Subject matter

The assessment and extension of service life of unreinforced brick masonry structures and infrastructure is a worldwide challenge for the development of resilient urban areas as well as preservation of historical assets. For an accurate assessment, the estimation of mechanical performance of masonry material is of importance.

To balance the invasiveness of the testing method with the knowledge acquired on mechanical properties, tests on horizontally-loaded cores have been used in the last 80 years as minor destructive test (MDT) for unreinforced brick masonry. As part of a research project for the assessment of masonry arch bridges, the International Union of Railways (UIC) provided the first recommendation to evaluate the compressive strength of masonry with core testing (UIC 778-3). After a first application mainly to infrastructure, the method was employed by some research groups to evaluate properties of existing masonry buildings. Additionally, a testing procedure to obtain shear properties of masonry was also developed in the framework of seismic assessment of buildings.

Currently the following inconsistencies have been found which further motivate the work of this TC:

• The core testing method to estimate compressive properties of masonry is generally used for infrastructure both from academics and practitioners. Its application to buildings is considered mainly in academic research, even though it is gaining interest in the professional world.
• The core testing method to estimate shear properties of masonry is used more by academics than by practitioners.
• A variety of testing methods are being used, considering different core geometries, bond patterns, testing set-up and instrumentation.
• Cross-comparison between the experimental results of core testing and standard tests on rectangular specimens, as wallets (EN 1052-1) and triplets (EN 1052-3), provides different outcomes for masonry types in different countries.

We aim at harmonising the testing procedures to evaluate the compression and shear properties of masonry by using core testing method. With respect to other minor destructive testing methods, core testing provides limited invasiveness to the structure/infrastructure, it has the potentiality to evaluate the complete nonlinear behaviour of masonry, it can be carried out with regular technical skills (e.g., using standard testing rig available in laboratory and using extraction procedures well established in practice). For these reasons, the development of testing guidelines (limited to unreinforced brick masonry) will further boost its use in engineering practice improving the reliability of structural assessment and thus the sustainable maintenance of the existing assets.

Terms of reference

To develop harmonised testing procedures, the following objectives are set:

• Develop a comprehensive state-of-the-art to set up of an inventory of current testing procedures and related experimental results to be summarised in two databases (one for both compression and one for shear properties).
• Identify influencing factors (boundary conditions, core diameter, core length, bond pattern, etc..) on the results of core testing method based on the analysis of the databases.
• Carry out an experimental testing campaign to define optimal testing procedures. Tests will be performed on a variety of masonry types in different countries to obtain a general validity of the method. Experimental results on cores will be compared with standard tests for masonry as well as with non-destructive test results. The comparison will be made also considering the complete nonlinear properties of masonry, when possible.
• Define guidelines for core testing to evaluate: i) compression properties (elastic modulus, compressive strength), and ii) shear properties (cohesion, friction coefficient).

To reach the objectives, first a literature review will be carried out to make an inventory of all available experimental data and related testing procedure used; as an outcome, two open-access databases will be created. Second, upon the analyses of the databases, influencing factors in the testing procedures will be identified. Third, a round-robin testing campaign across different institutes is foreseen. Eventually, guidelines for testing will be drafted and published as RILEM recommendations. Throughout the period in which the TC is active, dissemination activities will be planned, also involving national testing institutes, private companies and practitioners working in the field of the assessment of masonry structures and infrastructures.

Initially, the TC will be formed by members from academy and companies from the following countries: the Netherlands (3); Italy (4), Spain (1), Hungary (1), Poland (1), United Kingdom (1).

Detailed working programme

WP1 - State-of-the-art and databases

First experimental data will be collected from publicly available sources, such as conference and journal articles, and from technical reports available in testing institutes or engineering companies (usually not publicly available). Data will regard tests on field-extracted and lab-replicated core samples; whatever possible, information on companion tests, i.e., according to standard tests on rectangular specimens or non-destructive tests, will also be collected. Information on testing set-ups and testing procedures will also be gathered. For each core testing method, a database will be created and published open access.

WP2 - Identification of influencing factors

Based on the database, an analysis of the experimental outcomes of core testing methods in respect to companion tests will be carried out to identify potential influencing factors. It is expected that these factors could be properties of brick and mortar, boundary conditions, diameter and length of the core, bond pattern of the core, loading conditions, etc. Their influence will be tested in the round-robin activities in WP3; preliminary nonlinear finite element analysis will be considered to further refine the selection of influencing factors. Outcomes will be made available via open-access publications.

WP3 - Round-robin experimental testing

Experiments will be performed by the TC members at the different international institutes to test the method for a large variety of brick and mortar types typically used in existing buildings and infrastructure. The selection of materials will be made based on the outcome of WP1; however, it is expected that clay and calcium silicate bricks will be considered as well as cement, lime and cement-lime mortars. Based on the outcomes of WP1 and WP2, few variations of testing procedures will be selected and used for the testing. Cores with different bond patterns, having diameters ranging between 90 to 150 mm, will be considered. Companion tests will be also performed next to core testing to define correlations factors between properties. For both core testing and companion tests, the complete nonlinear behaviour of masonry and corresponding crack pattern will be evaluated and analysed to estimate elastic, strength and toughness properties. Experimental outcomes and related datasets will be thoroughly compared between the TC members and made available via open access publications.

WP4 - Definition of guidelines for testing

Based on the outcomes of the previous work packages, guidelines for core testing to evaluate compression and shear properties of masonry will be drafted. The guidelines will at least address the estimation of elastic properties, compressive strength, cohesion and friction coefficient. The outcome will be published open access in the journal Materials and Structures as RILEM recommendation.

WP5 – Dissemination

The outcomes of the TC work will be published in the open-access journal Materials and Structures. All experimental data collected or produced by the TC will be made available in the open-access repository of one European university for a period of at least 15 years. The work of the TC will be presented at relevant international conferences. A final international workshop (online or in hybrid form) will be organised with academic and industry partners to disseminate the work of the TC and illustrate the developed guidelines.

The expected total duration of the committee activities is 5 years. Below a tentative timeline is provided for each work package. The committee is expected to have regular meetings at least twice a year.