scholarly journals Design of Anchorage Zones of Pretensioned Concrete Girders: A Comparison of Nonlinear 3D FEM Results with Measurements on a Full Scale Beam

2020 ◽  
Vol 10 (22) ◽  
pp. 8221
Author(s):  
Wouter De Corte ◽  
Kizzy Van Meirvenne ◽  
Veerle Boel ◽  
Luc Taerwe
Keyword(s):  
Nonlinear Analysis ◽  
Crack Formation ◽  
Mechanical Strain ◽  
3D Fem ◽  
Strut And Tie ◽  
Concrete Girders ◽  
Force Transfer ◽  
Pretensioned Concrete ◽  
Convergence Problems ◽  
Good Agreement

Pretensioned concrete beams are widely used for constructing large load-bearing structures and bridging long spans. Crack formation may occur in the end zones of these elements due to tensile splitting, spalling and bursting actions. Investigation of these zones is typically done by means of analytical methods, strut and tie modelling, 2D linear or nonlinear analysis, or full 3D nonlinear analysis. Especially challenging in this last approach is the modelling of the force transfer from the strands to the surrounding concrete as it strongly influences the magnitude of the tensile stresses. This paper presents a 3D nonlinear analysis of the anchorage zone of a pretensioned girder, and a comparison with experimental results (mechanical strain measurements, embedded strain gauges). Material modelling, steel-concrete interaction properties, as well as convergence problems are addressed systematically. The comparison indicates that a good agreement is found, both for concrete and rebar strains, and that a friction coefficient of 0.7 can be adopted, although the results for values from 0.5 to 0.9 do not differ that much. The results demonstrate that a 3D nonlinear analysis provides an excellent insight in the behavior of the end zones of pretensioned girders which opens perspectives for an optimization of the end zone design based on this type of analysis.

OPTIMAL VELOCITY MODEL WITH RELATIVE VELOCITY

2006 ◽  
Vol 17 (01) ◽  
pp. 65-73 ◽  
Author(s):  
SHIRO SAWADA
Keyword(s):  
Nonlinear Analysis ◽  
Relative Velocity ◽  
Velocity Model ◽  
Fundamental Diagram ◽  
Optimal Velocity ◽  
Traffic Jam ◽  
Optimal Velocity Model ◽  
Linear And Nonlinear ◽  
The Stability ◽  
Good Agreement

The optimal velocity model which depends not only on the headway but also on the relative velocity is analyzed in detail. We investigate the effect of considering the relative velocity based on the linear and nonlinear analysis of the model. The linear stability analysis shows that the improvement in the stability of the traffic flow is obtained by taking into account the relative velocity. From the nonlinear analysis, the relative velocity dependence of the propagating kink solution for traffic jam is obtained. The relation between the headway and the velocity and the fundamental diagram are examined by numerical simulation. We find that the results by the linear and nonlinear analysis of the model are in good agreement with the numerical results.

Asymptotic modal approximation of nonlinear resonant sloshing in a rectangular tank with small fluid depth

2002 ◽  
Vol 470 ◽  
pp. 319-357 ◽  
Author(s):  
ODD M. FALTINSEN ◽  
ALEXANDER N. TIMOKHA
Keyword(s):  
Finite Depth ◽  
Modal System ◽  
Full Account ◽  
Inviscid Flows ◽  
State Response ◽  
Linear Damping ◽  
Convergence Problems ◽  
Run Up ◽  
Fourth Order Polynomial ◽  
Good Agreement

The modal system describing nonlinear sloshing with inviscid flows in a rectangular rigid tank is revised to match both shallow fluid and secondary (internal) resonance asymptotics. The main goal is to examine nonlinear resonant waves for intermediate depth/breadth ratio 0.1 [lsim ] h/l [lsim ] 0.24 forced by surge/pitch excitation with frequency in the vicinity of the lowest natural frequency. The revised modal equations take full account of nonlinearities up to fourth-order polynomial terms in generalized coordinates and h/l and may be treated as a modal Boussinesq-type theory. The system is truncated with a high number of modes and shows good agreement with experimental data by Rognebakke (1998) for transient motions, where previous finite depth modal theories failed. However, difficulties may occur when experiments show significant energy dissipation associated with run-up at the walls and wave breaking. After reviewing published results on damping rates for lower and higher modes, the linear damping terms due to the linear laminar boundary layer near the tank's surface and viscosity in the fluid bulk are incorporated. This improves the simulation of transient motions. The steady-state response agrees well with experiments by Chester & Bones (1968) for shallow water, and Abramson et al. (1974), Olsen & Johnsen (1975) for intermediate fluid depths. When h/l [lsim ] 0.05, convergence problems associated with increasing the dimension of the modal system are reported.

scholarly journals Dry Friction Interblade Damping by 3D FEM Modelling of Bladed Disk: HPC Calculations Compared with Experiment

2021 ◽  
Vol 2021 ◽  
pp. 1-16
Author(s):  
Luděk Pešek ◽  
Pavel Šnábl ◽  
Vítězslav Bula
Keyword(s):  
Finite Element Method ◽  
Dry Friction ◽  
Computational Time ◽  
Friction Contact ◽  
3D Fem ◽  
3D Finite Element ◽  
Bladed Disk ◽  
3D Finite Element Method ◽  
Good Agreement ◽  
Damping Estimation

Interblade contacts and damping evaluation of the turbine bladed wheel with prestressed dry friction contacts are solved by the 3D finite element method with the surface-to-surface dry friction contact model. This makes it possible to model the space relative motions of contact pairs that occur during blade vibrations. To experimentally validate the model, a physical model of the bladed wheel with tie-boss couplings was built and tested. HPC computation with a proposed strategy was used to lower the computational time of the nonlinear solution of the wheel resonant attenuation used for damping estimation. Comparison of experimental and numerical results of damping estimation yields a very good agreement.

HVPE GaN Growth on 4H SiC and Die Dicing

2016 ◽  
Vol 858 ◽  
pp. 1198-1201
Author(s):  
Alexander Usikov ◽  
Sergey Kurin ◽  
Iosif Barash ◽  
Alexander D. Roenkov ◽  
Andrei Antipov ◽  
...  
Keyword(s):  
Low Temperature ◽  
Laser Irradiation ◽  
Vapor Phase ◽  
Sapphire Substrate ◽  
Crack Formation ◽  
Mechanical Strain ◽  
Hydride Vapor Phase Epitaxy ◽  
Sapphire Substrates ◽  
Laser Scribing ◽  
Higher Temperature

Hydride Vapor Phase Epitaxy (HVPE) was used to grow 1-4 μm thick undoped GaN layers on 4H-SiC and sapphire substrates. To adjust mechanical strain and crack formation in the GaN/SiC samples, the AlGaN-based buffer layer was grown at low temperature (920-980°C) and the GaN layer was grown at a higher temperature (1000-1040°C). Laser scribing through the GaN layer or the SiC substrate was applied to fabricate dies from the GaN/SiC and GaN/sapphire samples. The laser irradiation passing through the GaN layer to the sapphire substrate or through the SiC substrate to the GaN layer, along two orthogonal directions created a net of micro-cavities in sapphire and melted grooves in SiC that promote easy breakage of the sample into rectangular dies.

Effect of C and Ge Concentration On The Thermal Stability of RTCVD Grown Si1-x-yGexCy Alloys

1997 ◽  
Vol 470 ◽  
Author(s):  
Patricia Warren ◽  
Stephane Retzmanick ◽  
Martin Gotza ◽  
Marc Begems
Keyword(s):  
Lattice Constant ◽  
Strain Relaxation ◽  
Mechanical Strain ◽  
Chemical Vapor ◽  
Misfit Dislocations ◽  
X Ray Diffraction ◽  
Cubic Silicon Carbide ◽  
Kinetics Of ◽  
Good Agreement

ABSTRACTSi / Si1-x-yGexCy / Si heterostructures containing up to 17 at.% Ge and 1.9 at.% C were grown on (001) silicon by low pressure Rapid Thermal Chemical Vapor Deposition, using a mixture of silane, germane and methylsilane, diluted in hydrogen. The samples were then annealed in a Rapid Thermal Processing furnace, under an atmospheric pressure of nitrogen, at temperatures ranging from 900 to 1130 °C.The samples were characterized using infrared spectroscopy and x-ray diffraction. SIMS profiling and TEM observation were performed on some of the samples.Substitutional C gradually disappeared, either precipitating out to form cubic silicon carbide (β-SiC), or simply vanishing into interstitial positions. In any case, the in-plane lattice constant remained constant after annealing, indicating that there was no mechanical strain relaxation by formation of misfit dislocations. The perpendicular lattice constant increased due to the decrease in substitutional C concentration, as well as it decreased due to the germanium out-diffusion. This variation of the strain during annealing was modeled, and allowed the determination of the kinetics of the substitutional carbon disappearance. The same behavior was observed for all samples. Indeed, the Cs disappearance rate was always increased for samples with higher initial Ge and C concentrations. The kinetics of this precipitation was found in very good agreement with previous published results.

On Blade Damping Technology Using Passive Piezoelectric Dampers

2012 ◽  
Author(s):  
Sebastian M. Schwarzendahl ◽  
Jaroslaw Szwedowicz ◽  
Marcus Neubauer ◽  
Lars Panning ◽  
Jörg Wallaschek
Keyword(s):  
Mode Shape ◽  
Mechanical Strain ◽  
Piezoelectric Element ◽  
Measured Data ◽  
Experimental Investigations ◽  
Response Functions ◽  
Ambient Conditions ◽  
Optimal Position ◽  
Measured Frequency Response ◽  
Good Agreement

This paper deals with a new damping concept for turbine blade vibrations utilizing piezoelectric material. A passive piezo damper consists of a piezoelectric element and a passive electric network connected to its electrodes. The damping performance depends on the size and location of the piezoelectric element with respect to the mode shape of the mechanical strain. Numerical and experimental investigations are carried out on a rigidly clamped simplified compressor blade at stand still and ambient conditions. An optimization process incorporating electromechanical finite element calculations determines the optimal position of the piezo damper in regard to the mode shape of interest. By applying the computed and measured Frequency Response Functions, the damping performance with and without piezo-damper are compared and referred to the measured material damping. The obtained numerical results are in very good agreement with the measured data, leading to a promising damping performance in real application.

scholarly journals Behavior predictions of deep beams with short straight bar anchorages using strut-and-tie models and nonlinear analysis

2016 ◽  
Vol 9 (5) ◽  
pp. 710-721
Author(s):  
R. A. SOUZA ◽  
S. BREÑA
Keyword(s):  
Nonlinear Analysis ◽  
Longitudinal Reinforcement ◽  
Deep Beams ◽  
Bond Slip ◽  
Crack Control ◽  
Strength Factor ◽  
Strut And Tie ◽  
Effective Strength ◽  
Laboratory Test Results ◽  
Strut And Tie Model

Abstract This paper investigates the laboratory test results of 12 deep beams available in the literature, where the longitudinal reinforcement was anchored into the support using short straight bar anchorages. Four different specimen groups with three different shear span-to-depth ratios (a/d) were selected and most of the deep beams failed by strut crushing after yielding of the main longitudinal reinforcement. In order to investigate the behavior of the selected deep beams, an enhanced strut-and-tie model assuming geometrical adaptability (possibility of update in the dimensions of the struts and ties as the main tie starts to yield) is proposed. The analytical results obtained using this approach may be considered as much as accurate than some conducted complex nonlinear analysis considering smeared fixed cracking model and bond-slip behavior. However, an improvement on the effective strength factor of bottle-shaped struts by means of an iterative strut-and-tie model is needed, once the effective strength factor prescribed by NBR6118 (2014) has shown to be over conservative for all ranges of span-to-depth ratio (a/d) investigated. Finally, the obtained results indicated that short bar anchorages did not seem to influence significantly the shear strength of the deep beams investigated, especially the strength of bottled-shaped struts when appropriate crack control reinforcement is present.

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