load testing for concrete bridges

huangyhg

load testing for concrete bridges
i am looking for a method or peice of equipment to use to determine whether or not an existing concrete bridge (built in 1921) will carry up to 40,000 lbs.  any ideas?
thanks, doug

aci has a general method for performing a full scale load test on a concrete structure. i had one conducted in 1990 on a building that had a "hard life". you apply load up to high percentage (about 90%, based on memory) of (carefully) calculated ultimate strength. we used sand about 4 feet deep (with geotechs monitoring in-place density) for the load. a qualified testing firm monitored deflections. see the aci code for current information.
i have done about half a dozen full-scale, static or rolling load tests on bridges and parking decks.  the process we use is to instrument the bridge with strain gages and deflection measurement devices (lvdt's or digital dial gages), then use an "overloaded" dump truck or similar to create as close to a "standardized" load as practicable (h18, h20, etc), run multiple tests and compare the data with computed stress distributions and deflections from a structual model of the bridge.  the most difficult part is modeling an old bridge because it's difficult to determine how it was constructed unless you have the validated drawings.
with the field information, we can also determine the structure's "global" response to load and usually assess its capability and viability.
mwest, some more details would be very helpful.
i guess you have a bridge without a certified capacity and no as-con drawings to calculate a capacity or unsufficient justification to assess the bridge's capacity.  do you have to allow for general traffic loads or a single movement (a loaded truck over a private bridge perhaps)?  your approach may vary, depending on the circumstances.