The collapse of the I-35W Bridge in Minneapolis, MN on August 1, 2007 brought into question the design and inspection of gusset plates in steel truss bridges. The experimental tests performed in this research study the sway-buckling strength and behavior of large-scale steel gusset plates in an isolated truss connection. Parameters studied include plate thickness,combination member loading, initial out-of-plane imperfection, diagonal compression member out-of-plane flexural stiffness, corrosion, and alternative retrofits to increase lateral stiffness. The flexural stiffness of the diagonal compression member and retrofit designs were unique to the testing program. The variables monitored during testing include gusset plate surface stresses and strains, member axial strains, out-of-plane displacement of the gusset plate free edge, and buckling capacity. The results were compared with previously established design models for predicting buckling capacity of gusset plates which include the Whitmore effective width, the Modified-Thornton method, and the FHWA Load Rating Guidelines. A parametric finite element model was developed to determine the lateral stiffness of the gusset plate connection and the additional stiffness provided by the alternative retrofit options. The results showed interaction between the diagonal compression member and gusset plate occurs, which affects sway-buckling capacity. Combination of member loads showed evidence of detrimental effects on sway-buckling capacity. Corrosion of the gusset plates along the top edge of the bottom chord did not lead to significant reduction in sway-buckling capacity. The two retrofit designs showed increases in both lateral stiffness and buckling capacity as well as economic benefits over traditional retrofit methods. Comparison of the results to the current design guidelines showed that the current methods are conservative and do not accurately represent the true behavior of gusset plate connections. The research concludes with two proposed models for future use in design and retrofit of gusset plates. The first is a member-gusset plate interaction model based on a stepped column analogy that takes into account the effects of member flexural stiffness and gusset plate stiffness. The second is a general design guideline developed for retrofit of gusset plate connections dominated by sway-buckling behavior which uses a stiffness based approach to increase the capacity of gusset plate connections. / Graduation date: 2012

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Civil infrastructure throughout the world serves as main arteries for commerce and transportation, commonly forming the backbone of many societies. Bridges have been and remain a crucial part of the success of these civil networks. However, the crucial elements have been built over centuries and have been subject to generations of use. Many current bridges have outlived their intended service life or have been retrofitted to carry additional loads over their original design. A large number of these historic bridges are still in everyday use and their condition needs to be monitored for public safety. Transportation infrastructure authorities have implemented various inspection and management programs throughout the world, mainly visual inspections. However, careful visual inspections can provide valuable information but it has limitations in that it provides no actual stress-strain information to determine structural soundness. Structural Health Monitoring (SHM) has been a growing area of research as officials need to asses and triage the aging infrastructure with methods that provide measurable response information to determine the health of the structure. A rapid improvement in technology has allowed researchers to start using new sensors and algorithms to understand the structural parameters of tested structures due to known and unknown loading scenarios. One of the most promising methods involves the use of wireless sensor nodes to measure structural responses to loads in real time. The structural responses can be processed to help understand the modal parameters, determine the health of the structure, and potentially identify damage. For example, modal parameters of structures are typically used when designing the lateral system of a structure. A better understanding of these parameters can lead to better and more efficient designs. Usually engineers rely on a finite element analysis to identify these parameters. By observing the actual parameters displayed during field testing, the theoretical FE models can be validated for accuracy. This paper will present the field testing of a historic wrought iron truss bridge, in a case study, to establish a repeatable procedure to be used as reference for the testing of other similar structures.

The Astoria-Megler Bridge is a 6.6 kilometer (4.1 mile) long bridge, connecting Oregon and Washington on US 101, with a continuous steel truss main span of 376 m (1232 ft). It is the second longest main span bridge of this type in the world. Due to vortex shedding, some of the long truss verticals exhibit wind-induced torsional vibrations. These vibrations can create large numbers of repeated stress cycles in the truss verticals and the gusset plate assemblies. The members and connections were not designed for such conditions and the impact of this behavior on the service life of the bridge is uncertain. A full-scale representation of one of the truss verticals observed to exhibit such wind induced torsional response was fabricated and tested in the Structural Engineering Research Laboratory at Oregon State University. Experimental data of the rotational behavior and the stress distribution along the vertical were collected using inclinometers, an angular rate sensor, and uniaxial and rosette strain gages. The data collected were compared with existing analytical methods and predictions from finite element models. The observed experimental results including twist angle, stress distribution, and stress magnitude were well captured by both the finite element model and the analytical equations. Using analytical expressions, the fatigue lives of the existing bridge verticals were predicted based on assumed storm duration and recurrence. / Graduation date: 2013

The I-35W Bridge over the Mississippi River in Minneapolis, MN had a catastrophic failure in the main span of the deck truss in 2007. This collapse has brought significant attention on the gusset plate connections in steel truss bridges throughout the U.S. Steel truss bridge gusset plate design has not received much focus in the past 40 years, and there is a lack of consensus within the design profession on the procedures to evaluate, design, and rate these critical elements. In the short term, based on the best available information on the gusset plate design, the Federal Highway Administration (FHWA) has issued preliminary guidance. Although some experimental research has been conducted on the ultimate strength of gusset plates, much of this work has been directed toward the performance of tension members and their connections. There has been limited experimental work on the compression capacity and stability of gusset plates, but most of this work is relevant primarily to bracing connections common in building structures. This research focuses on comprehensive experimental and analytical studies on steel truss bridge gusset plate behavior. The studies include comparisons of advanced analytical models with the responses from large-scale experimental tests using discrete and innovative full-field measurements. The calibrated finite element analysis models are then utilized to study a variety of gusset plate configurations. Improved mechanistic idealizations that better capture the observed behavior in the experiments and analytical studies are proposed as the result of this work. The design checks recommended in this thesis present a comprehensive methodology for determining the ultimate gusset plate resistance. This research provides a large database of original results that will be useful for future similar studies. In addition, this research provides modeling procedures that permit the study of steel truss bridge connections and their adjacent framing members using truss bridge sub-assemblies. Based on the comprehensive analytical studies, simple and accurate design calculation procedures to assess the nominal ultimate strength of steel truss gusset plate connections are recommended for steel truss bridge gusset plate connections.

This study investigates the complex issues surrounding the preservation of historic, single-lane, metal truss bridges. Essentially functionally obsolete, these structures are targeted for replacement due to current government transportation policies, funding requirements, and safety concerns. After these issues are discussed, a series of case studies from Hunterdon County, New Jersey, will highlight multiple bridge rehabilitation projects in which designs and plans were modified to suit the unique situations and conditions of each of these structures, without compromising historic integrity and improving safety. These bridges have important cultural value, and although in some cases the original structure may be lost or wholly reconstructed, the historic character of the bridge and area is retained. This thesis illuminates the difficulties that need to be overcome in attempting to successfully preserve historic, single-lane bridges and their rural context (while maintaining transportation functionality), and illustrates the important role of community involvement in the preservation process. / Department of Architecture