Empirical seismic fragility for the precast RC industrial buildings damaged by the 2012 Emilia (Italy) earthquakes

The paper analyses the seismic fragility of precast reinforced concrete buildings using observational damage data gathered after the 2012 Emilia earthquakes that struck Northern Italy. The damage level in 1890 buildings was collected, classified and examined. Damage matrices were then evaluated, and finally, empirical fragility curves were fitted using Bayesian regression. Building damage was classified using a six-level scale derived from EMS-98. The completeness of the database and the spatial distribution of the buildings investigated were analysed using cadastral data as a reference. The intensity of the ground motion was quantified by the maximum horizontal peak ground acceleration, which was obtained from ShakeMaps. Copyright © 2017 John Wiley & Sons, Ltd

La duttilità e la resistenza nelle connessioni delle travi PREM

Nella nota si riferisce degli esiti desunti dalle indagini numeriche effettuate su travi prefabbricate reticolari miste (PREM), caratterizzate da connessioni a traliccio. Tipicamente tali travi sono composte da un piatto di base di acciaio su cui viene saldato un traliccio a doppia staffa realizzato con barre di acciaio, la trave si completa poi con un getto integrativo di calcestruzzo. L’efficacia del sistema di trasferimento degli sforzi fra acciaio e calcestruzzo è affidato al sistema di connessione, le cui caratteristiche di resistenza, rigidezza e duttilità possono essere dedotte con una prova di scorrimento (push-out). Tali prove possono mostrare un comportamento fragile delle connessioni, da cui deriva la necessità di determinare le lunghezze della trave che comportano una rottura delle connessioni

Static stiffness of rigid foundation resting on elastic half-space using a Galerkin boundary element method

In this work, a simple and effective numerical model is proposed for studying flexible and rigid foundations in bilateral and frictionless contact with a three-dimensional elastic half-space. For this purpose, a Galerkin Boundary Element Method for the substrate is introduced, and both surface vertical displacements and half-space tractions are discretized by means of a piecewise constant function. The work focuses on a transversely isotropic substrate having the plane of isotropy parallel to the half-space boundary, hence the relationship between vertical displacements and half-space reactions is given by Michell solution, reducing to Boussinesq solution for an isotropic half-space. Several numerical tests are performed for showing the effectiveness of the model, on one hand by determining vertical displacements of flexible rectangular foundations subjected to vertical pressures, on the other hand by accurately determining the translational and rotational stiffness of rigid rectangular and L-shaped foundations. Particular attention is given to the determination of the center of stiffness in case of unsymmetrical foundations, since it turns out to be not coincident with foundation area centroid

Incremental Analysis of Elastoplastic Beams and Frames Resting on an Elastic Half-Plane

In this work, a simple and effective finite element-boundary integral equation (FE-BIE) approach for the static analysis of elastic beams and frames in bilateral frictionless contact with an elastic half-plane is extended to include the case of material nonlinearity. Elastic-perfectly plastic behavior is assumed for the supported structure and in particular for the foundation beam. Potential plastic hinges are placed along structural elements and modeled as nonlinear semirigid connections characterized by a rigid-plastic moment-rotation relationship. Incremental, load-controlled analyses of beams and frames resting on an elastic half-plane with several potential plastic hinges along the structural members are then performed. Numerical examples illustrate the effectiveness of the model in determining the stiffness degradation of the structure for increasing loads, together with ultimate loads and collapse mechanisms

Valutazione dello sforzo normale in travi prismatiche tramite parametri modali flessionali

In letteratura sono stati proposti diversi metodi, sia statici che dinamici, per la stima sperimentale dello sforzo normale agente in un’asta. Tali metodi in alcuni casi offrono anche la possibilità di valutare il carico critico delle aste compresse o la rigidezza rotazionale dei vincoli di estremità nelle catene di archi e volte in muratura. Facendo uso del modello di trave di Eulero-Bernoulli e supponendo note la rigidezza e la massa della trave, in questa nota si mostra che è sufficiente conoscere una frequenza propria di oscillazione e le ampiezze della corrispondente forma modale in tre punti della trave, per identificare univocamente lo sforzo normale e le rigidezze rotazionali dei vincoli di estremità. Inoltre si stabiliscono le condizioni sui dati che conducono ad una corretta identificazione

A FE-BIE coupled method for the static analysis of beams on 3D half-space

This contribution presents a simple and effective numerical model for performing static analyses of beams in frictionless and bilateral contact with a three-dimensional (3D) elastic and isotropic half-space. Such a problem can suitably represent the behaviour of strip footings and shallow foundations in building structures. A coupled finite element-boundary integral equation (FE-BIE) method, already introduced for beams on half-plane [1], is here extended to the case of beams on 3D half-space, by adopting a mixed variational formulation which assumes as independent fields both beam displacements, rotations and contact surface tractions. Mixed formulation includes the Green function of the 3D half-space [2]. The resulting numerical model makes use of locking-free \u201cmodified\u201d Hermitian shape functions [3] for the beam and piecewise constant function for the substrate tractions. For this purpose, only the contact surface underneath the foundation needs to be discretized with rectangular elements; furthermore, traction distribution in beam transverse direction is considered with an adequate mesh refinement of contact surface in both plane directions. Numerical tests of both Euler-Bernoulli and Timoshenko beams subject to several load conditions are dealt with. Results in terms of displacements, contact tractions and bending moment are obtained, showing the effectiveness of the model and its convergence to existing analytical and numerical solutions [4]. References [1] Tullini, N., Tralli, A., \u201cStatic analysis of Timoshenko beam resting on elastic half-plane based on the coupling of locking-free finite elements and boundary integral\u201d, Computational Mechanics, 45(2\u20133) pp. 211\u2013225 (2010). [2] Johnson, K.L., Contact mechanics, Cambridge University Press, Cambridge (1985). [3] Reddy, J.N., \u201cOn locking-free shear deformable beam finite elements\u201d, Computer Methods in Applied Mechanics and Engineering, 149(1-4), pp. 113\u2013132 (1997). [4] Biot, M.A., \u201cBending of an infinite beam on an elastic foundation\u201d, Journal of Applied Mechanics, 4, pp. A1\u2013A7 (1937)

Nonlinear analysis of composite beams with concrete-encased steel truss

Composite beams constituted by a concrete-encased steel truss welded to a continuous steel plate are analyzed using a nonlinear finite element formulation based on Newmark's classical model. The web member of the steel truss is made by deformed or structural steel rebars and behaves like a deformable shear connection. In order to avoid slip locking, finite elements based on second-order interpolation of longitudinal displacements and flexural rotations are employed. Simply supported composite beams subjected to a uniformly distributed transverse load are considered. The bending capacity is evaluated for short up to long spans, taking the nonlinear behavior of concrete, steel and shear connection into account. The effects of the shear connection ductility are put in evidence, showing that, for short spans, the interfacial stress transfer resulting from the yielding of connection may be penalizing. In fact, the high slip gradient arising in sections near the supports may lead to a premature concrete failure. In this case, the exact solution to the linear elastic problem for steel–concrete composite beams can be used for design purposes

Nonlinear analysis of RC box culverts resting on a linear elastic soil

In the analyses presented, the soil-structure interaction is accounted for by means of a FE-BIE approach, in which the structure is modelled with displacement-based beam finite elements, whereas the boundary between structure and substrate is described in terms of surface tractions by means of a boundary integral equation incorporating a suitable Green's function. This mixed formulation ensures full continuity between structure and substrate in terms of displacements and rotations. To take account of structural nonlinearities, potential plastic hinges are defined at the end sections of the beam elements in the form of semi-rigid connections characterized by a rigidplastic moment-rotation relationship. The incremental analyses carried out emphasize the effectiveness of the model in reproducing collapse mechanisms and stiffness loss of the structure for increasing loads. Moreover, the adopted formulation is able to capture both interfacial shear tractions and vertical normal tractions which develop along the substrate boundary under a variety of loading conditions

Prove di vibrazione armonica forzata su costruzioni pubbliche di tipo strategico ubicate in diverse località della Romagna

Nella presente nota si descrivono le attrezzature e le modalità di svolgimento delle prove di vibrazione forzata effettuate, mediante vibrodina, su costruzioni pubbliche di tipo strategico ubicate in diverse località della Romagna in seguito a convenzione con la Regione Emilia-Romagna nell’ambito dell’Osservatorio Sismico delle Strutture promosso dal Servizio Sismico Nazionale

Buckling and postbuckling finite-element analysis of pultruded FRP profiles under pure compression

Results of nonlinear finite element analyses of commercial PFRP I-section profiles subjected to pure compression are presented. One narrow-flange and four wide-flange shapes are analyzed for ten values of the column slenderness, involving 50 FE models. The imperfection sensitivity is investigated with reference to different imperfection shapes. For wide-flange columns, if the imperfection amplitudes are identified with the limiting amplitudes reported by the pultruders, extremely low ultimate axial loads are obtained, associated with unrealistic failure mechanisms and strong interaction between local and global buckling modes. In contrast, reduced imperfection amplitudes reported in the literature lead to well documented failure mechanisms and to a small influence of the buckling mode interaction. As is known, the local buckling of wide-flange shapes is triggered by the flange instability. Conversely, the local buckling of narrow-flange shapes generally is triggered by the web instability. Due to this property, the paper shows that, at equal cross-section area, the narrow-flange profiles may exhibit higher ultimate loads with respect to the wide-flange profiles in a broad range of column slenderness