Michal Kloiber

Utilization of dual-source X-ray tomography for reduction of scanning time of wooden samples

We present a novel dual-source/dual energy (DSCT/DECT) micro-tomography system including results of high-resolution DSCT reconstruction. The DSCT micro-tomography setup was designed as a multi-purpose X-ray imaging device equipped with two pairs of X-ray tubes and detectors in orthogonal arrangement with independent control of beam parameters. Both pairs (tube-detector) are mounted on a computer numerical control positioning system and can be independently set up to different geometries (e.g. with different magnification of each pair). In this work the simultaneous scanning of the object by two tube-detector pairs was used for approximately half reduction of tomography scanning time. The developed imaging procedure was applied for scanning of a wooden sample locally damaged during a semi-destructive test for assessment of wood quality. Prior to the tomography measurements the setup geometry was precisely adjusted in terms of magnification, horizontal and vertical tube-specimen-detector alignment of both pairs. DSCT measurements were carried out in sequence (2 × 90° for each tube) with identical 100μm image resolution. It was proven that the presented experimental setup combined with appropriate control technique significantly reduces tomography scanning time of materials with complex micro-structure.

In Situ Compression Stress-Deformation Measurements along the Timber Depth Profile

The paper presents a novel concept and a prototype of a diagnostic tool for in-situ assessment of timber in existing structures and buildings. The device enables direct determination of conventional compressive strength and modulus of deformation in arbitrary depth along timber profile. The measurement of the stress-deformation relationship is performed in a prepared hole of a very small diameter by means of a special small size symmetrical loading jack. Testing and verification of the new device behaviour during loading of wood along the fibres has been carried out on fir which is the most frequent wood species in European buildings. The comparison of stress-strain diagrams acquired by means of the new device with those measured in compliance with the European standard for testing of wood shows a very good correlation including the determination of the compressive strength values. This semi-destructive method causes a very gentle damage and can be also used for the assessment of historic timber structures.

A comparison of two distinct roof timber frame systems implemented in the past in house No. 414/I in Prague

ABSTRACT The house No. 414/I, situated in the Old Town of Prague, was bought in 1685 by the Italian architect Martino Allio, who rebuilt its roof using a purlin system, typical in Italy but very unusual in Central Europe. Significant evidence of the previous medieval structure was identified on site in the form of reused timber elements, dendrochronologically dated to the end of the 14th century. These elements allowed the reconstruction of the original arrangement: a rafter and collar roof structure with longitudinal framing, one of the earliest examples of this type recorded in Czech Republic. The use of selected diagnostic devices, coordinated with a detailed visual inspection, allowed for the determination of the nature and extent of the damage affecting the roof structure. This has highlighted that, although the current roof is the simplest and cheapest when compared to the original Gothic roof and a typical Czech baroque roof, its structural arrangement is not adequate for Czech climatic conditions.

Structural assessment of a lapped scarf joint applied to historical timber constructions in central Europe

ABSTRACT The article deals with assessment of suitable applications of all-wooden lapped scarf joints intended for use in retrofitting of existing historical timber structures in Central Europe. The first part of the article addresses the bearing capacity and stiffness of a lapped scarf joint. In the second part, four types of roof structures typical for the region were analyzed and potential application of the joints is discussed. The third part of the article describes the influence of the application of the lap joints on the force distribution of the repaired structure, since lower stiffness of one member induces forces elsewhere in the structure as it is transmitted by the other members to the rest of the structure. Extent and influence of the stiffness change on the force distribution is briefly discussed.

Lapped scarf joints for repairs of historical structures

Jiří Kunecký Hana Hasníková Michal Kloiber Václav Sebera Jan Tippner This paper presents a description of the repair of timber structures using a prosthesis scarf joint designed for the replacement of damaged parts of beams. This new scarf joint makes use of the strutting effect of inclined contact faces where the forces are transmitted through wooden coupling elements wooden pins or dowels. The scarf can be modified in four variants according to the relevant stress and is suitable for historically valuable timber structures. It meets both functional and aesthetic requirements. The designer structural engineer will learn in the methods the loading capacity or stiffness of the beam with the designed joint, its recommended dimensions and detailed geometry. The contractor will appreciate the description of the execution and maintenance of the joint. .

New Design Method for Lap Scarf Joint Used for Reconstruction of Timber Structures

The article describes a development of a new carpentry join suitable for reconstructions of timber structures; it is possible to replace only damaged parts of wooden beam with help of the joint. The mechanical behavior of the joint was analyzed in details. The inclined faces transfer the direction of loading and use of less stiff wooden dowels allows better distribution of stresses. The design methodic has been created so that the maximum of joint potential is used safely.

Reconstruction of a Baroque Open Beam Ceiling Based on Material Analysis

Reconstruction of a ceiling in the north-eastern wing of a former water fortress in Jeseník was carried out during the repair of its roof structure and replacement of the roof. The most damaged parts of the bearing ceiling beams were removed and partially replaced with new timber in the 70s of the 20th C. The way the work was carried out corresponded to the methods and approaches of the cultural heritage protection of that time. The replacement of damaged heads of ceiling beams with new timber that was fitted without connection to the original ceiling beams and only simply hanged on a metal girder can be considered highly provisional from the current perspective. That is why the repair of timber structures of the water fortress included also a reconstruction of the original ceiling system. Surveys focusing on the building archaeology and material assessing the condition of the incorporated timber were important for the final design of the repair and the concept of presentation of the Baroque ceilings.