Wan-Yang Gao

Bond-Slip Model for FRP Laminates Externally Bonded to Concrete at Elevated Temperature

AbstractThis paper presents a nonlinear local bond-slip model for fiber reinforced polymer (FRP) laminates externally bonded to concrete at elevated temperature for future use in the theoretical modeling of fire resistance of FRP-strengthened concrete structures. The model is an extension of an existing two-parameter bond-slip model for FRP-to-concrete interfaces at ambient temperature. The two key parameters employed in the proposed bond-slip model, the interfacial fracture energy, Gf, and the interfacial brittleness index, B, were determined using existing shear test data of FRP-to-concrete bonded joints at elevated temperature. In the interpretation of test data, the influences of temperature-induced thermal stress and temperature-induced bond degradation are properly accounted for. As may be expected, the interfacial fracture energy, Gf, is found to be almost constant initially and then starts to decrease when the temperature approaches the glass transition temperature of the bonding adhesive; the int...

Effect of Temperature Variation on the Full-Range Behavior of FRP-to-Concrete Bonded Joints

AbstractService temperature variations (thermal loadings) may significantly affect the behavior of the bond between externally bonded fiber reinforced polymer (FRP) and concrete. This paper presents an analytical solution for the full-range deformation process of FRP-to-concrete bonded joints under combined thermal and mechanical loadings. The solution is based on a bilinear bond-slip model and leads to closed-form expressions. The validity of the solution is demonstrated through comparisons with both experimental results and finite-element predictions. Numerical results from the solution are presented to illustrate the effect of thermal loading on the interfacial shear stress and slip distributions in addition to the global load-displacement response. Provided the material properties are not affected by temperature variations, a temperature rise is shown to increase the ultimate load, whereas a temperature reduction decreases the ultimate load; the latter can have serious implications for the safety of t...

Simple method for predicting temperatures in insulated, FRP-strengthened RC members exposed to a standard fire

AbstractFire safety is a significant concern for fiber-reinforced-polymer (FRP)–strengthened RC structures, particularly for indoor applications. To satisfy fire resistance requirements, fire insulation layers may be provided to protect FRP-strengthened RC members. This paper presents a simple, design-oriented method for predicting temperatures in insulated FRP-strengthened RC members under standard fire exposure. The proposed method consists of two sets of formulas: one set for predicting temperatures in unprotected FRP-strengthened RC members exposed to a standard fire; and another set to convert a fire insulation layer into an equivalent concrete layer. As a result, an insulated FRP-strengthened RC member can be analyzed as an unprotected RC member with an enlarged section for which a similar simple method has previously been established by these authors. In the present study, a finite element (FE) approach for the temperature analysis of insulated FRP-strengthened RC members was first developed and th...

Finite element modeling of insulated FRP-strengthened RC beams exposed to fire

This paper presents a finite element (FE) model for the thermo-mechanical analysis of insulated FRP-strengthened reinforced concrete (RC) beams exposed to fire. In the model, the effects of loading, thermal expansion of materials, and degradations in both the mechanical properties of materials and the bond behavior at FRP-to-concrete and steel-to-concrete interfaces due to elevated temperatures are all considered. The validity of the FE model is demonstrated through comparisons of FE predictions with results from existing standard fire tests on insulated FRP-strengthened RC beams.

Simple Method for Predicting Temperatures in Reinforced Concrete Beams Exposed to a Standard Fire

In performance-based fire safety design, the fire performance of a structure needs to be accurately evaluated, which requires the accurate prediction of temperatures in the structure. While a finite-element or a finite-difference analysis may be carried out for this purpose, structural engineers generally prefer a simpler method. This paper therefore presents a simple, design-oriented method for predicting temperatures in RC beams under a standard fire exposure. Results from finite element heat transfer analysis are first examined to identify the key parameters that determine temperature distributions in RC beams. On the basis of this knowledge, a simple method in the form of handy formulae and diagrams is derived from regression analysis of finite element temperature data, with due consideration of the effects of beam geometry and fire exposure duration. The accuracy of the proposed method is demonstrated by comparing its predictions with temperature data from both finite element analysis and laboratory tests. The proposed method is believed to be attractive to practicing engineers for use in the fire resistance evaluation of RC beams exposed to a standard fire because of its simplicity and accuracy.

Finite Element Modeling for Debonding of FRP-to-Concrete Interfaces Subjected to Mixed-Mode Loading

This paper presents finite element (FE) modeling of the debonding behavior of fiber reinforced polymer (FRP)-to-concrete interfaces subject to mixed-mode loading, which is realized through a peeling test of FRP composites externally bonded onto a concrete substrate. A cohesive zone model (CZM) is implemented into the FE model to represent the behavior of the FRP-to-concrete interface. Two element schemes (orthotropic plane stress element and beam element) were employed to simulate the behavior of FRP composite plate in the peeling test. The orthotropic plane stress element scheme, bearing a clear physical background and with an easy definition of the material property parameters following the composite mechanics, is found to be superior to the beam element scheme, and thus is utilized to conduct parametric studies. The influences of the peeling angle, the interfacial parameters (i.e., the configuration of the cohesive zone models, the interfacial damage initiation law (DIL), the interfacial damage evolution law (DEL), the coupling of mode-I and mode-II components), on the mixed-mode failure of the FRP-concrete-interface are carefully investigated. The results showed that the mode I component plays a critical role in the debonding failure of FRP-to-concrete interfaces even when the peeling angle is very small. The failure of FRP-to-concrete interface transits promptly from a mode II-dominated one to a mode I-dominated one when the peeling angle increases to a relatively small value (e.g., 4 degree) and subsequently the peeling force (i.e., the debonding strength of FRP) decreases dramatically. Such mixity of the mode I and mode II components should be appropriately considered for refining the analysis of FRP-strengthened RC beams and the FRP debonding strength design, for which a pure mode II interfacial failure was usually assumed.