JP2000017781A - Earthquake energy absorbing beam member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the rupture of a portion of a beam end due to the accumulation of fatigue by being intensively and repeatedly plastized during great earthquake and to increase energy absorbing efficiency. SOLUTION: The flange 11 of a beam member 1 in a sectional H-shape, integrated as a portion of a beam at the end of the beam, is accommodated to bending moment distribution arising in the beam during an earthquake, with the width increased from the center side of the beam of the end side. In this way, the flange 11 of the beam member 1 is yielded throughout the total length in a preset area at the same time during an earthquake.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seismic energy absorbing beam member which is used in a form incorporated into a beam end of a steel column / beam frame and has an elasto-plastic hysteresis characteristic having a large energy absorbing capacity at the time of an earthquake. It is about.

[0002]

2. Description of the Related Art The bending moment at the time of an earthquake in a beam of a steel-framed column / beam frame at the center of the beam becomes an inflection point as shown by a broken line in FIG. Fig. 6- (a)
As shown in Fig. 6, when the beam flanges have the same width over the entire length, the bending stress becomes maximum at the beam end.
As shown by hatches in (a) and (b), the yielding of the beam occurs at this end, and it is assumed that during a large earthquake, the same part of the beam end repeatedly breaks due to fatigue accumulation due to repeated plasticization. .

Conventionally, in order to prevent the beam end from being broken due to the accumulation of fatigue, it is conventionally required to increase the thickness of the beam flange or to increase the amount of steel material. It is a part having no length, so that plastic flow hardly occurs. After yielding (ε _y ), as shown in FIG. 8, the steel material has a stress (σ _y ) due to strain hardening accompanying an increase in plastic strain (ε). Has a characteristic of maintaining a constant rigidity even after yielding. Therefore, even if the amount of steel material is increased, the stress rise due to the extension of strain ( _s σ
_y ) may lead to breakage.

[0004] plasticization of the beam stresses increase due to increased strain to reach the bend after the action of moment M _P, breaking strain when the beam-portion as shown in FIG. 9 reaches the yield stress of σ _{y (s} σ bending moment _s M _P cause _y) occurs in a section above the bending moment M _P at the time of surrender.

In addition, as shown in FIG. 7, if the web of the beam member has a cross-sectional defect due to the formation of scar wrap, etc., the stress at the column-beam joint is increased due to the increase in stress accompanying strain hardening. Ascending raises a reduction in the proof stress of the web, so that it also occurs at a portion where the cross section is defective.

In view of the above background, the present invention proposes a beam member that plasticizes substantially simultaneously during an earthquake in a section near the beam end and efficiently absorbs energy.

[0007]

According to the present invention, a flange of an H-shaped beam member integrated as a part of a beam is provided at an end position of the beam so as to correspond to a bending moment distribution generated in the beam during an earthquake. By increasing the width from the center to the end of the beam, the flange of the beam member is simultaneously yielded over the entire length of the set area at the time of the earthquake, and the energy absorption efficiency at the time of the earthquake is increased.

The bending moment generated in the beam during an earthquake can be obtained by ignoring the normal bending moment due to the vertical load, as shown in FIG.
As shown by a broken line, the beam is distributed in a triangular shape in which the center of the beam is 0 and the ends are maximum. On the other hand, for a beam incorporating a beam member whose flange width increased from the center to the end of the beam,
Since the bending strength at a certain cross section is distributed in the axial direction as shown by the solid line, in the section where the beam member is incorporated within the entire length of the beam, any position in the axial direction yields due to the bending moment exceeding the bending strength at the time of the earthquake. Reaches the stress,
It will yield uniformly and become plastic.

When the beam has a uniform cross section over the entire length, the bending strength of the beam is constant in the axial direction from the beam center to the beam end as shown by the solid line in FIG. As described above, the plasticized region is concentrated at the end of the beam, and only one of the regions has accumulated fatigue due to repeated plasticization, but the beam member of the present invention has a uniform plasticity over the entire length of the set region. Therefore, the region of plasticization is expanded and the accumulation of fatigue does not occur.

[0010] Further, since the plasticized region has a certain length, a plastic flow occurs within the range of the length, so that there is no increase in stress due to strain hardening, and as shown in FIG. It shows the restoring force characteristic of a perfect elasto-plastic type, which is 0, and the possibility of breakage is reduced even if the strain is extended.

Since the amount of absorbed energy of a material to be plasticized during an earthquake is determined by the product of the plastic strain and the volume of the plasticized area, the plasticized region has a fixed length as in the beam member of the present invention. This increases the volume in the plasticizing range, so that a constant amount of absorbed energy can be obtained even if the plastic strain is small.

Further, the steel material has such a property that as the level of plastic strain is lower, the amount of accumulated plastic energy up to fracture increases with repeated plasticization. However, as in the present invention, the plasticized portion, which is an energy absorbing portion, is formed. As a result of being able to increase the volume, the level of plastic strain in the plasticized portion can be reduced, and the amount of accumulated energy until fracture can be greatly increased. From this, the column / beam frame incorporating the beam member of the present invention is a seismic frame with high deformation capability that is difficult to break.

The planar shape of the flange of the beam member is defined in claim 2.
Has a trapezoidal shape in which the bending strength of the flange is distributed so as to match the bending moment distribution during the earthquake over the entire length of the set region in the axial direction, and the bending moment in a certain cross section in the axial direction is When the bending strength is obtained, the bending moment in the other cross section becomes the bending strength in the cross section. Therefore, when the cross section with the flange of the beam member yields, the other cross section also yields at the same time.

More specifically, the relationship between the width of the flange center side end of the flange and the width of the flange beam end side end of the flange is determined as follows.

As shown in FIG. 3, a is the distance from the beam center to the end of the beam member on the beam center side, b is the distance from the beam end to the beam end side of the beam member, and the total plastic moment of the web is M1,
When the total plastic moment at the beam center end of the flange is M2, the total plastic moment M at the beam end of the flange is M2.
f (b) is a: b = (M1 + M2) :( M1 + Mf (b))
Thus, Mf (b) = b / a · (M1 + M2) −M1.

Assuming that the thickness of the flange is h and the width of the end of the flange at the center of the beam is B, the yield stress σa at the end of the flange at the center of the beam is σa = 6 · M2 / B · h ² , Assuming that the width of the end portion is B ′, the yield stress degree σb = 6 · Mf (b) / B ′ · h ² at the beam end portion of the flange, and σa
= Σb, B ′ = (Mf (b)
/ M2) · B = ｛b / a · (M1 / M2 + 1) − (M1
/ M2)｝ · B is derived.

Although it is proposed in JP-A-8-151686 to absorb the energy at the time of an earthquake by plasticizing the beam end, in this example, the base material of the column or beam is utilized by utilizing the characteristics of the material itself. In order to plasticize the haunch member while maintaining the elasticity of the haunch member, the haunch member is made of a material having a smaller yield strength than the base material, and the purpose is to obtain an energy absorbing effect by an external force at the primary design level. From that
It is conceivable that the distortion after the yield of the haunch member becomes large with respect to the external force at the secondary design level, and a sufficient energy absorbing effect cannot be expected.

On the other hand, in the present invention, the width of the flange is made to correspond to the bending moment distribution generated in the beam at the time of the earthquake, and in particular, the bending strength distribution of the flange is matched with the bending moment distribution at the time of the earthquake. By determining the shape, the bending strength of the beam body near the center of the beam where the beam member is integrated even when the bending moment at which the flange of the beam member reaches the bending strength has extra capacity for the bending moment Therefore, even if the same material is used for the beam body and the beam member, the beam body does not yield before the yielding of the beam member, and it is not necessary to use a material smaller than the yield strength of the beam body for the beam member. .

From the above, when the same material as the beam member is used for the beam body, or when a material having a higher yield strength than the beam member is used, the cross section of the beam body having extra capacity even after yielding of the beam member is reduced. It becomes possible to reduce.

Further, in the present invention, since the plasticized region extends over the entire length of the region set by the beam member, as described above, even if there is fatigue accumulation due to vibration during a large earthquake (external force at the secondary design level), the plasticized region is formed. Since no break occurs, a sufficient energy absorbing effect can be expected.

Further, in the above example, since the haunch member is of a vertical haunch type, the beam structure at the beam end becomes large, so that the lower end on the beam end side may protrude from the ceiling, which may affect the construction plan. However, since the flange of the beam member of the present invention has a horizontal haunch shape, it does not affect the architectural plan.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, the present invention relates to a beam member 1 integrated as a part of a beam at an end position of the beam in a steel column / beam frame. Corresponding to the cross-sectional shape of the beam body 2 located closer to the center
And an H-shaped cross section from the web 12.

In the drawing, a bracket 3 is provided on the column 4 side of the beam member 1.
And the beam member 1 is a part of the beam sandwiched between the beam body 2 and the bracket 3, but the beam member 1 may be directly joined to the column 4. The flange 11 and the web 12 are continuous with the flange and the web of the beam body 2.

The flange 11 of the beam member 1 has a trapezoidal shape whose width increases from the center to the end of the beam, corresponding to the bending moment distribution generated in the beam during an earthquake, as shown in FIG. As described above, the width B ′ of the end side end is determined from the width B of the beam center side end that is continuous with the flange of the beam main body 2.

When the width B 'of the end of the flange 11 on the beam end side, the width B of the end on the center side of the beam, and the effective span b of the beam are determined, the above equation is used to calculate the beam member 1 from the center of the beam. The distance a to the end on the center side of the beam is obtained.

For example, when the effective span of the beam is 6.0 m (b in FIG. 3 is 3.0 m), the width of the center of the flange 11 of the beam member 1 on the center side of the beam is 200 mm, and the width of the end of the beam end side is 200 mm. When a in FIG. 3 is set to 400 mm, M1 is 700 t · cm, M
When 2 is set to 2235 t · cm, the above equation B ′ = ｛b / a
From (M1 / M2 + 1)-(M1 / M2)｝ · B, a
= 1.7m.

The beam member 1 is formed by assembling a flange plate and a web plate processed into an equal trapezoidal shape into an H-shaped cross section by welding, or processing a flange of a roll-formed H-shaped steel into an equilateral trapezoidal shape by gas or NC cutting. The joining with the beam main body 2 or the joining between the beam main body 2 and the bracket 3 is performed by welding or with a splice plate and bolts.

In order to make the flange 11 less likely to break due to repeated plasticization, it is conceivable to use an extremely mild steel such as BT-LYP235 having a high elongation performance in the flange 11 portion. As described above, by suppressing the plastic strain of the flange 11 to a small value, the accumulated energy up to the fracture can be gained and the fracture can be delayed, so that the SN400 (SS40
Ordinary steel materials such as 0) and SN490 (SM490) are also used.

FIG. 5 shows an example of a frame using the beam 10 in which the beam member 1 of the present invention is integrated with the beam main body 2.

If a beam 10 in which the beam member 1 is incorporated in all of the beams constituting the frame is used, and the beam members 1 of all the beams 10 are yielded at the same time, the restoring force of the frame as a whole is lost after yielding. Since large deformation will occur, the yielding time of the beam member 1 of each beam 10 is changed to prevent the simultaneous yielding of all the beam members 1 or, as shown in FIG. The beam 10 in which the beam member 1 is incorporated in about half or less of the beams will be used.

[0031]

According to the present invention, in order to make the flange of the beam member integrated as a part of the beam at the end position of the beam correspond to the bending moment distribution generated in the beam at the time of the earthquake, the flange of the beam member at the time of the earthquake is formed. Yield can be performed simultaneously over the entire length of the set area. Yield occurs in an area having a certain length, resulting in an increase in energy absorption efficiency during an earthquake.

By uniformly plasticizing over the entire length of the region set by the beam member, the plasticized region is expanded and no accumulation of fatigue occurs, so that fracture due to accumulation of fatigue is prevented.

When the plasticized region has a certain length, a plastic flow occurs within the range of the length and the stress does not increase due to strain hardening. Become. Further, since the stress increase due to the strain hardening is eliminated, the design stress at the beam end can be reduced.

Since the plasticized region has a certain length, the volume in the plasticizing range increases, so that even if the plastic strain is small, the absorbed energy determined by the product of the plastic strain and the volume in the plasticizing range. You can make money.

Steel has the property that the lower the level of plastic strain, the greater the amount of cumulative plastic energy up to fracture with repeated plasticization. However, in order to obtain a certain amount of absorbed energy, the plasticity of the plasticized portion Since the level of strain can be reduced, the amount of accumulated energy until breakage increases. As a result, a column / beam frame incorporating the beam member of the present invention can form a seismic frame with high deformation capability that is difficult to break.

The width of the flange of the beam member is made to correspond to the bending moment distribution generated in the beam at the time of the earthquake, and in particular, the shape of the flange of the beam member is determined so that the bending strength distribution of the flange matches the bending moment distribution at the time of the earthquake. Therefore, even when the bending moment at which the flange of the beam member reaches the bending strength is applied, the bending strength of the beam body near the center of the beam where the beam member is integrated has a margin for the bending moment. In the case where the same material as the above or a material having a higher yield strength than the beam member is used, it is possible to reduce the cross section of the central portion of the beam main body which has extra capacity even after the beam member yields.

Even if the same material is used for the beam body and the beam member, the beam body does not yield before the beam member yields.
It is not necessary to use a material smaller than the yield strength of the beam body for the beam member.

Since the flange of the beam member of the present invention is of a horizontal haunch type, there is no influence on the construction plan.

[Brief description of the drawings]

FIG. 1 (a) is a plan view showing a beam incorporating a beam member,
(b) is an elevation view of (a).

FIG. 2 is a diagram showing a relationship between a bending moment distribution during an earthquake and a bending strength distribution of a beam.

FIG. 3 is a diagram showing a relationship between a total plastic moment of a web and a total plastic moment of a flange when a bending moment distribution and a bending strength distribution of a beam member match.

FIG. 4 is a load-deformation curve diagram showing a restoring force characteristic of a beam member.

FIG. 5 is an elevation view showing a frame using a beam incorporating a beam member.

Fig. 6 (a) is a plan view showing a conventional beam, (b) is an elevation view of (a), and (c) shows the relationship between the bending moment distribution during an earthquake and the bending strength distribution of the beam. FIG.

FIG. 7 is an elevation view showing a conventional column / beam joint.

FIG. 8 is a stress degree-strain degree curve diagram showing a state of stress increase accompanying strain hardening of a steel material.

FIG. 9 is a distribution diagram showing a state of a bending moment when a stress rises due to strain hardening.

[Explanation of symbols]

1 ... beam member, 11 ... flange, 12 ... web, 2 ...
Beam main body, 3 ... Bracket, 4 ... Column, 10 ... Beam.

Claims (3)

[Claims] 1. A beam member having an H-shaped cross section which is integrated as a part of a beam at an end position of the beam in a steel frame / column frame, wherein the width of the flange is a bending moment generated in the beam during an earthquake A seismic energy absorbing beam member that expands from the center to the end of the beam in response to the distribution and the flanges yield substantially simultaneously over the entire length of the axially set area during an earthquake. 2. The method according to claim 1, wherein the bending strength of the flange is distributed over the entire set length in the axial direction so as to match the bending moment distribution during the earthquake, and the flange has a trapezoidal planar shape. Seismic energy absorbing beam members. 3. The distance from the beam center to the end of the beam member on the beam center side is a, the distance from the beam member to the end on the beam end side is b, and the total plastic moment of the web of the beam member is M1. When the total plastic moment at the beam center end of the flange is M2, the width at the beam center end of the flange is B, and the width at the beam end side of the flange is B ′, B ′ = ｛b / A · (M1 / M2
The seismic energy absorbing beam member according to claim 2, which substantially satisfies the relationship of (+1)-(M1 / M2)｝ · B.