Multidisciplinary Approach for the Analysis of Structural Heritage at Risk: The Case Study of Stylite Tower at Umm ar-Rasas (Jordan)

ABSTRACT

The results of multidisciplinary research carried out on the Byzantine Stylite Tower in Umm ar-Rasas archaeological site (Jordan) are presented in this paper. The study is grounded on the precarious structural conditions of the tower, assessed by UNESCO since 2008. In 2019, during an archaeological campaign, an aerial photogrammetry survey was performed, allowing for the creation of a detailed 3D model of the tower. This new dataset was compared with existing Geomatics surveys (collected in 2016 with Terrestrial Laser Scanner) within a common reference system, showing that the tower leans dangerously in the northwest direction. With the combined use of the photogrammetric and historical investigations data, the structural vulnerability of the building was analysed in-depth. Starting from the new point cloud dataset, a multi-step geometrical modelling strategy was performed to define the structural model based on the actual geometry of the tower. 3D documentation with aerial photogrammetry made it possible, for the first time, to account for the actual 3D geometry of the upper cell in the structural analysis of the tower. Several possible out-of-plane mechanisms involving the upper cell walls and portions of the tower façades were analysed via kinematic analysis using the floor response spectra. The study revealed a new critical and risky scenario, which suggests a prompt intervention for the safe conservation of the tower.

KEYWORDS:

• 3D reconstruction
• heritage masonry tower
• out-of-plane mechanisms
• seismic vulnerability
• structural monitoring
• UAV photogrammetry

Acknowledgments

The authors wish to thank Dr Roberto Gabrielli for helpful discussions on paper issues and for providing the Stylite Tower point cloud obtained by TLS during the 2016 campaign.

This work was partially supported by the Italian Ministry of Foreign Affairs and International Cooperation within the project: “The heritage of the structures in the Jordan archaeological sites: construction, conservation and enhancement”, (https://www.ispc.cnr.it/it_it/2021/03/29/the-stylite-tower-and-the-castrum-of-umm-ar-rasas-jordan/).

Disclosure statement

No potential conflict of interest was reported by the author(s).

Notes

¹ The decision was adopted at the 28^th session of the World Heritage Committee, Suzhou, China 28 June — 7 July 2004 and WHC-04/28.COM/26.

² 34COM 8E — Retrospective Statements of Outstanding Universal Value (https://whc.unesco.org/en/decisions/4261, Accessed April 7, 2021).

³ Antiquities Law n. 21, 1988 and modified Low n. 23, 2004 (https://whc.unesco.org/en/statesparties/jo/laws, Accessed April 7, 2021).

⁴ Joint ICOMOS / World Heritage Centre Reactive Monitoring mission to Jordan, 17–21 November 2006 (https://whc.unesco.org/en/list/1093/documents/, Accessed April 9, 2021).

⁵ Umm Ar-Rasas Site Management Plan, ref. Um er-Rasas 20,180,227 (https://whc.unesco.org/en/list/1093/documents/, Accessed April 9, 2021).

⁶ Ref. 1819 Restoration of the ”Stylite” tower of Um Er Rasas 26 Jan 2007 (https://whc.unesco.org/en/list/1093/documents/, Accessed April 9, 2021).

⁷ WHC Expert Mission Report, Um er-Rasas, 28 June-8 July 2008, (https://whc.unesco.org/en/list/1093/assistance/, Accessed April 9, 2021).

⁸ Ref. 1966 Investigations and emergency measures for the restoration of the Stylite Tower of Um er-Rasas, 16-Feb-2009 (https://whc.unesco.org/en/list/1093/documents/, Accessed April 9, 2021).

⁹ WHC State of Conservation Report, 2019 (https://whc.unesco.org/en/soc/3936, Accessed April 7, 2021).

¹⁰ https://www.ispc.cnr.it/it_it/progetti-2/missioni-maeci/.