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3D Finite element analysis of end - plate steel joints
G.A. Drosopoulos,G.E. Stavroulakis,K.M. Abdalla 국제구조공학회 2012 Steel and Composite Structures, An International J Vol.12 No.2
This paper presents a numerical investigation of the mechanical behaviour of extended end - plate steel connections including comparison with full size experiments. Contact and friction laws have been taken into account with nonlinear, three dimensional finite element analysis. Material and geometric nonlinearities have been implemented to the model, as well. Results are then compared with experimental tests conducted at the Jordan University of Science and Technology. According to the most significant observation of the analysis, a separation of the column flange from the extended end - plate occurs. Other important structural parameters of the connection, like the impact of some column stiffeners on the overall response, local buckling of the column and friction of the beam to column interface, have been examined as well.
OSCILLATION CRITERIA FOR DIFFERENCE EQUATIONS WITH SEVERAL OSCILLATING COEFFICIENTS
Bohner, Martin,Chatzarakis, George E.,Stavroulakis, Ioannis P. Korean Mathematical Society 2015 대한수학회보 Vol.52 No.1
This paper presents a new sufficient condition for the oscillation of all solutions of difference equations with several deviating arguments and oscillating coefficients. Corresponding difference equations of both retarded and advanced type are studied. Examples illustrating the results are also given.
Oscillation criteria for difference equations with several oscillating coefficients
Martin Bohner,George E. Chatzarakis,Ioannis P. Stavroulakis 대한수학회 2015 대한수학회보 Vol.52 No.1
This paper presents a new sufficient condition for the oscillation of all solutions of difference equations with several deviating arguments and oscillating coefficients. Corresponding difference equations of both retarded and advanced type are studied. Examples illustrating the results are also given.
Comparisons of smart damping treatments based on FEM modeling of electromechanical impedance
C. P. Providakis,D.-P. N. Kontoni,M. E. Voutetaki,M. E. Stavroulaki 국제구조공학회 2008 Smart Structures and Systems, An International Jou Vol.4 No.1
In this paper the authors address the problem of comparing two different smart damping techniques using the numerical modelling of the electro-mechanical impedance for plate structures partially treated with active constrained layer damping treatments. The paper summarizes the modelling procedures including a finite element formulation capable of accounting for the observed behaviour. The example used is a smart cantilever plate structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric constrained layer and the host vibrating plate. Comparisons are made between active constrained layer and active damping only and based on the resonance frequency amplitudes of the electrical admittance numerically evaluated at the surface of the piezoelectric model of the vibrating structure.
Comparisons of smart damping treatments based on FEM modeling of electromechanical impedance
Providakis, C.P.,Kontoni, D.P.N.,Voutetaki, M.E.,Stavroulaki, M.E. Techno-Press 2008 Smart Structures and Systems, An International Jou Vol.4 No.1
In this paper the authors address the problem of comparing two different smart damping techniques using the numerical modelling of the electro-mechanical impedance for plate structures partially treated with active constrained layer damping treatments. The paper summarizes the modelling procedures including a finite element formulation capable of accounting for the observed behaviour. The example used is a smart cantilever plate structure containing a viscoelastic material (VEM) layer sandwiched between a piezoelectric constrained layer and the host vibrating plate. Comparisons are made between active constrained layer and active damping only and based on the resonance frequency amplitudes of the electrical admittance numerically evaluated at the surface of the piezoelectric model of the vibrating structure.
A new damage identification approach based on impedance-type measurements and 2D error statistics
Providakis, Costas,Tsistrakis, Stavros,Voutetaki, Maristella,Tsompanakis, Yiannis,Stavroulaki, Maria,Agadakos, John,Kampianakis, Eleftherios,Pentes, George Techno-Press 2015 Structural monitoring and maintenance Vol.2 No.4
The electro-mechanical impedance (EMI) technique makes use of surface-bonded lead zirconate titanate (PZT) patches as impedance transducers measuring impedance variations monitored on host structural components. The present experimental work further evaluate an alternative to the conventional EMI technique which performs measurements of the variations in the output voltage of PZT transducers rather than computing electromechanical impedance (or admittance) itself. This paper further evaluates a variant of the EMI approach presented in a previous work of the present authors, suitable, for low-cost concrete structures monitoring applications making use of a credit card-sized Raspberry Pi single board computer as core hardware unit. This monitoring approach is also deployed by introducing a new damage identification index based on the ratio between the area of the 2-D error ellipse of specific probability of EMI-based measurements containment over that of the 2-D error circle of equivalent probability. Experimental results of damages occurring in concrete cubic and beam specimens are investigated under increasing loading conditions. Results illustrate that the proposed technique is an efficient approach for identification and early detection of damage in concrete structures.
A near and far-field monitoring technique for damage detection in concrete structures
Providakis, Costas,Stefanaki, K.,Voutetaki, M.,Tsompanakis, J.,Stavroulaki, M. Techno-Press 2014 Structural monitoring and maintenance Vol.1 No.2
Real-time near and far-field monitoring of concrete structural components gives enough information on the time and condition at which damage occurs, thereby facilitating damage detection while in the same time evaluate the cause of the damage. This paper experimentally investigates an integrated monitoring technique for near and far-field damage detection in concrete structures based on simultaneous use of electromechanical admittance technique in combination with guided wave propagation. The proposed sensing system does not measure the electromechanical admittance itself but detect time variations in output voltages of the response signal obtained across the electrodes of piezoelectric transducers bonded on surfaces of concrete structures. The damage identification is based on the spectral estimation MUSIC algorithm. Experimental results show the efficiency and performance of the proposed measuring technique.