JP5006227B2 - Method for evaluating fire resistance of composite members - Google Patents

Description

  The present invention relates to a method for evaluating fire resistance in a composite member in which a steel member and a concrete member are joined to each other by a headed stud.

As a kind of the composite member, there is known a composite beam in which an H-shaped steel and a concrete slab are fastened by a headed stud and integrated with each other.
In such a composite beam, the H-section steel and the concrete slab can be integrated and can resist the bending force, and therefore, an advantage that a higher bending strength can be obtained as compared with the beam of the H-section steel alone. There is.

By the way, the shear strength qs per headed stud in the above-mentioned composite beam at normal temperature is evaluated by the following formula in the “Various composite structure design guidelines” of the Architectural Institute of Japan.
(1) In case of equal thickness slab qs ₁ = 0.5 × _sc a × (Fc × Ec) ^1/2
However, (Fc × Ec) ^1/2 ≦ 9000 kg / cm ²
Here, Fc is the compressive strength of the concrete, Ec is the Young's modulus of the concrete, and _sc a is the shaft cross-sectional area of the headed stud.

(2) In the case of deck synthesis slab qs = {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} × {0.5 × _sc a × (Fc × Ec) ^{1 / 2} }
However, (Fc × Ec) ^1/2 ≦ 9000 kg / cm ² , {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} ≦ 1
Here, nd is the number of studs with heads in one groove, bd is the average width of the grooves in the deck plate, Hd is the whole deck plate, and L is the length dimension of the headed studs.

However, the shear strength per headed stud in the composite beam at high temperatures such as in a fire is unclear and there is no specific evaluation standard.
For this reason, when the composite beam is used in a building that requires fire resistance, a method is employed in which the bending strength of the composite beam at a high temperature is evaluated only by the cross section of the steel member. The present condition is that the synthetic | combination effect of a member and concrete slab is not considered. The same applies to other composite members such as sandwich steel plates other than the composite beam.

Therefore, the present inventors previously proposed a method for designing a composite beam as found in Patent Document 1 below.
The method of designing a composite beam is, Fc' the compressive strength of the concrete at the time of a fire, Ec' the Young's modulus of the concrete at the time of a fire, the axial cross-sectional area of _B a head studs, shear headed stud in case of fire intensity _B Shigumay', temperature _B T of headed stud welding unit, the temperature at which the shear strength of the headed stud starts to decrease as _S T _1, shear strength per one above the headed studs in a fire _B q '
5000 kgf / cm ² <(Fc ′ · Ec ′) ^1/2 <9000 kgf / cm ²
Condition is satisfied that, and when the _B T ≦ _S T ₁ is
_B q ′ = 0.5 · _B a · (Fc ′ · Ec ′) ^1/2 (4) On the other hand, when _B T> _S T ₁ ,
_B q ′ = min (0.5 · _B a · (Fc ′ · Ec ′) ^1/2 , _B σy ′ · _B a)
It is characterized by deriving by.

Here, the equation (4) is a mode in which the integrity of the concrete slab and the steel beam is destroyed by the destruction of the concrete,
_B q ′ = _B σy ′ · _B a (5) is a mode in which the integrity of the concrete slab and the steel beam is destroyed by the breakage of the headed stud.

Therefore, according to the above conventional composite beam design method, after verifying the integrity of the concrete slab and steel beam in the event of a fire, the ultimate bending strength of the composite beam at high temperatures was derived. It is possible to improve the reliability of ultimate bending strength.
Japanese Patent No. 3775395

  However, since the conventional composite beam design method is for a composite beam in which a steel beam and an equal-thickness concrete slab are joined to each other by a headed stud, There was a drawback that it was difficult to evaluate fire resistance with sufficient accuracy.

Further, as will be described later, the present inventors conducted a fire resistance test on the shear strength _B q ′ per one headed stud at the time of fire obtained by the equations (4) and (5) of the design method. As a result, it was found that the design method underestimated the experimental value. As a result, when the specifications of the composite beam are determined based on the above design method, there is a tendency to over-design, and therefore development of an evaluation method with higher accuracy has been demanded.

  The present invention has been made in view of such circumstances, and with regard to various forms of composite members, the fire resistance of the composite members that enables highly accurate evaluation of the shear strength per headed stud at high temperatures. It is an object to provide an evaluation method.

In order to solve the above-mentioned problems, the invention according to claim 1 is directed to a single headed stud at a high temperature of a composite member in which a steel member and an equal thickness concrete member are joined to each other by a headed stud. A method for evaluating the fire resistance of a composite member for evaluating shear strength, wherein the temperature of the steel member is higher than a preset temperature or the root temperature of the headed stud at the time of fire obtained by analysis. The compressive strength Fc ′ of the concrete member and the tensile strength σu ′ of the headed stud at the evaluation temperature are derived, and the shaft member sectional area _sc a of the headed stud and the concrete member at normal temperature are configured. Based on the Young's modulus Ec of the concrete, the shear strength qs per one headed stud is
qs = min (qs ₁ , qs ₂ ) (1)
qs ₁ = 0.5 × _sc a × (Fc ′ × Ec) ^1/2 (2)
qs ₂ = _sc a × σu ′ (3)
It is characterized by evaluating by the calculation formula by

On the other hand, in the invention according to claim 2, the steel member and the concrete member placed on the deck plate are provided in the groove of the deck plate in advance and integrated with the steel member. A method for evaluating the fire resistance of a composite member for evaluating the shear strength per one headed stud at a high temperature of the composite members joined to each other. The temperature at the base of the stud with head or the temperature of the steel member higher than this is used as the evaluation temperature, and the compressive strength Fc ′ of the concrete member and the tensile strength σu ′ of the headed stud at the evaluation temperature are derived, per stud shank cross section _sc a of Young's modulus of the concrete constituting the concrete element at the normal temperature Ec, deck plate All Seiko Hd, based on the average width bd, 1 pieces of length L of the number nd and the headed studs of the headed studs in the grooves of the grooves of the deck plate,
Assuming {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} ≦ 1,
Shear strength qs per one headed stud
qs = min (qs ₁ , qs ₂ ) (1)
qs ₁ = {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} × {0.5 × _sc a × (Fc ′ × Ec) ^1/2 } (2) ´
qs ₂ = _sc a × σu ′ (3)
It is characterized by evaluating by the calculation formula by

Further, in the invention described in claim 3, in the invention described in claim 2, in place of qs ₂ obtained by the equation (3),
qs ₂ = {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} × _sc a × σu ′
Qs ₂ obtained by the above is used.

  Furthermore, in the invention according to claim 4, in the invention according to any one of claims 1 to 3, in place of the tensile strength (tensile strength) σu ′ of the headed stud in the formula (3) above, The yield strength σy ′ of the headed stud at the evaluation temperature is used.

  In invention of any one of Claims 1-4, (2) type | formula or (2) 'type | formula is a mode in which the integrity of concrete slab and a steel beam is destroyed by destruction of concrete, (3) The equation is a mode in which the integrity of the concrete slab and the steel beam is broken by the breakage of the headed stud.

And the preset temperature such as the fireproof temperature required for the building, the temperature of the root of the headed stud at the time of a fire obtained by analysis based on the structure of the building or the steel frame higher than the temperature Using the temperature of the member as the evaluation temperature, the qs _{1 of the} above formula (2) or (2) ′ and the qs _{2 of the} formula (3) are calculated from the specifications such as the compressive strength Fc ′ of the concrete member at this evaluation temperature. Furthermore, since the shear strength qs per one headed stud at a high temperature of the composite member is evaluated by selecting one of the smaller values according to the formula (1), the concrete slab and the steel beam in the event of a fire The ultimate bending strength of composite beams at high temperatures can be derived after verifying their integrity with

At this time, in the present invention, in the above formula (2) or (2) ′, in place of the Young's modulus Ec ′ of the concrete at the time of fire in the formula (4), which is the conventional evaluation formula described above, at room temperature The Young's modulus Ec of the concrete constituting the concrete member is applied. Further, in the above formula (3), the tensile strength σu ′ of the headed stud at the above evaluation temperature is applied instead of the shear strength _B σy ′ of the headed stud of the above formula (5) which is a conventional evaluation formula. ing.
As a result, the ultimate bending strength at high temperature of the composite beam can be evaluated with higher accuracy than the conventional evaluation method.

  That is, the inventors conducted an experiment to evaluate the shear strength per headed stud at high temperatures for a composite beam of equal thickness slab, as will be described in detail in the following examples. The results shown were obtained. In the figure, the ◯ plots indicate the specimens that collapsed due to the destruction of the concrete, and the ● plots in the figure indicate the specimens that collapsed due to the fracture of the headed stud.

On the other hand, as can be seen in FIG. 9, according to the proof stress calculation values according to the conventional evaluation formulas (4) and (5), both are less than the values obtained from the experimental results. It became clear that it would be evaluated. Accordingly, the present inventors have made various studies on the suitability of the variables in the above equations (4) and (5). Instead of the Young's modulus Ec ′ of the concrete in case of fire in the above equation (4), Instead of the above formula (2) or (2) ′ formula applying the Young's modulus Ec of the concrete constituting the concrete member and the formula (5) headed stud shear strength _B σy ′ According to the above equation (3) to which the stud tensile strength (tensile strength) σu ′ is applied, it has been found that the experimental result and approximate evaluation can be performed.

  As described above, according to the present invention, it is possible to further improve the reliability of the ultimate bending strength at high temperatures, and as a result, it becomes possible to optimally design the specifications of the composite beam. Without underestimating the ultimate bending strength at high temperatures, the structural stability of the composite member during a fire can be ensured, and the weight of the composite member can be further reduced by optimizing the amount of steel.

  Here, when determining the temperature at the high temperature (evaluation temperature) to be evaluated, when heated from the steel member side, a temperature gradient is generated in which the temperature gradually decreases from the steel member side toward the concrete side. For this reason, the root of the headed stud has the highest root. On the other hand, since the strength of concrete and steel frame members decreases as the temperature rises, breakage of the headed stud that receives shearing force and destruction of concrete that receives support pressure concentrate on the root of the headed stud. become.

  Therefore, when obtaining by analysis, it is appropriate to employ the temperature of the root of the headed stud as the evaluation temperature, and when it is desired to evaluate the safety side, it is higher than the temperature of the root of the headed stud. It is preferable to employ the temperature of the steel member.

Further, as in the invention described in claim 3, instead of qs ₂ obtained by the above equation (3) described in claim 2,
qs ₂ = {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} × _sc a × σu ′
Qs ₂ obtained by the above, or as in the invention according to claim 4, in place of the tensile strength σu ′ of the headed stud in the above formula (3) according to any one of claims 1 to 3. If the yield strength σy ′ of the headed stud is used, the evaluation on the safer side can be further performed.

Hereinafter, an embodiment in which the method for evaluating fire performance of a composite member according to the present invention is applied to a composite beam of equal thickness slab and a composite beam of deck composite slab will be described.
First, in this evaluation method, in the first step, specifications of each member (concrete slab (concrete member), steel beam (steel member), headed stud, deck plate) constituting the composite beam are set. Specifically, the amount, thickness, design standard strength of the concrete slab, the type and cross-sectional dimensions of the steel used for the steel beam, and the stud diameter, length, quantity, etc. of the headed stud are set.

  Next, in the second step, the temperature of each member at the time of a fire is obtained by analysis. Here, first, various settings related to the fire room (for example, settings of the fire room use, opening situation, combustible amount, compartment shape, etc.) are made, and a preset fire model (for example, Notification No. 1433, Kawagoe model) After analyzing fire properties such as fire duration and fire temperature using a two-layer zone model, a one-layer zone model, etc., the member temperature (for example, steel The temperature of the beam, the concrete temperature around the headed stud, the temperature of the stud welded portion, etc.) are obtained, and the temperature of the base of the headed stud or the temperature of the flange of the steel beam higher than this is set as the evaluation temperature.

  Next, in the third step, the Young's modulus Ec of the concrete constituting the concrete slab at normal temperature is obtained, and the compressive strength Fc ′ and the head of the concrete slab at the evaluation temperature are obtained using the analysis result of the second step. The tensile strength σu ′ of the stud with stud is derived.

  In addition, these values are based on the specifications such as the material and diameter of the headed stud to be used and the specifications such as the kind and strength of the concrete, and the relationship between temperature and strength as shown in FIGS. 4 and 5 in advance. By obtaining this, it can be easily obtained. For the compressive strength Fc 'of concrete at the above-mentioned evaluation temperature, for example, use the numerical value of the report (CEB Bulletin D'Information No.208 (RILEM-Committee 44 PHT)) of RIREM (International Union of Materials Structure Research). You can also.

  Next, in the fourth step, based on the values obtained in the first step and the third step, the shear per headed stud at the evaluation temperature of the composite beam of the equal thickness slab or the composite beam of the deck composite slab The proof stress qs is evaluated.

First, in the case of composite beams of equal thickness slabs,
qs ₁ = 0.5 × _sc a × (Fc ′ × Ec) ^1/2 (2) Equation qs ₂ = _sc a × σu ′ (3) Calculate qs ₁ and qs ₂ ,
qs = min (qs ₁ , qs ₂ ) According to the equation (1), any smaller value is evaluated as the shear strength qs per headed stud at the evaluation temperature.

On the other hand, when the composite beam is a deck composite slab,
qs ₁ = {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} × {0.5 × _sc a × (Fc ′ × Ec) ^1/2 } (2) 'Expression qs ₂ = _sc a × σu' (3) Calculate qs ₁ and qs ₂ , and then
qs = min (qs ₁ , qs ₂ ) According to the equation (1), any smaller value is evaluated as the shear strength qs per headed stud at the evaluation temperature.

In the case of the composite beam of the deck composite slab, instead of the above equation (3),
qs ₂ = {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} × _sc a × σu ′
If qs ₂ obtained by the equation (6) is used, {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} ≦ 1. A safer evaluation can be made rationally.

Hereinafter, a fire resistance experiment and a result of the composite beam of the equal thickness slab and the composite beam of the deck composite slab, which are the basis of the present invention, will be described.
Four specimens of H-shaped steel (steel member) 1 and concrete slab 2 having dimensions as shown in FIG.
Further, as a composite beam of the deck composite slab, a deck plate 4 is disposed on the H-section steel 1 having the dimensions as shown in FIG. 2 and is joined to the H-section steel 1 through the deck plate 4. Four pieces of concrete slabs 2 placed on the deck plate 4 were prepared by using the headed studs 3.

In each composite beam, a headed stud (19φ, length L = 110 mm) of JIS B 1198 was used as the headed stud 3. In the composite beam of the deck composite slab, the headed stud 3 was welded to the H-section steel 1 through the deck plate 4.
Here, FIG. 4 shows the high-temperature tensile test result of the above-mentioned headed stud 3 used, and FIG. 5 shows the high-temperature compression test result of the concrete constituting the concrete slab.

  Next, as shown in FIG. 3, the test body is set on a self-balancing type pressure frame 5, and a test piece of the test body is passed through a PC steel rod 7 by a hydraulic jack 6 provided on the upper portion of the pressure frame 5. A shear force was applied to the headed stud 3 in the test body by pushing up the pressure beam 8 disposed below. At this time, rollers (round bars) 9 are interposed at a plurality of locations between the concrete slab 2 and the pressurizing frame 5 so that the concrete slab 2 and the H-shaped steel 1 are not separated during pressurization. It was set to stop.

FIG. 3 shows a state in which the composite beam specimen of the deck composite slab is set, but the same applies to the composite beam specimen of the equal thickness slab.
Each of the four specimens of the composite beams of equal thickness slabs and the composite beams of the deck composite slabs prepared was monotonically loaded at room temperature. As for the other test specimens, after a predetermined load was loaded, while maintaining the load constant, as shown in the figure, heating was performed from the lower surface side of the concrete slab 2, that is, from the H-section steel 1 side. The temperature at which the predetermined load could not be maintained as the temperature increased was taken as the collapse temperature.

FIG. 6 shows an example of the temperature distribution of each component when the specimen of the composite beam of equal thickness slab reaches the collapse temperature.
As apparent from FIG. 6, since the specimen is heated from the H-section steel 1 side, the member temperature has a temperature gradient that gradually decreases from the H-section steel 1 side to the concrete slab 2 in the cross section. About the stud 3 with a head, the root becomes the highest temperature. And as both H-section steel 1 and concrete slab 2 become high in temperature, the strength decreases. Therefore, breakage of headed stud 3 that receives shear force and destruction of concrete slab 2 that receives support pressure Concentrate on the root of the headed stud 3.
By the way, when investigating the concrete slab 2 after the experiment, it was confirmed that the deformation of the headed stud 3 was concentrated at the root of the test body having a higher collapse temperature.

  Next, FIG. 7 shows the relationship between the shearing force acting on one of the headed studs 3 in the composite beam test specimen of equal thickness slab and the root temperature of the headed stud 3 at the time of collapse. FIG. 8 shows the relationship between the shearing force acting on one headed stud 3 in the composite beam test specimen of the deck composite slab and the root temperature of the headed stud 3 at the time of collapse. In both figures, the black circles in the figure are specimens that have collapsed due to the breakage of the headed stud 3, and the solid circles in the figure indicate the specimens that have collapsed due to the destruction of concrete.

As can be seen in FIG. 7, the specimens of the composite beams of equal thickness slabs all collapsed due to the breakage of the headed stud 3. Moreover, the damage of the concrete slab 2 was so light that the test body with a high collapse temperature was high.
And from the comparison with the proof stress calculation values by the formulas (1) to (3) indicated by solid lines and dotted lines in FIG. 7, according to the evaluation method of the present invention, it is very close to the experimental values and slightly safer. It can be seen that it can be evaluated. In the proof stress calculations of the equations (1) to (3), the values shown in FIGS. 4 and 5 were used as the compressive strength Fc ′ of the concrete slab and the tensile strength σu ′ of the headed stud, respectively.

On the other hand, as can be seen in FIG. 8, two specimens of the composite beam test specimen of the deck composite slab collapsed due to the breakage of the headed stud 3, and the other two bodies collapsed due to the destruction of the concrete. And the solid line and dotted line which show the calculation result of (1) type | formula, (2) 'type | formula and (3) type | formula in FIG. 8 which performed yield strength calculation similarly to the case of the composite beam test body by said equal thickness slab. From the comparison, it can be seen that, according to the evaluation method of the present invention, the composite beam of the deck composite slab can also be extremely approximate to the experimental value and evaluated slightly on the safe side.
Furthermore, it can be seen from the same figure that if the proof stress calculation result according to the above equation (6) is used instead of the above equation (3), the evaluation on the safer side can be carried out more rationally, especially at high temperatures.

  In the above embodiment, the case where the composite member of the present invention is applied to the composite beam of the equal thickness slab and the composite beam of the deck composite slab has been described, but the present invention is not limited to this. The present invention can be similarly applied to various composite members in which a steel member and a concrete member are joined to each other by a headed stud, such as a sandwich steel plate used for a wall.

It is a figure which shows the shape and specification of the test body of the composite beam by the equal thickness slab used in the Example of this invention. It is a figure which shows the shape and specification of the test body of the composite beam by the deck composite slab used in the Example of this invention. It is a side view which shows the state which set the test body of FIG. 2 to the pressurization flame | frame. It is a graph which shows the high temperature tensile test result of the headed stud used for the Example. It is a graph which shows the high temperature compression test result of the concrete used for the Example. It is a figure which shows an example of the temperature distribution of each structural member when the test body of the composite beam of equal thickness slab reaches collapse temperature in an Example. It is a graph which shows the result of the fireproof test by the test body of the composite beam of equal thickness slab, and the proof stress calculation result. It is a graph which shows the result of the fireproof test by the test body of the composite beam of a deck composite slab, and the strength calculation result. It is a graph which shows the result of the fireproof test by the test body of the composite beam of equal thickness slab, and the proof stress calculation result which concerns on the past and this invention.

Explanation of symbols

1 H-section steel (steel member)
2 Concrete slab (concrete member)
3 Stud with head 4 Deck plate

Claims (4)

A method for evaluating the fire resistance of a composite member for evaluating the shear strength per one headed stud at a high temperature of a composite member in which a steel member and a concrete member of equal thickness are joined together by a headed stud,
The temperature at the base of the stud with head or the temperature of the steel member higher than this at the time of a fire obtained by a preset temperature or analysis is set as an evaluation temperature, and the compressive strength Fc ′ of the concrete member at the evaluation temperature and The tensile strength σu ′ of the headed stud is derived, and based on the shaft sectional area sca of the headed stud and the Young's modulus Ec of the concrete constituting the concrete member at normal temperature, Shear strength qs
qs = min (qs ₁ , qs ₂ ) (1)
qs ₁ = 0.5 × _sc a × (Fc ′ × Ec) ^1/2 (2)
qs ₂ = _sc a × σu ′ (3)
The fire resistance evaluation method for a composite member, characterized in that the evaluation is based on a calculation formula according to the above. The steel member and the concrete member placed on the deck plate are preliminarily provided in the groove of the deck plate and joined to each other by a headed stud integrated with the steel member at a high temperature. A method for evaluating the fire resistance of a composite member for evaluating the shear strength per headed stud,
The temperature at the base of the stud with head or the temperature of the steel member higher than this at the time of a fire obtained by a preset temperature or analysis is set as an evaluation temperature, and the compressive strength Fc ′ of the concrete member at the evaluation temperature and derive the tensile strength σu' of headed studs, the shaft cross-sectional area _sc a of the headed stud, the Young's modulus of the concrete constituting the concrete element at the normal temperature Ec, the total blame Hd deck plate, deck plate Based on the average width bd of the grooves, the number nd of the headed studs in one of the grooves, and the length dimension L of the headed studs,
Assuming {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} ≦ 1,
Shear strength qs per one headed stud
qs = min (qs ₁ , qs ₂ ) (1)
qs ₁ = {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} × {0.5 × _sc a × (Fc ′ × Ec) ^1/2 } (2) ´
qs ₂ = _sc a × σu ′ (3)
The fire resistance evaluation method for a composite member, characterized in that the evaluation is based on a calculation formula according to the above. Instead of qs ₂ obtained by the above equation (3),
qs ₂ = {(0.85 / nd ^1/2 × (bd / Hd) × (L / Hd−1)} × _sc a × σu ′
The method for evaluating fire performance of a composite member according to claim ₂ , wherein qs ₂ obtained by the method is used.   4. The yield strength σy ′ of the headed stud at the evaluation temperature is used instead of the tensile strength σu ′ of the headed stud in the formula (3). 5. A method for evaluating the fire resistance of a composite member.

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