Sustained Biaxial Load on Slender Concrete Columns

A method of analysis was derived to predict the behavior of columns under various loading conditions. A mathematical model was formed by dividing the column into a number of smaller elements. Shrinkage, creep, and stress effects were considered for each element. A modified superposition method for determining creep under varying stresses was developed. To verify the method of analysis, 64 tests were performed on slender pinned end columns. The columns had a 5-in. square cross section and a height-to-thickness ratio of 31. The effects of magnitude and orientation of the end eccentricities, and various levels of sustained load were investigated. Types of tests included: short-term load to failure; sustained loading to failure; and sustained load followed by short-term loading to failure. Sustained loading was carried out in a controlled environment. The durations of sustained loading averaged over 7 months with a range of 12 hours to 2 years. Close agreement between similar tests and a good correlation between related tests were obtained. Predicted behaviors compared quite well with the test results.