Drift Capacity Research Articles

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.

Rapid repair of RC columns with post-tensioned external clamps

A recent technique for repair of damaged reinforced concrete (RC) columns is reviewed. The technique involves the application of external post-tensioned clamps. The clamps are composed of steel angles and high-strength steel rods. The pairs of angles are placed on the corners of the cross-section, and they are connected with steel rods to each other. To evaluate the effectiveness of the repair technique, four large-scale RC columns with insufficient transverse reinforcement were subjected to lateral displacement reversals and constant axial load. The tests were conducted in two phases: initial testing of columns with none to light transverse reinforcement, followed by the application of clamps on the damaged columns and further testing. The study focused on the efficacy of the clamps to a) restore the lateral-carrying capacity of damaged RC columns, and b) increase drift capacity. Variations in lateral expansion of the column core and their plausible correlations with damage and ‘repairability’ are examined. Within the conditions investigated, two key requirements are proposed for safe column repair: 1) the concrete in damaged columns with cross-sectional expansion exceeding 1% should be replaced or repaired before clamps are applied as a repair measure, and 2) clamps should be proportioned to resist 100% of the maximum plausible shear demand even though perceptible contributions to shear resistance attributable to the concrete were observed in columns repaired before excessive expansion occurred. In columns with crisscrossing inclined cracks leading to lateral cross-sectional expansion of up to 1%, clamps were observed to provide effective shear resistance comparable to what conventional transverse reinforcement can provide.

HSC-RSW with laterally installed XADAS dampers: Seismic performance

This study investigates the seismic behavior of high-strength concrete (HSC) rocking shear walls (RSW) equipped with X-shape Adding Damping and Stiffness (XADAS) dampers installed perpendicular to the wall via brackets. Unlike previous studies where dampers are integrated along the wall length, this research leverages the advantages of HSC to minimize sectional dimensions while employing laterally installed XADAS dampers to enhance the cyclic response, yielding flag-shaped hysteresis curves. The alignment angle of the XADAS dampers is also considered a crucial variable in assessing the overall seismic performance of the proposed HSC-RSW system. A novel constructional approach using brackets to install lateral XADAS dampers is implemented. Post-tensioning (PT) forces are applied as consistent axial strains in cables, achieved through predefined cable support displacements. A macro-FEM model is developed to validate the chosen experimental reference test and is subsequently used for further parametric studies. The parametric studies indicate that increasing concrete compressive strength (CCS) enhances the self-centering capability by reducing RSW strains and facilitating rocking. Additionally, incorporating XADAS dampers into the system improves energy dissipation, with a zero-degree alignment angle identified as optimal. Notably, the modeled HSC-RSW systems exhibit limited drift capacity (less than 2 %) compared to normal strength concrete (NSC)-RSW systems, where wall toes are conventionally prone to crushing.

Punching and lateral cyclic behavior of concrete slab-column connections reinforced with steel sheets

During an earthquake, slab-column structures with high gravity-shear ratios often experience increased local shear stress and deformation in the connection area, leading to reduced unbalanced moment capacity and drift capacity of the connections. This study aims to create a new and more efficient method of enhancing the unbalanced moment capacity and deformation capacity of reinforced concrete slab-column structures through using steel sheets as punching reinforcement. Tests were conducted to evaluate the effects of the thickness, extension length, and layout of this new type of punching reinforcement on the unbalanced moment capacity and deformation capacity of the connections when subjected to vertical and horizontal cyclic loads. The results indicated that as the steel sheet thickness increased, the unbalanced moment capacity of SC-2 and SC-3 rose by 24 % and 48 % respectively, while the drift capacity improved by 20 % and 40 % compared to SC-1. Furthermore, the failure mode shifted from stress-induced punching to drift-induced punching. Compared to SC-1, a cruciform layout with an additional diagonal arrangement of sheets increased the unbalanced moment capacity and drift capacity by approximately 17 % and 20 %, respectively. The extension length of the sheets reduced from 600 to 420 had negligible effect on the unbalanced moment capacity and deformation capacity. Utilizing experimental data, this study compared the relationship between the drift capacity and gravity shear ratio of connections reinforced with different shear reinforcements. The underlying causes for the observed lower drift capacity of the specimens are analyzed, and design recommendations for optimizing the steel sheets are subsequently proffered. After thoroughly analyzing the experimental results, a simplified calculation methodology for assessing the shear strength of steel sheets was developed, taking inspiration from the shear strength calculation approach outlined in ACI 318–19. The efficacy of this simplified approach was subsequently validated by comparing the experimental results with those predicted by current design codes. Furthermore, by comparing the experimental results with the predicted values, the relationship between the punching failure mode of connections and their punching strength was discussed.

Multi-objective optimization of active control system using population guidance and modified reference-point-based NSGA-II

The optimization of the active control system is pivotal in achieving an acceptable performance level while minimizing control costs. The optimal location of actuators, efficient control force, and adequate vibration reduction are critical objectives in control system optimization. This study introduces a novel optimization algorithm, the Population-Guided and Modified Reference-Point Based Non-Dominated Sorting Genetic Algorithm-II (PMR-NSGA-II), tailored for actuator placement and tuning that incorporates input and output user preference. The analysis focuses on optimizing the vibration control of a 20-story steel frame building. The PMR-NSGA-II could reduce the computational expenses of three objectives optimization by guiding the initial population using prospective population prediction and orienting the search towards a reference point. The pre-calculated input energy distribution guides the determination of the prospective initial population. The reference point, along with the allowable drift and actuator capacity constraints, focuses the search process to efficiently obtain the Pareto fronts with less effort wasted to explore the less preferred areas in the search space. The non-dominated sorting and elitist operators are also employed to fasten the convergence. The structural analysis is conducted via non-linear time history analysis with seven ground motions considered. The PMR-NSGA-II exhibits significant computational efficiency in the active control system optimization. Results demonstrate that PMR-NSGA-II could provide the near-optimal solution closest to the reference point with a smaller population size and a faster convergence rate than the NSGA-II. The computational time per generation of the proposed PMR-NSGA-II is 1.36 to 2.43 times faster than NSGA-II for the seven ground motions analyzed. By applying PMR-NSGA-II, the number of individuals that need to be assessed to reach convergence is reduced by 50 % to 88 % compared to NSGA-II. Ultimately, the near-optimal configurations could significantly reduce the building responses and increase the performance level of the building based on FEMA 356 and ASCE 41 acceptance criteria.

On estimating the drift capacity of reinforced concrete walls with lap splices at their bases

AbstractFailures in reinforced concrete (RC) structural walls have been reported to occur at longitudinal lap splices in earthquakes as far back as 1964 (Kunze et al. in JP 62:635–650, 1965) and as recently as 2023 (Pujol et al. in ES 63:777, 2024). Design codes such as ACI318-19 (2019) and JSCE Standard Specification for Concrete Structures (2007) have been adjusted accordingly and have banned the placement of lap splices near sections where longitudinal reinforcement is expected to yield in reinforced concrete structural walls. But minimizing lap splice vulnerabilities in new construction does not address existing buildings that may be vulnerable to earthquakes because of lap splices placed at or near critical sections. A simple, rapid assessment technique should be adopted to address the large number of existing buildings with potentially vulnerable RC walls. To investigate the deformation capacity of structural walls with lap splices near sections where longitudinal reinforcement yields, a two-part experimental program is ongoing: four large-scale walls with non-staggered lap splices were tested at Purdue University (Pollalis Drift capacity of reinforced concrete walls with lap splices, Purdue University: West Lafayette, 2021) and two large-scale walls with staggered lap splices have been tested at the University of Canterbury (Kerby et al. Experimental study of staggered lap splices in RC structural walls, 2023). Results from these six tests are added to a dataset of 15 previous tests of walls with non-staggered lap splices compiled by Almeida et al. (JSE 143:853, 2017). A method to estimate drift capacity of walls with lap splices is proposed based on estimates of lap splice strength, steel stress–strain relationships, and moment-area theorems. Two sets of assumptions can be used to produce estimates of drift capacity. The first set of assumptions applies when detailed information of reinforcement stress–strain relationships is available, and the second set of assumptions applies when reinforcement stress–strain relationships must be assumed. Both sets of assumptions produce reasonable estimates of the drift capacity of walls with lap splices, and the second set of assumptions can be used for rapid assessment given minimal information about the detailing and material properties of a wall.

Theoretical and experimental research on the rocking truss system with post-tensioned rocking connection

The weak story failure often occurs in steel frame structures and the collapse risk of the frames will increase because of concentrated plastic deformation in the soft story. The work presented in this paper aims to avoid the soft story mechanisms and the improve self-centering capacity of steel frames by employing the innovative rocking truss. Compared with the previous rocking system, it is more flexible in application and suitable for retrofit of existing buildings. The theoretical approach to quantifying the stiffness demand of the rocking truss was proposed and presented two critical parameters (equivalent bending stiffness ratio η and the rotation stiffness ratio λ) for the design of the rocking truss. The 1/3 scaled steel frame with rocking truss (SFRT) was tested and theoretical analysis results were validated by test results. The finite element model of SFRT was built following the boundary conditions of the test specimen. The numerical results are consistent with the experimental observations. The nonlinear static and dynamic analysis results of the SFRT were compared with those of the same steel frame (SF) with a bracing system. It was found that the rocking truss can reduce the maximum and residual drifts of the main frame as expected, and the plastic development of the RBS at the beam end in SFRT is less than that in SF with a bracing system. The parametric analysis of the rocking connections with different values of prestressing force was carried out. The results confirm that the rotational stiffness and load-bearing capacity of the rocking connection can be accurately evaluated by the theoretical force-displacement curve. The effect of the equivalent bending stiffness ratio η and the rotation stiffness ratio λ on the lateral deformation pattern of structures was discussed by theoretical analysis, and the design procedure of the rocking truss is recommended to satisfy the demand of uniform inter-story drift and self-centering capacity.

Extracting causal relationships from data generated by disparate structural experiments

This article presents a framework for inferring quantitative causal relationships from data generated by disparate structural experiments (DSEs). The term DSE is introduced to describe a set of experiments that, individually, aim to answer a unique research question (or set of questions), but the associated data are aggregated and used for a common purpose. In contrast to DSEs, controlled structural experiments (CSEs) are designed with a single goal (or small set of related goals) where the issue of confounding is addressed in the design of the test matrix. Consequently, the variable relationships established from CSE data can be directly interpreted as being causal. On the other hand, inferring causal relationships from DSE data requires addressing the issue of confounding in the analysis stage. The proposed framework leverages the language, principles, and methods from the broad field of causal inference that have been developed over the last few decades. Specifically, the overall approach centers on the matching technique, which was developed to extract causal relationships from observational data (i.e., data generated by an uncontrolled experiment). A case study is presented utilizing a data set generated by DSEs performed on reinforced concrete shear walls. Using the proposed framework, the causal effect of two key design variables on the drift capacity is quantified. The results obtained from the causal analysis are markedly different from those produced by traditional statistical techniques.

Seismic performance of flexural reinforced concrete columns subjected to varying axial forces

This paper examines the influence of variable axial force on the seismic performance of flexural domain reinforced concrete (RC) columns through experimental testing of five full-scale specimens. The test results demonstrate that fluctuating axial force, when combined with simulated cyclic seismic loading, significantly impacts the flexural behavior of RC columns. The behavior of RC columns under fluctuating axial loads was markedly different from that of columns under constant axial loads. A notable observation was that the failure mode of the columns transitioned from ductile flexural failure to flexure-shear failure when comparing columns subjected to constant axial loads to those subjected to fluctuating axial loads that alternated between compression and tension. This study further demonstrated that the lateral load capacity of the columns, along with their deterioration, was significantly influenced by both the fluctuating pattern and intensity of the axial forces, as well as the displacement ductility. An empirical equation was proposed to estimate the residual lateral load capacity of flexural domain RC columns under varying axial forces, providing a practical tool for designers to assess the behavior of columns under different loading conditions. To corroborate the conclusions drawn from the experimental investigation and gain further insights into the influence of fluctuating axial force on the seismic behavior of flexural domain columns, this study additionally proposes a finite element (FE) model. According to the experimental and numerical results, an empirical equation to estimate the ultimate drift capacity of RC columns subjected to varying axial force is also proposed.

Maximum Drift Demands of Earthquake Damaged Reinforced Concrete Columns Based on Residual Flexure Cracks

Assessment of existing reinforced concrete (RC) structures after an earthquake is a challenging task that must somehow relate qualitative and quantitative observations in the plastic hinge regions and the associated residual deformation capacity of damaged structures. Having an estimate available for the remaining drift capacity will result in more economical and informed decisions regarding demolition or strengthening options. This study aims to develop a practical methodology to estimate the maximum drift demand of an RC column based on the residual crack width. For this purpose, fiber-based frame elements are used to model the RC column considering appropriately concrete behavior in compression and tension stiffening effects. Afterwards, the accuracy and reliability of the proposed methodology are demonstrated by validating the computational approach with two cyclic experimental results from literature and new test data for a one-bay one-story RC frame conducted within the course of this study. A comprehensive parametric study is performed for RC columns with different axial loads, longitudinal and transverse reinforcement ratios, and ground motions to exhibit the stochastic behavior. The study identifies the axial load ratio as the predominant parameter. Key findings include strong correlations between maximum drift ratios and total residual crack widths, as well as maximum compressive strains, with regression analysis yielding equations for accurate drift ratio estimation. Simple predictive models are proposed to estimate the maximum deformation demands based on observed residual crack widths. Residual cracking exceeding 5 mm poses significant risk for the columns with axial load ratios above 0.4, with 90% probability of exceedance 2% drift ratio.

Crack pattern–based machine learning prediction of residual drift capacity in damaged masonry walls

AbstractIn this paper, we present a method based on an ensemble of convolutional neural networks (CNNs) for the prediction of residual drift capacity in unreinforced damaged masonry walls using as only input the crack pattern. We use an accurate block‐based numerical model to generate mechanically consistent crack patterns induced by external actions (earthquake‐like loads and differential settlements). For a damaged masonry wall, we extract the crack width cumulative distribution, we derive a crack width exceedance curve (CWEC), and we evaluate the drift loss (DL) with respect to the undamaged wall. Numerous pairs of CWEC and DL are thus generated and used for training (and validating) an ensemble of CNNs generated via repeated ‐folding cross validation with shuffling. As a result, a method for damage prognosis (Level IV of SHM) is provided. Such method appears general, inexpensive, and able to adequately predict the DL using as only input the CWEC, providing real‐time support for decision making in damaged masonry structures.

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 study of the response of reinforced concrete frames with and without masonry infill walls to earthquake motions

In developing countries prone to frequent earthquakes, it is common practice to use masonry infill walls as partitions in reinforced concrete frame buildings. Frames with infill have smaller drift demands and smaller drift capacities relative to similar frames without infill. Whether the relative reduction in drift demand offsets the plausible reduction in drift capacity remains open to discussion. This investigation provides experimental evidence on drift demands and drift capacities for both frames with and frames without infill. To make fair comparisons, only experiments where sets of nominally identical reinforced concrete frames, at least one frame with no infill and at least one frame with infill, are considered. Because many static experiments provide evidence for the reduction in drift capacity caused by infill, the objective of the dynamic experiments described in this study is to quantify the reduction in drift demand attributed to infill. Results of dynamic tests show that frames with infill drifted no more than one-third the amount similar frames without infill drifted in simulated base motions of the same intensity. Results of static tests show that the smallest drift capacities of frames with infill were approximately one-half of the drift capacities of similar frames without infill. These two experimental observations indicate that infill reduces drift demand more than it reduces drift capacity suggesting an overall beneficial effect of the infill. Field data were used to test this idea. Based on surveys of low-rise school buildings, RC frames with more full-height infill walls tend to have less earthquake damage than frames with less infill. A convenient method to quantify the amount of infill walls in buildings is computing wall ratios defined as the ratio of cross-sectional area of masonry infill walls on ground floor to total floor area above ground floor. Projections of the field data suggest that infill wall ratios of at least 0.5% in both directions of a building reduce the likelihood of severe structural damage by 300% compared with smaller ratios. The use of infill presents an inexpensive yet effective retrofit technique, even if only for temporary use, for strengthening buildings vulnerable to earthquake damage.

Bayesian-based probabilistic models for the ultimate drift capacity of rectangular reinforced concrete columns failed in flexure mode

To accurately predict the ultimate drift capacity of reinforced concrete (RC) columns failed in flexure mode under seismic loading, a probabilistic methodology is proposed to correct the biases in deterministic models and establish probabilistic models. Probabilistic correction models are constructed based on Bayesian updating, which can consider potential critical influences and also yield probability distribution associated with the model parameters and predictions. The probabilistic models are simplified to identify the significant informative terms by Bayesian updating. Then, the influences of the physical properties and size of the sample on the probabilistic models are discussed. The results show that the Bayesian-based correction method can increase the accuracy of predictions and quantify uncertainties. Additionally, adding new samples with different physical properties in Bayesian updating can expand the scope of application of probabilistic models, and the sample size should be at least two times the number of variables involved in Bayesian updating.

Cyclic performance of non‐ductile reinforced concrete columns retrofitted by partial steel plate jacketing: Experiment and numerical analysis

AbstractThis paper investigates the strengthening of non‐ductile reinforced concrete (RC) columns using partial steel‐plate jacketing to enhance ductile capacity. Quasi‐static cyclic loading tests were conducted on three rectangular RC columns with varying shear‐span‐to‐depth ratios, evaluating the effectiveness of steel‐plate jacketing. Results show improved ductile flexural response, high drift capacity, and maintained gravity‐loading capacity under high lateral displacements. A numerical investigation, adopting a multi‐spring fiber section model, predicted cyclic lateral strength, drift ratio, and failure mode, accurately simulating reinforcement behavior and capturing the shear‐strength enhancement due to steel‐plate jacketing. Numerical results demonstrated good agreement with experimental findings. Based on these outcomes, a simple design procedure for retrofitted concrete columns, applicable to design engineers, has been developed and reported in this paper. This study contributes valuable insights into the practical applications of steel‐plate jacketing for non‐ductile RC column retrofitting, offering a comprehensive approach to predicting their seismic performance.

Retrofitting RC beam-column joint subassemblies using UHPC jackets reinforced with high-strength steel mesh

Outdated building codes in seismic zones often did not require seismic detailing on beam-column joints, leaving many existing structures vulnerable to earthquakes. To address this issue, three different ultra-high-performance concrete (UHPC) jackets were proposed for retrofitting seismically-deficient exterior beam-column joints, with variables including construction method (cast-in-place or precast) and inclusion of high-strength steel bar meshes. The effectiveness of these jackets was investigated using cyclic loading tests on beam-column joint subassemblages. The results demonstrated that all three UHPC jackets considerably improved the strength, stiffness, and energy dissipation of the beam-column joint subassemblage, as well as both repairable and collapse drifts. However, the cast-in-place UHPC jacket, when not reinforced with steel meshes, failed to effectively improve the ultimate drift capacity of the original beam-column joint subassemblage. Moreover, retrofitting with precast UHPC jackets using chemical anchors failed to generate sufficient composite action. Only the cast-in-place UHPC jacket, when reinforced with high-strength steel meshes, successfully delayed localized joint shear damage and allowed for effective utilization of beam flexural capacity. It improved the joint shear strength by 66%, initial stiffness by approximately 35%, and total energy dissipation by 140%. Finally, strength models were suggested for evaluating the joint shear strength and beam flexural capacity of UHPC-retrofitted beam-column joints.

Seismic behavior of resilient composite steel plate shear wall using experimental investigations

Using composite encased steel plate shear wall (C-SPSW) has been attractively raised for enhancing the lateral seismic performance and increasing the useful floor area. Although, the experimental investigations have proved excellent dynamic behavior of C-SPSWs, structural damage as well as residual displacements are the main disadvantages of C-SPSWs, which are not consistent with low damage design (LDD) approaches. In the current study, the C-SPSWs performance is improved using the self-centering (SC) technique to control the both structural damage and reduce residual displacements as well. Five tests on C-SPSWs including three SC composite encased steel plate shear walls (SC-C-SPSWs) were conducted under gravity and lateral cyclic loads. The SC-C-SPSW consists of C-SPSW equipped with unbonded posttensioned tendons (UPT) to have resilience ability. For this aim, two symmetrical gaps were provided at the ends of the wall, and the UPTs were mounted at the wall ends and crossed into the foundation through the middle of the gaps. Under lateral load, the gap opening allows the elongation of UPTs that induce a high restoring forces, forcing the wall to have rocking movement above the foundation. In comparison with C-SPSWs, the SC-C-SPSWs exhibited low damages, higher shear strength capacity between 28% and 35%, larger ultimate drift capacity and more displacement ductility as 45–136% in average. Furthermore, the SC ability and the UPTs restoring forces effectively reduced the residual drift and the SC moment causes the recovery of the residual drift between 90% and 105%. Moreover, compared to C-SPSWs, the residual lateral strength of SC-C-SPSWs was improved by 30% in average.

Investigation of the bed joint reinforcement effect on the drift capacity of modern unreinforced masonry walls

Bed joint reinforcement significantly affects the shear capacity of masonry walls due to its effective ability to transfer shear forces through a diagonal crack, but how does this phenomenon impact its drift capacity? This paper presents an experimental study containing a series of four quasi-static cyclic tests conducted on masonry walls of same size. Two of them incorporated truss-type bed joint reinforcement, while the other two were completely unreinforced. All specimens were subjected to double bending boundary conditions to observe shear-controlled behaviour and were tested under two levels of compression load. The primary objective of this research is to determine the role of horizontal reinforcement in the seismic properties of unreinforced masonry walls focusing on the displacement capacity. The findings from this experimental study are expected to provide empirical evidence for subsequent numerical simulations and contribute to the development of analytical formulations. The results aim to enhance our understanding of the seismic response of masonry walls, ultimately informing design practices and seismic retrofitting strategies.

The diagonal shear behavior of masonry walls fabricated with historical lime-based mortar and retrofitted with near surface mounted method

The historical monuments in different regions of the world were constructed using local materials. Sarooj was a lime-based mortar utilized extensively in the construction of Unreinforced Masonry (URM) buildings in some Middle Eastern countries in the past centuries. However, few studies have been conducted on the mechanical properties of masonry fabricated with Sarooj and strengthening of the elements in which this type of mortar was used. In the present study, the in-plane shear behavior of URM wallettes fabricated with Sarooj mortar and retrofitted with Near Surface Mounted (NSM) Glass Fiber Reinforced Polymer (GFRP) bars is investigated through an experimental and numerical study. In this regard, first, diagonal shear tests are conducted on square wallettes. The test specimens include bare and retrofitted wallettes. The type of paste used for filling the grooves in the NSM method and the retrofitted face of the wallettes are the main variables whose effects are investigated in the experimental program. In addition to the NSM method, the in-plane behavior of walls retrofitted with a novel technique named Epoxy Filled Joint (EFJ) is investigated in the experimental phase of the present study. Then, through a numerical study, the wallettes retrofitted with the NSM method are simulated in Finite Element (FE) software Abaqus following a macro-modeling approach. The results of the experimental study confirmed that the strengthening of the URM wallettes with the NSM method not only enhanced their ultimate in-plane shear strength, but also improved the ultimate drift capacity of the wallettes. Furthermore, the shear stress-drift curves obtained from the FE model were in good agreement with those obtained from the tests. In addition, the test results showed that the EFJ method significantly increased the in-plane shear strength of the wallettes.

Experimental study of CRM-reinforced brick masonry panels: Cyclic shear-compression tests and compression tests

The preservation of the building heritage is often accompanied by the necessity of ensuring adequate structural safety of existing buildings. Existing masonry structures are usually characterised by a high seismic vulnerability due to their low tensile strength; moreover, despite the significant compressive capacity, often masonry panels are not able to guarantee the safety level required by the current building codes under gravitational loads, due to their slenderness and the possible out-of-plane actions. In recent years, several systems have been developed for the reinforcement of masonry buildings based on the use of composite materials externally bonded to the structural elements. Among them, the CRM system can be used for the static and seismic reinforcement of masonry piers as an alternative to the traditional reinforced plaster. The CRM system consists of the application on the panel surfaces of a mortar layer about 3 cm thick reinforced with a glass fibre grid and connected to the wall through transversal connectors. Despite its increasing use, to date, few experimental and theoretical studies have been carried out focusing on the lateral behaviour of reinforced panels, especially regarding their flexural response and drift capacity, as well as a little number of studies are available regarding the contribution provided by CRM layers on the buckling failure of panels induced by vertical loads. This work presents an experimental campaign carried out at the Laboratory of Structures and Materials of the University of Florence. A series of tests for the mechanical characterisation of materials composing the masonry and the reinforcement has been at first performed; then, quasi-static cyclic shear-compression tests and compression tests on solid brick masonry panels strengthened with CRM have been performed, considering the application of the CRM on a single or both faces of the walls. Tests allowed the assessment of the mechanical properties of the retrofitting system and its adhesion to the substrate and highlighted the advantages and limitations produced in the structural response of reinforced walls, both for horizontal and vertical loading.