Strength of Steel Columns with Biaxially Eccentric Load

An approximate method of determining the ultimate strength of wide-flange steel columns under biaxially eccentric load is developed. Eccentricity of load is the same at both ends. Equilibrium is enforced only at midlength, and displacements u and v of the center of gravity and the angle of twist \a/ are assumed to vary sinusoidally. Results are presented in the form of six sets of interaction curves which cover a wide range of eccentricities. Results of tests by others on 78 specimens with yield stresses ranging from 30 to 60 ksi are compared with the predictions of the interaction curves. The agreement is very good; 51% of the test values are within ± 5% of the predicted values, 80% are within ± 10% and 94% are within ± 15%. A simple procedure for using the interaction curves in the general case where eccentricities at one end differ from those at the other is suggested. Predicted strengths are in good agreement with tests on four specimens by others.