Fiber Reinforced Polymers (FRPs) are efficiently used
for strengthening and rehabilitation of reinforced
concrete (RC) structures especially for retrofitting
of bridges. However, the use of FRPs in buildings
is restricted because of the limited knowledge on
the fire endurance of FRP strengthened concrete structures.
Current structural fire research is mainly focused
on RC members (beams and columns) exposed to standard
fire scenarios. Limited studies have been carried
out on RC structural members strengthened with FRP
under design (realistic) fire scenarios. Current approach
for evaluating the fire resistance of FRP-strengthened
RC structural members is prescriptive in nature and
does not account for realistic fire scenarios and
loading conditions. There is insufficient information
on the behavior of FRP-strengthened RC beams under
realistic fire, loading and failure limit states.
This lack of knowledge is a major obstacle for using
FRP in buildings and parking structures. Further,
unlike concrete and steel, various types of FRP are
available in the market and this makes it hard to
characterize the high temperature performance of FRP-strengthened
structures. In lieu of fire tests, numerical models
can be applied for predicting the performance of FRP-strengthened
RC structures. This research is focused on development
of a numerical model for tracing the fire performance
of FRP strengthened RC beams under real fire exposures.
The proposed numerical model is based on macroscopic
finite element approach and uses sectioned moment
curvature relationships to trace the response of a
FRP-strengthened RC beam from linear elastic range
to collapse under any given fire exposure and loading
scenario. The FRP-strengthened RC beam is divided
into number of segments (meshing) with mid-section
of the segment representing the overall behavior.
The analysis is carried out by incrementing time till
failure of the beam. At each time increment, the fire
resistance analysis is performed three main steps,
namely; computing temperature due to fire exposure,
conducting heat transfer analysis is to establish
the temperature distribution within the cross section
of each segment, and carrying out strength analysis
by generating the moment-curvature relationships and
computing the deflection of the beam at any time increment.
The model accounts for high temperature material properties,
fire scenarios, load level, various strain components
(creep and transient strains), geometric nonlinearity,
softening effect of material, and realistic failure
Elevation of FRP-strengthened RC
Cross Section of the Beam and Discretization for Analysis
The proposed numerical model is capable
of predicting the response of FRP-strengthened RC
beams. The fire resistance of FRP-strengthened beams
is significantly influenced by the type of fire exposure,
load level and insulation schemes. Model do account
for all these critical parameters in analysis. However,
present methods of evaluating the fire resistance
based on standard fire exposure are conservative for
structural members exposed to severe fire conditions.
Temperature at the interface FRP/concrete
for various fire scenarios
Moment-curvature curves at various
fire exposure time
The computer model is capable of tracing
the behavior of FRP-strengthened RC beams from the
initial pre-fire stage to the failure of the beam
under realistic fire scenarios, load level, and all
possible failure criteria. Using the model, an optimum
fire insulation scheme for an FRP-strengthened RC
beam can be developed that will lead to an economical
and rational based design principles.
Blontrock, H. et al., ''Properties
of Fibre Reinforced Plastics at Elevated Temperatures
with Regard to Fire Resistance of Reinforced Concrete
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on Non-Metallic (FRP) Reinforcement for Concrete
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MD, 1999, pp. 43-54.
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the Design and Construction of Externally Bonded
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Reinforced Concrete Beams", Composite & Polycon,
American Composites Manufacturers Association, Tampa,
FL, USA, 2009.