| 1. |
- Bouckaert, Igor, et al.
(författare)
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A Hybrid Discrete-Finite Element method for continuous and discontinuous beam-like members including nonlinear geometric and material effects
- 2024
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Ingår i: International Journal of Solids and Structures. - 0020-7683 .- 1879-2146. ; 294
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- This paper introduces a novel formulation, called Hybrid Discrete-Finite Element (HybriDFEM) method, for modeling one-directional continuous and discontinuous planar beam-like members, including nonlinear geometric and material effects. In this method, the structure is modeled as a series of distinct rigid blocks, connected to each other through contact pairs distributed along the interfaces. Each of those contact pairs are composed of two nonlinear multidirectional springs in series, which can represent either the deformation of the blocks themselves, or the deformation of their interface. Unlike the Applied Element Method, in which contact pairs are composed of one single spring, the current approach allows capturing phenomena such as sectional deformations or relative deformations between two blocks composed of different materials. This method shares similarities with the Discrete Element Methods in its ability to model contact interfaces between rigid or deformable units, but does not require a numerical time-domain integration scheme. More importantly, its formulation resembles that of the classical Finite Elements Method, allowing one to easily couple the latter with HybriDFEM. Following the presentation of its formulation, the method is benchmarked against analytical solutions selected from the literature, ranging from the linear-elastic response of a cantilever beam to the buckling and rocking response of continuous flexible columns, and rigid block stackings. One final example showcases the coupling of a HybriDFEM element with a linear beam finite element.
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| 2. |
- Bouckaert, Igor, et al.
(författare)
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A strategy for generating pushover curves of block assemblies including post-peak branch using the discrete element method
- 2022
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Ingår i: Proceedings of 3rd EUROPEAN CONFERENCE ON EARTHQUAKE ENGINEERING & SEISMOLOGY.. ; , s. 839-
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Konferensbidrag (refereegranskat)abstract
- Pushover analyses are often used to evaluate the seismic performance of a structure. They give an estimate of the ultimate displacement a structure can undergo, as well as of the residual resisting forces in the post-peak response. When modelling masonry structures composed of multiple blocks, obtaining the post-peak branch of the pushover curve can be difficult with a classic displacement-control strategy. This paper describes a strategy designed to compute this branch for multi-block systems subjected to a given pattern of forces, without the need to apply a displacement-control algorithm. The strategy is general, therefore straightforwardly implementable in different software tools and applicable to complex block assemblies. In the present work, it is implemented in two different DEM software, namely LMCG90 and UDEC, and tested on a benchmark problem for evaluating the in-plane response of masonry walls.
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| 3. |
- Bouckaert, Igor, et al.
(författare)
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Assessment of the in-plane capacity of masonry walls with the Hybrid Discrete-Finite Element Method
- 2024
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Ingår i: ASSESSMENT OF THE IN-PLANE CAPACITY OF MASONRY WALLS WITH THE HYBRID DISCRETE-FINITE ELEMENT METHOD.
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Konferensbidrag (refereegranskat)abstract
- The most widespread numerical simulation method for structural response is undoubtedly the Finite Element Method (FEM). However, despite being powerful for modelling continuous structures, it is not fit for handling strong discontinuities. The Discrete Element Method (DEM) simulates interactions between rigid or deformable elements in contact, hence explicitly capturing the discontinuous nature of the structural response, particularly when subjected to extreme loadings. Nevertheless, it requires a time-stepping algorithm even for solving static or buckling problems. The Hybrid Discrete-Finite Element Method, shortly HybriDFEM, was recently introduced in the context of modelling one-dimensional beam-like members. Those members are divided along their longitudinal axis in a series of rectangular rigid blocks, and the deformation is concentrated at the interfaces between adjacent blocks, modelled as distributed nonlinear multidirectional springs. The method, developed within a FEM-like setting, allows for hybridisation with other finite elements (e.g., beam elements). Next to its ability to explicitly model pre-existing discontinuities along the member (e.g. masonry stereotomy), the method can be used for modelling continuous members with satisfactory accuracy by appropriately scaling the interface springs. As such, the HybriDFEM’s formulation can accommodate hybrid discrete-continuous systems. In this paper, the HybriDFEM formulation is extended to 2D, with rectangular blocks in contact on all four faces. First, the algorithm to detect blocks in contact will be explained. Second, specific characteristics of the HybriDFEM applied to masonry modelling are presented. Then, the method is benchmarked against a two-dimensional problem from the literature where the in-plane capacity of walls made masonry blocks is investigated.
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| 4. |
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| 5. |
- Bouckaert, Igor, et al.
(författare)
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MODELING OF FRAMES WITH HYBRIDFEM, A PSEUDO-DISCRETE-FINITE MODEL INCLUDING NONLINEAR GEOMETRIC EFFECTS AND NONLINEAR MATERIALS
- 2023
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Konferensbidrag (refereegranskat)abstract
- In this paper, a novel numerical method for strucural analysis, called the Hybrid Discrete-Finite Element Method (HybriDFEM), is presented. In this method, a structure is modeled as an assembly of rigid blocks in contact. All the deformation is concentrated at the interfaces, which are modeled as series of distributed nonlinear multidirectional springs. The method shares similarities with the Discrete Element Methods (DEM) in its ability to account for contact interfaces and/or block deformability, and with the Applied Element Method (AEM) in the representation of interfaces as a series of normal and shear springs. However, it is close to the FEM in the way it is formulated, which offers the possibility to readily link both methods for potential hybrid applications. This paper focuses on the modeling of continuous and discontinuous frames with the HybriDFEM. It is shown how the model can do so with a nonlinear material model, and considering (or not) nonlinear geometric effects through large nodal displacements. Different nonlinear solution procedures implemented in HybriDFEM are demonstrated, such as load-control and various displacement-controlled methods. This model is able to simulate contacts between rigid or deformable units, an important feature when it comes to the modeling of, e.g., unreinforced masonry structures, with a reasonable computational cost and a formulation that is cast within the framework of the classical FEM.
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| 6. |
- Gagliardo, Raffaele, et al.
(författare)
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Rigid block modelling approach for the prediction of seismic performance of adjacent interacting masonry structures
- 2022
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Ingår i: Proceedings of 3rd EUROPEAN CONFERENCE ON EARTHQUAKE ENGINEERING & SEISMOLOGY.. ; , s. 3245-
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Konferensbidrag (refereegranskat)abstract
- The current paper discusses the contents of the work completed for the project “SERA AIMS – BLIND PREDICTION COMPETITION”. The competition was focused on the prediction of the response of a masonry building composed of two adjacent interacting structural units under earthquake excitation. This research investigates the response of the experimental mock-up by using a numerical model based on the rigid block limit analysis and mathematical programming. The results of the analysis, namely, the failure modes and the corresponding collapse load multipliers, are related to base shear and peak ground accelerations observed for the damage and ultimate limit states using code provisions for the assessment of failure mechanisms in existing masonry structures. Finally, a preliminary comparison of numerical and experiemental results is presented.
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| 7. |
- Gagliardo, Raffaele, et al.
(författare)
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Seismic analysis of failure mechanisms in adjacent interacting stone masonry buildings via rigid block modeling
- 2023
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Ingår i: Bulletin of Earthquake Engineering. - : Springer Nature. - 1570-761X .- 1573-1456.
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Tidskriftsartikel (refereegranskat)abstract
- Groups of contiguous unreinforced stone masonry buildings are a common type of housing seen in old European downtowns. However, assessing their response to earthquakes poses several challenges to the analysts, especially when the housing units are laid out in compact configurations. In fact, in those circumstances a modeling technique that allows for the dynamic interaction of the units is required. The numerical study carried out in this paper makes use of a rigid block modeling approach implemented into in-house software tools to simulate the static behavior and dynamic response of an aggregate stone masonry building. Said approach is used to reproduce the results of bi-axial shake-table tests that were performed on a building prototype as part of the activities organized within the Adjacent Interacting Masonry Structures project, sponsored by the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe. The experimental mock-up consisted of two adjacent interacting units with matching layout but different height. Two rigid block models are used to investigate the seismic response of the mock-up: a 3D model allowing for the limit analysis of the building on one hand, and a 2D model allowing for the non-linear static pushover and time-history analysis on the other. The 3D model was built for the blind prediction of the test results, as part of a competition organized to test different modeling approaches that are nowadays available to the analysts. The 2D model was implemented once the experimental data were made available, to deepen the investigation by non-linear static pushover and time-history analysis. In both models, the stonework is idealized into an assemblage of rigid blocks interacting via no-tension frictional interfaces, and mathematical programming is utilized to solve the optimization problems associated to the different types of analysis. Differences between numerical and experimental failure mechanisms, base shears, peak ground accelerations, and displacement histories are discussed. Potentialities and limitations of the adopted rigid block models for limit, pushover and time-history analyses are pointed out on the basis of their comparisons with the experimental results.
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| 8. |
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| 9. |
- Godio, Michele, et al.
(författare)
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Experimental and numerical approaches to investigate the out-of-plane response of unreinforced masonry walls subjected to free far-field blasts
- 2021
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Ingår i: Engineering structures. - : Elsevier. - 0141-0296 .- 1873-7323. ; 239
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Forskningsöversikt (refereegranskat)abstract
- Masonry walls are bulky and heavy and have therefore the potential to act naturally as a protective system to blasts. Yet, they are known to have a limited flexural and torsional capacity, particularly when unreinforced. When exposed to shockwaves, they experience out-of-plane failure mechanisms which may affect the overall stability of the building and engender flying debris inside the building. The out-of-plane response of unreinforced masonry walls to blasts depends on many factors characterizing both the wall and blast action, making any sort of prediction difficult. In this context, experimental tests and numerical models become key tools that can be used to study the wall’s response on a case-by-case basis. This review covers the major experimental and numerical approaches to assess the out-of-plane response of unreinforced masonry walls subjected to blasts. A methodological appraisal is used for the test methods, focusing on the preparation of the test items and test setup, the boundary conditions and failure mechanisms investigated, as well as the commonly employed measurement techniques. The survey on the modelling approaches includes key topics such as level of detail and cost, and reports strategies to model the wall and blast scenario. The review provides a thematic analysis of the available literature, aimed to assist the analyst in selecting a suitable tool for the investigation of masonry in the field of blast engineering. Furthermore, the findings presented herein can support amendments of existing codes and guidelines pertaining to the design of protective masonry structures.
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| 10. |
- Godio, Michele, et al.
(författare)
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Experimental study on the hydromechanical behaviour of a natural unperturbed fracture under normal loading: Derivation of the equivalent hydraulic aperture and its digital reconstruction
- 2024
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report describes the laboratory work undertaken to characterize the hydromechanical behaviour of a natural rock fracture under varying normal loading. The hydraulic transmissivity of a granite specimen with a sealed (unopened) quasi-planar natural fracture of length 200 mm and width 200 mm was measured. The transmissivity measurements were conducted in the two perpendicular directions of the fracture, repeating them at five different normal compression stress levels, namely, ~0, 1, 2, 4, and 8 MPa, and flow gradients. The fracture was mechanically opened, and the measurements were repeated to investigate the effect of opening the fracture on its hydraulic transmissivity and hydromechanical behaviour. For one direction, the change in transmissivity was explored for high normal compression stress levels, up to ~40 MPa. Laminar flow conditions were ensured at every stage of the experimental campaign by working at very low Reynolds numbers (<1). The equivalent hydraulic aperture of the fracture was derived by resorting to the parallel-plate model theory. The hydraulic aperture was compared to the mechanical aperture, which was obtained by measuring the deformation of the specimen. In addition to the transmissivity tests, the geometry of the lateral walls and surfaces of the fracture was documented and measured by a series of tools, namely, digital scans, high-resolution pictures, optical readings by a stand microscope, and contact pressure-sheet measurements. The results achieved in this campaign shed light on the hydraulic transmissivity of sealed (unopened) and consequently opened natural fractures, and its dependency to the applied normal compression stress at low to very-low flow rates.
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