Concrete strength for fire safety design

Abstract

Idealised data have been derived for the compressive strength of a number of concretes for fire safety design. The data are derived from the author's own research including test series not published before and from more than 400 other test series comprising approximately 3000 specimens known from literature and personal contact. The data cover a variety of concretes with aggregates such as siliceous materials, limestone, granite, sea gravel, pumice, and expanded clay to fire-resistant concrete based on chamotte or Danish mo-clay. Processes are briefly described that are responsible for the deterioration of the materials when they are heated and when they are cooled down after a fire. In addition, it is explained how variations of the concrete composition influences the deterioration. Necessary characteristics of design methods are derived for variable fire courses based on analyses of consequences of material deterioration. The paper serves as a basis for a number of papers presenting calculation methods developed by the author for load-bearing capacity of any structure of any concrete at any time of any fire exposure. Some of these methods and related materials data are adopted in the CEN: ENV 1992-1-2 code and national codes such as the Danish DS411. The present paper serves as a part of the documentation for the methods and it is therefore also a supporting document for these standards.

Prestressed concrete thermal behaviour

“…The proposed relationships at elevated temperatures are compared separately with experimental data and the Hertz (2005) Abrams (1971) and Phan and Carino (1998). NSC typically loses 10-20% of its original compressive strength when heated to 3008C, and 60-75% at 8008C.…”

Heat transfer and structural response modelling of FRP confined rectangular concrete columns in fire

“…The compressive stress-strain model proposed by Lie [4] for unconfined concrete was used for the analysis of unwrapped reinforced concrete columns, along with the compressive concrete strength model proposed by Hertz [13] for modelling the mechanical response of concrete at elevated temperatures. The corresponding axial strain at ultimate compressive strength (or peak stress) was described by the model proposed by Terro [14].…”

“…Table 2 shows that the model is generally conservative, and under predicts the failure time by between 27% and 46%. The conservatism of the current model can likely be attributed to the fact that the model used the ultimate concrete strength model for unstressed concrete as proposed by Hertz [13] to simulate the structural behaviour of a preloaded concrete column under fire condition. Preloaded concrete may be 25% stronger than an unloaded concrete at elevated temperatures provided that the initial compressive stress from the preload is about 25 to 30% of the initial room temperature compressive strength [13].…”

“…The conservatism of the current model can likely be attributed to the fact that the model used the ultimate concrete strength model for unstressed concrete as proposed by Hertz [13] to simulate the structural behaviour of a preloaded concrete column under fire condition. Preloaded concrete may be 25% stronger than an unloaded concrete at elevated temperatures provided that the initial compressive stress from the preload is about 25 to 30% of the initial room temperature compressive strength [13]. Hence, the model under predicted the failure time by at least 25% in comparison to the failure time observed by Lie and Woollerton [29] during the fire test.…”

Constitutive Model for High Strength Concrete (HSC) at Elevated Temperatures

“…These properties are compressive strength, tensile strength, elastic modulus, creep strain, peak strain, thermal expansion, thermal conductivity and specific heat capacity. Concrete subjected to elevated temperatures in fire experiences a decrease in compressive strength, tensile strength, elastic modulus, an increase in peak strain and a change in the stress -strain relationship [4], [5]. Some models have been proposed for compressive strength, tensile strength, elastic modulus, peak strain and stress -strain relationship for normal strength concrete (NSC) at elevated temperatures but only a few models are available for high strength concrete (HSC) under fire.…”