The project

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, characterising many urban and rural centres, often part of the architectural and cultural heritage.

Unfortunately, these structures are extremely vulnerable to earthquakes: in general, seismic provisions were not considered in the past in the construction process, despite wide areas of the European territory are subjected to high or moderate seismic hazard (http://www.share-eu.org/). Other exceptional actions can compromise the structural integrity: induced seismicity, crushing, blasts… Besides, historic masonry buildings may suffer for long-term fatigue, cyclic stresses, durability of the materials and modifications.

The project deepens the study on innovative intervention strategies for the reduction of vulnerability and preservation of historic masonry buildings, focusing on evaluation methods for their effectiveness. In particular, it deals with the strengthening of existing masonry through Fibre-Reinforced Mortar (FRM): this modern, effective and compatible reinforcement strategy, consists in plastering the walls by means of mortars with fibre-based elements embedded (meshes or textiles).

The effectiveness of FRM in improving the in-plane and out-of-plane performances of masonry walls and vaulted elements has already been extensively investigated experimentally, testifying the interest of the construction refurbishment market all over the world. However, optimized intervention and design strategies have not been fully defined yet and specific, detailed standards are missing for FRM, although some Countries have recently edited the first dedicated guidelines for system qualification.

Experimental tests, mostly based on simplified setups and/or on reduced scale samples, though indispensable, do not permit solely neither to reproduce occurately how FRM intervenes in actual applications, nor to evidence clearly the benefits on the performances of whole buildings.

Numerical modelling permits to extend the experimental evidences to a wider number of configurations, allowing also to investigate on the optimization of the strengthening intervention. But computational methods develped for unreinforced masonry can not be adopted “as are” in the case of FRM, due to the complex interaction between the masonry support and the reinforcement.

A broad, structured predictive model for FRM strengthened masonry is necessary.

The goal of the conFiRMa project is the definition and calibration of a novel, robust, multi-level 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 for FRM and the designers need to evaluate the performances of the complex, actual configurations.

The measurable objectives are:

• the creation of a database including the available studies on FRM reinforced masonry;

• the calibration of a numerical model at a detailed level for FRM strengthened masonry elements subjected both to in-plane and out-of-plane actions (the fibre-based elements, the mortar matrix and the masonry are modelled distinctly);

• the definition of a numerical model at an intermediate level to allow less computational effort on more complex configuration such as whole masonry walls or entire buildings (e.g. layered elements);

• the evaluation of the applicability of the equivalent frame method for global analysis (based on lumped plasticity) to FRM strengthened masonry buildings.

The validation of the detailed modelling level is pursued though comparison with experimental data available in the literature (i.e. FRM characterization tests, diagonal compression tests, in-plane and out-of-plane bending tests). The sensitivity analysis identifies the impact of the different parameters on the FRM efficiency and on the resisting mechanisms.

The reliability of the intermediate level modelling is assessed by comparison with the detail level model results. Investigations on more articulated case studies, such as walls with openings and whole buildings, are performed.

Entire structures are modelled by applying also the global equivalent frame method, to evaluate, through comparison with the results of the intermediate level model, its capability in simulating, with the appropriate adjustments, FRM strengthened structures.

The main software adopted for the numerical simulation is OOFEM. It is a free finite element code with object oriented architecture for solving mechanical, transport and fluid mechanics problems that operates on various platforms. It is an efficient and robust tool for FEM computations, providing modular and extensible environment for future development. Originally developed by prof. B. Patzák at the Czech Technical University in Prague (the host), the code consists of more than 200k lines of source code in C++; it is freely available under General Public License, and it is being developed by an international community.