Piping and component restraints are required to follow the design requirements as mentioned in ASME Boiler and Pressure Vessel Code, Section III, Subsection NF. One of the requirements indicates the necessity of calculating the critical buckling stresses for the members that are subjected to a compressive loading. This paper discusses the prescribed requirements in the Code that specifically address the considerations of the stability and buckling load capacities of linear piping and component restraints (i.e., struts). The finite element modeling of various strut geometries and the results of the buckling analyses of slender structural members (slenderness ratio, Kl/r, greater than or equal to 100) using various finite element solution techniques are presented herein. Specifically, three types of finite element analyses are conducted in an effort to define the critical buckling load for the subject structural member. These three finite element analyses include the traditional linear (Eigen value) Euler method; the nonlinear, second order large deformation method; and finally, the nonlinear large deformation method that incorporates nonlinear elastic-plastic material behavior.
Additionally, two closed form solutions using strain energy method and Euler-Bernoulli beam theory are conducted on the same strut geometries. The results obtained from the aforementioned techniques are then compared both numerically and qualitatively with an appropriate explanation of the purpose and usefulness of each particular result with respect to the intent of the ASME B&PV Code, Section III, Subsection NF requirements. The results show significant variations based on differences in the assumptions and techniques employed in the respective analyses and simply applying the identical margin of safety to each technique does not yield consistent outcomes.
As a result of the discussion we get an insight about the axial compression allowable stress equations and factors as defined in the ASME B&PV Code and how they should be refined depending on the type of buckling analysis we choose to conduct.