Analysis Of Unreinforced Masonry Structures Research Articles

Sensitivity analysis on mechanical parameters of continuum models for simulating in-plane tests on existing masonry panels

Understanding and modeling the structural behavior of existing masonry buildings is a fundamental task in view of their management and conservation, especially in seismic-prone areas. Among the different modeling approaches for the computational analysis of unreinforced masonry structures, this work investigates the ability of two material continuum models, the modified masonry-like material and Mazars’ material, to simulate real in-plane failure modes of masonry panels, considering the influence of the variability of mechanical parameters on the results. As the first part of a broader benchmark, this work focuses on the study of two recurring test patterns for masonry panels subject to both horizontal and vertical loads, given the availability of experimental data. To account for the parameter variability that typically affects masonry materials, uncertainty propagation is performed in a probabilistic framework, and a gPCE-based proxy model makes it possible to turn time-consuming numerical runs into significantly faster analytical evaluations. Sensitivity analyses are carried out in terms of Sobol’ indices to evaluate the influence of input variability on the ultimate horizontal load. The most relevant masonry parameters for each model are thus highlighted and the issue of model calibration is finally addressed by relying on Bayesian inverse methods. This work also underlines the pros and cons of the different hypotheses, which underlie the two nonlinear constitutive laws.

The Striatus bridge

The paper describes the physical realisation of a 3D-concrete-printed, mortar-free, unreinforced masonry arched footbridge, designed for disassembly and reuse. The paper also details the novel integrated design, engineering and fabrication framework and the manufacturing and assembly processes used for the project. The research, motivated by the rapid growth in large-scale 3D concrete printing (3DCP), addresses the current lack of both design tools and integrated design-to-production solutions. It is guided by the insight regarding the applicability of design and analysis methods used in unreinforced masonry to large-scale, layered 3D printing with compression dominant materials such as concrete. Thus, the underlying computational framework and integrated design environment further extends and adapts advances in the computational design and analysis of unreinforced masonry structures to 3DCP masonry blocks. Adopting an unreinforced masonry paradigm for the design of 3DCP structures can make it possible to (i) reduce the amount of concrete used by allowing precise placement of concrete only where needed along the compressive flow of forces, (ii) reduce the amount of steel needed by reducing tensile and flexural strength requirements through a compression-appropriate design of both the global, shape and the block discretisation, and (iii) reuse components, repair the structures and recycle materials more easily. This paper builds on the relevance of the computational masonry paradigm to both delivering the ecological promises of 3DCP and to the development of a 3DCP-specific, design-to-production toolkit.

Comparative assessment of finite element macro-modelling approaches for seismic analysis of non-engineered masonry constructions

All around the world, non-engineered masonry constructions (NECs) typically have high vulnerability to seismic ground motion, resulting in heavy damage and severe casualties after earthquakes. Even though a number of computational strategies have been developed for seismic analysis of unreinforced masonry structures, a few studies have focussed on NECs located in developing countries. In this paper, different modelling options for finite element analysis of non-engineered masonry buildings are investigated. The goal of the study was to identify the modelling option with the best trade-off between computational burden and accuracy of results, in view of seismic risk assessment of NECs at regional scale. Based on the experimental behaviour of a single-storey structure representative of Indian non-engineered masonry buildings, the output of seismic response analysis of refined 3D models in ANSYS was compared to that of a simplified model based on 2D, nonlinear, layered shell elements in SAP2000. The numerical-experimental comparison was carried out under incremental static lateral loading, whereas nonlinear time history analysis was performed to investigate the dynamic performance of the case-study structure. Analysis results show that the simplified model can be a computationally efficient modelling option for both nonlinear static and dynamic analyses, particularly in case of force-based approaches for design and assessment of base isolation systems aimed at the large-scale seismic vulnerability mitigation of NECs.

A Macro-Distinct Element Model (M-DEM) for out-of-plane analysis of unreinforced masonry structures

Despite the vulnerability of unreinforced masonry (URM) structures to out-of-plane (OOP) loading, computational methods that can efficiently simulate OOP failure at the building scale are still limited. Current methods typically rely on simplified static analysis approaches or refined micro-modeling techniques that entail high computational expense, thus limiting their employment to reduced-scale and local problems. With a view to overcome these issues, a novel Finite-Distinct macroelement model which combines the efficiency of simplified modeling strategies with the multifaceted capabilities of discontinuum-based methods, is developed and implemented in the framework of the Distinct Element Method (DEM). Shear and flexural failure modes, either in-plane or out-of-plane, are accounted for by zero-thickness interface spring layers, whose layout is determined a priori as a function of the considered masonry bond pattern. Meanwhile, crushing failure is modeled through homogenized Finite Element macro-blocks. The proposed discretization scheme is conceived so that the model can also be used to simulate in-plane damage, for which the model has already been validated. Simplified expressions are proposed for determining equivalent mechanical properties of the interface spring layers, depending on their inclination. Similarly, analytically-based equations are used to significantly reduce the number of springs needed to adequately reproduce the OOP bending response at the joint level. Numerical simulations are compared to previous experimental quasi-static and dynamic tests on both brick and block URM components, characterized by markedly different vertical pressures, aspect ratios, boundary conditions and confinement; both one-way and two-way bending actions are considered. The results indicate that the model can satisfactorily reproduce the measured load–displacement curves in a reasonable timeframe, as well as the experimentally-observed failure mechanisms.

Numerical homogenization‐based seismic assessment of an English‐bond masonry prototype: Structural level application

SummaryA multiscale strategy is evaluated at a structural level for the analysis of unreinforced masonry structures. The mechanical characterization of the masonry is deduced from homogenization‐based micro‐scale finite element (FE) models. The derived data are here employed at a structural level via a discrete FE model. The discrete FE model is composed of quadrilateral rigid plates interconnected through vertical and horizontal interfaces. On the interfaces, between adjoining discrete elements, a model that accounts for the in‐ and out‐of‐plane behavior of masonry, with damage and plasticity, is adopted. Such interfaces represent the material pre‐ and post‐peak regimes, its orthotropy, and, depending on the micro‐model assumed, account by three‐dimensional shear effects that are especially important for multi‐leaf walls and complex regular textures. The discrete model has been implemented in an advanced structural analysis software where powerful built‐in features as the arc‐length method, line‐search algorithm, and implicit or explicit solver schemes are available.The multi‐scale model is applied for the dynamic study of a small English‐bond masonry house prototype subjected to a series of consecutive earthquake records. Detailed comparisons between the experimental and numerical data are presented, including the results obtained through a continuous total strain rotating crack model. Quasi‐static and dynamic analyses are conducted. Results demonstrate that when enough experimental information is available on the masonry components under tension, shear, and compression regimes, the approach predicts well the seismic structural response in terms of time‐history displacements, seismic capacity, and damage patterns. The required computational cost (CPU time) is very attractive.

SEISMIC FRAGILITY ANALYSIS OF UNREINFORCED MASONRY STRUCTURES CONSIDERING PARAMETER UNCERTAINTIES

Due to the high dispersion of structural parameters and high nonlinearity of seismic responses, it is particularly necessary to consider the structural parameter uncertainties in seismic fragility analysis of unreinforced masonry structures. Taking four unreinforced masonry structures with different storeys as the research object and the equivalent frame finite element models are established in OpenSees. The incremental dynamic analysis and the FOSM method are employed to investigate the impact of the uncertainties of ground motion and structural parameters on seismic fragility analysis. The analysis results indicate that the uncertainties of ground motion and structural parameters should be considered in the seismic fragility analysis of unreinforced masonry structures and the impact is greater when the structural seismic damage is severer. The impact of structural parameter uncertainty is almost the same as that of ground motion uncertainty. Compared with ground motion uncertainty, the impact of structural parameter uncertainty becomes even more obvious with the smaller number of structure storeys. The changing of median value of seismic fragility was investigated through sensitivity analysis, and it was found that the influence of structural damping ratio is 4 times that of other single parameter, demonstrating the highest sensitivity of seismic response to structural damping ratio.

Modeling Strategies for the Computational Analysis of Unreinforced Masonry Structures: Review and Classification

Masonry structures, although classically suitable to withstand gravitational loads, are sensibly vulnerable if subjected to extraordinary actions such as earthquakes, exhibiting cracks even for events of moderate intensity compared to other structural typologies like as reinforced concrete or steel buildings. In the last half-century, the scientific community devoted a consistent effort to the computational analysis of masonry structures in order to develop tools for the prediction (and the assessment) of their structural behavior. Given the complexity of the mechanics of masonry, different approaches and scales of representation of the mechanical behavior of masonry, as well as different strategies of analysis, have been proposed. In this paper, a comprehensive review of the existing modeling strategies for masonry structures, as well as a novel classification of these strategies are presented. Although a fully coherent collocation of all the modeling approaches is substantially impossible due to the peculiar features of each solution proposed, this classification attempts to make some order on the wide scientific production on this field. The modeling strategies are herein classified into four main categories: block-based models, continuum models, geometry-based models, and macroelement models. Each category is comprehensively reviewed. The future challenges of computational analysis of masonry structures are also discussed.

Disturbed Stress Field Model for Unreinforced Masonry

The traditional smeared crack macromodels for the analysis of masonry structures consider masonry as a homogeneous material with the effects of mortar joints included in an average sense. This approach, suitable for the analysis of large structures, implicitly excludes the possibility of representing local elastic and inelastic mechanisms involving mortar joints. In this study, an innovative formulation based on the disturbed stress field model (DSFM) is proposed for the analysis of unreinforced masonry structures. The advancement introduced by the model lies in the possibility of simulating the global average behavior of the composite material in combination with the local nonlinear shear slip response of both bed and head joints. This paper describes the formulation of the model; as well, it presents results obtained from the simulation of tests performed on shear walls demonstrating the ability of the DSFM to reproduce the structural response of masonry structures.

Cut-HDMR-based fully equivalent operational model for analysis of unreinforced masonry structures

Mesoscale models are highly competent for understanding behaviour of unreinforced masonry structures. Their only limitation is large computational expense. Fully Equivalent Operational Model forms an equivalent mathematical model to represent a particular phenomenon where explicit relationship between inputs and outputs are unknown. This paper explores the ability of a major variant of High Dimensional Model Representation (HDMR) technique, namely Cut-HDMR, to construct the most efficient Fully Equivalent Operational Model for nonlinear finite element analysis of mesoscale model of an unreinforced masonry structure. Conclusions are reached on various aspects such as, suitability of interpolation schemes and order of Cut-HDMR approximation.

Explicit finite‐element analysis for the in‐plane cyclic behavior of unreinforced masonry structures

AbstractA simple constitutive model is proposed for an in‐plane numerical analysis of unreinforced masonry structures, which are subject to cyclic loading, by using explicit dynamic procedures. The proposed model is implemented by using two‐dimensional plane‐stress finite elements. Three different constitutive relations that are based on the total strain in the global material system are used. Cracking and crushing are controlled through normal strains, whereas shear is controlled through shear strain. Separate hysteretic rules are adopted for each mode of damage. A numerical analysis of masonry walls that are subject to cyclic loading has demonstrated that the use of explicit procedures in conjunction with the proposed model results in an acceptable accuracy when compared with the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.

Analysis of masonry arches and vaults

AbstractA growing interest in the preservation of historic structures has created a need for methods for the analysis of load‐bearing unreinforced masonry structures, such as arches, vaults, and buttresses. Although the plasticity methods, first applied to medieval structures in detail by Heyman, provide a useful and intuitive approach to the understanding of the behaviour of masonry arches and vaults, their usefulness in performing actual assessments of such structures has limitations. The constitutive laws of the materials used in masonry structures are not always amenable to accurate treatment by the rigid–plastic simplification, and the complexity of many vaulted masonry structures makes the application of these methods difficult. Moreover, empirical studies have shown that these structures may be subject to three‐dimensional effects that are not entirely addressed by the application of plastic or elastic analysis in two dimensions. Progress has been made recently in the development of constitutive laws for ancient masonry structures and in the application of these to the analysis of unreinforced masonry structural systems. Various formulations of three‐dimensional finite element analysis, including discrete element methods, and plasticity methods have also proven useful.

Multisurface Interface Model for Analysis of Masonry Structures

The performance of an interface elastoplastic constitutive model for the analysis of unreinforced masonry structures is evaluated. Both masonry components are discretized aiming at a rational unit-joint model able to describe cracking, slip, and crushing of the material. The model is formulated in the spirit of softening plasticity for tension, shear and compression, with consistent treatment of the intersections defined by these modes. The numerical implementation is based on modern algorithmic concepts such as local and global Newton-Raphson methods, implicit integration of the rate equations and consistent tangent stiffness matrices. The parameters necessary to define the model are derived from microexperiments in units, joints, and small masonry samples. The model is used to analyze masonry shear-walls and is capable of predicting the experimental collapse load and behaviour accurately. Detailed comparisons between experimental and numerical results permit a clear understanding of the walls structural behavior, flow of internal forces and redistribution of stresses both in the preand post-peak regime.