Repositório Comunidade: DECDEChttp://hdl.handle.net/10362/4152017-07-14T09:11:11Z2017-07-14T09:11:11ZRecent Developments in the GBT-Based Numerical Modeling of Steel-Concrete Composite BeamsGonçalves, RodrigoHenriques, DavidCamotim, Dinarhttp://hdl.handle.net/10362/216902017-06-29T02:33:36Z2016-04-13T00:00:00ZTítulo: Recent Developments in the GBT-Based Numerical Modeling of Steel-Concrete Composite Beams
Autor: Gonçalves, Rodrigo; Henriques, David; Camotim, Dinar
Resumo: This paper presents the latest developments concerning the numerical modeling ofsteel-concrete composite beams using GBT-based (beam) finite elements. In particular, it is shown that GBT makes it possible to assess, accurately and with computational efficiency, the buckling (bifurcation) behavior of steel-concrete composite beams subjected to negative (hogging) bending. Two relevant buckling phenomena are considered, namely (i) local buckling of the web (plate-like), possibly involving the torsional rotation of the compression flange, and (ii) distortional buckling, combining a lateral displacement/rotation of the lower flange with cross-section transverse bending. The determination of the buckling loads is performed in two stages: (i) a pre-buckling analysis is first carried out, accounting for shear lag and concrete cracking effects, and (ii) an eigenvalue buckling analysis is performed next, on the basis of the calculated pre-buckling stresses, allowing for cross-section distortion and plate bending. Several numerical examples are presented, illustrating the application of the proposed GBT-based finite element and providing clear evidence of its capabilities and potential.2016-04-13T00:00:00ZEfficient GBT displacement-based finite elements for non-linear problemsGonçalves, RodrigoCamotim, Dinarhttp://hdl.handle.net/10362/216892017-06-29T02:33:42Z2017-03-24T00:00:00ZTítulo: Efficient GBT displacement-based finite elements for non-linear problems
Autor: Gonçalves, Rodrigo; Camotim, Dinar
Resumo: This paper addresses computational efficiency aspects of Generalized Beam Theory (GBT) displacement-based finite elements. It is shown that such efficiency can be significantly improved by using cross-section nodal DOFs (instead of deformation modes) since much smaller matrices need to be handled and the element stiffness matrix becomes significantly sparser. In addition, wall thickness variations, including holes, can also be considered.
The deformation mode participations, which constitute the trademark of GBT, are recovered through post-processing.
For illustrative purposes, several numerical examples, involving linear and non-linear (static) problems, are presented and discussed.2017-03-24T00:00:00ZFirst-order Generalized Beam Theory for Curved Members with Circular AxisPeres, NunoGonçalves, RodrigoCamotim, Dinarhttp://hdl.handle.net/10362/216882017-06-29T02:33:41Z2016-11-09T00:00:00ZTítulo: First-order Generalized Beam Theory for Curved Members with Circular Axis
Autor: Peres, Nuno; Gonçalves, Rodrigo; Camotim, Dinar
Resumo: This paper presents a first-order Generalized Beam Theory (GBT) formulation for thin-walled members with circular axis and undergoing complex global-distortional-local deformation. The fundamental equations are derived on the basis of the usual GBT kinematic assumptions (Kirchhoff, Vlasov and wall in-plane inextensibility), leading to a formulation able to retrieve accurate solutions with only a few cross-section deformation modes (cross-section DOFs). It is shown that the classic Winkler and Vlasov theories can be recovered from the derived formulation. A GBT-based finite element is use to analyze numerical examples illustrating the application and potential of the proposed formulation.2016-11-09T00:00:00ZViability and Applicability of Simplified Models for the Dynamic Analysis of Ballasted Railway TracksRodrigues, André Filipe da Silvahttp://hdl.handle.net/10362/216632017-06-24T02:38:31Z2017-06-01T00:00:00ZTítulo: Viability and Applicability of Simplified Models for the Dynamic Analysis of Ballasted Railway Tracks
Autor: Rodrigues, André Filipe da Silva
Resumo: The numerical models of the railway track are fundamental tools for the study of their
dynamic behaviour, with implications for the safety and comfort of rail transport and the
degradation and need for maintenance of the track. The importance of these models has
increased alongside the speed and capacity of the railway vehicles over the last decades.
Although the use of three-dimensional finite element models is becoming common
practice, simplified models are still relevant, due to their simplicity of implementation
and results interpretation, and low computational cost. However, the general validity of
these models has not yet been demonstrated in the relevant literature.
The present thesis aims to establish the applicability and viability of such simplified
models in the analysis of the dynamic behaviour of the ballasted railway track. The
following questions are considered:
1. Are these models able to approximate the real rail displacement due to the passage
of rail vehicles, despite their simplicity?
2. If yes, for which situations (i.e., track properties and loading conditions) can they
be used reliably?
3. In these situations, is it possible to define adequate parameters for the simplified
models based on the track’s geometry and mechanical properties?
To that end, three linear elastic models are implemented: a detailed three-dimensional
finite element model, a one-dimensional beam in discrete supports model, and a
one-dimensional beam on elastic foundation model. Transient and steady-state dynamic
solutions for a load moving at moderate and high speed are obtained. The vertical displacement
of the rail is chosen as the reference to measure the equivalence between the
models, since it is a common element between all models and is the interface between
the load and the track.
The three-dimensional model is validated by comparison with published experimental
measurements. Its results cover a representative range of the properties of the ballast
and subgrade, and are used as a reference to calibrate the simplified models using genetic
algorithms and non-linear programming.
It is concluded that a good approximation to the reference solution can be achieved,
particularly when the load moves slower than the velocity of propagation of the elastic waves in the soil. For high velocities and/or soft soils, the wave propagation becomes
more relevant to the dynamic behaviour of the track, and the simplified models become
less reliable.
Following a review of the existing literature, theoretical expressions for the determination
of the parameters of the simplified models are proposed. It is concluded that these
are suitable for the beam on discrete supports model, but not for the beam on elastic
foundation model, whose optimum parameters are less consistent across the different
properties of the track and load speeds.2017-06-01T00:00:00Z