Post‐Buckling Behavior of Tubular Beam‐Columns

Abstract

Behavior of fabricated tubular steel beam‐columns as commonly used in offshore structures is studied for the entire range of monotonic loading up to ultimate load including the post‐buckling branch of unloading, using assumed deflection method. In the present approach, equilibrium is established only at a critical section of a beam‐column using closed form analytical expressions for moment‐curvature‐thrust relationship of a fabricated tube. The computer model developed on the basis of this approximation is compared with tests and other analytical methods, and it is found that the assumed deflection method predicts the behavior of actual tubes with good accuracy, yet it simplifies the analysis drastically. A considerable amount of data has been obtained and presented concerning the behavior of cylindrical tubular beam‐columns. It is concluded from this numerical study that initial imperfection (out‐of‐straightness), lateral load at mid‐span, and bending moment at ends affect the behavior of a beam‐column in a similar manner. As these values increase, the ultimate strength is reduced significantly while their associated load‐deflection or shortening relations become flatter.