------   Impact Treatments for Improving the Fatigue Performance of Welds

Collaborators: R. Tehrani Yekta (MASc), K. Ghahremani (MASc), Prof. T. Topper, Prof. K. Papoulia
Financial Support: MTO, CISC (SSEF), NSERC

Brief Summary: Two master's thesis projects have looked at needle peening and ultrasonic impact treatment (UIT) for increasing the fatigue performance of welds. Impact treatments such as these work primarily by introducing compressive residual stresses near the surface of the treated weld toe, which have the affect of slowing or arresting completely the growth of small fatigue cracks. The research has included fatigue testing, metallurgical analysis, and nonlinear fracture mechanics analysis to study the effects of variable amplitude loading conditions on the treatment effectiveness, as well as the effect of treatment quality variations on the fatigue life increase resulting from UIT.

------   Fatigue Testing and Analysis of Aluminum Bridge Welds

Collaborators: R. Coughlin (MASc)

Brief Summary: This research project included fatigue tests, metallurgical analysis, and nonlinear fracture mechanics analysis to study the behaviour of aluminum bridge welds under variable amplitude loading conditions typical of highway bridges. In addition, a simulation-based study was performed to develop new fatigue correction factors for use in the CAN/CSA S6 and AASHTO highway bridge design standards for the fatigue design of aluminum welded connections with varying S-N curve slopes.

------   Fatigue Retrofitting of Welded Steel Bridge Connections by FRP Reinforcement

Collaborators: F. Vatandoost (MASc), K. Ghahremani, Prof. K. Soudki, Prof. T. Topper
Financial Support: MTO 

Brief Summary: A master's thesis project was undertaken to evaluate the effectiveness of prestressed carbon fibre-reinforced polymer (CFRP) strips for increasing the fatigue performance of welded cover plates in steel bridge girders. This project included an experimental study and a finite element (FE) and fracture mechanics analysis. In general, it was found that a very high prestress level was needed to overcome the tensile residual stresses in the weld toe region. A second project, undertaken within the scope of a broader PhD study, looked at the retrofit of web stiffener ends using adhesively bonded glass fibre reinforced (GFRP) angles. This study showed the proposed retrofit to be effective in reducing the local (hot-spot) stress, thus resulting in a significant fatigue life increase.

------   Steel-Precast Concrete Connections for Accelerated Bridge Construction

Collaborators: M. Bowser (MASc), Y.-T. Chen (MASc), M. Sjaarda, Prof. Y. Zhou (Chang'an), Prof. J.S. West
Financial Support: CISC (SSEF), Surespan Inc., NSERC

Brief Summary: Two master's thesis projects have been completed in this area, and several other graduate thesis projects are currently underway. The first project compared alternative shear connection solutions and proposed a novel "panel end connection" with temporary and accelerated bridge construction applications in mind. A finite element (FE) analysis-based study was then performed to show that the full capacity of the composite girder could be achieved, even with discrete shear connections at a spacing as large as the panel width. The second project involved experimental study of a pretensioned through-bolt connection and FE analysis of bridge girders with the load-slip behaviour of this connection type considered. The study found that the full composite capacity of the girder can still be achieved, despite the relatively low initial slip load of the pretensioned through-bolt.

------   Vibration Behaviour of Aluminum Pedestrian Bridges

Collaborators: A, Sychterz (MASc), P. Dey, Prof. S. Narasimhan
Financial Support: MAADI Group, AAC, NSERC 

Brief Summary: One master's and one PhD project are looking at the vibration of aluminum pedestrian bridges, with a view towards improving our ability to model the observed vibration behaviour and producing more reliable and economical aluminum pedestrian bridge designs. This research has included field monitoring of the 44 m long Daigneault Creek aluminum pedestrian bridge in Brossard, QC, as well as laboratory measurements of a 75' long modular aluminum "Make-A-Bridge" specimen, provided by MAADI Group. The measured vibration behaviour has been compared to analytical predictions and additional work is underway to compare and evaluate different pedestrian load models.

------   Corrosion Effects and Durable Material Selection in Highway Bridge Applications

Collaborators: N. Damgaard (MASc), J. Luckai (MASc), A. Masnavi (MASc), Prof. C. Hansson, Dr. D. Fernando (UQ), Prof. B. Adey (ETHZ), Prof. M.A. Polak
Financial Support: MTO

Brief Summary: Research in this area has included a master's thesis project on improving the corrosion performance of weathering steel highway bridges by applying metallizing coatings in regions where the natural corrosion resistance is seen to be insufficient. This project included corrosion testing of metallized samples and structural reliability analysis of corroding girders. A follow-up project, performed with researchers at the ETHZ, developed a methodology for determining when this approach makes sense from a life-cycle cost perspective. Two other master's thesis projects have looked at the assessment of concrete girders with flexural reinforcing exposed as a result of corrosion product build-up. These projects have resulted in the development and experimental validation of a new "modified area" concept for rapid assessment and retrofit prioritization.