This paper presents experimental and theoretical assessments of the structural behavior of circular steel fiber-reinforced concrete (SFRC) columns reinforced with glass fiber-reinforced polymer (GFRP) bars subjected to a concentric axial compressive load. Laboratory experiments were planned to evaluate and compare the effect of different design parameters on the structural behavior of column specimens based on experiments and finite element (FE) analysis. The experimental variables were (i) concrete types, i.e., conventional concrete (CC) and fiber-reinforced concrete (FC), (ii) longitudinal reinforcement types, i.e., steel and GFRP bars, and (iii) transverse rebar configurations, i.e., tied and spiral with different pitches. Sixteen column specimens were fabricated and categorized into four groups with respect to rebar configurations and concrete types. The results showed that the failure modes and cracking patterns of those four column groups were comparable, particularly in the pre-peak branches of load-deflection curves. Even though the average ultimate load of the columns with longitudinal GFRP bars was 17.9% less than that with longitudinal steel bars, the ductility index (DI) was 10.2% greater than their counterpart on average. The addition of steel fibers (SF) to concrete increased the axial peak load by up to 3.1% and the DI by up to 6.6% compared to their counterpart CC columns without SFs. The DI of specimens was increased by higher volumetric ratios (up to 12%) and spiral types (up to 5.5%). The concrete damage plastic (CDP) model for FC columns was updated in the finite element software ABAQUS 6.14. Finally, a new simple equation was theoretically proposed to predict the axial capacity of specimens by considering the inclusion of longitudinal GFRP rebars, volumetric ratio, and steel spiral/hoop ties. Good agreement between the proposed model predictions and the experimental/numerical results was observed.

This study presents the experimental and analytical evaluations on an innovative connection class under cyclic loading. The connection was an H- or I-shaped section as a short stub column (SSC) between the end-plate and the column. The stub section was bolted to the column flange on the one side and bolted to the beam along with the welded end-plate on the other side. Stiffeners were installed on the webs and flanges of the beam and stub to ensure the necessary stiffness of the connection. The variables included thickness of stub flange/web and height of stub web. The cyclic loading was applied on a sample of the proposed connection according to AISC ANSI/AISC 341-16 loading protocol. Experimental observations displayed that the proposed connection, one can either employ hot rolling sections or create the connection as a plate girder, in which case the flange thickness and stub web, as well as the distance between two flanges and their height, was obtained according to the demand and performance of the structure. The optimum cross-section of the stub was then obtained. Also, the analytical model was calibrated using the finite element method (FEM), and its performance was confirmed. The effective parameters of the proposed connection were determined by modeling in the FEM software, and the design method was presented.

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.