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Dimitrina Kindova-Petrova
Journal of Theoretical and Applied Mechanics, Volume 44, pp 69-82; https://doi.org/10.2478/jtam-2014-0023

Abstract:
Variable loadings cause fatigue to the structural elements leading to crack initiation and propagation, which results in a decrease in the fatigue life of the elements. In particular, cracks decrease the stiffness and the natural frequency thus, causing specimens to fail under normal working conditions. This paper presents the application of the vibration- based technique for detecting the location and the size of a fatigue crack in structures. The two presented methods are based on the measurements of the natural frequencies of the cracked beam. The crack is modelled by a rotational spring. The predicted crack depth and location are compared with the actual data obtained from finite element models.
Journal of Theoretical and Applied Mechanics, Volume 44, pp 71-82; https://doi.org/10.2478/jtam-2014-0011

Abstract:
This paper evaluates the nonlinear responses of a function- ally graded (FG) beam resting on a nonlinear foundation. After derivation of fundamental nonlinear differential equation using the Euler-Bernouli beam theory, a semi analytical method has been used to study the response of the problem. The responses can be evaluated for both linear and nonlinear isotropic and FG beams individually. Adomians Decomposition and successive approximation methods have been used for solution of nonlinear differential equation. As numerical investigation, the beams with simply supported ends and linear and nonlinear foundations have been analyzed using this method.
George D. Manolis, Asimina Athanatopoulou-Kyriakou, Kosmas D. Dragos, Argyris Arabatzis, Alexandros Lavdas,
Journal of Theoretical and Applied Mechanics, Volume 44, pp 3-24; https://doi.org/10.2478/jtam-2014-0007

Abstract:
In this work, we develop a technique for performing system identification in typical pedestrian bridges, using routine equipment at a minimal configuration, and for cases where actual structural data are either sparse or absent. To this end, two pedestrian bridges were examined, modelled and finally instrumented so as to record their dynamic response under operational conditions. More specifically, the bridges were numerically modelled using the finite element method (FEM) according to what was deduced to be their current operating status, while rational assumptions were made with respect to uncertain structural properties. Next, results from field testing using a portable accelerometer unit were processed to produce response spectra that were used as input to a structural identification software program, which in turn yielded the excited natural frequencies and mode shapes of the bridges. The low level of discrepancy is given between analytical and experimental results, the latter are used for a final calibration of the numerical models.
Journal Of Theoretical And Applied Mechanics, Volume 44, pp 3-20; https://doi.org/10.2478/jtam-2014-0001

Abstract:
The present article views a measuring system for determining the parameters of vessels. The system has high measurement accuracy when operating in both static and dynamic mode. It is designed on a gyro-free principle for plotting a vertical. High accuracy of measurement is achieved by using a simplified design of the mechanical module as well by minimizing the instrumental error. A new solution for improving the measurement accuracy in dynamic mode is offered. The approach presented is based on a method where the dynamic error is eliminated in real time, unlike the existing measurement methods and tools where stabilization of the vertical in the inertial space is used. The results obtained from the theoretical experiments, which have been performed on the basis of the developed mathematical model, demonstrate the effectiveness of the suggested measurement approach.
Philip N. Simeonov, Konstantina V. Kocheva, Valery K. Kochev, Georgi I. Georgiev
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-7-13101331-6

Aneta Gacovska, Elisaveta I. Pancheva
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-7-13101331-4

Nikolay Dimitrov, Boris Matev, Hristo Georgiev, Valentin Matev, Andrei Andreev,
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-7-13101331-20

Lina Malinova, Boycho Landzhov, Anastasia Bozhilova-Pastirova, Lazar Jelev, Dimka Hinova-Palova, Wladimir Ovtscharoff
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-7-13101331-16

Detelin Stefanov, Dimitrija Petkova, Diana Marinova, Galina Panayotova, Veneta Kapchina, Emil Molle
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-7-13101331-12

Bistra Mihailova, Elisaveta Stoimenova, Peter Petrov, Ekaterina Stoynova-Bakalova
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-6-13101331-19

, Stefan Sivkov, Tsvetanka Petleshkova, Antoaneta Fusova, Dobrinka Radoinova, Emilia Karaslavova
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-6-13101331-16

Iliyana V. Sazdova, Bilyana M. Ilieva, , Alexandra Milusheva, , , Ferenc Fülüp, , Hristo S. Gagov
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-6-13101331-10

Katya Milenova, Boris Kunev, Vladimir Blaskov, Sasho Vassilev, Irina Stambolova
Proceeding of the Bulgarian Academy of Sciences, Volume 66; https://doi.org/10.7546/cr-2013-66-5-13101331-8

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