Rigid Plastic Upper Bound Shear Capacity Model for RC Members without and with Very Small Amounts of Shear Reinforcement

Many existing reinforced concrete structures older than 40 years do not satisfy the requirements for the minimum shear reinforcement ratio and the maximum spacing of stirrups according to the current design codes. Consequently, the shear reinforcement is neglected when estimating the shear capacity of such structures. This omission of shear reinforcement can lead to an underestimation of the actual shear capacity of these structures. This paper presents a shear capacity model for reinforced concrete members with small amounts of shear reinforcement. The model enables estimation of the shear capacity of members with less shear reinforcement than the minimum shear reinforcement specified by the current design codes, as well as members with greater stirrup spacing than the maximum limit. The model considers the shear contributions from sliding in cracked concrete, dowel action of the longitudinal reinforcement and activated stirrups by the dowel action and the critical shear crack.

Comparison of the proposed model with experimental results shows a good agreement, highlighting its potential applicability in assessing the shear capacity of existing concrete structures.