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

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