Material Properties Of Masonry Research Articles

Static and Seismic Safety of the Inclined Tower of Portogruaro: A Preliminary Numerical Approach

Masonry towers are peculiar structures with complex structural behavior despite biased conclusions deriving from their geometrical regularity and simplicity. Their geometrical features and the epistemic uncertainty that masonry material bears strongly influence their static and seismic behavior. This paper investigates a remarkable and representative case study. The bell tower of Portogruaro (Italy) is a 57 m high tall construction, built in the XII-th century, and has a notable inclination. The Italian Guideline for the safety assessment of masonry towers is a key focus in this paper, highlighting the pros and cons of different suggested approaches. Some relevant proposals are presented in this paper in order to address the seismic safety assessment of masonry bell towers. The findings show that very slender structures do not meet the guidelines recommendations due to limitations in their current stress state. In addition, in similar cases, the recommended values for the mechanical properties of masonry material led to predicting non-withstanding structural behavior, questioning the correct choice of the adapted material properties. Advanced pushover analysis has been conducted in order to investigate the results of the simplified approach in terms of failure patterns and seismic safety estimation. The simulations are implemented for four different hypothetical scenarios of the existing masonry mechanical properties. The results obtained for the case study tower reflect a different perspective in the seismic assessment of masonry towers when specific approaches are defined. The preliminary results on the safety of Portogruaro Tower show a significant variability of seismic safety based on the adopted scenario, highlighting the necessity to pay attention to the preservation state of the present case and of similar ones.

A novel machine learning-based approach for nonlinear analysis and in-situ assessment of masonry

Predicting the local and global mechanical response of masonry structures or estimating their in-situ properties are critical and challenging for the design or assessment of these structures. This article presents a fast prediction/assessment model, developed using a conditional generative adversarial neural network (cGAN) to address this challenge. For the first time, the model shows to be capable of establishing a relationship between masonry microstructural features and full-field local/global mechanical response, and vice-versa, overpassing the path dependency of the non-linear mechanical problems. The strain maps and reaction forces of masonry panels are predicted at any load level from images of masonry panels, which embedded information regarding the materials properties and loading scenarios only in colours, without having any prior knowledge of the material properties and constitutive laws and without the need to access these fields in previous loading levels. Also, it is shown that the mechanical properties of masonry constituents can be predicted from full-field strain maps and loading scenarios using the developed model. This promises to become a revolutionary metamodel for the expensive finite element simulations of masonry or to support in-situ/laboratory experimental testing in the identification of masonry material properties.

Integration of NDT, 3D parametric modelling, and nonlinear numerical analysis for the seismic assessment of a vaulted stone-masonry historical building

This paper presents the integration of parametric modelling with NDT (NDT) and advanced numerical simulations for assessing the seismic response of an emblematic stone-masonry vaulted construction, the 16th-century church of the Society of Jesus located in Cusco, Peru. Revit parametric families allowed the creation of complex curved elements such as vaults and 3D geometrical models of the church based on a hybrid point cloud. The onsite survey results indicated that the main anomalies correspond to the presence of biological agents and cracking. In contrast, NDT allowed the estimation of the masonry material properties and the modal identification primarily of the towers. Finally, the application of pushover analyses allowed the estimation of the structure's maximum load capacity and post-peak behavoir. It was possible to determine that some collapse mechanisms (overturning of main façade and bell towers, and the generation of hinges in curved elements) can be activated in medium-strong earthquakes.

Variation in compressive properties of Indian brick masonry and its assessment using empirical models

Estimation of basic material properties of masonry and understanding its compressive behaviour is the initial crucial steps in analyzing the performance of masonry buildings. Masonry being a complex and inelastic material has a large variation in mechanical properties such as compressive strength and modulus of elasticity. The variation for Indian masonry is even higher, as most of the manufacturing and construction process is performed manually. Mechanical characterization of solid clay bricks, mortar cubes (1:4 cement-sand proportion) and masonry prisms are performed using laboratory tests to determine the compressive properties. The non-linear stress–strain behaviour of masonry and its constituents is also presented. Based on the results of the present study and past literature, variation in mechanical properties of Indian masonry & its constituents is studied based on two different mortar grades (1:4 and 1:6). It is observed that these properties have a large portion of aleatory variability, due to variations in constituent materials and workmanship. The relationship between the compressive strength and elastic modulus of brick, mortar and masonry is also presented. Further, the relative performance of different empirical models in predicting the properties of masonry is compared and their efficacy is examined using the statistical and error-assessment parameters. Results showed that the compressive strength of the Indian masonry can be determined using most of the empirical relations available worldwide, with reasonable accuracy; however, the elastic modulus of masonry cannot be estimated with the same level of confidence.

Stochastic strength prediction of masonry structures: a methodological approach or a way forward?

Today, there are several computational models to predict the mechanical behaviour of masonry structures subjected to external loading. Such models require the input of material parameters to describe the mechanical behaviour and strength of masonry constructions. Although such masonry material parameters are characterised by stochastic-probabilistic nature, engineers are assigning the same material properties throughout the structure to be analysed. The aim of this paper is to propose a methodology which considers material spatial variability and stochastic strength prediction for masonry structures. The methodology is illustrated on a case study covering the in-plane behaviour of a low bond strength masonry wall panel containing an opening. A 2D non-linear computational model based on the Discrete Element Method (DEM) is used. The computational results are compared against those obtained from the experimental findings in terms of failure mode and structural capacity. It is shown that computational models which consider the spatial variability of masonry material properties better predict the load carrying capacity, stiffness and failure mode of the masonry structures. These observations provide new insights into structural behaviour of masonry constructions and lead to suggestions for improving assessment techniques for masonry structures.

Structural assessment of iron tie rods based on numerical modelling and experimental observations in Milan Cathedral

Iron 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.

Limit analysis of masonry arch bridges through an adaptive GA-NURBS upper-bound approach

This paper investigates the application of a fast and reliable NURBS-based kinematic limit analysis approach for the assessment of the collapse behaviour of masonry bridges. This approach relies on the description of the geometry of the bridge structure by means of NURBS approximating functions. Starting from the known geometry, an assembly of rigid bodies can be generated, composed by very few elements which still provide an exact representation of the original geometry. The main properties of masonry material are accounted for through homogenisation and an upper-bound formulation for the limit analysis of the obtained mesh is devised. The approach is capable of accurately predicting the load bearing capacity of masonry bridges with arbitrary geometry and load configuration, provided that the initial mesh is adjusted by means of a suitably meta-heuristic approach (i.e., a genetic algorithm) until element edges correctly approximate the actual yield lines of the collapse mechanism.

LIMIT ANALYSIS OF MASONRY ARCH BRIDGES THROUGH AN ADAPTIVE GA-NURBS UPPER-BOUND APPROACH

This paper investigates the application of a fast and reliable NURBS-based kinematic limit analysis approach for the assessment of the collapse behaviour of masonry bridges. This approach relies on the description of the geometry of the bridge structure by means of NURBS approximating functions. Starting from the known geometry, an assembly of rigid bodies can be generated, composed by very few elements which still provide an exact representation of the original geometry. The main properties of masonry material are accounted for through homogenisation and an upper-bound formulation for the limit analysis of the obtained mesh is devised. The approach is capable of accurately predicting the load bearing capacity of masonry bridges with arbitrary geometry and load configuration, provided that the initial mesh is adjusted by means of a suitably meta-heuristic approach (i.e., a genetic algorithm) until element edges correctly approximate the actual yield lines of the collapse mechanism.

Fast and Reliable Limit Analysis Approach for the Structural Assessment of FRP-Reinforced Masonry Arches

This contribution is devoted to assess the capability of a new upper-bound approach for the limit analysis of FRP-reinforced masonry arches by comparing it to both experimental tests and a number of existing numerical procedures. The approach is based on an idea previously presented by the Authors and relies on the representation of the geometry of both the arch and of FRP reinforcement through Non Uniform Rational B-Spline (NURBS) functions. This allows generating a rigid body assembly starting from the assigned geometry composed by very few elements which still provide an exact representation of the original shape. A homogenized kinematic formulation for the limit analysis of the obtained rigid blocks assembly is derived, which accounts for the main properties of masonry material. FRP material is included exploiting the Italian CNR Recommendations for the design of FRP based reinforcing interventions. The approach is capable of accurately predicting the load bearing capacity of masonry arches of arbitrary geometry, provided that the initial mesh is adjusted by means of a suitably devised Genetic Algorithm (GA) until the active interfaces among blocks (e.g. hinges) closely approximate the actual failure mechanism.

Shear resistance of reinforced masonry beams with and without additional concrete or prestress

AbstractThis article investigates the transferability of the Simplified Modified Compression Field Theory (SMCFT) [2], which is known in reinforced concrete design and included in the fib Model Code for Concrete Structures 2010 (Volume 3) [1], to reinforced or prestressed masonry beams (RM beams) with or without an additional layer of concrete. The investigation for this work is the obsolete shear design concept that has been used until now for reinforced masonry under shear loading, which does not adequately reflect the actual load‐bearing behaviour of significant areas of masonry. The fundamentals of the SMCFT are explained and the transferability of the theory to RM beams is examined, taking into account in particular the different material properties of masonry compared to reinforced concrete. A first approach for future application is represented by the equations presented here for the determination of the shear force capacity of RM beams. The verification is performed through a comparison of the shear resistances determined experimentally (exp.) and by calculation (calc.).

Reliability of masonry walls subjected to in‐plane loading: A slip failure along head joints / Zuverlässigkeit von Mauerwerkswänden bei Belastung in der Ebene: Versagen entlang der Stoßfugenflucht

AbstractMasonry structures are a sustainable, economical and traditionally widely used type of construction. However, current masonry design codes are rather conservative, so there is a growing need for revision i.e. calibration of safety factors to improve the allocation of material resources. In this paper, we investigate the probability of occurrence of slip failure along head joints (perpends) in masonry subjected to in‐plane loading. An appropriate limit state function is established and the masonry material properties and loads are defined as random variables in order to simulate likelihood of occurrence of a slip failure regime along the head joints. Furthermore, an example of masonry wall with probabilistic analysis outcomes using Monte Carlo simulation is presented and recommendations for further work are provided.

In-Plane Shear Behavior of Traditional Masonry Walls

ABSTRACTThe evaluation of the material properties of masonry built with traditional lime mortar remains largely unclear to what extent the complex mechanical behavior of its constituents and sampling difficulties. This article presents the experimental results of a research project carried out on the four unreinforced masonry (URM) walls with four different types of lime mortars used in the Roman and Byzantine periods under shear-compression. Besides, an elasto-plastic damage (EPD) approach is adapted calibrating the parameters of Oliver’s damage model and the modified von-Mises yield criterion for the masonry constituents. For the modeling purposes, a new fictitious joint material approach is introduced to describe the constitutive behavior of both mortar and mortar-brick interface. The proposed approach can be useful to describe the behavior of mortar and mortar-unit interface in existing masonry structures.

Material properties of existing unreinforced clay brick masonry buildings in New Zealand

The material properties of New Zealand’s heritage clay brick unreinforced masonry (URM) buildings were investigated and are reported herein. Material data was collected from a total of 98 New Zealand clay brick URM buildings and a database was compiled that was comprised of various masonry material properties. The intention behind the reporting of information and data presented herein was to provide indicative values to the professional engineering community to aid as preliminary input when undertaking detailed building assessments for cases where in-situ testing and brick and mortar sample extraction are not feasible. The data presented is also used to support the relationships for URM material properties that have been recommended by the authors for incorporation into the next version of the NZSEE seismic assessment guidelines for URM buildings. Although researchers from Europe, USA, India and Australia have previously studied the material properties of clay brick unreinforced masonry, knowledge on New Zealand URM material properties was poor at the time the study commenced. Therefore, a research programme was undertaken that was focused on both in-situ testing and laboratory testing of samples extracted from existing New Zealand clay brick URM buildings.

Study on Homogenization Process of Masonry Using Numerical Simulation Based on Periodic Boundary Conditions

The homogenization technique has been used to derive equivalent material properties of masonry for many years, however, very few studies by most previous researchers concerntrated on the strain state of RVE, which is very important to calculate the equivalent material properties in the finite element modeling. In this paper, periodic boundary conditions is established automatically with the python re-development produce in ABAQUS environment, and is used to simulate the stress-strain relationship of RVE in different load cases based on ABAQUS. Equivalent elastic constants is derived and make a contrast to other researchers. The results indicated that the periodic boundary conditions derived in this article is feasible, and a reference is made for the finite element modeling of RVE.

Debonding resistance of FRP-to-clay brick masonry joints

Debonding at the FRP-to-masonry interface has been identified as the preferred failure mechanism in fibre-reinforced polymer (FRP) retrofitted masonry as it allows for some redistribution of forces. The results of 14 FRP-to-masonry bond tests are presented, where the FRP was near surface mounted (NSM) to stack-bonded clay brick masonry. These tests were conducted to investigate the effect that variables such as cyclic loading and FRP strip dimensions have on the debonding resistance of a NSM FRP-to-masonry joint. These results were then incorporated into a large database of FRP retrofitted masonry pull test results by various researchers over the past 10years. The database includes results for both externally bonded (EB) and NSM retrofitting techniques. From this database, local bond–slip parameters such as the maximum interface shear stress, τmax, and the maximum slip, δmax, were investigated to determine correlations between these values and masonry material properties. Further, 15 existing concrete and masonry bond strength (maximum load at the FRP-to-substrate interface) models in the literature were assessed for their use with masonry by comparing these models against the results in the pull test database. Based on the comparative statistics of the test-to-predicted bond strength it is concluded that a new FRP-to-masonry bond model is required which gives more accurate predictions. Results include a discussion on the global load–slip response and FRP-to-masonry interface behaviour.

In-situ testing of a low intervention NSM seismic strengthening technique for historic URM buildings

Due to the poor seismic performance of unreinforced masonry (URM) buildings there is a need for a cost effective minimally-invasive seismic retrofit technique. Most research considering out-of-plane seismic retrofit of URM walls has been conducted using laboratory-based studies with well defined but artificial boundary conditions, using constituent construction materials that attempt to simulate the material properties of masonry found in historic URM buildings. Thus, in-situ testing of retrofitted URM walls is required to provide data with which to validate the accuracy of laboratory-based studies. An experimental campaign was executed to investigate the performance of a near-surface mounted (NSM) carbon fibre reinforced polymer (CFRP) seismic retrofit solution. This campaign involved testing of five masonry walls loaded out-of-plane in four different buildings located in New Zealand. Testing confirmed that the CFRP retrofit technique is an excellent minimally-invasive and cost effective option for seismic strengthening of URM buildings. Details of the history of the buildings, and the methods used to undertake the field tests are reported, and experimental results are presented.

Prediction of fragment size and ejection distance of masonry wall under blast load using homogenized masonry material properties

The fragment hazard resulting from a nearby explosion is a major concern in the design of structures which may be subjected to blast loads. This paper presents a predictive method based on the theories of continuum damage mechanics and mechanics of micro-crack development, and numerical simulation to determine the probabilistic fragment size distribution and the launch distances. Theoretical derivations are presented to calculate fragment distribution. The fragmentation process is modeled according to the crack initiation and propagation, which depend on the material damage levels and are estimated using continuum damage mechanics theory. The proposed method involves two steps. First a finite element model is developed to estimate the material damage, fragment distribution and the ejection velocity. Then a simple algorithm is used to predict the fragment trajectory and the launch distance based on the fragment size and the ejection velocity. A masonry wall is used as an example in this study. The wall is modeled with both the distinctive consideration of the brick and mortar material properties and the homogenized masonry material properties. The reliability and efficiency of using the homogenized masonry material model in predicting the masonry wall damage and fragmentation are proven. The program AUTODYN is used in this study to conduct the numerical simulations with the proposed models linked to it as user subroutines. The numerical results indicate that the masonry fragments approximately follow the Weibull distribution, which is consistent with some empirical fragment distributions. The proposed method avoids using erosion technique, which inevitably results in a loss of fragment mass, and avoids discretizing the structure into particles or predefining the failure planes, which may lead to unrealistic prediction of damage propagation and evolution and therefore inaccurate fragmentation process and fragment size distributions.

Numerical derivation of homogenized dynamic masonry material properties with strain rate effects

Masonry is a composite material composed of bricks and mortar disposed in a regular arrangement. It is commonly used as load bearing or partition walls in building structures. Owing to limitations of computer power, detailed distinctive modelling of brick and mortar of a realistic masonry structure or a structure with masonry infilled walls is usually not possible. Moreover, no dynamic masonry material model can be found in the open literature. Dynamic masonry material properties are important for an accurate prediction of masonry failure and fragmentation under dynamic loads. In this paper, a continuum damage model with strain rate effect is developed for masonry materials based on the homogenization method. The equivalent elastic properties, strength envelope and dynamic increase factors (DIFs) of strength and moduli for the homogenized masonry material are numerically derived from the simulated responses of a representative volume element (RVE). A numerical model of an RVE is analyzed with detailed distinctive modelling of brick and mortar with their respective dynamic material properties obtained from laboratory tests. The homogenized material model can be used to analyse large-scale masonry structures subjected to dynamic loading.

Numerical derivation of averaged material properties of hollow concrete block masonry

The homogenization technique has been used to derive equivalent material properties of masonry units for many years. However, most previous research work has concentrated on the derivation of equivalent material properties of a solid brick masonry structure. Very few studies have been conducted to investigate the complex mechanical properties of a hollow concrete block masonry unit. In this paper, numerical simulations of laboratory tests are conducted to derive the equivalent material properties of a three-dimensional basic cell of hollow concrete block masonry. A double scalar damage model based on the concept of continuum damage mechanics is applied to modeling the failure of mortar joint and concrete. In the numerical model of the basic cell, the hollow concrete block and mortar with their nonlinear material properties are modeled in detail. By applying various displacement boundaries to the basic cell surfaces to simulate the displacement-controlled laboratory tests, the averaged stress and strain of the basic cell under different stress states are derived numerically. The homogenized or equivalent material properties of the hollow concrete masonry are determined from the averaged stress and strain relations of the basic cell. To check the validity of the derived equivalent material properties, the dynamic response and damage of a hollow concrete masonry panel subjected to airblast loading is modeled with the equivalent material properties or with the distinctive mortar and brick properties. The efficiency and accuracy of using the derived equivalent material properties in numerical modeling of hollow concrete brick masonry are demonstrated.

Evaluation of the Structural Safety of Historical Masonry Buildings

Structural stability problems due to the formation of cracks and local collapses are the governing criteria for the structural safety of historical masonry buildings. The character of these cracks can be studied by numerical analysis. Analytical studies of the structural preservation of historical structures have two aspects. Firstly, structural demand should be determined by a decisive structural analysis. Second, the strength capacity of the structural elements must be evaluated. A comparison of these two concluding stages results in the determination of the “ratio of safety.” In this paper, several steps of analytical study are proposed to evaluate the safety level of historical structures. Structural demand of any given structure can be determined by using finite element analysis, which can be used to single out the vulnerable parts of the structure. Then, an analytical method can be derived to calculate the strength capacity of these structural elements. In this method, the interaction relationship between bending moment and the axial force is generated by using the material properties of masonry. To illustrate the methods, a case study is performed on the Yivli Minaret in Antalya, Turkey, originally part of a Byzantine church converted into a mosque in 1230, and one of the oldest examples of multicupola construction in Anatolia.