How do you fasten the steel framework of a building to its concrete slab? Concrete anchor bolts are installed by drilling a hole in the concrete slab with a carbide drill, inserting the anchor and then expanding it into place with a special punch. The result is a threaded hole in the concrete slab to which structural pieces are fastened. How strong is this anchor and how can it be tested?

To test concrete anchors, several are placed in a test slab. A fixture is bolted to the anchor that is connected to a hydraulic cylinder. The cylinder exerts an upward force on the anchored bolt, trying to pry it out of the concrete. The amount and duration of this force depends on the size of the anchor, but if there is any movement of the anchor, it must be detected.

Instrumentation of the test setup includes an LVDT sensor for measuring very small displacements and a load cell to measure the applied force. The LVDT sensors are capable of measuring displacements of as little as a few ten-thousands of an inch. They require AC excitation and return an AC signal proportional to displacement. The strain gage load cells measure force and require a precision DC excitation. They return a very low level DC signal that must be amplified to be useful. A versatile signal conditioning system is needed to accept the low-level LVDT and load cell sensor inputs and produce a high-level +/-10 Vdc signal for the data acquisition system.

To record the force and displacement measurements a multi-channel data acquisition system is needed that can display the readings in engineering units and record them to a disk file suitable for importation into Excel for the final report.