JP4355936B2 - Beam structure with steel flange and web - Google Patents

Description

  The present invention relates to a beam structure including a flange such as a large beam and a web in a steel column beam structure.

  Conventionally, in the structure of a steel beam-structured column beam structure, the structure of a large beam plate is generally designed so that the bending yield of the flange material precedes the shear yield of the web material in the case of the commonly used H-shaped cross section. (For example, see Non-Patent Documents 1 and 2). This is because, if shear yielding of the web material precedes, it has been difficult to maintain stable yield strength against repeated deformation of the column beam frame during an earthquake.

  More specifically, in the Building Standard Law Enforcement Ordinance, for buildings of a certain height or higher, the deformation capacity expected for each type of structure is calculated by calculating the retained strength as a design method to ensure the strength of the building so that it does not collapse in the event of a large earthquake. It is stipulated that the required retained horizontal proof stress corresponding to (energy absorption capacity) should be exceeded (Non-Patent Document 1 describes the calculation of retained horizontal proof stress and the ultimate proof strength of the steel member for that purpose.) . In addition, in the incremental analysis method, which is a liquidation method, in p309 to 311 “Appendix-1 Calculation method of retained horizontal strength” of Non-Patent Document 1, an evaluation method of retained horizontal strength due to the occurrence of hinges due to yielding of members is introduced. At that time, it is recommended to refer to various standards such as “Guidelines for Steel Structure Plastic Design” for calculation of ultimate strength of steel members. However, the ultimate strength of a member with buckling is calculated in consideration of the buckling phenomenon.

At that time, in order to simplify the calculation, in the case of a steel structure, it can be evaluated only by the bending strength at the end of the beam in the range where the influence of the shearing force is small (details are described in Non-Patent Document 2). It is inferred that the “simple calculation method” is usually implemented by designing a cross section with sufficient shear strength that does not precede shear yielding, and has become the current design method. It is inferred that such a situation has become customary for structural designers, so that it has become customary to design so as not to yield shear before bending yield at the beam end. According to Non-Patent Document 2, p60-67, “The value of the total plastic moment when the member cross section is plasticized by receiving bending moment and shearing force at the same time is the total plastic moment when only the bending moment acts. However, there is a description that if the condition is satisfied, the influence of the shear force on the total plastic moment can be ignored.
"Guidelines for Structural Calculations and Explanation", 1991 edition, Japan Architecture Center, July 1, 1991, p195-197, p309-311 "Steel Structural Plastic Design Guidelines", Architectural Institute of Japan, November 1, 1975, p60-67

  However, in the case of a short span beam, if it is attempted to design so that the shear yield of the web does not precede, it is necessary to extremely increase the web thickness, resulting in an uneconomic beam structure.

  Further, in the conventional beam structure “preceding the bending yield of the beam flange”, it is necessary to take measures such as reinforcing the welded portion between the column and the beam flange so as not to break. This measure is implemented by increasing the flange width or increasing the thickness of the flange. However, it takes a lot of time and effort to increase the cost.

  The present invention aims to solve the above-described problems, and in the beam structure of the H-shaped section in the steel column beam structure, it is not necessary to increase the web thickness with a particularly short span beam, Another object of the present invention is to provide a beam structure that eliminates the need for conventional flange reinforcement at the beam end, and that can reduce costs and improve design flexibility.

The invention of claim 1 of the present invention is a beam structure comprising a flange and a web in a steel column beam structure in which a flange and a web are combined so that the web yields a shear yield prior to the bending yield of the flange. The cross-sectional shape of the flange and web at the beam end and the length of the beam should be set so that the shear yield of the web at the beam end is smaller than the shear force at the bending yield of the flange at the beam end. It is a characteristic beam structure.

  That is, according to the present invention, in the beam structure having an H-shaped cross section, not only the flange at the beam end is plasticized but also the shape of the beam flange and the web (cross-sectional shape and length) so that the beam web is plasticized. The plasticization region is mainly placed on the web of the beam so that the column beam joint and the beam do not break due to fatigue accumulation due to vibration during a large earthquake, and the plastic absorption energy at the time of the earthquake is increased.

According to a second aspect of the present invention, in the beam structure according to the first aspect, tw (plate end flange thickness), tw (beam end flange thickness) satisfying the formula tw / tf · L / B <2√3 It is a beam structure characterized by having a plate thickness of an end web, B (width of a beam end flange), and L (length of a beam).

  According to the beam structure of the present invention, the web is shear yielded prior to the bending yielding of the flange during an earthquake, and the column beam joint and the beam are prevented from breaking due to fatigue accumulation due to vibration during the earthquake. Plastic absorption energy increases.

  In particular, in the case of a short span beam with a small beam length, the conventional beam structure requires an extremely large web thickness if shear shear yield is not preceded. In the invention, the web that has been reinforced economically can be made to a reasonable thickness, and the cost can be reduced.

  In the conventional beam structure, measures to prevent breakage have been taken by increasing the beam width in order to prevent breakage due to flange bending stress (tensile force of the tension side flange), but this requires extra manufacturing effort and cost. It was something that took. On the other hand, if the beam structure is preceded by the web shear yield according to the present invention, it is not necessary to reinforce the flange at the beam end. Furthermore, in particular, in the case of a short span beam, there was only a method of reducing the beam formation in order to prevent breakage of the beam end due to the tensile force of the flange. However, according to the present invention, such a measure is not necessary. In addition, the degree of freedom in design is increased, and the steel frame can be easily manufactured, leading to cost reduction.

  Since this invention consists of the above structures, the following effects are acquired.

  (1) In the beam structure of the H-shaped section in the steel column beam frame, the web is sheared and yielded prior to the flange bending yield at the time of earthquake, so the web thickness is reduced especially with a short span beam. There is no need to increase the size, and conventional flange reinforcement at the end of the beam is not required, thereby reducing costs and improving design flexibility.

  (2) The combination of the flange and web alone can prevent the beam-column joint and beam from breaking and increase the plastic absorption energy during an earthquake.

  Hereinafter, the present invention will be described based on the illustrated embodiments. FIG. 1 is an (a) elevation view, (b) a cross-sectional view of a beam end, and (c) a plan view showing an example of a steel column beam frame having a beam structure of the present invention. In FIG. 1, a steel beam 1 and a steel beam 2 form a beam frame. In an H-shaped steel beam (large beam) 2 whose end is joined to the steel column 1 by welding or the like, a flange 2F at the time of an earthquake The dimension of the steel beam 2 is set so that the web 2W yields shear before the bending yielding. The steel beam 2 is manufactured by combining a flange material and a web material, or integrally formed by roll rolling.

  Assuming that the web member does not contribute to the total plastic moment at the beam end, the condition for the web 2W to shear yield before the bending yield of the flange 2F is as follows.

That is, the total plastic moment at the yield of the beam flange is
Mp = Zp × σy (1)
Zp = Af.times.H = B.tf.times.H (2)
Therefore,
Mp = B · tf × H × σy (3)
Mp: Total plastic moment at which the beam bends and yields Zp: Section modulus at which the beam bends and yields Af: Cross-sectional area of the tension side flange at the beam end H: Beam formation at the beam end B: Width of the beam end flange tf: Beam End flange thickness σy: Allowable tensile yield stress of steel at beam end flange

At this time, the shearing force Qmp generated in the beam is
Qmp = 2Mp / L = 2B.tf.times.H.times..sigma.y / L (4)
B: Length of beam

The web shear strength Qs is
Qs = Aw × τy = tw × H × τy = tw × H × σy / √3 (5)
Aw: Cross-sectional area of beam end web τy: Allowable shear yield stress of steel of beam end web = σy / √3
tw: thickness of the beam end web

In order for the shear yield of the beam end web to precede, it is a condition that the shear yield of the beam end web is smaller than the shear force during bending yielding of the flange. In other words,
Qs <Qmp
tw × H × σy / √3 <2B · tf × H × σy / L
Therefore, tw / √3 <2B · tf / L (6)

Therefore, when the relationship between the shape of the end cross section of the steel beam and the length of the beam satisfies the following conditions, the web 2W shear yields prior to the bending yield of the flange 2F.
tw / tf · L / B <2√3 (7)
If the dimensions of the steel beam 2 are set so as to satisfy this equation (7), the plasticized region will be the web of the beam mainly, and the column beam joint and beam will break due to fatigue accumulation due to vibration during a large earthquake. There will be no increase in plastic absorption energy during an earthquake.

1 shows an example of a steel column beam frame having a beam structure according to the present invention, in which (a) is an elevation view, (b) is a sectional view of a beam end portion, and (c) is a plan view.

Explanation of symbols

1 …… Steel column 2 …… Steel beam 2F… Flange 2W… Web

Claims (2)

In a beam structure consisting of a flange and a web in a steel column beam structure in which the web is sheared and yielded prior to the bending yield of the flange, the shear at the bending end of the flange at the beam end A beam structure in which the cross-sectional shape of the flange and web at the beam end and the length of the beam are set so that the shear yield of the web at the beam end is smaller than the force . The beam structure according to claim 1 ,
tw / tf · L / B <2√3
tf: Plate end flange thickness
tw: thickness of the beam end web
B: Beam end flange width
L: A beam structure characterized by having tf, tw, B, and L that satisfy the equation of the length of the beam.

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