Date of Award

Winter 2018

Project Type

Thesis

Program or Major

Civil Engineering

Degree Name

Master of Science

First Advisor

Erin S. Bell

Second Advisor

Ricardo A. Medina

Third Advisor

Eshan V. Dave

Abstract

In 2013, the newly designed Memorial bridge, located between Portsmouth, NH, and Kittery, ME, was opened to traffic. The structural system of the bridge is composed of truss elements with a unique “Gusset-less” connection which utilizes curved steel to transition from the chords to the diagonals where splice plates join the members. With such a unique connection, it is important to verify the design assumptions and assess the performance. In this study, the fatigue performance of the Gusset-less connection is investigated through an experimental fatigue test of a scale model of the connection.

In a high-cycle fatigue test, it is critical to ensure that consistency is maintained across all testing periods. This is especially challenging when the test setup is not standardized, and the laboratory infrastructure is limited. In this work a monitoring protocol was developed to systematically monitor the structural response of the test setup. Using this protocol, across a total of 1,600,000 fatigue load cycles the average difference in structural response was found to be 5% across the test setup. Using the most conservative assumptions, using a hot-spot stress of 14 Ksi at the toe of the weld, the AASHTO S-N curve, and a category C fatigue detail, the connection has been tested and the results show that the design expectations are exceeded.

The residual stresses were investigated in the top-flange of the fatigue specimen. The stresses indicate a compressive stress at the surface of the specimen, which is consistent with the residual stress profile of a sand blasted metal. The magnitude of the stresses was higher than the theoretical limits of the calculation method and therefore must be used qualitatively, not quantitatively.

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