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Solutions for enhancing the fire endurance of HSS columns filled with high strength concrete

NRCC-47362 Kodur, V.R.

January 2006

A version of this document is published in / Une version de ce document se trouve dans:

Engineering Journal, 43, (1), pp. 1-7, 2006

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Solutions for Enhancing the Fire Endurance of HSS Columns Filled with High-Strength Concrete V.K.R. KODUR This paper is published with permissionj'rom the National Research Council of Canada.

S

teel hollow structural section (HSS) columns are very efficient structurally in carrying compression loads and moments and are widely used in the construction of framed stmctures in oftice and industrial buildings. Often these

sections are filled with concrete to enhance the load-bearing capacity. The two components of the composite column complement each other ideally, in that the steel casing confines the concrete laterally, allowing itto develop its optimum compressive strength, while ,the concrete, in turn, enhances resistance to elastic local buckling of the steel wall. Another advantage of concrete filling is that it also increases fire resistance of the column withollt' the need for external fire protection for the steel. This increases usable space in the building. Properly designed concrete-filled columns can lead economically to the realization of architectural and stnlctural design with visible steel. without any restrictions on fire safety (Kodur and Lie, 1995; Klingsch and Wuerker, 1985). [n recent years, high-strength concrete (HSC) has become an attractive alternative to tl"aditional normal~strength concrete (NSC) since it fnrther incrcascs the load-carrying capacity of HSS columns (Prion and Baraka, 1994; Kodur, 1998). As well, the high stiffness of HSC prevents elastic local bnckling in the steel wall while the confinement within the steel HSS enhances the ductility, which sometimes is a major concem for HSC. These advantages have led to the increased use of HSC-filled HSS columns, nnd some of the recent buildings on the Wcst Coast of the United States using this type of construction are given in Table I (Ghosh, 1997). The.benefits from the use of HSC filling can be maximized if the external fire protection is eliminated. The enhancemeht of fire resistance of HSS columns, leading to the use of unprotected concrete-filled HSS columns, has been

Table 1. HSC·Filled HSS Columns In Buildings

Building

No, of Stories

f~,

MPa (psi)

Two Union Square (Seattle, WA)

62

97 (14,000)

Pacific First Center (Seattle, WA)

44

97 (14,000)

Gateway Tower (Seattle, WA)

63

76 (11 ,DOD)

600 California (Los Angeles, CAl

20

66 (9,600)

established forNSC filling [concrete strength below 55 MPa (8,000 psi)] by a number of studies (Kodur and Lie, 1995; Lie and Kodm, 1996a; Kodur, 1999). However, there is little information available in the literature on the fire performance of HSS COIUIlUlS filled with HSC [strength above 55 Mra (8,000 psi)]. Further, the behavior of HSC at elevated temperatnres is significantly different from that of NSC(Phan, 1996; KodUl· and Sultan, 1998). To develop fire resistance information on high~strength concrele~filled HSS columns, experimental and numerical studies were canied out on these columns. In this paper! results of the fire resistance of HSS columns fillcd with HSC concrete are presented I