Effect of axial force on allowable free spans of submarine pipelines

Analytical solutions are presented for computing allowable static and dynamic free spans of submarine pipelines subjected to axial and transverse loads. The pipeline is considered to be supported on an elastic semi-infinite soil bed at the two ends of the span. The governing equations for both static and free vibration analysis yield nonlinear algebraic equations for the allowable spans, which are solved numerically using Mathematica. Numerical results are presented in nondimensional form so that these can be directly used for any set or pipe data, loading and soil stiffness parameters. Results reveal that the conventional free span design neglecting the effect of axial force and based on span end conditions idealised as simply supported, fixed or with translational and rotational springs, in many cases, lead to either over-conservative or unconservative estimates.