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The purpose of the study was to investigate the spalling phenomenon in ultra-high performance fibre reinforced concrete (UHPFRC) beams on exposure to a standard fire curve (ISO 834) under a sustained load.

The variables in this study were steel fibre dosage, polypropylene (PP) fibres and loading levels. The research investigated seven beams – three of which contained steel fibres with 2 vol.%, another three had steel fibres with 4 vol.% dosage and the seventh beam had a combination of steel fibres (2 vol.%) and PP fibres (4 kg/m³). The beams were tested for 1 h under three loading levels (20, 40 and 60 per cent) based on the ambient temperature ultimate flexural strength of the beam.

Spalling was affected by the loading levels; it exacerbated under the load level of 40 per cent, whereas under the 60 per cent load level, significantly less spalling was recorded. Under similar loading conditions, the beams containing steel fibres with a dosage of 4 vol.% spalled less than the beams with fibre contents of 2 vol.%. This was attributed to the additional tensile strength provided by the excess steel fibres. The presence of PP fibres eliminated spalling completely.

There is insufficient research into the performance of UHPFRC beams at elevated temperature, as most studies have largely focussed on columns, slabs and smaller elements such as cubes and cylinders. This study provides invaluable information and insights of the influence of parameters such as steel fibre dosage, PP fibres, loading levels on the spalling behaviour and fire endurance of UHPFRC beams.

The paper aims to present an advanced 2 D transient heat transfer analysis capable of accounting for the effect of spalling in terms of amount, location and time. The model accounts for moving thermal boundary conditions to comply with the changing member cross section. The discussed numerical model provides a tool to quantify the effect of spalling on the flexural capacity of reinforced concrete beams.

The implementation of the presented numerical model in an in-house code and its validation has been discussed. The thermal subroutine has been sequentially coupled with the mechanical subroutine (sectional-analysis) to compute the variation of sectional moment carrying capacity with exposure time.

The temperatures predicted while considering spalling were in good agreement with experiments available in literature. The presented results also emphasise the importance of considering the time of spalling. The results also show that the fire rating of simply supported beams is also affected by spalling in the compression zone.

It should be acknowledged that the model does not predict spalling, rather is developed as a tool to study the effect of spalling. The model takes the information related to spalling in terms of the location, amount and time, as user input.

The paper quantitatively presents the effect of spalling on the predicted temperature variation across the beam cross section and the moment carrying capacity.

This study aims to investigate the influence of tendon layout, pre-stressing force, bond condition and concrete spalling on the structural behaviour of two-way post-tensioned flat slabs at elevated temperatures.

Fire tests of four scale specimens of two-way post-tensioned concrete flat slabs were performed and analysed. Three of them were provided with bonded tendons, while the other was unbonded for comparison. The fabrication of specimens, phenomena observed during testing, temperature distributions, deflections and occurrence of concrete spalling were examined.

Different degrees of concrete spalling observed at the soffit had significant effects on the temperature distribution and stress redistribution. This was the major reason for the progressive concrete spalling observed, resulting in loss of structural integrity and stiffness.

The structural behaviour of two-way post-tensioned concrete flat slabs at elevated temperatures is less understood compared to their one-way counterparts. Therefore, the present study has focused on the structural behaviour of two-way post-tensioned concrete flat slabs with bonded tendons in fire, a field in which relatively little information on experimental work can be found.

Incidents like the fire in the Channel Tunnel, where severe concrete spalling was determined, have led to requirements in limiting the spalling depth and involved zone to local and compatible magnitudes. Because the prevention of critical concrete spalling was also significant for the validity of the load-carrying capacity calculation for an existing railway tunnel, this paper aimed to investigate the spalling behavior of two contemplable concrete mixtures. The large-scale tests should show the load-carrying capacity over the whole duration of the fire exposure respecting all thermal and mechanical loads considered in the calculations.

In this paper, the fire behavior of two concrete mixtures for an existing railway tunnel are investigated. Small-scale tests prior to the main tests were conducted to identify an appropriate concrete mixture for the large-scale tests. During the large-scale tests, a tunnel segment is loaded with horizontal and vertical loads derived from a calculation taking into account the existing boundary conditions. Resulting restraint forces were calculated using the soil stiffness and tunnel fire design curve as fire scenario and applied via hydraulic jacks. To avoid additional restraint forces during the experiment, thermal strains due to fire exposure were allowed.

The results of the small-scale tests did not allow for a clear statement whether one concrete mixture would perform better regarding the spalling behavior. The two large-scale tests showed different results regarding the spalling behavior. Over the whole duration of fire exposure, the first test specimen remains nearly undamaged. During the test of the second specimen, spalling started about 3 min after burner activation. Because of the results, a suggestion for the concrete mixture of the first test was made, and this mixture was then used for the redevelopment of the existing railway tunnel.

The test setup was capable of incorporating all relevant boundary conditions for the analysis of an existing railway tunnel as part of an important north – south connection. The results have shown that a fire-proof construction is possible by adding polypropylene fibers to the concrete mixture. Additionally, it was possible to avoid the mounting of expensive and time-consuming fire protection measures like the installation of thermal insulation boards.

The purpose of this paper is to examine the effect of various polypropylene fibre additions (types and volume) to concrete with regard to explosive spalling when subject to high temperatures similar to those experienced in building or tunnel fires.

Medium strength concrete was manufactured with varying proportions of polypropylene fibres. Plain control samples were used to determine the original concrete strength and this was used as a benchmark following high temperature heat tests to evaluate the surface condition and final compressive strength. A pilot study was used to determine an appropriate heat source for the test. This was three Bunsen burners, however sufficient heat could not be generated within 150 mm concrete cubes and the concrete was shown to be a significant insulator and fire protection for structural members. The concrete test cubes were tested in a saturated condition which may reflect conditions where concrete is used in an external environment and thus is subject to soaking.

One hundred and fifty millimetre concrete cubes with and without fibres were placed into a furnace at 1,000°C. Explosive spalling was shown to be reduced with the use of polypropylene fibres but the final compressive strength of concrete was significantly reduced and had little residual structural value after a two hour period of heating.

As the concrete tested was saturated, this condition provided a worst case scenario with regards to the build up of hydrostatic and vapour pressure within the cube. A range of percentage moisture contents would produce a more evenly balanced view of the effects of fibres in concrete. A single grade of concrete was used for the test. As the permeability of concrete influences the rate at which steam can escape from the interior of a saturated concrete cube, testing a range of concrete strengths would show this aspect of material performance with regard to spalling and final residual strength. Further research is recommended with regard to moisture contents, strengths of concrete and a range of temperatures.

This research has significance for the designer, in that buildings subject to terrorist activity may suffer from impact damage and an outbreak of fire following the initial attack.

The use of polypropylene fibres in concrete to provide anti spalling qualities is relatively new and this research adds to the knowledge regarding fibre type and volume with regard to first spall time, total area and number of areas subject to spalling and the final compressive strength of concrete following two hours of raised temperatures.

This study examines the effect of temperature-dependent material models for normal-strength (NSC) and high-strength concrete (HSC) on the thermal analysis of reinforced concrete (RC) walls.

The study performs an one-at-a-time (OAT) sensitivity analysis to assess the impact of variables defining the constitutive and parametric fire models on the wall's thermal response. Moreover, it extends the sensitivity analysis to a variance-based analysis to assess the effect of constitutive model type, fire model type and constitutive model uncertainty on the RC wall's thermal response variance. The study determines the wall’s thermal behaviour reliability considering the different constitutive models and their uncertainty.

It is found that the impact of the variability in concrete’s conductivity is determined by its temperature-dependent model, which differs for NSC and HSC. Therefore, more testing and improving material modelling are needed. Furthermore, the heating rate of the fire scenario is the dominant factor in deciding fire-resistance performance because it is a causal factor for spalling in HSC walls. And finally the reliability of wall's performance decreased sharply for HSC walls due to the expected spalling of the concrete and loss of cross-section integrity.

Limited studies in the current open literature quantified the impact of constitutive models on the behaviour of RC walls. No studies have examined the effect of material models' uncertainty on wall’s response reliability under fire. Furthermore, the study's results contribute to the ongoing attempts to shape performance-based structural fire engineering.

The aim of the research was to investigate the effect of concrete strength on the fire resistance of structures. At first, it may seem contradictory that higher concrete strengths can decrease the fire resistance of building structures. However, if the strength of the concrete exceeds a maximum value, the risk of spalling (the detachment of the concrete surface) significantly.

Prefabricated structural elements are often produced with higher strength. The higher concrete strengths generally do not cause a reduction in the load bearing capacity, but it can have serious consequences in case of structural fire design. Results of two prefabricated elements, namely, one slab (TT shaped panel) and one single layer wall panel, were examined. Results of the specimen with the originally designed composition and a specimen with modified concrete composition were examined, were polymer fibres were added to prevent spalling.

As a result of the experiments, more strict regulations in the standards the author is suggested including more strict regulations in the standards. It has been proved that to ensure the fire safety of the reinforced concrete structures, it is required after polymer fibres even in lower concrete strength class than prescribed by the standard. In addition, during the classification and evaluation of structures, it is advisable to introduce an upper limit of allowed concrete strength for fire safety reasons.

As a result of the experiments, the author suggests including more strict regulations in the standards. It has been proved that to ensure the fire safety of the reinforced concrete structures, it is necessary to require the addition of polymer fibres even in lower concrete strength class than prescribed by the standard. In addition, during the classification and evaluation of structures, it is advisable to introduce an upper limit of allowed concrete strength for fire safety reasons.

This paper aims to understand the structural fire performance of two-way post-tensioned flat slabs, particularly their deformations and load-carrying mechanisms in fire, and to explore the behaviour of post-tensioned high-strength self-compacting concrete flat slabs with unbonded tendons in fire.

Four tests of post-tensioned high-strength self-compacting concrete flat slabs were conducted under fire conditions. Numerical modelling using the commercial package ABAQUS was conducted to help interpret the test results.

Two of the specimens with lower moisture contents demonstrated excellent fire resistance performance, while the others with slightly higher moisture contents experienced severe concrete spalling.

The test results were discussed in respect of thermal profiles, deflections, crack patterns and concrete spalling. The performance of post-tensioned high-strength self-compacting concrete flat slabs with unbonded tendons under fire conditions was better understood.

The exposure of concrete elements to high temperatures during fire can cause major risk to life safety and to the serviceability of a building. One of the main reasons for this is due to concrete spalling which caused by pore pressure and thermal stresses. Previous research has indicated that the inclusion of polypropylene fibres to concrete reduces explosive spalling. However, concrete containing polypropylene fibre can still be vulnerable to explosive spalling during fire. This paper presents the outcomes of a research investigating the effect of using steel fibres in addition to polypropylene fibres to reduce explosive spalling of concrete. The experimental part of this study evaluates the performance of six normal strength columns under a loading ratio = 60% of the design capacity and subjected to severe heating rate higher than ISO 834. The columns were cast using various dosages of steel and polypropylene fibres. Analyses of the main findings included evaluation of the measured concrete temperatures along with axial displacement recordings. The analysis demonstrates a clear assessment of the spalling levels of the various representative specimens. The study also compares the experimental axial displacement with theoretical predictions using DIANA. Conclusions drawn from the study indicate that adding steel fibresalong with polypropylene fibres can reduce the degree and severity of spalling if compared with concrete containing polypropylene fibres only. The spalling degree was reduced from 22.03% to 12.41% in best case and from 14.95% to 10.49% in average when steel fibres were used with polypropylene fibres.

The results of a recent study conducted at the US National Bureau of Standards, indicate that spalling in vitreous‐enamelled aluminium is caused by the corrosive attack of moisture and moisture‐salt mixtures at the enamel‐metal interface.