1,720,971 research outputs found
The comparative role of friction in local out-of-plane mechanisms of masonry buildings. Pushover analysis and experimental investigation
No full textIn masonry buildings without a box-type behaviour and subjected to seismic loadings, in-plane and out-of-plane failure mechanisms can take place where frictional resistances might play a predominant role. In this paper a detailed limit analysis of a simple out-of-plane failure mechanism is developed according to static force-based and displacement-based approaches. The main goal is to point out the great importance of the stabilising role of friction between interlocked walls compared to other extrinsic or intrinsic loading capacities, e.g. the effect of tie-rods and simply supported horizontal diaphragms with frictional resistance. The sensitivity of the load multiplier to these strength parameters is investigated both at the onset of the rocking mechanism and after the hinge formation and a parametric analysis is carried out for the first condition. The results are obtained with reference to different combinations of loading conditions, including the detrimental effect of the static thrust of masonry vaults.
Comparative results and pushover curves are developed to evaluate the loading and displacement capacities for each case analyzed and some experimental work is presented to validate the analytical results
Criteria for identifying vulnerability classes for rocking masonry church façades via fragility curves
No full textThe activation of out-of-plane (OOP) mechanisms in the façade walls of masonry churches has been frequently observed during seismic events and therefore represents an important source of vulnerability for this kind of structure. Although there is a wealth of literature on the OOP behaviour of masonry elements, there is a lack of specific analytical studies on the OOP behaviour of masonry church façades and, in particular, on the possibility of identify homogeneous vulnerability classes. To fill this gap, this paper is focused on: i) assessing the influence of some geometrical parameters of church façades on their vulnerability to the OOP mechanism of simple rocking, ii) defining reliable criteria for assessing homogeneous vulnerability classes, iii) validating the proposed criteria on a large scale. For these purposes, façades are modelled under free and restraint rocking conditions, being the latter ones represented by their interlocking with the sidewalls and the presence of steel tie rods. A sample of 500 façades is generated thanks to a Monte Carlo simulation, starting from the actual data of the façades of 14 existing masonry churches. Non-linear static analyses are carried out for the rocking response of the façades under different restraint conditions, aimed at verifying the achievement of three limit states: the onset of rocking, a moderate and a severe rocking motion, as conventionally defined according to the indications provided by the Italian seismic code. By investigating the influence of some geometrical parameters for a generic façade on its vulnerability to simple rocking, different criteria for identifying homogeneous classes of seismic vulnerability (high, medium and low) are proposed for each investigated limit state. Finally, by using incremental static analysis, multiple stripe analysis and acceleration-displacement response spectra, fragility curves are developed for each limit state and under different restraint and seismic input conditions in order to validate the proposed criteria on a large scale too
Upgraded formulations for the onset of local mechanisms in multi-storey masonry buildings using limit analysis
No full textUnreinforced stone masonry (URSM) buildings without a box-like behaviour are very vulnerable to out-of-plane failure modes in seismic prone areas. These may involve partial or total collapses of walls with severe civil protection implications in terms of hazard to people, structures, and road network in the surroundings. In this paper, an advanced macro-block model accounting for frictional resistances is used to calculate the onset load factors for two classes of local mechanisms in multi-storey URSM buildings: the rocking-sliding and the flexure mechanisms. Based on the application of the kinematic approach of limit analysis, the presented formulations are an upgrade of the load factors identified within the FaMIVE (Failure Mechanism Identification and Vulnerability Evaluation) procedure existing in the literature and developed by the last author. These take into account a revisited evaluation of the in-plane frictional forces for the rocking-sliding mechanisms and the torsion-shear-flexure interactions for the horizontal flexure mechanisms. Moreover, the position of the hinge along the height of the building is identified more accurately, since it can be found at the story level or between two storeys, depending on the accounted mechanism. Other innovative issues concern upgrades of the former formulations for the vertical and horizontal flexure mechanisms. The final perspective of the presented abacus of local mechanisms in multi-storey URSM buildings is the next implementation of the proposed formulations in the FaMIVE procedure, after a sensitivity analysis of the main physical and geometrical parameters affecting the “hierarchy” among the all possible mechanisms. The identification of the most probable mechanisms, through a comprehensive but at the same time relatively rapid assessment, can be very useful for civil protection purposes
Non-Linear Static and Dynamic Analysis of Rocking Masonry Corners Using Rigid Macro-Block Modelling
Full text linkThe corner failure is one of the most typical local mechanisms in masonry buildings vulnerable to earthquakes. The seismic assessment of this mechanism is poorly studied in the literature and in this paper it is addressed by means of both nonlinear static and dynamic analyses of rocking rigid blocks. The static approach is based on the displacement-based method and is aimed at predicting the onset of the 3D failure mechanism and its evolution through incremental kinematic analysis. This approach also considers the presence of a thrusting roof and the stabilizing contribution of frictional resistances exerted within interlocked walls. The capacity in terms of both forces and displacements is compared with the seismic demand through the construction of acceleration–displacement response spectra, with some originality. The nonlinear dynamic approach is based on the seminal Housner’s work on rocking rigid blocks and considers the influence of transverse walls, roof overloads and outward thrust, all included in an updated equation of one-sided motion. In particular, the process of defining an equivalent prismatic block, representative of the original corner geometry, is presented to convert the 3D dynamic problem into a 2D rocking motion. The wide suitability and advantage of such modeling approaches to assess the seismic response of rocking masonry structures with reference to specific limit states are demonstrated through a real case study, i.e. the collapse of a corner in a masonry school building during the 2016–2017 Central Italy seismic sequence. The compared results provide a good agreement of predictions in terms of both onset and overturning conditions, for which the static model appears to be more conservative than the dynamic one
Literature review of the in-plane behavior of masonry walls: Theoretical vs. experimental results
Full text linkIn-plane strength of masonry walls is affected by the resistant mechanisms activated in the walls, i.e., related to flexural or shear behavior. The latter one can occur in the walls according to different failure modes depending on both mortar and unit strengths and on the type of assembling, i.e., ‘regular’ or ‘irregular’ texture. In this paper, a critical review of the existing design formulations for the in-plane strength of masonry walls is firstly presented, with important information on the achievable failure modes depending on the geometrical and mechanical features of the masonry fabric. Then, experimental tests are collected from the literature and a comparison between theoretical and experimental results is carried out. The presented analyses are aimed to highlight the differences between the existing formulations and to identify the most suitable ones
Analisi Statiche e Dinamiche Incrementali per la Valutazione della Risposta Fuori Piano della Facciata di una Chiesa colpita dal Terremoto Centro Italia 2016-17
No full textQuesto lavoro presenta l’analisi sismica, con diversi approcci, del meccanismo locale di ribaltamento della facciata della chiesa di San Michele Arcangelo a Lisciano (AP), ricadente nella zona colpita dai recenti eventi sismici del Centro Italia 2016-2017. Il meccanismo in esame è quello del ribaltamento semplice con la condizione di vincolo laterale che viene modellato in ambito non lineare attraverso recenti approcci in campo statico e dinamico. Il modello utilizzato per l’approccio statico considera il vincolo laterale come espressione delle resistenze attritive che si sviluppano sulle superfici di contatto dei conci murari lungo l’altezza dei due cantonali della facciata. Tali resistenze si riducono durante l’evoluzione del meccanismo per la perdita di contatto progressivo tra la facciata e le pareti longitudinali e la variazione è di tipo non lineare. Il modello utilizzato per l’approccio dinamico è basato sulla definizione delle rigidezze elastiche che costituiscono vincolo orizzontale per un blocco assimilabile al sistema ad un grado di libertà. Diversi grafici mostrano il confronto tra i risultati delle analisi incrementali statiche e dinamiche condotte attraverso l’utilizzo di accelerogrammi reali e spettri ADRS opportunamente scalati. Tali approcci possono essere utilizzati per valutare la risposta sismica fuori piano di pareti murarie in relazione a determinati stati limite di riferimento, secondo la procedura PERPETUATE
Visual programming for macro-block analysis of multi-storey masonry buildings
No full textThis paper presents a Grasshopper (GH) plugin to evaluate the admissible out-of-plane mechanisms in multi-storey masonry buildings and visually display the possible locations for each admissible mechanism at which the failure can happen. Adopting the macro-block modelling approach, GH components are developed considered a limited number of geometric and construction parameters as inputs that allow the possible mechanisms. These include the quality of the connections between the building walls, applied strengthening devices, and the examined building location within an urban block. Modelling the building, all the potential mechanisms and their possible locations are demonstrated in a user-friendly and readable way. The plugin can finally compute the actual mechanism and its optimised geometry as well as the actual building out-of-plane capacity adopting the limit analysis method
In-plane behaviour of masonry walls: Numerical analysis and design formulations
Full text linkThis paper presents the results of several numerical analyses aimed at investigating the in-plane resistance of masonry walls by means of two modelling approaches: a finite element model (FEM) and a discrete macro-element model (DMEM). Non-linear analyses are developed, in both cases, by changing the mechanical properties of masonry (compressive and tensile strengths, fracture energy in compression and tension, shear strength) and the value of the vertical compression stress applied on the walls. The reliability of both numerical models is firstly checked by means of comparisons with experimental tests available in the literature. The analyses show that the numerical results provided by the two modelling approaches are in good agreement, in terms of both failure loads and modes, while some differences are observed in their load-displacement curves, espe-cially in the non-linear field. Finally, the numerical in-plane resistances are compared with the theoretical formulations provided by the Italian building code for both flexural and shear failure modes and an amendment for the shape factor ‘b’ introduced in the code formulation for squat walls is proposed
Modelling Strategies for the In-plane Behaviour of Iron-framed Masonry Structures: Parametric Analysis on Simple Panels and a Church Façade
No full textAn atypical ‘baraccato’ system made of masonry walls encaged in iron frames was realized in the Ischia Island after the earthquake of 1883; an interesting example is represented by the Santa Maria Maddalena Church. Unfortunately, while several experimental and numerical studies can be found in the recent literature for traditional ‘baraccato’ systems (mixed timber and masonry elements), no information is available for iron-framed masonry structures. To fill this gap, the paper presents several parametric non-linear static analyses with reference to, firstly, simple iron-framed masonry panels and, successively, the façade of the Santa Maria Maddalena Church. All the numerical analyses were carried out by means of two modelling approaches with different levels of detail, i.e. finite element (FE) and discrete macro-element (DME) models. The numerical analyses allowed to: assess the reliability of the two models (FE and DME) into predicting similar results for the panels and the church façade with reference to both the unstrengthened and the iron-framed strengthened configurations; analyse the influence of the investigated parameters; evaluate the contribution of the iron frames on the overall behaviour of the strengthened masonry elements; and drive the choice of the most suitable modelling strategy for the whole church
FRAGILITY CURVES FOR ROCKING MASONRY FAÇADES OF CHURCHES: A SENSITIVITY STUDY OF VULNERABILITY PARAMETERS
No full textOut-of-plane failure of façades is one of the most distinctive local mechanisms in masonry churches recognizable in the aftermath of a seismic event. The purpose of this paper is to de-rive large-scale fragility curves for masonry church façades using incremental static analysis, and to assess the influence of some parameters on their vulnerability. According to the dis-placement-based approach, pushover analysis is carried out considering both the geometric nonlinearities and the stabilizing contribution of frictional resistances exerted by the church sidewalls. The seismic demand is derived using acceleration-displacement response spectra (ADRS) for different limit states, obtained according to the Italian seismic code. The analyses are addressed with reference to a large sample of masonry churches generated starting from the geometric parameters of a reduced sample of churches hit by the seismic event of 21st Au-gust 2017 in the Ischia Island (Italy). Several geometric aleatory variables, i.e. the length, the height and the thickness of the façade, are treated by means of the Monte Carlo simulation (MCS) to generate a numerical sample of 400 facades. Considering two limit states for rock-ing (moderate and severe motion), fragility curves are derived for these facades subjected to the same single ground motion scaled at different values of PGA, using incremental static analysis (ISA) and multiple stripe analysis (MSA). Finally, on the same sample of 400 fa-cades, the sensitivity of the fragility curves to the friction coefficient, the length of masonry units and the position of the façade mass center is investigated
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