Issue 14, February 2008

Home | English | | | UGC | RGC
Think Big . Think Impact . Think Global - RGC Chair Urges Academics
Predicting the Influence of
Crosswinds on Vehicles
and Cable Bridges
Addressing the Injustice of Space and Housing
Globalisation of Popular Culture
Translations Bring Gao Xingjian's Work to Broader Audience
Best Practice for Project Briefings
New Measurement Aids Understanding of Cement Hydration

Economic growth and modernisation has resulted in greater demand for transport infrastructure, including long-span cable supported bridges which are designed to carry large volumes of vehicle traffic and railways and, in some cases, both forms of transport simultaneously.

By the end of year 2008, China will have 50 long span cable supported bridges, each with a main span of more than 400 metres. In Hong Kong, the Tsing Ma Bridge, completed as part of the Government's airport infrastructure programme in the 1990s, is the longest combined road/rail bridge in the world with a main span stretching 1377 metres.

Ambitious bridge projects are often constructed along coastal areas and cities that are vulnerable to typhoons and high-speed winds. A team from The Hong Kong Polytechnic University led by Professor Y. L. Xu, Chair Professor of Structural Engineering in the Department of Civil and Structural Engineering, has undertaken a series of studies focusing on the interaction between trains, vehicles, crosswinds and oscillating long span cable bridges.

The research has been supported by the Hong Kong Government's Highways Department and the Research Grants Council.

"We have focused on the Tsing Ma Bridge and adopted a systematic approach in our research, in particular wind and vehicular affects on the bridge," said Professor Xu.
"We established vehicle, train, bridge and wind models and looked at the overall interaction between the various elements."

Tsing Ma Bridge has an upper deck that is used by vehicular traffic, an enclosed lower deck used by fast trains and a second enclosed deck that can be used by cars, buses and trucks during typhoons. In extreme typhoon conditions the bridge, which links urban Hong Kong to the international airport, is closed.

Professor Xu and his team, using funding from the Research Grants Council, established a numerical model that applies simulated wind and traffic loads to predict the bridge's response to specific wind and traffic conditions.

The monitoring system installed on the Tsing Ma Bridge by the Highways Department provides field data to verify the numerical model, giving a clear picture of just how the bridge behaves in high wind conditions and under different railway and highway loads. Wind speed thresholds have been established to indicate when the top deck traffic needs to be re-directed to the enclosed deck and when the bridge should be closed completely.

"This project has helped us understand bridge-vehicle interaction during cross-winds," Professor Xu says. Research results continue to be applied to Hong Kong's bridges as well as long span cable supported bridges in mainland China. This research is facilitating understanding of the aerodynamic behaviour of vehicle-bridge systems and has attracted the attention of researchers and engineers internationally.

To facilitate further research and practical application, Professor Xu and his team have designed a 1:150 scale replica of the Tsing Ma Bridge. The model, manufactured in Guangdong, has been assembled and calibrated at The Hong Kong Polytechnic University. Sensors have been installed along the length of the model to measure the force, stress, vibration and displacement of the span in various load conditions. "Ultimately, this model will be used as a test platform to test various algorithms and methods developed by researchers around the world in the field of bridge structural health monitoring including system identification, model updating and damage detection," said Professor Xu.

Professor Xu You Liu
Department of Civil and Structural Engineering
The Hong Kong Polytechnic University