Unreinforced Masonry Shear Walls Research Articles

Accuracy of stochastic finite element analyses for the safety assessment of unreinforced masonry shear walls

ABSTRACT To examine structural safety and reliability, an accurate prediction of the variability of structural resistance must first be determined. This may be achieved through extensive physical testing or, more commonly in modern research, synthetic data generation, such as stochastic finite element analyses (SFEAs). Due to the prevalence and versatility of such techniques, and the need for a high level of confidence when performing a safety assessment, an understanding of the accuracy of data derived from SFEAs is essential. In this paper, SFEA models have been developed to predict the responses of 16 unreinforced masonry walls tested in a laboratory under cyclic in-plane lateral loading. Each SFEA has been developed to reflect the as-built conditions of these experimental specimens and focus on predicting the shear capacity of the failure mechanisms that unreinforced masonry shear walls are susceptible to. From the results of these SFEAs, the accuracy (quantified as model error) of this modelling strategy has been estimated by comparing the peak in-plane shear resistances of the laboratory and numerical models.

Evaluating the Role of Mortar Composition on the Cyclic Behavior of Unreinforced Masonry Shear Walls.

The mechanical behavior of unreinforced masonry (URM) shear walls under in-plane cyclic loading is crucial for assessing their seismic performance. Although masonry structures have been extensively studied, the specific influence of varying lime content in cement-lime mortars on the cyclic behavior of URM walls has not been adequately explored. This study addresses this gap by experimentally evaluating the effects of three mortar mixes with increasing lime content, 1:0:5, 1:1:6, and 1:2:9 (cement:lime:sand, by volume), on the cyclic performance of brick URM walls. Nine single-leaf wall specimens 900 mm × 900 mm were constructed and subjected to combined vertical compression and horizontal cyclic loading. Key parameters such as drift capacity, stiffness degradation, and energy dissipation were measured. The results indicated that the inclusion of lime leads to a moderate improvement in drift capacity and ductility of the walls, with the 1:1:6 mix showing the highest lateral capacity (0.55 MPa), drift at cracking (0.08%), and drift at peak capacity (0.31%). Stiffness degradation and energy dissipation were found to be comparable across all mortar types. These findings suggest that partial substitution of cement with lime can enhance certain aspects of masonry performance. Further research is recommended to optimize mortar compositions for unreinforced masonry applications.

Wavelet technique and FEA for modal identification in damaged URM shear walls

In existing masonry buildings, the structural capacity with respect to horizontal actions is due to the in-plane response of shear walls, usually evaluated in terms of effective stiffness and drift capacity. The objective of this work is to provide first results to the damage sensitivity in diagonal cracking of URM shear walls and a study methodology based on vibration tests to assess the structural health of existing masonry buildings. The state of pre-existing discontinuities caused by previous damage events or material degradation may play a role in the in-plane response of shear walls. For this, an experimental campaign was carried out on three typologies of UnReinforced Masonry (URM) walls, simulating different damage situations, subjected to Shear-Compression (SC) and vibration tests in order to correlate the structural behaviour with changes in modal parameters. From the vibrational response acquired during the SC test, the modal parameters related to the pre-damage and post-damage condition were identified using the Continuous Wavelet Transform identification technique. The experimental results are then used to implement a Finite Element Model (FEM) with a 2D homogenization approach to simulate the behaviour of URM walls. A parametric study through FEM analysis is carried out in order to investigate the change in modal parameters for different damage configurations and for triggering strut mechanisms.

A New Macro-Element for Predicting the Behavior of Masonry Structures under In-Plane Cyclic Loading

A new macro model for the finite element modeling of unreinforced masonry (URM) exhibiting in-plane nonlinear cyclic behavior is proposed. The ultimate objective is to predict the seismic response of multi-story URM buildings. The macro model enables the modeling of URM shear walls with a limited number of degrees of freedom (DOF) at low computation times. The macro model consists of a deformable elastic frame supported by diagonal struts with nonlinear behavior aiming to capture all dissipative phenomena occurring during seismic events. The nonlinear constitutive behavior of diagonal struts is inspired by models documented in the literature, ensuring a robust foundation for the proposed approach. This paper first provides a comprehensive review of the principal models currently available for URM analysis. It then articulates the rationale behind the development of this new numerical model, aiming to address the limitations encountered in existing methodologies and to offer a simple and fast tool for predicting the seismic behavior of URM buildings. Afterward, the new model is presented and tested with the simulations of two experimental campaigns performed on different URM walls. The comparison between experimental and numerical results shows that with a limited number of DOF and parameters, it is possible to obtain a prediction of the experimental results with satisfying accuracy.

The influence of regular openings and pre-compression loading on the in-plane strength parameters of unreinforced masonry shear walls

The influence of regular openings and pre-compression loading on the in-plane strength parameters of unreinforced masonry shear walls

A macro‐element with bidirectional interaction for seismic analysis of unreinforced masonry walls

AbstractPrior to implementing retrofitting measures for seismic action, it is necessary to evaluate the global capacity of unreinforced masonry (URM) buildings. Even with simplified assumptions, equivalent frame (EF) modeling adequately captures global responses and failure mechanisms in existing buildings, making it a popular modeling strategy among structural engineers. However, macro‐elements employed in the EF modeling of URM walls consider in‐plane (IP) and out‐of‐plane (OP) behaviors separately by decoupling their interaction and require independent verification for OP failure involving limit analysis. Such decoupling of interaction is justifiable if proper wall‐wall/wall‐floor connections and rigid‐diaphragm action of slabs are ensured; however, OP failure is likely a result of inadequate connections. Multiple components of ground motion excitation and plan eccentricity in buildings can activate bidirectional interaction in such circumstances. Due to OP damage, the interaction reduces the full IP strength of a URM wall, resulting in overestimating its lateral capacity. This paper proposes a frame‐like 3D macro‐element incorporating the effect of OP action on the IP shear response of URM piers under static and monotonic lateral loads. Only two parameters modifying IP shear stiffness and capacity are required to account for the interaction. Analytical expressions for the interaction parameters are proposed from a detailed micro‐modeling study. The paper also demonstrates, within the EF modeling, the applicability of the proposed macro‐element for seismic analysis of regular URM shear walls with openings.

Application of stochastic numerical analyses in the assessment of spatially variable unreinforced masonry walls subjected to in-plane shear loading

This paper develops a modelling strategy for the finite element analysis of perforated (arched) unreinforced masonry walls subjected to in-plane shear loading. An experimental baseline was used to facilitate an accurate calibration and assessment of the chosen modelling strategy. This study provides the procedure and the results relevant to a stochastic assessment of unreinforced masonry shear walls. These results may be used in future studies of the reliability of these structures and may be applied in the calibration of reliability-based design practices. Utilising a two-dimensional micro-modelling approach, the capacity of a monotonic loading scheme to capture the envelope of a cyclically applied load was examined. It was found that, while the elastic stiffness of the laboratory specimens was overestimated by the finite element models, the peak load and global response was accurately recreated by the monotonically loaded models. Once the applicability of this procedure had been established, a series of spatially variable stochastic finite element analyses were created by considering the stochastic properties of key material parameters. These analyses were able to estimate the mean load resistance of the experimentally tested walls with a greater accuracy than a deterministic model. Furthermore, these analyses produced an accurate estimate of the variability of shear capacity of and the observed damage to the laboratory specimens. Due to the fact that the tested walls failed almost exclusively in a rocking mode, a failure mechanism highly dependent upon the structures’ geometry, the variability of the peak strength was minimal. However, the observed damage and presence of some sliding and stepped cracking indicates that the proposed methodology is likely to capture more variable and unstable failure modes in shear walls with a smaller height-to-length ratio or those more highly confined.

Effects of Lateral Constraints and Geometrical Characteristics on Deformation Capacity of the Persian Historic Unreinforced Masonry Shear Walls under Uncertainty Conditions

In the most structural codes, deformation capacity of the unreinforced masonry shear walls is estimated based on their structural behavior(failure mode) and aspect ratio. In this paper, deformation capacity was determined for the Persian historic brick masonry walls by considering the effects of various parameters such as lateral constraints, aspect ratio and thickness. Also, to take into account the uncertainties in material and geometry of the walls in their deformation capacity, partial factor γdu was proposed, somehow, deformation capacity of shaer wall is determined by multiplying this factor in the computed deformation. Accordingly, the in-plane behavior of 48 different specimens of masonry walls with four lateral constraint configurations (contribution of transverse walls and also top slab), four distinct aspect ratios(height to length) of 0.5, 0.75, 1.0 and 1.5, three traditional wall thicknesses of 0.20, 0.35 and 0.50 m, under pre-compression load of 0.10 MPa were computed using nonlinear pushover analyses. Then, the obtained force-deformation curves were idealized by bilinear curves (linear elastic – perfectly plastic) to make them easier for comparison objectives as well as to be more adopted in practical purposes. The latter results indicated that deformation capacity of the shear walls decreases by stiffer lateral constraints, more thickening; and decrease in height-to-length aspect ratio. In addition, it was observed that the transverse walls (vertical constraints on two sides, and at two ends of the base shear walls) were more efficient in reducing deformation capacity than the top slab (horizontal constraint). As a result, according to the numerical calculations, the ultimate drift value for the Persian historic brick masonry walls determined between 1.3% and 2.7%. Eventually, the partial factor of γdu to consider uncertainty in modulus of elasticity and thickness assessment in deformation capacity of the Persian historic masonry shear walls achieved in the range of 1.3 to 1.7.

Polypropylene as a Retrofitting Material for Shear Walls

In recent years, on account of their excellent mechanical properties, composite materials (made of epoxy-bonded carbon, glass, or aramid fibers) have been used to reinforce masonry walls against in-plane actions. These materials have proven to be an effective solution for the strengthening of unreinforced masonry (URM) walls. Lately, research has shifted to the study of different types of fibers to avoid the use of epoxy adhesives, whose long-term behavior and compatibility with masonry are poor. This paper describes an experimental program that investigated the behavior of URM shear walls strengthened with two types of commercially available polypropylene products: short fibers (fiber length = 12 mm) and polypropylene nets. This investigation aimed to evaluate the influence of polypropylene reinforcement, embedded into an inorganic matrix, in terms of the improvement of the lateral load-carrying capacity, failure mechanism, ductility, and energy dissipation capacity of URM wall panels, where nine walls were subjected to in-plane loads using a racking test setup. The study showed that using two layers of polypropylene fibers embedded into a cementitious matrix greatly increased the in-plane load capacity of the brickwork masonry. On the other hand, the test results indicated that polypropylene nets, used as a repair method for cracked shear walls, cannot improve the structural performance of the walls.

Bestimmung des Teilsicherheitsbeiwerts für Wandscheiben aus unbewehrtem Mauerwerk

AbstractPartial safety factors for resistance applied in the design equation of semi‐probabilistic formats can be obtained from the evaluation of a test database. These partial safety factors are influenced by two factors, the material uncertainty and the model uncertainty. This topic is covered in a former publication [1]. It includes the determination of a partial factor for the model uncertainty of unreinforced masonry shear walls. In this study the authors examine the next step, and calculate the partial factor of resistance applying the same method, as recommended i n EN 1990 – Annex D. In addition to the Coefficient of Variation (COV) for the model uncertainty, the calculation of the resistance partial factor considers deviations in geometry, as well as loading and material properties. The influence of the material uncertainty on structural performance is considered in the calculation by means of a weighted average of all COV values for various types of material properties, based on the number of relevant failure modes in the test database. In the last step, the resistance partial factors for models defined in DIN EN 1996‐1‐1/NA and DIN EN 1996‐1‐1/NA – Annex K are calculated by applying the probabilistic methods recommended in EN 1990 – Annex D and the model bias.

Experimental shear testing of timber-masonry dry connections for the seismic retrofit of unreinforced masonry shear walls

Abstract The mechanical coupling of timber products to the masonry walls of unreinforced masonry (URM) buildings is generating considerable interest in terms of seismic vulnerability mitigation. An extensive experimental investigation on timber panel to masonry wall connections realised with screw anchor fasteners is presented. A total of 64 shear tests under monotonic, cyclic and semi-cyclic loading conditions were performed on site in a historic URM building. The examined parameters were: masonry type, timber panel product and material, load-to-grain direction, fastener geometry and steel grade. The outcomes of the campaign are then reported and discussed focusing on the strength and stiffness properties and on the dissipation capacity and residual strength of the connection under cyclic load. Moreover, a log-normal distribution fitting is proposed for the maximum load and slip modulus measurements of all the cyclic test configurations analysed. Finally, the principal experimental observations are listed along with recommendations for future work or use in practice.

Bestimmung eines Modellteilsicherheitsbeiwertes für unbewehrte Mauerwerkswände unter Knickbeanspruchung

AbstractThe design/verification method in the Eurocodes is based on the partial safety concept. Eurocode 6 suggests a constant partial safety factor for the material γM for all design/verification problems, without consideration of model uncertainty in the design/verification formula. In the following, a model partial safety factor is determined for the problem of unreinforced masonry walls mainly subjected to vertical loading. For that purpose, the newly proposed formula for EC 6, annex G will be considered [1–3]. In order to cover all aspects in tests and to use the results for design purposes, several methods have been included in EN 1990 Annex D for design based on test data. In this study, the recommended methods in Annex D of EN 1990 for resistance of the material are used to extract the partial safety factors. A database including more than 119 experimental tests on unreinforced masonry shear walls is used to compare the model prediction and the test results and to determine the model partial safety factor.

Research of Influence of the Shape of Unreinforced Masonry Shear Walls Made of Calcium Silicate Masonry Units

We performed tests on 6 calcium silicate masonry units which were laid in thin layer mortar with uneven head joints. Walls were divided into two series and denoted by convention as HOS (Jasiński 2016) and HOS-H. Those two series differed in overall dimensions of test elements. Three walls from HOS series had identical external dimensions: l = 4.50 m, h = 2.45 m (h/l = 2.45m/4.50m), and thickness t = 180 mm. The walls were tested at different values of initial compressive stress σc = 0; 0.1; 1.0 and 1.5 N/mm2. The HOS-H elements were prepared as unreinforced test elements with the length l = 2.25 m height h = 2.45 m (h/l = 2.45m/2.25 m) and thickness t=0.18 m, and tested at initial compressive stress equal to σc = 0.1; 0.75; 1.5 N/mm2. The tests showed that the wall shape had a negligible effect on the morphology of cracks and the failure mechanism. An increase in wall length caused a roughly proportional increase in values of cracking and failure stresses. Shorter walls were under considerably greater cracking and failure stresses. An increase in wall length led to a significant decrease in values of shear strain angle regardless of initial compressive stress. The reverse situation occurred at the moment of destruction. Values of shear strain then increased with an increasing length of the wall.

Determination of partial factor for model uncertainty for unreinforced masonry shear walls

AbstractExperiments in structural engineering can play an important role in the prediction and characterization of the material properties and behaviour of structural components. In order to cover all aspects in tests and use the results for design purposes, several methods have been included in EN 1990 Annex D for design based on test data. The calculation of characteristic values and design values for material resistance are the main aspects. In this study, the recommended methods in Annex D of EN 1990 for resistance of the material will be used to extract the partial safety factors for masonry structures based on the formulation of design and characteristic values. A database including more than 100 tests on unreinforced masonry shear walls will be used to evaluate the results. The resistance model for shear walls based on the recommendation in the Eurocode will be compared with the test results. The main aim will be to compare the model prediction and the test results. Deviation of the prediction from the test is caused by model error or model uncertainty. The test database includes results for three types of masonry units – fired clay, calcium silicate and autoclaved aerated concrete. The evaluation of partial factors for masonry shear models will be undertaken based on the scatter and the model bias for the whole database. Further analysis will also be performed for each type of masonry unit for classification of the outcome.

Evaluation of seismic displacement demand for unreinforced masonry shear walls

Unreinforced, non-engineered low-strength brick masonry structures comprise a large percentage of buildings in the Himalayan region and have been extensively damaged in recent earthquakes. Due to t...

On the in-plane shear response of the high bond strength concrete masonry walls

Conventional unreinforced masonry walls subject to in-plane shear loading fail due to exceedance of shear and tensile bond strengths. This paper examines whether or not the in-plane shear capacity of masonry walls would increase with the increase in the bond strengths through experimental and numerical investigations. For these investigations, shear walls were built with high bond strength polymer cement mortar; they were applied in thin layers of 2 mm thickness each. Material tests were carried out to characterise the bond and the compressive strengths of the high bond strength thin layer mortared masonry; the bond strengths were found approximately double that of the conventional 10 mm thick cement mortars. The shear walls, however, exhibited significantly lower capacity (contrasting the expectation) and displayed base course sliding mode of failure. To ascertain the validity of the experimental results, a combined surface contact—interface element micro finite element (FE) modelling technique was formulated; the results adequately reproduced the experimental datasets. The validated FE model was then applied to examine the effect of the aspect ratios and pre-compression levels to the failure modes, deformation and strength of the high bond strength shear walls and is shown that once the pre-compression exceeds 15% of the masonry compressive strength, the base sliding failure mode changes to the diagonal cracking mode with corresponding increase in in-plane shear capacity. Therefore, it is concluded that the increase the bond strength without regard to pre-compression could adversely affect the safety of the high bond strength unreinforced masonry shear walls.

Direct displacement based seismic design for timber flexible diaphragms in masonry shear wall buildings

A method for analyzing the seismic performance of timber flexible diaphragms based on the direct displacement based seismic design (DDBD) principles has been developed. The method utilizes knowledge of timber diaphragm seismic behavior, such as natural period calculation, force–displacement and ductility–damping relationships, developed previously by the authors. Accuracy of the method is illustrated through analysis of four prototype buildings and comparison to recorded data and numerical results. All four prototype buildings have timber diaphragms in conjunction with either reinforced or unreinforced masonry shear walls. Excellent agreement is found between the results from the proposed DDBD approach, and those from both the recorded data and finite element analysis. The proposed method provides a rational and consistent design methodology for flexible diaphragm buildings, which is lacking in ASCE-7.

Reliability Verification of Unreinforced Masonry Wall

Unreinforced masonry (URM) is known as sustainable building material and is on the top of worldwide building materials consumed in residential buildings. The reliability level of a designed URM shear walls (URMW) has major influence on safety and cost of masonry constructions. Assessing the reliability level of different URMW is the purpose of this paper.The verification methods for combination of in-plane shear and compression according to the latest version of German National Annex of Eurocode 6are presented. The design models available in the code are rephrased and direct deterministic equations are introduced to predict the capacity. Limit State and Reliability Verification of URM Wall.On this base, several limit state are established and reliability analysis using crude Monte Carlo method are run. The effect of uncertainty on assessed reliability is highlighted. The distinction between linear and non-linear application of partial safety factors are assessed. The result of reliability analysis, based on the available probabilistic information on material with uncertainty models for designed URMW is presented in the article.The principal results are the actual reliability level found in the study regarding various masonry walls designed according to the latest German National Annex code DIN EN 1996-1-1 /NA: 2012-05 on different load situation. A review on the common target reliability index for structures according to different codes is done and the assessed reliability is compared with the target value.

A simplified model for analysis of unreinforced masonry shear walls under combined axial, shear and flexural loading

A macro-computational model is presented in this study for simulating the nonlinear static behavior of masonry walls. The adopted strategy is based on modeling the nonlinear behavior of masonry elements considering it as an orthotropic material and then extending it with a simple method to masonry walls. The model is capable of considering shear and flexural deformations in the global behavior. It can also predict all possible failure modes in masonry such as compressive crushing, bed-joint sliding, rocking, diagonal tension cracking and diagonal stepped cracking. Suitable material constitutive models and failure criteria are adopted for each failure mode under biaxial stress states. The contact density model has been modified and used for simulating the shear behavior in the masonry joints. It is shown that the analysis results are in good agreement with experimental observations, while the analysis time is significantly lower comparing to the usual numerical approaches such as finite element methods. Moreover, the proposed model can be used as a macro-model for analysis of large structures and provides reasonable accuracy.

Modeling of influence of heterogeneity on mechanical performance of unreinforced masonry shear walls

Most of the existing analytical models for masonry walls were based on the homogeneous tools although masonry was well known as heterogeneous materials. In this contribution, a heterogeneous model was used to simulate the fracture behaviors of masonry wall under shear-compression load. The masonry model was considered as a three-phase composite composed of units, joints and unit–joint interfaces. The mechanical properties of elements were assumed to conform to a given Weibull distribution to reflect the heterogeneity of masonry materials. The fracture process, including crack initiation and propagation, was captured. The influences of heterogeneity of the masonry materials on their fracture behaviors, load–displacement responses and peak loads were analyzed in detail. The numerical results have a general agreement with the experimental investigations.