ORIGINAL ARTICLE Comparative performance of sub-standard interior reinforced concrete beam–column connection with various joint reinforcing details Teeraphot Supaviriyakit Æ Amorn Pimanmas Received: 18 November 2006 / Accepted: 14 May 2007 / Published online: 7 June 2007 Ó RILEM 2007 Abstract This paper discusses the effect of some important parameters on cyclic behavior of sub- substandard interior beam–column connection. The objective is to investigate the effect of joint shear stress, anchorage bond of longitudinal beam bar within the joint and horizontal joint reinforcements on the joint performance. The experiment consisted of five half-scale beam–column specimens. The control specimen (J1) represented a typical non- ductile beam–column joint in mid-rise RC buildings constructed in low seismic zone. In specimen J2, the bond between concrete and longitudinal bars was completely removed initially. In specimen J3A and J3B, a substantial amount of horizontal joint rein- forcement was provided in joint core. In specimen J4, the column size was enlarged to reduce shear stress in joint. The experimental result demonstrated brittle joint shear failure in control specimen (J1), speci- mens J3A and J3B, beam splitting failure in specimen J2 and ductile flexural failure in specimen J4. Based on experimental results, it was found that the initial lost of bond did not cause a substantial reduction in joint capacity. Moreover, provision of substantial horizontal joint reinforcements in specimen J3A and J3B did not produce a comparable improvement in the seismic performance. With increased column size in specimen J4, the energy dissipation characteristics were greatly improved as indicated by large spindle- shaped cyclic loops. Keywords Substandard beam–column connection  Reversed cyclic load  Un-bonded beam bar  Joint reinforcement  Joint shear failure 1 Introduction The mechanism of force transfer within beam– column joint of a rigid frame during seismic events is known to be complex [1, 2], involving bending in beams and columns and shear and bond stress transfer in joint core. Figure 1 shows forces acting on a joint core under lateral load. The horizontal shear force at the mid-level of the joint may be calculated as, V jh ¼ T þ C 0 c þ C 0 s  V c ð1Þ V jh ¼ T þ T 0  V c ð2Þ where T is tension force, T 0 is tension force on opposite column face, C 0 c and C 0 s are compression force on concrete and steel, respectively and V c is column shear force. T. Supaviriyakit  A. Pimanmas (&) School of Civil Engineering and Technology, Sirindhorn International Institute of Technology, Thammasat University, Patumthani 12121, Thailand e-mail: amorn@siit.tu.ac.th Materials and Structures (2008) 41:543–557 DOI 10.1617/s11527-007-9266-5