Feasibility of using seven-wire steel strands as conventional reinforcement in structural concrete members

Concrete beams and columns in high-rise buildings and long-span bridges are often required to sustain large flexural and axial loads. Meeting these demands with conventional reinforcement often leads to steel congestion and poor concrete placement. To address this challenge, this study investigates the feasibility of using unstressed seven-wire steel strands (Grade 1860 MPa) as longitudinal reinforcement in reinforced concrete (RC) members. Although they offer high strength, these strands show limited ductility, lack a clear yield point, and are not yet covered by design codes. An experimental program was conducted involving four reinforced concrete beams under pure flexure and four half-scale short columns under pure axial compression. Results showed that strand-reinforced beam specimens exhibited comparable flexural strength but demonstrated reduced pre-yield stiffness and ductility relative to their corresponding conventionally reinforced beams. In columns, strand-reinforced specimens displayed 10–14% lower compressive strength compared to their rebar-reinforced counterparts. To further explore the structural behavior of the beams, a MATLAB-based algorithm was created to perform sectional analysis and assess their curvature ductility behavior. In addition, a numerical model was developed using a fiber-based analysis approach in OpenSees to study the structural behavior of the columns. Based on these findings, design charts are proposed for the use of unstressed steel strand both in beams and columns. Furthermore, to provide practical design tools for column cases beyond those examined in this study under pure axial compression, axial–moment interaction diagrams were developed. • Experimental and numerical studies were performed on RC members with steel strands. • Strand-reinforced beams exhibited lower stiffness and ductility than RC beams. • Strand-reinforced columns demonstrated 10–14% reduction in compressive strength • Design charts and interaction diagrams were developed for strand-reinforced columns.