A Structural Paradox in the Church of the Nativity: FE Static Analyses

The colonnades of the Church of the Nativity in Bethlehem are topped by wooden architraves above which the masonry walls of nave and transept were erected. During the archaeologic campaign carried out in the Thirties of the last century the presence of relieving arches was discovered between the architraves and the walls, hidden for centuries under thick layers of plaster and walls mosaics. Each arch covers the span between two columns and rests on the underlying architrave without any direct link other than that provided by friction at the interface. This peculiar construction system caused over time a crush of the most compressed parts of the architraves and was thought as one of the possible causes of some cracks now visible in the central column of each corner. Here the resultant of the horizontal components of the two thrusts coming from the two arches of the corner should be transferred to the architraves by friction, as no particular connection, like nails or iron rods, was found between masonry and architraves. But, the standard friction coefficient between wood and masonry is not enough to ensure this interaction at the interface and, according to the approximate calculations made with linear elastic models, an overturning of the central columns and of the structure above should occur. Nevertheless, despite some weakness planes surveyed in these columns, there are no signs of incipient collapse and both corners seem to be quite stable. The aim of this paper is to use appropriate numerical simulations to create different scenarios that might justify the present static situation. The numerical analyses will take into account the nonlinear behavior of masonry, the orthotropic behavior of the wooden architraves and the unilateral contact between masonry walls and architraves.