1,721,020 research outputs found
Limit analysis of masonry structures: upper bound approach based on homogenization and local mesh refinement
No full textWe present an upper bound limit analysis tool for plane stress problems in masonry. A given masonry construction is discretized into planar rigid-perfectly plastic finite elements, whose kinematics is described by rigid body velocities and plastic strain rates. To properly represent the collapse behaviour of the heterogeneous masonry material, the plastic strain rates must follow the homogenized kinematic conditions derived for running bond masonry textures. For a given load configuration, a rigid-plastic limit analysis problem can be defined and solved to find a mechanism and an associated collapse load. Local mesh refinement is finally applied to optimize the representation of the mechanism and minimize the collapse load
Seismic vulnerability of masonry historical structures: A simple adaptive nurbs FE approach for the limit and the subsequent non-linear static analysis with few dofs
No full textThe present contribution deals with an innovative evaluation of the vulnerability and static seismic behavior of existing masonry structures and monumental buildings. For a given masonry construction, a discretization through few NURBS surfaces is realized. NURBS surfaces are converted into shell elements which are assumed rigid and infinitely resistant. The non-linearities typical of the masonry material (almost no tensile strength, frictional behavior in shear, and relatively larger resistance in compression) are imposed at interfaces between adjacent elements, which represent in this way possible fracture lines. Once defined a horizontal load configuration, an adaptive upper bound limit analysis is applied. As final result, the collapse mechanism and the collapse load multiplier are found. Then, to provide the complete non-linear structural response, a FE model composed of elastic elements representing macro-blocks and non-linear contact-based interfaces or plastic damaging strips corresponding to the cracks is derived. On such model, static non-linear analyses can be performed easily at a fraction of the computational burden needed by standard approaches. Several examples including masonry churches, vaults, and buildings are presented. Finally, a novel limit analysis computational technique based on a discretization through NURBS solid elements is introduced and future perspectives of the research are drawn
Advanced Structural Investigation Through Structural Health Monitoring and Adaptive Limit Analysis: the Case of a Damaged Masonry Arch Bridge in India
No full textIn the following work, a Structural Health Monitoring (SHM) procedure combined with adaptive limit analysis is presented with reference to a damaged masonry arch bridge located near Mumbai (India). SHM is performed by monitoring the crack growth under different load conditions. Vibrating wire displacement transducers have been used for this purpose. Then, an adaptive upper bound limit analysis based on a Non-Uniform Rational B-Spline (NURBS) geometrical model, capable of taking into account the existing cracks, has been followed to investigate the residual load-bearing capacity. The obtained results show that the damaged masonry bridge still presents a margin of safety under traffic loads
Analysis of Gothic Masonry Arches Through a Fully Three-Dimensional Kinematic Limit Analysis Approach
No full textA kinematic limit analysis approach for three-dimensional curved rigid blocks is presented. To maintain the exact geometry of curved structures in a three-dimensional context, NURBS solids are used. Under the hypotheses of rigid elements and frictional behavior at interfaces, a kinematic limit analysis problem is defined and solved through a linear programming formulation. The Gothic arches in the Carmo convent, Lisbon (Portugal), are studied to prove the efficiency of the method
Seismic vulnerability assessment for historical masonry aggregates
No full textIn this contribute, the authors propose a comprehensive limit analysis approach based on consolidated and innovative techniques for the exact identification of local mechanisms in masonry aggregates. On a three-dimensional (3D) model of the whole aggregate both pre-assigned mechanisms (CINE) and adaptive meshes (NURBS) are used. The computation of the horizontal load multiplier is carried out through the application of the Principle of Virtual Powers with a classic upper bound point of view. The analysis results show that, compared with the simple overturning collapse mechanism, the other collapse mechanisms are only activated under specific stress conditions. Some typical walls are selected to have an insight into the possibilities and limitations of the procedure proposed
Three-dimensional adaptive limit analysis of masonry arch bridges interacting with the backfill
No full textIn this paper, the collapse behavior of masonry arch bridges interacting with the backfill is investigated through an adaptive procedure based on the kinematic theorem of limit analysis and a NURBS (Non-Uniform Rational B-Spline) representation of the geometry. The initial model is subdivided into few macro-blocks considered rigid and with dissipation occurring only along element interfaces, in turn represented by planar or curved NURBS surfaces. The properties of the materials are considered using homogenized failure domains and the initial mesh subdivision is then adjusted by means of a Genetic Algorithm. Particular attention is focused on the characterization of the arch-backfill interaction problem. The backfill is here represented first in terms of equivalent vertical and horizontal loads and then by following a direct modeling through NURBS curved macro-blocks. In particular, this latter approach allows to take into account the backfill contribution also in terms of internal dissipation. However, material parameters must be defined with particular attention: the use of a very rough discretization with the assumption of rigid blocks requires the utilization of equivalent ultimate resistance values for backfill-backfill interfaces to correctly estimate the internal dissipation at failure. Meaningful numerical examples dealing with different geometries and considering both load-carrying capacity and foundation settlement problems are reported. Finally, two geometrically complex examples are analysed through a recently presented modeling strategy via NURBS solids
Adaptive NURBS based local failure analyses of retrofitted masonry aggregates
No full textIn this paper, the vulnerability of historical masonry aggregates due to local failures is assessed through a novel kinematic limit analysis that is based on NURBS geometry representation and Genetic Algorithm-mesh adaptation. The mesh adaptation allows finding the shape of the collapse mechanism with good precision. The contribution of the most common reinforcement systems, such as tie rods, is taken into account and the collapse mechanism modifications due to the presence of tie rods are evaluated. A historical masonry aggregate located in the historical center of Arsita (Teramo, Italy) is presented as case study
Automatic assessment of partial failure mechanisms in retrofitted historical masonry aggregates through adaptive nurbs limit analysis
No full textThe aim of this work is to propose a new automatic procedure for the seismic assessment of partial failure mechanisms in historical masonry aggregates. Starting from the geometrical survey, a three-dimensional model of the whole aggregate is derived. The model is discretized through few NURBS surfaces (Non-Uniform Rational Bezier Spline) and imported into the MATLAB environment. A procedure of kinematic limit analysis is applied to a preselected part of the construction. The walls selected are subdivided into few elements, each one is a portion of the initial NURBS surface and is assumed as a rigid body. Rigid-plastic interfaces are defined on the boundary of each element. As a result, the kinematic limit analysis provides a local mechanism involving the selected walls and an associated kinematic multiplier. An optimization procedure, here conducted by using a Genetic Algorithm, is applied with the aim of finding the collapse multiplier. The procedure can take into account the most spread reinforcement techniques adopted in historical constructions, such as tie-rods and FRP strips, which maintain a local response to horizontal loads. An application to a historical masonry aggregate, located in the center of Arsita (Teramo, Italy), is finally presented
Fast Adaptive Limit Analysis of Masonry Arch Bridges in Presence of Differential Settlements of Bridge Piles
No full textIn this work, we present a fast and reliable NURBS-based kinematic approach for the evaluation of the settlements-response of masonry arch bridges. This method is based on a discretization of the arch through NURBS rigid blocks. Here, the use of NURBS (Non-Uniform Rational B-Spline) approximating functions allows composing mesh through very few elements maintaining the exact representation of the three-dimensional curved shape. The main non-linear properties of masonry (almost null tensile strength, high crushing resistance, and frictional behavior in shear) are assigned at interfaces, which represent possible hinges between the curved macro-blocks. Starting from a known displacement applied at the external boundaries, a simple linear programming problem can be written to determine the discontinuous displacement field. Then, a meta-heuristic mesh-adaptation procedure is applied to exclude mesh dependency effects. The initial mesh is adjusted by modifying the shape of macro-blocks until interfaces coincide with the correct position of cracks. The settlement-response is so obtained
ANUB-Aggregates: a fully automatic NURBS-based software for advanced local failure analyses of historical masonry aggregates
No full textMasonry structures constitute the great majority of buildings in historical centers where construction activities were carried out by adding structural portions to pre-existing ones: as a result, masonry aggregates are currently the most common structural typology in such contexts. The structural behavior of masonry aggregates, which are complex systems of different buildings interacting with each other, is generally affected by several factors, such as the different steps of construction, uncertainties about interlocking between walls, presence of different and irregular masonry textures and multi-leaf walls, which make such a structural typology very difficult to study. During recent seismic events in Italy, a wide number of local collapses has been observed in masonry aggregates of historical centers, highlighting the important role of local mechanisms in the seismic assessment of such structures. In this paper, an efficient software called ANUB-Aggregates (Adaptive Nurbs Upper Bound limit analysis for masonry Aggregates) is proposed for the seismic assessment of partial failure mechanisms in historical masonry aggregates. The theoretical core of this program is a kinematic NURBS-based limit analysis with meta-heuristic mesh adaptation. The use of NURBS allows studying aggregates containing vaulted structures, or any other typology of curved elements, without additional computational effort. Moreover, the mesh adaptation scheme assures the representation of the correct collapse mechanism by finding the real position of fracture lines. Starting from the three-dimensional model of the whole aggregate, the code ANUB-Aggregates provides the analysis of more macro-elements interacting with each other with different interlocking hypotheses, evaluating both simple and complex failure mechanisms. As proof of the effectiveness of this applicative, the analysis of two historical masonry aggregates is presented
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