Tubular steel frames, which are extensively used in offshore applications, are usually analyzed by ignoring the flexibility of joints. Nevertheless, the flexibility of chord walls at brace connections may have profound effects on the behavior of tubular structures; it influences displacements of the frame, distributions of stresses, fatigue lives of joints, buckling capacities of compression members, and the dynamic response of the structure. The flexibility of joints must be considered in the analysis. This research will develop two analytical models. One will be suitable for the global frame analysis, and the other, a local analysis. The former will provide an efficient tool to compute nominal member forces and moments, similar to the conventional rigid frame model, except that the new model will account for joint flexibilities. The latter will consider a partial frame to facilitate a more detailed analysis; in addition to reflecting the flexibility of a joint and the frame actions of the adjoining members, this model will enable the detailed description of the joint geometry, including weld profiles, to predict the distribution of stresses in tube walls. These two models, when developed, will facilitate highly accurate analyses of tubular frames. The two models will be utilized to investigate the influence of joint flexibilities in various tubular structures. For this purpose, three types of jacket frames will be considered, and each frame will be analyzed for two different heights, 400 and 800 feet high. This study will provide insights and useful guidance to design engineers regarding the effects of joint flexibility for tubular frames frequently encountered in practice.
