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Fire resistant design of austenitic structural stainless steel
J. Construct. Steel Res. Vol.
46, Nos. 1-3, pp. 45&459, paper number 243, 1998 01998 Elsevier Science Ltd. All rights resewed Printed in Great Britain PII: SO145974X(98)00150-8 0143-974XI98 $19.00 + 0.00
ELSEVIER
Fire Resistant Design of Austenitic Structural Stainless Steel N.R. Baddoo The Steel Construction
and B.A. Burgan
Institute, Silwood Park, Ascot SL5 7QN Paper Number 243
Full paper on enclosed CD-ROM
Owing to their durability, aesthetic appeal and corrosion resistance, the use of stainless steels in construction is continuously increasing. Eurocode 3 Part 1.4 covers the design of structural stainless steels and was issued in 1996. However, there is a shortage of design guidance on the fire resistance of structural stainless steels, and this hinders the materials’ wider use in certain applications. This paper proposes a methodology for predicting the structural behaviour of austenitic stainless steel beams and columns at elevated temperatures. It is mainly based on the results of a sponsored test programme carried out by The Steel Construction Institute on grade 1.4301 (304) austenitic stainless steel. Both isothermal and anisothermal material tests were carried out, with the specimens strained beyond 3%. Material strength reduction factors at elevated temperatures were developed from the results of anisothermal tests. A comparison between the behaviour of carbon steel and stainless steel at elevated temperatures concludes that stainless steel grade 1.4301 (304) retains higher strength reduction factors than carbon steel at temperatures above about 500°C (and significantly higher values of Young’s Modulus). The member test programme consisted of fire tests on four columns (length 3.4 m) and two beams supporting concrete slabs (span 4.25 m). The performance of the stainless steel beams and stainless steel columns with a non-slender cross-section, both in terms of fire resistance and critical temperature, was superior to that of carbon steel beams and columns at similar utilisation factors. The behaviour of stainless steel at elevated temperatures differs from carbon steel for the following reasons: ??
the strength of stainless steel degrades in a different manner from that of carbon steel, 458
Fire Resistant Design of Structural Stainless Steel
459
stainless steel retains a higher Young’s Modulus at elevated temperatures than carbon steel, austenitic stainless steel work hardens at a higher rate than carbon steel, thus cold formed corners are significantly stronger than the base material and retain their superior strength up to temperatures of 600°C to 8OO”C, austenitic stainless steel expands some 30% more than carbon steel. Fire resistant design for carbon steel in Eurocode 3: Part 1.2 was reviewed. With appropriate strength reduction factors derived from anisothermal tests, accompanied by test results on stainless steel members, there is no reason why the scope of this standard cannot be extended to cover stainless steels also. Design approaches for austenitic stainless steel columns and beams supporting concrete slabs are proposed, however further material and member tests, supplemented by numerical analyses, are in progress to verify these approaches. In particular, it is important to study the behaviour of members with slender cross-sections since many roll formed stainless steel members will be slender and the design approach in Eurocode 3: Part 1.2 for slender carbon steel cross-sections is very conservative. It is proposed that this methodology be used as a basis for extending the scope of Eurocode 3: Part 1.2 Structural Fire Design from carbon steel to include stainless steels. 0 1998 Elsevier Science Ltd. All rights reserved
KEYWORDS
Austenitic stainless steel, fire, design, beams, columns, Eurocode 3: Part 1.2.
46, Nos. 1-3, pp. 45&459, paper number 243, 1998 01998 Elsevier Science Ltd. All rights resewed Printed in Great Britain PII: SO145974X(98)00150-8 0143-974XI98 $19.00 + 0.00
ELSEVIER
Fire Resistant Design of Austenitic Structural Stainless Steel N.R. Baddoo The Steel Construction
and B.A. Burgan
Institute, Silwood Park, Ascot SL5 7QN Paper Number 243
Full paper on enclosed CD-ROM
Owing to their durability, aesthetic appeal and corrosion resistance, the use of stainless steels in construction is continuously increasing. Eurocode 3 Part 1.4 covers the design of structural stainless steels and was issued in 1996. However, there is a shortage of design guidance on the fire resistance of structural stainless steels, and this hinders the materials’ wider use in certain applications. This paper proposes a methodology for predicting the structural behaviour of austenitic stainless steel beams and columns at elevated temperatures. It is mainly based on the results of a sponsored test programme carried out by The Steel Construction Institute on grade 1.4301 (304) austenitic stainless steel. Both isothermal and anisothermal material tests were carried out, with the specimens strained beyond 3%. Material strength reduction factors at elevated temperatures were developed from the results of anisothermal tests. A comparison between the behaviour of carbon steel and stainless steel at elevated temperatures concludes that stainless steel grade 1.4301 (304) retains higher strength reduction factors than carbon steel at temperatures above about 500°C (and significantly higher values of Young’s Modulus). The member test programme consisted of fire tests on four columns (length 3.4 m) and two beams supporting concrete slabs (span 4.25 m). The performance of the stainless steel beams and stainless steel columns with a non-slender cross-section, both in terms of fire resistance and critical temperature, was superior to that of carbon steel beams and columns at similar utilisation factors. The behaviour of stainless steel at elevated temperatures differs from carbon steel for the following reasons: ??
the strength of stainless steel degrades in a different manner from that of carbon steel, 458
Fire Resistant Design of Structural Stainless Steel
459
stainless steel retains a higher Young’s Modulus at elevated temperatures than carbon steel, austenitic stainless steel work hardens at a higher rate than carbon steel, thus cold formed corners are significantly stronger than the base material and retain their superior strength up to temperatures of 600°C to 8OO”C, austenitic stainless steel expands some 30% more than carbon steel. Fire resistant design for carbon steel in Eurocode 3: Part 1.2 was reviewed. With appropriate strength reduction factors derived from anisothermal tests, accompanied by test results on stainless steel members, there is no reason why the scope of this standard cannot be extended to cover stainless steels also. Design approaches for austenitic stainless steel columns and beams supporting concrete slabs are proposed, however further material and member tests, supplemented by numerical analyses, are in progress to verify these approaches. In particular, it is important to study the behaviour of members with slender cross-sections since many roll formed stainless steel members will be slender and the design approach in Eurocode 3: Part 1.2 for slender carbon steel cross-sections is very conservative. It is proposed that this methodology be used as a basis for extending the scope of Eurocode 3: Part 1.2 Structural Fire Design from carbon steel to include stainless steels. 0 1998 Elsevier Science Ltd. All rights reserved
KEYWORDS
Austenitic stainless steel, fire, design, beams, columns, Eurocode 3: Part 1.2.