High-strength concrete columns under eccentric load

The behavior of high strength concrete tied columns was investigated. A total of 11 columns were tested under monotonic loading having two different eccentricities. The main variables investigated were: (1) the mechanical ratio, (2) the spacing, and (3) the configuration of transverse reinforcement. Test results indicate that, under monotonically increasing axial load, the cross ties with a 135 degrees hook at one end and 90 degrees bent at the other end provide ductility comparable to ties supporting the intermediate longitudinal bars. Also the use of four different equivalent rectangular stress blocks (ERSBs) in predicting the ultimate strength of members made of high strength concrete was evaluated. It is concluded that calculations made using the ACI 318-02 stress block always gives an upper bound, whereas a lower bound is obtained by the CSA A23.3-94 approach. Capacities calculated using the ERSB proposed by Bae and Bayrak, and Ozbakkaloglu and Saatcioglu also agree quite well with the test results