1,720,969 research outputs found
Spatial stochastic D-RBA and limit equilibrium analysis of unreinforced masonry pier-spandrel structures
No full textThis study investigates the effect of spatially varying material properties on the in-plane seismic behaviour and capacity of an unreinforced pier-spandrel masonry system. The discontinuous nature of masonry is represented via a system of rigid blocks that can mechanically interact with each other along their boundaries. In the discontinuous modelling strategy, denoted as discrete rigid block analysis (D-RBA), deformations are lumped at the joints, and masonry units are replicated using two rigid blocks with a potential crack plane using the discrete element method (DEM). The obtained collapse mechanisms are automatically classified into two main categories via an algorithm processing the results of D-RBA. The adopted methodology offers a robust and time-efficient categorization of different collapse modes obtained from the computational model, which is required for better understanding the possible mechanisms developing in pier-spandrel structures and their occurrence rate. Accordingly, the most recurrent failure mechanisms are further investigated via upper- and lower-bound theorems of limit equilibrium analysis (LEA) by adopting an ad hoc coded optimization algorithm to ensure the solution's uniqueness. The results show that the DEM-based modelling approach provides a comprehensive understanding of the structural behaviour and capacity of pier-spandrel systems subjected to in-plane lateral loads. Further, the proposed probabilistic assessment workflow offers a broader perspective than deterministic analysis
The effectiveness of the DIC as a measurement system in SRG shear strengthened reinforced concrete beams
Full text linkSteel Reinforced Grout (SRG) materials are generating considerable interest as strengthening system of reinforced concrete (RC) structures. They are finding increasing use in several civil engineering applications mainly due to the advantages they offer over traditional material such as high strength to weight ratio, ease of application, durability and low price. This paper describes the results of an experimental investigation carried out on SRG shear strengthened RC beams and gives evidence of the Digital Image Correlation (DIC) effectiveness as a measurement system. The tests performed had two main objectives: (i) assess the effectiveness of continuous and discontinuous U-wrapped jackets comprising a different number of layers and strips; (ii) assess the shear crack distribution during the tests by means of the DIC measurements. The results confirmed that reinforcing RC beams with SRG jackets can increase the load-bearing capacity; when the beam was reinforced with a continuous two-layered SRG strip, an increase of 84% was observed (compared to the unreinforced beam). The Linear Variable Differential Transformers (LVDT) measurements validated the results obtained by means of the DIC
A crack growth strategy based on moving mesh method and fracture mechanics
Full text linkA numerical model based on moving mesh strategy is proposed to simulate the evolution of internal material discontinuities in a continuum medium. The approach combines concepts arising from structural mechanics and moving mesh methodology, which are implemented in a unified framework to predict crack growth on the basis of Fracture Mechanics variables. In particular, moving computational nodes are modified starting from a fixed referential coordinate system on the basis of a crack growth criterion to predict directionality and displacement of the tip front. The use of rezoning mesh methods coupled with a proper advancing crack growth scheme ensures the consistency of mesh motion with small distortions and an unaltered mesh typology. In addition, the moving grid is modified from the initial configuration in such a way that the recourse to re-meshing procedures is strongly reduced. The numerical formulation and its computational implementation show how the proposed approach can be easily embedded in classical finite element software. Finally, numerical examples in the presence of internal material discontinuities and comparisons with existing data obtained by advanced numerical approaches and experimental data are proposed to check the validity of the formulation.</p
Visual programming for the structural assessment of historic masonry structures
No full textThe objective of this work is to formulate a new methodology the assessment of masonry structures that is using a fully digital procedure to automatically build up a reliable structural model, limiting expensive destructive tests. Data arising from laser scanning surveys and digital photogrammetry techniques are employed to generate a detailed 3D model that can be automatically imported in a Finite Element (FE) software environment. This is used to perform a non-linear static analysis aiming at investigating on possible collapse modes of the structure. As the focus is not on the actual structural capacity of the structure, such results are not strongly dependent on material parameters employed, which are set based on engineering judgement only. This preliminary structural analysis is employed to generate a possible configuration of failure surfaces through the Control Surface Method (CSM), which is here proposed for the first time. These are associated to the 3D models and implemented into a visual coding which embeds an upper bound limit analysis of the problem assuming a no-tension material hypothesis. Based on such failure surfaces, Genetic Algorithms are used to generate other possible collapse mechanism and search for the actual failure mode corresponding to the minimum value of the loads multiplier. The work-flow is all integrated into a computational tool implemented in the visual programming environment offered by Grasshopper and Rhino3D. The procedure is validated by the analysis of one benchmark case, whose results are presented and discussed
Mechanistic model for the compression strength prediction of masonry columns strengthened with fibre–polymer composites
Full text linkA mechanistic model is presented for the strength prediction of squared columns made of masonry with a periodic arrangement and strengthened with a fibre–polymer composite jacketing. The formulation is based on an incremental plasticity theory that relies on equilibrium, compatibility, and kinematic equations. The strength domain of brick units and mortar joints is bounded by a multi-surface yield criterion: a Mohr–Coulomb strength domain with a linear cap in compression and a Rankine cut-off in tension. An elasto-plastic response with limited ductility is assumed for both masonry components. Differently, the FRP response is assumed elastic with a brittle failure governed by a limited tensile strain. Phenomenological-based assumptions are undertaken and justified. Details are also provided for the computational implementation of the procedure. The model accuracy is validated against experimental data on masonry squared columns and compared with existing standard-based formulas. Results demonstrate it provides real-time and accurate compressive strength solutions for squared masonry columns with or without a polymer-based wrapping and yet requiring few input parameters for the masonry constituents and reinforcement
Dynamic crack growth based on moving mesh method
No full textA new methodology to predict dynamic crack propagation under generalized loading conditions is proposed. The numerical modeling combines structural mechanics and moving mesh method with the purpose to predict geometry variation produced by the evolution of existing material discontinuities. In particular, moving mesh method is implemented to enforce crack tip displacements by using an explicit crack criterion based on referential and moving configurations. In this framework, the use of mesh regularization method based on proper rezoning equations is able to reduce the use of remeshing attempts, typically required by standard crack propagation procedures. Dynamic crack growth is predicted by a rate dependent criterion, expressed in terms of crack angle and driven forces based on energy release rate definition. The model is quite suitable to predict the evolution of material discontinuities, typically observed in composite structures. Numerical implementation, developed in the framework of a finite element formulation and details on the solving procedure, are presented. The proposed modeling is validated by several comparisons with experimental and numerical data, which show accuracy and robustness of the numerical approach. Moreover, sensitivity analyses in terms of mesh dependence and time required for the solving procedure are also developed
An optimised multi-level method for the pushover analysis of historic masonry structures accounting for the actual masonry pattern
No full textIn this paper, we propose an optimised multi-level method to efficiently account for the actual masonry pattern in the pushover analysis of historic masonry structures. The method begins with a rigid block-based limit analysis accounting for the actual masonry pattern to identify realistic failure mechanisms. Next, macro-blocks that outline the failure mechanism are identified using a novel optimised procedure that includes a heuristic search, which minimises the number of blocks and non-linear interfaces in the subsequent analyses. Subsequently, macro-blocks are modelled as homogeneous material interacting via cohesive-frictional interfaces in a finite element environment where pushover analysis produces force–displacement curves. Validation against various structural benchmarks with regular and irregular masonry patterns and different loading configurations demonstrates the method's accuracy and competitiveness compared to micro-modelling approaches. Results show up to a 90% reduction in computational time and the number of blocks, with a maximum difference of about 5% in numerical prediction of force capacity
Seismic assessment of URM pier spandrel systems via efficient computational modeling strategies
No full textPredicting the seismic behavior of unreinforced masonry (URM) structural systems is a complex task, given various inherent sources of uncertainty associated with material properties, geometry, and boundary conditions. As the selection of computational strategies is a trade-off between prediction accuracy and computational cost, it is often challenging to find a consensus. To this end, this study presents three computational modeling strategies that can be used in the seismic analysis of URM structures. The first two approaches utilize the discrete element method (DEM) and are based on pre-defined macro-block mechanisms, whereas the third approach makes use of the computational thrust line analysis (CTLA). Such methods provide accurate predictions on the in-plane lateral load-carrying capacity of URM pier-spandrel structures with a reasonable computational cost and fewer input parameters, making them efficient compared to detailed numerical models. The results are found to be in good agreement with the experimental data on two full-scale pier-spandrel systems with either timber lintel or shallow arch above a central opening. This study also provides a detailed comparison of the applied methods and suggests multi-level use of proposed modeling strategies for better informed decision-making, starting from the most simplified method (CTLA) towards the advanced solutions as more information is collected
A digital tool based on genetic algorithms and limit analysis for the seismic assessment of historic masonry buildings
No full textNew technologies are changing the way engineers work within the construction sector. Newly developed software solutions have provided effective methods to explore the design space at the interface between Structural Engineering and Architecture, allowing more efficient design strategies. These technologies are based on the integration of parametric generation and visualisation of geometries with powerful numerical solvers, employing user-customised routines. While the construction industry is rapidly moving the design of new construction towards a fully digitalised process, the assessment and the analysis of existing structures with such tools are still largely unexplored. In this context, a visual script for the structural assessment of out-of-plane mechanisms in historic masonry structures subject to seismic loading has recently been proposed by the authors. This relies on two successive steps of analysis, which are integrated into a digital work-flow. Datasets describing the geometric configuration of masonry structures are employed to automatically generate a non-linear Finite Element (FE) model and investigate possible collapse modes. A preliminary global analysis is performed using the commercial software ABAQUS CAE. This, in combination with the Control Surface Method (CSM), allows identifying the most likely failure mechanisms which are described by the geometry of the macro-blocks. The parametric modelling of the macro-blocks geometry allows exploring the domain of possible solutions using the upper bound method of limit analysis. A Genetic Algorithms (GA) solver is used to refine the geometry of the macro-blocks and search the minimum of the upper-bound load multipliers, which guarantees equilibrium. The script is implemented in the visual programming environment offered by Rhino3D+Grasshopper. In this paper, a set of parametric analyses considering various input variables such as friction coefficient and opening incidence are performed to verify both the sensitivity and the accuracy of the proposed method
The role of uncertainties in the seismic assessment of masonry churches affected by compound rocking failure mechanism: Macro-block limit analysis investigations
No full textFaçade overturning is one of the most common failure mechanisms observed in single-nave masonry churches when subjected to seismic action. Several factors, including geometry, masonry patterns, mechanical properties, and loading conditions, influence the force and displacement capacities of these masonry churches. This study aims to assess the impact of various model parameters on the seismic assessment of single-nave masonry churches subjected to the compound rocking failure mechanism by adopting macro-block limit analysis. The analysis of variance (ANOVA) is employed to investigate the influence of geometrical and mechanical parameters under the assumption of complete knowledge of the structure. Furthermore, probabilistic analysis explores how incomplete knowledge may affect the structural assessment of the compound rocking failure mechanism in single-nave masonry churches. The findings of this study highlight the importance of accurate modelling and surveying in evaluating the seismic vulnerability of single-nave masonry churches and can be useful for developing effective seismic risk mitigation strategies
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