Abstract
Beam-column joints (BCJs) constructed until the 1970s carry a low shear capability due to the absence of shear reinforcement. Fiber-reinforced polymers (FRP) are more reliable than other materials to strengthen a weak BCJ. To date, plenty of analytical models have been developed to analyze the actual contribution of the FRP to the shear strength of RC BCJs. However, the models developed are either too complex in computational efforts or based on empirical coefficients that result in compromised results. The models that formulate the contribution of FRP to the shear strength of the FRP-strengthened deficient interior BCJ are very limited, and such models are too complex. An adequate BCJs’ FRP strain equation must still be developed to address these issues. Therefore, the FRP effective strain equation and contribution of FRP to RC BCJs are derived in this research work using an updated database of the appropriate BCJs. The initial analytical model of Bousselham, which Del Vecchio later improved, is further extended to FRP-strengthened deficient interior BCJs. For this purpose, an updated database of the 32 tests around the world of FRP-strengthened interior BCJs deficient in seismic reinforcement is prepared. Firstly, the experimental effective FRP strain is derived using the experimental database. Then, a power-type equation is derived for the effective FRP strain by considering the crucial parameters of the FRP-strengthened interior BCJs. Finally, the experimental shear strengths and those determined with the proposed equation of the FRP-strengthened joints are compared. The average ratio between the experimental and analytical (proposed model) joint shear strengths of the considered specimens ensured the accuracy of the suggested model. The suggested approach makes computing the FRP enhancements required to avoid shear failure in interior joints easy and reliable for researchers and field engineers interested in seismically reinforcing existing structures.
Highlights
IntroductionThe RC beam-column joints are the most susceptible element of the RC structure [1]
During earthquakes, the RC beam-column joints are the most susceptible element of the RC structure [1]
In the procedures provided by codes and standards for the design of structures strengthened with externally bonded Fiber-reinforced polymers (FRP) (American Concrete Institute ([21]; Canadian Standards Association [22]; Fédération Internationale du Béton [23]; National Research Council (CNR) [24], there are no expressions for determining the increased strength of beam-column joints strengthened with FRP or other materials
Summary
The RC beam-column joints are the most susceptible element of the RC structure [1]. The objective of all analytical models was to determine how much the shear strength of the beam-column junction increased because of joint confinement by the strengthening approach. The complexity of the procedures, the lack of updated data of experimental results of under-designed RC BCJs, the lack of general equations for interior FRC-strengthened under-designed RC BCJS, the use of empirical equations based on assumptions, and the use of techniques that require high computational efforts to determine the contribution of FRP are all issues that have been identified far. To calculate the increase in the shear capacity of non-seismic internal beam-column joints due to FRP strengthening, the effective FRP strain is recommended to be fine-tuned. Bousselham’s [20] approach (later utilized by Del Vecchio [19] for corner non-seismic RC BCJs) is expanded to obtain an equation for the effective FRP strain for substandard interior joints. The current updated and extensive database of experimental testing of FRP reinforced inadequate RC BCJs will be used to determine the effective FRP strain equation
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