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    Dam Incidents and Failures – Cases in the Czech Republic
    (Sciendo, 2023-03-31) Kotaška, Stanislav; Říha, Jaromír
    Dam incidents and failures mainly occur during extreme floods. In the Czech Republic (CR), large-scale regional floods were recorded in different regions in 1985, 1987, 1997, 2002, 2006, 2010, and 2013, while local floods especially occurred in 1991, 1996, 1997, 1998, 2002, 2004, 2005, 2009, and 2010. During these events, numerous incidents and total breaches of small dams were recorded, and a few large dams were also critically endangered, although they were not completely breached. This paper presents a comprehensive summary of incidents and failures affecting small dams in the CR since 1985. The most significant incidents concerning large dams are listed as well. The statistics show that 62 small dams were completely breached and that 350 were seriously damaged over 35 years in the period 1985–2020. The annual frequency amounts to 1.85 collapsed and 10 small damaged dams per year. The most common causes of the complete breaching of dams were overtopping (85 %) and internal erosion (15 %).
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    A numerical study of two different specimen fixtures for the modified compact tension test – their influence on concrete fracture parameters
    (Gruppo Italiano Frattura, 2016-01-01) Holušová, Táňa; Seitl, Stanislav; Cifuentes, Héctor; Fernández-Canteli, Alfonso
    The modified compact tension test (MCT) may represent a new test configuration for the performance of static and other kinds of fatigue tests on concrete-like materials. Core drilling can be employed to obtain specimens which are cylindrical in shape and have a standard diameter of 150 mm, this being appropriate for the determination of the residual life of structures. This contribution focuses on the evaluation of MCT specimen fracture behavior during static tests. Cracks evolution are simulated numerically using ATENA finite element (FE) software, while the results are represented as L-COD diagrams, i.e. load vs. crack opening displacement measured on the loading axis. After numerical calculations, the results for two different fixtures are compared and the advantages or drawbacks for each solution are discussed.
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    Column stability during welding
    (IOP Publishing Ltd., 2019-02-24) Vild, Martin; Bajer, Miroslav; Barnat, Jan
    This research is part of the project of strengthening of steel members under load using plates welded parallel to the member axis. Buckling load resistance of columns has to be checked during welding under compressive load. A part of a cross-section is ineffective due to high temperature near the weld. The centre of gravity is shifted and the decisive cross-section is loaded by additional bending moment. Moreover, the weld causes deformations which are higher than in case of regular welding. This paper presents authors’ method determining the buckling load resistance of the compressed member during welding. The method takes into account the column cross-section, slenderness, and effective intensity of the welding heat source. The column is treated as a stepped member and its Euler’s critical load is decreased. The deformation of the column and the stress are determined with regards to second order effects. The method is validated by experiments performed in the laboratory of Department of Metal and Timber Structures at Brno University of Technology in November 2017. Columns with cross-sections HEA 100 and SHS 100×5 with the length of 3 m were loaded by the maximal force determined using the analytical method and under this constant load the weld bead was being laid from the bottom of the column to 15 cm above the mid-height. Then, still during welding, the force was gradually increased until the column failed via flexural buckling. Measured values of load resistance, deformations and temperatures are compared with the authors’ analytical method. All six specimens resisted the maximum calculated load and failed at slightly higher loads.
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    Influence of the gripping fixture on the modified compact tension test results: evaluation of the experiments on cylindrical concrete specimens
    (VŠB-TUO, 2015-12-18) Holušová, Táňa; Lozano, Miguel; Fernández-Canteli, Alfonso; Komárková, Tereza; Kocáb, Dalibor; Seitl, Stanislav
    The modified compact tension test (MCT) might become in the future a stable test configuration for the evaluation of fracture-mechanics parameters or also for description of fatigue behavior of composites materials such as concrete. Core drilling is used for sampling of existing structures. These samples have cylindrical shape with the selected thickness to avoid the stress concentration. This contribution focuses on the evaluation of the fracture behavior during static and quasi static tests. Static tests are performed on standard specimen with diameter 150 mm and length 300 mm. The quasi-static tests are performed using two different gripping fixtures. The results for quasi-static tests are represented as L-COD diagrams (i.e. load vs. crack opening displacement) measured on the loading axis. The comparison of results and discussion of advantages and disadvantages are introduced.