Abstract
Compressive Force Path concept is a proposed shear design method to explain shear behavior in reinforced concrete beams. This concept identifies 04 behaviors based on the shear span to beam depth (a/d) ratio and provides detailed shear design and transverse reinforcement detailing procedure for each behavior. Therefore, author of this paper intended to use this concept as a practical tool for the designing of RC beams particularly for Type II (2 ≤ a/d < 5) and Type III (1 < a/d < 2) behaviors to validate the concept. Total 08 beams of 100×200×1800 mm size beams were cast; out of which, 04 beams were designed according to ACI Code approach while, rest were designed and detailed using CFP concept strategy. The beam sizes in this study are identical and all parameters are constant except shear span 'a'. The two-point loading test results of RC beams showed that the shear resistance of concrete is better estimated by the CFP concept with a good prediction of cracks pattern, load carrying capacity and actual behavior of the beams in shear as compared to the beams designed according to ACI Code approach. However, most of the beams, particularly a/d ratio less than 4.44 were observed to be deficient in serviceability and failed in shear in spite of attaining theoretical predicted loads.
Highlights
Shear design of RC beams is based on the sectional model as Vn = Vc + Vs (Eq (11-2) of ACI 318M-08 [1]); where, Vn is the nominal shear resistance offered by section, Vc is the shear strength of concrete calculated by Eq (11-5) of ACI 318M-08 [1] and Vs is the contribution of transverse reinforcement in shear resistance
According to Compressive Force Path (CFP) concept, shear resistance of an RC member depends on the strength of concrete in the region of the path through which compressive force is transferred to the supports and shear failure is associated with the development of the excessive tensile stresses in the region
Kotsovos and Pavlovic [5] identified shear design and transverse reinforcement detailing rules for these two behaviors of RC beams to achieve theoretical flexural capacity estimated through well-established ACI 318M-08 [1] for a tension controlled section while, there is no detail for the prediction of the failure mode
Summary
According to CFP concept, shear resistance of an RC member depends on the strength of concrete in the region of the path through which compressive force is transferred to the supports and shear failure is associated with the development of the excessive tensile stresses in the region (refer to Figure 1). This concept identifies 04 behaviors for an RC beam having a constant cross section and flexure reinforcement, if it is subjected to two-point loading with variable a/d ratio. For Type III beams, brittle failure is associated with the failure of horizontal member of the frame; stirrups should be provided throughout between support and Kink as shown in Figure 3, to increase the load carrying capacity of the section with increasing suppression of shear stresses
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