Seismic Strengthening of Reinforced Concrete Exterior Beam-Column Joints with Fiber Reinforced Cementitious Mortar Composites

This thesis investigates the seismic strengthening of reinforced concrete (RC) exterior beam-column joints using fabric reinforced cementitious matrix (FRCM), also known as textile reinforced mortars (TRM) or textile reinforced concrete (TRC). The study focuses on FRCM systems incorporating basalt and carbon fabrics combining experimental testing and numerical approaches. The research first assesses the accuracy of current building code provisions for predicting shear strength in exterior RC beam-column joints. Through compiling 203 experimental results from literature, four major building codes are evaluated: second-generation Eurocode 8, EN-1998-1-2004, NZS-3101-1:2006, and ACI 352R-02. Moreover, the assessment includes correlation analysis of key parameters affecting shear strength, including concrete compressive strength, joint geometry, axial load, and joint shear reinforcement ratios. Furthermore, based on identified correlations with critical parameters, a simplified empirical formula for shear strength is proposed and validated using Monte Carlo cross-validation, showing improved prediction accuracy across the dataset. The experimental program then investigates FRCM systems employing both carbon and basalt fibers for strengthening seismically deficient exterior RC beam-column joints. The investigation includes a control specimen and two strengthened specimens, with specimens initially loaded to 85% of their ultimate capacity to simulate realistic seismic damage conditions before FRCM application. Full-scale specimens designed to represent pre-1970s construction practices are subjected to loading protocols simulating seismic demands. Building on the joint strengthening program, the study includes bond characterization through pullout testing of carbon and basalt fibers using the same cementitious mortar used for joint strengthening. This provides an understanding into fiber-matrix interactions that influence strengthened joint performance. Furthermore, a numerical investigation is conducted developing a three-dimensional finite element modeling in DIANA 10.5 software for FRCM strengthened joint, validated against experimental results. The validated numerical model is then employed to study the effect of configuration schemes on joint shear strength of RC beam-column joints. The results reveal that joint safety check in EC-08 (second generation), provides good accuracy with slight underestimation, while ACI 352R-02 demonstrates the highest consistency and lowest coefficient of variation. Furthermore, the experimental findings on joint strengthening shows that both carbon and basalt FRCM strengthening systems achieve significant strength enhancement while providing comparable ductility improvement. Both strengthening systems effectively modify the failure mechanism from brittle joint shear failure to a more favorable beam-joint interaction failure mode. In addition, the fiber-matrix bond behavior indicates that basalt FRCM systems achieves higher peak bond forces at longer embedment lengths than the carbon (uncoated) FRCM systems which were also employed in joint strengthening. Therefore, the study has four key contributions: (1) development of an empirical model for exterior RC joint shear strength prediction, (2) experimental evaluation of carbon and basalt FRCM strengthening effectiveness at subassemblies level, (3) investigation of associated fiber-matrix bond behavior at material level, and (4) development of 3D finite element model for FRCM-strengthened exterior RC joints.