Strut And Tie Model

The study of behavior of RC beam column joints under seismic loading and endeavors for predicting the joint shear strength has started long back [Hanson and Connor, 1967 as reported by Park and Pauley, 1975], however, the collapse of many RC buildings in recent past earthquakes has been attributed to failure of beam-column joints. The prediction of accurate joint shear strength is difficult task since it depends on complex interactions of various parameters. Many researchers have proposed analytical models for predicting joint shear strength; however, theses analytical models are generally based on limited set of experimental results. From the literature, the crucial parameters affecting the joint shear strength have been identified as beam

The idea behind the strut and tie approach as proposed by Paulay and Priestley in 1992 is, under seismic forces the joint develops two mechanism i.e. diagonal strut mechanism depends on the concrete compressive strength and the truss mechanism based on the bond strength between concrete and reinforcemnt. With this concept, Ortiz in 1993 developed strut and tie model for predicting the joint shear strength for unreinforced and reinforced exterior joints. Later, Parker and Bullman (1997) considered the diagonal concrete strut mechanism for resisting joint shear force and neglected the tie effect. In the same year, Hwang and Lee (1999) proposed iterative algorithm for predicting joint shear strength based on softened strut and tie model considering equilibrium, compatibility and constitutive laws for cracked reinforced concrete sections. Again in 2002 the same authors proposed a simplified strut and tie model. Pantelides et al. (2002) developed strut and tie model based on the experimetnal test results on unconfined exterior joints. This model considers the failure of joint either by the crushing of compressive strut or by the failure of compression nodes. Similar to Hwang and Lee (1999), in 2008 Wong et al. developed a modified rotating angle strut and tie model based on modified compression field theory (MCFT). Vollum and Parker (2008) proposed an iterative

Taylor (1974) proposed a model based on principal stress approach considering only concrete tensile strength and column axial load parameters. Scott et al. (1994) proposed a theoritical model based on single diagonal concrete strut and neglecting the effect of both horizontal and vertical stirrups. The concrete compressive strength and geometry of beam and column have been considered as governing parameter in this model. Priestley (1997) and Hakuto et al. (2000) suggested the principle tensile stress approach to calculate the joint shear strength without joint shear reinforceemnt. Attalla (2004) presented a theorotical model considering the compression-softening phenomenon associated with the cracked reinforced concrete in compression. The effect of joint geometry and the presence of transverse beams are also consiered on joint shear strength. A fifth order polynomial equation was proposed by Tsonos (2002 and 2007) to find the ultimate joint shear strength. The model considers the combination of softened diagonal strut mechanism similar to Hwang and Lee’s (1999) consideration and the truss mechanisms. Tsonos’s model satisfies the constitutive laws by complying with Mohr’s circle compressive and tensile principal stresses and adopted the fifth degree parabola for concrete biaxial strength curve. Wang et al. (2011) proposed a theorotical model for both interior and exterior joints based on