Tomáš Čejka

The application of carbon composites in the rehabilitation of historic baroque vaults

The stabilization and reinforcement of damaged barrel vaults with lunettes over an arcaded walk, applying composite strips based on high-strength carbon fibers and epoxy resin, was performed during the restoration of a historic monastery. The application of reinforcing composite strips in the soffit of damaged barrel vaults was preceded by relatively extensive experimental research and theoretical analyses. This method significantly reduces the interventions into and the degradation of the original historic structure (surface application) and is reversible.

Strength assessment of historic brick masonry

AbstractThe identification of residual service life of a structure is an exceptionally demanding task in the case of reconstructed or newly modernised buildings. The identification of residual service life requires the study and knowledge of the mutual interaction of a building with its external environment, in particular, the time variable effects and impacts which lead to degradation processes and phenomena affecting and, in the absolute majority of cases, degrading the physical, mechanical and other properties of materials and structures. The article presents the results of in-situ and laboratory research of strength parameters of masonry from the start of the 20th century applying destructive and non-destructive tests. Besides, a probabilistic model and a procedure for the determination of masonry strength are described. It appears that the probabilistic approach leads to a design value by ca 5% higher than the deterministic approach.

Strengthening of Masonry Structures Using FRP — Experimental Research

The article deals with the problems of the failure mechanism and the load-bearing capacity of masonry barrel vault structures and masonry columns strengthened with fabric of carbon fibres. The executed experimental research of the effect of strengthening segmental barrel vaults and masonry columns by carbon fabric showed a prominent growth in the ultimate bearing capacity and ductility of barrel vault structures and masonry columns. The application of carbon fabric (CFRP) in the vault area exposed to tensile stresses limited not only the appearance and development of characteristic tensile cracks at these vault cross-sections, but also significantly increased the vault stability against buckling. The position of strengthening elements — the carbon fabric (CFRP) — affected the failure mechanism of the masonry vaults and masonry columns.

THE EFFECT OF DEGRADATION PROCESSES ON THE SERVICEABILITY OF BUILDING MATERIALS OF HISTORIC BUILDINGS

The article presents an analysis of degradation processes and partial results of an experimental research into materials and structures exposed to the effects of external environments with an emphasis on the effects of moisture and chemical degradation processes on major mechanical properties of sandstone.

The Response of Masonry Barrel Vaults to Repetitive Static and Dynamic Loads and Example of Rehabilitation of Historic Barrel Vaults

The article will present the main results of experimental and theoretical research into non-reinforced barrel vault constructions and barrel vault construction reinforced with composites based on high-strength fibres and epoxy resin, or special polymer cement mortar. Vaulted constructions of historic and heritage buildings are extremely sensitive to deformations of the supporting construction, and their response to seismic effects may often be accompanied by cracking and mechanical vault failures. The results of research and study into the dynamic behaviour of barrel vaults brings new knowledge applicable in the prevention of vault failures in regions with an increased intensity of natural or technical seismicity, for the identification and localisation of failures using e.g. MAC or COMAC criteria. It can also be valuable in their serviceability assessment and service life extension. The second part of the article presents the results of theoretical and experimental analysis and a practical example of the stabilisation and reinforcement of 16 extensively damaged barrel vaults (with a 3.05 m span) with large lunettes situated over the cloister in the Premonstrate Monastery in Tepla (built in the 16th century), located in a seismically active region of West Bohemia.

Physical and mechanical characteristics of building materials of historic buildings

The article presents partial results of laboratory research into physical and mechanical characteristics of materials most commonly used as walling units in masonry structures of historic and heritage buildings. Core boreholes and specimens for the laboratory research of selected characteristics were sampled from accessible places of historic buildings, which had not been restored or reconstructed. The results of the research brought new knowledge about the unreliability (variance) of the properties of historical, mainly natural building materials, and, at the same time, pointed out the need for further research and extension of knowledge necessary for the assessment of residual physical and mechanical characteristics of historic masonry structures.

CONTRIBUTION TO THE POTENTIAL OF USING FRP MATERIALS IN THE REHABILITATION AND STABILIZATION OF TIMBERED BUILDINGS

Wooden log, timbered perimeter and interior walls ranked among the most common building constructions used from the Early Middle Ages. In most cases, the local natural resources, i.e. wood, clay, straw and stone, were used for building houses with wooden framing. This article outlines typical defects and failures of timbered houses, “classic” techniques for the rehabilitation of these defects and failures indicating the potential of using composite materials based on highstrength fibres and epoxy resin in the rehabilitation and strengthening of timbered buildings.

DEFECTS AND FAILURES OF JOINTS OF HISTORIC ROOF TRUSSES AND POSSIBILITIES OF USING FRP MATERIALS IN THEIR REHABILITATION AND STABILIZATION

The survey of selected historic roof trusses performed within the NAKI DF12P01OVV037project revealed numerous failures and defects of joints of roof truss elements of historic and listed buildings. Based on the results of the survey, the article outlines potential rehabilitation and reinforcement techniques of joints of roof truss elements in which the most frequent defects and failures were found using composite fabrics based on high-strength carbon fibres and epoxy resin (CFRP).

REHABILITATION OF HISTORIC HALF-TIMBERED WALLS WITH COMPPOSITE MATERIALS BASED ON HIGH-STRENGTH

The major requirements for present day cultural heritage conservation include the minimization of interventions in historic structures, non-invasiveness and, last but not least, reversibility of rehabilitation and strengthening interventions. Due to these requirements, composites based on high-strength fibres and epoxy resin are increasingly applied during the rehabilitation, renovation and strengthening of building structures. The article points out potential applications of these materials in the renovation, rehabilitation and strengthening of half-timbered constructions.

Assessment of compressive strength of historic mixed masonry

AbstractThe majority of load-bearing masonry structures of historic buildings are built of mixed or stone masonry composed of regular or irregular (so-called quarry) masonry units – bricks, sedimentary and metamorphic rock – possessing often very different physical and mechanical characteristics. The identification of residual mechanical properties of stone or mixed masonry of irregular walling units requires the application of a suitable diagnostic method, the assessment of the phase of degradation processes and the choice of an appropriate probabilistic model for the strength of mixed masonry. The presented experimental research involves the analysis of the heterogeneity (homogeneity) of mixed masonry of a church from the 17th century. The probabilistic model for masonry strength is developed on the basis of destructive and non-destructive testing of masonry units and mortar. It appears that the probabilistic approach leads to a design value by 75% higher than the deterministic approach.