The discipline of structural engineering concerns the theory, analysis, and design of structures under a variety of load conditions. Courses cover analytical and numerical methods of analysis, as well as design to current standards. Course material is applicable to building and bridge structures of reinforced concrete and steel, as well as to timber, masonry, and composite structures.
Faculty research addresses the behavior of structures constructed with high performance materials; changes in structural behavior due to creep and shrinkage of concrete, relaxation of steel, and time dependent deterioration; computational modeling to conduct limit state analysis; rehabilitation of existing structures; development of alternative structural systems to improve performance; characterization of load and resistance uncertainties and probabilistic assessment of structural performance under extreme loads; structural reliability analysis; and reliability-based design optimization. Much of our recent work addresses bridge and building structures. Two current projects addressing bridge structures are:
Evaluation of Camber and Deflection of Bridge Girders
Many state departments of transportation currently rely on empirical equations to determine camber and long-term deflection for prestressed concrete beams. These mathematical expressions often do not take into consideration the type of concrete used and its creep and shrinkage properties, the age of the girder when the deck is placed, variations in support conditions, transitions from a non-composite to a composite system, and the age of the bridge when the deck is replaced for deck replacement projects.
The goal of the project is to develop a methodology that addresses these deficiencies by explicitly considering the age of girder and deck at the time when camber or displacements are calculated, creep and shrinkage properties of beam and deck concrete, influence of temperature gradients, and prestress losses induced due to time dependent effects.The proposed methodology allows for the calculation of camber and deflections at any time during the service life of the bridge and applies to composite pre-stressed concrete and steel bridge superstructures. The overall framework for the prediction methodology is based on principles of engineering mechanics, although components of the methodology are based on empirical models such as the estimation of the modulus of elasticity and prediction of creep and shrinkage properties.
The Effectiveness of Diaphragms on PC Girder Bridges
Bridge diaphragms, often in the form of cross-bracing or solid reinforced-concrete blocks poured between girder webs, are principally used to prevent girder instabilities during construction, enhance gravity load distribution among girders, and aid in horizontal load sharing from over-height vehicle collisions. However, studies have suggested that intermediate diaphragms, those placed near the center of the bridge span, have relatively minor influence on in-service structural behavior. A question thus arises whether diaphragms can be reduced in number, or eliminated entirely for some types of bridges, such as low skew, low curvature prestressed concrete (PC) bridges. This may be particularly practical when sections that are more resistant to instability, such as box beams or bulb-tees, are used in the bridge design.
If structurally feasible, reducing or eliminating intermediate diaphragms could bring significant benefits, such as a reduction of fitment problems, time and cost of construction, as well as a longer-term minimization of maintenance problems associated with diaphragm-to-girder connection deterioration. The purpose of this study is to address this question and assess the need for diaphragms on low skew, low curvature PC girder bridges. The first phase of the research is to develop and validate finite element models for a wide range of PC bridge structures, and to assess the effect of diaphragms on girder stability during construction, as well as the distribution of traffic loads among girders on in-service bridges. During the second research phase, results of the models will be used to develop design guidelines for the placement of intermediate diaphragms on PC girder bridges.
C. Eamon, Ph.D., P.E., University of Michigan
Fatmir Menkulasi, Ph.D., Virginia Tech University