Measurement of vibration frequencies of ties in masonry arches by means of a robotic total station

Measurement of the vibration frequencies of eight ties set in masonry arches of a church by means of a robotic total station is described. The instrument made continuous recordings (up to ten per second) of the three-dimensional positions of a reflector situated at 1/2 or 1/4 of the length of the tie during vertical oscillation induced by an impulsive load. The recording slips, vibration amplitudes (and their accuracy), hourly diagram and experimental spectra of vibrations, and the corresponding frequencies were calculated. The results were verified by comparing them with the vibration frequencies and indirectly the tension and fixed support constraint calculated from accelerometric measurements. The study provides interesting information on the accuracies of the reflector’s three-dimensional coordinates, but highlighted certain limits in the application of robotized total stations for measuring vibration frequencies of ties in masonry arches.