Existing Masonry Walls Research Articles

Structural assesment and numerical analysis of existing reinforced concrete frame structure

The subject of this study is the presentation of in-situ tests on the existing structure and structural analysis of the Faculty of Political Sciences building at the University of Zagreb which sustained damage in the series of earthquakes that hit Zagreb and Petrinja in 2020, as well as the structural strengthening efforts undertaken thereafter. The load-bearing structure of this mid-20th century building is a reinforced concrete frame system (column-beam). Filling between frames is masonry made of solid bricks. The floor structure is reinforced concrete ribbed slabs, characteristic of the construction period. Structure has a basement and six floors above ground. In-situ testing revealed that the compressive strength of concrete was at least 30.7 MPa, and tensile strength of steel reinforcement to that of B 240. It was determined that that the existing masonry walls did not have sufficient shear resistance due to the degradation of the bonding material. Numerical model was made considering the peak ground acceleration of ag/g = 0.249, and the importance factor of γI = 1.2. The analysis showed that the existing building complied with 19% ag/g of today’s applicable regulations for designing earthquake-resistant structures. The main strengthening included the installation of external steel trusses on both facades connected to the external column or facade frame, thus not affecting the existing floor plan. RC walls were added to side of main building volume in the transvers direction and to the staircase portion in both directions as additional bracing. Since the calculations assumed the behavior of the frame for the existing load-bearing structure of reinforced concrete beams and columns, the joints were additionally reinforced by wrapping them with CFRP fabric to enhance reinforcement, since these areas are very sensitive to seismic action.

Shake table test on a five-story residential masonry building strengthened by engineered cementitious composites based on minimum disturbance

Multi-storey masonry structures are popular structural systems for residential buildings in China in the 1970 s, which need strengthening urgently due to poor seismic performance. To save construction time and achieve minimum disturbance, a single-sided engineered cementitious composites (ECC) strengthened method for masonry structures was proposed. To investigate the effectiveness of the strengthening method, two 1/4-scaled 5-storey masonry structures, including a reference unreinforced structure (US) model and a corresponding retrofitted structure (RS) model, were designed and tested by shake table tests. The comparisons between the US model and the RS model were analyzed in terms of the natural frequency, acceleration amplification factor, acceleration response, and storey drift response. The results show that the strengthening method can improve the seismic performance of the masonry structure. The connection method can ensure that the existing masonry walls and ECC layers work together. The initial natural frequency of the RS model is 1.3 times that of the US model. The maximum storey drift of the US model is 3.0 times that of the RS model at PGA = 0.550 g. To ensure the strengthening efficiency, the acceptable structural aspect ratio range for the strengthening method was suggested, and an improved strengthening method was proposed.

Flexural Strengthening of Stone Masonry Walls Using Textile-Reinforced Sarooj Mortar.

The majority of historical buildings and structures in Oman were built using unreinforced stone masonry. These structures have deteriorated due to ageing of materials, environmental degradation, and lack of maintenance. This research investigates the physical, chemical, and mechanical properties of local building materials and the results of an experimental study on the out-of-plane bending effectiveness of an innovative strengthening method applied to existing masonry walls. The technique consists of the application of a basalt textile-reinforced sarooj mortar (TRM) on one face of the walls. Bending tests of masonry wall samples (1000 mm width, 2000 mm height, and 350 mm depth) were carried out on one unreinforced specimen and three different cases of reinforced specimens. The performance of unreinforced and reinforced specimens was analyzed and compared. The strengthened specimens were able to resist moments of out-of-plane bending 2.5 to 3 times greater than those of unreinforced specimen (160-233% increase). Moreover, the strengthened walls were able to sustain higher deformations (deflections) than the unreinforced specimen ranging from 20 to 130%. The results showed that using TRM was effective for the out-of-plane strengthening of stone masonry using a local material (sarooj) that is compatible with existing stone masonry building materials.

Renovation not demolition: a case study of saving carbon on a private residence

This article describes a residential project to create a spacious, contemporary family home on the site of a 1960s building, following an early decision to renovate the existing structure, retaining as much of the fabric as possible. The design approach aimed to simplify the form of the building while also improving its thermal performance and airtightness. Existing masonry walls were retained on the front and side elevations, while internal walls were removed to create open-plan living spaces, requiring a steel sway frame to be installed. A new, almost fully glazed rear elevation was created, with the first-floor wall rebuilt in timber frame. Existing foundations, concrete strip footings and the concrete ground-bearing slab were largely retained. A new insulated concrete slab was installed where the ground floor was extended, and concrete was broken out locally to allow the installation of new pads where load concentrations exceeded the capacity of the existing foundations. A carbon assessment indicates that the renovation scheme saved around 45% of the embodied carbon of a hypothetical rebuild scheme, with a footprint of 111kg CO2e/m2 compared with 199kg CO2e/m2 for the rebuild scheme.

Cyclic shear-compression tests on CRM reinforced brick masonry walls

In recent years, Composite Reinforced Mortar (CRM) systems were applied as externally bonded reinforcement of existing masonry walls. In the research field, experimental tests have been carried out using diagonal-compression configurations, showing improvements in ultimate load and deformations capacities of panels.The experimental test of reference to define the lateral response of masonry walls is the shear-compression test: few studies were carried out using this setup, therefore limited analysis is still available about the efficiency of the reinforcement in terms of displacement capacity, stiffness, and hysteretic behavior.In this work, an experimental campaign was carried out to evaluate the CRM effect on the seismic response of brick masonry walls. First, mechanical characterization of reinforcement components was carried out, through tensile tests on bare yarns, clamping grid tests on reinforced mortar coupons, and single-lap shear bond tests. Subsequently, quasi-static cyclic shear-compression tests on three walls with dimensions of 1000x250x1225 mm were carried out. Amongst tested walls, one was maintained unreinforced, one was reinforced by the application of a CRM system on two sides, and the last was reinforced by the application of CRM on one side only. The paper presents the main results of the experimental campaign, showing the effectiveness of CRM for the in-plane shear behavior of brick masonry walls.

Experimental and numerical investigation on the seismic performance of masonry walls reinforced by PC panels

The use of precast reinforced concrete (PC) panels to strengthen existing old masonry structures was presented in this study. Quasi-static tests were done on one unreinforced masonry wall and three reinforced wall specimens with varied connection forms to study the seismic performance of the masonry walls reinforced by PC panels and verify the effectiveness of the applied connection forms. The hysteretic response of all reinforced masonry walls differed significantly when different connection forms were applied, according to experimental results. Based on the experimental results, the proposed reinforcement method using one-sided connected PC panels can effectively improve the seismic performance of existing masonry walls in terms of shear strength, stiffness, and energy dissipation capacity. Finally, the numerical simulation models for the specimens were established to further investigate the damage mechanisms, and the hysteresis curves and failure modes of specimens obtained from numerical analysis were in good agreement with the experimental results, indicating that the proposed analytical model can be practically used to predict the performance of masonry structures strengthened by the new reinforcement technique.

Shaking table tests on a 5-storey unreinforced masonry structure strengthened by ultra-high ductile cementitious composites

Multi-storey unreinforced masonry structures have been widely used as residential building structures in China during the decade of 1970–1980. Recent earthquake events have shown that these buildings may exhibit severe damages due to their relatively brittle seismic resistance mechanism. The use of ultra-high ductile cementitious composites (UHDCC) layers can be an attractive minimal-disturbance strengthening option for masonry structures resulting in low intervention costs and quick construction. UHDCC is a high-performance engineered cementitious composite that offers a tensile strain capacity higher than 5%, thus significantly improving the low tensile strength and ductility of the masonry wall. To investigate the seismic behavior of UHDCC-strengthened masonry structures, shaking table tests were carried out on two three-dimensional 5-storey masonry structures including a conventional test structure (CS) and a strengthened test structure (SS). The results show that the proposed strengthening method can effectively improve the seismic performance of multi-storey unreinforced masonry structures due to the excellent cohesion achieved between the existing masonry walls and the UHDCC external strengthening layers. The strengthened method changes the damage state of masonry structures from shear failure to a more ductile failure, and the strengthened masonry walls can exhibit a multi-cracking response. The initial natural period of the SS specimen was found 0.58 times that of the CS specimen. The base shear and maximum roof drift of the SS specimen are 4.8 and 3.4 times that of the CS model, respectively. This study provides reference results for the application of UHDCC layers to strengthen multi-storey unreinforced masonry structures.

Steel based retrofitting interventions for existing masonry walls: a comparative numerical investigation

AbstractMasonry buildings constitute a significant portion of the architectural heritage all over the world, also in regions affected by a high seismic hazard. Since this constructional material is characterized by lack of tensile strength, as well as small deformation capacity, masonry structures could result hugely damaged if shaken by seismic forces. In order to avoid collapses and reduce structural damage, innovative retrofitting interventions are necessary to improve the seismic behavior of masonry structures. In this context, steel‐based techniques could be considered among the most suitable solutions. In fact, by using such a high‐performant material, additional strength and ductility may be conferred to existing masonry structures. Based on these premises, the present paper focuses on a numerical investigation of two different retrofitting techniques: the CAM© system and the application of steel grids on both faces of a masonry wall. In particular, on the base of an experimental test carried out within the research project In.CAM.M.I.N.O. on an unreinforced masonry wall tested in condition of constant vertical force and horizontal loads, a reference FE Model has been calibrated in Abaqus by using a macro‐modelling approach with a damage‐plasticity material model for the masonry. Then, based on the reference model, the efficiency of the two systems has been investigated and compared by means of numerical analyses, in order to evaluate the strength and ductility increases obtainable by the application of the two retrofitting techniques.

Seismic behavior of masonry walls strengthened by precast reinforced concrete panels with different connection details

Strengthening old masonry structures with precast reinforced concrete (RC) panels is a new strengthening method, which can save resources and construction time. Three connection methods, including RC dowelling keys, grouting agent and post-cast bands, were employed to ensure that the precast RC panels and the existing masonry wall work together. To investigate the seismic behavior of the strengthened structure, eight masonry walls were tested under quasi-static cyclic loading, including four reference walls and four strengthened walls. Experimental results show that the proposed strengthened method can effectively improve certain aspects of the seismic performance of existing masonry walls, such as shear strength, stiffness and energy dissipation capacity. The failure modes of all specimens were discussed. The shear capacity of original and strengthened masonry walls was evaluated using the existing design equations and proposed equations, respectively. The three proposed connection methods can ensure cooperation between the existing masonry wall and the precast RC panels. Among them, the post-cast band is the most effective measure, which is able to transfer 60%-80% load from the masonry wall to the precast RC panels.

Sustainable Mortars for Application in the Cultural Heritage Field.

A large part of the world’s architectural heritage is composed of masonry buildings located in seismic areas, and its vulnerability has been shown by the damage caused by the last earthquakes. Meeting the safety demands of cultural heritage buildings according to the performance-based seismic codes requires a deep knowledge of the mechanical properties of material components. Traditional mortars are among these. However, significant samples of structural mortars cannot be taken from existing masonry walls to perform mechanical tests, but tests can, alternatively, be conducted on samples realized according to traditional instructions for composition. Based on a historical study of mix proportions, this paper presents the results of a mechanical test campaign of traditional mortars. The samples were obtained combining lime and pozzolan according to the proportions derived from ancient treatises. The laboratory tests were performed taking into account three different types of limes, and a discussion involving the results presented in the literature is provided. Besides the contribution to fulfilling the lack of knowledge about the mechanical properties of traditional lime mortars, the test results are good references for on-site preparation of mortars for use in restoration. There is a focus on natural pozzolanic lime mortars, widely used in the Neapolitan area and, in general, in the whole Italian territory.

In-plane strengthening of masonry buildings with timber panels

The in-plane strengthening of masonry walls plays a key role in the improvement of the global seismic behaviour of masonry buildings. Various strengthening techniques are currently available, such as coatings, confinement or injection and the use of cement-based materials or steel- or fibre-reinforced polymers or mortars. In this work, two innovative strengthening techniques for existing masonry buildings were investigated: the use of glued or nailed timber wall panels connected to the outer and/or inner face of the masonry wall. Their effectiveness in reducing the seismic vulnerability of existing masonry walls was assessed in tests and numerical simulations. The test results demonstrated improvements in strength, rocking displacement capacity and energy dissipation capacity. The numerical analyses, conducted with non-linear models calibrated on experimental results available in the literature, confirmed the advantages of these interventions, comparing the effects of using monolithic or coupled glued or nailed wall panels, provided that particular attention is given to their connection to the existing structure.

A retrofitting technique using steel grids for existing masonry panels: a numerical and analytical study

The current research focuses on a numerical and analytical study aimed at investigating the efficiency of a steel-based reinforcement system suitable for existing masonry walls. The application of such a retrofitting technique, which consists of glued thin steel grids applied on both faces of a masonry panel, is reversible, cheap and easy to be executed and appears to be suitable especially for buildings with concrete slab or inter-stories beams to which the steel elements could be anchored. The study is based on a reference experimental test carried out at the “Politehnica” University of Timisoara (Romania), within the European FP6 project PROHITECH. The reference test provided the application of a constant vertical compression and cyclic horizontal displacements to an unreinforced brick-cement mortar wall in full-scale (1500 × 1500 × 250 mm), to which was conferred a double-fixed constraint condition. Based on the experimental evidences, a reference numerical model has been implemented in ABAQUS, by adopting a plastic-damage material and a macro-element approach for the masonry modelling. Hence, in order to determine a design criterion of the studied system, a comparison with the analytical formulations available in the current Italian and European codes for the unreinforced configuration is presented in this study. Then, a wide parametric study on the investigated retrofitting technique has been carried out by varying thickness and spacing of steel grid elements, as well as the geometrical ratio of the panel (height/length). On the basis of the numerical results, a capacity formulation has been proposed, which takes into account the steel distribution in the masonry panel. The obtained outcomes revealed that the strength increase achievable by adopting the studied reinforcement system could be compared to the efficiency of a reinforced masonry wall of new construction and it is strongly influenced by the geometrical ratio of the wall, as well as the steel distribution.

Integrated Seismic and Energy Retrofitting System for Masonry Walls Using Textile-Reinforced Mortars Combined with Thermal Insulation: Experimental, Analytical, and Numerical Study

Taking into consideration the seismic vulnerability of older buildings and the increasing need for reducing their carbon footprint and energy consumption, the application of an innovative system is investigated; the system is based on the use of textile-reinforced mortar (TRM) and thermal insulation as a means of combined seismic and energy retrofitting of existing masonry walls. Medium-scale tests were carried out on masonry walls subjected to out-of-plane cyclic loading. The following parameters were investigated experimentally: placement of the TRM in a sandwich form (over and under the insulation) or outside the insulation, one-sided or two-sided TRM jacketing and/or insulation, and the displacement amplitude of the loading cycles. A simple analytical method is developed and found in good agreement with the test results. Additionally, numerical modeling is carried out and also found in good agreement with the test results. From the results obtained in this study, the authors believe that TRM jacketing may be combined effectively with thermal insulation, increasing the overall strength and energy efficiency of the masonry panels in buildings.

Spandrel panels in masonry buildings: Effectiveness of the diagonal strut model within the equivalent frame model

Modeling of masonry buildings subjected to seismic actions still represents an open problem in structural engineering. The equivalent frame model is the most used approach to analyze the seismic behavior of both existing and new masonry constructions but, despite this, several aspects are being researched to improve its effectiveness. Among these, modeling of spandrel panels plays a key role to correctly analyze the in-plane seismic response of unreinforced masonry walls. Actually, horizontal mono-dimensional beam-like elements provided of both strength and displacement capacity are used to schematize the spandrel panels, also according with the most of current national and international codes.In this paper an alternative strut and tie scheme to model the spandrel panels, suitable to be used within the equivalent frame approach, is presented: the compressed masonry material is schematized with an equivalent diagonal no-tension truss, whose length and effective compressed area are obtained with limit equilibrium conditions, while tensile-resistant element is represented by no-compression truss. Such model allows a more realistic representation of the mechanical behavior of spandrels because both amount of axial force within the spandrel and the reduced elastic flexural and shear stiffness due to progressive cracking of material are taken into account. Moreover, the local failures of both compressed masonry and/or tensile-resistant elements are better identified and, consequently, also the failure mechanisms of the whole equivalent frame are better detailed.The proposed schematization has been used to simulate the seismic behavior of some reference case studies of existing masonry walls, strengthened with different steel ties arrangement. These walls have been modelled with a hybrid equivalent frame model which consists of mono-dimensional beam-like element for piers, fully rigid offsets for the nodal panels and a strut and tie scheme for spandrels.

Quasi-static cyclic tests of confined masonry walls retrofitted with mortar overlays reinforced with either welded-wire mesh or steel fibers

Overlays made of high-slump mortar reinforced with a steel welded-wire mesh are one of the most common techniques to retrofit low-rise confined masonry walls. An alternative to this technique is the use of Steel Fiber-Reinforced Mortar (SFRM) overlays to strengthen and enhance the shear capacity of existing masonry walls. In this paper, test results are presented of two full-scale, multi-hollow clay brick confined walls strengthened with reinforced mortar overlays. The overlays consisted of a high-slump mortar reinforced with a) welded-wire reinforcement in one wall and b) hooked end steel fibers in the second wall. Overall height and length of the walls were 2.5 m and 4.24 m, respectively. Both walls were tested under in-plane, quasi-static, reversed cyclic lateral loads. Performance of the retrofitted walls is evaluated in terms of crack patterns, hysteretic response, and lateral strength and displacement capacity. The test data show that both retrofit techniques performed very well and they each restored the strength and deformation capacity to that of the original walls.

Cylindrical samples of brick masonry with aerial lime mortar under compression: Experimental and numerical study

This research presents an experimental and numerical study focusing on the compression test of cylindrical samples core drilled from existing masonry walls. This method is suitable for the minor destructive assessment of the mechanical properties of historical masonry, like that composed of aerial lime mortar joints and solid clay bricks. This particular material combination, frequently found in the vast majority of the built cultural heritage, was utilized to build representative specimens that were stored in the laboratory for one year until their testing. Cylindrical samples of 150 mm diameter were extracted from the masonry walls by using a dry core-drilling procedure, and then regularized to be tested under compression in the laboratory. A comparison is presented between the experimental results on cylindrical samples and those obtained from standard compression tests on prismatic samples consisting in stack bond prisms. Numerical simulations by finite element micro-modelling of the compression tests on the core samples were carried out to investigate the experimental behaviour of the specimens and evaluate the compressive strength of the material from this nonstandard technique. The combined experimental and numerical study allows the assessment of important mechanical parameters for the compressive characterisation of masonry composed of aerial lime mortar joints and solid clay bricks.

In Plane Behaviour of Masonry Walls Reinforced with Mortar Coatings and Fibre Meshes

ABSTRACTConcerning strengthening techniques for existing masonry walls, the trend is toward the use of Fibre Reinforced Mortar (FRM) with both a significant increase of the mortar strength, and a drastic thickness reduction of the added external layers. In the present analysis, the focus is posed on some new lime mortar types which possess a very high strength in tension, although the elastic modulus remains in a normal range, leading so to a considerable toughness increase. The G-FRM system is composed with a glass fibre mesh which must possess a tensile resistance larger than the one of the mortar area including it, and this allows introducing some ductility in the composite. A total of 14 diagonal compression tests of masonry walls reinforced with G-FRM have been completed at LISG (Structural Engineering and Geotechnics Laboratory, University of Bologna), encompassing different FRM combinations. More precisely, the walls were reinforced with three different lime mortar compounds with layer thicknesses of 12, 15 and 30 mm, and reinforced with two different glass fibre meshes and two different arrangements of steel micro-wire strips. The performed tests showed that the interpretation of the observed behaviour needs a sound theoretical basis of the experimental setup, avoiding the simple analysis reported in standards and codes. A finite element model of the experimental setup was prepared, able to identify the features of the observed behaviour. Following this suggestion, a new theoretical model based on Mohr-Coulomb plasticity was defined and applied to the interpretation of a large database of experimental tests with a very good agreement.

Architectural Design for Re-functioning Historic Ottoman Warehouses: Case Study in Istanbul

Restoration of historical buildings is important because they maintain cultural and historical continuity and transmit the cultural and social values from our precedents to the future generations. Historical buildings need to adapt themselves to a changing cultural, social, economic and political context. In this paper re-functioning project of a historic Ottoman warehouse is presented. The aim of the project is to re-gain this historical structure for public use by re-newing it to the modern comfort level and making the required functional changes. The main structural system of the warehouse consists of thick masonry stone walls. The idea in the proposed restoration project is to build a two story steel structure inside the available volume of the warehouse. The columns of the new steel construction run parallel to the existing structural system of the historic building and are fixed at their base to the existing building foundation. So there is no connection between the proposed steel structure walls and the existing masonry walls, and this will save the historic fabric of the warehouse. The project proposal shows the details of planned restoration stages, the process of programming the new interior space, construction materials, and lighting and ventilation solutions. Furthermore in this project two and three dimensional computer drawings were used. Finally the proposed parallel steel structure is able to re-gain the warehouse and re-new it to be used as a modern housing and workshop.

Out-of-plane behavior of reinforced masonry walls: Experimental and numerical study

Abstract In the paper, the results of an experimental and numerical study on the out-of-plane bending effectiveness of a modern strengthening technique applied to existing masonry walls are presented. The technique consists in the application, on both wall faces, of a mortar coating reinforced with glass fiber-reinforced polymer (GFRP) meshes. Four point bending tests of full scale masonry samples (1000 width, 3000 mm height) were carried out considering three types of masonry (solid brick, 250 mm thick, rubble stone and cobblestones, 400 mm thick). The performances of plain and reinforced specimens were analysed and compared. It emerged that strengthened specimens are able to resist out-of-plane bending moments almost 4–5 times greater than those of plain specimens; moreover they can overcome deflections more than 25 times higher, due to the presence of the GFRP mesh, which contrasts the opening of cracks. The cracking and the ultimate bending moments of reinforced samples can be analytically predicted using relationships quite close to those used in the design of reinforced concrete beams subjected to combined axial and bending actions. The results of nonlinear static analyses performed on a 2D numerical model were also presented, so to comprehend the mechanical behaviour of reinforced masonry walls. Their agreement with the experimental results proved the reliability of the simulations; moreover, the extension of the 2D model to a 3D one, necessary to analyze the behavior of perforated walls, was also made.

Structural behaviour of masonry panels strengthened with an innovative hemp fibre composite grid

Sustainability goals are essential driving principles for the development of innovative materials in the construction industry. Natural fibres represent an attractive alternative as reinforcing material due to both good mechanical properties and sustainability prerequisites. The present work investigates the shear behaviour of masonry panels strengthened with a mortar-based system reinforced with an innovative hemp fibre composite grid. The objective of the study is to assess the feasibility of using the proposed strengthening system for external retrofit of existing masonry walls and to compare its performances with typical retrofitting solutions.