JP5605202B2 - Composite girders and steel - Google Patents

Description

  The present invention relates to a composite girder obtained by synthesizing a steel girder and a concrete slab or a steel concrete composite slab using a slip stopper, and particularly relates to a synthetic girder excellent in bending load bearing performance.

  At present, in Japan, composite girders using the allowable stress design method for the elastic range up to the yield of steel are the mainstream. However, in order to realize further rationalization and cost reduction, a design method that considers the performance after yielding steel is being sought.

As a method for calculating the bending load capacity of a composite girder in consideration of the performance after yielding, there is a method using plastic theory (Non-patent Document 1). This method consists of the three cross sections shown in FIG.
a) Compact cross-section: a cross-section that can reach the all-plastic bending moment
b) Non-compact cross section: A cross section that can reach yield at the extreme edge of the compression zone but does not reach full plasticity due to the occurrence of local buckling.
c) Slender cross section: Of cross sections that do not yield in compression due to the occurrence of local buckling, a) For compact cross sections, the bending load capacity is calculated assuming that the total plastic bending moment is equal to the bending load capacity. (In Fig. 9 and Fig. B _eff is the effective width of the slab, f _'Cd compressive strength of the concrete, f _yd is the yield strength of the steel member, M _u synthesis digits bending load-bearing capacity, M _p is the full plastic bending moment, N _{c, f} the plastic axial force deck, N _pl ( +) Represents the plastic axial force (tensile side) of the steel member).

  On the other hand, in the steel material field, considering the performance after steel material yielding, after work hardening is started in Patent Document 1, the work hardening index is 0.2 or more and uniform with respect to the yield stress YP in the strain range up to 6%. An H-shaped steel excellent in earthquake resistance having a flange made of a steel material having a stress increase rate (YB / YP) which is a ratio of plastic deformation stress YB in strain to 1.33 or more is disclosed.

  By the way, in the method using plastic theory, even if a compact cross section is adopted, as shown in FIG. 10, there is a case where the floor slab is destroyed and the slab is collapsed and the total plastic bending moment is not reached.

In contrast, in Eurocode 4 (Non-Patent Document 2), as shown in FIG. 11, D _p is the distance from the floor slab upper surface to the plastic neutral axis, D _t is the total height of the composite girder section, and M _p is the total plastic bending. 0.15 ≦ D _p / where moment, _Mu is the bending load capacity, and b is the reduction factor of the bending load capacity In the range of D _t ≦ 0.40, the bending load bearing capacity M _u synthesis digits and be reduced to bM _p, since the bending load bearing capacity is reduced up to 15%, a great demerit. In Eurocode 4, D _p / In the case of D _t > 0.40, the bending load capacity is calculated by other methods such as elastic beam theory, which is a region in which plasticization of the steel material is not allowed.

  The H-section steel described in Patent Document 1 is intended to improve the buckling resistance and plastic deformation ability during an earthquake for a large strain range of up to 6% after work hardening starts. However, in the composite girder, the steel girder and the floor slab are deformed integrally, so that such a large strain does not occur.

  In the case of a composite girder, the floor slab is crushed before reaching a strain of about 3% at the maximum, and the concept of Patent Document 1 having a different target fracture mode and strain level cannot be applied.

  An object of this invention is to provide the composite girder excellent in the bending load bearing capacity manufactured based on the design method in consideration of the performance after yielding of steel materials.

The object of the present invention can be achieved by the following means.
1. A steel girder having a web and a flange, and a concrete slab or a steel-concrete composite floor slab are synthesized using slip stoppers, and the composite girder satisfies D _p / D _t ≦ 0.4. Stress increase rate (σ _1.0% / σ) which is the ratio of stress σ _1.0% at 1.0% strain to yield stress σ _y with a positive gradient of nominal stress / nominal strain at any strain from point to 3.0% strain A composite girder comprising a web and a flange made of a steel material having _y ) of 1.08 or more.
Where D _{t is} the total height of the composite girder section, D _{p is} the distance from the top surface of the composite girder section to the plastic neutral axis. A composite girder characterized in that the composite girder described in 1 is used in a region determined as a cross section (compact cross section) capable of reaching a total plastic bending moment in a bridge axis direction.
3. A steel material used for a steel girder having a web and a flange, which is included in the composite girder of 1 or 2,
Stress increase rate (σ _1.0%), which is the ratio of the stress σ1.0% at 1.0% strain to the yield stress σ _y with a positive nominal stress / nominal strain gradient at any strain from the yield point to 3.0% strain / Σ _y ) Steel material with 1.08 or more.

According to the present invention, the bending load reduction region of Eurocode 4 (0.15 <D _p / Even in the case of D _t ≦ 0.4), a composite girder that can reach the total plastic bending moment is obtained, which is extremely useful in industry.

An example of an analysis model (example of a non-linear FEM analysis model) for evaluating a bending load bearing property of a composite girder is shown (a) is a perspective view, and (b) is a cross-sectional view. The figure which shows the stress-strain relationship of a steel material model. M _u / M _p and D _p / Diagram showing the relationship of D _t. M _u / The relationship between the stress increase rate of M _p and the steel material (change in compressive strength of concrete when the slab width is 470 mm), (a) is the stress increase rate (σ _1.0% / σ _y ), (b) is the stress increase rate (σ _{2.0 %} / Σ _y ), (c) is a graph showing the case of stress increase rate (σ _3.0% / σ _y ). M _u / M _p and the stress increase rate of the steel material D in relations _{(σ 1.0% / σ y)} p / D _t = 0.4 (estimated value) Added figure. Application example of the composite girder flange, web, and horizontal girder. Application example to a compact cross section. The figure which shows the relationship between a composite girder bending moment and the classification of a cross section (prior art reference 1). The figure explaining the assumption of the stress distribution at the time of all plastic moments in a compact section, and calculation of bending load capacity (prior literature 1). The figure explaining the collapse of the floor slab by the action of a bending moment. Bending load reduction diagram (Eurocode 4).

The present invention defines the tensile properties of the steel used in the synthesis of digits of steel girder, with Eurocode 4 (Non-Patent Document 2), the bending load bearing capacity M _u synthetic digit a region which has been a reduction in bM _p M _u / M _p ≧ 1.0, and a composite girder having excellent bending load bearing performance is characterized. M _u / M _p is the bending load bearing capacity M _u If 1.0 or more is in the full plastic bending moment M _p in dimensionless values, it reached full plastic bending moment, if it is less than 1.0, in not reached the full plastic bending moment It means that there is.

In the following description, first, a steel material model on Bending load bearing capacity M _u synthetic digit by nonlinear FEM analysis, which revealed the strength and synthetic digit sectional specifications of the influence of the concrete. At that time, D _p / By changing D _t to the stress-strain relationship of steel, the stress-strain relationship of concrete, and the cross-sectional dimensions of the slab, 0.067 ≦ D _p / D _t ≦ 0.443, then M _u / M _p and D _p / Based on the diagram showing the relationship of D _t , M _u / _Determine the effect of steel properties (stress increase rate of steel) on M _p .
[Nonlinear FEM analysis]
Figure 1 shows an example of a composite digit analysis model for nonlinear FEM analysis. A half model that takes symmetry into account was used, and the floor slab and fulcrum plate were modeled as solid elements, and the other upper and lower flanges, webs, horizontal and vertical stiffeners were modeled as shell elements. For the fulcrum part, a model was adopted in which the fulcrum part plate was sandwiched from above and below. The loading point was assumed to be a load with uniform distribution. The floor slab and steel girders were connected by rigid elements, assuming complete adhesion.
[Steel model]
Fig. 2 shows the stress-strain relationship of the steel material model. Using the formula (1) proposed by the Japan Society of Civil Engineers Steel Structure New Technology Subcommittee (Non-patent Document 3), the parameters shown in Table 1 were substituted.

In Fig. 2, the SM570 model simulates the SM570 steel, and the steel A to steel C models match the basic specifications with the SM570 model, σ _y = 450 N / mm ² , YR (yield ratio) = 79%, yield The steel material A, steel material B, and steel material C were changed in descending order of the stress increase after yielding.

  The nominal stress / nominal strain gradient is positive for any strain from the yield point to 3.0% strain. Here, the reason why the range of strain with a positive nominal stress / nominal strain gradient is set to 3.0% from the yield point is that, as a result of performing multiple analyses, the maximum value of strain generated in steel girders is about 3%. Based on what happened.

  Thus, even when the same yield strength and the same YR are used so as to satisfy the specifications of SM570, it is possible to follow various paths after yielding. Steel A has a nominal stress / nominal strain gradient of almost zero in the strain region greater than 3.0%. Therefore, using equation (1), the nominal stress at any strain from the yield point to 3.0% strain is used. / Under the condition that the gradient of the nominal strain is positive, the stress increase after yielding is maximized.

[Concrete strength]
The bending capacity of composite girders is affected by the strength of concrete. Here, as parameters for compression strength fc of the concrete, fc30: fc = 30 N / mm 2, fc40: fc = 40 N / mm 2, fc50: fc = 50 N / mm 2, fc60: fc = 60 N / mm ^The stress-strain relationship shown in the Japan Society of Civil Engineers Concrete Standard Specification (Non-Patent Document 4) was applied.

[Cross section of composite girder]
The bending load capacity of the composite girder is affected by the cross-sectional dimensions of the composite girder, especially the ratio of the cross-sectional area of the floor slab and steel girder. Here, the steel girder cross section was constant, and the floor slab width b _c was changed to 350 mm, 470 mm, and 1340 mm. D _p / which is the ratio of the distance from the top of the slab to the plastic neutral axis to the total height of the composite girder section D _t is 0.067 ≦ D _p / Analysis was performed in the range of D _t ≦ 0.443.

[Analysis results (stress after yielding - Effect of the slope of the strain curves on Bending load bearing capacity M _u Synthesis digits)
Figure 3 shows the analysis results _Mu / M _p and D _p / Showing the relationship of D _t. The figure also shows the Eurocode 4 reduction diagram. In this analysis, the failure mode was all slab collapse.

From Fig. 3, it can be seen that the higher the stress increase after yield, the more M _u / M _p increases. In the case of steel A and steel B, the bending load reduction area of Eurocode 4 (0.15 <D _p / D _t ≤0.4) and M _u / M _p > 1.0, reaching the all-plastic bending moment.

For steel C, D _p / M _u / at D _t = 0.4 M _p ≈1.0, and the almost plastic bending moment has been reached in almost all of the bending load reduction region of Eurocode 4.

On the other hand, for the SM570 model, D _p / D _t > 0.17 and _Mu / It can be seen that M _p <1.0 and the total plastic bending moment is not reached.

From the above, even when the basic specifications are σ _y = 450 N / mm ² , YR (yield ratio) = 79% and the SM570 model is matched, the nominal stress / nominal strain at any strain from the yield point to 3.0% strain The greater the slope of, and the greater the slope of the stress-strain curve after yielding, the greater the bending load capacity of the composite girder.
[Analysis results (effects of stress increase after breakdown on the bending load bearing capacity M _u of synthetic digit)]
Next, a study was conducted to quantify the stress increase after yielding. Figure 4 shows M _u / It shows a relationship between the stress increase rate after the surrender and M _p. In FIG. 4, the vertical axis represents M _u / M _p (bending load bearing capacity M _u obtained in FEM analysis is divided by the full plastic bending moment M _p value dimensionless), the horizontal axis is calculated from the steel model, FIG. 4 (a) Yield stress increase rate is stress sigma _{of 1.0%} of the ratio in the strain of 1.0% with respect to the stress _{σ y (σ 1.0% / σ} y), 4 (b) is in stress sigma _{of 2.0%} of the ratio in the strain of 2.0% with respect to the yield stress sigma _y there stress increase rate _{(σ 2.0% / σ y)} , a diagram 4 (c) stress increase rate is stress sigma _3.0% of the ratio in the strain of 3.0% with respect to the yield stress sigma _y is _{(σ 3.0% / σ y)} . Table 2 shows the stress increase rate of each steel material model.

From FIG. 4, in the case of using the σ _2.0% / σ _y and σ _3.0% / σ _y in the horizontal axis, for each strength concrete fc30~fc60 M _u / When σ _1.0% / σ _y is used for the horizontal axis, while the relationship with M _p is nonlinear, M _u / The relationship with M _p is almost linear and M _u / The relationship between M _p and the stress increase rate becomes clear. From this result, σ _1.0% / σ _y is used as an index of the stress increase rate of each steel material model.
[Relationship between analysis results (M _u / M _p and steel stress increase rate (σ _1.0% / σ _y ) ]]
In Fig. 3, the curve of each steel material is D _p / Figure 5 shows the point where D _t = 0.4 is calculated by linear interpolation and added to the relationship between _Mu / M _p and the stress increase rate of steel (σ _1.0% / σ _y ) in Fig. 4. From FIG. 5, when σ _1.0% / σ _y is 1.08 or more, D _p / D _t ≦ 0.4 at M _u / M _p ≧ 1.0, Eurocode 4 bending load reduction area (0.15 <D _p / It can be seen that even when D _t ≦ 0.4), the total plastic bending moment can be reached.

From the above results, in the composite girder according to the present invention, the steel girder has a positive nominal stress / nominal strain gradient at any strain from the yield point to 3.0% strain, and 1.0% strain with respect to the yield stress σ _y . stress increase rate which is the ratio of stress sigma _1.0% in (σ _1.0% / σ _y) is provided with a web and flanges made of steel material is 1.08 or more, as a result, D _p / D _t ≦ 0.4 at M _u / Satisfies M _p ≧ 1.0 and excels in bending load bearing performance.

The stress increase rate of steel (σ _1.0% / σ _y ) can be calculated by material tests. At this time, the yield stress σ _y may be a value of 0.2% offset strain, for example, depending on the target structure. 6 and 7 show specific application examples of the composite girder according to the present invention.

Figure 6 shows the rate of increase in stress (σ as the ratio of the stress σ _1.0% at 1.0% strain to the yield stress σ _y with a positive nominal stress / nominal strain gradient at any strain from the yield point to 3.0% strain. An example of a composite girder in which a steel material having _1.0% / σ _y ) of 1.08 or more is applied to a flange and a web is shown. You may apply with respect to other members, such as a cross beam and a stiffener (not shown), as needed.

  FIG. 7 shows an example of the case where the composite girder according to the present invention is used in a region where the cross section is determined as a cross section (compact cross section) that can reach the total plastic bending moment in the bridge axis direction.

A positive bending region in which the bending moment is positive is determined as a cross section (compact cross section) that can reach the total plastic bending moment, and the composite girder according to the present invention is used in this region. This allows D _p / D _t is the Eurocode 4 bending load reduction area (0.15 <D _p / Even in the case of D _t ≦ 0.4), the total plastic bending moment can be reached.

JP 2002-88974 A

Japan Society of Civil Engineers, “Steel / Synthetic Structure Standard Specification, General Rules / Structure Planning / Design”, P244-250, 2007.3 European Committee for Standardization (CEN) (2003): Eurocode 4, Design of composite steel and concrete structures, 1994-2 Japan Society of Civil Engineers Steel Structure New Technology Subcommittee Final Report (Research on Seismic Design), pp.61-62, May 1996 Japan Society of Civil Engineers Standard Specification for Concrete [Structural Performance Review], 2002.

Claims (3)

A steel girder with a web and flanges were synthesized using the stop shift a concrete slab or the steel-concrete composite deck, a synthetic digit satisfies D _p / D _t ≦ 0.4, said steel girder is yield Stress increase rate (σ _1.0% / σ) which is the ratio of stress σ _1.0% at 1.0% strain to yield stress σ _y with a positive gradient of nominal stress / nominal strain at any strain from point to 3.0% strain A composite girder comprising a web and a flange made of a steel material having _y ) of 1.08 or more.
Where D _{t is} the total height of the composite girder section, D _{p is} the distance from the top surface of the composite girder section to the plastic neutral axis.   A composite girder using the composite girder according to claim 1 in a region determined as a cross section (compact cross section) capable of reaching a total plastic bending moment in a bridge axis direction. A steel material used for a steel girder comprising a web and a flange, which is included in the composite girder according to claim 1 or 2,
  Nominal stress / nominal strain gradient is positive and yield stress σ at any strain from the yield point to 3.0% strain _y The rate of increase in stress (σ _1.0% / Σ _y ) Is a steel material of 1.08 or more.