Applied Mechanics and Materials Vol. 827

Abstract: The aim of the paper is focused on the analysis of the stress measurement in the railway substructure in the turnout with the movable frog prototype designed for a high speed. The evaluations were compared the measurement and the results obtained with theoretical presumptions. The Discrete Wavelet Transformation for the decomposition of the stress measurement and its evaluation is described. Two sections in the turnout with the movable frog were used for the measurement and signal analysis.

Abstract: The paper presents the detection and localization of the induced cracks on small specimens based on a modal analysis. The cracks were induced to cement specimens of dimensions 40 × 40 × 160 mm in three different positions. Their position was detected using different techniques based on natural mode shape changes between virgin and damage states of the specimen. The sensitivity of these techniques to the damage level and position was investigated, compared and then discussed in the conclusion.

Abstract: The investigated existing footbridge, on which the dynamic experimental analysis was concentrated, was built across Vltava River in Prague in 1984. Since putting into operation, the footbridge was apparently sensitive to dynamic excitation by passing pedestrians. Above that in the course of its existence the considerable part of the footbridge deck was overflowed by two great floods that happened in August 2002 and in June 2013. After the second flood, a visible damage on the footbridge deck was detected by a visual inspection. The described dynamic experiment was divided into two basic parts. The experimental modal analysis was carried out first and then the dynamic load test was realized. It was focused to the deck vibrations induced by different pedestrians groups. It was found out the footbridge deck vertical accelerations exceed the pedestrian comfort limit in some normal situations. On the basis of comparison between modes of natural vibrations, which were evaluated by the experimental modal analysis and the equivalent ones from previous dynamic experiments, it was validated that the discovered deck damage caused the partial variation of fundamental dynamic footbridge behavior.

Abstract: A significant dynamic load may be induced by synchronize movement of larger spectators group (like as jumping, bouncing, jouncing, swaying or abruptly rising) on a sport stadium during a sport event. This load could generate discomforting grandstand vibrations and in some extreme cases, the large grandstand vibrations are detectable by spectators even visually. A dynamic experiment is described in the paper which was realized on a steel cantilever grandstand during two football matches in the place where the most active spectators were concentrated. Vertical grandstand accelerations were observed in three points that were located at the ends of three grandstand main beams. The results of the experiment had shown predictably that the most excessive grandstand vibrations were induced by fans in the particular situations when the home team scored a goal and during the fans celebration after the matches especially. In these particular situations, the detected vibrations could be perceived by spectators as uncomfortable.

Abstract: Cement is an extremely energy consuming material and its production leads to the emission of a vast amount of greenhouse gases. Cementitious concrete is a universal building material, which is used for the production of various structural elements. The paper describes the problem of cement production and its impact on the environment. This research deals with application of aluminous cement as binder component for the manufacture of refractory composites and with possibilities of further utilization of environmentally friendly materials with pozzolanic properties as a partial replacement of used aluminous cement. These materials are originating as waste in the building industry or by the recycling of cast-off materials. To reduce the costs and adverse effects on the environment was the binder system modified by finely ground ceramic powder and metakaolin. The experimental results present the values of flexural and compressive strength investigated on a series of composite specimens with dimensions of 40×40×160 mm³ and 10, 20 and 30 % of cement replacement. The aim of the present work is to apply the mentioned pozzolanic materials and reach the suitable composite with the sufficient heat resistance and residual mechanical parameters after gradual temperature loading.

Abstract: The presented article deals with the influence of the drying process on the micro-mechanical properties of the composite middle lamella. The purpose of the composite middle lamella is to connecti individual cells. Micromechanical properties were obtained using nanoindentation and directly continuous stiffness measurement technique. Indentation modulus of tested samples was 11.45 GPa for natural dried wood and 12.51 GPa for artificial dried wood.

Abstract: Present paper is focused on the experimental assessment of three sandstones from different quarries. Mechanical testing was carried out besides water absorption test and determination of frost resistance what is the crucial material parameter for all types of porous rocks. Gradual deterioration due to action of frost was monitored using non-destructive testing – ultrasonic pulse method. Obtained results well describe failure mechanism of studied sandstones of different basic physical properties. It was conducted that main part of deterioration was performed at the beginning of the freeze-thaw cycling.

Abstract: Performed research work is focused on the experimental determination of volume changes of high-performance concrete. Studied topic is an essential problem of all cement based composites because of its influence to mechanical and durability properties due to crack formation. Special high-performance cement based mortars are often used for quick rehabilitation and renovation of current concrete structures where minimal level of total volume changes is required. Interpretation of final results is highly dependent on the way of measuring, as it is documented in the present experimental program.

Abstract: Presented article deals with the influence of PET fiber production on the bending strength of cement-based composite when incorporated into the fresh mortar, and comparison of results of 3-point and 4-point bending test. Cement paste samples were reinforced with 2 wt. % of primary or recycled PET fibers. The bending test was performed on prismatic samples with dimension of 40 × 40 × 160 mm. It was found that samples with recycled PET fibers, compared to primary ones, exhibit a decrease in bending strength. In the case of 4-point bending tests, the samples with recycled PET fibers exhibited higher bending strength than reference samples without any fibers. However, in the case of 3-point bending tests, the samples with recycled PET fibers had lower bending strength than the reference ones. The results suggest that recycled PET fibers could be used as an alternative to reinforce cement-based composites.

Abstract: Digital image correlation (DIC) became indispensable when monitoring and analyzing adevelopment of displacement or strain fields. The method is capable of capturing strain localization, itis not limited to a relative measurement of discrete points as conventional methods and appears to bemore accurate than measurements by means of extensometers or strain-gauges that often suffer fromimperfect attachment to the measured surface. As open source DIC tools appear, the method becomesfeasible and the development is supported by the growing computational power of modern computers.The presented paper introduces open source 2D DIC tools and simple rules to follow when employingthe method. The presented case study on behavior of fiber reinforced high-performance concretedemonstrates a computational feasibility, accuracy and sensitivity of the method for a relatively lowfinancial cost.