Behavior of FRP-strengthened reinforced concrete beams under fire conditions.

摘要

Fiber reinforced polymers (FRP) have emerged as an attractive proposition for retrofitting and strengthening of deteriorating concrete structures due to advantageous properties such as light weight, corrosion resistance and high strength. When FRP is used in strengthening of structural members in buildings, resulting strengthened member has to satisfy relevant fire resistance requirements specified in building codes and standards. Similar to other construction materials, FRP loses its strength and stiffness properties with temperature. However, the degradation in FRP properties is faster as compared to concrete or steel reinforcement due to deterioration of FRP matrix and loss of bond even at modest temperature. To address some of the current knowledge gaps, experimental and numerical studies was carried out with the aim of developing a fundamental understanding on the performance of FPR-strengthened RC beams under realistic fire, loading, and restraint scenarios.;A numerical model was developed for tracing the response of FRP-strengthened RC beams under realistic fire, loading and restraint conditions. The model is based on a macroscopic finite element approach and utilizes time-dependent moment-curvature relationships to trace the response of the beam from pre-fire stage to failure under fire conditions. All of the critical factors, namely; high temperature material properties, fire induced bond degradation and axial restraint force, and different strain components that have significant influence on the fire response of FRP-strengthened RC beams were incorporated in the model.;For validation of the model, four FRP-strengthened RC beams were tested by exposing the beams to fire. The test parameters included different fire scenarios (standard and design fire), type of insulation, effect of anchorage zones and axial restraint conditions. Data generated from fire tests was used to validate the computer model by comparing various response parameters which included cross sectional temperatures, debonding of FRP, mid-span deflection, and fire resistance. The validated model was then applied to conduct a set of parametric studies to quantify the influence of various factors, such as fire scenario, load level, axial restraint, bond degradation, thermal properties and different insulation schemes, on the fire response of FRP-strengthened RC beams. Results from parametric studies shows that fire resistance of FRP-strengthened RC beam is enhanced under most design fire exposures. Provision of optimum insulation schemes, can enhance the fire resistance of FRP-strengthened RC beams. The fire resistance is not improved much by increasing the insulation thickness beyond an optimum thickness level. Higher load levels, lower restraint forces and increased bond degradation at FRP/concrete interface leads to a lower fire resistance in FRP-strengthened RC beams.;Results from parametric studies and fire experiments were utilized to develop guidelines for achieving optimum fire resistance in FRP-strengthened RC beams. These design guidelines, can facilitate wider use of FRP in strengthening of RC beams in buildings where fire safety is one of the key design consideration.