Structural Behavior of Circular Macro-Synthetic-Fiber Concrete Columns Reinforced by CFRP Bars

This study investigates the axial compression performance and theoretical analysis of macro-synthetic-fiber-reinforced concrete (MSFRC) columns reinforced with carbon-fiber-reinforced polymer (CFRP) bars. A comprehensive testing program was developed to assess and compare the structural behavior of columns made with both traditional and advanced materials. Key variables included plain concrete (PC), macro-synthetic-reinforced concrete (MSRC), longitudinal steel/CFRP bars, and variations in the steel spiral/hoop bar pitch. Sixteen specimens were fabricated in four groups (CRPC, CRMSP, SRPC, and SRMSP) to capture these variations. The results showed consistent failure modes across all specimens, with good alignment between experimental outcomes and theoretical predictions. Axial compression strengths for CRPC and CRMSP specimens reached, on average, 89.57% and 91.83% of the strengths observed in SRPC and SRFC specimens, respectively. The ductility index (DI) of CRCC and CRMSP columns was 8.54% and 12.14% higher than that of their SRPC and SRMSP counterparts. Furthermore, the CRMSP and SRMSP columns demonstrated higher axial strain than their CRCC and SRPC equivalents, with average increases of 19% and 11% under peak compression loads, respectively. Although North American codes currently do not propose the use of CFRP bars as compressive elements in reinforced concrete (RC) and do not provide specific design guidelines [5-8], the proposed theoretical model accurately predicted the performance of the tested columns. The test result of compression strength was close to proposed equations considering the axial contribution of CFRP longitudinal bars and integrated additional factors such as steel spiral/hoop reinforcement, volumetric reinforcement ratios, and concrete type after concrete cover spalling.