All ETDs from UAB

Advisory Committee Chair

Ian Hosch

Advisory Committee Members

Jason Kirby

Christopher Waldron

Document Type

Thesis

Date of Award

2016

Degree Name by School

Master of Science in Civil Engineering (MSCE) School of Engineering

Abstract

Many DOTs mainly across America and some departments outside the states have been experience fatigue failures of some highway cantilever support structures. Fatigue of these structures have been analyzed intensively for research purposes, but the American Association of State Highway and Transportation Officials (AASHTO) have adopted fatigue design pressures for cantilevered signals, signs, and light supports introduced by the researchers extend the life of new structures. The fatigue design pressures were developed by applying virtual wind spectrums on various computer models of cantilever support structures and luminaire structures. The main goal of this thesis was to utilize experimental natural wind gusts and strain data to study the fatigue torsion effects of natural wind gusts on a quadri-chord truss cantilever sign support structure creating shear strain reversals. Quasi-static forcing and response findings of the system have been observed within the experimental data. The characteristics of the natural wind gusts and shear strains were included in a factorial analysis to understand the cause and effects of the shear strains the sign support structure experienced. A finite element analysis (FEA) computer model was utilized to compare the theoretical shear strains of the model by using the general natural wind pressure equations according to the American Society of Civil Engineers (ASCE) code. After the comparisons, AASHTO’s current fatigue design pressure for cantilever support structures experiencing natural wind gusts was applied to the model to compare the magnitude of the theoretical strains against the strains from the experimental data. The quasi-static nature of the natural wind gust influenced by its velocity was found to create quasi-static responses in the quadri-chord truss cantilever sign support structure, in addition to the anticipated natural response of the structure. Recommendations for future studies have been made for DOTs, researchers, and designers to continue studying the new quasi-static phenomenon discovered from the experimental data.

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