NUMERICAL ANALYSIS OF HYBRID FIBRE REINFORCED CONCRETE BEAM COLUMN JOINT

Abstract

This thesis investigates the hybrid effect of incorporating both metallic and nonmetallic fibers into concrete at a full-scale beam-column joint section subjected to seismic loading. The research aims to evaluate the improvements in mechanical properties and overall performance of the beam-column joints achieved through the addition of hybrid fibers. The experimental study employed one normal grade concrete mix (M25) and four different hybrid fiber combinations: hooked end steel fiber with basalt fiber, and crimped steel fiber with polypropylene fiber. These mixtures were designed and tested in the laboratory to determine their compressive, tensile, and flexural strengths following relevant Indian Standard code provisions. The full-scale beam-column joint section was designed according to the Bureau of Indian Standards (BIS), incorporating ductile detailing as per seismic design requirements. The same geometric configuration was modeled using the finite element software ANSYS v21. Numerical models of concrete and steel were developed, incorporating non-linear stress-strain relationships in uniaxial compression and tension based on the experimental data. The finite element models were subjected to two loading conditions: steady static loading and non-linear reverse cyclic displacement-controlled loading, simulating seismic effects. The study evaluated key performance parameters, including initial crack load, initial crack deflection, ultimate load capacity, and ultimate deflection. The results showed that the hybrid combination of 0.40% basalt fiber with 0.80% hooked end steel fiber outperformed the other mixtures in terms of compressive strength, flexural strength, energy dissipation capacity, and stiffness degradation. Notably, the hybrid effect of 0.80% crimped steel and 0.20% polypropylene fiber exhibited the highest tensile strength and best resistance to initial cracking, likely due to the micro filament nature of the polypropylene fibers. However, increasing the polypropylene content to 0.40% led to a gradual decrease in both tensile and flexural strengths. iv The findings of this research contribute to the understanding of the synergistic effects of hybrid fiber reinforcement in concrete, particularly for critical structural elements such as beam-column joints subjected to seismic loading. The enhanced mechanical properties and improved crack control achieved through hybrid fiber reinforcement can potentially lead to more resilient and durable structures, mitigating the risk of catastrophic failures during seismic events.