Masters Theses

Date of Award

8-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Major Professor

David W. Goodpasture

Committee Members

James H. Deatherage, N. Mike Jackson, Edwin G. Burdette

Abstract

The research presented in this document was conducted to identify the optimum design and layout of small foundations known as landing pads. The ultimate goal of this research was to compare the stress performance of varying styles of pads and to determine the best design. It was also important to develop a foundation that was aesthetically pleasing. Experiments were performed in the shop of Astec, Incorporated and on the campus of the University of Tennessee, Knoxville to determine an "ideal" shape and examine its structural integrity. Development of these "idealized" shapes was initiated by performing basic structural analysis on popular shapes currently utilized in the industry. Basic structural analysis consisted of the following :

  • Mathematical estimation of deflection for an isolated cross-section and span length
  • Calculating bending stress with the use of shear and moment diagrams for isolated sections
  • Mathematical estimation of shear stress for an isolated cross-section
Determination of an optimum shape was done by performing laboratory experiments and utilizing stress analysis software. For laboratory experimentation, these shapes were re-created by constructing polyvinyl chloride (PVC) models. The models were built to scale and were tested under loading conditions simulating loads applied from portable equipment. The main purpose of these tests was to visually examine the effects and behavior of the pad under load and to determine maximum stresses through the use of strain gages. Displacement was measured in the laboratory with dial gages and compared to design criteria for deflection limits. Comparisons of behavior between PVC and steel were taken into account with the use of stress analysis software also. This was necessary to predict the behavior of the PVC models and provide validity for the software results. The selected shapes were created in a well known stress analysis software package known as STAAD/Pro©. The stress analysis modeler in STAAD/Pro© allowed the simulation of real world testing outside of the laboratory. The models were given properties for both A36 Carbon Steel and PVC. The models were analyzed by applying static loads, which represented both equipment weight and the overturning moment due to wind. Research revealed that the performance of the landing pads depended on subgrade conditions. The ultimate load for each landing pad increased as the stiffness of the subgrade increased. Of the three landing pads with only four stiffeners, the triangular stiffened landing pad performed the best. Ultimately, the STAAD/Pro© software provided results that were consistent with the basic structural analysis methods and the strain gage testing methods used in the laboratory. The laboratory research was not a very effective comparison to the values obtained in the computer aided stress analysis, however. Strain gage locations were determined initially with Ansys DesignSpace©. However, boundary conditions were initially incorrect, so strain gages were not pinpointed at the areas of highest stress. Deflection properties were proportional and relatively small in all pads, and the research and did not determine a clear-cut choice as to which pad should be used.

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