Behavior Of Masonry Structures Research Articles

Photoelasticity and DIC as optical techniques for monitoring masonry specimens under mechanical loads

To evaluate the complex behaviour of masonry structures under mechanical loads, numerical models are developed and continuously implemented at diverse scales, whilst, from an experimental viewpoint, laboratory standard mechanical tests are usually carried out by instrumenting the specimens via traditional measuring devices. Extracted values collected in the few points where the tools were installed are assumed to represent the behaviour of the whole specimen but this may be quite optimistic or approximate. Optical monitoring techniques may help in overcoming some of these limitations by providing full-field visualization of mechanical parameters. Photoelasticity and the more recent DIC, employed to monitor masonry columns during compression tests are here presented and a lab case study is compared listing procedures, data acquisitions, advantages and limitations. It is shown that the information recorded by traditional measuring tools must be considered limited to the specific instrumented points. Instead, DIC in particular among the optical techniques, is proving both a very precise global and local picture of the masonry performance, opening new horizons towards a deeper knowledge of this complex construction material. The applicability of an innovative DIC procedure to cultural heritage constructions is also discussed.

Methods and Challenges for the Seismic Assessment of Historic Masonry Structures

ABSTRACTDespite the high vulnerability of historic structures to earthquakes, the approaches for evaluating seismic demand and capacity still appear inadequate and there is little consensus on the most appropriate assessment methods to use. To develop an improved knowledge on the seismic behavior of masonry structures and the reliability of analysis tools, two real-scale specimens were tested on a shake table, and several experts were invited to foresee failure mechanism and seismic capacity within a blind prediction test. Once unveiled, experimental results were simulated using multi-block dynamics, finite elements, or discrete elements. This article gathers the lessons learned and identifies issues requiring further attention. A combination of engineering judgment and numerical models may help to identify the collapse mechanism, which is as essential as it is challenging for the seismic assessment. To this purpose, discrete modeling approaches may lead to more reliable results than continuous ones. Even when the correct mechanism is identified, estimating the seismic capacity remains difficult, due to the complexity and randomness of the seismic response, and to the sensitivity of numerical tools to input variables. Simplified approaches based on rigid body dynamics, despite the considerable experience and engineering judgment required, provide as good results as do advanced simulations.

An Investigation of the Seismic Behaviour of an Ancient Masonry Bastion Using Non-Destructive and Numerical Methods

Determining the structural behavior of masonry structures is a challenge due to their lack of homogeneity. The seismic behavior of masonry structures is especially complex. The aim of this study was to examine the structural behavior of Zaganos Bastion using both experimental and numerical methods. The Operational Modal Analysis technique, including the Enhanced Frequency Domain Decomposition Method, and the Stochastic Subspace Identification Method were used to illustrate experimentally the dynamic characteristic of the bastion. A finite element model was developed using ANSYS software in order that the dynamic characteristics of the bastion, including natural frequencies and mode shapes, could be calculated numerically. Seismic analysis was carried out using the 1999 Kocaeli earthquake ground motion record to determine the linear and nonlinear seismic behavior of the bastion. The Turkish Earthquake Code and its general technical specifications were used to evaluate the seismic results. The results show that the maximum and minimum principal stresses exerted on the masonry components exceeded the code requirements at some points, but in general the requirements for the stresses were satisfied.

Discrete element modeling of masonry structures: Validation and application

The failure mechanism and maximum collapse load of masonry structures may change significantly under static and dynamic excitations depending on their internal arrangement and material properties. Hence, it is important to understand correctly the nonlinear behavior of masonry structures in order to adequately assess their safety and propose efficient strengthening measures, especially for historical constructions. The discrete element method (DEM) can play an important role in these studies. This paper discusses possible collapse mechanisms and provides a set of parametric analyses by considering the influence of material properties and cross section morphologies on the out of plane strength of masonry walls. Detailed modeling of masonry structures may affect their mechanical strength and displacement capacity. In particular, the structural behavior of stacked and rubble masonry walls, portal frames, simple combinations of masonry piers and arches, and a real structure is discussed using DEM. It is further demonstrated that this structural analysis tool allows obtaining excellent results in the description of the nonlinear behavior of masonry structures.

Theorems for masonry solids with brittle time-decaying tensile limit strength

In this paper, we introduce a phenomenological model approximating the behaviour of masonry structures, which is based on a low-tension elastic–brittle (EB) assumption with evolutionary tensile behaviour. The EB model is conceived by embedding a decaying tensile strength in the material behaviour, and it is able to achieve good agreement with the real behaviour of masonry. Since the model is quite sophisticated, non-holonomic, and the EB solution depends—amongst other things—on the loading path, it is worthwhile to investigate the relationships with more manageable and stable models rather than searching for unreliable solutions that depend on poorly predictable data. Namely, whereas it is quite clear and largely agreed upon that structural models widely applied in engineering (like perfectly plastic or no-tension models or other ones) are well-conditioned problems, the same does not apply to brittle structures. In this case, exact solutions are hard to be found and are scarcely attractive from the engineering point of view since they also depend on the load history and on unverifiable variables such as the local tensile strength. In view of these considerations, in this paper it is proved that stress fields in tensioned EB problems can be approached by highly stable solutions, on the upper and lower sides of the relevant complementary energy, and that the approximation gets closer as the limit tensile strength of the brittle material becomes lower.

Simulation of Shake Table Tests on Out-of-Plane Masonry Buildings. Part (VI): Discrete Element Approach

ABSTRACTAlthough many experimental tests and numerical models are available in the literature, the numerical simulation of the seismic response of existing masonry buildings is still a challenging problem. While the nonlinear behavior of masonry structures is reasonably predictable when the out-of-plane behavior can be considered inhibited, when the in-plane and out-of-plane responses coexist and interact, simplified models seem unable to provide reliable numerical predictions. In this article, taking advantage of the experimental tests carried out in a shaking table on two masonry prototypes at LNEC, a macro-element approach is applied for the numerical simulations of their nonlinear response. The adopted approach allows simulating the nonlinear behavior of masonry structures considering the in-plane and out-of-plane responses. Since it is based on a simple mechanical scheme, explicitly oriented to representing the main failure mechanisms of masonry, its computational cost is greatly reduced with respect to rigorous solutions, namely nonlinear FEM approaches. Two modeling strategies are adopted, namely a regular mesh independent from the real texture of the prototypes and a detailed one coherent with the units disposal. The numerical results are discussed and the correlation between the nonlinear static analyses and the dynamic response is provided.

A preliminary approach of dynamic identification of slender buildings by neuronal networks

The study of the dynamic behavior of slender masonry structures is usually related to the preservation of the historic heritage. This study, for bell towers and industrial masonry chimneys, is particularly relevant in areas with an important seismic hazard. The analysis of the dynamic behavior of masonry structures is particularly complex due to the multiple effects that can affect the variation of its main frequencies along the seasons of the year: temperature and humidity. Moreover, these dynamic properties also vary considerably in structures built in areas where land subsidence due to the variation of the phreatic level along the year is particularly evident: the stiffness of the soil–structure interaction also varies. This paper presents a study to evaluate the possibility of detecting the variation of groundwater level based on the readings obtained using accelerometers in different positions on the structure. To do this a general case study was considered: a 3D numerical model of a bellower. The variation of the phreatic level was evaluated between 0 and −20m, and 81 cases studies were developed modifying the rigidity of the soil–structure interaction associated to a position of the phreatic level. To simulate the dispositions of accelerometers on a real construction, 16 points of the numerical model were selected along the structure to obtain modal displacements in two orthogonal directions. Through an adjustment by using neural networks, a good correlation has been observed between the predicted position of the water table and acceleration readings obtained from the numerical model. It is possible to conclude that with a discrete register of accelerations on the tower it is possible to predict the water table depth.

Lateral load testing of an existing two story masonry building up to near collapse

Laboratory testing, although necessary to understand failure mechanisms of individual masonry walls, spandrels or small scale building models, cannot fully mimic the real system behavior of masonry structures. In order to observe the performance of an existing two story masonry structure, cyclic lateral load testing up to near collapse was conducted. The test building was sliced approximately in the middle through the reinforced concrete slabs of both stories and one side was strengthened with the objective of obtaining a strong reaction wall. The other side of the structure was taken as the test structure with a floor plan of approximately 10 m × 10 m. Hydraulic actuators attached at the slabs of both stories were employed to impose one way cyclic displacement excursions. Flexural and shear deformations on a number of walls were measured and crack propagations were monitored. The structure was tested up to a lateral strength drop of approximately 20 % from the ultimate load, which occurred at a drift ratio of about 0.60 %. The failure of the walls in the building, which were mostly failed in a diagonal tension mode, was concentrated on the first story. Results of this valuable test provide important data on the performance of an actual masonry building and were employed to assess the applicability of various stiffness and strength and simplified load-deformation models in the literature.

Examine the Possibility of Increasing the Size of Openings According to Seismic Behavior of Masonry Structures Isolated with Sliding Layer Compared with the Fixed Structures Under Naqan Earthquake

Masonry buildings have a large share in the context of large and small towns, For example, in the city of Bam more than 90 percent of the buildings with brick and masonry structures, which are about 40% of the amount of masonry structures. According to reports, all masonry buildings are damaged in the earthquake of 20 to 100 percent. Research shows that the bulk of the damage to buildings caused by non-compliance with the provisions of the Building Regulations 2800, including the opening of the wall, the opening in the wall, resulting space restrictions, the wall of the building and etc. In this paper, a masonry structures under earthquake made great naqan modeling the structures in abaqus software in the form of macro, and the first to be connected and then a layer of sand sliding sought to separate the topside of the use and analyzed them. After this, the effect on the seismic behavior of the proposed system and create havoc in the corners of the openings are possible. Find answers to the two-state system; it is found that the proposed isolation system, while considerably reducing damage, the size of the openings can be considered more of a standard.

Use of Digital Image Correlation to Track Strain Evolution in Compressed Masonry Piers

In order to develop a constitutive material model and to verify its consistency when implemented in a computational code, it is necessary to understand the material and to carry out a comprehensive experimental analysis. This can be a challenging task in the case of composite materials and structures, such as masonry, when using conventional measurements. Strain gauges and allow recording strains at a limited number of discrete points and do not provide sufficient amount of data, thus increasing the cost of the analysis. From that reason a full-field non-contact measurements, such as Digital Image Correlation (DIC), became very popular and valuable for analysis of structures subjected to mechanical loading and precise detection of the onset of strain localization. The presented study deals with tracking the strain localization using DIC in the case of masonry piers loaded by the combination of bending and compression. In such case the strain localizes into more compliant mortar joints while the complete collapse occurs when the masonry blocks fail to transfer tensile stress due to transversal expansion. The obtained data will be used for the validation of a finite element model to predict the behavior of masonry structures.

Improving Seismic Performance of Masonry Structures with Openings by Polypropylene Bands and L-Shaped Reinforcing Bars

AbstractA previous study using a scaled-down model of single-room masonry structures tested on a shaking table has shown that strength may be considerably increased by tying up the masonry walls by polypropylene (PP) bands, wrapping the walls using steel wire mesh, and providing horizontal L-shaped reinforcing bars at corners. The effectiveness of the same economic approaches and their combinations has been studied for similar scaled-down models with proportionate openings representing doors and windows, as a logical further scope of the previous study testing these models on a shaking table. As the presence of openings influences the crack and damage propagation leading to failure, the present study may give a more realistic picture of the seismic behavior of masonry structures with openings. Experiments have shown that PP bands were more effective than horizontal L-shaped reinforcing bars in arresting cracks and preventing collapse of the models, even those severely damaged. Further, the most important ...

Computational Methods for Masonry Vaults: A Review of Recent Results

The present paper makes a critical review of some methods and models, now available in the technical litera-ture and commonly used in the analysis of masonry vaults up to their collapse, by highlighting advantages and drawbacks of each approach. All methods adopted to describe the mechanical behavior of masonry structures, in order to be reliable, must take into account the distinctive aspects of masonry, namely the scarce (or zero) tensile strength, the good resistance in compression and the occurrence of failure mechanisms through rotation-translation of rigid macro-blocks. Classic no-tension material models disregard the small existing tensile strength and make the assumption of (1) infinitely elastic be-havior in compression and (2) isotropy, giving thus the possibility to deal with either semi-analytical approaches (espe-cially for arches) or robust numerical procedures. More advanced but rather complex models are nowadays able to deal al-so with anisotropy induced by texture, small tensile strength and softening in tension, as well as by finite strength in com-pression. Traditionally – and nowadays it is still an opinion commonly accepted, in contrast with step by step complex procedures, Limit Analysis has proved to be the most effective Method for a fast and reliable evaluation of the load bear-ing capacity of vaulted masonry structures: classic lower and upper bound theorems recall respectively the concepts of equilibrium and occurrence of failure mechanisms with rigid elements. The so-called Thrust Network Method moves its steps from lower bound theorems, whereas FE limit analysis approaches with infinitely resistant elements and dissipation on interfaces take inspiration from the upper bound point of view. An alternative to Limit Analysis is represented by tradi-tional FEM combined with either elastic-plastic or damaging models with softening, commonly used for other materials but recently adapted also to masonry. They are able to provide a large set of output numerical information but further studies are still needed to ensure their proper application.

Simulations of FRP reinforcement in masonry panels and application to a historic facade

The aim of the paper is to propose and assess a simplified FE modeling strategy to simulate the global behavior of masonry structures externally reinforced with FRP composite strips applied with a grid configuration and anchored properly at their ends.The nonlinear behavior of the masonry is represented by a mascroscopic smeared crack approach. The FRP strips are simulated by using simple nonlinear truss elements kinematically compatible with the finite element mesh of the masonry under the hypothesis of perfect adhesion. A two-step procedure is followed. First, the comparisons with the experimental results on in-plane loaded masonry panels reinforced with CFRP and GFRP strips validate the approach. Next, the in-plane seismic behavior of the main facade of Camponeschi Palace, a building of historical importance located in the city of L’Aquila (Italy), is used as a realistic example to evaluate the proposed approach for large masonry systems. The obtained results show that the model is able to capture fairly well the damage scenario induced by the 2009 L’Aquila earthquake. The effects of the FRP reinforcement on the in-plane behavior of the facade are presented and discussed.

Experimental study of masonry wall exposed to blast loading

The challenge of protecting the nation against the attack of terrorism has raised the importance to explore the understanding of building materials against the explosion. Unlike most of the building materials, brick masonry materials offer relatively small resistance against blast loading. In this research, a brick masonry wall was exposed to varying blast load at different scaled distances. Six tests with different amounts of explosives at various distances were carried out. Pressure time history, acceleration time history and strain at specific location were measured. The parameters measured from experimental pressure time history and acceleration time history is compared with those determined by ConWep to establish the correlations between experimental determined records and ConWep values. The experimental results were also compared with some researchers. These correlations may assist in understanding the behaviour of masonry structures subjected to explosive loading.

The Effect Of Earthquake Characteristics On TheCollapse Of Historical Masonry Buildings:Case Study Of The Mosque Of TakiyyaAl-Sulaymaniyya

Different factors influence the collapse behaviour of masonry structures, and one of the major factors is the characteristics of the earthquake itself. This effect is going to be more complicated for historical constructions, which involve different structure members with different geometries. The present study focuses on the effect of earthquake characteristics on the collapse behaviour of historical masonry structures. The effect of earthquake direction and the frequency content of the earthquake are discussed. A brief background of the selected case study and modelling process are given first, and the geometry of the whole structure is created where micro modelling strategy is employed. The collapse analysis of the structure is performed under an artificial model based on the earthquake characteristics. Unidirectional earthquakes are applied to the structure from different angels in order to investigate the weakest situation. Finally, different earthquake models are generated with different frequency contents according the soil profiles and applied consequently on the structure to explore the worst situation.

Modeling and numerical analysis of the bond behavior of masonry elements strengthened with SRP/SRG

Steel Reinforced Polymers (SRPs) and Steel Reinforced Grout (SRG) strengthening systems have been recently introduced as an alternative solution to the traditional systems based on the use of fiber reinforced polymers materials (FRPs). Few studies on SRP/SRG are available in the current literature and all have shown the potentialities of SRP/SRG in improving structural performances of masonry and concrete elements and, at the same time, their difference with respect to FRPs particularly in terms of bond behavior. Aim of the present paper is to propose a simple approach devoted to study the bond behavior of masonry structures strengthened with SRP/SRG systems. The approach, based on experimental evidences and theoretical considerations mainly consists of deriving approximate bond stress-slip laws for the strengthening/support interface layer, able to reproduce the local bond stresses transferring mechanism. Finite Element (FE) analyses are then developed with reference to the experimental tests available in the current literature by adopting the bond stress-slip laws obtained through the proposed approach. The deduced results show the reliability of the proposed approach in simulating the bond behavior of masonry elements strengthened with SRP/SRG and the possibility to investigate further peculiarities characterizing this kind of strengthening systems.

Behavior of clay hollow-brick masonry walls during fire. Part 1: Experimental analysis

Understanding the behavior of masonry structures when exposed to fire and predicting their fire-resistance is a major need that has been expressed by brick manufacturers. Whereas clay brick masonry is widely used because of its thermal and sound insulation performance; fire-resistance is certainly its weakness if improper design methods are used.These design methods require prior exhaustive experimental tests, which should not be limited to evaluating standard fire-resistance as a global standard criterion but should also permit a detailed analysis of the thermo-mechanical behavior of masonry walls.In this paper, four wall-tests are presented to illustrate the behavior of clay masonry walls during fire. Selected wall-tests are generically representative of the overall results obtained during a more extended experimental campaign.The experimental results are presented and analyzed with regard to the risk of spalling on the fire-resistance of masonry. The analysis contains a detailed investigation of temperature, deformation and local mechanical degradation phenomena in the tested walls.Finally, the study is concluded by summarizing end-point parameters that significantly control the fire-resistance of clay masonry walls and deserve consideration in any modeling approach.

Mechanical Properties and Freeze-Thaw Durability of Strengthening Mortars

An innovative experimental procedure is described that is used as a preliminary design stage for the pre-qualification of strengthening mortars applied to historical masonry buildings. In the analysis of the behavior of masonry structures and their constituent materials, increasing importance has been assumed by the study of the long-term evolution of deformation and mechanical characteristics, which may be affected by both loading and environmental conditions. Through static and fatigue tests conducted in the laboratory on different dimensional reinforced masonry specimens, it has been possible to investigate the durability of strengthening materials. This methodology is useful to select, from a range of alternatives, the most suitable strengthening mortar for historical masonry, and to avoid the errors associated with materials that are not mechanically compatible. Special attention was devoted to fatigue and thermo-hygrometric aspects, the effects of which on masonry are often significant enough to hinder the validity of repair works. The experimental procedure has been effectively used in the biggest restoration building site in Europe, the Royal Palace of Venaria.

Research on the Basic Mechanical Behavior of Masonry Structure

This paper analyzes the hole and open hole wall without cracking load, crack distribution and the order of appearance. We use MSC.Macr software and two-dimensional four-node element and the constitutive relation proposed masonry. Masonry shear wall is failed criterion for the force and deformation of elastic-plastic finite element analysis, wall cracking load is ultimate shear capacity. The predicted values of cracking load, ultimate shear load-bearing capacity and maximum horizontal deformation of wall agree better with testing results.

Unreinforced Masonry Walls: Nonlinear Finite Element Analysis with a Unified Constitutive Model

This paper presents a unified model for characterizing the behavior of masonry structures. The model is based on the Disturbed State Concept (DSC) with modified hierarchical single yield surface (HISS) plasticity, which is called DSC/HISS-CT and which is used to simulate the behavior of masonry structures. The model uses two HISS yield surfaces for compressive and tensile behavior. The proposed constitutive model is verified by comparing numerical predictions with results available from test data; the comparisons are found to be highly satisfactory. A new explicit formula is also presented to estimate the strength of unreinforced masonry structures.