The Church of the Nativity in Bethlehem: analysis of a local structural consolidation

The paper presents an innovative technique for the reinforcement of a wall of the Church of the Nativity in Bethlehem against earthquakes. The choice of this particular technique stems from the peculiarity of the site, recently added to the UNESCO list of World Heritage sites, and important to both Christian and Islamic religions. A design earthquake, making reference to the local seismicity and parameters of an equivalent Italian site, provided the input data for 3D modal analysis of the entire Church. This revealed that the structure is characterized by clear local modes of vibration, which, according to the most recent studies on masonry structures, suggest local analysis based on Limit Analysis procedures. Due to the lack of firm connections with the orthogonal walls of the façade and the transept, in the event of an earthquake the Church is at risk of collapse through the simple overturning of the wall, here considered, around its own base. In order to prevent this, the Authors conceived and designed a novel tension structure, whose main features are lightness, non-invasiveness and reversibility, the main requirements imposed by all Restoration Charters. The structural consolidation proposed consists of an innovative double system of steel tension structures in the horizontal plane, fixed to the wall but 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.