The Static Analysis Of Circular Tubular With Local Joint Flexibility(LGF)

Circular tubular structures are widely used in offshore jacket platform, long-span bridges and tall structures due to low mass, big stiffness and low drag coefficient. In such structures, the braces tube were usually welded directly onto the outer surface of the chord to generate a welded tubular joint, chord member at the connection has to sustain the loading transferred from the braces in its radial direction, which causes the chord wall in a flexural state. And because of the radial stiffness of the chord member is smaller than the axial stiffness of the brace member the chord surface near the brace/chord connection has a significant deformation, that is the local joint flexibility(LJF). It is indicated that the local stiffness around the joint connection has a clear effect on the static behaviors of a tubular structure. It will lead to the nominal stress redistribution of the structure, change the deformation of the structure, and reduce the critical load of the member. For convenience in design stage, the static behavior of a tubular structure is generally simulated initially by plane and spatial frameworks with either rigid joints or completely flexible joints, and the local joint flexibility around the brace/chord connection is not considered. Obviously, the internal forces(including axial force, shear force and bending moment) in each tube member is underestimated if a rigid brace/chord connection is used in the simulation, and this will cause an unsafe design for predicting the loading carrying capacity and serviceability. However, the displacement and the internal forces of each tube member are overestimated if a completely flexible joint connection is used in the simulation, which results in an uneconomical design Based on these considerations, the local joint stiffness or flexibility is necessary to be taken into account in the design of an unstiffened tubular structure to provide more accurate prediction on the static behavior of such tubular structures for design purpose.Main research contents are listed as follows,(1)The ideas and methods to simulate LJF use equivalent springs are presented.(2) The simplified analytical models to analyze the static behavior for The plane T, Y–joints Circular tubular structures and the space T- joints Circular tubular structures with LJF are presented. And the relevant Fortran computer program is writeen.(3) Finite element software ABAQUS was used to model the 3-D FEA models. Through comparison with finite element results of some examples, the accuracy and reliability of the presented models are evaluated.(4) Parameters analysis is carried out to investigate the influence of geometric parameters on static behavior for the plane T,Y-joints Circular tubular structures with LJF. The parameters include the ratio of length to diameter α, the ratio of diameter β, the ratio of thickness γ.