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

Lateral forces can move entire spans This and other examples are from Hurricane Katrina but the principle is the same.

Displaced Joint

“Pounding” from longitudinal movement

Pedestals provided lateral restraint

Support Length

Dropped Spans

Lateral Shift

Column Retrofit (Steel jackets & FRP Wraps)

Open Finger Joints

Unreinforced & Masonry Abutments

Floor Beam Hanger Detail