Static Measurement of Beam Deformations via Close-Range Photogrammetry

Preliminary results from a pilot study of beam deformation measurement using digital close-range terrestrial photogrammetry (DCRTP) are reported. The study consisted of both a laboratory and a field exercise. In the laboratory exercise, photogrammetric deflection measurements of a steel beam under single-point loading were made and compared with dial gauge readings and elastic beam theory. Laboratory results showed an accuracy ranging from 0.51 to 1.3 mm (0.02 to 0.05 in.). It was shown that DCRTP provides a feasible way of evaluating the global deflected shape of a structure, which is otherwise not practical using traditional instruments. In the field exercise, the initial camber and dead-load deflection of prestressed concrete bridge girders were measured photogrammetrically and compared with level rod and total station readings. Field results fit well to the rod-measured girder camber, and an average difference of approximately 3.2 mm (0.13 in.) was achieved compared with elevation measurements made with the total station. A comparison of the photogrammetric measurements with the dead-load deflection diagram was also made. Work is in progress to improve the accuracy of photogrammetric measurements for field applications. It is anticipated that DCRTP will provide highway agencies with a cost-effective alternative to high-cost systems using metric cameras or laser technology with the potential for several types of measurements in bridge applications.