The Church of the Nativity in Bethlehem: Analysis of a Local Structural Consolidation

Abstract

An innovative technique for reinforcing a wall of the Church of the Nativity in Bethlehem against earthquakes is proposed. The use of such a technique was required due to the peculiarity of the site, recently added to the UNESCO list of World Heritage sites, which is important to both Christian and Islamic religions. Local seismicity data and the parameters of an equivalent Italian site provided the input data for a design earthquake, and 3D modal analysis of the entire Church revealed that the structure is characterized by clear local modes of vibration. As per the most recent studies on masonry structures, local assessment based on limit analysis procedures was performed. This showed that in the event of an earthquake, a Crusade-era wall addition is at risk of collapse via simple overturning around its own base, due to the lack of firm connections with the orthogonal walls of the facade and the transept. Hence, a novel double system of horizontal steel tension structures was designed to consolidate the wall, conforming to the main restoration Charter requirements, i.e. lightness, non-invasiveness and reversibility, and being hidden from the sight of visitors. In the absence of reliable local regulations, all analyses, computations and checks on the proposed intervention were carried out with reference to the Italian technical regulations.