Moe Cheung

Operational Requirements for Long-Span Bridges under Strong Wind Events

In the absence of intensive wind tunnel tests, this study provides an effective and accurate approach to estimate the operational driving speed limit on bridges subjected to different road conditions and wind intensities, through a convenient continuous simulation technique CSP. A fast and vigorous simulation tool, vehicle performance simulation, is developed to effectively model the performance of vehicles traveling on bridges by considering the interactions between wind, vehicles, and the bridge. The CSP, on the other hand, dramatically reduces the data generation time and makes a reliability analysis of vehicles possible. The application of the proposed method on the Confederation Bridge in Canada is presented as a numerical example. The simulation result overrides the general impression that only high-sided vehicles are sensitive to wind attacks, and this work demonstrates that light-weighted vehicles are also likely to suffer from instability problems on bridges under relatively low wind velocity. In addition, different types of vehicle can undergo different instability mechanisms under the same wind condition and these vehicle instability mechanisms vary with wind velocity.

Behaviour of Concrete Beams Reinforced with Hybrid FRP Composite Rebar

Extensive research has led to a better understanding of the application of various corrosion protection methods in reinforced concrete (RC) structures and the use of fiber reinforced polymer (FRP) rebars is a typical example. However different fibres come along with different deficiencies, such as low elastic moduli and poor alkaline resistance in glass fibre (Saikia et al. 2007); brittle fracture and high cost in carbon fibre. Taking advantages of the strength of different fibres and the cost effectiveness of steel fibre, a hybrid composite rebar was recently developed. Steel fibers and glass fibers are distributed within the core, while aramid and carbon fibers created a shell for strength and corrosion protection. A series of concrete beams reinforced with the proposed hybrid rebars were tested and it was demonstrated that the beams have the ability to undergo large inelastic deformations, and the ductility indexes were found to be similar conventional steel-reinforced beams. Besides, accelerated alkaline ageing tests were performed using concrete pore solutions at different temperatures, and the service life and alkaline resistance of the proposed rebar were proven to be very good.

Closure to “Operational Requirements for Long-Span Bridges under Strong Wind Events” by Moe M. S. Cheung and Ben Y. B. Chan

Bilal Bakht; J. Peter C. King; and F. M. Bartlett, M.ASCE Bridge Seismic Engineer-in-Training, Ministry of Transportation and Infrastructure, Victoria, BC V8W 3C8, Canada; formerly, The Boundary Layer Wind Tunnel Laboratory, Univ. of Western Ontario, and Dept. of Civil and Environmental Engineering, Univ. of Western Ontario, London, ON N6A 3K7, Canada (corresponding author). E-mail: bilal .bakht@gov.bc.ca Managing Director, The Boundary Layer Wind Tunnel Laboratory, Univ. of Western Ontario, London, ON N6A 3K7, Canada. Professor, Dept. of Civil and Environmental Engineering, Univ. of Western Ontario, London, ON N6A 3K7, Canada.

Performance and Operational Allowable Speed Limit for Vehicles on Cable Stayed Bridges

The ever increasing numbers of fatal vehicle accidents worldwide on cable-stayed bridges under serviceable wind conditions, has rung the alarm bells for engineers to consider the safety issue in an operation level. The new generation of structural designs also involves the efficient and comfortable use of the structure by the end user. When this ‘design for the user’ concept is applied to bridges, investigation of vehicles traveling on long span bridges subjected to strong wind attacks not only allows the designer to have more understanding about the actual performance of a bridge at the operation level, but the safety and comfort of the drivers can also be studied. However, reliability analysis on a vehicle-bridge-wind system is such a time consuming process that it is usually considered infeasible in actual practice, especially when dealing with highly non-linear cable-stayed bridges. This study has constructed a general, yet efficient, vehicle stability analysis framework which makes possible the estimation of the maximum allowable vehicle velocity on cable-stayed-bridges subjected to different wind intensities. Non-linear properties such as the cable sag, geometrical non-linearity, and wind induced buffeting and fluttering effects are studied and implemented into the analysis framework. In addition, the numerical simulation procedure is optimized using the partial iterative process and the continuous simulation technique, which can significantly reduce the time needed for performing the reliability analysis. The result of the numerical example demonstrated that both high-sided vehicles and small vehicles are likely to undergo vehicle instability problems on cable-stayed bridges subjected to wind loading. It is also suggested that the allowable speed limit for vehicle traveling on cable-stayed bridges are significantly lower than the limit on box-girder bridges. Under serviceable wind loadings, the stability of a vehicle depends very much on the speed of vehicle, the roughness conditions on the deck, and the degree of the coupling effect between the bridge and the vehicle.