18.104.22.168 Elements requiring design shear reinforcement (Vsd > VRd1)
P(1) In beams, bent-up bars shall not be used as shear reinforcement except in combination with stirrups. At least 50 % of Vsd shall be resisted by vertical stirrups.
P(2) Where inclined shear reinforcement is used, the angle between the reinforcement and the longitudinal axis of the beam should not be less than 45°.
P(3) Where the load is not acting at the top of the beam, or when the support is not at the bottom of the beam suspension reinforcement should be provided to transfer the load to the top of the design truss system.
P(1) For shear design, the member is assumed to consist of compressive and tensile zones separated by a distance equal to the internal lever arm z. The shear zone has a depth equal to z and width bw. The internal lever arm is calculated perpendicular to the longitudinal reinforcement by ignoring the effect of any bent-up longitudinal reinforcement.
(2) The notation used is given in Figure 4.13.
The parameters given in Figure 4.13 are:
a — the angle of the shear reinforcement with the longitudinal axis.
— the angle of the concrete struts with the longitudinal axis.
— tensile force in the longitudinal reinforcement.
— the compression force in the concrete in the direction of the longitudinal axis.
— denotes, for a member with constant depth, the internal lever arm corresponding to the maximum bending moment in the element under consideration. In the shear analysis, the approximate value z = 0.9 d can normally be used. In elements with inclined prestressing tendons, longitudinal reinforcement at the tensile chord should be provided to carry the longitudinal tensile force due to shear defined by Equation (4.30).
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