Survey and preliminary assessment of a baroque vault for refurbishment planning

Jan Bayer, Miloš Drdácký, Jan Válek

Cite this article
Bayer, J., Drdácký, M., Válek, J. (2024) ‘Survey and preliminary assessment of a baroque vault for refurbishment planning’, Architecture Papers of the Faculty of Architecture and Design STU, 29(1), pp. 2-8. https://www.doi.org/10.2478/alfa-2024-0002

 

SUMMARY

Care for the long-term sustainable preservation of a quality environment is increasingly arising interest in extending the functionality of existing buildings and their new use. Refurbishment and repurposing of buildings, together with maintenance, have accounted for almost fifty percent of construction production in the last twenty years in Europe. This trend is likely to grow, as it is estimated that by the middle of our millennium, eighty percent of the buildings occupied will be buildings standing today. Refurbishment has a number of advantages over new construction or demolition and rebuilding of structures. There are also potential disadvantages associated with refurbishment, which primarily represent requirements for design interventions that create a work structurally safe and robust. Here, the designer often encounters a lack of information about geometry, materials and construction details. It is therefore necessary to devote sufficient time and financial resources to comprehensive surveys using modern means of non-destructive or gently destructive testing which is very costly and time consuming. Hence, it is often useful to perform a preliminary cost-effective assessment of the feasibility of the intended project. This article presents a methodology and an example of such a preliminary survey and assessment of the mechanical response of a brick masonry Baroque vault of a former Jesuit College to the static load, initiated by an intention to change its use in selected areas and the indicative allowable load of the floor had to be estimated. The construction documents did not contain detailed data on the geometry of the vaults, there was no documentation of the thickness of the vaults or the height of the embankments and the dimensions and composition of the floor layers above the vaults. The material properties of the building materials used for the construction of vaults were also unknown. The analysis was preceded by local investigations, the aim of which was to survey the geometric shape and to non-destructively examine -by using georadar- the composition of inaccessible parts between the lower surface of the vaults and the upper surface of the ceiling. The geometry of the extrados and intrados of the vaulted ceiling is precisely determined by geodetic surveying. The internal composition is estimated according to the response of passing electromagnetic waves. The IDS type ground radar was used for the task and the slice software was used for evaluation. To visualize the reflections, the signal was linearly amplified with depth, an interval of displayed frequencies was selected and the distance between the antenna and the top was subtracted. To better visualize non-homogeneities and eliminate noises, the signal was “smoothed” by averaging over 3×3 boxes. From the course of hyperbolic reflections, the speed of signal propagation was retrospectively refined. Radargrams showed vault structures in all studied rooms. The density of the selected network allows them to be sufficiently described. In all rooms a concrete slab with reinforcement in both directions is probably present. Material properties are estimated according to the experience of the authors with similar historical buildings and a literature search. The data obtained were used for the analysis. For the stress calculation in the vaults the radar estimated dimension of the vault thickness of 25 cm and the more likely dimension of 30 cm were used. In addition, radar-estimated thicknesses of embankments and floor layers were applied. For vaults, these have relatively complicated material properties with a rugged spatial geometry in which imperfections can have a significant impact on the stress distribution in the structure and the calculation should therefore ideally consider material and geometric nonlinearity. The demands on such a calculation are disproportionately high in comparison with the importance of the considered construction, for which reason the calculation using two simplified models was chosen. The first planar model considers a strip of barrel vault with a width of 1 m without taking into account the load from the transverse vault and is made according to the focused geometry taking into account geometric nonlinearity and excluding tension. The second model is a linear spatial model of the entire vault according to the geodetic survey. The calculation was performed with ANSYS 17.2 using SHELL181 and MASS21 finite elements. The spatial model considers the vault as a shell, transmitting even bending stresses, which were calculated in large areas of the vault. These stresses are considerable even when unloaded, and the model does not adequately reflect the actual behaviour of the vault, because there are no defects in it today. It is therefore very conservative. The calculated stresses in the vault from the effect of the considered live load of 5 kN/m2 represented an increase in stress of approximately 25% compared to the stress from the dead load of the vaulted ceiling structure. The presented analysis does not replace a static calculation of vaults and must be understood as a highly qualified expert estimate of the behaviour of the structure on the acting and considered loads. Nevertheless, it helped to decide on the feasibility of the intention to adapt the building for a new use.

Keywords: non-destructive survey, mechanical response, load carrying capacity estimate, baroque vault