STRUCTURAL BEHAVIOR OF FIBER REINFORCED CONCRETE ELEMENTS UNDER MONOTONIC STATIC LOADING: AN INVESTIGATION OF LOAD-DEFLECTION RESPONSE, CRACKING BEHAVIOR, STIFFNESS, AND FAILURE MODES

Abstract

This study investigates the structural behavior of fiber reinforced concrete (FRC) elements subjected to monotonic static loading, with emphasis on load-deflection response, cracking characteristics, stiffness degradation, and failure mechanisms. An experimental program was conducted on reinforced concrete beams incorporating glass fibers (GF), polypropylene fibers (PP), and hybrid glass-polypropylene fiber combinations at various volume fractions (0.5%, 1.0%, 1.5%, and 2.0%). Twelve full-scale beam specimens (150 mm × 250 mm × 2800 mm) were fabricated and tested under four-point bending until failure. The study measured first cracking load, ultimate load capacity, mid-span deflections, crack patterns, crack width progression, stiffness evolution, ductility indices, and energy absorption capacity. Results indicate that fiber reinforcement significantly enhances structural performance: hybrid fiber specimens (1.5% GF + 0.5% PP) achieved 68% higher ultimate load capacity, 124% greater ductility, and 187% improved energy absorption compared to control specimens. The optimal fiber combination exhibited superior crack control with 47% reduction in maximum crack width and 63% increase in crack spacing. Post-cracking stiffness was enhanced by 54% in hybrid FRC beams. Failure mode analysis revealed a transition from brittle concrete crushing to ductile progressive failure with improved post-peak behavior. The study establishes comprehensive relationships between fiber content, structural response parameters, and failure characteristics, providing design guidelines for FRC structural applications.