An Explanation of the Behavior of Bottle-Shaped Struts Using Stress Fields

The behavior of bottle-shaped struts was investigated using isolated concrete specimens with various amount and configurations of transverse reinforcement in which compressive stresses resulting from applied load through rigid plates was able to disperse creating transverse tensile stress within the specimens. The behavior of the specimens was observed and recorded to evaluate current provisions regarding compressive stress limitations, reinforcing requirements, and to unify the treatment of bottle-shaped struts by ACI 318-02 and AASHTO LRFD. The results from the experimental investigation indicated that both ACI-318-02 and AASHTO LRFD provisions for bottle-shaped struts are conservative in their specifications for compressive stress limits and reinforcing requirements. Finally, a transition stress field developed by M. Schlaich was modified to model the observed behavior and failure mechanisms of the specimens, which was dependent on the amount of transverse reinforcement provided. The transition stress field exploits the tensile strength of concrete by incorporating a bi-axial failure criterion, with a statically admissible stress field with finite dimensions. The transitions stress field is presented as an alternate method of modeling the behavior of bottle-shaped struts.