Mechanics and durability of lime-based textile reinforced mortars

Application of lime-based textile-reinforced mortars (TRMs) for strengthening of masonry structures have received a growing attention in recent years. An extensive effort has been devoted to understanding of the performance of these composites and their effectiveness in improving the seismic safety of existing masonry structures. Nevertheless, several aspects regarding the durability and mechanics of these composites still remain unknown. This letter is an effort on highlighting those aspects considering both experimental and numerical modelling approaches

Durability analysis of bond between composite materials and masonry substrates

Tese de doutoramento em Engenharia CivilIn recent years, composites materials have been increasingly accepted as effective strengthening technique for civil engineering structures, particularly in the case of reinforced concrete. The reliability of this technique, when externally applied, depends on the long-term bond behavior between these materials and the masonry substrate, but research in this area is still very limited. The main purpose of this thesis is to create a basis for a general approach to durability of masonry components strengthened with composite materials. As far as the research method is concerned, a combined experimental and numerical approach has been chosen. Through systematic testing, fundamental knowledge is developed concerning the physical and mechanical properties of the basic materials and the strengthened components under environmental degradation. The strengthened specimens are subjected to different hygrothermal conditions including water immersion and cycles of temperature with constant relative humidity. Non-destructive investigation tests are made for both un-exposed and exposed specimens. Analysis of the interface behavior for different exposure conditions are carried out and the results are discussed. Predictive models are also used for simulating the observed degradation and the reliability of each model is investigated in comparison to experimental results. The numerical studies are conducted at two levels. Firstly, the bond behavior is modeled following detailed and simplified approaches. In the detailed approach, all material constituents with suitable constitutive laws are modeled. The model provides valuable information regarding less known aspects of bond behavior such as effect of mortar joints. In the simplified approach, the bond behavior is modeled using interface elements. A tri-linear bond-slip law is proposed based on the available experimental data and is used as the constitutive law for the interface elements. Both models are validated with experimental data. Secondly, the effect of local bond degradation on the global response of FRP-strengthened masonry panels is investigated. For the bond between FRP and masonry, the interface elements are used adopting the proposed bond-slip law. Based on the experimental results produced in this study, a degradation model is proposed and used for the interface behavior. The nonlinear performance of the strengthened panels after ageing in different environmental conditions is investigated and discussed.Nos últimos anos, os materiais compósitos têm sido cada vez mais aceites como uma técnica de reforço eficaz para estruturas de engenharia civil, particularmente em betão armado. A fiabilidade desta técnica, quando aplicada por colagem externa, depende do comportamento da aderência, a longo prazo entre esses materiais e o substrato de alvenaria, mas a investigação nesta área é ainda muito limitada. O principal objetivo deste trabalho é criar uma base para uma abordagem geral sobre a durabilidade dos componentes de alvenaria reforçados com materiais compósitos, recorrendo a uma abordagem experimental e numérica. Através de ensaios desenvolve-se conhecimento fundamental sobre as propriedades físicas e mecânicas dos materiais, e sobre os componentes reforçados submetidos a degradação ambiental. Os provetes reforçados são submetidos a diferentes condições higrotérmicas, incluindo imersão em água e ciclos de temperatura com humidade relativa constante. Ensaios não destrutivos são realizados sobre provetes não-expostos e expostos. O comportamento de interface para diferentes condições de exposição é discutido. Modelos de previsão são também utilizadas para simular a degradação observada e a fiabilidade de cada modelo é investigada em comparação com os resultados experimentais. Os estudos numéricos são conduzidos a dois níveis. Primeiro, o comportamento da aderência é modelado seguindo abordagens detalhadas e simplificadas. Na abordagem detalhada todos os componentes materiais com leis constitutivas adequadas são modelados. O modelo fornece informações sobre aspetos menos conhecidos da aderência, como o comportamento das juntas de argamassa. Na abordagem simplificada, o comportamento da aderência é modelado usando elementos da interface. Uma lei trilinear de comportamento do tipo bond-slip é proposta com base nos dados experimentais para elementos de interface. Ambos os modelos são validados com dados experimentais. Em segundo lugar, os efeitos locais de degradação da aderência sobre a resposta global dos painéis reforçados de alvenaria são investigados. Para a aderência entre FRP e alvenaria utilizam-se elementos da interface, adotando-se a lei de comportamento proposta. Com base nos resultados experimentais produzidos neste estudo, propõe-se um modelo de degradação que se utiliza o comportamento da interface. O desempenho não linear de painéis reforçados, após envelhecimento em diferentes condições ambientais, é investigado e discutido

Real-time assessment of tunnelling-induced damage to structures within the building information modelling framework

During the initial design phases of complex multi-disciplinary systems such as urban tunnelling, the appraisal of different design alternatives can ensure optimal designs in terms of costs, construction time, and safety. To enable the evaluation of a large number of design scenarios and to find an optimal solution that minimises impact of tunnelling on existing structures, the design and assessment process must be efficient, yet provide a holistic view of soil-structure interaction effects. This paper proposes an integrated tunnel design tool for the initial design phases to predict the ground settlements induced by tunnelling and building damage using empirical and analytical solutions as well as simulation-based meta models. Furthermore, visualisation of ground settlements and building damage risk is enabled by integrating empirical and analytical models within our Building Information Modelling (BIM) framework for tunnelling. This approach allows for near real-time assessment of structural damage induced by settlements with consideration of soil-structure interaction and non-linear material behaviour. Furthermore, because this approach is implemented on a BIM platform for tunnelling, first, the design can be optimised directly in the design environment, thus eliminating errors in data exchange between designers and computational analysts. Secondly, the effect of tunnelling on existing structures can be effectively visualised within the BIM by producing risk-maps and visualising the scaled deformation field, which allows for a more intuitive understanding of design actions and for collaborative design. Having a fully parametric design model and real-time predictions therefore enables the assessment and visualisation of tunneling-induced damage for large tunnel sections and multiple structures in an effective and computationally efficient way

PVA fiber/matrix interface characterization in alkali-activated slag/fly ash system: Effect of SiO2/Na2O ratio

Bond behavior between fiber and matrix plays crucial role in the nonlinear properties and performance of fiber reinforced composites. However, the available information on the fiber/matrix interface properties in composites made of alkali-activated materials is still quite limited which have hindered the scientific design and production of these materials. This study presents an experimental investigation for evaluating the bonding characteristics of PVA fiber/alkali-activated matrix interface by performing single fiber pullout tests. Four SiO2/Na2O ratios (0.8, 1.0, 1.2 and 1.5) within the alkaline activator were used for mixture preparation to investigate the effect of chemistry of the matrix on the bond performance. All the specimens were tested after 28-days curing. The interface characteristics including chemical bonding energy, interfacial frictional force as well as the slip-hardening properties were determined from the fiber pullout tests. It was found that the chemical bonding energy increased initially and then decreased with increment of SiO2/Na2O ratio, indicating an optimal alkaline activation condition at SiO2/Na2O ratio of 1.0-1.2. At the same time, the interfacial frictional strength and the slip-hardening properties did not change significantly by increasing the SiO2/Na2O ratio. These changes with SiO2/Na2O ratios were further correlated with the chemical nature of the reaction products to provide preliminary insight into the interfacial bonding properties of PVA fibers to the alkali-activated slag/fly ash matrices

Durability of textile reinforced concrete: existing knowledge and current gaps

This paper aims to provide a review of the current literature on the durability of textile-reinforced concrete and mortar (TRC/TRM) composites. Most previous studies have focused on the role of chemical attacks, freeze-thaw conditions, and high temperatures on the mechanical performance of these composites. Information on the long-term performance of TRCs under synergistic action of mechanical and environmental loads is scarce. Considering the variety of fabrics and matrices used for the production of TRC composites, the existing data are still very limited and comprehensive studies are needed in this field. Additionally, due to the lack of standard procedures, different approaches are often followed for durability or post-ageing mechanical tests, or sufficient data on the curing and post-ageing preparation procedures followed are not provided. These have led to incompatibility of the existing data and in some cases contradictory results on the durability of these materials.The support to the third author through grant SFRH/BD/131282/2017 is acknowledged

Seismic evaluation of masonry structures strengthened with reinforced concrete layers

Coating the walls with reinforced concrete layers is a conventional method of strengthening masonry structures in Iran. However, due to the lack of analytical and experimental information about the behavior of strengthened masonry wall with this method, the design of these walls is generally conducted based on empirical relations and decisions which may result in uneconomical or under-designed strengthening details. This paper aims at developing a rational method for design and seismic evaluation of unreinforced masonry walls strengthened with reinforced concrete (RC) layers. In the proposed method four failure modes are considered for these walls and the strength relations and acceptance criteria for each of them are provided in accordance with FEMA 356 and ASCE 41 relations for reinforced concrete and masonry walls. The accuracy of the proposed method in predicting the nonlinear behavior and governing failure modes of the strengthened walls is validated by comparing the results with available experimental and performed numerical results

Numerical analysis of the in-plane behaviour of TRM-strengthened masonry walls

Application of Fibre Reinforced Polymers (FRPs) for Externally Bonded Reinforcement (EBR) of masonry structures has received extensive attention during the past decade. FRPs are found to be hardly compatible with historical masonry. As an alternative, the use of innovative composite materials based on continuous fibres embedded in inorganic matrices (also referred as TRM) has found recent attention. However, only few information is available in the literature regarding the mechanical properties and effectiveness of TRMs for strengthening of masonry structures. This paper presents the numerical simulation of the nonlinear behaviour of TRM-strengthened masonry panels under in-plane actions. The modelling strategy is initially validated by simulating tensile response of TRMs and validation with available experimental results. The effect of different tension softening models on the tensile response ofTRMs is also investigated. The adopted modelling strategy is then used to predict the in-plane response of masonry panels strengthened withTRM composites under compressive and monotonic lateral-loading. The FE model predicts the key parameters in the behaviour of strengthened masonry, including the load-displacement response, crack development, failure mode and reinforcement contribution to the global performance. The results, presented and critically discussed, indicate that strengthening based on TRM significantly improves the performance of masonry walls under shear loading.- (undefined

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

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

Experimental investigation on the long-term durability of bond between FRP and masonry substrates

The characterization of long-term behavior of bond between Fiber-Reinforced Polymers (FRPs) and masonry substrates in a service environment is a crucial issue for design purposes, which requires a full body of experimental and theoretical information. Most of the research in this area has been devoted to FRP-concrete specimens, and the available data for FRP-strengthened masonry components are still lacking. This paper presents the experimental investigation on degradation of bond between glass FRP composite sheets and masonry bricks by performing accelerated aging tests. Masonry bricks strengthened with GFRP sheets are prepared following the wet lay-up procedure and exposed to thermal cycling and constant relative humidity. Single-lap shear bond tests are finally performed for investigating the degradation of the bond after exposure to environmental conditions and the results are presented

Bond behaviour and durability of FRP composites applied externally to masonry structures

The several advantages associated to the use of FRP composites for civil structural applications (mainly reinforced concrete and masonry) has led to a considerable increment in use during the last years. However, the performance of FRP composite strengthening systems when exposed to harsh environmental conditions is a matter of great concern, which justifies the recent research efforts towards the characterization of the deterioration effects. This paper discusses some of the most relevant environmental agents and their effect on the durability of FRP-strengthened concrete and masonry constructions. The results of a comprehensive series of accelerated ageing tests (water immersion and hygrothermal exposure) on external GFRP-strengthened masonry and respective constituent materials recently carried out at University of Minho are presented and discussed in detail.The financial support from the project FP7-ENV-2009-1-244123-NIKER is gratefully acknowledged. The Portuguese Science Foundation through grant contract SFRH/BD/80697/2011