1,721,235 research outputs found
IP-OOP interaction in URM infilled frame structures: A new macro-modelling proposal
No full textReinforced concrete frame structures with unreinforced masonry (URM) infills represent a common construction practice all over the world. To correctly assess the seismic performance of these structures, prediction of the behaviour of masonry infills under in-plane (IP) and out-of-plane (OOP) loading, as well as their interaction, is of primary importance. Different approaches are available in the literature with different levels of approximation for assessment of the IP-OOP infill response, showing increasing interest in this field. In this context, this paper presents a new macro-element model which can simulate the behaviour of URM infill walls under seismic IP and OOP actions. The model is the evolution of an approach based on a 4-strut configuration characterized by one horizontal strut, one vertical strut and two diagonal struts representing the infill wall. The struts are modelled by fibre-section beam-column elements and their compressive behaviour is defined by empirical strength and strain parameters. The paper also presents some equations to obtain the empirical parameters mentioned, based on the actual mechanical properties of infill walls. In the paper, the validation of the proposed model with the experimental results available in the literature is discussed. Further, the improved capacity to simulate the arching mechanism in infill walls under OOP loads and the better reliability in capturing the interaction between the IP and OOP behaviours are described
Masonry structures: A proposal of analytical generation of fragility functions for tsunami impact – Application to the Mediterranean coasts
No full textEvaluation of tsunami vulnerability of coastal buildings is gaining high interest in recent years in the areas with high tsunami hazard. Fragility evaluation is a fundamental step to obtain a quantitative estimation of the probability of building damage and in order to define possible strategies for risk mitigation. Several empirical fragility curves are available for masonry structures. However, an empirical fragility curve is generally based on field surveys after tsunami events, not always available. Conversely, analytical fragility curves are based on prediction approaches. In this paper, a proposal for the evaluation of analytical fragility curves for masonry structures typical of the Mediterranean coasts based on simplified structural analyses and damage indexes is presented. The proposal considers the uncertainties in both the structural demand and capacity probabilistically. Several Monte Carlo simulations on some masonry structure types have been carried out to evaluate the fragility related to each fixed damage state assuming the inundation depth as intensity measure. Finally, the validity of the results is discussed by comparisons with empirical fragility curves available in the literature
Variable Friction Dampers (VFD) for a modulated mitigation of the seismic response of framed structures: Characteristics and design criteria
No full textIn this paper a new approach for the energy dissipation is discussed based on the use of Variable Friction Dampers (VFDs). The VFD device is borrowed from braking systems mechanical engineering, able to modulate its capability of dissipation, providing a constant pure friction force coupled with an additional (variable) damping force with the increasing of the displacement. Resorting to a previous study, the characteristics and the efficiency of the “braking” system in terms of reduction of the displacements and the restoring forces is described for SDOF systems under seismic excitations and compared with the performances achievable by classic constant friction dampers (CFDs). Then, a design criterium based on structure stiffness, viscous damping and seismic demand is proposed evaluating its effectiveness through a statistical assessment of the dynamic response of SDOF models subjected to natural accelerograms. The results obtained by the proposed design approach have proven that is a robust approach and indicate that the device can be really considered suitable for the improvement of the energy dissipation and the reduction of the drift in framed structures in an extended range of the seismic demands (from low to high) differently from the classic friction devices whose characteristics make them effective in a smaller range of the seismic intensities
Cyclic response of masonry infilled RC frames: Experimental results and simplified modeling
No full textThe recent large interest in nonlinear seismic analysis methods, static and dynamic, has required proper
strategies of modeling based on reliable, and at the same time easy to use, constitutive laws for the
structural elements. Regarding the behavior of framed structures, special attention has to be devoted to
infills because of the key role they play in modifying overall stiffness, strength and ductility under
seismic excitation. Pointing out the attention on this topic the paper discusses a criteria for modeling the
structural behavior of infills based on a macromodeling approach, that is to say on the substitution of
infills with diagonal pin jointed struts. Is here shown how multilinear plastic link elements governed
by a hysteretic Pivot model, available in different FEM codes, can be appropriately used to model the
equivalent struts to perform linear or nonlinear analyses. In order to enlarge experimental knowledge on
cyclic behavior of infilled frames structures and as reference for developing the above mentioned
modeling strategy, an experimental campaign on single-storey, single-bay, fully infilled frames with different
kinds of masonry and subjected to lateral cyclical loads, was carried out, and some others available in the
literature are referred to. Validation of Pivot modeling approach was carried out comparing experimental
results and computer simulations of the experimental tests. In the paper hysteresis parameters values
calibrating Pivot law are also given for involved masonry infills typologies and some proposals for correlation
between strength and stiffness of infilled frames and of masonry infills are provided as a tool for the quick
calibration of the Pivot model in practical applications
Prediction of the additional shear action on frame members due to infills
No full textInfill masonry walls in framed structures make a significant contribution to the response under seismic actions. With special regard to reinforced concrete (RC) structures, it is known that internal forces modifications caused by the frame-infill interaction may be not supported by the surrounding frame because of the additional shear forces arising at the ends of beams and columns. Such additional forces may lead to the activation of brittle collapse mechanisms and hence their prediction is basic in capacity assessment, especially for structures that disregard the details for seismic zones. In this paper a parametric study is carried out addressed to the prediction of the shear forces mentioned before. The results of this study can be used as a support when the simplified model is adopted consisting in the substitution of infill with an equivalent pin jointed concentric strut, because in this case the structural analysis fails in the prediction of the shear forces in question. Through the paper, in which existing RC infilled frames designed only for vertical loads are discussed, analytical laws, depending on the level of the axial force arising in a concentric strut equivalent to infill, are proposed, the above analytical law allowing to correct the local shear forces in the frame critical sections, which are not predictable in the case of substitution of infill with an equivalent concentric strut
Out-of-Plane Behavior of URM Infill: Accuracy of Available Capacity Models
No full textThe aim of this paper is to check the accuracy of analytical capacity models available for the prediction of out-of-plane strength of unreinforced masonry (URM) infill walls. The accuracy of the available models is checked by detailed comparison with the existing experimental results. In doing so, both types of capacity models are evaluated: Type I for the prediction of the strength in the undamaged state, and Type II for the prediction of strength reduction in the in-plane damaged state. Results from the calculations are discussed, and the best among the available models are recommended. Furthermore, the influence of orthotropy of the infill masonry in the out-of-plane capacity predicted by the models is discussed. The paper also highlights the prospect of using the capacity models in the cases of infill-beam gap and infill with openings. In the paper, the best pairs of models (composed by a model for the prediction of the out-of-plane strength in the undamaged state and a model for the prediction of the reduction of the out-of-plane strength in the damaged state, not necessarily provided by the same author) for URM infill walls, are suggested for the first time
Cyclic response of masonry infilled RC frames: Experimental results and simplified modeling
No full textThe recentlargeinterestinnonlinearseismicanalysismethods,staticanddynamic,hasrequiredproper
strategiesofmodelingbasedonreliable,andatthesametimeeasytouse,constitutivelawsforthe
structural elements.Regardingthebehaviorofframedstructures,specialattentionhastobedevotedto
infills becauseofthekeyroletheyplayinmodifyingoverallstiffness,strengthandductilityunder
seismic excitation.Pointingouttheattentiononthistopicthepaperdiscussesacriteriaformodelingthe
structural behaviorofinfills basedonamacromodelingapproach,thatistosayonthesubstitutionof
infills withdiagonalpinjointedstruts.Ishereshownhowmultilinearplasticlinkelementsgoverned
by ahystereticPivotmodel,availableindifferentFEMcodes,canbeappropriatelyusedtomodelthe
equivalentstrutstoperformlinearornonlinearanalyses.Inordertoenlargeexperimentalknowledgeon
cyclicbehaviorofinfilled framesstructuresandasreferencefordevelopingtheabovementioned
modelingstrategy,anexperimentalcampaignonsingle-storey,single-bay,fullyinfilledframeswithdifferent
kindsofmasonryandsubjectedtolateralcyclicalloads,wascarriedout,andsomeothersavailableinthe
literaturearereferredto.ValidationofPivotmodeling approachwascarriedoutcomparingexperimental
resultsandcomputersimulationsoftheexperimentaltests.Inthepaperhysteresisparametersvalues
calibratingPivotlawarealsogivenforinvolvedmasonryinfills typologiesandsomeproposalsforcorrelation
betweenstrengthandstiffnessofinfilledframesandofmasonryinfillsareprovidedasatoolforthequick
calibrationofthePivotmodelinpracticalapplications
Analysis of local shear effects in brick masonry infilled RC frames
Full text linkMasonry infills panels placed among framed structures meshes have a relevant influence in presence seismic actions in terms of strength stiffness and global displacement capacity. In the case of RC structures, the modifications of internal forces due to infill-frame interaction may be not compatible with surrounding frame members strength especially considering additional shear forces arising at the ends of beams and columns in contact with the panel under lateral actions. Such effects may be in many cases the cause of unexpected brittle collapse mechanisms which compromise the safety of the entire structure. In this paper by means of a double (micromodeling and macromodeling) procedure regarding RC meshes infilled with hollow brick masonry, a parametric study is provided defining a connection between local shear forces in critical frame regions and axial force on diagonal pin jointed strut. Proposed strategy allows to predict effective local shear forces using the simple macromodeling approach to reproduce the effect of masonry infills in models
Strutture intelaiate in c.a. con tamponamenti: Analisi degli effetti locali in presenza di azioni sismiche
Full text linkLa presenza di tamponamenti in muratura all’interno delle maglie di strutture intelaiate induce, in presenza di
azioni laterali, una sostanziale modificazione della risposta globale rispetto a quella dei telai nudi in termini di
rigidezza, resistenza e capacità di spostamento. Per le strutture in c.a. la variazione del regime di sollecitazione che
si osserva sulle membrature che circoscrivono i tamponamenti può rivelarsi non compatibile con la resistenza di cui
queste sono dotate. In particolare, l’insorgere di sforzi di taglio aggiuntivi alle estremità di pilastri, travi e,
conseguentemente, nei nodi può eccedere le capacità resistenti di queste regioni, stimate in fase di progetto,
causando meccanismi locali di rottura fragile. Attraverso una procedura di modellazione duplice
(micromodellazione e macromodellazione) di maglie tamponate campione in c.a., viene proposto uno studio
parametrico utile a definire uno strumento che, qualora si utilizzino modellazioni a puntone diagonale equivalente
concentrico, consente di legare le sollecitazioni di taglio effettive nelle zone di contatto fra tamponamento e telaio
al livello di sforzo normale assorbito dal puntone. Il criterio proposto consente quindi di adottare la modellazione
più semplice per i tamponamenti, acquisendo comunque informazioni sugli effetti locali da essi prodott
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