The fire resistance of reinforced concrete beams, computed as per three codes, namely, ACI 216.1, Eurocode 2, and AS 3600, is compared with that predicted from finite element analysis. A macroscopic finite element model, capable of tracing the behavior of restrained reinforced concrete beams from pre-fire stage to collapse, is used in the analysis. The model accounts for high temperature material properties, fire-induced strains (thermal, transient, and creep strains in addition to mechanical strain) and restraint effects as a result of fire exposure. Since restraint has a significant effect on fire resistance of reinforced concrete beams, the comparison is carried out for four cases of reinforced concrete beams with different boundary conditions. The first case represents a simply supported beam, while the other three cases represent axially restrained, rotationally restrained, and axially and rotationally restrained beams, respectively. Through the results of the case studies, it is shown that there is a large variation in the fire resistance predictions from the three codes, with Eurocode 2 being the most conservative and ACI 216.1 being the least conservative. It is also shown that the degree of axial restraint, rotational restraint, and type of failure criteria have significant influence on the fire resistance of reinforced concrete beams.

One of the new techniques to reduce explosive spalling in concrete subjected to fire is to add a cocktail of polypropylene fibers and steel fibers into the concrete mixture. This method is still in the early stages of development and requires more research to investigate the efficiency of introducing such a combination of fibers in reducing explosive spalling in fire. The purpose of this paper is to present the results of an experimental study conducted to investigate the performance of reinforced concrete columns containing steel and polypropylene fibers under different loadings and subjected to severe fire conditions. Two loading levels were investigated representing 0.6 and 0.76 of the ultimate strength limits of ACI 318. Columns containing polypropylene (1 kg/m3) and steel fibers (80kg/m3) showed a higher fire resistance by an average factor of 1.76 compared to columns containing PP fibers (1 kg/m3) only. The paper also assesses the effect of adding steel and polypropylene fibers on the severity of concrete explosion under fire. Measurements of axial displacements and concrete temperatures are presented in this paper. The paper compares the obtained experimental values of the axial displacements with theoretical values calculated using a previously developed simple approach.

A hydrocarbon fire test was conducted on nine concrete slabs incorporating three different types of binders: 100% ordinary portland cement (OPC), 50% OPC, and 50% ground-granulated blastfurnace slag (GGBFS), and alkali-activated slag (AAS). The specimens (780 mm [30.71 in.] x 360 mm [14.17 in.]) were made with three different thicknesses (100 mm [3.94 in.], 200 mm [7.87 in.] and 400 mm [15.75 in.]). Specimens were tested at an age of six months when the strengths were about 75 Mpa (10,877 psi). The specimens were exposed to the hydrocarbon fire on one side. Explosive spalling only occurred in the 400 mm (15.75 in.) AAS concrete specimen that had a lower moisture content and higher permeability than the OPC and OPC/slag concretes. This suggests that the well-renowned moisture clog theory is unlikely to be a predominant mechanism of spalling in AAS concrete. It is speculated that high thermal gradients caused explosive spalling in the AAS concrete specimen.

Effects of elevated temperature exposure and various factors, including water-to-cementitious material ratios (w/cm), curing conditions, heating rates, test methods, and polypropylene (PP) fibers, on (1) pore pressure buildup and potential for explosive spalling and on (2) degradation of mechanical properties in normal-strength (NSC) and high-strength concrete (HSC) are presented. Degradations of mechanical properties were measured using 100 x 200 mm cylinders, heated to temperatures of up to 600 °C at 5 °C/min, and compared with results of other studies and existing codes. Pore pressures were measured using 100 x 200 x 200 mm blocks, heated to 600 °C at 5 °C/min and 25 °C/min. Experimental evidences of the complex, temperature-dependant moisture transport process that significantly influenced pore pressure and temperature developments are described.

This paper presents the state-of-the-art review and research needs assessment of the fire performance of reinforced concrete (RC) columns. The literature review revealed that almost all of the fire tests have been undertaken on RC columns under standard fire scenarios and were narrow in scope due to limitations in test equipment and loading capacities. There have been limited analytical studies on modeling the fire behavior of RC columns and were mainly based on elemental approach and either neglected spalling or used a very simple and crude model for representing spalling. Most of the current provisions, in codes and standards, for evaluating fire resistance are based on prescriptive approaches and do not include significant parameters that affect fire resistance. Based on this comprehensive review, research needs for developing rational fire design methods for RC columns through a performance-based approach, is highlighted.