Damaged Masonry Walls Research Articles

Experimental study on seismic performance of damaged masonry walls reinforced with high-polymer cementitious composite material

Masonry structures are one of the most traditional and economical structural forms that are extensively used worldwide. However, severe damage to the masonry structures during past earthquakes addresses their vulnerability to seismic loadings. Therefore, it is critical to develop effective and efficient seismic reinforcement measures for masonry structures. This study proposes a structural retrofitting method for masonry walls that employs a corrosion protection liner (CPL) and high-polymer cementitious composite material (HPCCM). Cyclic in-plane pseudo-static tests were performed on six masonry wall specimens comprising three unreinforced and three seismically damaged masonry walls retrofitted with CPL-HPCCM. This experimental study explored the hysteretic behavior, deformation capacity, and failure mechanism of masonry wails after rehabilitation with the proposed retrofitting method under cyclic loading. The test results indicate that the CPL-HPCCM structural retrofitting method is an effective structural retrofitting technique that significantly enhances the lateral load-bearing capacity and energy dissipation capability of masonry walls. Even for the severely damaged masonry wall specimens, the lateral load-bearing capacity, lateral stiffness, and overall ductility of the wall specimens after retrofitting with CPL-HPCCM were restored to or improved beyond those of the intact wall specimens. Compared with the non-retrofitted specimens, the lateral load-bearing capacity of the CPL-HPCCM retrofitted specimens exhibited a substantial improvement, with a minimal increase of 14.6 %. In addition, the CPL-HPCCM method also enhanced the energy dissipation capacity of the wall specimens over 1.95 times compared to the non-retrofitted specimens. Finally, a lateral load-bearing capacity prediction equation was proposed for CPL-HPCCM-reinforced masonry walls based on experimental results.

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.

Shear damage repair of masonry walls using different materials

In this research, the effects of different repairing materials and techniques used on damaged Masonry walls under an in-plane lateral loading were investigated. Seven clay brick walls with dimensions of (1200 × 935 × 115) mm were tested. The walls were tested until a visible crack was observed, later repaired, and tested again up to failure. The repairing materials consisted of grid configured strip materials (metal, plastic, flat webbing ‘textile’ and wild cane ‘organic’ strips), near surface mounted (NSM) steel re-bars and steel wires in mortar joints. Based on the experimental results, the repairing materials/techniques restored the shear strength by about 48–103% of the original strength. The ductility factor of the repaired walls ranged from 4.5 to 48.3 (flat webbing ‘textile’ highest). The energy dissipation ratio of the repaired walls ranged from 4.3 to 12.7 (flat webbing ‘textile’ highest). Prediction equations for shear strength are presented giving reasonable results compared to the experimental results.

Effects of textile-reinforced concrete on the cyclic shear behavior of damaged confined brick masonry walls

Masonry walls are very fragile and prone to damage from the effects of earthquakes. However, after an earthquake, some of confined walls can continue to carry loads after repair and reinforcement. Strengthening is an effective measure for improving the seismic performance of damaged walls. In this study, the seismic performance of textile-reinforced concrete-strengthened damaged masonry confined walls was experimentally investigated. Apparently cracked and pre-damaged confined brick masonry walls were repaired and retrofitted with TRC (textile-reinforced concrete). The effect of anchoring on improving seismic performance was investigated, and a restoring force model of damaged confined brick masonry walls reinforced with TRC was established. The damaged masonry confined walls reinforced by TRC had better integrity and ductile behavior during the failure model, compared with unreinforced walls. Load-displacement curves of walls reinforced with TRC exhibited good postpeak behavior, and they had higher shear capacity, ductility factor, and energy dissipation. TRC surface reinforcement could provide a good restraint to damaged walls and improve the brittle failure characteristics of the walls. The number of cracks in each wall was significantly reduced, and the rate of decrease of stiffness was slowed down. For different strengthening methods, the initial stiffness, shear capacity, ductility factor, energy dissipation increased by 0.08-0.52, 0.04–0.22, 0.019–0.55, and 0.33–0.91 times, respectively, compared with unreinforced walls. Additionally, the application of anchorage measures significantly improved the shear bearing capacity and energy dissipation of the reinforced walls. Based on the experimental results, model curves of the restoring force of TRC-strengthened damaged masonry walls were given and analyzed according to the experimental results.

Experimental study on seismic behavior of masonry walls retrofitted with steel-member and high-performance polymer mortar

In this paper, an innovative retrofitting method using steel-member and high-performance polymer mortar was purposed for masonry walls. In order to study the effectiveness of the proposed retrofitting method, three specimens of concrete tie-column confined masonry wall were designed and manufactured. The quasi-static tests were conducted in two stages: before and after retrofitting. Damage progression, hysteretic behavior, stiffness degradation, and energy dissipation were compared and analyzed. The results show that after retrofitting with the proposed method, bearing capacity of damaged walls is increased by 17.66%–42.37%. The initial stiffness can be restored to 85% of the original wall. The energy dissipation capacity is increased by 270.20%–330.55%. The proposed method can effectively improve the seismic behavior of damaged masonry walls. Finally, evaluation methods of bearing capacity for masonry walls before and after retrofitting were given, the calculated results were in reasonably good agreement with test results.

Seismic performance of crack-damaged masonry wall structures via shaking table tests

Masonry fence walls in run-down areas have cracks of various shapes, and these cracks can weaken the walls very seriously. However, research on this subject has been scarce, and the effect of different crack types on the seismic performance of unreinforced masonry walls needs to be investigated. In this study, two U-shaped wall structures were built: one without any cracks and the other with diagonal, horizontal, and vertical cracks on three sides. The effects of these cracks on the seismic performance characteristics (i.e., the drift ratio and base shear) are evaluated by comparing the dynamic responses of the two wall structures. Through shaking table tests exerting horizontal bi-direction ground motions, both the out-of-plane and in-plane responses of the walls are investigated. Diagonal cracks are found to be more likely to cause the early collapse of masonry walls than vertical and horizontal cracks. These results provide valuable knowledge that will facilitate the appropriate reinforcement for damaged masonry walls that might need urgent repair.

Strengthening of Damaged Masonry Walls Using Engineered Cementitious Composites: Experimental and Numerical Analysis

Engineered cementitious composites (ECC) are special types of high‐tensile and high‐ductility concrete that are designed using a micromechanics approach, with a tensile strain capability of more than 3%. Due to their higher strain hardening capacity, ECC can be applied as a strengthening material on structural walls, which improves the structural strength and inelastic deformation capacity. This study presents an experimental and numerical analysis of brick masonry wall strengthened by traditional mortar, ECC, and ECC with 40% fly ash (FAECC) subjected to uniaxial compression. The tests, such as compressive strength, indirect tensile strength, and bond strength, were conducted. Based on the experimental results, a numerical model is developed, and a failure prediction for the existing masonry structure is made. The compressive strength of ECC is observed to be higher than normal mortar and FAECC whereas the indirect tensile strength of both ECC and FAECC was almost similar, which is higher than that of normal mortar. The bond strength of ECC and FAECC is found to be 70% higher than that of normal mortar. It is evident that brick masonry units strengthened by ECC have a higher compressive strength than masonry units strengthened by conventional mortar and FAECC. It also controls crack development and spalling of masonry units. Then, a micromodelling along with CDP model is made in Abaqus/CAE software and an excellent correlation between experimental and numerical results was noted. The suggested models were shown to be capable of predicting the common behaviour of masonry units.

Experimental investigation on the in-plane seismic performance of damaged masonry walls repaired with grout-injected ferrocement overlay

• The performance of damaged masonry wall with and without reinforcement was discussed. • The strengthening technique is based on the use of ferrocement overlay. • The use of the strengthening technique requires low cost and low-tech workmanship. • The seismic response of damaged wall is significantly improved by GFOR. This experimental study compares two scaled unreinforced masonry (URM) walls before and after being repaired by grout-injected ferrocement overlay reinforcement (GFOR), with the aim of investigating the effectiveness of an alternative ferrocement overlay technique. In the experiment, loading was performed on a multistory opening URM wall to induce damages, and the reinforced wall (defined as FRM) was retested using the same procedure. A comparative analysis of the seismic performances of the two walls in terms of failure modes, bearing capacity, hysteresis curve, energy dissipation capacity, and deformation behaviors was performed. The experimental results indicated the following. (i) The application of GFOR on the damaged URM wall altered its diagonal shear failure into the flexural-dominant mode. (ii) The ultimate resistance and residual strength of FRM increased by 6% and 13%, respectively, compared with those of URM. (iii) The ultimate and residual deformations of FRM increased by 110% and 60%, respectively, compared with those of the URM. (iv) The ductility of the overall walls improved from 2.48 to 2.72. This study verified the reasonability and effectiveness of the application of GFOR to damaged masonry structures.

Textile reinforced mortars (TRM) for repairing and retrofitting masonry walls subjected to in-plane cyclic loads. An experimental approach

Masonry walls exhibit low tensile strength and high material heterogeneity, which makes them especially vulnerable against cyclic loading conditions, such as those typical in earthquakes. This paper presents the experimental results obtained from tests on three masonry walls reinforced with textile reinforced mortar (TRM) materials subjected to in-plane cyclic loading. These full-scale masonry walls were tested in the LARGE laboratory at the University of Alicante (Alicante, Spain). The walls had been built using a traditional construction technique, with solid clay bricks layered with lime mortar. One specimen was tested and damaged by in-plane cyclic loading and was subsequently strengthened by a vertical layer of TRM with an overlapping of 200 mm. It was then tested again until failure in a second test. In addition, another undamaged specimen had been previously reinforced with the same TRM technique and tested until failure, thus providing a third test. A network of sensors and digital image correlation systems were used to monitor displacements and crack patterns. The comparison between these experimental results made it possible to assess the effectiveness of TRM in restoring the structural integrity of damaged masonry walls and almost doubling their load-bearing capacity under cyclic loads. Conclusions obtained here provide valuable information to the scientific community, architects and structural engineers about the strengthening and repair of severely damaged masonry walls.

FRCM strengthening systems efficiency on the shear behavior of pre-damaged masonry panels: an experimental study

Existing masonry constructions are highly vulnerable to seismic actions, as demonstrated by the severe earthquakes which stroke the Italian territory in recent years, causing great damages, especially in old masonry buildings. Therefore, restoring damaged buildings, with the aim to recover or improve their structural capacity, is a key aspect in the post-seismic interventions. Fiber reinforced composite materials could be effectively used to this purpose. One aspect which is worth to investigate is the application of these reinforcement typologies on damaged structural elements. Even though many experimental campaigns are available concerning the mechanical improvement given by composite materials applied on undamaged structural elements, only few can be found considering strengthening of already damaged masonry walls. The objective of the work here presented is to evaluate the shear response of damaged masonry panels strengthened using fiber reinforced cementitious matrix (FRCM). Two unreinforced brick masonry walls were subjected to diagonal compression tests, producing an extended state of damage. Afterwards, the same walls were strengthened with FRCM and diagonal compression tests were again performed. Comparisons were done between the results of the unreinforced samples and the pre-damaged strengthened ones, in terms of shear strength and post-peak behavior. The FRCM retrofitting system was also used to strengthen an undamaged masonry panel, which was tested in order to analyze similarities and differences with respect to results obtained for pre-damaged samples. The experimental campaign allowed to study the sole contribution of the reinforcement to the shear capacity of the wall panels. Results showed that the presence of FRCM reinforcements on damaged masonry panels influenced the shear behavior of the samples, which experienced a more ductile failure.

In situ repair technique of infill masonry walls in steel frames damaged after an earthquake

The present paper first reviews the scientific information about masonry buildings in terms of the structural performance of different masonry walls, usual pre-earthquake retrofitting methods, and post-earthquake repair methods. From this, it is found that limited information is available on applicable repair methods for damaged masonry walls after the occurrence of an earthquake event. There is an essential need from the perspective of disaster management strategies to provide urgent aid to casualties of moderate seismic events well before preparing damage assessment data and a comprehensive retrofitting program for the earthquake-affected area. For this reason, three experiments were designed to investigate the effect of brick masonry infill on a simple steel frame and the success rate of a new method of repairing damaged infill. In the proposed repair method, cracks in the damaged masonry infill are stitched by crimped wire meshes in the shape of Band-Aids and cementitious plaster is used to coat the attached wire meshes. The crimped wire meshes must be fastened to the infill with hooked driven nails and must be attached perpendicular to diagonal crack paths and the four corners and centre of the infill. This method is presented for efficient and simple in situ repair interventions to provide temporary residency for casualties. Usage of plasters including accelerated cement or application of accelerated curing methods can reduce the time of repair construction and prepare the proposed method for urgent aids against aftershocks. No inappropriate structural effects of the steel frame-infill interaction were observed during these tests. Furthermore, the results indicated that the repair method not only restored the lost strength of the damaged infill but also recovered the stiffness and ductility of the reference specimen based on the experimental evidence. Following the experiments, a practical design methodology for the required crimped wire mesh specification based on the length of the infill diagonal cracks was recommended.

Retrofitting of masonry walls by using a mortar joint technique; experiments and numerical validation

This paper presents research on a conventional but practical retrofitting method for masonry walls along with the numerical modelling of it under in-plane lateral shear–compression loading. The latter is capable of predicting the experimental collapse load and overall behaviour quite accurately. The retrofitting approach is based on building a wall parallel to an existing single-leaf wall and bonding the two leaves together using a mortar (collar) joint, merging the two individual panels into a unified double-leaf wall. Experiments on this retrofitting approach for both undamaged and damaged masonry walls have been introduced in the present paper. The tests revealed that the pre-damage application can increase the strength by 50% while the post-damage one can restore the initial strength. A micro-scale numerical model has been devised by considering the bricks as rigid elements and the mortar joint as a nonlinear failure surface. The model was implemented in the commercial Finite Element (FE) software MIDAS FEA and the numerical results were verified against the available experimental data.

In-plane behavior of seismically damaged masonry walls repaired with external BFRP

This paper investigates the in-plane seismic behavior of eight unreinforced masonry (URM) walls before and after being retrofitted by basalt fiber reinforced polymer (BFRP). Among these eight specimens, one served as the reference specimen, without any strengthening scheme; three were directly strengthened with BFRP after construction; four were cyclically tested to the pre-defined damage level, and then repaired with BFRP. The mixed strengthening configuration was designed for the retrofitted URM walls. All these walls were tested to failure under a same loading strategy. Different parameters, including layer number, strip width, and vertical compression level, were considered in the laboratory tests. The experimental study shows that the failure modes between the reference specimen and retrofitted walls are different. Testing results are discussed in terms of lateral strength, ultimate drift, stiffness degradation, energy dissipation, and FRP strain. Finally, an improved design model is proposed for strength consideration of FRP retrofitted masonry walls.

Static cyclic in-plane shear response of damaged masonry walls retrofitted with NSM FRP strips – An experimental evaluation

An experimental study was conducted to assess the effect on strength and ductility of retrofitting unreinforced masonry (URM) shear panels with near surface mounted (NSM) carbon fibre reinforced polymer (CFRP) strips. A total of sixteen wall panels, 1200mm×1200mm, were subjected to vertical pre-compression combined with increasing reversing cycles of in-plane lateral displacement. All wall panels were previously tested (prior to retrofitting) under compression and cyclic shear using three different pre-compression levels resulting in various levels of damage. The damaged walls were repaired, retrofitted with NSM FRP strips and retested under pre-compression stress levels of 2.8MPa, 2MPa and 1.4MPa. The retrofitted walls displayed higher displacement capacities compared with URM walls highlighting the effectiveness of retrofitting URM walls under earthquake loading. The ultimate loads were not enhanced due to retrofitting under higher pre-compression levels. However the presence of the reinforcement did restore the ultimate loads to those observed for the original undamaged URM state. This meant that overall, the reinforcement was effective in increasing the energy dissipation capacity of the walls compared to URM. The improvements in the behaviour of the URM walls due to retrofitting were generally similar, irrespective of the amount of damage the URM walls experienced prior to retrofitting. The paper discusses the effect on strength, displacement capacity, energy dissipation and ductility achieved by FRP retrofitting of the damaged (lightly and highly) URM panels compared to the undamaged URM panels under different pre-compression levels. The broader aim of the research is to identify techniques for improving the seismic performance of existing URM walls under in-plane shear loading.

Repair of in-plane shear damaged masonry walls with external FRP

Extensive damage in a large number of existing masonry buildings during recent earthquakes has shown the need for structural repairing techniques for masonry structures. Externally bonded fibers (FRP) is a retrofitting technique that has been shown that can be used to repair or strengthen reinforced concrete and masonry structures. Masonry walls strengthened with FRP can have large increase in strength, but the effect of the of the presence of damage in the walls at the time of the repair has not been studied. Four full-scale shear-dominant clay brick masonry walls, initially damaged in shear by loading them up to their maximum strength, were repaired using two configurations of externally bonded carbon fiber strips and tested under cyclic shear loading up to failure. It was observed that the maximum strength and deformation capacity, as well as the cracking pattern and failure mode, of the repaired walls was similar to that of undamaged walls that were strengthened with the same reinforcing schemes.

Damaged masonry walls in two-way bending retrofitted with vertical FRP strips

Unreinforced masonry (hereafter termed ‘masonry’) structures comprise a significant proportion of the building stock in many countries worldwide, however their walls do not behave well under out-of-plane loading, such as that experienced during seismic events. Consequently, many existing masonry structures require some form of retrofit to comply with existing codes. As part of ongoing research at The University of Adelaide on the out-of-plane bending behaviour of masonry walls, eight full-scale walls (with window openings) were tested under reversed-cyclic loading. Four of the severely damaged walls were subsequently retrofitted using externally bonded (EB) (three walls) and near-surface mounted (NSM) (one wall) fibre-reinforced polymer (FRP) strips and tested again to quantify the increase in strength and ductility relative to the original capacities. A debonding mechanism not yet quantified for retrofitted masonry walls was observed and identified as displacement induced (DI) debonding. It is a result of a differential out-of-plane displacement at either side of a crack in the wall. NSM strips are more susceptible due to their orientation. This paper presents the results of the wall tests along with detailed accounts of the wall failure modes.

コンクリートブロック塀の耐震安全性に関する研究 : 地震被害調査および既存塀の構造実態・補強方法に関する調査

In order to propose the new design method for concrete masonry garden walls and strengthening methods for existing walls with poor seismic resistance, the field investigations of damaged and/or survived masonry walls during the 1995 Hyogoken-nanbu earthquake, damaged masonry walls during the 1997 Kagoshimaken-hokuseibu earthquake and existing garden walls in Oita City were conducted. As the results, the intersecting walls seems to play an important role for preventing significant earthquake damage. Based on the results of field investigation for the existing walls in Oita City, strengthening methods for masonry garden walls with poor seismic resistance are discussed in this paper.