1,721,032 research outputs found
Flexural strength and notch sensitivity in natural building stones: Carrara marble and Dionysos marble.
No full textThe tensile behaviour of marble at failure is analysed. A series of monotonic and cyclic bending tests were carried out in the laboratory on geometrically similar specimens of different size. The strain distribution was monitored with strain gauges and laser interferometry techniques. Three and four point bending configuration were considered. It is shown that cyclic loads in a three point bending configuration induce permanent tensile deformation
Numerical Analysis of Mechanical Damage in Ribbed Masonry Vaults under Differential Settlements
No full textThe present study takes advantage of a parametric model, which allows one to create automatically complex structural models of ribbed masonry vaults. Two numerical modelling strategies are discussed: a 3D continuum and a 3D contact-based model. The effects of settlements are studied by imposing vertical displacement at the vault supports up to collapse. Predictions of each modelling strategy are compared with actual damage observation. A representative square vault of Milan Cathedral is studied here, aiming to understand the causes of the damage documented through the years. The structure is noted to have suffered structural damage in the vaulting system due to a long history of soil settlements. The geometry is based on a photogrammetric scanning, and the three-dimensional solid models are created through parametric reconstruction procedures, including details such as springing, arch, ribs, web, and rubble-fill. Both modelling strategies allow to highlight the vulnerability of masonry vaults due to settlements. Significant differences in prediction capabilities are noted when large displacements and separation of elements are involved. The simulations show the possibility of predicting and interpreting different complex damage phenomena as arch block damage or sliding, and web–arch detachment, which is frequently observed in historical structures
Automated Mapping of the roof damage in historic buildings in seismic areas with UAV photogrammetry
No full textThe paper presents a fast methodology to quantify the damage to the roof in historic buildings, suggested soon after a light seismic event occurs, in order to evaluate the necessity of provisional interventions to prevent further damages. The survey is based on UAV photogrammetry, a well-known technique that allows inspection and digital documentation even in hardly accessible or dangerous areas. The research aims to analyze the feasibility of the automated mapping of roof damage using an image classification procedure based on supervised machine learning. The procedure is summed up in an efficient workflow, where UAV photogrammetry is combined with other 3D survey techniques, such as terrestrial photogrammetry and laser scanning, to provide comprehensive documentation and quantitative data on a historical building. The methodology was validated on a large historical building, now suffering from a serious state of neglect, which roof was never surveyed before and with different damage types. The output orthoimage of the tiled roof allowed us to understand the past interventions and the current serious damage state with promising outcomes regarding the speed of the survey method
Marble behaviour under monotonic and cyclic loading in tension
No full textThe tensile behaviour of marble at failure is analysed. A series of monotonic and cyclic bending tests were carried out in the laboratory on geometrically similar specimens of different size. The strain distribution was monitored with strain gauges and laser interferometry techniques. Three and four point bending configuration were considered. It is shown that cyclic loads in a three point bending configuration induce permanent tensile deformation
Vulnerability analysis of the historical buildings in seismic area by a multilevel approach
No full textAn investigation procedure is proposed by the authors to study the vulnerability of the diffuse historic building patrimony in seismic area previously considered as minor, but meaningful testimonies of cultural heritage. The research suggests a "minimal" investigation program, which can support the designers in their projects. The knowledge of existing buildings is approached by considering different analysis levels: history, materials, structural morphology of the wall section, observed damage mechanisms, effectiveness of retrofitting techniques. The methodology, calibrated on four historic centres situated in Umbria (Italy), allowed to define an abacus of the typical collapse mechanisms. This procedure is useful to define the seismic vulnerability also for other similar centres and to critically evaluate the past and future repair techniques
Crack patterns in double-wall industrial masonry chimneys: Possible causes and numerical modelling
No full textThe origin of crack patterns in industrial masonry chimneys is investigated. This information is of utmost importance in defining any preservation project, and designing suitable repair interventions. Attention is focused on a 66 m-tall chimney built at the end of the XIX century, which is representative of numerous coeval chimneys of similar geometry. The base and the shaft of the chimney are double-walled: vertical ribs and horizontal diaphragms partially connect the walls of the shaft; the crown is single-walled. Vertical cracks can be observed in the lower part, horizontal cracks in the upper part, and zig-zag cracks in the central part. The structural behaviour of the chimney was investigated by means of finite elements, under gravity loads and thermal variations. Most of the cracks can be explained by thermal effects, if the anisotropic strength of masonry is duly accounted for. Therefore, new cracking phenomena can be excluded, and suitable repair interventions may allow an adequate level of safety to be attained
Identificazione di anomalie nella stratigrafia di intonaci storici mediante termografia IR
No full textThe authors present the results of infrared (IR) thermography tests carried out on a masonry specimen representative of an historic building with lime-based plaster, which presents artificial anomalies, e.g., lack of adhesion among the layers of plaster and inclusions of various materials. The procedures here applied show the conditions for observing possible defects on a building element with such as non-invasive technique. It provides a fundamental support to the development of an in-depth knowledge of historical structures and allows setting
the necessary interventions to ensure a constant care to the built heritage
Structural assessment of iron tie rods based on numerical modelling and experimental observations in Milan Cathedral
No full textIron ties contribute to the stability of structural systems having vaults and arches. The axial force in the iron ties is not easily to be measured but this knowledge is important for assessing the safety of these members. In the case of breakage of iron tie rods, the assessment study needs to understand the causes of the failures. Experimental data are collected, and models are used for their interpretation. The aim of this paper is to propose a new integrated experimental and numerical approach for the structural analysis of tie rod tensions in historical buildings. The study considers an application at Milan Cathedral, where recently some iron tie failures were observed. The collected data taken into account are: (a) Point cloud measurement of the geometry (b) Understanding of construction phases, (c) Soil-settlement measurement in the last 50 years, (d) Experimental measurement of the iron ties axial force, and (e) Documentation of damage and iron tie failures in the last century. It is here proposed to use an advanced numerical model for simulating, interpreting and predicting the measured response of the iron ties. The finite element numerical model includes detailed geometry of elements, material properties of masonry based on texture observations and iron ties modelling. The paper shows how the actual structural configuration, the choices on material properties, the consideration of construction stages or load history and soil settlements affect the tension state in the iron ties. In particular, it is demonstrated through the carried-out analysis the possibility to correlate the tension force in the ties with soil settlements. Finally, the developed numerical model can be used also during practical maintenance operations of iron tie replacement, by predicting the stressed state, the possible lateral displacements of the pier and the associated structural safety
Seismic vulnerability methods for masonry buildings in historical centres: validation and application for prediction analyses and intervention proposals
No full textA valid approach for the limit analysis of existing masonry buildings in seismic areas concerns the application of single or combined kinematics models involving the equilibrium of structural macro-elements. They can be more reliable in describing the real structural behaviour than common equivalent static procedures, based on the “box” behaviour of the structure and on the elasto-plastic behaviour of the masonry. The main results of the application of different procedures for the static analysis of masonry buildings in seismic area are discussed in the paper. Urban centres suffering different levels of damage and different typologies of buildings are compared
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