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Modeling the Fire Performance of FRP-strengthened Reinforced Concrete Beams

Principal Investigators: Venkatesh Kodur, Ph.D.
Research Assistants: Aqeel Ahmed
Funding Agency:  
Period:  



Research Objective

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.

Research Approach

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 criteria.

Elevation of FRP-strengthened RC Beam

 



Cross Section of the Beam and Discretization for Analysis

 

Research Results

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

 

Research Implications

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.

References

  • Blontrock, H. et al., ''Properties of Fibre Reinforced Plastics at Elevated Temperatures with Regard to Fire Resistance of Reinforced Concrete Members,'' Proceedings, 4th International Symposium on Non-Metallic (FRP) Reinforcement for Concrete Structures, American Concrete Institute, Baltimore, MD, 1999, pp. 43-54.
  • ACI Committee 440, "Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures," (ACI 440.2R-02), American Concrete Institute, Farmington Hills, MI, 2004, pp. 3.
  • Williams, B. et al., "Fire Insulation Schemes for FRP-Strengthened Concrete Slabs," Composites Part A, Vol. 37, 2005, pp. 1151-1160.
  • Williams, B. et al., "Fire endurance of Fiber-reinforced polymer strengthened concrete T-beams", ACI Structural Journal, Vol. 105, No. 1, January-February 2008.
  • Blontrock, H. et al., "Fire Tests on Concrete Beams Strengthened with Fibre Composite Laminates," Third PhD Symposium, Vienna, Austria, 2000, pp. 10.
  • Kodur V.R. and Dwaikat M.B, "A numerical model for predicting the fire resistance of reinforced concrete beams," Cement and Concrete Composites, Vol. 30, 2008, pp. 431-443.
  • Kodur V.R. and Dwaikat M.B, "Performance based fire safety design of reinforced concrete beams", Journal of Fire Protection Engineering, 2007, pp. 1-22.
  • Kodur V.R., Ahmed A., and Dwaikat M.B., "Modeling the Fire Performance of FRP-strengthened Reinforced Concrete Beams", Composite & Polycon, American Composites Manufacturers Association, Tampa, FL, USA, 2009.
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