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

PurposeThis paper aims to answer two questions. First, are there any differences in the fire performance of columns made of normal and of high-strength concrete? Second, under which circumstances does the fire design govern the cross-sectional dimensions of concrete columns? Is it feasible to replace columns out of normal strength concrete by more slender high-strength concrete columns?Design/methodology/approachThe author conducted numerical studies using the finite element code “Infocad” of the German company “Infograph”. The studies included the effect of different parameters on the fire performance of columns out of normal and high-strength concrete, i.e. the load ratio and eccentricity, boundary conditions and times of fire exposure.FindingsResults from the numerical investigations showed that high-strength concrete columns suffer much more from heating than normal strength concrete columns. This is the outcome of the unfavourable mechanical properties of high-strength concrete at elevated temperatures. Although the relative fire performance of columns out of high-strength concrete is worse than that of columns out of normal strength concrete, initial load reserves are beneficial to achieve even high fire ratings.Originality/valueMany researchers addressed in experimental and numerical studies the fire performance of columns out of normal and high-strength concrete. A special emphasis was often laid on the spalling of fire-exposed high-strength concrete. However, there are no systematic investigations when the fire design governs the cross-sectional dimensions of high-strength concrete columns. Based on a previous comparison of the relative fire performance of columns out of normal and high-strength concrete, this paper, hence, addresses the question whether there is a reasonable lower limit for the use of these columns. This is an important aspect for designers since there is a tendency to replace columns out of normal strength concrete by columns out of high-strength concrete. Higher concrete strengths allow for smaller cross sections of the columns, and designers may, hence, increase the usable space of buildings.

Experimental study on seismic performance of partially precast steel fiber high-strength concrete columns with high-strength steel bars

To study the cyclic behavior of partially precast steel fiber high-strength concrete columns with high-strength steel bars, four full-sized square column specimens were fabricated and tested under constant axial load and horizontal cyclic load. The effects of the strength of precast concrete shell and the diameter of cast-in-place column core were analyzed in detail. The results show that partially precast steel fiber high-strength concrete columns have good seismic performance and deformation ability. Compared to the concrete column with lower strength of precast concrete shell, the concrete column with higher strength of precast concrete shell showed higher bearing capacity and energy dissipation capacity while lower ductility. Moreover, with the increase of the diameter of cast-in-place column core, the bearing capacity and the deformation ability of the specimen decreased. Finally, based on the experimental research and theoretical analysis, a calculation model for predicting the maximum bearing capacity was proposed, and the results obtained from the formulas were in good agreement with those from the experiments.