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Dynamic Interactions of a Train Moving Over a Rail Suspension Bridge with Multiple Support Settlements
Yau, Y. D. ; Frýba, Ladislav
With the consideration of multiple support settlements, interaction responses of a train running over a rail suspension bridge will be investigated. The suspension bridge is modeled as a single-span suspended beam with hinged ends and the train as successive moving oscillators with identical properties. To conduct this dynamic problem with non-homogeneous boundary conditions, the total deflection response of the suspended beam is divided into two parts: the static component and the dynamic deflection. Then, the coupled equations of motion for the suspended beam carrying multiple moving oscillators are converted into a set of nonlinearly coupled generalized equations by Galerkin’s method, and solved using the Newmark method using incremental-iterative procedure. From the present numerical demonstrations, the differential movements of bridge supports will significantly affect the dynamic response of the running vehicles but insignificant influence on the bridge response.
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The effect of chemical degradation of surface layers on mechanical properties of wood
Drdácký, Miloš ; Kloiber, Michal ; Frankl, Jiří ; Bryscejn, Jan ; Tippner, J.
The aim of the research was the determination of the effect of chemical degradation on the surface layers of wooden constructional elements and their mechanical properties and also the depth which the damage reaches. The degradation of wood surface layers was caused by chemical reactions of some compounds contained within fire-prevention coatings applied repeatedly on wooden constructions of historic buildings in the past. These include e.g. ammonium sulphate and ammonium phosphate. This paper presents experimental procedures and results obtained through measuring of mechanical properties in the damaged layer of fibrillated wood and in wood without damage. The observed properties were wood compressive and tensile strength and wood hardness. The results proved a loss in cohesion and changes in mechanical properties only in a thin surface layer.
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Portable Testing Device for In-situ Testing of Building Material
Vavřík, Daniel ; Jandejsek, Ivan
Examination of brittle buildings materials using mechanical tests requires sampling of studied elements and materials (stones, bricks or concrete). In case of existing integral structures the best suitable sampling method is core drilling. It is preferred to test samples in situ in all cases where it is possible to avoid changes of the material properties during transportation and storing. Moreover it is possible to prepare other samples operationally wen some uncertainty occurred if in situ testing is possible. For such a purpose, a portable testing device has been designed and manufactured. This device is primary devoted for so called split test technique which is based on well know testing of Brazilian disk. Analytical equation used for evaluation of the split test is based on several assumptions which have to be verified. For such verification Digital Image Correlation technique was used in our work.
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Investigation of C/PPS Composites Degradation Process Using Acoustic Measurement
Fíla, Tomáš ; Valach, Jaroslav ; Kytýř, Daniel ; Šperl, Martin
The article deals with assessment of fatigue degradation of C/PPS composites using simple acoustic measurement technique. Changes in natural frequency and attenuation decrement were chosen as indicators of fatigue damage accumulation in the studied composite material. New testing device was developed for acoustic measurement. The experimental setup was designed to chime the specimen by repeatable force of stiff striker exciting a specific natural mode of vibration and to record the acoustic response of the specimen to the impact simultaneously. From the power spectral density of the signal the natural frequency was obtained. Using the same signal, the attenuation decrement was estimated from regression of the its envelope.
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GPU computation in engineering practice
Fischer, Cyril
In many research fields the numerical problems demand extremely large computational power. As a consequence, researchers are constantly demanding new and more powerful computers. Recently, the graphics chip producer NVIDIA launched the CUDA parallel computing architecture, which enables scientists to utilize the extreme power available on modern and relatively cheap Graphical Processor Units (GPUs). Necessity to change the common approach together with significant difference in the GPU architecture prevents the wide usage of the graphics hardware.
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Microstructural models of trabecular bone - comparison of CT-based FE models
Jiroušek, Ondřej ; Zlámal, Petr
In the article a detailed comparison of techniques used to developed detailed FE models of trabeculra bone microstructure is presented. The FE models are built using a stack of microtomographic images of trabecular bone. Compression test of a cylindrical sample taken from human proximal femur is virtually performed using FE models developed using different procedures. Effect of improper segmentation, mesh smoothing, mesh density, use of hexahedral/ tetrahedral elements, linear/ quadratic shape function is evaluated in parametric study. Material model is based on nanoindentation and numerical elastic properties of sample are compared to experimental results.
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