Effect of upgrading concrete strength class on fire performance of reinforced concrete columns

Abstract

High strength concrete (HSC) has become a commonly used material over the last decades, in particular in tall buildings where it allows to increase the net marketable area. As it carries loads more efficiently than normal strength concrete (NSC), it is also specified where architectural considerations call for small support elements. The reduction in member size that can be obtained with HSC results in an increase in usable area. Alternatively, for a fixed column size, longer spans can be supported which leads to a reduced number of supports. HSC also provides advantages in terms of durability. These advantages have resulted in the increased use of HSC observed lately in various applications of civil engineering.An important requirement for building structures is the performance under fire situations. Previous research has shown that HSC behaves differently than NSC at elevated temperature (Phan and Carino, 1998). The most notable differences regard the relative loss of compressive strength with temperature and the occurrence of spalling. For these two aspects, the performance of HSC is lower than that of NSC, i.e. HSC experiences higher rates of strength loss with temperature and a higher susceptibility to spalling. In addition, HSC is often used to reduce the size of structural members. However, this reduction may be detrimental to the fire performance as it leads to faster temperature increase in the section core of the members, and in-

Is it reasonable to use high-strength concrete columns under fire conditions?

“…The outcome of the study agrees with previous findings of Gernay et al (2017) on circular concrete columns. Despite their quicker heating, slender high-strength concrete columns benefit from high initial reserves.…”

“…It was found from the numerical results that tensile stresses in the fire-exposed columns could reach up to 8.69 MPa, which can result in spalling of the columns unless they are sufficiently reinforced. Gernay et al (2017) conducted a numerical analysis using the finite element code Safir. They focussed on the effect of higher concrete strengths on the fire performance of reinforced concrete columns.…”

“…The studies focussed on the fire performance of columns out of normal and high-strength concrete, depending on the load ratio and eccentricity, boundary conditions and times of fire exposure. Gernay et al (2017) already investigated on the relative fire performance of high-strength concrete columns. However, there was to date no systematic investigation on the question whether there is a reasonable lower limit for fire-exposed high-strength concrete columns.…”