ORIGINAL ARTICLE Fracture stability and residual strength assessment of reinforced concrete beams Trisha Sain Æ J. M. Chandra Kishen Received: 17 April 2007 / Accepted: 6 December 2007 / Published online: 8 April 2008 Ó RILEM 2008 Abstract In conventional analysis and design pro- cedures of reinforced concrete structures, the ability of concrete to resist tension is neglected. Under cyclic loading, the tension-softening behavior of concrete influences its residual strength and subsequent crack propagation. The stability and the residual strength of a cracked reinforced concrete member under fatigue loading, depends on a number of factors such as, reinforcement ratio, specimen size, grade of concrete, fracture properties, and on the tension-softening behavior of concrete. In this work, a method is proposed to assess the residual strength of reinforced concrete beams subjected to cyclic loading. The crack extension resistance based approach is used for determining the condition for unstable crack propa- gation. The effect of reinforcement is modeled as a closing force counteracting the effect of crack opening produced by the external moment. The effect of percentage reinforcement and specimen size on the failure of reinforced beams is studied. Finally, the residual strength of the beams are computed by including the softening behavior of concrete. Keywords Reinforced concrete  Residual strength  Fracture  Fatigue  Crack extension resistance  Tension softening Nomenclature B Width of beam C Fatigue law constant D Depth of beam E Elastic modulus of concrete L Length of beam A st c/s area of reinforcement P ini Initial cracking load C s Clear cover F S Force in steel G f Fracture energy K max Maximum stress intensity factor DK Stress intensity factor range K I Stress intensity factor K Ic Critical stress intensity factor K Ic ini Crack initiation toughness K R Crack extension resistance K IF Stress intensity factor due to steel force K IM Stress intensity factor due to bending moment M Bending moment M soft Moment of resistance due to process zone M Ut Moment of resistance due to uncracked concrete N Fatigue load cycle T Ut Tensile force provided by uncracked concrete T st Tensile force provided by reinforcement Y M , Y S Geometry factor a 0 Initial notch length l ch Characteristic length T. Sain  J. M. Chandra Kishen (&) Department of Civil Engineering, Indian Institute of Science, Bangalore 560012, India e-mail: chandrak@civil.iisc.ernet.in Materials and Structures (2008) 41:1451–1463 DOI 10.1617/s11527-007-9342-x