Phase-field modelling of failure in hybrid laminates

In this paper, the complex failure process of unidirectional hybrid laminates under uniaxial loading condition is reproduced and investigated by a one-dimensional phase-field model. The key ingredients of the approach, describing the mechanical response of a hybrid composite made of two different layers, are: (i) a phase-field method, based on a variational formulation of brittle fracture with regularised approximation of discontinuities for the two layers, (ii) cohesive law for the adhesive interface that connects the layers and (iii) robust and consolidated numerical strategy for the solution of the non-linear discretised problem. Explicit and well detailed simulations are shown for four peculiar failure mechanisms and the outcomes validated against experimental results available in literature. The model is able to discriminate among these different failure mechanisms according to the geometrical and mechanical properties of the hybrid composite. Both delamination of the adhesive interface is followed and crack patterns within the materials are fully determined. Finally, the proposed approach opens new perspective studies in higher dimension settings

Progressive collapse: the case of composite steel-concrete frames

Residual strength and alternate load paths are two fundamental design strategies to ensure adequate resistance against progressive collapse of structures. This paper presents an experimental study carried out on two full-scale steel and concrete composite frames to investigate their structural behaviour in case of a column collapse. The study focusses on the redundancy of the structure as provided by the beam-slab floor system as well as by the ductile beam-to-column joints. The specimens were ground floor sub-frames ‘extracted’ from two reference buildings designed in accordance to the Eurocodes. The frames have the same overall dimensions, but a different, symmetric and asymmetric, configuration of the column layout. In both tests, the collapse of an internal column was simulated. The paper presents the main features of the frames and the principal outcomes of the test on the symmetric frame

Steel-concrete frames under the column loss scenario: An experimental study

Accidental events, such as impact loading or explosions, are rare events with a very low probability of occurrence. However, their effects often lead to very high human losses and economic consequences. An adequate design against these events should reduce the risk for the life of the occupancy, minimize the damage extension and enable a quick rebuilding and reuse. A structure fulfilling these requirements is ‘robust’. Different strategies can be pursued for accidental events, and among them, methods based on the residual strength or the alternate load path are frequently adopted because applicable to a vast range of structures. Adequate design strategies based on them require an in-deep knowledge of load transfer mechanisms from the damaged to the undamaged part of the structure. As to the frames, the important role of joint ductility was pointed out in recent studies. Besides, the flooring systems substantially affect the spread of the damage, but the research on this subject is still very limited. The present study focuses on steel-concrete composite frames under the column loss scenario. It aims to better understand the influence of both frame continuity and floor systems in the development of 3D membrane action. Two geometrically different 3D steel-concrete composite full-scale substructures were extracted from reference buildings and tested simulating the column collapse scenario. This paper illustrates the preparatory studies, the main features of the specimens and the outcomes of the first test. The test provided an insight in the need for an enhanced design of joints and pointed out the key features of the response of the floor system

Stability of Boundary Conditions for the Sadowsky Functional

It has been proved by the authors that the (extended) Sadowsky functional can be deduced as the Γ -limit of the Kirchhoff energy on a rectangular strip, as the width of the strip tends to 0. In this paper, we show that this Γ -convergence result is stable when affine boundary conditions are prescribed on the short sides of the strip. These boundary conditions include those corresponding to a Möbius band. This provides a rigorous justification of the original formal argument by Sadowsky about determining the equilibrium shape of a free-standing Möbius strip. We further write the equilibrium equations for the limit problem and show that, under some regularity assumptions, the centerline of a developable Möbius band at equilibrium cannot be a planar curve

Robustezza Di Sistemi Intelaiati Misti Acciaio-Calcestruzzo: Il Caso Di Collasso Di Una Colonna // Robustness Of Framed Steel-concrete Composite Systems: The Case Of A Column Collapse

Negli ultimi anni, la ricerca di soluzioni costruttive finalizzate alla mitigazione dei danni causati da eventi eccezionali ha suscitato un grande interesse da parte della comunità scientifica internazionale. Tali azioni possono essere fronteggiate sia attraverso criteri di sovraresistenza che di ridondanza strutturale e la combinazione di questi criteri può portare alla definizione di metodi di progetto efficaci ed economicamente efficienti. Uno dei principali obiettivi delle strategie di intervento è quello di realizzare sistemi strutturali in grado di attivare meccanismi di ridistribuzione dei carichi in modo che questi possano essere trasferiti, dalla parte danneggiata alla parte non danneggiata della struttura. Il lavoro svolto fa parte di un Progetto di Ricerca Europeo che ha l'obiettivo di definire nuovi criteri di progetto per strutture miste acciaio-calcestruzzo nei confronti di azioni eccezionali. La prima parte della ricerca si concentra sul comportamento di due telai 3-D nei confronti del collasso di una colonna interna. Due prove a scala reale saranno eseguite su una parte di queste strutture. Simulando il collasso completo di una colonna sarà possibile studiare la ridondanza del sistema tridimensionale fornito dalla soletta attraverso l'attivazione delle forze membranali. Il presente articolo illustra lo studio preliminare condotto in fase di progetto delle prove. // The last years were characterized by a growing interest about the development of strategies for the mitigation of the damages caused by accidental events. Accidental actions can be resisted by residual strength and alternate load path methods and combination of these strategies can lead to an effective and cost efficient design procedure for progressive collapse mitigation by redistributing the loads within the structure. One of the main objective of these strategies is the development of structural systems able to activate mechanisms to transfer the loads from the damaged to the undamaged part of the structure. This paper illustrates the preliminary work carried on within a European Research Project, aimed at developing new design concepts for steel-concrete composite frames against accidental actions. The first part of the study investigates the behavior of two geometrically different steel-concrete 3-D composite frames subjected to the loss of an internal column. Two full-scale experimental tests will be performed on a part of these structure. By simulating the total loss of the impacted column, the experiments enable investigation of the redundancy of the 3-D slab system in terms of activation of membrane effects. The present paper presents the preliminary study for the design of the tests

Robustness of Moment Resisting Steel-Concrete Composite Frames: The floor resisting mechanism in the case of column collapse

This paper illustrates the preliminary work carried on within a European Research Project, aimed at developing new design concepts for steel-concrete composite frames against accidental actions. Accidental actions can be resisted by residual strength and alternate load path methods. Combination of these strategies can lead to an effective and cost efficient design strategy for progressive collapse mitigation by redistributing the loads within the structure. The first part of the study investigates the behavior of two geometrically different steel-concrete 3D composite frames subjected to the loss of an internal column. Two full-scale experimental tests will be performed on a part of the structure, and the present paper presents the preliminary studies for the design of the tests. By simulating the total loss of the impacted column, the experiments enable investigation of the redundancy of the 3D slab system in terms of activation of membrane effects. Another important structural resource is the redundancy of the global structure through ductile joint design; this is a further major issue investigated by the project

Robustness of steel-concrete flooring systems - An experimental assessment

Recently, the interest in the mitigation of the damages caused by accidental events increased significantly. The knowledge of loads transfer mechanisms from the damaged to the undamaged part of the structure is the key for developing adequate design strategies. Despite the potential important role of flooring systems, research of this subject is still limited. A European Research Project aims at achieving an insight into the case of steel-concrete composite frames with solid concrete slabs. Two geometrically different 3D composite sub-frames are subjected to the loss of an internal column. The sub-frames are a full-scale portion of 5 stories 3D frames. Equivalence between the sub-frames and the full-frames required a series of careful numerical analysis, which enabled definition of the boundary restraints of the specimens and of the loading sequence in the test. The present paper illustrates these preparatory studies and gives some preliminary information about the outcomes of the first test. Robustheit von Verbunddecken – Eine experimentelle Bewertung. In den letzten Jahren ist das Interesse an der Begrenzung von durch Unfälle bedingten Schäden gewachsen. Die Kenntnis der Lastübertragungsmechanismen von den beschädigten zu den unbeschädigten Tragwerksteilen ist der Schlüssel zur Entwicklung geeigneter Bemessungskonzepte. Trotz der wichtigen Erkenntnis über den Einfluss der Deckenwirkung stehen keine ausreichenden Forschungsergebnisse zu dieser Thematik zur Verfügung. In einem europäischen Forschungsprojekt werden Tragsysteme aus Verbundrahmen mit Stahlbetonplatten untersucht. Dabei werden zwei geometrisch unterschiedliche 3D-Versuchsrahmen auf die extreme Annahme eines Stützenausfalls untersucht. Die Versuchsrahmen sind vollmaßstäblich ausgebildet und repräsentieren den unteren Teil des Rahmentragwerks eines fünfstöckigen Gebäudes. Die Auflagerbedingungen und die Belastungssequenzen der Versuchsrahmen wurden durch zahlreiche numerische Untersuchungen ermittelt, um denjenigen des Rahmensystems vom Gebäude zu entsprechen. Der vorliegende Beitrag zeigt diese Vorstudien und berichtet über einige experimentelle Ergebnisse aus dem ersten Versuch

Behaviour and Degenerative Changes in the Basal Forebrain Systems of Aged Rats (12 Months Old) after Levo-Acetyl-Carnitine Treatments

One group of six male control rats [12 months old] and one group of six male rats of the same age, singularly maintained in a cage, and treated with acetyl-L-carnitine-HCl [(gamma-trimethyl-beta-acetyl-butyrobetaine-HCl: Sigma-Tau code ST200 or ALCAR: 60 mg/kg/day[7]/po)] for six months were tested in the spatial learning/memory Morris mazewater task and for atrophy and cell loss in seven myelo- and cytostructurally defined basal forebrain (BF) cholinergic regions [Freddi et al., 2009]. Coronal sections 25 ?m thick were cut through the BF regions and processed every 200 ?m for choline acetyltransferase (ChAT) immunohistochemistry. The ALCAR-treated rats had significantly shorter exit times on the Morris maze-water task test than the control rats (average \ub1 SD 28.3 \ub1 12.4 s vs. 61.16 \ub1 4.67 s; t = 6.07, DOF = 10, P = 0.0001). Degenerative morphological changes in the BF ChAT-positive cells were observed in the substantia innominata pars anterior of the control rats but not in the treated animals (P < 0.05). In the BF, the counted and estimated average number of ChAT + cells in the 12-month-old ALCAR-treated rats (ChAT-ALCAR-12+ [Nos. 2,3,4]) was higher but not significantly (15.288 \ub1 3281) than that counted and estimated in the 12-month-old control rats [(ChAT-CT-12 [Nos. 1,2,3]) (11.508 \ub1 3868), t = 1.82, DOF = 10, P = 0.319]. In the substantia innominata pars posterior, the ChAT+ cells were significantly more numerous (P < 0.05) in the 12-month-old ALCAR-treated rats (ChAT-ALCAR-12 + [Nos. 2,3,4]) than in the control rats (ChAT-CT-12 [Nos. 1,2,3]). Above all, these results dem-onstrate that treatment with ALCAR from the age of 6 up to 12 months significantly attenuated spatial learning/memory impairment on the Morris maze-water behavioral task (P < 0.001) and also importantly reduced degeneration in size and number of cholinergic cells in the nucleus basalis magnocellularis of the BF. Accordingly, the surviving cholinergic neurons found in the BF of the ALCAR-treated rats might play an important role in modulating cortical activity and facilitating processes of attention, learning and memory