An efficient Rayleigh-Ritz approach is presented for analyzing the lateral-torsional buckling (“tripping”) behavior of permanent means of access (PMA) structures. Tripping failure is dangerous and often occurs when a stiffener has a tall web plate. For ordinary stiffeners of short web plates, tripping usually occurs after plate local buckling and often happens in plastic range. Since PMA structures have a wide platform for a regular walk-through inspection, they are vulnerable to elastic tripping failure and may take place prior to plate local buckling. Based on an extensive study of finite element linear buckling analysis, a strain distribution is assumed for PMA platforms. The total potential energy functional, with a parametric expression of different supporting members (flat bar, T-stiffener and angle stiffener), is formulated, and the critical tripping stress is obtained using eigenvalue approach. The method offers advantages over commonly used finite element analysis because it is mesh-free and requires only five degrees of freedom; therefore the solution process is rapid and suitable for design space exploration. The numerical results are in agreement with NX NASTRAN [1] linear buckling analysis. Design recommendations are proposed based on extensive parametric studies.
