A vertical strut of the 1232-foot long, self-anchored Paseo Suspension Bridge fractured when the temperature hit at a record low of 9°F below zero. During inspection the following day, it was found that its lower pin was frozen and did not allow for free movement of the superstructure. The objective of this study is to pinpoint one of the four reasons for this incidence or their combination: overstressing, thermal contraction, fatigue, and reduction in fracture toughness at low temperatures. To achieve this objective, material property and fatigue testing was performed on samples of strut material while the bridge and strut were analyzed under service loading conditions. This study indicated that the strut material practically has an infinite life under normal conditions. The root cause of the failure is overstressing of the vertical strut due to a frozen pin that became frozen because the design of the bridge did not allow the pin to be maintained. The mechanically frozen pin condition was attributable to salt and sand accumulation in the strut housing. To prevent this to the new struts and other similar structures, it is recommended that both upper and lower pins be greased during special inspections and the lower housings be partially sealed to prevent salt and sand accumulation near the pins. Alternatively, a rotation monitoring system can be installed to remotely monitor the rotation of all four vertical struts and alert officials should the pins become mechanically frozen.
G. Chen et al., "Failure Investigation of the Steel Strut of Paseo Suspension Bridge," University of Missouri-Rolla, Jun 2005.
Civil, Architectural and Environmental Engineering
Missouri Department of Transportation
Keywords and Phrases
Fracture; fatigue resistance; suspension bridge; frozen pin; crack initiation life; crack propagation life
RDT-05-008 & RI-03-015
© 2005 University of Missouri-Rolla, All rights reserved.
01 Jun 2005