Diagnosis and Seismic Analysis of the Our Lady of Conception Church, Portugal

Abstract

The Our Lady of Conception church, located in village of Monforte (Portugal), is classified as a Public Interest Building and is not in use nowadays. The church is constituted by the nave, the chancel, the sacristy, and the corridor to access the pulpit. The total longitudinal and transversal dimensions of the church are equal to 21.10 and 12.50 m, respectively. The structure presents masonry walls with different thickness, buttresses, and barrel vaults. Due to an intervention carried out in the past, the church presents also ring beams at the top of the walls and concrete slabs. The structure presents severe damage, and a study was performed. The study involved the damage survey, dynamic identification tests, and the structural analysis. The damage survey showed that, in general, the masonry walls are in good conditions, with exception of the transversal walls of the nave, which present severe cracks. The ribs of the vault of the nave present also severe cracks. As consequence, the infiltrations of the rainwaters have increased the degradation of the vault and paintings. Furthermore, the external floor presents settlements in the southwest direction. The dynamic identification test was carried out under the action of ambient excitation and allowed to estimate the dynamic properties of the church, namely frequencies, mode shapes, and damping ratios. A numerical model was prepared and calibrated, based on the first four experimental modes estimated in the dynamic identification tests. The average error between the experimental and numerical frequencies of the first four modes is equal to 4 %. The results of the seismic analysis showed that the transversal direction of the church is the most vulnerable direction, in which the load factor is equal to 0.35. In the pushover analysis in the transversal direction, the transversal walls present diagonal cracks and the vault of the nave presents severe damage. In the pushover analysis in the longitudinal direction, the collapse of the church corresponds to the out-of-plane collapse of the main facade (load factor equal to 0.65).