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Development and Verification of Innovative Modelling Approaches for the Analysis of Framed Structures Subjected to Earthquake Action
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Advisor(s)
Abstract(s)
The last decades have witnessed significant progresses in the development of improved
numerical models for structural analysis, as proven by hundreds of dissertations, theses,
reports and journal papers dedicated to advanced constitutive models of materials and
algorithms to model sectional, element and structural response. Nevertheless, the seismic
behaviour of structures involves a number of nonlinear material and geometrical
phenomena that, ultimately, are impossible to capture exhaustively in a single model.
Furthermore, past studies showed that the most correct modelling options from the
scientific viewpoint are sometimes challenged by experimental evidence.
This thesis intends to contribute to the ongoing effort of progressively bridging the
existing gap between solid theoretical principles adopted in nonlinear modelling and
experimental results from shake table or other experimental techniques. Such goal is
firstly pursued through the application of a sensitivity analysis to the simulation of the
dynamic behaviour of three distinct structures with distributed plasticity beam-column
fibre-based elements based on Euler-Bernoulli beam theory. The latter were tested in
international blind prediction challenges wherein the author and/or supervisors
participated with encouraging results.
The goodness-of-fit for each approach is assessed through comparisons between
numerical and experimental results in terms of lateral displacements as well as
accelerations (when available), following two post-processing strategies: a more
conventional one based on the error associated to the peak values measured during each
record, and another using the frequency content characteristics of the entire response
history. Sensitivity parameters included equivalent viscous damping, element
discretization scheme, strain penetration effects, material constitutive models, numerical
integration algorithms and analysis time-step size. The conclusions, which are interpreted
in the light of state-of-the-practice recommendations and established theoretical
frameworks, address fundamental modelling decisions for engineers and researchers.
The referred sensitivity analysis identified the simulation of strain penetration effects as
particularly relevant. They can significantly impact the seismic response of structures,
contributing up to 40% of the overall lateral deformation of RC framed structures. Within this context, the last chapters of the thesis present a novel bond-slip model for
RC structures that simulates the member-end deformations associated with strain
penetration effects. The model, which in its final form is implemented as a zero-length
element, was developed so that it is compatible with any general fibre-based frame
analysis software. In a nutshell, the element response is determined from cross-sectional
fibre integration, where at each rebar the anchorage mechanism is explicitly modelled
through a series of virtual integration points distributed along the anchorage length. The
analysis is carried out by an algorithm that enforces both equilibrium and compatibility at
every integration point, making use of a state-of-the-art bond stress-slip cyclic
constitutive relation applicable to a wide variety of anchorage conditions. Therefore,
features such as the expected failure mode (pullout or splitting), or parameters such as the
concrete strength, embedment length, cyclic degradation, amplitude of steel strains, rebar
type (plain or ribbed), transverse pressure, level of confinement and bond conditions can
be explicitly modelled.
The element was implemented in a structural analysis software and its performance was
assessed against several experimental tests, showing an encouraging accuracy while
retaining appreciable computational efficiency.