Ben Y.B. Chan

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.

Nonlinear dynamic analysis of fiber reinforced ultra-long span cable stayed bridges

The central span, which is the most critical part of a cable-stayed bridge, has almost reached the technical limit for traditional materials, construction technology and bridge system capability. The idea of Ultra-long Span Cable Stayed Bridge (USCSB) is proposed in this paper by introducing a hybrid type cable stayed bridge as a competent system. The new system leads to huge reduction in deck weight and critical stresses in the pylon zones by using a hybrid advanced composite deck. A multi-scale modeling technique is adapted which represents material design at the micro/macro-level, and accurate homogenization of the advanced composite components properties and evaluation of the resulting anisotropic characteristics. The dynamic performance under wind and seismic excitations, and the potential deficiency of such a bridge system is investigated via state-of-the-art computer simulations and large-scale dual shaking table experiments. The investigation result demonstrated that adopting a fiber reinforced polymer deck system can efficiently reduce internal deck stresses due to the high strength of FRP materials and the tubular type of lay-up structural system, increase its load carrying capacity of cable stayed bridges and hence, have a great potential extent the span length of stay cable supported bridge system. At the same time, due to the relatively low Youngs modulus and shear modulus of fibrous materials, deflection at full loading and torsional resistance should be carefully controlled by using a convex initial configuration with sufficient internal bracing. Moreover, investigation results also suggested that wind induced coupling excitation is likely to occur in such a light-weighted system with low shear and torsional stiffness.

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.