Preserving Long Span Bridge Suspension Systems

Long span bridges with suspension systems require periodic inspection and maintenance to ensure critical components continue to function properly. In most cases, these vital components are not redundant, and replacement of the non-redundant members can be costly or in some cases not feasible.

Suspension bridge main cables are typically constructed of thousands of high strength galvanized steel wires. Main cables are typically inspected by the owner on a periodic basis to evaluate the condition and obtain a factor of safety. Based on these results, repair and preservation techniques may be explored to prolong the lives of the cables. Over the past 20 years, dehumidification has become a technology embraced worldwide to protect and preserve main cables.

Anchorage saddle enclosures, constructed of steel plate at deck level, are subject to high levels of roadway salts during winter months and stopping corrosion from occurring poses a challenge, particularly at interfaces. These enclosures play an important role in protecting the main cable in that, if these enclosures fail, exposed strands of main cable become vulnerable. In tandem with dehumidification, proper sealing and maintenance of saddle enclosures is necessary to prolong the lives of the main cables.

Suspender ropes on tied arch and suspension bridges are the key elements in transferring the dead and liveload from the deck to the arch or main cables. These elements are typically inspected visually on a biennial inspection regimen looking at the bearing assemblies as well as the portions of the ropes at both points of connection. Proactive maintenance of sealing details to prevent brine and water infiltration is required to prevent corrosion of ropes and bearing assemblies. Laboratory testing to establish the ultimate strength and factor of safety of ageing ropes has also been found to be informative. Preservation of long span bridge suspension systems can be achieved through ever-refined technology and active maintenance. This paper will present the best practices utilized by professionals worldwide.

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