As traffic and congestion increase, so does the likelihood of collisions. The solution to this problem is usually through a rehabilitation process with two primary options: (1) widening/expansion of existing roadway and bridges and (2) complete replacement (new construction) of roadway and bridges. The first option is the most feasible and cost-effective. While roadway widening/expansion pose minimal issues, the same cannot be said of bridge widening. An existing bridge presents a multitude of challenges during the planning and design phases, during construction, and throughout the structure's service life. Special attention is required in both the design and detailing of the widening in order to minimize construction and maintenance problems. The primary objective of this dissertation is to present a better understanding of structural behavior and capacity by studying an existing widened structure: a bridge that has been in service for over 40 years (constructed in 1972 and widened in 2002). The load demand on this bridge has doubled over the years. Consequently, the widened structural system is composed of four-span continuous prestressed concrete bridge segments. To better understand the widened 2002 bridge used in this study, an initial comparative analysis was performed, comparing the original 1972 bridge and the 2002 widened bridge. This comparative analysis included a determination of bridge capacity, distribution factors, and load-rating factors using current American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Specifications design codes. However, the original codes used for the two bridges should also be noted, as follows: (1) the AASHTO Load Factor Design (LFD) Code was used for the original bridge; and (2) a combination of the AASHTO LFD and AASHTO LRFD Specifications were used for the existing widened bridge. Linear three-dimensional finite element models were developed for both bridges to obtain the maximum moment and shear values with varying HL-93 load cases for these analyses. To develop models that describe the possible existing condition of the 2002 widened bridge, a nonlinear model of one of the critical members in the structure was developed by changing the most critical parameters. The critical parameters are categorized as material properties and prestress losses. Sensitivity studies were conducted using parametric models for simulations with moving loads for the different load cases using the HL-93 truck. The load-rating and reliability indexes were computed for all the cases under different loading conditions. The parameters that have the most influence on load rating and reliability are also presented in the analyses. The information generated from these analyses can be used for better–focused visual inspection and widened bridge load rating criteria, and can also be used for developing a long–term widening structural monitoring plan. Additionally, this study will be used as a benchmark for future studies, and to establish a procedure and methodology for future bridge widening projects.


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Graduation Date





Catbas, F. Necati


Doctor of Philosophy (Ph.D.)


College of Engineering and Computer Science


Civil, Environmental, and Construction Engineering

Degree Program

Civil Engineering









Release Date

August 2020

Length of Campus-only Access

3 years

Access Status

Doctoral Dissertation (Open Access)