Frequency and damping evolution during experimental seismic response of civil engineering structures

The results of the seismic tests on several reinforced-concrete shear walls and a four-storey frame are analysed in this paper. Each specimen was submitted to the action of a horizontal accelerogram, with successive growing amplitudes, using the pseudodynamic method. An analysis of the results allows knowing the evolution of the eigen frequency and damping ratio during the earthquakes thanks to an identification method working in the time domain. The method is formulated as a spatial model in which the stiffness and damping matrices are directly identified from the experimental displacements, velocities and restoring forces. The obtained matrices are then combined with the theoretical mass in order to obtain the eigen frequencies, damping ratios and modes. Those parameters have a great relevance for the design of this type of structures

Actividades do laboratório ELSA no domínio da avaliação e reforço de estruturas em zonas sísmicas

O Laboratório ELSA (Laboratório Europeu de Avaliação Estrutural), do Centro Comum de Investigação (CCI) da Comissão Europeia, em Ispra, Itália, desenvolve desde 1992 uma intensa actividade de investigação de carácter experimental e numérico no domínio do comportamento sísmico de estruturas. Este trabalho de investigação é desenvolvido em estreita colaboração com outros organismos de investigação (universidades, laboratórios nacionais,...) pertencentes aos Estados Membros ou outros Estados com os quais existam acordos de cooperação. O laboratório ELSA dedica atenção especial às áreas de investigação na avaliação do comportamento de estruturas sujeitas à acção dos sismos. Para além da avaliação da vulnerabilidade estrutural, são também investigadas técnicas de reparação e reforço adequadas a cada tipo estrutural. A avaliação da eficiência destas técnicas é feita através da realização de ensaios Pseudo-Dinâmicos em modelos de grande escala de estruturas de edifícios, pontes, bem como partes de edifícios com valor cultural (interesse histórico e monumentos)

Pseudodynamic tests on a full-scale 3-storey precast concrete building: global response

In the framework of the SAFECAST Project, a full-scale three-storey precast building was subjected to a series of pseudodynamic (PsD) tests in the European Laboratory for Structural Assessment (ELSA). The mock-up was constructed in such a way that four different structural configurations could be investigated experimentally. Therefore, the behaviour of various parameters like the types of mechanical connections (traditional as well as innovative) and the presence or absence of shear walls along with the framed structure were investigated. The first PsD tests were conducted on a dual frame-wall precast system, where two precast shear wall units were connected to the mock up. The first test structure sustained the maximum earthquake for which it had been designed with small horizontal deformations. In the second layout, the shear walls were disconnected from the structure, to test the building in its most typical configuration, namely with hinged beam–column connections by means of dowel bars (shear connectors). This configuration was quite flexible and suffered large deformations under the design level earthquake. An innovative connection system, embedded in the precast elements, was then activated to create emulative beam–column connections in the last two structural configurations. In particular, in the third layout the connectors were restrained only at the top floor, whereas in the fourth layout the connection system was activated in all beam–column joints. The PsD test results showed that, when activated at all the floors, the proposed connection system is quite effective as a means of implementing dry precast (quasi) emulative moment-resisting frames

Stiffness-Displacement Correlation from the RC Shear Wall Tests of the SAFE Program: Derivation of a Capacity Line Model

The response of 13 reinforced concrete shear walls submitted to successive seismic tests has been postprocessed to produce time histories of secant stiffness and displacement oscillation amplitude. For every wall an envelope curve of displacement amplitude versus stiffness is identified which is fairly modelled by a straight line in double logarithmic scale. This relatively simple model, when used as a capacity line in combination with the demand response spectrum, is able to predict in an approximate manner the maximum response to the applied earthquakes. Moreover, the graphic representation of the demand spectrum and a unique model capacity line for a group of equal walls with different assumed design frequencies on them gives a visual interpretation of the different safety margins observed in the experiments for the respective walls. The same method allows as well constructing vulnerability curves for any design frequency or spectrum. Finally, the comparison of the different identified line models for the different walls allows us to assess the qualitative effect on the behaviour of parameters such as the reinforcement density or the added normal load

Modèle de béton armé équivalent pour l'analyse du comportement des voiles de très faible élancement. Programme SAFE

Within the SAFE research project squat reinforced concrete walls have been tested pseudo-dynamically at ISPRA. This paper describes the modeling of the structures T5 and T12 of the program. Numerical calculations done by LMT are presented. Modeling is based upon "equivalent reinforced concrete medium" coupled with damage mechanics and plasticity. Beams and truss elements are used in order to elaborate an efficient, non time consuming simplified method. Comparison with experimental results demonstrate the efficiency of the modeling tools to understand the nonlinear behavior of very squat walls.Le programme SAFE concerne des essais pseudodynamiques effectués à ISPRA sur des voiles en béton armé très faiblement élancés. La modélisation choisie au LMT pour calculer le comportement non linéaire des structures T5 et T12 du programme est ici présentée. Les maquettes sont modélisées selon le principe du «béton armé équivalent». Les maillages du béton et de l'acier sont découplés et des éléments barres ou poutres sont utilisés pour modéliser la structure. La loi constitutionnelle du béton est basée sur la mécanique de l'endommagement tandis que celle de l'acier suit une loi élastoplastique. La comparaison entre les résultats expérimentaux et numériques prouve la capacité de la nouvelle méthode de simuler le comportement non linéaire des voiles de très faible élancement

5G network slicing with QKD and quantum-safe security

We demonstrate how the 5G network slicing model can be extended to address data security requirements. In this work we demonstrate two different slice configurations, with different encryption requirements, representing two diverse use-cases for 5G networking: namely, an enterprise application hosted at a metro network site, and a content delivery network. We create a modified software-defined networking (SDN) orchestrator which calculates and provisions network slices according to the requirements, including encryption backed by quantum key distribution (QKD), or other methods. Slices are automatically provisioned by SDN orchestration of network resources, allowing selection of encrypted links as appropriate, including those which use standard Diffie-Hellman key exchange, QKD and quantum-resistant algorithms (QRAs), as well as no encryption at all. We show that the set-up and tear-down times of the network slices takes of the order of 1-2 minutes, which is an order of magnitude improvement over manually provisioning a link today

Efficient and reliable nonlocal damage models

We present an efficient and reliable approach for the numerical modelling of failure with nonlocal damage models. The two major numerical challenges––the strongly nonlinear, highly localized and parameter-dependent structural response of quasi-brittle materials, and the interaction between nonadjacent finite elements associated to nonlocality––are addressed in detail. Reliability of the numerical results is ensured by an h-adaptive strategy based on error estimation. We use a residual-type error estimator for nonlinear FE analysis based on local computations, which, at the same time, accounts for the nonlocality of the damage model. Efficiency is achieved by a proper combination of load-stepping control technique and iterative solver for the nonlinear equilibrium equations. A major issue is the computation of the consistent tangent matrix, which is nontrivial due to nonlocal interaction between Gauss points. With computational efficiency in mind, we also present a new nonlocal damage model based on the nonlocal average of displacements. For this new model, the consistent tangent matrix is considerably simpler to compute than for current models. The various ideas discussed in the paper are illustrated by means of three application examples: the uniaxial tension test, the three-point bending test and the single-edge notched beam test.Peer ReviewedPostprint (author’s final draft

Homogenization and seismic assessment : review and recent trends

The mechanics of masonry structures has been for long underdeveloped in comparison with other fields of knowledge. Presently, non-linear analysis is a popular field in masonry research and advanced computer codes are available for researchers and practitioners. The chapter presents a discussion of masonry behaviour and clarifies how to obtain the non-linear data required by the computations. The chapter also addresses different homogenisation techniques available in the literature in the linear and rigid-plastic case, aiming at defining a catalogue and at discussing the advantages and disadvantages of the different approaches. Special attention is given to stress assumed models based either on a polynomial expansion of the micro-stress field or in the discretization of the unit cell by means of a few constant stress finite elements CST with joints reduced to interfaces. Finally, the aspects of seismic assessment are presented and case studies involving the use of macro-block analysis, static (pushover) analysis and time integration analysis are discussed.(undefined

Am J Prev Med

CC999999/Intramural CDC HHS/United States2017-02-19T00:00:00Z26456878PMC531651