1,721,047 research outputs found
The Rolling Shear Influence on the Out-of-Plane Behavior of CLT Panels: A Comparative Analysis
No full textEffect of panel zone on non-linear behaviour of mrfs in the light of seismic codes
No full textThis paper deals with a critical analysis of the current seismic design criteria provided by Eurocode 8 for Moment Resisting Frames. This approach is based on the capacity design principle, in which the design is governed by the strength and stability of the structural elements and by hierarchy ofstrength, this in order to allows development of high dissipative collapse mechanism. The drawbacks of this approach is that the maximum required inter-storey drifts, at service limit states, are not directly satisfied. This leads to an enlargement of geometrical dimensions of the elements, producing significant over-strength and nullifying the use of high behaviour factors. In this paper, an alternative design criterion is proposed. According to this the design is governed by maximum inter-storey drift at service limit state, whereas the satisfaction of capacity design rules is contextually verified. This means to design the structure with seismic actions corresponding toservice earthquakes (i.e. unitary q-factor). Linear and non-linear static analyses on 3, 6 and 9-storey steel frames were performed to compare the design methodologies in terms of push-over curves (i.e.over-strength), interstorey- drifts and collapse mechanisms. Furthermore, the effect of panel zone on the global seismic response of frames was taken into accountin the performed analyses. It has been properly modelled using one of the most diffused literature model, the so called Krawinkler's 'frame model', accounting both its elastic and plastic behaviour
Feasibility of Timber Pegged Joints for Seismic Design of Structures
No full textThis paper investigates the feasibility of employing timber pegged joints in modern seismic-resistant structures or for retrofitting existing structures. The behavior of timber pegged connections has been investigated for about twenty years, but seismic design aspects are not treated in existing standards. In the framework of the force-based design approach, this paper analyzes and defines seismic design aspects and rules for timber pegged connections that are easy-to-use in engineering practice. A large database (more than 350 test results) has been elaborated and the data processed with the purpose of (1) analyzing the effectiveness of the European Yield Model for evaluating the maximum strength of the connection, accounting for the particular embedding behavior due to the presence of timber peg; (2) assessing and defining the capacity design rules to design the dissipative regions (i.e., overstrength factor); and (3) defining the available ductility of the connection with identification of ductility class intervals. The obtained results proved that timber pegged joints have a good potential to be used in seismic-resistant structures. In fact, data processing identified a suitable value for the overstrength factor (useful to project the joint with the capacity design) similar to that used for steel-dowelled connections, and defined a likelihood range of ductility classes. Finally, it is highlighted that the European Yield Model can be a practical tool to calculate connection strength, provided that some modifications are included to consider peg behavior
Minimum energy approach for the in-plane shear resistance of masonry panels
No full textGran parte del patrimonio edilizio esistente in zona sismica, soprattutto nei paesi in via di sviluppo, è costituito da edifici in muratura, largamente diffusi anche in tutti i centri storici europei. I collassi e i danni rilevati a seguito di eventi sismici hanno evidenziato la necessità di interventi e soprattutto di tecniche di analisi idonee. In un edificio in muratura ben progettato e realizzato, ove i meccanismi di collasso per azioni fuori piano possono essere esclusi, il comportamento nel piano delle pareti in muratura diventa un aspetto chiave da esaminare nelle valutazioni di vulnerabilità sismica. Partendo da quest'ultima considerazione, questo lavoro presenta un approccio per la l'analisi del comportamento nel piano di pareti murarie sottoposte a compressione e taglio. La procedura utilizzata considera la muratura come un materiale elastico non resistente a trazione, definisce pertanto una sagoma reagente contenuta nell'ambito del pannello murario soggetta a soli sforzi di compressione e risolve una procedura numerica la cui soluzione corrisponde al minimo dell'energia potenziale per il pannello. Vengono presentati confronti fra i risultati numerici e alcune prove sperimentali presenti in letteratura per diverse geometrie di pannello.Great part of the existing buildings in seismic areas and in particular in developing countries is represented by masonry buildings, diffused also in the major part of historical centres in Europe. Damages due to seismic events have evidenced the large demand of rehabilitation together with suitable assessment methods for these structures. When out of plane mechanism can be avoided, the contribution of in-plane shear resistance of the masonry walls is a key aspect to consider in the vulnerability analysis of the whole structure. Based on this last consideration, this paper presents an approach to the analysis of in-plane behaviour of masonry walls, involving a minimum energy strategy. The results of the numerical analyses presented are compared with those obtained by laboratory tests on brick masonry panels
Mechanical Modelling for Simplified Seismic Analysis of Existing RC Churches and Fragility Curves
No full textThis paper proposes an efficient model for estimating the seismic performance of reinforced concrete (RC) churches and for developing typological fragility curves using a mechanical approach. The study focuses on evaluating the vulnerability of RC church buildings in Naples, using a sample of seven churches with the “Sacri Cuori di Gesù e Maria” Church as the primary case study. This church has been then analyzed in the non-linear filed by means of the software SAP2000. The influence of different modelling hypotheses, e.g., roof’s inclined, absence of box-type behavior, has been evaluated. A simplified model based on elastic analysis and limit analysis has been implemented to solve the 2D static scheme and to evaluate the seismic performance of the churches for different code-based Limit States. As a result, an efficient generation of bilinear capacity for the detailed study of a single church is available; it is also useful for the generation of fragility curves. Validation against non-linear SAP2000 results showed that while detailed models offer comprehensive insights, the proposed simplified model effectively captures the essential behavior of the structures and provides reliable seismic vulnerability assessments. The computed fragility curves indicate that the seismic performance of this building’ class is medium to high, emphasizing the need of extended analysis aimed at the definition of proper interventions to increase the level of seismic safety. Therefore, the proposed model proves to be a practical tool for large-scale seismic vulnerability evaluations and the rational deployment of risk mitigation resources
Seismic Fragility Assessment of Inner Peripheries of Italy through Digital Crowd-Sourcing Technologies
No full textThe structural and seismic fragility assessment of minor historical centers of the Inner Peripheries of Italy is a key phase of the preservation process of the historical and cultural features of a portion of the Italian building stock, whose reuse is crucial for the reversal of shrinking trends and the stimulation of population growth. In this framework, the opportunities offered by digital crowd-sourcing technologies with respect to performing probabilistic structural safety assessment at a large scale are investigated herein. The objective of this research was to exploit data and information available on the web such that the key building features of an area of interest are collected through virtual inspections, historical databases, maps, urban plans, etc. Thus, homogeneous clusters of buildings identified in the area of interest are catalogued and associated with specific building classes (chosen among those available in the literature), and the buildings’ levels of seismic fragility are determined through the development of fragility curves. The research outcomes show that the proposed approach provides a satisfactory initial screening of the seismic fragility level of an area, thus allowing for the identification of priority zones that require further investigations or structural interventions to mitigate seismic risk
Structural behaviour of stop-splayed scarf joint reinforced with timber pegs
No full textIn restoring ancient timber structures, employing traditional connections would be advisable with the aim of minimal modification of the overall structural behaviour. Moreover, instead of steel connectors or adhesive resins and rods, commonly used in interventions, employing timber pegs can be an efficient solution. Nevertheless, the lack of design rules for traditional timber joints or for timber pegged connections in European codes doesn't encourage this more conservative approach. In this study, stop-splayed scarf joints behaviour before and after reinforcement with steel pins or timber pegs is experimentally investigated, in order to understand the role of the fastener inside this carpentry joint and check the reliability of existing design methods. The experimental program has two steps: in the first one, three samples of fir scarf joints without fasteners, with timber pegs and with steel pins have been tested, trying to define the forces distribution among the different resisting elements. In the second phase, two samples of simple shear plane joints, made with the same timber and fastened with both timber pegs and steel pins have been tested to improve the analysis of fastener role in reinforced scarf joint behaviour
Seismic vulnerability assessment of minor Italian urban centres: development of urban fragility curves
No full textThis paper presents a novel hybrid-based methodology devoted to develop urban fragility curves and damage probability matrices to predict likelihood seismic damage scenarios for small and medium Italian urban centres, considering URM buildings only. The concept of urban fragility curve consists of a single curve mean-representative of the seismic fragility of an entire area accounting for the combinations of building classes and their percentage, then they differ from those typological. The methodology has been developed with reference to Rocca di Mezzo, a small Italian urban centre located in the central Apennine area, Italy. Based on CarTiS inventory, building classes have been firstly recognized and urban fragility curves, representative for damage scenarios at Ultimate Limit State, developed. To predict damage scenarios from low to high-intensity earthquakes, an approach to define multi-damage urban fragility curves and damage probability matrices has been also presented. To this aim, a damage scale suffered by building classes has been defined by converting the final outcomes of the AeDES form (used in Italy for post-earthquake surveys) in the damage levels provided by the European Macroseismic Scale (EMS98). Data coming from urban fragility curves have been compared with the actual damage scenario recorded in Rocca di Mezzo after the 2009 L’Aquila’s earthquake, in terms of both peak-ground acceleration and Mecalli-Cancani-Sieberg scale. The achieved results showed a good accordance between theoretical predictions and actual damage scenarios, coherent also with the damage scenarios occurred in other Italian historical centres hit by severe earthquakes over the years. Thus, the methodology can provide a first important indicator to support the development of emergently plans devoted to identify priority of interventions in such areas particularly vulnerable with respect to others
Open issues on non-linear modelling for seismic assessment of existing masonry buildings
No full textThe difficulties on the assessment of the seismic capacity of existing masonry buildings through non-linear FEM analyses have been examined in this paper, in the framework of the equivalent frame modeling. A significant problem lies in identifying an adequate equivalent frame idealization of the walls, i.e., capable of providing an acceptable response of the numerical model. Indeed, the geometrical complexity characterizing real masonry buildings, often due to irregular distribution of the wall openings, leads to choices and expedients which are impossible to codify and may only be defined on a case-by-case basis. Consequently, an adequate engineering judgment, which must obviously be considered when the results are being interpreted, is required. Linear and non-linear analysis were adopted on equivalent frame schemes of existing walls highlighting the problems of identifying geometric patterns, as well as defining the mechanical model of the spandrels or the influence of connection degree between orthogonal walls on the seismic behavior. In this paper some possible solutions to the problems are proposed, also with reference to specific study cases
Role of timber pegs in reinforcing stop-splayed scarf joints
No full textThe effectiveness of an all-timber solution, based on the uses of timber pegs, to reinforce stop-splayed scarf joints with transverse key has been investigated in this paper. An experimental program on unreinforced and timber pegged reinforced scarf joints subjected to tensile loadings has been carried out. Two timber pegs made with ash, and having a diameter equal to 20 mm, have been used as fasteners to reinforce the scarf joints. The experimental outcomes have been analysed and critically discussed, focusing on the role of timber pegs in reinforcing scarf joints. Three fundamental aspects have been investigated: load-bearing capacity, ductility and influence of slenderness ratio (between thickness of members and diameter of the peg) due to the introduction of timber pegs. Test results showed that timber pegs provide adequate robustness to the connections because they modified both force-displacement constitutive behavior (increasing load-bearing capacity, stiffness and ductility) and failure mechanisms from brittle to ductile. It has been also proved that greatest slenderness ratios are effective in enhancing the ductility of the connections; thus, at the same thickness of members, pegs with reduced diameters could be preferred in reinforcing scarf joints. From testing, important findings on the qualitative behavior of scarf joints reinforced by timber pegs are emerged, but the reduced number of specimens did not allow conclusive considerations and future investigations will be necessary to support the obtained results
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