JPS6347451A - Method for preventing transverse bending of steel beam having h-shaped cross-section - Google Patents

Abstract

(57) [Abstract] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] This paper relates to improvements in methods for preventing lateral buckling.

[Prior Art] A typical example of a conventional method for preventing lateral buckling of the steel H-shaped cross-section beam (1) shown in FIG. 10 is as shown in FIG. 11(a) ib). In other words, either: ■ As shown in Figure 11(a), the cross section of the beam (2) is increased to increase its resistance to bending and torsion, or ■ As shown in Figure 11(b), the displacement of the beam (lateral movement) is increased. , rotation), stiffeners (3
) on the beam (1).

(Problems to be Solved by the Invention) Among the lateral buckling prevention methods described above, the method of enlarging the cross section is not preferred because it causes a significant increase in the weight of the steel material and reduces cost.

Furthermore, the method of attaching the stiffener (3) has drawbacks such as the fact that it takes time and effort to process the stiffener (3) and attach it to the stiffener (1).

Furthermore, many buildings require fire-resistant coatings, but not only do ordinary fire-resistant coatings make little contribution to preventing lateral buckling, but it is also impossible to apply fire-resistant coatings in addition to applying the above-mentioned lateral buckling prevention method. , which increases the covered area, resulting in a significant increase in cost.

The present invention aims to eliminate the drawbacks of conventional lateral buckling prevention methods and provide a low-cost and effective lateral buckling prevention method.

(Means for solving the problem) In order to achieve the above object, in the method for preventing lateral buckling of a steel H-shaped cross-section beam according to the present invention, the beam is surrounded by a concrete fireproof material with small diameter reinforcing bars. A method of coating was adopted. Note that the part covered with the fireproof material may be only the flange part of the beam or may cover the entire cross section.

[Effect]

Generally, lateral buckling of a beam is coupled buckling of bending and torsion, so its resistance is determined by bending performance, torsion performance, and buckling length.

As described above, the present invention covers the beam around the beam with a concrete fireproofing material reinforced with lightweight reinforcing bars, which increases resistance to bending and twisting, improves the fireproof performance of the beam, and prevents lateral buckling. This is a strategy.

(Embodiment of the invention) Figures 1 and 2 show examples of the present invention. Figure 1 shows a beam (F type) whose flange part is coated, and Figure 2 shows a beam where both the flange part and the web part are coated. ja) of each beam (A type) is a front view, (b) is a sectional view, and FIG. In the figure, (1) is an H-shaped cross-section beam, (4) is a reinforcing bar, (
5) is the refractory material, H is the height of the beam, B is the width of the beam, tc,
tf is the coating thickness.

As shown in the figure, the flange part or both the flange part and the web part of the Junsei H-shaped cross-section beam are covered with concrete fireproofing material with reinforcing bars. The reinforcing bars used for reinforcement can be lightweight and small-diameter reinforcing bars, and the reinforcing method is to wrap the flange.
Care should be taken to ensure that even if the coating material cracks, it will not peel off from the flange. Note that reinforcement in the axial direction of the beam is not required. The coating thicknesses tc and tf are the minimum thickness normally specified for fire resistance, that is, 4 cm (3 cm) for 1 hour fire resistance.
2-hour fire resistance of 5 cm (4 am) or more. Note that the numbers in parentheses above are when lightweight aggregate is used.

The F type, A type, and S type beams were tested using the test equipment shown in FIG. 4.

In Figure 4, (a) is a front view, (b) is a cross-sectional view of the loading point, (C) is a cross-sectional view of the fulcrum, OQ is the test floor, (2) is the load point, (b) is the test beam, and P is the load. A load P is applied via a load beam (2) to a load point 03 of the test beam α, which is supported at both ends by fulcrums (11). That is, an equal moment of bending moment is generated in the central section, and this is the test section for lateral buckling. The moment in the test section of the test beam at this time is M, the calculated moment at yield of the H1 section beam without coating is 5111p, the inclination angle of the coating beam at the load point 0 steep is θ, the steel H without coating The inclination angle of the mold cross-section beam at yield is θ6.

Test results using the above test device are shown in FIGS. 5 to 9.

Figures 5, 6, and 7 are F type, A type, and S type.
It is a diagram showing the relationship between the moment and the inclination angle of the type of test beam. In the figure, O has a slenderness ratio of 45, △ has a slenderness ratio of 90, and the mouth has a slenderness ratio of 1.
This is the case of 35.

It can be seen that the F-type and A-type beams have greater resistance to lateral buckling than the S-type beams.

Figure 8 shows the moment during lateral buckling of the test beam (here S
Figure 9 is a diagram showing the relationship between the inclination angle at the time of lateral buckling (shown here as the ratio divided by the inclination angle Sθ at the time of yielding of the uncoated beam). This is a line section that shows the relationship between the slenderness ratio and the slenderness ratio. In the figure, Mar is the moment of lateral buckling of the test beam, λ/Sry is the slenderness ratio, O is the S type, Δ is the F type, and the mouth is the A type test beam.

FIG. 8 shows the magnitude of the lateral buckling strength of the covered beam according to the present invention, and FIG. 9 shows a significant increase in the deformation capacity, that is, the energy absorption capacity, of the covered beam during an earthquake.

(Effects of the Invention) In the present invention, a steel H-shaped cross-section beam is coated with a concrete fireproof coating with reinforcing bars, so that the following excellent effects can be achieved.

■ The lateral buckling resistance of the beam increases significantly.

■ It has a large ability to absorb energy during earthquakes, and can be used to form gauze members with excellent earthquake resistance.

■ The larger the slenderness ratio, the higher the lateral buckling strength, making economical design possible.

■ The reinforcement is arranged only in the direction perpendicular to the axis of the beam, and the reinforcing bars used can be lightweight and small in diameter, so the cost increase with this method is small.

■ To summarize the above, the lateral buckling resistance of beams with the same span increases significantly, and when the external force is the same, the spacing between the beams can be increased, so the use of the present invention is economical. This makes it possible to form fire-resistant members with excellent earthquake resistance.

[Brief explanation of drawings]

Figures 1 and 2 show a covered beam that is an embodiment of the present invention. Figure 1 is a front view of the beam with a flange covered, (a) is a front view, (b) is a sectional view, and Figure 2 is a cross-sectional view. (a) is a front view, (b) is a cross-sectional view of the beam with the flange portion and web portion covered, (a) is a front view, (b) is a cross-sectional view of the beam without coating, and In the figures, (a) is a front view of the testing machine, (b) is a cross-sectional view of the load point, (C) is a cross-sectional view of the fulcrum, and Figures 5 to 7 are F type, A type, and S type beams, respectively. Figure 8 is a line diagram showing the relationship between the moment and the beam inclination angle, Figure 8 is a line diagram showing the relationship between the moment and slenderness ratio, and Figure 9 is a line diagram showing the relationship between the product of the inclination angle and moment and the slenderness ratio. Figure 10 is a cross-sectional view of a steel H-shaped cross-section beam, Figure 11 is a cross-sectional view showing measures to increase the horizontal bending strength of a conventional beam, and (a) is a cross-sectional view of a steel beam with an enlarged cross-section. , (b) are cross-sectional views of the arm fitted with stiffeners. In the figure, (1) is a steel H-shaped cross-section beam, (3) is a stiffener, and (4
) is the reinforcement arrangement, (5) is the concrete fireproof material, M is the moment applied to the beam, Mar is the moment at the same lateral bending,
5l) lp is the calculated moment at yield of the uncoated beam, θ is the inclination angle of the loaded beam, and Sep is the inclination angle at yield of the uncoated beam. Agent Patent Attorney Tadashi Sato Figure 11 (a) (b)

Claims (3)

[Claims] (1) A method for preventing lateral buckling of a steel H-shaped cross-section beam, which is characterized by covering the steel H-shaped cross-section beam with reinforced concrete fireproofing material. (2) The method for preventing lateral buckling of a steel H-shaped cross-section beam according to claim 1, wherein the portion covered with the fireproofing material is only the flange portion of the steel H-shaped cross-section beam. (3) The method for preventing lateral buckling of a steel H-shaped cross-section beam according to claim 1, wherein the portion covered with the refractory material is the entire cross section of the steel H-shaped cross-section beam.