of absolute values of the tensile force acting on one of the brace members and the compressive force acting on the other brace member.

Therefore, it is obtained from the specifications uniquely obtained from the brace member 2 and the peripheral frame steel frame 1 itself, E, λ, L, i, I, A, m (4 in the figure), κ, and the degree of fixation of both. The compressive stress σ acting on the brace member 2 from the buckling length coefficient γ of the entire length of the brace member 2 and the ratio n of the absolute values of the tensile force and the compressive force obtained from the engagement between the peripheral frame steel frame 1 and the column beam frame. Can be designed to be less than or equal to σ _c obtained by the above equation.

であれば、この斜め格子形ブレースは、格子間隔を座屈長さとした弾性座屈を生じる。 Incidentally, the molecule π ² E / λ ^{2 on} the right side of the equation shown in [Equation 2] is the Euler buckling stress in the brace member 2 that receives the compressive force of the slenderness ratio λ. Therefore, in the denominator on the right side,

If so, this slanted lattice brace produces elastic buckling with the lattice spacing as the buckling length.

で表すことができる。 In the case of inelasticity, the stress σ _cr generated in the brace member 2 that receives the compressive force is equal to or less than the Euler buckling stress, and if a general Johnson parabola is adopted as the buckling line,

Can be expressed as

Here, σ _y is the yield stress of the material, Λ is the critical slenderness ratio, and is expressed by the following equation.

Therefore, in this case, defines a sigma _c obtained by the equation of [Equation 2], for a sigma _cy obtained by the equation [Expression 5], so that the sigma _c ≧ sigma _cy, the specifications Design.

In the above-described embodiment, the case where a general-purpose H-section steel is used as the brace member 2 has been described. However, the present invention is not limited to this, and members having various other cross-sectional shapes can be used.
Moreover, as the steel type of the brace member 2, it is possible to use a structural material that satisfies various elasticity theories such as carbon steel, stainless steel, and aluminum alloy.

It is a schematic diagram showing the item of a diagonal lattice brace in embodiment of this invention. It is a schematic diagram which shows structures, such as an abdominal material or a brace of a truss to which the buckling analytical formula used as the premise of this invention is applied. It is a front view which shows the diagonal grid | lattice brace to which embodiment of this invention is applied.

Explanation of symbols

1 Peripheral frame steel frame 2 Brace member

Claims (3)

A rectangular peripheral frame steel frame incorporated along the columns and beams constituting the column beam frame, and a plurality of brace members made of the same material and having the same cross-sectional area disposed in the peripheral frame steel frame And the plurality of brace members are arranged in a lattice shape with the central axis positioned in the same plane and inclined with respect to the horizontal, the crossing portions are rigidly joined, and both ends are A structure design method of a slanted inclined brace rigidly joined to a peripheral frame steel frame,
The following specifications of the brace member subjected to compressive force E: Young's modulus of the material constituting the brace member λ: a slender ratio with the lattice spacing of the brace member as a buckling length, and λ = L / i
L: lattice spacing of the braces i: secondary radius of cross section of the brace member in the out-of-plane direction, i = (I / A) ^1/2
I: Cross-sectional secondary moment in the out-of-plane direction of the brace member A: Cross-sectional area of the brace member m: Maximum number of divisions of one brace member by the intersecting brace members γ: Buckling of the entire length of the brace member Length coefficient, 0.5 ≦ γ ≦ 1
κ: Additional coefficient of buckling stiffening rigidity of the brace member, 1 ≦ κ ≦ 2
n: The ratio of the absolute values of the tensile force acting on one of the brace members and the compressive force acting on the other brace member, and the compression stress σ acting on the brace member is

A structural design method for a slanted lattice brace, characterized in that the design is made so that it is less than or equal to σ _c defined in 1.   The structural design method for an oblique lattice brace according to claim 1, wherein the brace member is disposed with its weak axis direction facing out of the surface of the column beam frame.   A rectangular peripheral frame steel frame incorporated along the columns and beams constituting the column beam frame, and a plurality of brace members made of the same material and having the same cross-sectional area disposed in the peripheral frame steel frame The plurality of brace members are arranged in a lattice shape with the central axis positioned in the same plane and inclined with respect to the horizontal, the crossing portions are rigidly joined, and both end portions are the periphery An oblique lattice brace characterized in that the brace member that is rigidly joined to a framed steel frame and receives a compressive force is designed by the structure design method for an oblique lattice brace according to claim 1 or 2.

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