Nowadays using high strength steel in concrete structures has been vastly increased. The use of high strength steel instead of conventional steel in concrete structures has several advantages, including the decreased rebar cross section area, reduction in reinforcement congestion, and cost saving due to decreased amount of rebars. Current design codes such as ACI 318-14 limit the design yield strength of flexural members in different applications, including flexure, shear, torsion, etc. For instance, ACI 318-14 limits the yield strength of flexural members in special moment frames to 420 MPa and for the other structures to 550 MPa. The main reason for such limitations is due to lack of test data in using high strength steel in concrete structures. In this study, in order to get a better understanding of structural behavior of high strength steel, an experimental program has been conducted to investigate the flexural behavior of A4 high strength steel as reinforcement in concrete beams. In the present study, fourteen reinforced concrete beams which were 200 mm wide, 300 mm high, and 2600 mm long were tested under static loading in four point bending configuration. The experimental parameters were yield strength of longitudinal reinforcement (435 MPa or 600 MPa), yield strength of stirrup (435 MPa or 600 MPa), tension steel ratio, compression steel ratio, and concrete compressive strength (35 MPa or 65 MPa). The behavior of beams up to failure were investigated based on load-midspan deflection diagram, moment-experimental curvature diagram, load-concrete strain at farthest compression fiber diagram, load-steel strain, ultimate flexural capacity, and failure mechanism. Results showed that ductility of concrete beams reinforced with A4 high strength steel was lower in comparison to concrete beams reinforced with A3 normal strength steel. Failure mechanisms in all specimens were justify; LINE-HEIGHT: 90%; MARGIN: 0in 0in 8pt" Keywords: high strength steel, reinforcement congestion, reinforced concrete beams, static loading, ductility
