The initial phase of the project engaged the two universities on the development and calibration of the original algorithms that will allow designers to quantify the effectiveness of the interventions experimentally studied in the "CONSTRAIN" project (Fig.1, 2). The activity saw the collection and analysis of the results of the experimental tests relating to masonry piers, spandrels, out-of-plane bending of walls, floor and roof masonry beams.

Image

Fig.1 "CONSTRAIN" reinforcement of stone masonry walls: reinforcement on both sides (a), and on one side (b)

Image

Fig.2 "CONSTRAIN" reinforcement of brick masonry walls: reinforcement on both sides (a) and on one side only, in the case of a wall with one (b) or multiple wythes (c)

The analysis of the experimental data allowed the definition of the mechanical response through analytical models, to evaluate the contribution of the reinforcement (Fig.3). Simple correlations have been developed to facilitate the evaluation of the performance of the reinforced elements by the designers. These results were collected in Report 1.1 (Analytical Sizing Models).

Image

Fig.3 Comparison between the analytical correlations and the experimental curves for masonry piers (a) and spandrels (b) of the "CONSTRAIN" project

Subsequently, finite element numerical models were developed, capable of simulating the actual behavior of the experimental samples tested in the "CONSTRAIN" project, using the software OOFEM by the University of Trieste and Abaqus SIMULIA by the University of Ljubljana. Particularly, OOFEM is an open source finite element program, developed by the University of Prague. The numerical models in OOFEM have been developed with an intermediate level of detail, with equivalent multilayer solid elements (representative of reinforced masonry), while in Abaqus the models have a higher degree of detail, using different solid finite elements for each material. For this activity, the two universities worked closely together to define the parameters to be taken into account in the modeling and to validate the numerical models with the results of the experimental tests of "CONSTRAIN" (Fig.4).

Image

Fig.3 Confronto tra le correlazioni analitiche e le curve sperimentali per i maschi murari (a) e le fasce di piano (b) del progetto "CONSTRAIN"

Fig.4 Numerical analysis in OOFEM: (a) representation of the in-plan test model on masonry piers; (b) comparison between the numerical analyses and the experimental curves of the P-B2 samples of the "CONSTRAIN" project

The calibrated numerical models calibrated were used in parametric analyses, aimed at evaluating the impact of masonry geometries and boundary conditions on the reinforcement performance (Fig.5). Parametric analyses allow to extend experimentally treated cases and provide new results faster and more cost-effectively.

Image

Fig.5 Abaqus analysis of the effect of reinforcement on masonry piers with a 0.56 aspect ratio (height/width): Force-displacement curves (left) and strain concentrations (right). Gray curves correspond to walls with a 1.0 aspect ratio

In parallel, benchmark examples of wall configurations of increasing complexity were defined for the application of the simplified modeling criteria and the analytical correlations developed. A series of examples of single structural elements (piers and spandrels), portals, one- and two-storey walls (Fig.6), and an entire building (Fig.7) were analyzed. The construction of simplified numerical models uses the equivalent frame method. These were simulated in both unreinforced and reinforced configurations, using "CONSTRAIN" reinforcement techniques. Graphical comparison and critical discussion of the results of the simulations performed with the different software were performed.

Image

Fig.6 Some examples of structural elements and configurations evaluated with the analytical-mechanical method and with equivalent frame models

The activity involved the University of Trieste and the companies Fibre Net and GI ZRMK for the comparison of the results obtained with the commercial calculation programs Midas Gen, PRO-SAP and 3Muri, which require different modeling strategies and the definition of the parameters to be used. These strategies have been collected in Report 1.4 (Definition of parameters for simplified automatic calculation programs).

Image

Fig.7 Force-displacement curves of an example of a two-story building in the unreinforced state (URM), reinforced on one side (R1) and reinforced on two sides (R2)

All partners have collaborated, in relation to their specific areas of expertise, in the drafting of Guidelines for the design and application of "CONSTRAIN" strategies. These define the procedure for the use, design, installation and maintenance of the reinforcement. The strategy for defining the parameters to be used in seismic performance analyses was discussed in the document and some examples were developed. The operational aspects for the correct implementation of the interventions are also explained. The document is structured into chapters, each dedicated to a specific role of the reader, dividing the information by owners, investors, designers and contractors.

Finally, partners conducted research on potential case studies for the future application of the proposed reinforcement strategy. In Italy, a group of social housing buildings in Udine, owned by ATER Udine, dating back to the 50s, has been identified. These buildings represent a significant part of the constructions built at the time, as they were built with design provided by the Ministry of Public Works. In Slovenia, a historic building in Ljubljana has been identified, subject to the protection of the external facades and some internal frescoes (Fig.8). The technical documentation and original drawings have been collected to evaluate the structural aspects. The partners carried out the inspection and survey of the buildings to verify the correspondence of the built environment with the available graphic drawings. 

Image

Fig.8 Historical drawings of the front view of the main façade of the building in Ljubljana

In-situ investigations were carried out on the building in Udine, where possible with limited invasiveness, to acquire further information on the characteristics of the materials (Fig.9). For the historic building in Ljubljana, on the other hand, inspections were carried out to verify the state of affairs and visual investigations on the structure to estimate its characteristics. The documents and surveys are reported in Report 3.1 (Collection of graphic drawings of selected buildings and description of characteristics).

Image

Fig.9 Masonry characterization tests: (a) Compression test with flat jacks; (b) creep Shove-test

The seismic vulnerability analyses of the pilot buildings were supported by the use of Midas Gen software for the building in Italy and 3Muri for the one in Slovenia. The results showed that, at present, the seismic resistance of both buildings is insufficient compared to the requirements of current regulations. 

The intervention in Udine aims to minimize the impact on the occupants, intervening mainly on the surfaces outside the apartments. For the building located in Ljubljana, subject to constraints of the superintendence for the protection of the external appearance, were identified the internal walls on which the installation of the surface reinforcement is allowed. The simulations are continuing on models that deal with the reinforced state with the "CONSTRAIN" techniques. At the same time, the executive drawings of the reinforcement interventions and the study of their intervention costs are developed.

With regard to the communication and dissemination of results, the University of Trieste participated in two international conferences in the field of civil engineering, in which it had the opportunity to communicate and disseminate the first results of the ongoing activities:

• REHABEND Congresso “Construction Pathology, Rehabilitation Technology and Heritage Management” (7-9 maggio 2024): presentazione della memoria dal titolo “The strengthening of floor and roof masonry ring beams with fibre-based composite materials: experimental tests”;(link)
• HIVIB Symposium “16th International Symposium on Human-Induce Vibrations and Seismic Influencer on Structures” (15-18 maggio 2024): presentazione della memoria del titolo “Seismic performance of CRM strengthened masonry: from experiments to analytic approach” (link)

The posters of the seminars and thematic conferences that will take place in October and November are soon to be published on the news section of this site, aimed at:

• members of professional associations (Engineers) - 8 meetings of 3 hours (4 in Italy, 4 in Slovenia) 
• PA technicians, Civil Protection, National Association of Building Contractors - 6 meetings of 3 hours (3 in Italy, 3 in Slovenia).