Influence of damage to a timber truss roof structure on the stress distribution in a 17th century brick masonry vault

• Decay of the timber elements in a joint resulted in the displacement of the truss. • Despite the failure of a support joint in a truss, the structure had not collapsed. • The three-dimensional analysis helped to recognise the static work of the structure. • The general safety of the timber roof and the masonry vault was not endangered. Church masonry buildings are among the most precious monuments of civil engineering and the world heritage. Their inspection usually represents a complex task, and the non-invasive testing methods are recommended to assess the structural condition. Although diagnostic methods performed ‘in situ’ are not always accurate, collecting data from different historic periods is useful to build a database for a further evaluation of such historic structures. This work describes the inspection of the historic 17th century church structure and a preliminary assessment of its safety. During an air raid on Poland in the first days of World War II (1939), the roof was burnt down, which caused collapse of two segments of the masonry vault, which were reconstructed in the 1940 s as a timber structure and a combined king-post roof truss with diagonal struts was built. Currently, the failure state of the timber truss has been recognised above the presbytery, where the tie-beam rests on the external wall and the saddle, which supports the main rafter of the king-post truss. The semi-destructive (SDT) and non-destructive (NDT) tests were used to determine the geometric and cross-sectional properties of the structure ‘in situ’ with the purpose to evaluate the safety state of the timber members and the brick masonry vault. The numerical, three-dimensional, FEM analysis showed that the safety of the timber roof was ensured only owing to the temporary support on the chancel arch and the additional load on the masonry vault did not pose a threat to its safety.