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Mortar-based composites are an emerging technology for the repair and strengthening of reinforced concrete and masonry structures. In most cases, the effectiveness of the retrofitting work relies on the substrate-to-composite bond capacity but in some applications, connectors are also used to prevent debonding and improve the performance of the retrofitted structure. Indeed, the use of connectors is recommended by design guidelines and suppliers are required to test them for acceptance. The paper presents a laboratory investigation on steel reinforced grout connectors, made by rolling ultra-high tensile strength steel textiles, comprising either galvanized or stainless-steel micro cords. Tensile tests were first carried out for mechanical characterization. Pull-out tests were then performed on connectors installed in holes drilled in wall panels and injected with either cement or lime mortars. Concrete, tuff masonry, brickwork and limestone masonry were used as substrate materials. Test results are commented to analyze the effect of textile rolling on tensile response, of textile and matrix properties on pull-out strength and failure mode, as well as to highlight their significance for design purposes.

In 2017, the Rilem Technical Committee 250-CSM coordinated a Round Robin initiative, in which 19 research institutions tested 28 Fabric Reinforced Cementitious Matrix (FRCM) composites, with the support of 11 industrial partners. Two years after the publication of the first papers on the results of this wide investigation, it is still worth further analysing its outcomes to highlight the fundamental properties of mortar-based reinforcements and give an overview of the various available fabrics and matrices, which are currently used in structural rehabilitation activities. Equally, a better understanding still needs to be gained on the causes of the variability observed in test results. These include the quasibrittle behaviour of the inorganic matrix and its sensitivity to manufacturing, curing and handling. Test implementation, such as gripping method and measuring techniques, also plays a crucial role in the reliability and repeatability of experimental outcomes.

Steel Reinforced Grout (SRG) is a mortar-based composite recently developed for structural retrofitting, which provides high tensile strength with limited increase in mass and in stiffness, and whose effectiveness relies on the good interaction between steel cords and inorganic matrices. Many companies already supply SRG systems for rehabilitation activities and the scientific community has been working intensively on experimental and numerical investigations to demonstrate their effectiveness for structural applications, which also led to the inclusion of SRG in national and international standards for product qualification and design. However, a clear view of the mechanical properties of these systems is still lacking, due to their variability, which, in turn, strongly depends upon cord layout, textile architecture, and characteristics of the matrix. This paper provides an overview of the mechanical properties of SRG composites on the basis of the tests carried out at Roma Tre University and of the other experimental evidences available in the literature. The results of tensile tests on bare textiles and SRG coupons with different inorganic matrices, and of bond tests on masonry and reinforced concrete substrates are collected and the performances of the different SRG systems are compared. The influence of the mortar matrix on crack spacing, ultimate strain and tension stiffening in tensile tests is analysed. The capacity of the steel cords to ensure a proper shear transfer through interlocking within the matrix and the effect of cord density on failure mechanisms in bond tests are also discussed.

Innovative strengthening systems made of composites with mortar-based matrix are currently applied as external bonded reinforcement for the rehabilitation of masonry structures. The present note will provide an overall view on the use of these systems, which are the object of the ongoing research carried out within the RILEM TC 250 - Composites for Sustainable strengthening of Masonry. Referring to on field application and recalling recent experimental outcomes, pros and cons on the use of mortar based composites for strengthening historic masonry structures under both design loads and seismic action will be critically discussed.

La città di Roma è attualmente interessata dai lavori per la costruzione di una nuova linea metropolitana che attraverserà il centro storico della città. In questa nota viene presentata un’analisi numerica 3D agli Elementi Finiti relativa all’interazione tra lo scavo di un pozzo profondo 30 m, necessario per l’immissione delle macchine EPB da usare per la realizzazione delle gallerie di linea, e le vicine Mura Aureliane nei pressi di Porta Asinaria. Questo studio si inquadra in una più ampia attività di ricerca condotta dagli Autori negli ultimi anni volta a valutare mediante strumenti di calcolo integrati di tipo geotecnico e strutturale l’impatto sul patrimonio storico ed architettonico della costruzione di infrastrutture in area urbana.

The conservation of our architectural heritage, so vast and rich in historical and artistic terms, requires a multidisciplinary approach to understand the ongoing phenomena and to implement countermeasures against degradation factors and natural and anthropic risks. In this paper an integrated, geotechnical and structural, research for the investigation of the stability conditions of the Ninfeo di Genazzano is presented. The structure, which tracks back to the Renaissance and is attributed to Bramante, was built near Rome and is at present in ruins. The interpretation of the instability phenomena, already suggested in architectural studies of the past century, was carried out using a numerical approach based on the Finite Element method. Advanced constitutive laws were adopted to describe the key features of the mechanical behaviour of soil strata and masonry structures and of their mutual interaction. The comparison between the numerical results and the current conditions at the investigated site proves the predictive capabilities of the developed models and their potentiality in the context of evaluation and preservation activities of historical-architectural heritage.

Negli ultimi anni in tutta Europa si sta assistendo ad un crescente impulso nella costruzione di infrastrutture sotterranee in ambiente urbano. La realizzazione di tali opere è causa di cedimenti del terreno e quindi di potenziali danni sulle strutture, i quali sono solitamente valutati adottando approcci basati per lo più su metodi empirici, tenendo conto delle caratteristiche delle strutture e dell’interazione terreno-struttura in maniera semplificata. In questa memoria sono illustrati i primi risultati di un approccio di analisi integrato terreno-struttura, volto a stimare più accuratamente gli effetti indotti dallo scavo e la formazione di eventuali dissesti sulle strutture murarie. L’approccio proposto è presentato con riferimento ad un caso di studio reale, quello del sottoattraversamento dell’Acquedotto Felice da parte di due gallerie della nuova Linea C della Metropolitana di Roma. L’analisi è condotta attraverso il metodo degli elementi finiti utilizzando un modello costitutivo per la muratura sviluppato dagli scriventi e implementato nel codice di calcolo Abaqus. I risultati ottenuti dall’analisi d’interazione sono infine posti a confronto con quelli derivanti dal monitoraggio effettuato durante lo scavo.

In questa nota viene descritto un approccio numerico agli Elementi Finiti per la modellazione dei danni indotti dallo scavo di gallerie superficiali su strutture in muratura. Il comportamento meccanico della muratura, schematizzata come una struttura periodica costituita da blocchi e giunti, è descritto alla scala macroscopica come un mezzo omogeneo anisotropo. Il terreno, un materiale argilloso di media consistenza, è invece modellato attraverso un semplice legame costitutivo elastico-perfettamente plastico. Le analisi numeriche, condotte con il codice di calcolo Abaqus, hanno riguardato il comportamento di pareti in muratura e sono state condotte, in questa prima fase, adottando condizioni di deformazione piana per il terreno e di tensione piana per la struttura. Esse hanno fornito alcune prime indicazioni circa i complessi meccanismi di interazione terreno-struttura che si manifestano in corrispondenza di differenti valori del volume perso durante lo scavo della galleria.