Discrete versus average integration in shear assessment of spiral links

Abstract

Common transverse reinforcement of reinforced concrete members with circular cross section consists of round ties or spirals. Its purpose in members that are not subjected to significant shear loading is to provide proper confinement for concrete, and eliminate buckling of the longitudinal reinforcement bars. If spirals are to be used as both a shear resister and confining enabler for reinforced concrete beams, then under combined action of moment and shear, spirals will be required to provide or contribute to proper shear resistance. Hence a proper assessment for spiral shear contribution is required.

Utilising confinement reinforcement for shear resistance in reinforced concrete structures

“…Some simplifying assumptions have been made in this study as a result of the complexity involved in modelling the exact geometrical configuration of the tested beams. Simplifying the geometry of the spirals by representing them with bar elements is a major generalisation which can contradict the argument presented in Jaafar (2009) regarding the importance of considering the geometrical properties of the spirals in assessing their shear contribution. Yet, as mentioned earlier, 3D analysis was attempted but, owing to the complexity involved, a 2D analysis was adopted instead.…”

“…Based on crack-sectional analysis where a discrete method is considered and a variable crack inclination angle is assumed, the prediction for spiral shear contribution using the optimised discrete method that Jaafar (2009) proposed was a reasonable and safe prediction (Table 2). It is important to note that there is no control over the exact location of the inclined failure surface.…”

“…However, the shear force sensitivity becomes lower for small spiral spacing (case of SB5, SC3 and SC4). The reason for such behaviour has been discussed in Jaafar (2009) where it was shown that shear force sensitivity is a function of spiral geometry, spacing and crack inclination angle.…”

Discrete crack sectional analysis for shear evaluation of RC beams

“…The location of crack crossing the spiral/normal link is based on the discrete method described by Jaafar (2009). The shear contribution of the intersected spiral is calculated, and then the moment with respect to point c. As a crack propagates further into the beam, the position of any new pieces of spiral that it crosses is recorded.…”

“…A general sectional crack technique, based on the discrete method to predict the shear contribution of spiral links, was described in Jaafar (2009). The prediction encouraged us to improve this technique in order to eliminate some of the major assumptions taken regarding the shear contribution of concrete and the linear crack shape.…”