Studying Taiwan's quake-proof bridges
Published on: Sunday, April 24, 2016
Kota Kinabalu: The collapse of two key bridges in Kundasang during the near 6-magnitude earthquake with the epicentre in Ranau last June cut off access to Sabah's foremost vegetable growing farmlands. This raised the prices of vegetables as supply reaching the market dwindled.An acceptable earthquake code was demanded by local cost-conscious developers and consulting engineers downplaying the seriousness of another more serious magnitude strike in Ranau actually not affecting Greater Kota Kinabalu or other areas. However, recent damaging earthquakes suggest that this is not necessarily true, e.g. earthquakes larger than those used in design collapsed bridges in Kobe and Taiwan; and smaller events collapsed spans in US, e.g. Loma Prieta.
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In any region where the PGA (Peak Ground Acceleration) increases significantly with return period, this is not likely to be true.Risk mitigation methods to reduce earthquake losses need a great effort for development and implementation.The most difficult in mitigating earthquake hazards is that an earthquake strikes without notice. There is no way to accurately predict when an earthquake will occur, nor what its magnitude will be.
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Earthquakes can be devastating, resulting in deaths, injuries and extensive infrastructure damage. Losses will occur in just one or two minutes. Systematic approaches to evaluating earthquake risks, including direct and indirect losses such as economic impact, should become an important issue in our engineering and building community.
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Sabah has a lot to learn from the Republic of China or Taiwan, especially in earthquake resistant construction, including for bridges, as earthquakes are inevitable in Taiwan for years as well as research products in seismic retrofitting of truss bridges or so along the Pan Borneo Highway.Near-fault ground motions in Ranau epicentre can be different from ordinary ground motions in that they often contain strong coherent dynamic long period pulses and permanent ground displacements. The dynamic motions are dominated by a large long period pulse of motion that occurs on the horizontal component perpendicular to the strike of the fault, caused by rupture directivity effects.Near fault recordings from recent earthquakes, such as Chi-Chi earthquake (Taiwan), indicate that this pulse is a narrow band pulse whose period increases with magnitude, as expected from analysis.Hence, the Sabah Public Works Department (JKR) invited Taiwan's National Centre of Research on Earthquake Engineering (NCREE) research fellow, Dr Hung Hsiao-Hui, to deliver a paper entitled 'Consideration on Design and Construction of Bridge Structure in Taiwan'. It was jointly researched with Division Head of the NCREE, Professor Sung Yu-Chi of the National Taipei University of Technology, last Wednesday (April 6) here at the Sabah Road Day 2016 themed 'Sustainable Road for Development' at the Magellan Sutera Resort.A state or country's land surface transportation is a vital component of society. Bridges and highways link airports, bus and train stations, harbours, manufacturing plants, farms, offices and residences.This transportation network must continue functioning during and after a natural hazard such as an earthquake so that the lifelines of society may be restored as soon as possible.Of all the components of the land surface transportation system bridges are the most vulnerable to earthquake damage. In Taiwan, a rare and severe earthquake, such as the 1999 Chi-Chi earthquake, would cause many casualties.Recent earthquakes such as US' Loma Prieta in 1989, Northridge in 1994 and Kobe, Japan in 1995 and Chi-Chi earthquake in Taiwan in 1999 have demonstrated the need to find new ways to build earthquake-resistant bridges and highways, and to retrofit existing bridges.Recognising the shortcomings evident in both existing bridges and design is crucial to plan for future earthquakes that may be more powerful.However, it is not commonly known that frequent moderate earthquakes may affect the regular operation of facilities and industries in Taiwan, thus, greatly threatening people's lives and impacting Taiwan's competitiveness."During an earthquake, a bridge can collapse by faulty components, pier damage, or support failure due to the large magnitude seismic cross fault or near fault shock, soil liquefaction, poor structural system or insufficient seismic capacity contributed to by inadequate arrangement of reinforcement and poor unseating prevention devices," she said.Advances in the state-of-the-art of seismic design for highway bridges can be strongly correlated to the occurrence of damaging earthquakes over the years as Taiwan kept improving its seismic standards for better safety."Design details to prevent undesirable failure patterns, such as shear failure, joint failure and foundation failure are improved. The design demand should be based on plastic moment capacity of the selected ductile components," she said.Her presentation input will serve the Pan Borneo Highway consideration along Ranau or Lahad Datu well.Stay up-to-date by following Daily Express’s Telegram channel.
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