CTLGroup designed, installed, and operated a structural monitoring system to measure and record the response of selected floor beams during load tests of the Canton Lake Spillway Bridge. The aim of the load testing was to estimate the current load carrying capacity of the aging bridge, which is owned by the U.S. Army Corps of Engineers.
The bridge consists of sixteen spans, each having two main longitudinal girders connected through five transverse floor beams (two end beams and three intermediate beams). The monitoring system was designed to evaluate the axial strains due to flexure of the floor beams under load as test trucks passed over the bridge. The load test consisted of positioning 1-2 dump trucks with a prescribed load at 18 different positions on each span.
The monitoring system developed by CTLGroup included a total of 21 vibrating wire strain gages installed at key floor beam locations. The long gage length vibrating wire sensors were mounted between blocks epoxied to the surface of the concrete floor beams. Deformation of the structure under load produced relative movement between the mounting blocks causing a change in tension of the enclosed steel wire in the sensor. The vibration frequency of the enclosed steel wire was measured using a spectrum analyzer as tension changed, and the frequency measurements were correlated to the change in strain at the surface of the floor beam. Data acquisition equipment produced by Campbell Scientific, Inc. were used to measure and record the response data during the testing.