1,720,968 research outputs found
Seismic retrofitting solutions for precast RC industrial buildings struck by the 2012 earthquakes in Northern Italy
No full textIn 2012, the North of Italy was hit by a seismic sequence characterized by two main events occurred on May 20 and 29 with MW 6.1 and 6.0, respectively. Those earthquakes were particularly severe toward precast Reinforced Concrete (RC) structures not designed for seismic resistance. In the past years, the authors implemented a database collecting damage data and typological information on the industrial buildings struck by the Emilia earthquakes. That database was used to develop empirical fragility curves, which highlighted the considerable vulnerability of precast buildings conceived in accordance with pre-seismic code provisions. More recently, the interventions of seismic retrofitting on the same buildings, funded by the Emilia-Romagna region and designed by engineers which were directly hired by the companies, were examined in detail and critically revisited. A selection of these interventions is presented in this paper, which analyzes the effectiveness of the various retrofitting solutions, with a specific attention to the force transfer mechanisms between existing structures and strengthening systems. The interventions are divided between column strengthening (based, for example, on RC or steel jacketing) and interventions aimed at providing the building with a suitable earthquake resistant system (based, for example, on either the use of the existing cladding panels or the implementation of new bracing systems). Graphical representations of the analyzed solutions with the relevant construction details are provided
Cyclic test on a precast reinforced concrete column-to-foundation grouted duct connection
No full textA full-scale specimen of a column-to-foundation grouted duct connection suited for buildings and industrial structures is tested in cyclic bending combined with axial compression. The positioning of the steel ducts along the sides of the column cross-section allows for using traditional reinforcement cages for the column, with longitudinal bars at both mid-side and corners of the cross-section. Splice length and amount of transverse reinforcement along the splice are defined based on Eurocode 2 provisions for laps of reinforcing bars. A total of 19 loading cycles are carried out, achieving a drift of 5.3% in correspondence of a degradation of 15% of the peak resistance. The shear slip measured at the column-foundation interface results to be smaller than 5% of the deflection. Conversely, to predict accurately the test results, the slip of the projecting bars within their ducts cannot be neglected. It is proposed to take account of this slip by introducing an apparent strain. For the tested specimen, the apparent strain turns out to be equal to the yield strain of the reinforcement. A comparison with a monotonic bending test, previously conducted on the same connection, shows a strongly smaller deformability when the loading protocol is cyclic. Hysteretic energy and drift ductility for the proposed connection are close to those concerning a cast-in-place specimen of comparable capacity, which was described in a recent paper. The test results show an over-strength of 1.4 and a gain in ductility of 1.8 compared with the design values of bending resistance and curvature ductility computed for the cross-section at the column-foundation interface
Effetto delle condizioni di maturazione sulla resistenza a compressione del calcestruzzo impiegato in opere di interramento ferroviario
No full textA Ferrara sono in corso i lavori per l’interramento di un’importante linea ferroviaria. I diaframmi previsti dal progetto, dello spessore di 800 mm, sono stati realizzati nel periodo Luglio 2020-Maggio 2021, per complessivi 70000 m3 di getto. Il controllo di accettazione del calcestruzzo è stato effettuato mediante l’esecuzione di 1414 prove di compressione su provini cubici maturati per 28 giorni in ac qua alla temperatura di (20r2) °C. Un confronto con prove condotte su campioni maturati in condizioni ambientali di temperatura ed umidità relativa evidenzia significative differenze rispetto alle condizioni standard e può fornire utili informazioni sullo sviluppo della resistenza in opera. Infine, sulla base di prove su carote prelevate da un diaframma, si esamina l’andamento della resistenza con la profondità.Works for burying an important railway line are currently in progress in Ferrara, Italy. The required 800 mm-thick
retaining walls were cast starting from July 2020 and completed on May 2021, involving about 70000 m3 of concrete. The conformi ty control of this concrete was carried out through 1414 compression tests on cubic specimens cured in water for 28 days at (20 +/-2) °C. A comparison with test results on specimens cured at ambient temperature and relative humidity shows significant differ ences with respect to standard curing conditions, and may provide useful information on the strength development in the structure.
Finally, the strength distribution with depth is discussed based on tests on cores drilled from one of the retaining walls
Giovani, lavoro e cittadinanza sociale
No full textA partire dai dati di una ricerca su scala regionale, si analizzano alcune delle principali problematiche del rapporto tra giovani e sindacato e si indicano alcune strategie per la costruzione di un rapporto più efficac
3D orthotropic damage model for the failure analysis of LVL wood truss with steel connector through a regularized extended finite element method
No full textAny three-dimensional finite element analysis of the failure of wood trusses necessarily incurs several markedly nonlinear effects, including the co-existence of orthotropic ductile and brittle failure modes depending on entangled tensile, shearing, and compressive stress states, and the mesh dependency inherent in the adoption of softening stress state laws. The complexity of the modelling process is even more severe in the presence of steel connectors. Furthermore, the experimental evidence shows that the failure modes and patterns often vary in a significant way even for the same specimen geometry and in the presence of highly engineered timber because of the persistence of defects and heterogeneities. Therefore, ad hoc computational models should be able to capture this peculiar variability of failure configurations. All these issues are properly tackled by the present nonlinear finite element procedure. The adoption of a regularized extension of the extended finite element method, indeed, allows for transitioning from the continuous interpolation of the displacement field within an orthotropic elastic-damaging material to a regularized discontinuous kinematic description based on a length-enriched extended finite element method. The present formulation is successfully validated by simulating experimental data concerning a set of failure tests on Laminated Veneer Lumber trusses with pulled steel connector
Numerical failure analysis of built-up columns composed of closely spaced pultruded FRP channels
No full textThe results of geometrically nonlinear analyses on 43 built-up Pultruded Fibre-Reinforced Polymer (PFRP) columns with closely spaced chords and intermittent interconnections are presented. A comparison between columns with the end sections entirely loaded and columns loaded at the end battens only is reported, showing no appreciable difference in the P-δ response. The effects due to variations of column length and battens spacing are then investigated. It is found that stocky columns with small battens spacing attain pre-buckling failure at the web-flange junctions of the chords for loads approximately equal to 70% of the crushing load. Slender columns fail by global buckling, whereas intermediate-slenderness columns may experience interaction between local and global buckling. A design method is finally proposed
Fragility functions for local failure mechanisms in unreinforced masonry buildings: a typological study in Ferrara, Italy
No full textUnreinforced masonry buildings undergoing seismic actions often exhibit local failure mechanisms which represent a serious life-safety hazard, as recent strong earthquakes have shown. Compared to new buildings, older unreinforced masonry buildings are more vulnerable, not only because they have been designed without or with limited seismic loading requirements, but also because horizontal structures and connections amid the walls are not always effective. Also, Out-Of-Plane (OOP) mechanisms can be caused by significant slenderness of the walls even if connections are effective. The purpose of this paper is to derive typological fragility functions for unreinforced masonry walls considering OOP local failure mechanisms. In the case of slender walls with good material properties, the OOP response can be modeled with reference to an assembly of rigid bodies undergoing rocking motion. In particular, depending on its configuration, a wall is assumed either as a single rigid body undergoing simple one-sided rocking or a system of two coupled rigid bodies rocking along their common edge. A set of 44 ground motions from earthquake events occurred from 1972 to 2017 in Italy is used in this study. The likelihood of collapse is calculated via Multiple Stripe Analysis (MSA) from a given wall undergoing a specific ground motion. Then, the single fragility functions are suitably combined to define a typological fragility function for a class of buildings. The procedure is applied to a historical aggregate in the city center of Ferrara (Italy) as a case study. The fragility functions developed in this research can be a helpful tool for assessing seismic damage and economic losses in unreinforced masonry buildings on a regional scale
Pullout tests on the connection to an existing foundation of a steel warehouse rebuilt after the 2012 Emilia (Italy) earthquakes
Full text linkThe tests described in this paper were aimed at evaluating the tensile capacity of the anchorages connecting an automated pallet warehouse with an existing RC foundation. The warehouse is a new steel structure erected in the place of a previous warehouse collapsed due to the Emilia earthquake, but whose foundation remained undamaged. The investigated fastening consists of 10 post-installed, bonded threaded rods with diameter (d) and embedment depth (h(ef)) of 20 and 500 mm, respectively. Neither anchor arrangement nor embedment depth (h(ef) > 20d) was covered by current standards for fastening design. To reproduce the in-situ actual conditions of the fastening, an unconfined test configuration was used. The maximum loads achieved were more than 3 times greater than the seismic demand for the fastening. The tests highlighted the crucial role played by the reinforcing steel which was present in the foundation. Concrete-related failure mechanisms, such as the combined pullout and concrete cone failure mechanism typical of bonded anchors, were not activated. The observed crack patterns rather suggest the onset of a flexural failure mechanism of the concrete slab. This feature is confirmed by analytical calculations showing that, at the maximum loads achieved in the tests, the top reinforcement was likely to be yielded. In six preliminary unconfined tension tests on single anchors, steel rod failure was achieved, associated with limited cracking of the concrete surface in proximity of the anchor
Effect of uncertainties on seismic fragility for out-of-plane collapse of unreinforced masonry walls
No full textA new approach for the evaluation of fragility curves of UnReinforced Masonry (URM) walls is proposed. Uncertainties on geometrical and mechanical properties, as well as on magnitude and position of the applied loads, are considered using fuzzy set theory. Fuzzy set theory has been broadly applied to civil engineering problems, particularly to reinforced concrete structures, though its application to masonry, to the authors’ knowledge, is investigated here for the first time to evaluate the seismic response of masonry walls in the presence on vague and imprecise information. The proposed procedure allows computing fragility curves based on available typological databases, integrated with experimental tests and survey data. One of the main advantages of this procedure is that it can account for the variability of structural typologies on a territorial scale. The effectiveness of the method is shown through numerical examples concerning walls made of fired clay bricks and lime mortar, which are typical construction materials in the Po River Plain, in Northern Italy. Linear kinematic and nonlinear time-history analyses are used to calculate the seismic response. The computed fuzzy-like fragility curves include both aleatory and epistemic uncertainties. An extensive sensitivity analysis based on suitable sets of representative input parameters is carried out to validate the proposed procedure
NUMERICAL EVALUATION OF THE LOCAL BUCKLING MOMENT FOR PULTRUDED FRP BEAMS
Full text linkThe interest of the scientific community in obtaining the local buckling stresses for pultruded FRP (PFRP) shapes is shown by the huge number of published studies on this subject. The main objective of the present paper is to provide accurate estimates of the local buckling moment for PFRP beams. These estimates are fundamental for defining the nondimensional slenderness parameter introduced by the Italian Design Guide CNR DT 205/2007 [1] for beams in pure bending. One of the most technically sound formulations is that proposed by Kollár [2], who derived explicit expressions for the critical normal stresses of flange and web panels of PFRP beams that depend on the rotational stiffness of the web-flange junction in compression. This formulation is based on a consolidated approach for estimating the flange buckling strength of typical steel profiles [3].
In the present paper, a literature review is initially reported. In particular, it is shown that the approximate expression for the critical stress provided in [3] for steel members tends to underestimate the local buckling strength, especially in the case of wide-flange cross-section profiles. This underestimation becomes particularly evident for PFRP beams. For example, in [4], on the basis of the results of 10 bending tests, an average ratio of 1.2 between experimental and predicted local buckling moments was obtained. Anyway, it has clearly been shown that the web-flange junctions play a crucial role in determining the buckling and ultimate strengths of PFRP beams [5]. Therefore, the experimental and numerical characterization of the junction behaviour is necessary [6]-[7]. The rotational spring stiffness used in Kollár’s model to reproduce the behaviour of the web-flange junction seems sensitive to the shear modulus of the flanges [4] and to the ratio Io,f/Io,w [8], with Io,f and Io,w being the ratios between transverse and longitudinal Young’s moduli for the web and flanges, respectively. Hence, in the present paper estimates of this stiffness based on a series of finite element buckling analysis results are finally reported. The influence of possible differences in the mechanical properties between flange and web panels is suitably taken into account
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