Experimental investigation of the effect of stirrup usage on the beam capacity of fixed-end reinforced concrete beams with web reinforcement

Section 7.4 of the 2018 Turkish Building Earthquake Code (TBDY 2018), titled "Special Rules for the Design of Cast-in-Place Reinforced Concrete Building Structural Systems under Earthquake Effects", defines the sectional requirements for reinforced concrete beams with high ductility levels. According to Article 7.4.1.c of the code, when the beam depth exceeds one quarter of the clear span, web reinforcement must be placed on both faces of the beam web along the beam depth. The total area of longitudinal web reinforcement shall not be less than 30% of the larger of the top or bottom longitudinal reinforcement areas at the support sections. In addition, the diameter of the web reinforcement shall not be less than 12 mm, and the spacing of the reinforcement shall not exceed 300 mm. The spacing of horizontal web cross-ties along the beam depth shall not exceed 600 mm, while the spacing along the beam axis shall not exceed 400 mm [31]. In this thesis, the effects of using horizontal web cross-ties in reinforced concrete beams with web reinforcement on beam capacity and behavioral mechanisms were investigated through flexural tests conducted under fixed-end boundary conditions rather than simply supported systems. Experimental findings indicated that, for beams with a/d<2, the use of horizontal web cross-ties increased the moment capacity, load-carrying capacity, and shear strength of the beams; however, the expected improvement in ductility and energy dissipation was not observed. Although horizontal cross-ties enhanced strength within the beam deformation mechanism, they also led to earlier crack initiation, while a higher deformation capacity was observed. Consequently, for beams with a/d <2, it was observed that arranging cross-tie spacing more closely than the limits permitted by the code did not provide a statistically significant contribution to the anticipated increases in strength and ductility.