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Assessment of the Fire Resistance of Steel Hollow Structural Section Columns Filled with Steel Fibre Reinforced ConcreteKodur, V. R.

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Ser TH1 R427 no. 731 c. 2 BLDG

National Research Conseil national l*i Council Canada de recherches Canada

Assessment of the Fire Resistance of Steel Uollow Structural Section Columns Filled with Steel Fibre Reinforced Concrete /

1 n t d n a l repor t ( I n s t i t u t e f

by V.K.R. Kodur Internal Report No. 731

Date of Issue: November 1996

CISTI / ICIST NKC/CNRC IRC Ser R e c e i v e d on: 11-20-96 I n t e r n a l repor t .

ASSESSMENT OF THE FIRE RESISTANCE OF STEEL HOLLOW STRUCTURAL SECTION COLUMNS FILLED WITH STEEL FIBRE

REINFORCED CONCRETE

by

V.K.R. Kodw

ABSTRACT

Computer programs were developed and used to investigate the influence of various factors on the fire resistance of steel hollow structural section (HSS) columns filled with steel fibre-reinforced concrete (SFRC). Results from the parametric studies were used to develop simple equations for calculating the fue resistance of steel fibre- reinforced concrete-filled HSS columns with circular and square cross sections. The validity of the calculation procedure was established by comparing the calculated fire resistances with those obtained from fire tests on columns. The proposed equations, which are suitable for incorporation in design codes, provide a rational and easy-to-use design method for evaluating the fire resistance of hollow steel columns filled with steel fibre-reinforced concrete for any value of the significant parameters that determine it, such as load, cross-sectional dimensions, effective length and concrete strength.

ASSESSMENT OF THE FIRE RESISTANCE OF STEEL HOLLOW ~

STRUCTURAL SECTION COLUMNS FILLED WITH STEEL FIBRE REINFORCED CONCRETE

by

V.K.R. Kodur

INTRODUCTION

Steel hollow structural section (HSS) columns are very efficient structurally in resisting compression loads and are widely used in the construction of framed structures in industrial buildings. HSS columns, like other structural members must be designed to satisfy the requirements of serviceability and safety limit states. One of the major safety requirements in building design is the provision of appropriate fire protection to structural members. The basis for this requirement can be amibuted to the fact that, when other measures for containing or suppressing the fire fail, structural integrity is the last line of defence.

HSS columns are often filled with concrete to achieve increased load-bearing capacity. Concrete filling also increases fire resistance. Through the utilization of a concrete core, external fire protection required for the steel can be eliminated, thus increasing the usable space in the building. Further, properly designed concrete-filled hollow steel columns can lead, in an economic way, to the realization 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 of Canada (NRC), 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 HSS columns filled with different types of concrete were canied out. Studies on HSS columns filled with plain concrete [ I ] and bar-reinforced concrete [2] have been completed. Simple expressions for determining the fire resistance of these columns were established. The expressions for determining the fire resistance of HSS columns filled with plain concrete were incorporated in the National Building Code of Canada [3].

Results from the studies on hollow steel columns filled with plain concrete have shown that reductions in the loads on the columns have to be made to obtain predictable fire resistances. If the columns are filled with bar-reinforced concrete, fire resistances remain predictable even under high loads [4]. The reinforcement limits the minimum size of the column, however, and there is additional cost for the installation of the rebars in the column [5]. Steel fibre-reinforced concrete (SFRC) filled HSS columns, which have load limitations and costs that lie between those of plain and bar-reinforced concrete filled columns, in many cases provide cost-effective fire protection [6] .

In this report, the results of the parametric studies on the fire resistance of HSS columns filled with SFRC are described. Data from these studies is used to develop simple expressions for the calculation of the fire resistance of concentrically-loaded circular and square HSS columns filled with SFRC, that are suitable for incorporation in building codes.

EVALUATION OF FIRE RESISTANCE

To develop the expressions for the calculation of the fire resistance of the columns, mathematical models, for predicting the behaviour of circular and rectangular HSS columns filled with SFRC and exposed to fire, were developed r5,71. The models - - - incorporate realistic stress-strain relationships and thermal properties for structural steel and SFRC at elevated temperatures, and account for the effect of moisture. Full details on the development of the models are given by Kodur and Lie [5,7].

In the models, the fire resistance is calculated in various steps, consisting of the calculation of the temperature 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.

The fire temperature is calculated using the ASTM El 19-88 [8] or CANiULC- SlOl [9] standard fire-temperature equation. A finite difference technique is used to compute the temperatures across the cross section of the column. The strength of the column, which decreases 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 a point 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 incorporated into computer programs. By specifying the mechabical and thermal properties of structural steel and SFRC at elevated temperatures, the fire resistance of circular or rectangular HSS columns filled with SFRC can be evaluated. The validity of the computer programs has been established by comparing the results of the model to test data [5,7].

PARAMETRIC STUDIES

The fire resistance of HSS columns filled with SFRC depends on a number of factors such as load, cross-sectional dimensions, concrete strength and type of aggregate. The computer programs were used to conduct parametric studies to investigate the influence of these parameters on the fire resistance of HSS columns filled with SFRC. The studies were canied out through computer-simulated fire tests.

Fig. 1 shows the typical circular and square HSS columns, with SFRC filling, investigated in this study. The parameters that were investigated include the outside diameter or width of the column, the steel wall thickness, the effective length of the column, the load, the concrete strength and the type of concrete aggregate. The outside diameter of the steel sections for the circular HSS columns was varied from 141.3 to 404.6 mm, while the outside dimension of the square HSS columns was varied from 101.6 to 304.8 mm. The wall thicknesses considered were the minimum and the maximum thichesses listed in the CISC Handbook of Steel Construction [lo]. The effective lengths of the columns were varied from 2500 to 4500 mm. The ranges of these parameters, used for computer-simulated tests on circular and square SFRC-filled HSS columns, are given in Tables 1 and 2.

The effect of concrete strength was investigated by calculating the fire resistance of the columns for three concrete strengths, namely, 20,35 and 55 m a . The type of aggregate also has an effect on fire resistance. For the purpose of obtaining information on the extent of influence of the type of aggregate on the fire resistance of the column, all calculations were performed for both siliceous and carbonate aggregate concrete.

In the calculations, the material properties described in the ASCE Structural Fire Protection Manual [ l 11 were used. Detailed results of the parametric studies on circular and square HSS columns filled with SFRC were published by Kodur [12,13].

In the following, the effect of the various factors that determine the fire resistance of HSS columns will be further discussed for circular columns filled with SFRC.

Effect of Outside Diameter

In Fig. 2, the fire resistance of an HSS column filled with SFRC is shown as a function of the outside diameter of the column for two selected reference loads. It can be seen that the outside diameter has a significant influence on the fire resistance 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.

Effect of Steel Wall Thickness

The influence of the steel wall thickness on the fire resistance of HSS columns filled with SFRC is shown in Fig. 3. For the larger columns, the fire resistance decreases slightly with increasing wall thickness while, for the smaller columns, the fire 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 h 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 h, there is still some contributton 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.

Effect of Load

The influence of the load on the fire resistance of HSS columns filled with SFRC is shown in Fig. 4, where the fire 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 min, which lie in the practical region, the fire resistance of the columns increases steeply with decreasing load. The influence of load on fire resistance is relatively higher for the larger columns.

Data from experimental studies 1141 and its comparisons with calculated fire resistances [5] showed that the fire resistance of HSS columns filled with SFRC remains predictable even for loads up to 1.1 times the factored resistance of the concrete core according to CANICSA-S16.1-M89 [15].

Effect of Length

In Fig. 5, the fire resistance of the HSS columns filled with SFRC is shown as a function of effective length for two concrete strengths and two load levels. The fire resistance decreased with an increase in effective length. The curves show that in the range of effective lengths of 2.5-4.5 m, the fire resistance is approximately inversely proportional to the 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.

Effect of Concrete Strength

Fig. 6 shows the variation of fue resistance of SFRC-filled HSS columns with compressive strength of concrete for various loads. The curves show a moderate influence of the concrete strength on the fue resistance of the column, which increases nearly linearly with the concrete strength. The influence of compressive strength is relatively greater for the higher loads than for the lower loads.

Effect of Type of Aggregate

The effect of the aggregate type on the fire resistance of an SFRC-filled HSS column is shown in Fig. 7 for siliceous and carbonate aggregate concretes. In the practical region of fire resistance, namely for fire resistances above 45 min, the fire resistance of an HSS column filled with carbonate aggregate concrete is higher by 20% or more than that of a similar column filled with siliceous aggregate concrete. This occurs mainly because carbonate aggregate has a substantially higher heat capacity than siliceous aggregate due to an endothermic reaction that takes place in carbonate aggregate at about 700°C [l 11.

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 SFRC. The concrete strength and the type of aggregate have moderate 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 SFRC [13] indicated that their behaviour is similar to that of circular HSS columns.

EXPRESSION FOR CALCULATING FIRE RESISTANCE

Data &om the parametric studies was used to develop simple equations for the calculation of the fue resistance of circular and square HSS columns filled with SFRC. It was possible to express the fire resistance of these columns, as a function of the parameters that determine it, by equations similar to those developed for the calculation of the fire resistance of HSS columns filled with plain concrete [I] and bar-reinforced concrete [2]. The use of equations for columns filled with SFRC, similar to columns filled with plain and bar-reinforced concrete, will simplify the procedure for the calculation of the fire 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 SFRC are:

1. the outside diameter of the column, 2. the load on the column, 3. the effective length of the column, 4. compressive strength of concrete, and 5. type of aggregate in concrete mix.

Based on the relationships between the fire resistance and the above parameters found in the parameixic studies, the following equation for the fire resistance of circular hollow steel columns filled with SF'RC was established empirically:

( f , + 20) R=f,

(KL - 1000)

where:

R = fire resistance in minutes, fi = specified 28-day compressive strength of concrete in MPa, K = effective length factor, L = unsupported length of the column in D = outside diameter of the column in mm, C = service load in kN, and fi = a constant to account for the type of aggregate. For circular columns, the value of

f, is equal to 0.075 for siliceous aggregate concrete and 0.085 for carbonate aggregate concrete.

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 [5,7] showed that the fire resistances of SFRC-filled HSS columns were predictable for fire resistances in excess of 3 h. These studies also indicated that premature failure did not occur for loads up to 1.1 times the factored resistance of the column concrete core according to the Standard CANKSA-S16.1-M89 [15]. In addition, experimental and parametric studies have been canied out for columns with a concrete strength between 20 and 55 MPa, an effective length between 2500 and 4500 mm, an outside diameter between 141.3 and 404.6 mm, and Class 1,2 and 3 sections.

In summary, Eq. (I) 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) 5 180 min, 2. load on the column (C) 5 1.1 times the factored compressive resistance of the concrete

core according to CANICSA-S16.1-M89 [15], 3. specified 28-day concrete compressive strength ( f , ) : 20-55 MPa, 4. effective length of column (KL): 20004500 mm, 5. outside diameter of the column (D): 141.3404.6 mm, 6. outside diameter (D) to thickness (t) ratio not to exceed Class 3 section according to

CANJCSA-S16.1-M89 [15].

To verify the validity of the formula, the fire resistances, calculated with Eq. (I), were compared to those calculated using the computer program in Fig. 8. Because the fire resistances predicted by the computer lie, with a few exceptions, on the conservative side [5], values of the factor fi in Eq. (1) were selected to produce slightly higher fire resistances than those calculated using the model.

The conservative fire resistances produced by the computer program, can further be seen in Table 3, where the fire resistances of circular HSS columns filled with SFRC, calculated using Eq. (I), are compared to those obtained from tests at NRC as well as to the results calculated for these columns using the mathematical model. For the first column, the fire resistance computed by the model (185 min) is lower than that obtained from the tests (199 min) while, for the second column, the computed fire resistance (254 min) is about 10% higher than the test result of 227 min. The fire resistances computed with Eq. (1) are generally conservative; about 15-20% less than those obtained from tests.

Square HSS Columns

The results from the computer simulated studies [13] show 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 SFRC.

where: -

R = fire resistance in minutes, f = specified 28-day compressive strength of concrete in MPa, K = effective length factor, L = unsupported length of the column in mm, D = width of the column in mm, C = service load in !d, and f2 = a constant to account for the type of aggregate. For square columns, the value of f2

is equal to 0.065 for siliceous aggregate concrete and 0.075 for carbonate aggregate concrete.

Because the fire resistances predicted by the model are less conservative for the square columns than for the circular columns, the values of f2 have been selected to be somewhat lower than the values of fi for the circular columns. In terms of cross-sectional area required to support a given load in a fire situation, circular columns can be seen to be more efficient than square columns. Several reasons may be proposed to explain the relative efficiency of circular columns over square columns. For example, the steel shell of square columns is more prone to local buckling than that of circular columns, thus reducing the containment of the concrete and allowing spalling to occur. In addition, due to the shape of square columns, an unequal temperature field develops during a fire and generates large internal stresses in the concrete compared to those in a circular column. These internal stresses reduce the relative load-carrying capacity of the square column.

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 square column should be 101.6-304.8 mm

The fire resistances calculated with Eq. (2) are compared to those obtained from the computer program in Fig. 9. The fire resistances obtained from the equation are somewhat more conservative that those obtained from the computer program. However, both methods produce, in most cases, conservative fire resistances in comparison with test results, as can be seen in Table 3, where the fire resistances obtained from both methods are compared to results,of tests conducted by NRC and by the Comite Intemational pour le Developpement et l'Etude de la Construction Tubulaire (CIDECT), published by Grandjean et a1 [16], as well as with the results calculated for these columns using the computer program.

DISCUSSION

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, the parameters were determined which provided fire resistances that reasonably lie on the conservative side.

The fire resistances, calculated with Eqs. (1) and (2), are compared to test results obtained from tests on 12 columns conducted at NRC and other laboratories 2161 in Fig. 10. Four 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, canying identical loads, sometimes showed significant differences in fire resistance when tested at different laboratories. This discrepancy was mainly attributed to variations in end fixity 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.

DESIGN APPLICATIONS

The proposcd relationships result in a convenient way of obtaining firc resistances of HSS columns filled with SFRC and may bc uscd to predict thc fire rcsistance in lieu of laboratory testing or detailed numerical adalysis. A designer can obtain the desired fire resistance for a column by varying parameters such as load, column-section dimensions, column length and type of aggregate. These equations, when incorporated into the normal course of design, provide a simple but rational approach for computing structural fire resistances. Hence, these equations can be incorporated into building codes.

CONCLUSIONS

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

1. The important parameters that influence the fire resistance SFRC filled HSS columns are the outside diameter or width of the column, its effective length, the load on the

column, the concrete strength and the type of aggregate in the concrete. The thichess of the steel wall does not significantly affect the fire resistance of the columns.

2. Two expressions are proposed for calculating the fire resistance of circular and square SFRC-filled HSS columns in terms of the various parameters that influence it. Using the proposed 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.

3. 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.

ACKNOWLEDGEMENT

This work was camed out at the National Fire Laboratory of the institute for Research in Construction, National Research Council of Canada, in partnership with the Canadian Steel Construction Council and the American Iron and Steel Institute. The author would like to thank Messrs. John MacLawin and John Latour for their assistance with the experiments conducted for the development of the mathematical models used in this study.

NOTATION

C = applied load 0; D = outside diameter or width of a column (mm); K = effective length factor; L = unsupported length of the col& (mm); KL = effective length of the column (mm); R = fire resistance (min); t = wall thickness of a column (mm); f: = specified 28-day concrete strength (MPa); f, = a constant to account for the type of aggregate, in SFRC filled circular HSS

columns; f2 = a constant to account for the type of aggregate, in SFRC filled square HSS

columns.

REFERENCES

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. No. 3. 1994. D. 382-385.

~ ~~ ~

Lie, T.T. and JLcdur,'+.~.~., "Fire resistance of steel columns filled with bar- reinforced concrete." Journal of Structural Engineering, ASCE, Vol. 122, No. 1, - - 1996, p. 30-36. National Building Code of Canada, Appendix D, National Research Council of Canada, Ottawa, Ontario, 1995. Chabot, M. and Lie, T.T., "Experimental studies on the fire resistance of hollow steel columns filled with bar-reinforced concrete", IRC Internal Report No. 628, National Research Council of Canada, Institute for Research in Construction, Ottawa, Ontario, 1992. Kodur, V.K.R. and Lie, T.T., "Fire resistance of circular steel columns filled with fibre-reinforced concrete", Journal of Structural Engineering, ASCE, Vol. 122, No. 7, p. 776-782, 1996. Lie, T.T. and Kodur, V.K.R., "Fire protection of hollow steel columns through concrete filling", Proceedings, 1st CSCE Constr. Spec. Conf., Canadian Society of Civil Engineers (CSCE), Montreal, Canada, 1995, p. 215-224. K o h , V.K.R. and Lie, T.T., "Evaluation of the fire resistance of rectangular steel columns filled with fibre-reinforced concrete", Canadian Journal of Civil Engineering (in press). "Standard methods of fire tests on building construction and materials", ASTM E119- 88, American Society for Testing and Materials, Philadelphia, PA, 1990. "Standard methods of fire endurance tests of building construction and materials", CAN/ULC-S101. Underwriters' Laboratories of Canada, Scarborough, Ontario, - 1989.

10. "Handbook of steel construction", Canadian Institute of Steel Construction, Willowdale. Ontario. 1991. ~ ---. ~~ ~~- ~

11. Lie, T.T. ed.,"~truc&al fire protection", Manuals and Reports on Engineering Practice No. 78, ASCE, New York, NY, 1992.

12. Kcdur, V.K.R., "Factors affecting the fire resistance of circular hollow steel columns filled with steel fibre-reinforced concrete", IRC Internal Report No. 598, National Research Council of Canada, Institute for Research in Construction, Ottawa, Ontario, 1996.

13. Kodur, V.K.R., "Factors affecting the fire resistance of square hollow steel columns filled with steel fibre-reinforced concrete", IRC Internal Report No. 590, National Research Council of Canada, Institute for Research in Construction, Ottawa, Ontario, ~ ~

1996. 14. Kodur, V.K.R. and Lie, T.T., "Experimental studies on the fire resistance of circular

hollow steel columns filled with steel fibre reinforced concrete", IRC Internal Report No. 691, National Research Council of Canada, Institute for Research in Construction, Ottawa, Ontario, 1995.

15. "Limit state design of steel structures", CANICSA-S16.1-M89, Canadian Standards Association, ~oi%mto, Ontario, 1989.

16. Grandjean, G., Grimault, J.P. and Petit, L., "Determination de la duree au feu des profils creux remplis de beton", Rapport final, Commission des Communautks Europeennes, Recherche Technique Acier , Luxembourg, 1981.

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

Diameter

324

405

wall Thickness

Concrete 1 1 strength Aggregate

Carbonate (For all

Columns)

TABLE 2. Parameters Investigated in the Parametric Study of Square Columns

Outside Dimension

0 102

127

152

178

203

254

305

Effective T Concrete strength

m 20,35, 55

(For all Columns)

Aggregate type

Siliceous, Carbonate

(For all Columns)

TABLE 3. Comparison Between Calculated and Measured Fire Resistances

Column

Dimensions (mm)

D 1 t (a) Circular HSS Columns

1 / 324 1 6.4 / 3,000 1 57.0 1 C 1 1600 1 199 / 185 154 2 / 356 1 6.4 / 3,000 1 53.5 1 C 1 1500 1 227 / 254 192

@) Square HSS Columns

Column length (mrn)

3 4 5 6

Concrete strength

@Pa)

152 203 150 200

Aggregate type

6.4 12.7 5.0 5.0

Load OrN)

3,000 3,000 2,520 2,520

Fire Resistance (min)

Test I Model I Equation

42.0 42.0 40.3 52.0

C C C C

350 700 250 740

80 110 81 88

48 74 40 63

35 52 52 74

(a) Circular HSS Column (b) Square HSS Column

Figure 1. Layout of Typical SFRC-filled HSS Column Investigated in Parametic Study

I I I I I I I 1

- - Load: 31 0 kN

---- Load: 1250 kN - -

- -

- -

-

- -

/

I I e ~j I I I I

0 50 100 150 200 250 300 350 400 450

Outside diameter, mm

Figure 2. Fire Resistance as Function of Column Outside Diameter

I I 1 I I I I

Outside diameter -

405 mm -

- -

----- 356 mm - -

324 mm - -

273 mm

- 219 mm - 168 mm 141 mm 1 0

0 2 4 6 8 10 12 14 16

Wall thickness, mm

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

0 0 2000 4000 6000 8000

Load, kN

I I I

-.--- Outside diameter: 405 mm -

\ ---- Outside diameter: 273 rnm

\ Outside diameter: 141 mm .\ - .\ .\ -\ -

I .\ I +\ - \

.\. \

\. \

\. - \

\. \ \. -

\ \. \ x. \ x. \ \

x. - '. '-'. .. -a\.

-I

I -. I +--.-.

Figure 4. Fire Resistance as Function of Load for Various Outside Diameters

0 0 1 2 3 4 5

Effective length, m

- - Strength:

- 35 MPa

-

-

- 35 MPa " -.

- \ 20MPa ----- \ -- \ -. \ Load: 31 0 kN

-. ' -. '. - . . - ---- Load: 1250 kN

I I I I

Figure 5. Fire Resistance as Function of Effective Length of Column

Concrete strength, MPa

140

120

100 r: .- E 6 80 0 C a C

.- 60 F a, L

ii 40

20

0

Figure 6. Fire Resistance as Function of Concrete Strength

-

-

- - 0 / -

0 0

0

0 0 )

- - 0 ,))

0 , 0

0 - / -

Load: 310 kN - - ---- Load: 1250 kN

I I I I I I 0 10 20 30 40 50 60 70

180 I I I

Siliceous aggregate - ---- Carbonate aggregate

-

-

-

-

60 - -

40 - -

20 - -

0 1000 2000 3000 4000

Load, kN

Figure 7. Fire Resistance as Function of Load for Siliceous and Carbonate Aggregate Concrete

Figure 8. Comparison of Fire Resistance for SFRC-Filled Circular HSS Columns with Model Predictions

200

150 s .- E

$ s m - " .- " l o o 2 2 .-

L L

50

0 '

I I I / /

0 0 / /

0 0 / 0 o / o

/

0 0 0 "/'

O 0 0 O/' 0 - 0 0

- 0 /

0

0 0 8.'

€I %/ o 8 O O/'O

0

- o 8 o 8 ~ : 0 - 0 0 0 0

O 0 9/ O / 0

O / O 0 @/I

* ~ O O O - 8/ O - 2'0 0 0

/ 0 0

/

// 0 8 /

/ / I I I

0 50 100 150 200

Fire resistance from computer program, min

Fire resistance from computer program, min

Figure 9. Comparison of Fire Resistance for SFRC-Filled Square HSS Columns with Model Predictions

50 100 150 200

Fire resistance from test, min

I I I I 0 0

NRC circular columns 0

0 0

CI NRC square columns 0 0

- CIDECT square columns 0 0

0 0

0 .

0

0' . 0 - 0

0 0

0 0

0 0

0 0

7 0 0

0

4' ., 0 . 0

0 - 0 - 0 0

0 0

0 0

CIQ 0

0 I I I I

Figure 10. Comparison of Calculated Fire Resistance with that from Tests