Francesco Morelli

Speedup of post earthquake community recovery: the case of precast industrial buildings after the Emilia 2012 earthquake

The Emilia, May–July 2012, earthquake hit a highly industrialized area, where some tens thousands industrial buldings, mainly single storey precast structures, are located. Due to the likelihood of strong after shocks and the high vulnerability of these structures, the authorities first asked for a generalized seismic retrofit after the strong shakings of May 20th. In order to accelerate community recovery, this requirement was later loosened, leaving out the buildings which had undergone a strong enough shaking without any damage; the strong enough shaking was defined with reference to the ultimate limit state design earthquake. To the authors’ knowledge, it is the first time that the information on the earthquake intensity and structural damage is used for such a large scale post earthquake simplified safety assessment. In short, the earthquake was used as large experimental test. This paper shows the details of the models and computations made to identify the industrial buildings which have been considered earthquake tested and therefore not compelled to mandatory seismic retrofit. Since earthquake indirect (e.g. due to economic halt) costs may be as large the direct ones, or even larger, it is believed that this method may considerably lower the earthquake total costs and speed up the social and economic recovery of a community.

Development, design and experimental validation of a steel self-centering device (SSCD) for seismic protection of buildings

The paper describes the development of an original steel self-centering device (SSCD) for improving the level of seismic protection of new and pre-existing structures. In particular, the proposed hysteretic device exhibits two technical features essential to protecting structures against the effects of an earthquake: re-centering and recovery of the structure’s original dissipative resources (Dissipative Elements) after a seismic event. The overall mechanical behavior of the hysteretic device was first defined in terms of its main internal components. A refined parametric analysis was then conducted by varying the mechanical properties of the steel elements responsible for seismic energy dissipation; this allowed optimizing the retrofitting/protection capacities of the system. To this end, various grades of steel, used not only in traditional structural engineering applications, but also in automotive engineering and packaging, were selected, and specimens of each subjected to experimental monotonic and cyclic tests to determine the most suitable for our purposes. A full-scale prototype SSCD was finally fabricated and checked through cyclic tests to evaluate its mechanical and dissipative performance.

Influence of Tension Stiffening on the Flexural Stiffness of Reinforced Concrete Circular Sections

Within this paper, the assessment of tension stiffening effects on a reinforced concrete element with circular section subjected to axial and bending loads is presented. To this purpose, an enhancement of an analytical model already present within the actual technical literature is proposed. The accuracy of the enhanced method is assessed by comparing the experimental results carried out in past research and the numerical ones obtained by the model. Finally, a parametric study is executed in order to study the influence of axial compressive force on the flexural stiffness of reinforced concrete elements that are characterized by a circular section, comparing the secant stiffness evaluated at yielding and at maximum resistance, considering and not considering the effects of tension stiffness.

PERFORMANCE-BASED NONLINEAR RESPONSE HISTORY ANALYSIS FRAMEWORK FOR THE “PROINDUSTRY” PROJECT CASE STUDIES

Within the PROINDUSTRY project a Performance-based analysis framework is defined for seismic assessment of industrial structures, based on Nonlinear Response History Analysis (NL RHA) using in particular the Incremental Dynamic Analysis (IDA) method. This paper describes the choice of the PBEE and IDA analysis methods starting from an overview of state-of-the-art methods. The choice is analyzed in relation to: analysis goals for the selected case studies (design-based vs. risk-based), availability of databases/tools for hazard analysis and GMs selection, accuracy of criteria to scale and match GMs to a target spectrum (UHS, CMS, etc.) and treatment of record components. Three possible approaches of GMs selection are described and analyzed: (1) UHS-coherent Unscaled (Design), (2) UHScoherent GMs scaled to Sa(T1) (Risk/Loss), (3) CMS-coherent GMs scaled to Sa(T1), (Risk/Loss). Within the scopes of PROINDUSTRY, the approach (1) is proposed, as a tradeoff between simplicity of conventional PBEE design methods and probabilistic robustness for a heterogeneous portfolio of structures/facilities. M. Faggella, R. Laguardia, R. Gigliotti, F. Morelli, F. Braga, W. Salvatore.

SEISMIC RETROFIT OF AN INDUSTRIAL STRUCTURE THROUGH AN INNOVATIVE SELF-CENTERING HYSTERETIC DAMPER: MODELLING, ANALYSIS AND OPTIMIZATION.

Abstract. Recent earthquakes, as the one that hit Fukushima in Japan in 2011 or the one that produced extensive damage in Turkish petrochemical facilities during the Kocaeli earthquake of 1999 or, more recently, the seismic events in May 2012 in Emilia (Italy), highlighted the increasing need of providing adequate protection to industrial installations. Industrial facilities often store a large amount of hazardous material and, in case of seismic event, there is a high probability that accidental scenarios as fire, explosion, toxic or radioactive dispersion may occur. In these cases, the ensuing disaster certainly harms the people working in the installation and it may endanger the population living in the neighborhood or in the urban area where the industrial installation is located. The consequences of such accidental scenarios can be disastrous in terms of casualties, economic losses and environmental damage. Within this work, the seismic behavior of an industrial structure is studied through several Incremental Dynamic Analyses, IDA, and particular attention is given to the selection of suitable performance criteria and the modelling of non linear phenomena (II order effects, buckling, mechanical non-linearity, etc.). The seismic behavior is then enhanced applying to the structure an innovative typology of self-centering hysteretic damper, whose mechanical characteristics are optimized through the execution of IDAs on the retrofitted structures. A final comparison between the seismic behavior of the original structure and of the retrofitted one highlights the advantages of the innovative self-centering hysteretic dampers.

Efficiency of seismic isolation on industrial plants - Case study of a gas tank

The research leading to these results has received funding from the European Unions Research Fund for Coal and Steel (RFCS) research programme under grant agreement n° [RFSR-CT-2013-00019].

Dataset on the cyclic experimental behavior of Steel frames with Reinforced Concrete infill Walls

This paper presents the experimental data on the cyclic behavior of Steel frames with Reinforced Concrete infill Walls (SRCW). Two specimens, characterized by a different shear studs distribution, have been tested: the first one is provided with shear studs positioned only in the four corners of the steel frame; the second one presents shear studs all distributed along the perimeter of the steel frame except for the zone of the dissipative fuses. The overall setup, loading protocol, collapse mechanisms, force-displacement curves for both the whole system and the main single components are described for the two tested prototypes.

Experimental tests on real-scale EBF structures with horizontal and vertical links

The paper presents data achieved during an experimental test campaign executed on real-scale one storey/one bay EBF steel structures with vertical and horizontal links. Experimental tests were executed in displacement control by applying cyclic loading histories following ECCS45 protocol and constant amplitude-imposed displacements. Data provide indications concerning the energy dissipated by each prototype during tests, the corresponding shear force - angular distortion curves of the dissipative link and, besides, the force-displacement behavior of the steel prototypes until failure.

Influence of shear studs distribution on the mechanical behaviour of dissipative hybrid steel frames with r.c. infill walls

This paper studies the influence of the shear studs distribution, in terms of local and global effects, on the behavior of dissipative hybrid Steel frames with Reinforced Concrete infill Walls (SRCWs). Dissipative SRCWs have been recently proposed as seismic resistant systems, capable of coupling the high stiffness of reinforced concrete walls with the advantages of dissipative systems, in which the energy dissipation takes place in localized and replaceable elements. However, experimental tests showed that the global behavior and the failure mechanism of such systems are strongly influenced by the shear studs distribution along the steel frame—reinforce concrete wall interface. In this paper, this issue is studied through suitable numerical models, calibrated on the base of the available experimental results. Several modeling options and strategies are considered and their influence on the final results has been assessed. The resulting numerical model is used to analyze the mechanical behavior of such system and to perform parametric analyses varying the shear studs distribution. The results obtained help the understanding of the mechanical behavior and of the resisting mechanisms activated on the studied system, supplying relevant information for the development of more accurate design rules.

Ground motions and scaling techniques for 3D performance based seismic assessment of an industrial steel structure

This paper presents a performance-based earthquake assessment of an industrial structure, aiming at identifying suitable techniques to select and scale natural ground motions for 3D analysis and improve the structural response prediction of complex structures. To this end, an industrial structure characterized by the presence of large masses placed at a significant height and of different horizontal resisting systems, such as moment resisting frames, inverted V bracings and diagonal bracings, is investigated. The structural response is computed via both nonlinear static and dynamic analyses. Two sets of natural ground motions, one coherent with the Uniform Hazard Spectrum and one with the Conditional Mean Spectrum, are selected and scaled with different criteria. The efficiency and sufficiency of each selected ground motion set and scaling criteria is assessed through a probabilistic treatment of the key engineering demand parameters. Results indicate that for the structure analyzed, characterized by different behavior in the two orthogonal directions, the use of more complex ground motions selection and scaling techniques does not improve necessarily the reliability of results or allow the use of a lower number of ground motion recordings.