Bridge protection systems
Bridge protection systemspreventship collisiondamage to abridgeby either deflecting an aberrant ship from striking thepiersof a bridge, or sustaining and absorbing the impact.[1]
History
[edit]Protecting bridges againstship collisionsgot attention of architects and regulators in the last third of the 20th century due to a marked increase in the frequency of collision accidents: worldwide, 30 major bridges collapsed in the 1960-1998 timeframe after being rammed by ships or barges, 321 persons were killed. The rate of smaller accidents is much higher: there were 811 serious accidents that did not cause a collapse just in the United States between 1970 and 1974, with 14 persons killed. Minor collisions are routine: theUS Coast Guardgets 35 reports per day.[2]
In the US, the turning point was the collapse of theSunshine Skyway Bridgein 1980. Since then,[2]
- A "Committee on Ship/Barge Collision" appointed by theNational Research Councilissued a report on the history of ship collisions with bridges[3](1983);
- TheLouisiana Department of Transportation and Developmentissued vessel collision protection criteria for the bridge piers in Louisiana (1984);
- Eleven states together with theFederal Highway Administrationcommissioned guidelines for the bridge protection design in the United States (1988);
- TheAmerican Association of State Highway and Transportation Officials(AASHTO) issued a Vessel Collision Design Guide Specification[4]in February, 1991, based on the previous study;
- TheInternational Association for Bridge and Structural Engineeringpublished its "Ship Collision with Bridges"[5]guide in 1993;
- AASHTO adopted theLRFDbridge design specifications[6]with provisions for bridge protection (1994).
Designs
[edit]There are several types of bridge protection systems used:[7]
- Fender systemsattached to the pier with the goal to absorb the vessel impact. Their ability to withstand a typical ship collision is low. Fenders are built using a variety of materials:[8]
- thin-walled concretebox;
- thin-walled steelmembranesteel;
- rubber.
- artificial islandsbuilt with sand and rock core that is protected byriprap.The islands are quite effective in protecting the pier by pushing the ship away, but cause environmental damage to the river bottom and, whilesettling,might shift the bridge piers;[8]
- dolphinsare made ofpilesdriven into the river bottom in a group, with space in between sometimes filled with rocks and capped with concrete. The collision is absorbed via deformations of the structure;[8]
- pile-supportedsystems on dedicated piles that are driven into the bottom either vertically or at an angle ( "batterpiles "). The piles are connected together with rigid or flexible links, can be attached to the pier, and sometimes are fitted with fenders;[8]
- floating systems(cable nets andpontoons) have multiple problems from low efficiency to high construction and maintenance costs and environmental impacts, and are therefore used as a last resort, when the location of the bridge precludes the use of other designs.[8]
- Starlingsare widenings of the bridge piers near their base, typically extending some distance above water level, providing some degree of reinforcement of the pier against impact.[9]
Alternatives
[edit]Physical bridge protection systems designed to prevent catastrophic collisions are expensive and represent a "significant" share of overall construction costs. Therefore, alternatives are typically considered during the design phase:[10]
- fortifying the piers and superstructure to the point where they will be able to handle the impact, either on their own, or with the help of a fender system;
- increasing the span length, so that the piers are away from thefairwayand thus protected by the shallow water around them;
- improving thenavigational aidsto reduce the probability of a catastrophic impact (60-85% of the collisions are due topiloterror.[11]
Regulations
[edit]Highway designs in the US are subject to the AASHTO specifications,[4][6]but the text does not contain specific procedures and recommendations.[2]Railway bridges are built according to the "Manual for Railway Engineering"[12]published by theAmerican Railway Engineering and Maintenance-of-Way Association(AREMA).[8]
InAustralia,the subject is covered in the Australian standard AS 5100.2:2017, "Bridge design, Part 2: Design loads".
References
[edit]- ^Knott & Prucz 2000,60.2.5.
- ^abcKnott & Prucz 2000,60.1.1.
- ^National Research Council, Ship Collisions with Bridges — The Nature of the Accidents, Their Prevention and Mitigation, National Academy Press, Washington, D.C., 1983
- ^abAASHTO, Guide Specification and Commentary for Vessel Collision Design of Highway Bridges. American Association of State Highway and Transportation Officials, Washington, D.C., 1991.
- ^IABSE(1993).Ship Collision with Bridges: The Interaction Between Vessel Traffic and Bridge Structures.Structural engineering documents. International Association for Bridge and Structural Engineering.ISBN978-3-85748-079-9.Retrieved2024-03-30.
- ^abAASHTO, LRFD Bridge Design Specifications and Commentary, American Association of State Highway and Transportation Officials, Washington, D.C., 1994.
- ^Wuttrich et al. 2001,p. 17.
- ^abcdefKnott & Prucz 2000,60.8.1.
- ^"Parts of a bridge and gloss".scotlandsoldestbridges.co.uk.Retrieved29 March2024.
- ^Knott & Prucz 2000,60.8.
- ^Knott & Prucz 2000,60.8.2.
- ^AREMA, Manual for Railway Engineering, Chapter 8, Part 23, American Railway Engineering Association, Washington, D.C., 1999.
Sources
[edit]- Knott, Michael; Prucz, Zolan (2000). "Vessel Collison Design of Bridges".Bridge Engineering Handbook(PDF).Boca Raton:CRC Press.
- Wuttrich, Rafal; Wekezer, Jerry; Yazdani, Nur; Wilson, Claudia (2001)."Performance evaluation of existing bridge fenders for ship impact".Journal of Performance of Constructed Facilities.15(1): 17–23.doi:10.1061/(ASCE)0887-3828(2001)15:1(17).