Houghton Lift Bridge, Houghton, MI – Mechanical rework and painting of the double deck, vertical lift bridge at Houghton, MI had potentially changed the weight of the movable span. Lunda Construction, the primary contractor, was required by the Michigan D.O.T. to check the balance between the span and counterweights for proper and safe operation. At each corner of the bridge a large cable connects the span to the counterweight over a motor driven sheave. How could Lunda check the overall balance of this counterweighted cable system?

Binsfeld Engineering was contracted to measure the torque simultaneously on the four drive shafts to determine if an imbalanced condition existed at any of the four corners. With Micro-Measurementstorque sensitive strain gages and telemetry transmitters attached to each drive shaft, torque data was recorded concurrently as the span was raised and lowered. By comparing the lifting torque to the lowering torque, and correcting for friction, it was verified that the movable span was slightly heavier than the combined counterweights (a desired condition) and that all four corners were within acceptable balance with each other.