STATIC BENDING AND FREE VIBRATION ANALYSIS OF SPANNING PIPELINE WITH AXIAL FORCE ON RIGID SOIL

For a rising upward case of an unburied spanning pipeline, a new pipe model with an axial force on rigid soil is built. With small deflection beam theory, the deformations and internal forces formulae of the separated segment rising from supported soil and the spanning segment are derived under self-weight loading. Setting the static deflection as a modal function, the first order natural frequency formula is given by the energy balance method. The static deflections under self-weight and the first order natural frequency of a simply supported beam, a fixed-fixed supported beam and the presented model are compared under an axial force case. The research shows that the present model leads to a small difference in deflection and a very small difference in internal forces from the spanning pipeline model considering the soil deformation. Comparing with the simply-supported model and fixed-fixed model recommended in the present rules, the presented model is more reasonable both in static and free vibration characteristics for an unburied spanning pipeline. The recommended model and the formulae provide a calculation for the both internal force and natural frequency of the unburied spanning pipeline with the model as a simply-supported beam model or a fixed-fixed beam model, or in between them, and also complement the inadequacy in the present rules.