Probabilistic sensitivity analysis to understand the influence of micromechanical properties of wood on its macroscopic response

This paper investigates the influence of the uncertainty in different micromechanical properties on the variability of the macroscopic response of cross-laminated timber plates, by means of a probabilistic sensitivity analysis. Cross-laminated timber plates can be modelled using a multiscale finite element approach which although suitable, suffers from high computational cost. Investigating parametric importance can incur considerable time penalty since conventional sensitivity analysis relies on a large number of code evaluations to produce accurate results. In order to address this issue, we build a statistical approximation to the code output and use it to perform sensitivity analysis. We investigate the effect of a collection of parameters on the density and Young’s moduli of wood. Additionally, the influence on the response of cross-laminated timber plates subject to bending, in-plane shear and compression loads is investigated due to its relevance within the engineering community. The presented results provide a practical insight into the importance of each micromechanical parameter, which allows research effort to be focused on important wood properties

Influence of wall-to-floor connections and pounding on pre- and post-diction simulations of a masonry building aggregate tested on a shaking table

This paper presents numerical simulations within the frame of the project SERA-AIMS (Seismic Testing of Adjacent Interacting Masonry Structures). The study includes blind pre-diction and post-diction stages. The former was developed before performing the shaking table tests at the laboratory facilities of LNEC (Lisbon), while the latter was carried out once the test results were known. For both, three-dimensional finite element models were prepared following a macro-modelling approach. The structure consisted of a half-scaled masonry aggregate composed by two units with different floor levels. Material properties used for the pre-diction model were based on preliminary tests previously provided to the participants. The masonry constitutive model used for the pre-diction study reproduced classical stress-strain envelope, whereas a more refined model was adopted for the post-diction. After eigenvalue analysis, incremental nonlinear time history analysis was performed under a unique sequence based on the given load protocol to account for damage accumulation. In the post-diction, the numerical model was calibrated on the data recorded during the shaking table tests and nonlinear dynamic analysis repeated under the recorded accelerogram sequence. The interaction between the two units was simulated through interface elements. Moreover, the timber floors were accounted following different strategies: not modelling or considering nonlinear wall-to-floor connections. Advantages and disadvantages are then analysed, comparing the pre-diction and post-diction results with the experimental data. Numerical results differ from the experimental outcomes regarding displacements and interface pounding, although a clear improvement is visible in the post-diction model

Preliminary structural and seismic performance assessment of the Mosque-Cathedral of Cordoba: The Abd al-Rahman I sector

This manuscript discusses some preliminary results on the structural and the seismic performance of the Mosque-Cathedral of Cordoba, a UNESCO World Heritage. The area is characterized by a moderate seismic hazard. The building was built from the 8th to the 16th century and it has undergone several transformations. Owing to the complexity of the building, this work has focused on the assessment of the Abd al-Rahman I sector, which is the most aged part of the complex. For that, first, a 3D numerical finite element model of the sector has been done in the OpenSees framework and calibrated. To do so, an experimental non-destructive campaign has been carried out. Second, the model has been used to evaluate the structural behaviour, under vertical and horizontal loads, considering different scenarios. Finally, the crack patterns and the seismic safety have been obtained. The results showed that the numerical damage obtained for the gravitational loads is in good agreement with the data collected from the in situ surveys. Also, particular attention should be paid to the cymatiums, as they are the most demanded part of the system. Regarding its seismic performance, the building presents a higher capacity in the direction of the arcades. For the seismic demand, slight damage is expected in both principal directions of the building, which could be easily repaired. Damage concentration is expected in the contact between the perimetral wall and the arcades. This work has expanded the study of the features of the Mosque-Cathedral of Cordoba to the structural and seismic analysis with advanced numerical FE computing, which has not been done to date. To the authors’ knowledge, this is the first time that a macro-modelling approach with solid elements is presented for the seismic assessment of heritage buildings using the OpenSees framework. The methodology to do so is also presented. Apart from showing how advanced numerical analyses can provide useful information to assess the existing damage on monumental buildings, this work aims at contributing to the assessment of the vulnerability and the safety of one of the most emblematic mosque-like buildings of the world.20 página

Multiscale seismic vulnerability assessment and retrofit of existing masonry buildings

The growing concern about the protection of built heritage and the sustainability of urban areas has driven the reoccupation of existing masonry buildings, which, in the great majority of the cases, were not designed or constructed to withstand significant seismic forces. This fact, associated with territorial occupation often concentrated in areas with high seismic hazard, makes it essential to look at these buildings from the point of view of the assessment of their seismic vulnerability and retrofitting needs. However, to be effective and efficient, such an assessment must be founded on a solid knowledge of the existing methods and tools, as well as on the criteria that should underlie the selection of the most appropriate to use in each context and situation. Aimed at contributing to systematise that knowledge, this paper presents a comprehensive review of the most relevant vulnerability assessment methods applicable at different scales, as well as the most significant traditional and innovative seismic retrofitting solutions for existing masonry buildings.This research was funded by the Portuguese Foundation for Science and Technology (FCT) through the postdoctoral grant SFRH/BPD/122598/2016.info:eu-repo/semantics/publishedVersio

Shake-table testing of a stone masonry building aggregate: overview of blind prediction study

City centres of Europe are often composed of unreinforced masonry structural aggregates, whose seismic response is challenging to predict. To advance the state of the art on the seismic response of these aggregates, the Adjacent Interacting Masonry Structures (AIMS) subproject from Horizon 2020 project Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA) provides shake-table test data of a two-unit, double-leaf stone masonry aggregate subjected to two horizontal components of dynamic excitation. A blind prediction was organized with participants from academia and industry to test modelling approaches and assumptions and to learn about the extent of uncertainty in modelling for such masonry aggregates. The participants were provided with the full set of material and geometrical data, construction details and original seismic input and asked to predict prior to the test the expected seismic response in terms of damage mechanisms, base-shear forces, and roof displacements. The modelling approaches used differ significantly in the level of detail and the modelling assumptions. This paper provides an overview of the adopted modelling approaches and their subsequent predictions. It further discusses the range of assumptions made when modelling masonry walls, floors and connections, and aims at discovering how the common solutions regarding modelling masonry in general, and masonry aggregates in particular, affect the results. The results are evaluated both in terms of damage mechanisms, base shear forces, displacements and interface openings in both directions, and then compared with the experimental results. The modelling approaches featuring Discrete Element Method (DEM) led to the best predictions in terms of displacements, while a submission using rigid block limit analysis led to the best prediction in terms of damage mechanisms. Large coefficients of variation of predicted displacements and general underestimation of displacements in comparison with experimental results, except for DEM models, highlight the need for further consensus building on suitable modelling assumptions for such masonry aggregates

Influence of traditional earthquake-resistant techniques on the out-of-plane behaviour of stone masonry walls: Experimental and numerical assessment

Preprint versionThe main goal of the work is to assess the efficiency of traditional earthquake resistant solutions to improve the out-of-plane performance of stone masonry walls. Therefore, the present paper presents the results of an experimental campaign and numerical analysis performed on three stone masonry walls with a U-shaped plan configuration. Two of them were built with traditional earthquake-resistant techniques usually found in European Mediterranean area, namely steel ties and timber-laced reinforcements embedded at the corners of the walls. These techniques are specifically intended to enhance wall-to-wall connections and, thus, improve the out-of-plane behaviour of the walls. The experimental campaign included qualitative assessment procedures, non-destructive tests for the material characterization and a quasi-static test for the characterization of the out-of-plane response. Additionally, a finite element numerical model was built, calibrated with the experimental results, allowing to perform a parametric study to evaluate the influence of the number of reinforcements and geometrical configuration on the out-of-plane behaviour of stone masonry walls.- (undefined

Methodology for seismic vulnerability assessment of existing masonry buildings in urban centres. Application to the Eixample district in Barcelona

(English) Unreinforced masonry buildings (URM), which prevail in many historic and urban centres, can be considered to be significantly vulnerable to seismic actions due to their peculiar constructive and structural features that could influence their seismic performance, even in low to moderate seismic hazard areas. These existing structures were usually designed considering only gravity loads without any seismic design requirements. Hence, they may endure severe consequences in the event of an earthquake due to the presence of many specific sources of structural vulnerability, such as the material's limited resistant capacity and ductility, the buildings’ height, very slender load-bearing walls, semi-flexible horizontal diaphragms, irregular plan configurations, presence of vertical extensions, large façade openings, among other structural features.The scientific literature currently offers a variety of methods for assessing seismic vulnerability of existing buildings on a large scale, as it is considered a challenging task. The selection of the appropriate approach is determined by several factors, including the purpose and nature of the study, the amount of data and resources available, the investigated building typologies, the level of analysis effort, and the cost required for the studies.The aim of this research is to contribute to the seismic vulnerability assessment of existing masonry buildings of the Eixample district of Barcelona, though the derivation of a general methodology, intensively based on numerical simulation due to lack of seismic damage observations from past earthquakes. This approach could be applied to similar problems involving the vulnerability assessment of historic urban centres in low to moderate seismic regions, by applying the necessary modifications. The first step of the proposed methodology is elaborating a detailed building taxonomy of the masonry buildings of the Eixample district according to their structural, material and geometrical characteristics, relevant to their seismic behaviour and possible sources of vulnerability. The most representative building typologies are selected based on the aforementioned building taxonomy, by using available statistical data of structural features of the analysed building stock. The next step is developing sophisticated numerical models of the previously identified representative masonry buildings, by using an efficient and realistic simulation of their seismic response based on the Finite Element Method (FEM). Non-linear static (pushover) analysis are performed for both main directions (parallel and perpendicular to the façade) in order to better understand their global seismic behaviour in terms of capacity and failure mechanisms. Moreover, parametric analyses are carried out to investigate the influence of different structural parameters on the building’s seismic performance. The N2 method is applied for the evaluation of the buildings’ seismic performance for the seismic hazard scenarios in Barcelona. The final step is the proposal of new forms of the Vulnerability Index Method (VIM) for both main directions, by defining the classes and calibrating the weights of the specific vulnerability parameters. The methodology is applied eventually to the Eixample district of Barcelona’s urban centre, by including two cases: a large number of existing masonry buildings and a typical urban block.(Español) Los edificios de obra de fábrica no armada (URM), abundantes en muchos centros urbanos históricos, resultan frecuentemente vulnerables ante las acciones sísmicas, incluso en zonas de baja o moderada peligrosidad sísmica, debido a sus características constructivas y estructurales. Por lo general, estas estructuras fueron diseñadas teniendo en cuenta únicamente las cargas gravitatorias y sin verificar su comportamiento sísmico. Ante un terremoto, dichas estructuras pueden sufrir graves consecuencias debido a varias fuentes específicas de vulnerabilidad estructural, como son la limitada capacidad resistente y limitada ductilidad del material, la altura de los edificios, los presencia de muros de carga muy esbeltos, forjados flexibles o semiflexible, las configuraciones de planta, frecuentemente irregulares, la presencia de extensiones verticales (remontas) y la frecuente presencia de grandes aberturas de fachada, entre otras.Como consecuencia del desafío que supone la evaluación de la vulnerabilidad sísmica de los edificios existentes a gran escala, en la literatura científica actual se han propuesto una gran variedad de métodos orientados hacia su caracterización. La selección del método más adecuado viene determinada por varios factores, entre los cuales se hallan el propósito y la naturaleza del estudio, la cantidad de datos y de recursos disponibles, las tipologías de los edificios investigados, el esfuerzo computacional requerido para el análisis y el coste de la investigación.El objetivo del presente trabajo reside en contribuir a la evaluación de la vulnerabilidad sísmica de los edificios de obra de fábrica existentes en el distrito del Eixample de Barcelona. Ello se lleva a cabo mediante la elaboración de una metodología general basada principalmente en la simulación numérica debido a la ausencia de observaciones, en el caso investigado, relativas a daños sísmicos producidos terremotos ocurridos en el pasado. Esta metodología podría aplicarse, con las modificaciones necesarias, a casos similares relativos a la evaluación de la vulnerabilidad de centros urbanos históricos en regiones de sismicidad baja a moderada. El primer paso de la metodología propuesta consiste en elaborar una taxonomía detallada de los edificios de obra de fábrica del distrito del Eixample en función de las características estructurales, materiales y geométricas que resultan relevantes para la caracterización de comportamiento sísmico. Los tipos de edificios más representativos se han seleccionado en base a dicha taxonomía, utilizando para ello datos estadísticos disponibles sobre sus características estructurales. El siguiente paso ha consistido en desarrollar modelos numéricos avanzados de los edificios seleccionados. Para este fin se ha utilizado el Método de los Elementos Finitos (MEF) por su simulación eficiente y realista de la respuesta sísmica. Se han realizado análisis estáticos no lineales (pushover) para las dos direcciones principales (paralela y perpendicular a la fachada) de los edificios, con el fin caracterizar su comportamiento sísmico global en términos de capacidad y mecanismos de fallo. Además, se han realizado análisis paramétricos con la finalidad de investigar la influencia de diferentes parámetros estructurales en el comportamiento sísmico. Se ha aplica el método N2 para la evaluación del comportamiento sísmico de los edificios para distintos escenarios de peligrosidad sísmica en Barcelona. Finalmente, se han propuesto unos formularios modificados para la aplicación del Método del Índice de Vulnerabilidad (VIM) según las dos direcciones principales, de los edificios. Ello ha comportado una definición de las clases de vulnerabilidad y la calibración de los pesos de los parámetros específicos de vulnerabilidad consistentes en (1) un conjunto amplio de edificios de obra de fábrica existentes y (2) el caso específico de un bloque de edificios típico del entorno urbano investigado.Finite Element Model, Pushover Analysis, N2 method, Vulnerability Index Method.Postprint (published version