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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering

First Advisor

Nadim J. Wehbe


An experimental research study was conducted at South Dakota State University to evaluate the composite action exhibited by steel box truss towers in flexure. Three tower configurations, each with three specimens, were constructed and tested. Strain, slip, deflection, and load measurements were used to assess the performance of each configuration. The specimens were 40 feet long and simply supported. Composite action between adjacent trusses was developed with bolted angle connectors spaced at 10 foot intervals along the specimens. The control configuration consisted of a continuous 40 foot tower segment. The second configuration consisted of a 20 foot tower segment with 10 foot segments attached to each end with splice connectors. The third configuration consisted of two 20 foot tower segments spliced at mid span. Point loads were applied six feet from mid span in both directions. Load was applied as increments of mid span deflection until failure. The study included a literature review, construction, instrumentation, and testing of the specimens, analysis of experimental results, and a finite element parametric study. Experimental results were analyzed to determine the degree of composite action displayed by each configuration. Composite action was characterized by comparing the effective stiffness shown in testing to the stiffness of a similar specimen with fully developed composite action. The parametric study was used to develop a relationship between connection spacing and tower stiffness. Experimental results indicated that bolt slip in splice connectors was initiated at a certain critical load, above which the specimens displayed a reduced stiffness. The configuration with splices at quarter points exhibited a higher degree of composite action than the configuration with splices at mid span. In addition, the configuration with splices at quarter points performed similar to the control specimen throughout the entire load range. Based on effective stiffness, all three configurations can be modeled conservatively by taking the moment of inertia as the summation of the moments of inertia of the individual trusses about their own centroidal axes. In the parametric study, five connection spacing lengths were analyzed, and the results yielded a linear relationship between connection spacing and tower stiffness.

Library of Congress Subject Headings

Towers -- Design and construction -- Evaluation
Trusses -- Design and construction -- Evaluation
Steel, Structural


Includes bibliographical references (page 130)



Number of Pages



South Dakota State University


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