Comparative Assessment of Steel vs. FRP Reinforcement in Concrete Beams

Thesis Abstract

This study addresses the reliability and performance implications of using steel versus FRP reinforcement in reinforced concrete beams under flexural and shear loading, motivated by concerns over corrosion resistance, long-term durability, cost-effectiveness, and service-life guarantees in aggressive environments. The aim is to systematically compare structural behavior, failure mechanisms, and long-term performance of steel and FRP reinforced concrete beams to inform material selection in seismic and non-seismic regions. Specific objectives include (1) to evaluate initial stiffness, flexural capacity, and deflection characteristics of beams reinforced with steel and with FRP under controlled laboratory conditions; (2) to quantify crack development, crack width, and post-crack behavior using crack mapping and digital image correlation (DIC) techniques; (3) to assess durability under accelerated corrosion and chloride exposure for steel and moisture/temperature cycling for FRP, and to model residual strength after fatigue loading; (4) to develop predictive models for ultimate load, ductility, and serviceability limits incorporating material properties and geometric variables; (5) to perform a life-cycle cost–risk assessment for typical bridge and building applications, integrating material costs, maintenance, and replacement probabilities; and (6) to provide design recommendations aligned with prevailing codes and to identify gaps in current design provisions for FRP reinforcement. Methodologically, the study adopts a comparative experimental design complemented by numerical simulation and performance modeling. The population comprises reinforced concrete beam specimens sourced from a standard mix design representing medium-strength concrete (f?c ? 30–35 MPa) and restrained reinforcement configurations. A total of 40 beam specimens are prepared 20 with steel reinforcement and 20 with FRP reinforcement, each group subdivided to explore variations in reinforcement ratio, beam depth, and longitudinal reinforcement layout. Data collection instruments include strain gauges, linear variable differential transformers (LVDTs) for deflection, digital image correlation (DIC) systems for full-field strain/ crack analysis, non-destructive testing (ultrasonic pulse velocity and rebound hammer tests), and environmental chambers for accelerated aging. Static three-point and four-point bending tests are conducted to failure under monotonic loading, supplemented by cyclic fatigue loading to assess post-yield behavior and residual capacity. For durability, selected specimens undergo accelerated corrosion (for steel) and moisture/temperature cycling (for FRP) to quantify durability indices and strength degradation. Analytical methods entail descriptive statistics and inferential analyses, with regression analysis to correlate reinforcement type, geometry, and material properties with ultimate moment capacity and ductility. ANOVA tests compare mean performance metrics between steel and FRP groups across variables such as reinforcement ratio and beam section. DIC-derived crack width and displacement fields are analyzed to identify characteristic failure modes and to quantify crack propagation rates. Finite element models in ABAQUS are calibrated against experimental results, enabling parametric studies on larger-scale members and different boundary conditions. The probabilistic reliability analysis incorporates Monte Carlo simulations to capture material property variability and loading uncertainties, producing reliability indices and nominal life-cycle costs. The theoretical lens integrates the Theory of Structural Fatigue and Durability, and the Corrosion-Resistant FRP theory, with considerations of the Limit States Design framework to bridge experimental findings with design practice. Expected findings include (i) FRP-reinforced beams exhibit higher initial stiffness variability due to anisotropy but show superior corrosion resistance and longer service life in aggressive environments; (ii) steel-reinforced beams achieve higher ductility and energy dissipation under cyclic loading, with more pronounced yielding and crack bridging behaviors; (iii) FRP beams reveal smaller crack widths and more favorable crack distribution under service loads, though long-term performance is sensitive to moisture-induced degradation and environmental exposure; (iv) predictive models yield accurate estimations (R2 > 0.85) of ultimate capacity and deflection bounds when calibrated with experimental data; (v) life-cycle cost analysis demonstrates trade-offs between higher initial FRP material costs and reduced maintenance in coastal or deicing-prone regions. The study contributes to knowledge by providing robust, transferrable comparative data on steel and FRP reinforcement in concrete beams, refining design guidance for FRP usage, and offering validated models for predicting long-term performance and cost implications. Conclusions emphasize context-dependent material selection, with recommendations for code provisions to better accommodate FRP reinforcement, strategies for durability enhancement, and directions for future research on hybrid reinforcement configurations and environment-specific design criteria.