Keyed shear connections with looped U‐bars subjected to normal and shear forces Part II: rigid‐plastic modeling of the ultimate capacity

When the structural capacity of precast concrete structures is to be determined, reliable and practical models for estimation of the ultimate load carrying capacity of the structural connections are essential. In this paper, rigid-plastic upper bound solutions for the load carrying capacity of keyed shear connections subjected to shear and normal forces are derived and compared to experimental results. The solutions are based on two idealized failure mechanisms involving complete key cut off and local key corner shearing, respectively. The solutions furnish a tool to design connections for the most ductile failure mode, which according to experimental observations is the one with local key corner shearing. Comparison with test results shows that satisfactory overall agreement is found, when appropriate material parameters are adopted. This includes an effectiveness factor, which in this study has been taken from previous studies of similar problems, and an internal angle of friction for mortar in the range of 30°–34°. The agreement is better for combinations of shear and compression, whereas the case of shear combined with large tension forces (i.e., half the yield capacity of the U-bars) is overestimated by the solutions. Based on the results, it can be recommended that the solutions may be applied in practice using the lower limit for the internal angle of friction, and provided that precaution are taken in cases where the connections are utilized to transfer tension.