engleski

Zagreb Cathedral – Structural assessment of timber roof structure

The roof of the Zagreb Cathedral, dating from the general reconstruction in 1890-ties, withstood the 2020 earthquake in Croatia with remarkably good resilience. However, the restructuration project after the quake initiated extensive activities on the condition survey and consideration of possible measures for ensuring the future longevity, structural stability, and seismic resistance of the structure. The assessment encompassed the determination of wood species, anatomical structure, hygrotechnical conditions, as well as physical, mechanical, and biological properties of wood and load-bearing capacity of timber. It was demonstrated that visual grading and density measurements on drill cores proved adequately chosen main inputs for determining mechanical properties. The (quasi) nondestructive testing (NDT) - stress-wave, screw withdrawal and resistance drilling - proved useful additional methods yet fully effective only in combination with microscopic evidence on cores. A newly developed method of fairly invasive but completely re- constructive sample withdrawal of 50×50×800 mm beams yielded the MOEstat and standard test values on small clear samples (bending, MOEstat, shear ǁ and compression ǁ). NDT tests and small clear samples varied in conformity and measurement uncertainty but usefully complemented the main results and indicated the required corrections in mechanical classification. Special attention was paid to the detailed survey and analysis of timber joints and the consequent stability of the structure in the future. Dead loads, snow loads, and wind loads were considered in structural analysis models. Also, the history of seismic responses was also analysed. Such analyses form a sound base for the technical design of reinforcements as well as necessary repair and reconstruction measures of the roof structure.

Zagreb Cathedral ; timber structures ; NDT ; standard wood testing ; structural analysis

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