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• Factors influencing model updating results by Douglas-Reid method are analyzed. • Performance of continuous model updating algorithms are assessed. • Robustness to the influence of varying environmental conditions is checked. • Encouraging results are obtained for integration with Structural Health Monitoring. The opportunities of Operational Modal Analysis and Finite Element model updating for non-destructive structural assessment have attracted significant research interest in recent years. In order to keep the computational efforts associated with model updating as low as possible, different strategies have been proposed over the years to approximate the model response. Among them, response surface models and the Douglas-Reid method are the most popular. However, systematic investigations about the factors affecting their model updating performance in view of Structural Health Monitoring applications are currently very limited. The present paper focuses the attention on the Douglas-Reid method, and analyzes the influence of different factors on the accuracy and reliability of model updating results. Comparisons with different updating approaches, such as grid search and the Inverse Eigensensitivity method, are also reported. The final objective is assessing the performance of the Douglas-Reid method for indirect monitoring of selected updating variables in the context of Structural Health Monitoring applications. Robustness and accuracy of model updating results under varying environmental conditions are evaluated to this aim, highlighting the interesting applicative perspectives of the method in the context of vibration-based Structural Health Monitoring, in spite of the very limited number of similar applications reported in the literature. [ABSTRACT FROM AUTHOR]

Abstract: Seismic risk mitigation in urban areas is a very relevant issue in European regions, such as Italy and Greece, characterized by the presence of a large stock of heritage structures. Enhancing the knowledge about the dynamics of structures is definitely useful in view of seismic assessment and design of risk mitigation interventions. However, this task can be difficult in the case of heritage structures, since several uncertainties affect material properties and structural patterns. In this paper, the opportunities provided by dynamic identification techniques for the non-destructive evaluation of heritage structures are discussed with focus on an interesting case study. This refers to the characterization of a modern heritage reinforced concrete building as a preliminary step towards seismic assessment. The structure under investigation is the Tower of the Nations, located in the Mostra D'Oltremare urban park in Naples, Italy. The paper shows how the combination of ambient vibration tests and model refinement can represent a valuable tool for an indirect non-invasive structural assessment of historical structures. Their proper analysis and modeling, in fact, is usually very challenging from the scientific and technical viewpoint due to their unique structural configurations, the several modeling uncertainties and the need to keep destructive investigations very limited. In this framework the present paper shows how a rational choice of the updating parameters and of the objective function can support the model optimization taking into account the ultimate objectives of the analysis, namely the setting of a reliable model for the assessment of the seismic performance of the structure in the linear regime. As a result, the paper describes the refinement of the model of the Tower of the Nations, in a way able to minimize the scatter with the experimental data and, at the same time, enhance the accuracy of response spectrum and seismic time-history linear analyses. [Copyright &y& Elsevier]

Abstract: A common assumption in the theoretical background of Operational Modal Analysis (OMA) methods concerns the input, which is not measured and consists of a Gaussian white noise characterized by a flat spectrum in the bandwidth of interest. Even if a number of applications have shown that OMA works also when the input spectrum is smooth enough, if this assumption is not fulfilled, the modal identification process may become more complex or even fail due to dominant frequency components of the input appearing in response spectra. Thus, specific techniques and strategies have to be applied to sort out structural dynamic properties from frequencies of the input. It is often possible to identify such non-structural frequencies in the case of spurious harmonics due to rotating equipment, but they can be erroneously identified as structural or even bias the estimates, for instance when such harmonics are close to structural modes. About civil structures, spurious frequencies can be due to rotating machines but also to interaction with adjacent constructions. In the present paper, attention is mainly focused on the issue of modes from surrounding structures appearing in the response of the structure under investigation. Thus, natural frequencies of a sample structure are mixed together with those due to interaction with similar surrounding structures, and its response spectra are characterized by several close peaks in a narrow bandwidth. In order to discriminate modal from spurious frequencies, an integrated use of output-only techniques is illustrated and applied to a real test case. An approach aiming at robust evaluation and monitoring of dynamic properties for fast post-earthquake emergency support is proposed and the experimental field validation is discussed in detail. [Copyright &y& Elsevier]

Steel–concrete composite members are an interesting option for structural designers, but the reliability of design procedures both in the case of gravity and seismic loads is in continuous development. The issue is very complex, since behaviour of continuous composite beams results from local phenomena of interaction such as partial shear connection and bond.Furthermore, composite beams in buildings generally are not characterised by a full continuity due to the beam to column connections; thus the analysis and the detailing of such parts have a key role in the development of suitable design procedures.In the present paper, some computational aspects related to the modelling of composite flexural members are discussed with reference to continuous and semi-continuous structural systems widely used in practice. [Copyright &y& Elsevier]

Abstract: This paper assesses the experimental results of monotonic (pushover) tests carried out on partially encased composite steel–concrete columns connected to the foundation block through the traditional bolted steel end plate and an innovative socket type system. These tests show that the structural response of the traditional connection is significantly influenced by the behaviour of the anchorage bolts. The latter cause large fixed end rotations and possess limited energy dissipation. Conversely, innovative composite steel–concrete base column connections with socket systems exhibit adequate overstrength, inelastic deformations and energy absorption capacity. Furthermore, socket-type connections are characterized by spreading of inelasticity at the base of the composite columns without damage localization on concrete and interface components. It can thus be argued that the innovative connection type assessed in this study is a viable solution for applications in framed structures fulfilling capacity design requirements, e.g. structural systems in earthquake prone regions. [Copyright &y& Elsevier]

Structural safety assessment of urbanised areas exposed to seismic risk is a complex task and can be approached at different scales. Fragility functions are the most effective tool to perform an estimation of the structural risk, since they describe the exceeding probability of the limit state of interest given a level of ground shaking. The formulation of a fragility function is based on the selection of an Intensity Measure of the ground shaking, commonly represented by peak-ground or spectral parameters or by macroseismic intensity grades. In the present paper, a novel approach to estimate the seismic vulnerability at a large scale of urbanised areas is presented. The scenario earthquakes are selected according to the current formulation of the seismic hazard disaggregation provided by National and International codes, i.e. through the disaggregation in terms of magnitude (M), epicentral distance (R) and number of standard deviation from the median ground motion (ε). To this aim, a vectorial seismic Intensity Measure is assumed to compute structural safety at large scale, and a change of variables is made to turn the traditional fragility curve into a matrix. Typological fragility matrices are processed and combined to define the so-called Urban Fragility Matrices, representative of the vulnerability of selected urban sectors. The procedure is then implemented and validated referring to the city of Pozzuoli (Southern Italy) and its effectiveness validated with reference to the damage survey relative to the 4th October 1983 seismic event which struck the city, resulting a good matching between predicted and observed scenarios. • A novel methodology for probabilistic safety assessment of buildings at large scale has been proposed. • Source-to-site disaggregation of ground motion has been taken into account used to define the seismic fragility. • A new tool, called urban fragility matrices, has been introduced to assess seismic fragility at large scale. • The proposed methodology has been validated with respect to the case study of Pozzuoli (southern Italy). [ABSTRACT FROM AUTHOR]

Wastewater disposal systems are complex systems composed by several interconnected elements. In the aftermath of dramatic natural events, such as the earthquake, the failure of any of these elements can result in the deterioration of the environment as well as in the risk for the exposed population, due to leakage of untreated or un-properly treated wastewater on soil and/or its discharge into superficial waters. This paper presents a multi-disciplinary methodology for the evaluation of the seismic vulnerability of municipal or industrial wastewater treatment plants, based on damage observation of available earthquake reports. Specific fragility curves and threshold values expressed in terms of Peak Ground Acceleration (PGA) are presented and compared with existing functions. The methodology fully comply requirements of most relevant and effective risk analysis tools or for land-use planning and can be adopted for the definition of structural priorities of plants. [ABSTRACT FROM AUTHOR]