Periodic Reporting for period 1 - conFiRMa (Strengthening of existing masonry buildings with Fibre-Reinforced Mortar: calibration of a reliable numerical model to assess the structural performances)
Berichtszeitraum: 2020-11-01 bis 2022-10-31
In the building sector, the theme of sustainability in the use of territory cannot disregard actions aimed at limiting the soil consumption, by encouraging the refurbishment and reuse of existing buildings and preserving historical centers. Masonry, composed of brick or stone units jointed through weak lime mortar, represents the par excellence and most widespread construction material for historic buildings in Europe and worldwide. The safe usability and preservation of historic masonry buildings is an urgent issue for society, due to the intrinsic vulnerability of masonry. In fact, these structures proved to be extremely vulnerable to earthquakes, despite wide areas are subjected to high or moderate seismic hazard. Other exceptional actions can compromise the structure’s integrity: induced seismicity, caused by anthropogenic activities, crushing or blasts… Besides, historic masonry buildings demonstrated to suffer of structural deficiencies related to long-term fatigue, cyclic stress, durability of the materials and to modifications.
The “conFiRMa” project fell within the context of the study on innovative intervention strategies for the reduction of vulnerability and preservation of historic masonry structures and, in particular, dealt with the strengthening of existing masonry through Fibre-Reinforced Mortar (FRM). It is a modern, effective and compatible reinforcement strategy, which consists in plastering the walls by means of mortars with fibre-based elements embedded (meshes or textiles).
The project primarily addressed to the definition and calibration of a robust numerical model for predicting the behaviour of historic masonry structures strengthened with FRM systems, so to fill the current gap between the wide set of simplified laboratory experimental results available in the literature for FRM and the professional designers need to evaluate the performances of the complex, actual configurations. A broad numerical study on the structural performances of FRM strengthened masonry was performed, identifying the resisting mechanisms of such strengthened material, investigating on the interaction among the structural components and reproducing the damage evolution process under critical loading conditions. According to a “Multi-Level Approach”, different modelling strategies were calibrated, varying the scale of investigation: starting from a very detailed-level modelling for advanced research at the small scale level, followed by an optimization procedure to get a more computationally efficient multi-layer model, based on layered elements, to reliably simulate the behaviour of entire masonry walls and structures, until attain to very simplified models for the global analysis of structures to be used in the everyday professional practice.
The “conFiRMa” project fell within the context of the study on innovative intervention strategies for the reduction of vulnerability and preservation of historic masonry structures and, in particular, dealt with the strengthening of existing masonry through Fibre-Reinforced Mortar (FRM). It is a modern, effective and compatible reinforcement strategy, which consists in plastering the walls by means of mortars with fibre-based elements embedded (meshes or textiles).
The project primarily addressed to the definition and calibration of a robust numerical model for predicting the behaviour of historic masonry structures strengthened with FRM systems, so to fill the current gap between the wide set of simplified laboratory experimental results available in the literature for FRM and the professional designers need to evaluate the performances of the complex, actual configurations. A broad numerical study on the structural performances of FRM strengthened masonry was performed, identifying the resisting mechanisms of such strengthened material, investigating on the interaction among the structural components and reproducing the damage evolution process under critical loading conditions. According to a “Multi-Level Approach”, different modelling strategies were calibrated, varying the scale of investigation: starting from a very detailed-level modelling for advanced research at the small scale level, followed by an optimization procedure to get a more computationally efficient multi-layer model, based on layered elements, to reliably simulate the behaviour of entire masonry walls and structures, until attain to very simplified models for the global analysis of structures to be used in the everyday professional practice.
The project developed through the following steps:
- Literature review and creation of a broad, updated database including the available studies on FRM reinforced masonry, with systematic study of the experimental evidences, comparisons and analysis of the aspects to consider for reliable simulations;
- Identification of a suitable and optimised numerical strategy able to account for the relevant recognised aspects;
- Calibration of a numerical model at the detailed level (detailed modelling of components and mutual interfaces) for the simulation of the behaviour of FRM coupons and of FRM strengthened masonry elements subjected both to in-plane and out-of-plane actions. The model was calibrated on the basis of available experimental tests on individual components and interfaces and validated through comparison with experimental test results available in the literature. Sensitivity studies allowed to estimate the influence of materials characteristics, of geometric parameters and of some crucial detail aspects (e.g. the minimum bond length and delamination phenomena);
- Definition of a numerical model at the intermediate-scale level by using layered elements, to allow less computational effort for the simulation of more complex and wider configurations. The layers characteristics were calibrated and validated through comparison with the outcomes of the detail level simulations and the model was then applied to the simulation of wider masonry assemblages and structures such as full-scale piers, spandrels, vaults, whole masonry walls and entire buildings;
- Evaluation of the applicability, with the appropriate calibrations and adjustments, of the simplified modelling strategies commonly used in everyday professional practice (the equivalent frame method based on lumped plasticity) to the analysis of FRM strengthened masonry walls and buildings. Some case studies were selected and the results coming from the multi-layer approach and the equivalent-frame approach were compared.
The study results have been published/submitted for publication in journals and magazines and presented at various international conferences, seminars and workshops. The project-related achievements were also promoted on the project webpage and on the social media. The input files of the developed numerical models have been stored in an on-line repository and made freely available for consultation, download and use.
- Literature review and creation of a broad, updated database including the available studies on FRM reinforced masonry, with systematic study of the experimental evidences, comparisons and analysis of the aspects to consider for reliable simulations;
- Identification of a suitable and optimised numerical strategy able to account for the relevant recognised aspects;
- Calibration of a numerical model at the detailed level (detailed modelling of components and mutual interfaces) for the simulation of the behaviour of FRM coupons and of FRM strengthened masonry elements subjected both to in-plane and out-of-plane actions. The model was calibrated on the basis of available experimental tests on individual components and interfaces and validated through comparison with experimental test results available in the literature. Sensitivity studies allowed to estimate the influence of materials characteristics, of geometric parameters and of some crucial detail aspects (e.g. the minimum bond length and delamination phenomena);
- Definition of a numerical model at the intermediate-scale level by using layered elements, to allow less computational effort for the simulation of more complex and wider configurations. The layers characteristics were calibrated and validated through comparison with the outcomes of the detail level simulations and the model was then applied to the simulation of wider masonry assemblages and structures such as full-scale piers, spandrels, vaults, whole masonry walls and entire buildings;
- Evaluation of the applicability, with the appropriate calibrations and adjustments, of the simplified modelling strategies commonly used in everyday professional practice (the equivalent frame method based on lumped plasticity) to the analysis of FRM strengthened masonry walls and buildings. Some case studies were selected and the results coming from the multi-layer approach and the equivalent-frame approach were compared.
The study results have been published/submitted for publication in journals and magazines and presented at various international conferences, seminars and workshops. The project-related achievements were also promoted on the project webpage and on the social media. The input files of the developed numerical models have been stored in an on-line repository and made freely available for consultation, download and use.
The benefits of FRM systems on the structural performances of existing masonry elements have already been investigated experimentally in the literature, but the results are strictly related to the selected configurations in terms of materials, geometry, load pattern and boundary conditions. Numerical simulations permit to extend the experimental evidences to a wider number of configurations and to investigate on the performances of whole buildings. But a consistent model able to predict the performances of FRM strengthened masonry buildings had not been developed yet: the available numerical studies consisted mostly in models calibrated and applied for the reproduction of a specific test setup and combination of materials.
In this context, the project “conFiRMa” contributes to fill the gap between the wide set of simplified laboratory experimental results available for FRM and the professional designers' need to evaluate the performances of the complex, actual configurations, for a reliable, optimised design of the intervention. The three different levels of modelling approach offer the opportunity to investigate efficiently and coherently at different scales of analysis, ranging to detail aspects to global performances. Moreover, the project outcomes provide useful considerations for the standardization of the FRM design strategies, which is currently still an open task.
The scientific community (in particular the “Civil Engineering" and the “Computer sciences and informatics” sectors) can take advantage of the project achievements in structural refurbishment and of the open source numerical models developed. The improved knowledge in the use of FRM systems can also increase the mastery and competitiveness of professional sectors (professionals engineers, fibre-based elements manufacturing companies) in the design of modern strengthening interventions and, indirectly, reflects positively on the whole society, as final user of safer and preserved building heritage, encouraging the refurbishment and reuse of existing buildings, valorising historical centres and limiting the soil consumption.
In this context, the project “conFiRMa” contributes to fill the gap between the wide set of simplified laboratory experimental results available for FRM and the professional designers' need to evaluate the performances of the complex, actual configurations, for a reliable, optimised design of the intervention. The three different levels of modelling approach offer the opportunity to investigate efficiently and coherently at different scales of analysis, ranging to detail aspects to global performances. Moreover, the project outcomes provide useful considerations for the standardization of the FRM design strategies, which is currently still an open task.
The scientific community (in particular the “Civil Engineering" and the “Computer sciences and informatics” sectors) can take advantage of the project achievements in structural refurbishment and of the open source numerical models developed. The improved knowledge in the use of FRM systems can also increase the mastery and competitiveness of professional sectors (professionals engineers, fibre-based elements manufacturing companies) in the design of modern strengthening interventions and, indirectly, reflects positively on the whole society, as final user of safer and preserved building heritage, encouraging the refurbishment and reuse of existing buildings, valorising historical centres and limiting the soil consumption.