Design Bridges for Extreme Events
	Home  |  Solution Center  | Company Profile  |  Directory  |  More About Us  |  Order Online  |  Services   |  Event Calendar  |  Opportunities  |  Misc. |  Links Design of Bridges for Extreme Events Lubin Gao, Ph.D., P.E. Bridges should be designed for extreme events that a bridge may be exposed to during its service life. An extreme event could result from any natural hazard, i.e. volcanic eruption, earthquake, landslide, hurricane, tornado, flood and wild fire, or man-made hazards such as bombing, collision, fire or terror attack, if the bridge is close to the site of the hazard. The consequence of the combination of a hazard and human activities, so called a natural or man-made disaster, could be significant in addition to the damage or destruction of the bridge. A natural disaster could even be an event that causes the end of civilization. Man-made disasters are the loss of life and facilities that caused by made-made hazards. Comparing to natural disasters, the impact of made-made disasters may be concentrated in a small area, but it could be serious to a bridge structure. This site maintained by Dr. Lubin Gao, P.E. provides some informative and historical data of the bridge disasters. Copyright by Lubin Gao, Ph.D., P.E. and SAS Suite LLC. All Rights Reserved. Natural Hazards A natural hazard is a physical event from an environmental change resulting in the impact on human life. Following are a list of such hazards that have potential effect on a bridge and that should be evaluated in the design process of the bridge: Geological Hazards: such as Earthquake, Landslide, Volcanic eruption etc. Water Hazards: such as Flood, Tsunami etc. Climatic Hazards: such as Cyclonic Storm, Tornado, Blizzard and Heat wave etc. Fire: Wild Fire Man-Made Hazards A man-made hazard is a man-made event that results in the significant impact on human life, such as explosion, fire and collision. Because of its man-made characteristics, it may cause severe damage or destruction to a structure. Man-made hazards could be derived internationally or un-intentionally. A terror attack of bombing is an example of the first kinds and a fire that burns down a bridge resulting from a traffic accident of gasoline tank is an example of the second kinds of man-made hazards. Negligence or errors in design or construction of a structure that results in the collapse of the bridge or severe loss of life during construction of the bridge is also an example of the man-made hazards. Explosion Collision Man-Made Fire Terror Attack Negligence or Error in Design or Construction Characteristics of Hazards The main characteristics of hazards, natural or man-made include Sudden Hard to Prediction Excessive Loads Destructive Return Periods One of the important problems of designing bridges for extreme events is to predict the effects, such as loads and damages of the structure during the extreme events resulting from a natural hazard or man-made hazard. Significant efforts should be put into the estimates of the likelihood of the occurrence of a given duration and intensity of events. The return period of an event is to measure the probability of a certain event. It is defined as the frequency with which you would expect, on average, a given event to recur. Risk Assessment Risk assessment involves the prediction of the chances of a specific set of events occurring and their consequences. Exceedance probability curve can be used to help decision-making. The vertical axis of an exceedance probability curve is the measure of losses, economical or social. The horizontal axis the return periods in years of a specific set of events.
	Design Event The design life of new highway bridges is 75 years in accordance with the AASHTO Specifications. For extreme events resulting from natural or man-made hazards, the magnitude of effects of the event on the structures should be determined by the risk assessment to achieve the cost effectiveness balancing the initial cost and the losses or cost to retrofit the damage from the event. The return period determined by the risk assessment and the intensity of the effects of the event are to be used in the design of the bridge.
	Disasters of Bridges The disasters of bridges resulting from an extreme event, natural hazard or man-made hazard, could be intensive. This link leads you to some of the well-known cases. A List of Bridge Failures Excerpted from the paper “Bridge Failures – A Summary and Evaluation” by Lubin Gao, Ph.D., P.E. and Richard A. Lawrie, FACI , P.E., presented on New York City Bridge Conference, 2007.
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