National Repository of Grey Literature 50 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
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.
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.
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).
Mechanical analysis of scarf joint fastened using cylindrical wooden dowel
Tippner, J. ; Milch, J. ; Kunecký, Jiří ; Kloiber, Michal ; Brabec, M. ; Sebera, V.
Traditional all-wooden woodworking joints play an important role in the behaviour of timber structures. These joints are also widely used when historically valuable constructions are being reconstructed and the connections are usually the masterpieces that testify to the high carpentry skills and knowledges of the overall mechanical behaviour. Within historical timber structures traditional carpentry joints were used while wooden dowel fixed mutual position of elements. Main aim of this study was to contribute to knowledge base about prediction and analysis of the mechanical performance of frequently used scarf joints made from spruce wood fastened using oak dowels. The objectives were to determine the joints' slip moduli and load-carrying capacity by means of theoretical and experimental approaches, in next to assess the mechanical behaviour of dowels through experimental investigation, and finally to perform a strain analysis of dowels. For these purposes, the optical technique employing three-dimensional full-field digital image correlation was used. The experiments were done on the full-scale specimens meeting the requirements of European standards (EN 383 and EN 26891), which were made from Norway spruce (Picea abies L. Karst.) and English oak (Quercus robur L.). The mechanical load consisted in tensile parallel and perpendicular to grain direction within the main components. The results of this study showed good correlation between theoretical approach based on based on Beam on Elastic Foundation theory and European yield model theory and experimental observations.
The Cloak Bridge in Český Krumlov – measuring of mechanical properties
Kloiber, Michal ; Sebera, V. ; Hrivnák, Jaroslav ; Tippner, J. ; Kunecký, Jiří
Timber bridges are often exposed to harsh conditions of the environment. The exposure of the timber structure often leads to its deterioration. Standard test procedures to determine typical properties of wood cannot be used as there is the requirement of the minimum interference with the structure. Several non-destructive testing (NDT) methods for the determination of timber condition have been developed and are used. However, the results of NDT can be used to predict mechanical properties of timber elements only to a limited degree. Semi-destructive testing (SDT) methods are a compromise. In the paper a functional model of a device that allows for the measurement of conventional strength and modulus of deformation of timber in compression parallel to the grain is presented. The device is inserted to a bored hole and pushes the jaws apart with a small test jack loading the bore walls. This paper presents possible use of the device for surveys of timber bridges.
Analysis of mini-jack technique for in situ measurement of strength
Kloiber, Michal ; Tippner, J. ; Kunecký, Jiří ; Sebera, V. ; Milch, J. ; Hrivnák, Jaroslav
The paper presents a recently developed diagnostic technique for in situ determination of modulus of deformability (MODL) and conventional strength (CSL) parallel to the grain using the mini-jack inserted in bored hole. The mini-jack compression technique simulates the standard compression test, it is compared to that to examine its prediction strength (correlation coefficients). The paper shows an influence of moisture content of wood on experimental measurements using this technique. The measurement was carried out at spruce samples at three moisture contents of 12, 18 and 24%. The results of the tests prove a very good correlation of the strength determined by the proposed technique and wood density and strength determined at universal testing machine in compression parallel to the grain. The effect of the moisture content on the measurement by the mini-jack technique was proved to be significant. Beside that, the newly-developed instrument was also studied using digital image correlation (DIC) technique to analyze induced strains around the bored hole. This was studied on halved spruce samples. The DIC revealed symmetric character of the loading and significant differences between strains induced in tangential and longitudinal directions.
Assessment of the quality of wooden roof structure, ceiling structures in probes, joinery elements and masonry of the historic building named “Nove Probosstvi”, Prazsky Hrad, nam. sv. Jiri č.p. 34
Drdácký, Miloš ; Frankl, Jiří ; Kloiber, Michal
The report includes the results of the study focusing on the material properties of historical wooden roof structure and assessment of the state regarding the planned building reconstruction.
Survey report from the endoscopic survey of ceiling beams on the ground floor of the northwest part of the Karlštejn Castle
Kloiber, Michal ; Hrivnák, Jaroslav
On the basis of an order from the administration of the Karlštejn State Castle, during the local research on 11 October 2017, an endoscopic survey of selected ceiling beams on the first ground floor in the northwestern part of the Karlštejn Castle was carried out.
Survey report: Construction and technical assessment of the state of timber, trace analysis and surveying of a timbered barn in Skalička 3
Kloiber, Michal ; Růžička, Petr ; Buzek, Jaroslav ; Hrivnák, Jaroslav ; Bláha, Jiří
Surveys whose aggregate output is this survey report included the determination of the extent of damage to the timber, surveying, and trace analysis of the original craftsman working of a timbered barn belonging to house no. 3 in the village of Skalička u Hranic, which is located in the Přerov district in the Moravian region called Pobečví. The report has been drawn in response to the demand by the Wallachian Open Air Museum located in Rožnov pod Radhoštěm, which contained a request to diagnose the timber elements using NDT devices and carry out their trace analysis. The findings will contribute to a qualified assessment and proposal of a harmless transfer of this unique timbered building.
Assessment of masonry structures in the room No. 303 on the first floor of Upper Castle of Kunštát State Castle
Drdácký, Miloš ; Frankeová, Dita ; Kloiber, Michal ; Koudelková, Veronika ; Lesák, Jaroslav ; Válek, Jan ; Viani, Alberto
Non-destructive evaluation techniques have been adopted to assess the present situation of the walls with recently discovered frescoes in the rebuilt part of the castle. IR thermography, videoscope and ground penetrating radar were used for the classification of masonry, especially for the detection of hidden structural elements. Samples of historic mortars were analysed by thermal analysis and scanning electron microscopy. The analyses showed that binder of mortars consists of dolomitic lime.

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