Determination of Support Minimum Rigid Stiffness for Piping Analysis

Pipe supports are represented as spring constants in piping analysis, and therefore a formal procedure is required to determine the spring constant values. Two current approaches are to enforce deflection criteria to ensure support rigidity or calculate the support stiffness values directly. However, the former approach results in overly conservative support designs and the latter approach becomes an iterative process of designing the supports and observing the response of the piping system. To avoid the issues presented by these methods, an alternative approach is presented which involves increasing values of support stiffness until change in natural frequency of the system diminishes. This method can help establish a lower bound (minimum rigid) stiffness above which there will be no significant change in the seismic response of the piping system. Using this approach only requires the support designs to have stiffness values at or above the minimum value without being concerned with detailed stiffness calculations or using deflection limits. This paper presents the methods and results of an expansive study to establish minimum rigid stiffness values for piping analysis.