A low-cost photogrammetric methodology to obtain geometrical data of masonry arch bridges

The geometry of bridges is one of the parameters that define their structural strength. The geometry of modern bridges is the result of computer-aided design (CAD) modelling and computer-aided engineering analysis and, in consequence, the collapse loads are well-known. For ancient bridges (i.e. masonry arched bridges), when the CAD geometry is unavailable; it becomes necessary to find a methodology that facilitates the acquisition of such data in order to determine the critical loads. This works aims to develop a low cost photogrammetric methodology for acquiring the geometrical data of masonry arched bridges. This methodology was applied to 20 arches of 11 masonry bridges and the results compared against the classic approach with planimetric method using a Leica TCRM 1205 Total Station. The maximum error in the span could reach 2.32% in the case of the image with greater perspective. Based on the acquired geometry, and in terms of strength, the structural analysis for the different bridges shows that the average error in the load capacity between both methodologies is 4.01%, while the average difference for the load positioning is 5.54%.