Non-contact based photogrammetric technique for testing of rigid blocky masonry arch

Abstract

In case of dry jointed stone structural systems, the stone blocks can be assumed to be rigid with relative predominant displacements occurring along the joints giving rise to geometric non-linearity in these systems. The testing of such discontinuous systems becomes challenging task with contact-based measuring instruments such as LVDTs as the blocks are free to displace and/or rotate with six degrees of freedom. This technique is more often used for surveying of large existing structures in the field of civil engineering and its applicability to testing of structural systems has not been explored to a larger extent yet. The photogrammetry with motion module has been observed to be the one of the most reliable and feasible methods of instrumentation for dry jointed stone structural systems. With few quality control measures adopted from taking photos to the processing stage, sufficient accuracy of measurements can be achieved. In the present study, non-contact-based technique, photogrammetry is used for testing of a typical dry-stone corbel vault taking a scaled down model of an existing vaulted gallery of Ta Prohm, Cambodia. The findings from the study have been in agreement with the observed distress in the existing corbel vaulted galleries. It has been proved to be efficient, low cost method that uses simple handheld digital cameras giving reliable results with an accuracy up to 0.4 millimetres. Thus, photogrammetry is a way forward for testing of discontinuous structural systems such as dry-stone masonry.