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Bridge Vulnerabilities
Oct 2010
What puts bridges at risk?
• Ability to withstand seismic forces and displacements
What puts bridges at risk?• Hazard factors (proximity, magnitude, duration…)• Site factors (soil conditions e.g. soft saturated soils)• Bridge design
– Bridges built before 1980 often have inadequate provisions for horizontal loading since modern seismic design codes weren’t adopted until late 1970’s
– Structural continuity; redundancy; skewed or curved– Seat width (support length); bearing type (high rockers)– Reinforcing details, especially in reinforced concrete piers– High piers; piers with varying heights
• Bridge condition– Fatigue; corrosion– Retrofitted?– Flagged?
• Consequence of failure (lifeline route, high AADT)
It’s all in the details.
Many of the following examples are from Hurricane Katrina but the concept is the same.
Shear blocks provides lateral restraint
7 Sept 2005 (85)
Lateral forces can move entire spans
8Sept2005 (8)
This and other examples are from Hurricane Katrina but the principle is the same.
Displaced Joint
8Sept2005 (12)
“Pounding”from longitudinal movement
8Sept2005 (16)
Pedestals provided lateral restraint
8Sept2005 (43)
Support Length
8Sept2005 (44)
Dropped Spans
8Sept2005 (62)
Lateral Shift
OConnor 19Oct (54)
Column Retrofit(Steel jackets & FRP Wraps)
Open Finger Joints
Unreinforced & Masonry Abutments
Floor Beam Hanger Detail
los molinos bridge sand boil
lateral spread 100_8525
Huamani pier
Huamani approach
Huamani approach 2
Huamani approach 2
fallen rock in bottom chord
cracked box culvert
bridge damge T3 101
100_8938
100_8783
100_8780
100_8779
100_8761
100_8753
100_8752
100_8751
100_8746
100_8658
100_8657
100_8658
100_8650
100_8590
100_8562
100_8561