Fire performance of Fibre Reinforced Polymer (FRP) bars in reinforced concrete: an experimental approach
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Date
28/11/2019Author
McIntyre, Emma Ruth Elizabeth
Reid, Emma Ruth Elizabeth
Metadata
Abstract
During the past two decades, Fibre Reinforced Polymer (FRP) bars have been applied
as viable alternatives to internal steel reinforcement of concrete, owing to their
numerous benefits over steel reinforcement including comparatively high tensile
strength and non-corrosive properties. However, there are limitations on the use of
FRP as reinforcement, where fire resistance of structures is required, due to a lack of
understanding of the behaviour of FRP materials at elevated temperature. This
hinders application of FRP materials in many cases.
To understand the complexities of FRP bars’ response at elevated temperature, this
thesis examines current design guidance and literature to highlight gaps in
understanding. The experimental work within the thesis focusses on three
commercially available FRP bars; two Glass FRP (GFRP) bars and one Carbon FRP
(CFRP) bar. Bench-scale characterisation tests using Dynamic Mechanical analysis
(DMA) and Thermogravimetric analysis (TGA) have been performed to understand
the deterioration of FRP bars at elevated temperature. The experimental work has
defined a glass transition (Tg) and decomposition temperature (Td) range for each of
the FRP bars.
Using the results from the bench-scale characterisation tests and direct tensile tests,
a novel predictive model for the reduction in tensile strength of FRP materials at high
temperature has been proposed. A study on the bond capacity of fibre reinforced
polymer (FRP) bars in concrete at elevated temperature demonstrated the
requirement for cold anchorage of the reinforcement.
To further determine the impact of cold anchorage on FRP reinforced concrete (RC)
beams, tests were carried out with both continuous and lap spliced FRP at ambient
temperature and under sustained load with transient localised heating. Cold
anchorage of the reinforcement was maintained throughout testing and confirmed
with local temperature measurements. The results demonstrate that cold anchorage
(i.e. maintained below the onset of the glass transition range) of FRP bars is necessary
to ensure their safe use as internal reinforcement in concrete, unless unrealistically
deep concrete cover is provided. Cold anchorage may be provided in a number of
ways; continuity of reinforcement across compartments, bent bars in the anchorage
zone or increased concrete cover at anchorage zones. Where this is provided the
performance of FRP bars is demonstrated – for the particular conditions of the current
study – to be satisfactory under full service loads and at reinforcement temperatures
exceeding the decomposition of the polymer matrix (>380°C for the bars in the current
study).
The research has identified a minimum suite of tests necessary to characterize thermo-mechanical
behaviour of proprietary FRP bars. By understanding the effects of
temperature on the polymer resin matrix and on the FRPs’ tensile and bond
properties, and by rationally optimizing the placement and anchorage of the bars, this
thesis has demonstrated FRP reinforcements may be designed as fire-safe alternatives
to steel reinforcement for concrete.