1,721,034 research outputs found
Partitioned Modelling for Nonlinear Dynamic Analysis of Reinforced Concrete Buildings for Earthquake Loading
No full textA plastic-damage orthotropic 3D model for nonlinear analysis of masonry structures under earthquake loading
No full textThe response of masonry structures under seismic loading is very complex, as it is governed by the anisotropic and quasi-brittle nature of masonry. In recent past, this has driven the development of mechanical descriptions at different scales of representation, including micro-, meso- and macro-scale models and multi-scale approaches. In general micro- and meso-scale descriptions enable an accurate prediction of crack patterns and damage-induced anisotropy, as they explicitly allow for masonry bond and the interaction between units and mortar joints. Nevertheless, at present their use is restricted to the simulation of the nonlinear response up to collapse of masonry components like walls and arches, but not entire building structures because of the excessive computational cost required. Thus, in the analysis of realistic masonry structures, macro-models representing masonry as a continuum material are usually employed as they are much more computationally efficient. However, accurate response predictions entails complex material formulations calibrated on the physical response at structural component level or on more expensive micro or mesoscale models. In most previous macroscale models, masonry is modelled by using 2D representations, focusing on the monotonic response up to collapse. Moreover, very few masonry macroscale models allow for strength and stiffness degradations under cyclic loading, which strongly affect the behaviour when masonry structures are subjected to earthquakes. Isotropic descriptions are often utilised in practice, as they are generally simpler and computationally robust. However, they may not be representative of masonry characterised by regular bond patterns. In this paper, a novel 3D material model for the nonlinear analysis of masonry structures under seismic loading is described. The model is based on uncoupled damage and plasticity, which guarantees computational efficiency and robustness at the local level. The elastic behaviour and yield surface account for the orthotropic behaviour linked to the specific regular bond pattern, where stiffness and strength degradation and opening-closure of cracks are accurately represented. The potential of the proposed macroscale modelling strategy is shown in several numerical examples on masonry walls and building structures under earthquake loading
Calibration of brick-masonry material parameters through Inverse Analysis and Proper Orthogonal Decomposition
No full textCalibration of brick-masonry material parameters through Inverse Analysis and Proper Orthogonal Decomposition
No full textAccurate safety assessment of existing structures usually requires the use of advanced numerical approaches. As far as brick-masonry structures are concerned, mesoscale models with nonlinear interfaces offer a sound representation of masonry behaviour under different loading conditions. However material calibration for interfaces representing brick-mortar joints is hard to be performed using conventional experimental procedures. In this respect inverse analysis has been successfully applied by the authors for the identification of brick-mortar interface elastic parameters. This approach involves a large number of FE simulations which can become prohibitive when investigating strength parameters because of the high computational cost usually required in nonlinear analysis. In this work, an alternative numerical strategy using Proper Orthogonal Decomposition and Kriging interpolation is proposed. The advantages of the method are shown considering an accurate 3D nonlinear mesoscale model for brick-masonry and a low-invasive experimental set-up
An inverse analysis procedure for material parameter identification of mortar joints in unreinforced masonry
Full text linkMany old unreinforced masonry (URM) structures still in use need to be assessed considering the safety requirements proposed by current codes. Because of the complexity of the URM response, sophisticated numerical descriptions are required for an accurate structural assessment. When inverse analysis is used for the identification of material properties, the study of the effects of measurement errors is essential for assessing the robustness of the adopted procedure. In this work, inverse analysis techniques utilising Genetic Algorithms are employed to calibrate elastic material parameters of an advanced mesoscale model for URM. In order to apply this strategy to in-situ low-invasive investigations, a non-conventional flat-jack test setup is proposed. The potential and limitations of the method are analysed using computer-generated pseudo-experimental data with different noise limits. This allows the evaluation of the influence of the measurement equipment precision on the stability of the inverse problem
Identification of seismic damage in masonry structures by two-step SSI and parametric inverse analysis
No full textMasonry structures represent large part of the historical and cultural built heritage in Europe. The assessment of their structural behaviour is critical for the preservation and conservation of buildings, monuments and infrastructures especially in seismic areas. In particular, one relevant issue is the evaluation of damage and residual load-bearing capacity of historical masonry structures affected by earthquakes. Such evaluation is necessary to assess structural safety, in order to define posteriori actions such as evacuation, retrofitting or demolition.
A successful technique aimed at better knowing the dynamical behaviour of a structure is Operational Modal Analysis (OMA), in which the modal properties of the system are identified based on vibration data collected when the structure is under operating conditions. In Structural Health Monitoring (SHM) analysis, any variation of such modal properties could be considered as an indicator of modifications induced in the structure, such as change in mass or stiffness due to environmental agents or development and propagation of damage. The identification of the location, the type and the severity of the damage entails the solution of a further inverse problem, in which modal data, possibly coupled to other sources of information, are exploited for the assessment of such damage.
In this paper, a novel comprehensive procedure is proposed for the identification of damage in masonry structures after a seismic event. The procedure relies on the acquisition of operational vibration data before and after an earthquake. In a first phase, those data are analysed by means of Stochastic Subspace Identification (SSI) to estimate frequencies and modal shapes of the linear system in undamaged and damaged conditions respectively. Afterwards, such modal properties are used as input for the inverse problem of estimating material parameters for an approximate numerical model representing the structure.
The proposed methodology is applied to a pseudo-experimental case study in which the acceleration data are provided as the output of a mesoscale numerical representation of a 3D masonry building. The same building is then modelled with a macroscale approach using a homogenous isotropic model, whose damaged and undamaged features are identified by means of inverse analysis against the SSI output. The results show the potential of the proposed approach, where simple and non-destructive measurements are coupled to advanced computational methodologies to provide a comprehensive framework for damage identification after seismic events
Rational Selection of Experimental Data for Inverse Structural Problems
No full textInverse analysis has been established as an effective tool for parameter identification of physical models in many fields of
civil engineering. One of the main issues in inverse analysis is defining the well-posedness of the problem when a limited set of data is
considered. In fact as shown in previous work, the location and the number of the sensors providing the experimental data greatly affect the
accuracy of the inverse procedure. In this paper it will be shown that, under certain circumstances, it is possible to approximate the
global field as a linear combination of the experimental data. This provides a rational basis for the choice of the experimental equipment by minimising the effect of the measurement error on the solution of the inverse problem. A numerical application regarding the estimation of the main parameters of an advanced mesoscale model for masonry structures highlights the practicality of this study
Macroscale model calibration for seismic assessment of brick/block masonry structures
Full text linkThe accurate prediction of the response of masonry structures under seismic loading is one of the most challenging problems in structural engineering. Detailed heterogeneous models at the meso-or microscale, explicitly allow for the specific bond and, if equipped with accurate ma-terial models for the individual constituents, generally provide realistic response predictions even under extreme loading conditions, including earthquake loading. However, detailed meso-or microscale models are very computationally demanding and not suitable for practical design and assessment. In this respect, more general continuum representations utilising the finite element approach with continuum elements and specific macroscale constitutive relationships for masonry assumedas a homogeneous material represent more efficient but still accurate alternatives. In this research, the latter macroscale strategy is used to model brick/block ma-sonry components structures, where a standard damage-plasticity formulation for concrete-like materials is employed to represent material nonlinearity in the masonry. The adopted material model describes the softening behaviour in tension and compression as well as the strength and stiffness degradation under cyclic loading. An effective procedure for the calibration of the macroscale model parameters is presented and then used in a numerical example. The results achieved using the calibrated macroscale model are compared against the results of simula-tions where masonry is modelled by a more detailed mesoscale strategy. This enables a critical appraisal of the ability of elasto-plastic macroscale nonlinear representations of masonry mod-elled as an isotropic homogenised continuum to represent the response of masonry components under in-plane and out-of-plane earthquake loading
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
- …
