An innovative method for remote measurement of minimum vertical underclearance in routine bridge inspection

This paper presents an innovative and low cost procedure for the complete and accurate measurement of minimum vertical underclearance in a safe environment for operators. This procedure draws on the principles of terrestrial convergent photogrammetry which makes possible the reconstruction of the bridge components and surrounding features in 3D space. Using the measured 3D coordinates, an algorithm was developed in the Matlab software to calculate the vertical underclearance. Furthermore, a procedure based on 3D curve fitting was developed to estimate the mathematical expression of the beam curve. The resulting methodology is suitable and advantageous for implementation in routine bridge inspection because it provides a more extensive and accurate measurement of vertical underclearance under much safer conditions. In addition, the estimate of the beam equation can be used not only for clearance measurement but also for periodic monitoring of the beam shape over time.