Optical Tooling for Precise Structural Measurements

An experimental application of optical tooling to a structural engineering problem was made in the Truss Bridge Research Project at Northwestern University. The methods and equipment used to measure translations and rotations at joints and members of a 100-ft half-scale steel bridge are described. In view of the precision required in these measurements, an optical instrumentation system was used, capable of measuring translations to 0.001 in. and rotations to 0.00005 radians with respect to three coordinate axes. The instruments and techniques of optical tooling are described briefly, as well as the manner in which they were organized for this study. The instruments and techniques used are standard; the targeting of the structure is unique, and the success of this portion of the investigation depended on it. Also unique are the mathematical analysis of the instrumental data and the method given for computing the rotations and translations of a typical point on the structure. Both the instrumental application and the mathematical treatment are general in nature, and they have a wide range of application to problems of measurement of small changes in space structures.