•Textile-reinforced mortar upgrades the structural performance of masonry buildings.•The method consists in applying a composite overlay to either one or both wall faces.•Experimental procedures and ...results are presented and commented.•Analytical methodologies are presented and discussed.
The emerging need to upgrade the structural performance of buildings and structures has been recently alleviated with the newly developed textile-reinforced mortar (TRM) composites. This need becomes vital for unreinforced masonry structures (URM) which are most vulnerable to earthquakes. Very often the seismic strengthening technique opted for these structures involves the application of a composite material overlay to either one or both faces of the walls. As opposed to fibre-reinforced polymers (FRP), in TRM the high-strength fibres are embedded in an inorganic matrix. In consequence, the matrix, usually a cementitious mortar, offers compatibility with substrates, lower costs, and better performance at high temperatures, while permeability is enhanced and reversibility is achieved. Given these advantages, it is not surprising that TRM has gained considerable popularity for strengthening masonry structures. This paper addresses the characteristics of TRM composites and gives an insight into relevant experimental procedures and results of retrofitted masonry elements to illustrate the effectiveness of TRM for enhancing strength and deformation capacity. Finally, analytical models regarding the capacity of columns, spandrel beams and piers are briefly discussed.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Shear fuses are structural elements that protect surrounding members from damages by undergoing substantial yielding, and then are easily replaced after a major earthquake event. Butterfly-shaped ...shear fuse is a promising type of structural system, which can effectively align member's flexural capacity to the imposed moment demand due to its unique geometry. Although recent studies suggest that butterfly-shaped fuses exhibit substantial ductility and energy dissipation, their impact on the global performance of multi-story buildings requires further investigation. This study presents a comprehensive risk-based evaluation of a six-story eccentrically braced steel frame retrofitted with butterfly-shaped fuses. Two nonlinear finite element models of the original prototype building and retrofitted building with butterfly-shaped fuses are developed in OpenSees and incremental dynamic analysis is conducted. The results are used to derive global and story-based fragility and seismic demand hazard curves. Furthermore, earthquake-induced losses associated with structural and non-structural assemblies are quantified and the impact of butterfly-shaped fuses on the distribution of story acceleration and drift demands are evaluated.
The results show that butterfly-shaped fuses significantly improve the structure's performance in terms of all drift-related damage states and the improvement is more pronounced at severe damage states. In particular, the risk of exceeding complete damage state in the retrofitted building's lifetime is reduced to approximately one-fourth of the original building's values. Furthermore, shear fuses effectively mitigate weak story formation at lower stories due to their large energy dissipation and ductility. The improved drift-related performance reduces the drift-induced loss of structural and non-structural assemblies, resulting in 44.64% smaller total annual loss for the studied building. In addition, although butterfly-shaped fuses reduce the probability of exceeding slight damage state for the floor acceleration, their impact is negligible at higher acceleration-related damage states.
•Probabilistic seismic performance is conducted for rehabilitated EBF systems.•The results are used to derive global and story-based fragility and seismic demand hazard curves.•Loss evaluation of a multi-story steel building equipped with butterfly-shaped fuses is conducted.•Butterfly-shaped system reduces the induced loss by improving the drift-related performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
With the development of performance based earthquake engineering, the recognition of performance based seismic design (PBSD) is continuously growing in academia and industry. Meanwhile, with the ...gradual awareness of earthquake threat to the existing aged buildings, researchers are focusing more on the novel retrofitting technologies to enhance the structural capacity. Based on this background, a novel precast steel-reinforced-concrete and ultra-high-performance-concrete composite braced-frame is developed for the externally attached seismic retrofitting, and a stochastic capacity spectrum method (CSM) based displacement-oriented design strategy is proposed and well validated via a case study. In general, the novel external composite substructure combines the superiority of substructure technology, precast technology, energy-dissipation technology and high-performance material technology, and is a promising structural form in the seismic retrofitting. The proposed design strategy derives from the classic CSM, and its procedure is in alignment with the PBSD to make the designed building to satisfy various predetermined functional requirements during use. The incorporation of probability factors makes evaluation results more comprehensive and objective, and the control of displacement targets makes structural systems more performant under different demand levels. The case study indicates that the stochastic CSM-based design strategy can be well coupled with the novel external composite substructure during the whole retrofitting process (i.e., three design parts), which demonstrates the superior applicability and stupendous potentials of the proposed design strategy for the subsequent in-depth research.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Past earthquakes revealed that the brittle nature of unreinforced masonry (URM) structural walls often leads to extensive cacking and shear damage, which can seriously affect the structural integrity ...and thus compromise the safety of the entire building. Hence, finding an effective seismic retrofitting solution that can increase the safety of existing masonry building stock is of great importance. This paper explores the potential of alternative seismic retrofitting solutions for URM masonry walls - near-surface mounted austenitic stainless-steel helical bars. Being cold rolled from a plain round wire and subsequently tensioned through a free-twisting process, such a reinforcement can not only offer high durability, but also superior mechanical and bond properties, as well as effective redistribution of loads through the retrofitted masonry. In addition, the relatively high flexibility of the bars allows them to be mounted continuously along the joints of the wall, leaving the aesthetic of the retrofitted masonry intact. A total of nine single-leaf clay brick walls were tested under cyclic displacement reversals to examine the seismic performance of the reinforcement in terms of increasing in-plane shear capacity and ductility. Test specimens comprised cantilever walls with various retrofitting patterns, including flexural and shear helical reinforcements installed in the mortar joints or into the vertical slots cut into the masonry. The results showed considerable improvements in the ductility and energy dissipation of the walls after the retrofitting. For most of the retrofitted walls the value of q factors exceeded 4.0, which is greater than the typical q factors for reinforced masonry, thus indicating that large increases in ductility were achieved. The paper highlights the potential of helical stainless-steel bars as a seismic retrofitting reinforcement capable of preserving the structural integrity of masonry structures at increasing displacement demands without affecting the aesthetic of the surface of the walls.
•Helical reinforcement for URM offered desirable balance between flexibility, strength, and bond.•URM walls retrofitted with helical bars showed improved ductility and energy dissipation.•Novel retrofitting patterns utilising “wiggled” vertical bars were investigated.•Retrofitting with helical bars allows for preserving natural aesthetics of masonry.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
This paper presents a state-of-the-art review on the available seismic upgrading techniques of existing masonry structures, which comprise a very common structural material including most of the ...surviving historic structures worldwide. Due to their increased age and vulnerability, masonry buildings and structures are generally in greater need of structural retrofitting than newer ones constructed with more modern materials. The discussed techniques are divided into three major categories, according to the way they affect the building's load-bearing mechanism. The first one includes those which target individual structural elements aiming to enhance their cyclic behavior. The second one includes those techniques which aim to improve the overall structural integrity of a given structure. Finally, methods which aim at reducing the internal seismically induced forces using special devices comprise the final category. Both conventional and novel upgrading techniques are covered, but the emphasis is clearly on the latter, while the integration of seismic upgrading techniques with measures for energy upgrading is briefly discussed for masonry building envelopes.
•Seismic upgrading the existing URM structures is gaining more and more attention.•Techniques to upgrade individual elements and the overall integrity of URM structures.•Conventional and novel techniques are reviewed in terms of strengths and weaknesses.•Combining seismic & energy retrofitting is feasible for masonry building envelopes.
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Earthquakes cause serious damage to buildings and result in heavy losses to society, therefore, it is necessary to enhance the seismic capacity of existing buildings via structural retrofitting. The ...traditional retrofitting approaches are based on the component-level, but their improvement effect for the overall structure is not obvious. The ultimate goal of seismic retrofitting is to improve the overall seismic performance of the whole structure, thus a variety of external sub-structure retrofitting methods have been developed at home and abroad since the 1970s. The external sub-structure is connected with the existing structure as a whole on the structural-system-level, and it is of great significance for lifeline projects or non-interrupted buildings. At this stage, the external sub-structure retrofitting technology has received wide attention in the seismic community and is still developing in bloom. This paper gives a state of the art review of the advances and research interests of the external sub-structure retrofitting technology. First, the general concepts of the external sub-structure retrofitting technology are given, including (1) retrofitting principle and (2) retrofitting superiority. Then, the typical types of the external sub-structure retrofitting technology are summarized, including (1) external frame sub-structures, (2) external frame-brace sub-structures, (3) external wall sub-structures and (4) other external sub-structures. Finally, some critical issues of the external sub-structure retrofitting technology are extracted, including (1) interfacial shear transferring mechanism, (2) joint property and connection performance, (3) combination with precast-assembly technology, (4) combination with prestress technology, (5) numerical approach and assessment indicators, (6) optimization strategy and design procedure, (7) environment interaction and maintenance cost, and (8) application in practical engineering. The future perspectives of the external sub-structure retrofitting technology are also pointed out, and the contents can provide some reference for the subsequent research as well as the developing trend in the future.
•State of the art review and future perspectives of the well-known external sub-structure retrofitting technology.•Give the general concepts and summarize the typical types of the external sub-structure retrofitting technology.•Extract eight critical and technical issues of the external sub-structure retrofitting technology worthy of attention.•Point out the further developing trends and potential technical improvements of the external sub-structure retrofitting technology.
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Any seismic retrofitting plan on historical monuments has to follow the principles of minimal intervention, recognizability and reversibility. A feasibility study is here proposed for a new type of ...glass-based bracing, particularly suitable to strengthen soft storeys, typically represented by the presence of colonnades. This has the advantages of being stiff, slender and, most of all, transparent, recognizable and completely reversible. The bracing is a large laminated glass pane contoured by a thin steel lamina (frame), which confines the glass and provides a restraint against the pane rotation under horizontal actions. Since glass is a brittle material, we propose a system of gaskets and aluminum inserts, specifically designed to avoid contact stress concentration, especially at the corners of the glass pane. A paradigmatic case study, corresponding to a colonnade extrapolated from a representative historic building, has been analyzed in detail. Discrete element modeling has been used to simulate the dynamic response of the ancient masonry composed of stone blocks under horizontal seismic-like ground motion. Since the glass-based bracing represents a source of concentrated stiffness, we evaluate its correct placement inside the colonnade in order to avoid hammering effects, otherwise the bracing could even worsen the seismic capacity of the original structure. Another crucial issue is the connection of the bracing to the old masonry and foundations, for which possible technical details are provided. We show that a correct design and positioning of the bracing can improve the seismic capacity of the system with minimal visual impact.
•The concept design for a glass-based transparent shear wall is presented.•It consists of a laminated glass pane, hooped by a thin contouring steel frame.•It is applied in the seismic retrofitting of listed buildings with colonnades.•Bracing-structure interaction under real seismograms is analyzed via DEM model.•Construction details for a possible field application are provided.
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The current techniques used for strengthening existing buildings made out of masonry infilled frames are characterized by high impact on the daily internal activities, as people living or working in ...the building need to move out while the retrofitting activities take place.
The seismic vulnerability of infilled concrete frames is related to their high stiffness that, being due to the presence of masonry infills, induces a very brittle failure mechanism. The available retrofitting techniques do not allow to decrease the frames stiffness without making demolitions, especially for what concerns the double layer infills, a typology that characterizes a large part of the Italian buildings built from 1970s. For such infills only traditional techniques are available, mostly lime/cement-based mortars strengthened with various fibers that increase the frame stiffness. This study proposes an innovative technique for the out-of-plane strengthening of masonry double layer infills. The system is based on a 3D printed system made of recycled plastic, placed between the two masonry layers composing the infill and acts: i) triggering preferential in-plane sliding surfaces for reducing stiffness and therefore damaging, ii) warranting out-of-plane stability avoiding the snap-through mechanism, iii) ensuring low environmental impact by using recycled materials and, iv) no disrupting the daily internal activities. The full scale out of plane test is carried out on an infill specimen previously damaged in the in plane direction, by using a hydraulic jack placed at mid-height of the infill. The experimental results are compared with analytical models available in literature combined with a model specifically developed for the resistant mechanism provided by the plastic devices. The obtained results suggest that plastic joints are effective in preventing instability and can be used as effective strengthening system for concrete frames with masonry infills.
•Specially developed seismic retrofitting system for double layer infills.•Innovative snap-through mechanism control-based seismic retrofitting devices.•Manufacturing of the structural components with 3d printing technique and recycled plastic.•No disrupting of the daily internal activities.•Low water consumption, aggregates and binder, reuse of plastic waste, no demolitions.
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•Optimization study on minimum number and location of seismic retrofitted columns.•Empirical results obtained through time-history analysis on a three-story school.•Retrofitting 60.2% of the columns ...could withstand ground acceleration of 0.2 g.
Seismic retrofit technology has been significantly developed to reduce building damage during earthquakes. However, earthquakes are unpredictable natural disasters that should be dealt with flexibly. Hence, the seismic retrofitting method should be independently studied. In this study, the minimum number and the location of seismic retrofitted reinforced concrete columns required for school buildings in service are derived through an optimization technique. A time-history dynamic analysis of the frame structure comprising columns and beams is conducted using a three-dimensional finite element model to obtain empirical results. The study subject is a school building, which is a three-story RC structure with non-seismic details consisting of 62 RC columns on each floor (i.e., a total of 186 columns). The optimization analysis showed that retrofitting only 60.2% of the columns could withstand a peak ground acceleration of 0.2 g applied at the shear critical regions at both column ends.
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