An analysis of the behavior of the one hole malleable iron conduit clamp

A generalized analytical methodology for determining the load-deflection behavior of the malleable iron one hole conduit clamp is developed. This clamp is used in the support of electrical conduit in industry and nuclear power plants. Four different types of one hole malleable iron conduit clamps are analyzed using two dimensional plane stress finite element models. The ANSYS 4.4a computer program with the following nonlinear options: large displacement option, interface option, plasticity option, and its bilinear material stress-strain capabilities, are used. The analytical methodology gives similar results to those measured in the clamp tests conducted by Tennessee Valley Authority, Knoxville, Tennessee.

For the vertical and horizontal loading conditions a total of nine different analyses are made. These analyses envelope all the different configurations tested for both loading directions. The comparisons between the analytical and test results show close agreement with the load­ deflection curves up to the point where the test results approach the maximum load of the curve. The major cause for lack of disagreement is the local collapse of the clamp, the approximation of the bolt stiffness and the approximate boundary conditions between the clamp, spacer, and conduit.

For the axial loading condition, four analyses are made. These four clamps envelope all the different axial configurations tested. The comparison between the analytical and test results show close agreement with the load-deflection curves. A relaxed preload is approximated to develop a normal force on the conduit. Friction factor values were developed for different sizes, vendors and conduit finishes. A system approach is developed to predict the approximate load-deflection curve with reasonable results as compared to the tests. The approximate behavior of the clamp due to rotation and axial stiffness of the clamp have a large effect on the load-deflection curve. These system analyses are expected to give average deflections if the stiffness characteristics are well known.

The techniques used in developing the finite element mesh have practical application for use in studying other one hole malleable iron clamps. The ease in data preparation of the ANSYS 4.4a (1991) finite element program and the specific boundary conditions described between the clamp, spacer and the conduit, and the modeling of the bolt and clamp have practical application for other investigations. These analytical methods can be used to determine the behavior of this type of clamp.