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Report on the structural survey of Judith's Tower in Prague 1. Part II
Drdácký, Miloš ; Kloiber, Michal ; Frankl, Jiří ; Zíma, Pavel ; Wolf, Benjamin
For the intended restoration of the object, a survey of structures that show faults or for which knowledge of material characteristics is needed for calculations confirming the reliability of the structures was requested. During the implementation of the order, there were difficulties that affected the necessity of its execution in two stages. The user of the tower cooperated with the authors of this report without any problems, and therefore it was possible to carry out the work listed below in the necessary scope and quality.
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Wooden construction of the movable roof of the garden pavilion in Český Krumlov castle
Bláha, Jiří ; Kloiber, Michal
A remarkable technical monument is situated on one of the garden terraces belonging to the state castle and chateau in Český Krumlov. The umbrella-shaped roof of the lookout pavilion can be lifted about a meter above the masoned parapet allowing the visitor a beautiful view of the World Heritage town panorama when the weather is fine. In windy conditions or in case of heavy rain the roof could be lowered and the pavilion thus closed. The lifting is operated by means of a wooden lever mechanism with a counterweight box hidden in the basement level of the building. The unique construction was built in 1823 and needed to be partially altered in 1830-1835. However, since then it has been preserved in a surprisingly authentic state even allowing practical demonstrations of its original function. Prior to recent repairs in 2016, a comprehensive non-destructive survey was conducted. The extent of the damage discovered was determined by measuring the speed of elastic wave propagation using stress waves (Fakkop 2D) and measuring the mechanical resistance when drilling with a thin bit using resistance micro-drilling (Resistograph). Another method based on loading timber by means of a\nminiature loading jack inserted into a drilled hole was selected to determine the current mechanical properties.
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Comparison of mechanical properties of wood determined by local gently destructive tests and fully destructive tests on building elements
Drdácký, Miloš ; Kloiber, Michal ; Valluzzi, M. R. ; Casarin, F.
Demolition or repair of historic buildings is a valuable source of test materials for testing nondestructive and gently destructive methods for estimating the mechanical properties of built-in wood. The article uses the results of one such opportunity, when it was possible to study the mechanical properties of wood obtained by local measurements on a larger sample of historic and new wooden beams and compare them with the properties calculated from destructive tests of structural elements. Thirty-one wood elements (nineteen recovered from disassembled buildings and twelve new) were subjected to considerately destructive local tests using a loading mini-jack method. In this method, a small loading jack is inserted into a precisely drilled hole and a load test of the wood in compression along the fibers is performed on a part of the hole wall while measuring the achieved deformation under load. Red and white firs, and pine species constituted the recovered elements - red fir and larch the new ones. Destructive tests (in bending and compression) were also carried out on ten recovered and six new elements, and results were correlated with those of considerately destructive tests. Comparison of the assessed mechanical properties shows reasonably good correlation and promising conclusions for practical applications.
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Methodology of traditional working of construction timber for structural repairs of historical buildings
Kloiber, Michal ; Růžička, Petr ; Tippner, J. ; Kunecký, Jiří
The publication deals with a methodological description of traditional (manual) wood working for structural measures in repairs of historical buildings. The methodology includes the results of experimental testing performed during timber logging in various seasons (winter, spring, summer), results for different ways of working (cutting, splitting, hewing, and combination of hewing with floating), results of verifying the elimination of growth (residual) stresses in wood selection and working (selection of wood without natural defects and intentional interventions during working). The resulting methodology meets the protection standards of cultural heritage, in particular the requirement to minimize interference with the original material, while using the original working technology for newly incorporated elements including material selection. The methodology describes the prerequisites for use and the necessary marginal conditions, material selection, handling and storage of logs, woodworking technology (hewing, splitting, and cutting), but also storage of worked elements until the actual structural repair, while presenting the version of minimum interference with the original material using traditional (manual) working of timber on specific examples of structural elements.
Plný tet:  PDF
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Longitudinal log splitting in repairs of timber structures
Kloiber, Michal ; Hrivnák, Jaroslav ; Bryol, R. ; Tippner, J.
The range of technologies used has lacked a description of the traditional longitudinal log splitting, which was often used in order to utilize the maximum possible volume of timber extracted for constructions (especially rural timbered buildings). Longitudinal splitting supports carpentry sustainability as well as allows for accurate replication of the original elements (in dimension, shape, technology). Therefore, the research focused on the design of a procedure practically usable and applicable in the common practice for repairs of timber structures, especially historical monuments. Such a procedure is longitudinal splitting using wedges (metal and wooden) and mallets. The aim of the heritage conservation procedure was to practically describe the technical solution, the technological procedure of longitudinal log splitting allowing the use of hand tools only. The procedure respects the protection of cultural heritage standards, in particular the requirement to minimize interference with the original material, while retaining high accuracy of reproduction of the original properties of structural elements.
Plný tet: PDF
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Procedures used to detect the condition of timber in historical structures
Kloiber, Michal
Within the scope of the lecture, methods of structural and technical surveys and their use were presented. The need for this kind of diagnostics, its significance for design projects, and various forms of survey outcomes were discussed, such as identification of tree species, identification of damage type, a detailed evaluation of moisture content in wood, identification of biological damage scope, and evaluation of damage degree.
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Research report from the evaluation of the wooden construction of the movable roof of the garden pavilion Paraplicko in Cesky Krumlov Castle
Kloiber, Michal ; Bláha, Jiří ; Buzek, Jaroslav
The umbrella-shaped roof of the lookout pavilion can be lifted about a meter above the parapet wall by means of a unique lever mechanism. The impulse to write out the report was an order from the Český Krumlov Castle Administration with the seat of the Castle No. 59, Český Krumlov - Latrán which required to assess the condition of all important timber elements using NDT instruments and, in particular, to measure mechanical properties of wood. For that purpose the two apparatuses designed at ITAM were used to measure continually the mechanical resistance during the pressing of the jaws in the drilled hole and the resistance during the pushing of the steel pin to the surface. Gained results should contribute to design a gentle restoration of the unique lifting device
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Wooden joints with wooden connectors viewed from dialectic perspective
Kunecký, Jiří ; Hasníková, Hana ; Kloiber, Michal
The paper deals with a critical evaluation of a technology of conservation of decayed wooden structures, especially using the technology of wooden joints equipped with wooden connectors. This technology is nowadays widespread among the people working in the field pf protection of cultural heritage. The main aim was to address price, safety issues, understanding of the principals and contexts of this type of technology. Rational arguments are used to eradicate the myths present in this area and put the light of ratio to debate on this issue.
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Traditional working and quality of timber during repairs of timber structures
Kloiber, Michal ; Růžička, Petr
Extensive field experience with repairing timber structures shows two main limiting factors for the quality of work that are often circumvented or simplified. First, it is the quality of the timber for the repairs (replacements, additions) and the resulting problem when the recommended criteria for the selection of suitable material are not met, with regard to the long-term coexistence of the new timber with the original material. Second, a critical factor is the way in which the timber is worked - the preferred traditional working is for various reasons replaced by counterfeits. Due to the limited scope of this paper, we can only pay attention to the most blatant case, which is working of logs by hewing.
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Creep behavior of oak pegs under tension in dry and wet conditions
Kunecký, Jiří ; Kloiber, Michal ; Hasníková, Hana ; Hrivnák, Jaroslav ; Sebera, V. ; Tippner, J. ; Milch, J.
Carpentry joints equipped with oak pegs are well suited for applications where increased moisture is not a significant factor. However, for the use in outside conditions, e.g. in the repairs of historical timber bridges, the pegs connecting the two halves of the joint may deform and change their original shape. This happens especially during long-term loading and can be augmented significantly by environmental changes. Creep behavior can play a crucial role for some types of carpentry joints, especially when precise contacts of faces in the joint are required. The paper deals with experimental testing of creep behavior of 16 mm oak pegs under dry and wet conditions loaded by the combination of shear and bending between two planks made of spruce in the direction parallel to grain. The results show that the decrease of theoretical stiffness values over time plays a significant role in the force redistribution in the joint especially due to moisture effects (drop 50-70% of the original stiffness).
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