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Fire Resistance of Steel Hollow Structural Section Columns Filled with Bar-Reinforced Concrete

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~ .- . . . .

National Research Consell national

1+1

Council Canada de recherches Canada Institute for lnstitut de

Research in recherche en Construction construction

Internal Report No. 678

Date of issue: March 1995

CISTI/ICIST NRC/CNRC Internal report : Institute -- Bev Creighton

Received on: 03-23-95

Internal r e p o r t : Institute SNALYZED

for Research in Construction Canada

by T.T. Lie and V.K.R. Kodur

This is an internal report of the lnstitute for Research in Construction. Although not intended for general distribution, it may be cited as a reference in other publications.

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FIRE RESISTANCE OF STEEL HOLLOW STRUCTURAL SECTION COLUMNS FILLED WITH BAR-REINFORCED CONCRETE

T.T. Lie and V.K.R. Kodur

ABSTRACT

Parametric studies, using mathematical models, were carried out to determine the influence of various factors on the fire resistance of steel hollow structural section (HSS)

columns filled with bar-reinforced concrete. Data from the parametric studies were used to develop simple expressions for calculating the fire resistance of bar-reinforced concretc- filled HSS columns with circular and square cross sections. Thc validity of thc calculation procedure was established by comparing the calculated fire resistances ivith those obtained from fire tests on columns. The procedure, which is suitable for incomoration in design codes, provides a rational and easy-to-use design method for evaluating the fire resis&ce of hollow steel columns filled with bar-reinforced concrete for anv value of the sirmificant parameters that determine it, such as load, cross-sectional dimenGons, effective l&th and concrete strength.

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FIRE RESISTANCE OF STEEL HOLLOW STRUCTURAL SECTION COLUMNS FILLED WITH BAR-REINFORCED CONCRETE

by

T.T. Lie and V.K.R. Kodur

INTRODUCTION

Hollow structural steel columns are very efficient structurally in resisting compression loads and are widely used in the construction of framed structures in

buildings. By filling these columns with concrete, the load bearing capacity of the columns can be increased substantially. In addition, a high fire resistance can be obtained without the necessity of additional surface fire protection for the steel. The elimination of surface protection increases the usable space in a building. Klingsch and Wuerker [l] summarized the benefits of concrete-filled steel columns as follows: "Their consequent application can lead in an economic way to the realisation of architectural and structural design with visible steel without any restrictions on fire safety."

For a number of years, the National Fire Laboratory, National Research Council Canada W C ) , has been engaged in research studies, aimed at developing simplified methods that can be used by the construction industry, for evaluating the fire resistance of structural members. Both experimental and numerical studies on the fire resistance of stccl hollow structural section (HSS) columns filled with different typcs of concrete were carried out. A study on hollow steel sections filled with plain concrete has been

completed [2]. Simple expressions for determining the fire resistance of these columns were established and incorporated in the National Building Code of Canada.

The studies on hollow steel columns filled with plain concrete have shown that substantial reductions in the loads on the columns have to be made to obtain predictable fire resistances. This problem can be overcome by the addition of bar reinforcement. Chabot and Lie [3] have demonstrated, through laboratory tests on steel-bar-reinforced concrete-filled steel columns, that predictable fire resistances can be obtained, even when very high loads are applied.

In this report, the results of the studies on the fire resistance of hollow structural steel columns filled with bar-reinforced concrete are described. Data from these studies are used to develop simple expressions for the calculation of the fire resistance of

concentrically-loaded circular and square HSS columns filled with bar-reinforced concrete, that are suitable for incorporation in building codes.

FIRE RESISTANCE CALCULATION METHOD

To develop the expressions for the calculation of the fire resistance of the columns, mathematical models for the prediction of the fire resistance of rectangular and circular HSS columns, filled with bar-reinforced concrete, were used [4,5]. The models

incorporate realistic stress-strain relationships and thermal properties for structural steel, concrete and reinforcing steel at elevated temperatures, and account for the effect of moisture.

In the models, the fire resistance is calculated in various steps, which consist of the calculation of the temperatures of the fire, to which the column is exposed, the

temperatures in the column, its deformations and strength during the exposure to fire, and finally its fire resistance.

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The fire temperature is calculated using the ASTM E l 19-88 [6] or CANAJLC- SIOl [7] standard fire-temperature equation. A finite difference technique is used for computing the temperatures across the cross section of the column. The strength of the column, which decreased with duration of exposure, is computed as a function of the time of exposure to fire, using a stability analysis. -

The fire resistance of the column is derived by calculating the strength of the column as a function of the time of exposure to fire. The strength reduces gradually with time and eventually reaches apoint at which the strength becomes so low that it is no longer sufficient to support the load. At this point, the column becomes unstable and is assumed to have failed either by buckling or by compression. The time required to reach the point at which a column becomes unstable, leading to failure under a given load, is taken as the fire resistance.

The numerical procedure, contained in the mathematical model, was programmed for computer processing. By specifying the mechanical and thermal properties of

structural steel, concrete and reinforcing steel at elevated temperatures, the fire resistance of circular or rectangular HSS columns filled with bar-reinforced concrete can be

evaluated. The validity of the computer programs was established by comparing the results of the model to test data [4,5].

FACTORS INFLUENCING FIRE RESISTANCE

Using the computer programs, the influence of various factors on the fire resistance of HSS columns filled with bar-reinforced concrete was investigated through computer-simulated fire tests. These factors include cross-sectional dimensions, amount of reinforcing steel, concrete strength, concrete cover to the reinforcing steel and type of concrete aggregate.

Fig. 1 shows a typical HSS column, with circular cross section and bar-reinforced concrete filling, investigated in this study. The parameters that were investigated are given in Tables 1 and 2. HSS columns with circular, as weU as with square cross section, were considered in this study. The outside diameter of the steel sections for the circular HSS columns was varied from 168 to 406 rnm, while the outside dimension of the square HSS columns was varied from 178 to 305 mm. The wall thicknesses considered were the

minimum and the maximum thicknesses listed in the CISC Handbook of Steel

Construction [8]. The effective lengths of the columns were varied from 2.5 to 4.5 m. The influence of the amount of steel reinforcements was studied for three steel percentages, representing a small, medium and high percentage of reinforcement. The effect of concrete streneth was investigated bv calculating the fire resistance of the columns for three concyete strengths, &meli 20,35 and-50 MPa. To investigate the influence of the concrete cover, the fire resistances of the columns were calculated for two cover thicknesses, namely, for 20 and for 50 mm. For the purpose of obtaining

information on the influence of the type of aggregate on the fire resistance of the column, all calculations were performed for siliceous as well as for carbonate aggregate concrete.

In the calculations, the material properties described in the ASCE Structural Fire Protection Manual [9] were used. Detailed results of the parametric studies on circular and square HSS columns filled with bar-reinforced concrete were presented by Lie and Denham [10,11].

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In the following, the influence of the various parameters that determine the fire resistance of HSS columns will be further discussed for circular columns filled with bar- reinforced concrete.

Outside Diameter of the Column

The fire resistance of an HSS column is shown as a function of the outside diameter of the column for two loads in Fig. 2. The fire resistance increases significantly with the increase in diameter of the column. The curves in the figure show that the fire resistance increases more than quadratically with the column outside diameter. The

increased fire resistance can partially be attributed to the increase in strength of the column with the increase in diameter and partially to the longer time it takes the concrete core to reach temperatures at which it has lost so much strength that it can no longer support the load.

Steel Wall Thickness

Fig. 3 shows the influence of the stccl wall thickncss on the tirc resistance of HSS columns filled with bar-reinforced concrcte for a load of 400 kN. For the larger columns, the fire resistance decreases slightly with the wall thickness while, for the m-ller columns, the fue resistance increases somewhat. However, the influence of wall thickness is not significant in the entire range of columns studied. An explanation for the decrease in fire resistance with increase of wall thickness for the larger columns is, that at the time of failure, which occurs after more than 3 hours exposure to fire, the steel has virtually lost

all of its strength. Therefore, at the time of failure, the column is supported only by the concrete core, which decreases in area with increasing steel wall thickness. For the smaller columns, however, which fail after an exposure time on the order of 1 hour, there is still a significant contribution of the steel to the strength of the column. The thicker the steel, the greater the contribution of the steel to the strength of the column, which more than compensates for the loss in strength due to the reduction of the concrete core area with steel wall thickness.

Effective Length

The influence of the effective length on the fire resistance of the HSS columns is shown in Fig. 4 for three concrete strengths and two load levels. The fire resistance decreased with increase in effective length. The influence of the effective length is greater for lower loads. The decreased fire resistance for longer columns can be attributed to increased slenderness which, in turn, reduces the load-canying capacity.

Load

The influence of the load on the fire resistance of HSS columns is shown in Fig. 5, where the fue resistance is plotted as a function of the axial load for three column outside diameters. It can be seen that for fire resistances above 45 minutes, which lie in the practical region, thc fire resistance of the columns increases steeply with decreasing load. The influence of load on fire resistance is greater for columns with larger diameter.

Tests [3] and comparisons with calculated fire resistances [5] showed that the fire resistance of HSS columns filled with bar-reinforced concrete remains predictable even for loads up to 1.7 times the factored resistance of the concrete core according to CANICSA- S16.1-M89 [12].

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Percentages of Steel Reinforcement

The fire resistance of the HSS columns increases by a relatively small amount with an increase of the percentage of steel reinforcement. The results of the parametric studies indicated that the increase is about 10% when the steel percentage was increased from 1.5

to 6%. The presence of reinforcement, however, provides containment for the concrete core and, therefore, substantially increases the duration of exposure to fire and the load to which the column can be subjected without the occurrence of premature failure, compared to plain concrete-filled columns.

Concrete Strength

Fig. 6 shows the variation of fire resistance of HSS columns with concrete strength for various loads and effective lengths. The curves show a moderate influence of the concrete strength on the fire resistance of the column, which increased nearly linearly with the concrete strength. The influence is relatively greater for the higher loads than for the lower loads. The influence of the concrete strength is also greater for the shorter columns than for the longer columns.

Concrete Cover

An increase of concrete cover increases the fire resistance of HSS columns filled with bar-reinforced concrete by a small amount as can be seen in Fig. 7. The effect of the concrete cover on the fire resistance of the column is greatest for the column with an effective length of 4.5 m. In general, the thicker the cover thickness, the slower the temperature rise of the steel reinforcement and its loss of strength.

Type of aggregate

The effect of the aggregate type on the fire resistance of a concrete-filled HSS column is shown in Fig. 8 for siliceous and carbonate aggregate concretes. In the practical region of fire resistance, namely, for fue resistances above 45 minutes, the fire resistance of an HSS column filled with bar-reinforced carbonate aggregate concrete is higher by

10% or more than that of a similar column filled with siliceous aggregate concrete. This is mainly caused by the higher heat capacity of carbonate aggregate concrete, which, due to an endothermic reaction at about 700°C, increases to a multiple of the heat capacity of siliceous aggregate concrete [9].

In sunmmy, the results from the parametric studies indicated that the cross- sectional size, the effective length of the column and the load have strong influence on the fire resistance of circular HSS columns filled with bar-reinforced concrete. The concrete strength and the type of aggregate have moderate influence, while the concrete cover to the reinforcement and the amount of steel reinforcement have a small influence. The steel wall thickness does not significantly influence the fire resistance of the column. An examination of data from the parametric studies of square HSS columns filled with bar- reinforced concrete [lo], indicated that their behaviour is similar to that of circular HSS columns.

EXPRESSIONS FOR CALCULATING FIRE RESISTANCE

Based on the data from the parametric studies, expressions were developed for the calculation of the fire resistance of circular and square HSS columns filled with bar- reinforced concrete.

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It was possible to express the fire resistance of these columns, as a function of the

parameters that dctcrmine it, by equations similar to those developed for the calculation of thc fire resistance of HSS columns filled with plain concrete 121. The usc of equations for columns filled with bar-reinforced concrete, shilar to columrisfilled with plaid concrete, will simplify the procedure for the calculation of the f r e resistance of these columns.

In the following, the equations that show the relationship between the fire resistance and the parameters that determine it, will be given for columns with circular cross sections as well as for columns with square cross sections.

Circular HSS Columns

As shown earlier, the most important parameters that determine the fire resistance of hollow steel columns filled with bar-reinforced concrete are:

1. The load on the column

2. The outside diameter or the outside width of the column 3. The effective length of the column

4. Concrete strength

5. Type of aggregate

6. Percentage of steel reinforcement 7. Concrete cover to the reinforcement

Based on the relationships between the fire resistance and the above parameters, found in the uarametric studies. the followine formula for the fire resistance of circular hollow steel columns, filled wi& bar-reinforGed concretes, was established empirically:

where:

R = lire resistance in minutes

f, = specified 28-day concrete saength in MPa K = effective length factor

L = unsupported length of the column in mm D = outside diameter of the column in mrn C = applied load in kN

f, = a constant to account for the type of aggregate, percentage of steel bar-

reinforcement and the thickness of the concrete cover to the bar-reinforcement. The values off, are given in Table 3 for siliceous and carbonate aggregates, various steel percentages and concrete cover thicknesses.

Since Eq. (I), which provides a relationship between the fire resistance and the parameters that determine it, is based on the results of experimental and parametric studies, it is necessary to set limits of applicability on the values of the parameters within the range of values investigated in the studies. The studies [4,5] showed that the fire resistances of bar-reinforced HSS columns were predictable for fire resistances up to more than three hours. These studies also indicated that no premature failure occurred for loads up to 1.7 times the factored resistance of the column concrete core according to the

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Standard CANICSA-S16.1-M89 [12]. In addition, the experimental and parametric studies have been carried out for columns with a concrete strength between 20 and 55

MPa, an effective length between 2000 and 4500 mm, an outside diameter or outside width between 165 and 410 a steel percentage between 1.5 and 5%, a concrete cover to the main reinforcing bar between 20 and 50 mm, and Class 1,2 and 3 sections.

In summary, Eq. (1) is deemed to be applicable when the following limits are set on the parameters that determine the fire resistance of the column:

1. Fire resistance (R): S 180 min

2. Load on the column (C):

<

1.7 times the factored compressive resistance of the concrete core according to CANICSA-S. 16.1 -M89

3. Specified 28-day concrete compressive strength (t,): 20-55 MPa 4. Effective length of column (KL): 200011500 mm

5. Outside diameter or width of the column (D): 165-410 mm 6. Percentage of main reinforcing bars (P): 1.5-5%

7. Concrete cover to the main reinforcing bars (S): 20-50 mm

8. Width (D) to thickness (t) ratio not to exceed Class 3 section according to CAN/CSA- S.16.1-M.89

In Fig. 9, the fire resistances, calculated with Eq. (I), are compared with those calculated using the computer program Because the fue resistances, predicted by the model, lie on the safe side [5], values of the factor fi, in Eq. (I), were selected to producedslightly higher fire resistances that those calculated using the model.

The conservative fire resistances, produced by the computer program, can further be seen in Table 4, where the fire resistances of circular HSS columns, calculated using Eq. (I), are compared with those obtained,from tests at NRC and by the Comitk

International pour le Developpement et 1'Etude de la Construction Tubulaire (CIDECT) [13], as well as with the results calculated for these columns using the mathematical model. For all the columns, the fire resistances computed by the model are lower than those obtained kom the tests. The fire resistances computed with Eq (1) are generally within fifteen percent of those obtained from tests, except for the column with a very high fire resistance. For this column, the equation produces a fire resistance that is about 30% conservative in comparison with that obtained in the tests.

Square HSS Columns

The results from the parametric studies [lo] indicate that the fire resistance of. square columns is influenced by similar parameters to those of the circular columns. Using a similar procedure as that for circular HSS columns, the following expression was

established for evaluating the fire resistance of square HSS columns filled with bar- reinforced concrete.

where:

R = fire resistance in minutes

f, = specified 28-day concrete strength in MPa K = effective length factor

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L = unsupported length of the column in mm D = width of the column in mm

C = applied load in kN

fi = a constant to account for the type of aggregate, percentage of steel bar-

reinforcement and the thickness of the concrete cover to the bar-reinforcement. The values of f2 are given in Table 5 for siliceous and carbonate aggregates, various steel percentages and concrete cover thicknesses. Because the fire resistances predicted by the model are less conservative for the square columns than for the circular columns, the values off2 have been selected to be somewhat lower than the values of fi for the circular columns.

The validity limits for the square columns are the same as those for the circular HSS columns, except for the outside dimension of the column. which for the sauare column should be 175 to 305 mm.

In Fig. 10, the fire resistances calculated with Eq. (2) are compared to those obtained from the computer program. The fire resistances obtained from the equation are somewhat more conservative than those obtained from the computer program, particularly for the higher fire resistances. However, both methods produce, in most cases,

conservative fire resistances in comparison with test results, as can be seen in Table 6, where the fire resistances obtaincd from both rncthods arc comparcd to results of tcsts conducted by NRC and by CLDECT.

DISCUSSION AND CONCLUSIONS

In order to keep Eqs. (1) and (2) simple, approximate relationships between the fire resistance and the parameters that determine it were used, which in some cases included the use of linearized relationships. Because of the use of approximate

relationships, it was strived to obtain fire resistances that reasonably lie on the safe side. How the fire resistances, calculated with the Eqs. (1) and (2), compare to test results is shown in Fig. 11, where the calculated fire resistances are compared to the fire resistances obtained fkom tests on 29 columns conducted at NRC and other laboratories [13]. Five columns had circular cross sections, while the remaining columns had square cross sections. For some of the columns, the type of aggregate used in the concrete mix was not known. For these columns, the fire resistances were calculated by assuming that the aggregate in the concrete was carbonate, which resulted in slightly higher fire

resistances than those for siliceous aggregate concrete.

It is evident that there is considerable variation between the calculated and experimental values. This occurred because of the large scatter of experimental results. For example, tests on nominally identical columns, carrying identical loads, sometimes showed significant differences in fire resistance when tested at different laboratories. This discrepancy was mainly attributed to variations in end fixicity of the various testing

machines. The coefficients in Eqs. (1) and (2) were selected such that the equations predict fire resistances that are generally conservative.

Based on the results of this study, the following conclusions can be drawn:

a The parameters that have the greatest influence on the fire resistance of bar-reinforced concrete-filled HSS columns are the outside diameter or width of the column, its effective length, the load on the column and the concrete strength. The influence of

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the type of aggregate in the concrete, the percentage of steel reinforcement and the concrete cover to the reinforcement is considerably smaller. The thickness of the steel wall does not significantly affect the fire resistance of the columns.

The fire resistance of circular and square bar-reinforced concrete-filled HSS columns can be calculated by two equations that reflect the influence of the various parameters that determine it, one for the circular and one for the square columns. Using the equations, the fire resistance of these columns can be calculated for any value of the significant parameters that determine it, such as load, column-section dimensions or concrete strength, with an accuracy that is adequate for practical purposes. By varying these parameters, an economical design, that satisfies the fire resistance requirements for structures, can be determined.

The fire resistance of the columns is determined by the same parameters as those that determine the structural resistance of the columns and can, therefore, be integrated in the normal course of structural design. The simplicity of the equations makes them suitable for incorporation into building codes.

ACKNOWLEDGMENT

This work was carried out at the National Fire Laboratory of the Institute for Research in Construction, National Research Council of Canada, with the support of the Canadian Steel Construction Council and the American Iron and Steel Institute. The writers would like to thank Michael Denham and Martin Chabot for their contribution in processing the theoretical and experimental results, and John MacLaurin and John Latour for their assistance with the experiments, conducted for the development of the

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REFERENCES

1. Klingsch, W., and Wuerker, K., New developments in fire resistance of hollow section structures, Symposium on Hollow Structural Sections in Building Construction, ASCE, Chicago, IL, 1985.

2. Lie, T.T. and Stringer, D.C., Calculation of fire resistance of steel hollow structural steel columns filled with plain concrete, Canadian Journal of Civil Engineering, Vol. 21, 1994, p. 382-385.

3. Chabot, M. and Lie, T.T., Experimental studies on the fire resistance of hollow steel columns filled with bar-reinforced concrete, IRC Intemal Report No. 628, National Research Council of Canada, Institute for Research in Construction, Ottawa, Ontario,

1992.

4. Lie, T.T. and Irwin, R.J., Fire resistance of rectangular hollow steel sections filled with bar-reinforced concrete, IRC Internal Report No. 63 1, National Research Council of Canada, Institute for Research in Construction, Ottawa, Ontario, 1992. 5. Lie, T.T., Fire resistance of circular steel columns filled with bar-reinforced concrete,

Journal of Structural Engineering, ASCE, Vol. 120, No. 5, 1994, p. 1489-1509. 6. Standard Methods of Fire Tests on Building Construction and Materials, ASTM El 19-88, American Society for Testing and Materials, Philadelphia, PA, 1990.

7. Standard Methods of Fire Endurance Tests of Building Construction and Materials,

CANiULC-S101, Underwriters' Laboratories of Canada, Scarborough, Ontario, 1989.

8. Handbook of steel construction, Canadian Institute of Steel Construction, Willowdale. Ontario. 1991. . . -.-- ~ ~> ~- ~

9. Lie, T.T., Ed., Structural fire protection, Manuals and Reports on Engineering Practice No. 78, ASCE, New York,

NY,

1992.

10. Lie, T.T. and Denham, E.M.A., Factors affecting the fire resistance of square hollow steel columns filled with bar-reinforced concrete, IRC Intemal Report No. 650, National Research Council of Canada, Institute for Research in Construction, Ottawa, Ontario, 1993.

1 1. Lie, T.T. and Denham, E.M.A., Factors affecting the fire resistance of circular hollow steel columns filled with bar-reinforced concrete, IRC Internal Report No. 651, National Research Council of Canada, Institute for Research in Construction, Ottawa,

Ontario, 1993.

12. Limit state design of steel structures, CANICSA-S16.1-M89, Canadian Standards Association, Toronto, Ontario, 1989.

13. Grandjean, G., Grimault, J.P. and Petit, L., Determination de la duke au feu des profils crew remplis de bkton, Rapport final, Commission des Communautes Europeennes, Recherche Technique Acier

,

Luxembourg, 198 1.

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NOTATION

C = applied load (kN);

D = outside diameter or width of a column (mm); K = effective length factor;

L = unsupported length of the column (mm);

KL = effective length of the column (mm);

P = area of the main bar-reinforcement as a percentage of the concrete core area

PA)

\'"I

R = fire resistance (rnin);

S = concrete cover to the main bar-reinforcement (mm)

t = wall thickness of a column (mrn); f, = specified 28day concrete strength @Pa);

fl = a constant to account for the type of aggregate, percentage main bar reinforcement and the thickness of the concrete cover to the bar-reinforcement in bar-reinforced concrete-filled circular HSS columns;

fj = a constant to account for the type of aggregate, percentage main bar reinforcement and the thickness of the concrete cover to the bar-reinforcement in bar-reinforced concrete-filled square HSS columns.

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11

TABLE 1. Parameters Investigated in the Parametric Study of Circular Columns

TABLE 2. Parameters Investigated in the Parametric Study of Square Columns Outside Diameter (mm) 168 219 273 324 365 406

TABLE 3. Values off, in Equation (1) for Circular Columns

W

a

l

l

Thickness (mm) 4.8 9.5 4.8 12.7 6.4 12.7 6.4 12.7 6.4 12.7 6.4 12.7 Outside Diameter (mm) 178 203 254 305 Effective Length (m) 2.5,3.0, 4.5 (For all columns) Wall Thickness (mm) 4.8 12.7 6.4 12.7 6.4 12.7 6.4 12.7 Reinforcement (%) 2.0,2.5, 5.1 2.3,2.9,5.7 1.2,2.6,5.2 1.4,3.0,6.1 1.3,2.6, 5.6 1.5,2.9, 6.2 1.6,2.6,5.3 1.7,2.9, 5.7 1.3,2.8, 5.4 1.4,3.1,5.8 1.5,2.9, 5.8 1.6, 3.0, 6.2 Effective Length (m) 2.5, 3.0,4.5 (For all columns) Concrete Strength (MPa) 20,40,55 (For all columns) Reinforcement (%) 2.0,2.5, 5.1 2.3, 2.9, 5.7 1.2, 2.6, 5.2 1.4,3.0, 6.1 1.3,2.6, 5.6 1.5,2.9,6.2 1.6,2.6, 5.3 1.7,2.9, 5.7 Concrete Strength @Pa) 20,40,55 (For all columns) Concrete Cover (mm) 20,55 (For all columns) Concrete Cover (mm) 20,55 (For all columns) Aggregate Type Siliceous, Carbonate (For all columns) Aggregate Type Siliceous, Carbonate (For all columns)

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TABLE 4. Comparison Between Calculated and Measured Fire Resistances for Circular HSS Columns

TABLE 5. Values off* in Equation (2) for Square Columns

TABLE 6. Comparison Between Calculated and Measured F i e Resistances for Square HSS Columns

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,-19.5 mm b o n

23 mm cover

to main rebors

273.1 rnrn

mrn

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I I I I I I I I

-

-

Load: 400

kN

-

--

Load: 1400

kN

-

-

-

-

-

-

-

-

-

-

0 I I I I I I

0

50

100

150

200

250

300

350

400

450

Outside diameter, rnm

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0

0

2

4

6

8

10

12

14

16

Wall

thickness,

rnrn

I I I I I I I Outside diameter:

-

--

406

mrn

-

-

-

356

mm

-

-

324

mm

-

-

273

mm

-

-

219 mm

-

-

---

168 mm I I I I I I I

FIG. 3. Fire Resistance as a Function of Wall Thickness for Various Column Outside Diameters

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2 3

Effective length,

m

I I I I STRENGTH:

-

55 MPa

-

35 MPa

-

-

20 MPa

-

-

55 MPa 35 MPa

-

\ 20 MPa \

-

\

-.

\

-

1

\.

-

Load: 400 kN

\ !

-1

-.\.

1

-

--

Load: 1400 kN

--

-

, I I 1 I

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--

Outside diameter: 406

rnrn

--

Outside diameter: 273 rnrn

-

Outside diameter: 168 rnm

0

2000

4000

6000

8000

Load, kN

FIG.

5.

Fire Resistance

as

a

Function of Load for Various Column

Outside Diameters

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FIG. 6. Fire Resistance as a Function of Concrete Strength 160 140 120 c

.-

E

1 0 0 -

6

0 c 80 (I)

.-

(I)

2

2

60

i

i

40 20 0 I I I I I

-

-

Load: 400 kN

-

-

Load: 1600 kN

-

-

EFFECTIVE LENGTH: KL = 2.5 m

-

-

KL = 3.0 m

-

'

/'

-

/' / 4'

-

,'/

/ KL = 4.5 m

-

KL=2.5m

5

'

I

-

KL = 3.0 m

-

--

-

-

- -

KL = 4.5 m

-

I I 1 I I 0 10 20 30 40 50 60

(23)

I I I I I

EFFECTIVE LENGTH:

-

KL =

2.5 m

-

KL =

3.0

m

-

-

-

-

-

KL=4.5 m

/

-

-

-

I I I 1 I

Concrete cover,

mm

(24)

200

1

80

160

K

.-

140

E

6 120

0 C

100

V)

.-

V)

80

2

i

i

60

40

20

0

0

1000

2000

3000

4000

Load, kN

FIG. 8. Fire Resistance as a Function of Load for Siliceous and Carbonate Aggregrate Concrete I I I

-

-

-

Siliceous aggregate

-

--

Carbonate aggregrate

-

-

-

-

-

-

I 1

(25)

0

50

100

150

200

Fire resistance from computer program, min

FIG. 9. Cornpalison of Fire Resistance for Circular HSS Columns from Eq.

(1)

(26)

Fire resistance from computer program, min

FIG. 10. Comparison of Fire Resistance for Square HSS Columns from Eq. (2)

(27)

Fire resistance from test, min

250

200

c

.-

E

r- 0

.-

C

m

150

a,

E

2

C cL,

100-

m

c. U)

.-

U)

2

2

i

i

50

0

FIG.

11.

Comparison of Calculated Fire Resistance with that from Tests

I I I I

NRC square columns

El

CIDECT square columns

0

NRC circular columns

-

0

CIDECT circular columns

-

-

0

...'

-

0

0

.,."

q

0."

0

-

0

.cl

m ..-.o

L8

.a'

El

Q ' n o

-

.-

El El

-

...a

.a

" I I I I

0

50

100

1

50

200

250

Figure

TABLE 2.  Parameters Investigated  in  the Parametric Study of Square Columns Outside Diameter (mm) 168 219 273 324 365 406
TABLE 4.  Comparison Between Calculated and Measured Fire Resistances for  Circular HSS Columns
FIG.  1.  Layout of Typical HSS Column Investigated in the Parametric Study
FIG. 2. Fire Resistance  as  a  Function of  Column Outside Diameter
+7

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