Fire Resistance Of Reinforced Concrete Beams Research Articles

Study on the fire resistance of RC beams reinforced with BFRP and HFRP bars

For non-metallic reinforcement to be successfully integrated into residential and commercial construction, extensive research is required to understand the structural performance of Fiber Reinforced Polymer (FRP) reinforced concrete (RC) elements in various conditions, including the effect of elevated temperatures on structural performance. To accomplish this, a full-scale investigation was performed on the structural performance of FRP-RC elements subjected to elevated temperatures. The study involved conducting fire tests on beams, where the midsection was heated from below (tension zone) and the sides while being simultaneously loaded with 50% of their ultimate loads. The beams were reinforced with Basalt FRP (BFRP) bars and a hybrid composite of Carbon and Basalt Fibers (HFRP) bars. The HFRP-RC beams showed better resistance to the combined effect of loading and elevated temperatures compared to BFRP-RC beams. This study provides insights into the behavior of FRP materials in RC structures subjected to high temperatures, and contributes to the advancement of knowledge in this field.

Effect of concrete cover thickness on deflection of reinforced concrete beams exposed to fire

Fire is one of the extreme loads acting on constructional structures. When a fire occurs, fire causes negative effects on reinforced concrete (RC) structures. Specifically, fire increases the deformation demand and reduces the load-carrying capacity of RC structures. When these changes approach a certain extent, failure of structures occurs. RC beams, a part of structures, is directly affected by fire, in which the concrete cover plays an important role in the temperature of steel reinforcement. This paper presents the simulation results on the effects of concrete cover thickness on the deflection of RC beams exposed to fire. To achieve this aim, RC beams simultaneously subjected to loads and exposed to ISO 834 fire were analyzed. The simulations were performed using SAFIR software. The thermal analysis results were used to analyze the deflections of fire-exposed RC beams with respect to fire time. The analytical results show that the deflection increases almost linearly with the fire time in the first stage and then the nonlinearity increases rapidly until complete collapse. The thickness of concrete cover plays an important role on the relationship between the deflection and the fire time of RC beams. When the thickness of concrete cover increases from 20 mm to 45 mm, the fire resistance of RC beams increases by 67%.

A simplified method to predict the fire resistance of RC beams strengthened with near-surface mounted CFRP

A simplified method was proposed to predict the fire resistance of flexure-dominated reinforced concrete (RC) beams strengthened with near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP). Based on the results of previous experimental observations and theoretical analyses, “steel yielding after FRP slipping” and “FRP fracture after steel yielding” were presumed to be the possible failure modes for NSM-FRP strengthening system under fire. An algorithm was thus developed to evaluate the fire resistance of the strengthening system. A series of pull-out tests were carried out to obtain the bond-slip relationships of NSM-FRP at different elevated temperatures for the proposed algorithm. Then this method was used to predict the fire resistance of nine RC beams strengthened with NSM-FRP, which were subjected to a sustained load and the ISO834 standard fire. The predictions showed good agreement with the test results, indicating the effectiveness of the proposed method. This study provides a helpful reference for the fire resistance design of flexure-dominated RC beans strengthened with NSM-FRP in engineering practice.

Contribution to the Numerical Modelling of the Spalling Phenomenon: Case of a Reinforced Concrete Beams

The paper presents a numerical study of reinforced concrete (RC) beams in fire, in which spalling is taken into account in a simplified manner and its effects on the structural response are investigated. Finite element simulations are conducted using the software SAFIR. The criteria to determine the onset of spalling are the temperature reached in the finite element: concrete layers are removed when their temperature reaches \(400\,{^{\circ }}\hbox {C}\). The effect of spalling on the temperature distribution inside the beam section and on the time of failure is discussed. Different configurations are studied, in terms of extent of spalling along the beam and type of supports. Further, it is also shown that the extent of spalling has significant influence on the fire resistance of RC beams and that this is by reducing the failure time and/or by reducing the yield strength and tangent modulus.

Fire resistance of RC beams under design fire exposure

This paper presents the development of a design approach for predicting the fire resistance of reinforced concrete (RC) beams exposed to design fire. The proposed method is based on the energy-based time equivalence method in combination with a correction factor that is formulated as a function of concrete cover depth and compartmental characteristics. In the proposed approach, the fire resistance period of an RC beam under design fire exposure can be deduced from that of the same RC beam under standard fire exposure; the latter can be predicted using a set of explicit equations previously developed by the authors. The fire resistance data of RC beams under design fire exposure, which were used to formulate and validate the proposed approach, were generated using a reliable finite-element approach. The proposed design approach is shown to be accurate in predicting the fire resistance of RC beams under design fire exposure.

Experimental study on the fire resistance of RC beams strengthened with near-surface-mounted high-Tg BFRP bars

A lack of knowledge regarding the fire resistance of fiber reinforced polymer (FRP) reinforced/strengthened concrete structures has impeded the wide acceptance and use of these materials. This paper presents the results of both mechanical property tests performed on basalt FRP (BFRP) bars during and after exposure to high temperatures and the fire resistance of reinforced concrete (RC) beams strengthened with near-surface-mounted (NSM) high-Tg BFRP bars. Experiments were conducted on 108 effective tensile test specimens and 7 four-point bending beam specimens. The results indicate that a resin matrix with a higher Tg value and good compatibility after pultrusion curing process with fiber were very useful for improving the heat resistance of FRP bars, meaning that NSM FRP strengthened RC beams could exhibit improved fire resistance. The FRP bars maintained sufficient anchorage if only two ends of the NSM FRP bar were protected against fire by stretching them into supporting components or wrapping them with U-shaped fire protection boards. The NSM high-Tg FRP strengthened RC beams could potentially exhibit the same level of fire resistance as the RC beams. These preliminary conclusions improve the prospects of using FRP materials in engineering applications.

Effect of high temperature on properties of steel slag aggregate concrete

The use of slag as a fire-resistant aggregate was investigated in concrete and in structural members. Three mixtures of three-fractional concrete with type CEM I 52.5N cement were prepared: the reference mixture (dolomite fractions of 0–4mm, 4–8mm and 8–16mm) and two mixtures with coarse slag fractions (4–8mm and 8–16mm) and a fine dolomite fraction (0–4mm). At 56 days the specimens were exposed to high temperatures. Their residual mechanical properties (flexural strength, compressive strength and static modulus of elasticity) and residual mass were tested after cooling, and results were compared among specimens. To determine the fire resistance of a structural member with slag in the concrete mixture, fire resistance of reinforced-concrete beams with slag was compared with that of reinforced-concrete beams with dolomite. In these experiments, concrete beams were exposed to high temperature according to the ISO 834 temperature curve for 60min. The temperature increase within the beams during their exposure to high temperature in the furnace was also observed. Bearing capacity was tested after fire exposure and compared with bearing capacity of the beams at room temperature. The results showed that slag in combination with Portland cement did not increase fire resistance of concrete and its structural members. In order to create a structural member with improved fire resistance, slag should be combined with a binder that can better adapt to slag expansion under high temperature or be used as a partial replacement for coarse aggregate in concrete.

Design equation for predicting fire resistance of reinforced concrete beams

An approach for evaluating the fire resistance of reinforced concrete (RC) beams is presented in this paper. A macroscopic finite element model is applied to study the influence of various parameters on the fire resistance of RC beams. Data from parametric studies is utilized to develop a simplified expression for evaluating the fire resistance of an RC beam as a function of influencing parameters. The validity of the proposed approach is established by comparing the fire resistance predictions with those obtained from finite element studies as well as from fire resistance tests. Predictions from the proposed equation are also compared with fire resistance estimates from current codes of practice. The applicability of the approach to design situations is illustrated through a numerical example. The proposed rational approach expresses fire resistance in terms of conventional structural and material design parameters, and thus facilitates easy evaluation of fire resistance. The proposed approach provides better estimates than those from current codes of practice and thus can be used to evaluate the fire resistance of RC beams with an accuracy that is adequate for design purposes.

Effect of Fire Induced Restraint on Fire Resistance of Reinforced Concrete Beams

The effect of fire induced restraint on the fire response of reinforced concrete (RC) beams is addressed in this paper. A macroscopic finite element model, capable of tracing the behavior of restrained RC beams from pre-fire stage to collapse in fire is used in the analysis. The model is applied to investigate the effect of five parameters; namely, degree of axial restraint, span-to-depth ratio, fire scenario, load level, and failure criteria on the fire response of restrained RC beams. Through the results of the parametric study, it is shown that the five parameters have significant influence on fire resistance of RC beams. It is also shown that, fire induced restraint has negative effect on fire resistance of slender RC beams having high span-to-depth ratio.

Flexural response of reinforced concrete beams exposed to fire

The flexural response of reinforced concrete (RC) beams exposed to fire is investigated in this paper. A macroscopic finite element model, capable of tracing the behaviour of RC beams from pre-fire stage to collapse in fire is used in the analysis. The model includes the three stages associated with fire resistance analysis, namely establishing the fire temperature–time development, calculating the heat transfer through the structure from fire and the structural analysis. The model is applied to investigate the effect of six parameters, namely the fire scenario, load level, concrete cover thickness, aggregate type, failures criteria and span length on the fire response of RC beams. Through the results of the parametric study, it is shown that the type of failure criterion, load level, fire scenario, concrete cover thickness and aggregate type have significant influence on fire resistance of RC beams. It is also shown that, while the span length has significant influence on the overall fire behaviour, it h...

Performance-based Fire Safety Design of Reinforced Concrete Beams

A numerical model, in the form of a computer program, is presented for tracing the fire behavior of reinforced concrete (RC) beams over the entire range of loading from pre-fire conditions to collapse under fire. The three stages associated with the analysis of fire resistance; namely, establishing the fire temperature-time development, calculating the heat transfer through the structure from the fire, and the structural analysis are explained. The model, which accounts for nonlinear material properties at elevated temperatures, is capable of predicting the fire resistance of RC beams under realistic fire scenarios, load levels, and failure criteria. The validity of the numerical model is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. Through the results of numerical study, it is shown that the type of failure criterion, load level, and fire scenario have significant influence on fire resistance of RC beams. The computer program can be used to undertake performance-based fire safety design of RC beams for any value of the significant parameters, such as fire exposure, concrete cover thickness, section dimensions, concrete strength, concrete type, and load intensity.

A numerical model for predicting the fire resistance of reinforced concrete beams

A numerical model, in the form of a computer program, for tracing the behavior of reinforced concrete (RC) beams exposed to fire is presented. The three stages associated with the numerical procedure for evaluating fire resistance of RC beams; namely, fire temperature calculation, thermal analysis and strength analysis, are explained. A simplified approach to account for spalling under fire conditions is incorporated into the model. The use of the computer program for tracing the response of RC beams from the initial pre-loading stage to collapse stage, due to the combined effect of fire and loading, is demonstrated. The validity of the numerical model is established by comparing the predictions from the computer program with results from full-scale fire resistance tests. Through the results of numerical study, it is shown that the type of failure criterion has significant influence on predicting the fire resistance of RC beams.