Date of Award

Spring 5-2021

Document Type


Degree Name

Doctor of Philosophy (PhD)


Materials and Infrastructure Systems

First Advisor

C. Shawn Sun


Some of the Louisiana’s bridges built in the 1950s and 1960s used two-girder or truss systems, in which floorbeams are carried by main members and the continuous (spliced) stringers are supported by the floorbeams. The main members are either two edge (fascia) girders or trusses. When the flexural capacity of continuous stringers is calculated, the moment gradient factor (Cb) is not accurately calculated considering the lateral torsional buckling (LTB) at the negative moment section. In particular, the bracing effect of the non-composite concrete deck is not accounted for, and as a result, the current practice has underestimated the LTB strength of continuous stringers significantly, which would cause either expensive bridge rehabilitation or unnecessary bridge postings. This dissertation presents the re-assessment of methodology behind flexural capacity of continuous stringers with the effort focusing on more realistic values for Cb. Theoretical solution and finite element analyses were addressed to examine Cb in continuous stringers. The analysis results were also calibrated using the lab testing data. Recommendations were provided on how to determine Cb more accurately and load rate the continuous stringers more reasonably.

Chapter 1 presents a literature review including various codes and specifications, and relevant work by several researchers. Chapter 2 addresses a theoretical solution for the LTB resistance of continuous stringers. Chapter 3 illustrates the finite element analyses of the continuous stringers accounting for various bracing conditions and load cases. Chapter 4 addresses the lab testing findings and discusses the bracing effect due to various types of bracings, including the intermediate steel diaphragms, timber ties, and non-composite concrete deck. Chapter 5 presents the conclusions and recommendations on load ratings of continuous stringers with non-composite deck.