Numerical Investigation on the Buckling Failure of Slender Tubular Member with Cutout Presence

Abstract

Pitting corrosion often leads to the creation of small holes in steel tubular member of platform structures when a protective coating is damaged. A single pit on slender compression element can cause a significant reduction in the buckling capacity of the member. Euler formula is no longer applicable for determining the critical buckling load when cutout presence on the member. This research was conducted to numerically study the effect of a circular hole on the buckling capacity of slender steel tubular member. A variation on hole positions was at 0.125 L, 0.25 L, 0.375 L, and 0.5 L, where L is the length of the member. The hole was taken to be 0.5 pipe diameter. Two nonlinear geometric 3D Finite Element models were developed to analyzed the member critical buckling load: (a) buckling analysis, where the problem was formulated as eigenvalue problem based on the nonlinear incremental equilibrium equations, and (b) nonlinear analysis, where the nonlinear equilibrium equations were developed and solved by several schemes to get the load – deflection curve. For the both models, the tubular member was discretized into: (a) shell elements, and (b) solid elements. The numerical results were verified by experimental investigation. The results showed that: (a) the presence of cutout reduced the buckling load significantly, (b) the reduction ranging from 3% to 10% depending on the hole positions, (c) the maximum reduction occurs when the hole position was in the middle of the member length, (d) compared to experimental results, the critical buckling load obtained from buckling analysis deviated 1~4% while those of nonlinear analysis deviated 1~5%, (e) the buckling mode corresponded with member bent away to opposite side of the cutout position.

Experimental and numerical investigations on overall buckling of steel pipe truss with circular cutout on the compression element

“…1, and the smallest eigenvalue was used, and (b) nonlinear analysis, where the nonlinear equilibrium equations (Eq. 2) were solved by Newton-Raphson method to get the load -deflection curve [2]. are the linear stiffness matrix, first order nonlinear, and second-order nonlinear tangent stiffness matrices of the structure, respectively.…”

“…are the linear stiffness matrix, first order nonlinear, and second-order nonlinear tangent stiffness matrices of the structure, respectively. {Q} and {P} are, respectively, the displacement and load vectors, while {ΔQ} is the incremental displacement, and {ΔP} is the incremental load vector [2]. A variation on hole positions was at 0.125 L, 0.25 L, 0.375 L, and 0.5 L, where L is the length of the compression element.…”

“…Since the compression element with cutout is connected to other elements to form a structural system, the existence of hole will affect the overall buckling of the structure. History records a considerable number of buckling failures occurred in the tubular steel platform structure due to the combination of pitting corrosion and fatigue problems [1].…”

“…When defect like a hole resulting from pitting corrosion presence on the member, the Euler's buckling formula given in Eq. (1), where Pcr , E, I, k and L is respectively, the critical buckling load, modulus of elasticity, cross sectional moment of inertia, effective length factor which depends on the end support conditions, and length of the member, is no longer Some experimental studies on the buckling capacity of tubular member with circular cutout at different location on the element have been reported, and the effect of diameter as well as number of holes on the buckling failure of the member element has also been carried out [1].…”

“…In the following sections, a description of experimental model and numerical model of the truss structure being investigated is performed. The structure represents component and simplification of a typical jacket type offshore platform structure discussed in reference [1] that has been scaled 160 geometrically from the prototype.…”