Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Civil Engineering

First Advisor

Arden Sigl


With increasing public awareness of the nations [sic] infrastructure, one of the most common concerns and sources of liability among local governments, and in this case private corporations, is the safety of existing bridges. As with most governments and businesses, economics and budget dictate how much inspection, testing, repair and replacement can take place on a highway or railway system. When bridges reach a point in their life where they have outlived their expected usefulness, it becomes ever more critical to periodically determine the structural integrity of the bridge. To make such a determination, frequent inspections must be performed to locate areas within the structure that show fatigue, fracture, or deformation. This study focuses on a bridge built in the late nineteenth century. Bridges constructed with in this period of time, consisted mainly of iron truss bridges in various shapes and styles. Functionally, there are only two different types of truss bridges, those that are statically determinate structures and those that are statically indeterminate structures. Statical indeterminacy is determined by the simple formula b + r > 2j where b is the total number of members (elements) in the bridge, r is the total number of reactions and j is the number of joints .8 By application of this formula, it is evident that bridge 1509 is an indeterminate structure. 56 + 3 > 2 (28) or 59 > 56 Statically indeterminate trusses, unlike determinate trusses, allow load sharing from one member to another. Specifically, should one member be weakened for some reason, nearby truss members would help the weakened member carry its assigned load through a redistribution of forces. This built-in redundancy is the sole basis of this investigation. This study will propose an analysis. method which will attempt to identify any force redistribution within the bridge trusses due to local weakening of a member or joint. Instrumentation and testing was [sic] designed with three goals in mind: First, to determine whether or not the structure is functioning as it was designed, and later reinforced. Second, to specifically identify weakened areas of the bridge. And third, to provide a background for future testing on the assumption that future testing will show variations in member forces as a method of testing for early detection of failure.

Library of Congress Subject Headings

Dakota, Minnesota & Eastern Railroad Corporation
Truss bridges -- South Dakota -- Testing
Railroad bridges



Number of Pages



South Dakota State University