Heavy truck traffic on highway bridges is known to produce impact load
s that cause large vibrations. This phenomenon can reduce the expected
service life of many highway bridges. A means to mitigating those del
eterious vibrations using an automatic control system that requires no
pumps or line power is proposed. A semiactive hydraulic bridge vibrat
ion absorber that can be retrofitted to an existing bridge is describe
d. The bridge/vehicle system is modeled, and a practical feedback cont
rol that uses either strain-gauge or accelerometer readings to sense t
he state of the system is synthesized. The results of an experimental
test of the new system indicates reductions of peak amplitudes of 65-7
0%.