Abstract

Churches are part of heritage structures that take an important role in Europe's cultural identity. As such, these structures must be protected to prevent catastrophic collapse and any damage must be reported timely to establish planning to maintenance and restoration. This can be achievable when the churches are monitored periodically with regular intervals. However, this monitoring strategy has not been available in most of the Europe’s churches for a number of reasons, complexity of the structures and limited budget are just two of them. Laser scanning has been widely used in capturing rich three-dimensional (3D) topographic data of visible surfaces of a structure with high accuracy. This paper presents a methodology to determine the shape and possible deviation from verticality of the church’s tower for monitoring deformation using a terrestrial laser scanner. The 500-year old wooden tower of St. Bavo Church in Haarlem, Netherlands is selected as a case study. First, point clouds of the tower captured from different views are registered into the same coordinate system. Second, a RANSAC method is employed to extract point clouds of a whole façades of the tower. Next, a point and surface-based method is proposed to compute the deformation of the surface from its data points. The results indicate that there is slightly different deformation between the tower facades in the same story and in neighbour stories. Moreover, the maximum total relative deformation at Story 7 of the tower by 0.63m.

Abstract

This paper highlights the main objectives and some of the results of an extensive structural health monitoring (SHM) project begun in Khiva, Uzbekistan. The research team consists of experts from the University of California, Berkeley (Berkeley, USA) and Urgench State University (Urgench, Uzbekistan). According to archaeological data, the city of Khiva was established approximately 1500 years ago. The project started from Itchan Kala, the walled inner town of the city of Khiva. This paper describes results obtained for the Juma Mosque located inside of Itchan Kala. A continuous SHM became essential to ensure its preservation for humanity because a few structural anomalies were reported in the past. The ongoing project consists of three major phases. First, a terrestrial laser scanning (TLS) was deployed to capture and monitor anomalies of the monument’s geometry in 3D. A laser scanner was used, and the monument’s geometry was captured as a collection of points, which is called a “point cloud”. Second, there is a plan to monitor the monument by in-situ measurements conducted by accelerometers, position transducers and thermocouples in the next phase. The high-sensitivity accelerometers will be used to study the resonant frequencies due to the ambient vibrations. The position transducers and thermocouples will be used for measuring the thermal expansion and retraction of the monument’s minaret. They will also be used for monitoring the crack openings. Third, a finite-element (FE) model based on the as-found geometry of the point cloud will be generated. Its calibration will be based on the collected data to ensure acceptable correlations with the results of the conventional measurements. The FE model will be used for future restoration efforts to evaluate the performance and efficiency (if any) of the proposed restoration measures. This paper focuses on the results obtained for the Juma Mosque’s minaret. It discusses the major findings of the laser scanning project and estimates the minaret’s residual inclination and its taper. The paper shows that the minaret can be approximated by a truncated cone. A preliminary FE model of the minaret was developed, which will be updated based on the results of the upcoming ambient vibration study.