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incident heat flux measured with and without the presence of a sample at a) the centre of the panels (left hand side) and b) at 3/4 th the height of the panels at the centre of the panels (right hand side) shows that the presence of a sample increased the incident heat flux received by the exposed surface of the sample. For example, when considering the centre point of the target samples at 500 mm standoff, the incident heat fluxes were 21.5 and 20.6 kW/m² for vermiculite and concrete samples, respectively. This compares with 18.36 kW/m² when the heat flux gauge was in free space. However, once the RPA was moved closer to the target sample, the incident radiant heat flux increased drastically in the presence of a sample. When the sample was 200
Source publication
Gas-fired radiant panel arrays (RPA) are commonly used in both standardised testing of building materials and experimental fire research to impose a known thermal boundary condition on a sample. When remote from the sample, RPA provides an incident radiant heat flux of known magnitude. However, gas-fired RPAs also produce convective flows of hot ex...
Contexts in source publication
Context 1
... sample surfaces (of concrete and vermiculite) were then introduced with an embedded heat flux gauge to quantify the influence of the sample. Figure 10 shows the incident heat fluxes measured at the centre of the samples (i.e., directly in front of the mid-point on line A), and at 300 mm on line A. Distance from The Panels (mm) ...
Context 2
... the distance between the RPA and the target sample was a 100 mm, the difference increased to 37%. Figure 10 shows that the hot gases found within the boundary have a measurable influence on the measured values of the incident heat fluxes. However, Figure 8 shows that the there is an increase in the value of incident heat flux even at 200mm, which lies outside the extent of the zone of convective influence generated by the RPA. ...
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Citations
... A recent preliminary study by the authors also demonstrated that the potential for a non-negligible radiative feedback between the target sample and the RPAcausing an increase in the panel surface temperature [14] particularly at smaller separation distances between the RPA and the target samples. This feedback has the potential to invalidate the fundamental assumption of constant panel temperature throughout the duration of an experiment. ...
... This process was repeated at various points across the surface of the RPA. Additional details of the approach used are reported in Ref. [14]. Once these data were gathered, the boundary of the zone of convective influence was (semi-arbitrarily) defined using the criterion given in Equation (1): ...
... To investigate this, and using a mobile RPA at the University of Edinburgh [3,14,15], incident heat fluxes at various separation distances were measured under a range of conditions. Experiments were repeated for varying set-ups, namely: the HF gauge in isolation, the HF gauge embedded in a vermiculite sample, the HF gauge embedded in a concrete sample, and the HF gauge embedded in a water-cooled aluminium plate. ...
... A mobile, gas-fired radiant panel array (RPA) was used for the spalling experiments. The working principles of the RPA are reported elsewhere [9][10][11]. The concrete planks were positioned horizontally (as shown in Figs. 2 and 9) and were tested in a mechanically unrestrained condition (i.e., the samples were free to thermally expand on heating). ...
A novel concrete mix has been developed that can achieve high levels of self-prestressing through the controlled expansion of the concrete sample with cast-in carbon fibre reinforced polymer (CFRP) bars. Experiments have shown that the mechanical properties and durability of the mix are not adversely affected by the mix's self-expanding nature. However, the behaviour of this mix at elevated temperatures is largely unknown, raising legitimate concerns regarding the fire performance of the resulting self-prestressed concrete elements. The research presented in this paper investigates the behaviour of concrete elements manufactured from self-prestressed, self-compacting concrete (SPSCC) when exposed to severe heating-such as would likely be experienced during a building fire. Nine specimens, with dimensions (600 mm × 200 mm × 45 mm) were tested under one-sided exposure to an experimentally simulated ISO 834 standard heating regime. The results showed that the SPSCC samples were acutely prone to explosive spalling under these conditions. The results also suggest that the comparatively higher moisture content of SPSCC samples, as compared with conventional concrete mixes of similar composition and mechanical properties, appeared to be the most critical factor for heat-induced concrete cover spalling. Higher prestress (compressive) forces also appeared to exacerbate the spalling likelihood of SPSCC samples. The addition of 2 kg/m 3 of polypropylene (PP) fibres led to the complete elimination of spalling in SPSCC samples. The self-prestress levels in samples with PP fibres were 30 % less than those without PP fibres, for reasons which require additional investigation. Differential thermal expansion between the internal CFRP bars and the concrete was observed to restrain the elongation and thermal curvature of the samples during heating, up until the point where the bars debonded from the surrounding concrete due to elevated temperature and (presumed) increased tensile stress in the tendon anchorage zones. The results provide compelling evidence supporting the need to include PP fibres within high-performance, self-prestressing, self-compacting concrete slabs.
... The levels of prestress in the samples at the time of testing are given in Table 2. A thermocouple (TC) tree was installed during casting of the HSSCC samples and SPSCC D to record in-depth temperatures during the heating tests using a radiant panel array (RPA) [7], [8]. Figures 1 and 2 show the cross section of the samples (with TC tree) and the locations of the CFRP tendons, as well as the front view of the samples with the heat-exposed area for all the samples except SPSCC samples A, B, and C; the heat exposed area for SPSCC (A-C) was 400 mm by 200 mm. ...
... Spalling experiments were carried out using a gas-fired RPA at the University of Edinburgh. The details and benefits of this testing approach are outlined in [8], [11], [12]. The RPA can achieve high heat fluxes that enables its users to simulate a variety of in-depth heating regimes, including simulation of the in-depth heating that would occur during an ISO 834 standard fire test in a fire testing furnace. ...
1. ABSTRACT A novel concrete mix has been developed at Empa that can achieve high levels of self-prestressing through controlled chemical expansion of the concrete (while hardening) with embedded high modulus carbon fibre reinforced polymer bars. This controlled expansion has been shown to not adversely affect the mechanical properties and durability of the mix at ambient temperature. Until now, the behaviour of self-prestressed concrete elements at elevated temperatures has not been extensively studied. These novel structural elements consist of high performance self-compacting concrete with a compressive strength of more than 50 MPa; scoping experiments have shown that it is susceptible to heat induced explosive spalling when subjected to steep thermal gradients. To investigate this behaviour, three self-prestressed, self-compacting concrete (SPSCC) samples were prepared and cast into moulds with dimensions 500 mm × 200 mm × 45 mm; and one 600 mm × 200 mm × 45mm. Each sample (or plank) was reinforced with two ultra-high-modulus (UHM) carbon fibre reinforced polymer (CFRP) tendons (E11 = 502 GPa). Five high-strength self-compacting concrete (HSSCC) samples (600 mm × 200 mm × 45 mm) were also cast and mechanically prestressed. A further three non-prestressed HSSCC samples were also cast. The samples were subjected to severe heating on one surface at an age of more than three months. Thermal exposure was accomplished using a mobile gas-fired radiant panel array (RPA) at the University of Edinburgh. The effects of the type of concrete mix and the method of prestressing (i.e., mechanical versus self-prestressing) on the samples' behaviour under exposure to one-sided heating was studied. This paper also investigates the effects of mechanical prestressing (i.e., pre-compressive concrete stress), the effects of super absorbent polymers (SAP) within the concrete mix, and the samples' moisture content on the heat-induced spalling behaviour of the planks.
This research study concerns an experimental, budget-friendly, electricity powered
apparatus for bench-scale fire testing. The apparatus consists of various elements, of which the most important are ceramic heating pads, used to impose heat fluxes on exposed surfaces of specimens. The test method allows to control the heating pads’ temperature and to adjust the distance between the heating pads and the specimen to obtain well-defined heat fluxes up to 50–60 kW/m2. Higher heat fluxes and temperatures can be obtained by setting the heating pads in full power mode, with or without the use of a thermal shield, which can lead to heat fluxes up to 150 kW/m2. The heating and thermal boundary conditions imposed by the apparatus are characterised and discussed, and the thickness of the convective boundary layer at the heating pads’ surface is estimated significantly lower than in the case of gas-fired radiant panels. The performance of the apparatus is analysed for various
conditions: controlling the temperature of the heating pads, in an open environment or with the presence of thermal shields, and in full power mode. A few examples of application of the apparatus to fire test typical construction materials (steel and glass) are also presented. These results emphasise the well-defined heating conditions in temperature-controlled mode. The study finally discusses the advantages and limitations of the apparatus, as well as many possibilities of future applications and improvement for future research studies.
