Maria Rosa Valluzzi

Shear behavior of masonry panels strengthened by FRP laminates

Abstract The present experimental study, performed on brick masonry panels strengthened by Fiber Reinforced Polymer (FRP) laminates, was aimed to investigate the efficiency of an alternative shear reinforcement technique. A series of nine unreinforced masonry (URM) panels and 24 strengthened panels have been subjected to diagonal compression tests. Different reinforcement configurations were evaluated. Experimental results pointed out that FRP reinforcement applied only at one side of the panels did not significantly modify the shear collapse mechanisms (diagonal splitting) of the URM; while double-side configurations provided a less brittle failure and a noticeable ultimate capacity increase. Performances of the different reinforcement configurations are compared in terms of strength and mechanism of failure; finally, experimental results are also used to calibrate existing analytical formulations for ultimate shear strength prediction.

Design choices and intervention techniques for repairing and strengthening of the Monza cathedral bell-tower

Abstract A presentation is given of the fundamental design choices and of the selection of the most appropriate materials and techniques which have been made for strengthening the Monza cathedral bell-tower, based on investigation and structural assessment carried out prior to and during the design process. The results of the experimental and numerical investigation will first be given in order to explain the reasons for the design choice.

Structural Aspects of The Conservation of Historic Masonry Constructions in Seismic Areas: Remedial Measures and Emergency Actions

Preservation of historic buildings is a demanding task, especially in seismic zones, where vulnerable constructions can suffer severe damages and losses. The last earthquake that struck the Abruzzo region in Italy in 2009 caused a particularly extensive damage. Lessons learned by previous experiences and the knowledge acquired through researches allowed facing the first emergency period involving universities, civil protection, and the Cultural Heritage Ministry. The result of this collaboration was the survey and the realization of emergency interventions for thousands of buildings in few months after the earthquake, waiting for the definition and design of definitive solutions.

Compression and Sonic Tests to Assess Effectiveness of Grout Injection on Three-Leaf Stone Masonry Walls

The results of an experimental campaign on multi-leaf stone masonry panels (scales 1:1 and 2:3), in original conditions and after consolidation with natural hydraulic lime grout injection are presented. The specimens were constructed with one of the most common structural techniques, widely employed on minor historical buildings throughout Europe. Experimental research included a series of destructive (DT) monotonic and cyclic uni-axial compression tests on three-leaf and single-leaf stone masonry panels. Mechanical tests were complemented by non-destructive tests (NDT) on the walls before and after strengthening. Both NDT and DT allowed assessment of the effectiveness of grout injection as a consolidation technique and gave better insights on its influence on the behavior of this type of masonry. An attempt to establish a relation between sonic velocity and mechanical parameters for this specific type of masonry was also carried out.

Experimental Assessment of Bond Behaviour of Fibre-Reinforced Polymers on Brick Masonry

Existing masonry structures represent a significant amount of the architectural heritage. Many of these buildings are vulnerable to earthquakes. Consequently, they need structural improvements in order to meet the seismic requirements of recent building guidelines. In the last decade, there has been a growing interest in the application of Externally Bonded-Fibre Reinforced Polymers (EB-FRP) as strengthening and repair materials because of their high-performance mechanical characteristics, feasibility of application in civil structures, resistance to chemical attacks and other potentials. Brick masonry components are the most suitable substrates susceptible to improvements because of their more regular surface in comparison with stonework or rubble masonry. The bond behaviour of FRP, applied on a masonry substrate, is a critical issue for the effectiveness of the technique. In this paper, the results of an experimental assessment of the local behaviour of EB-FRP applied on clay bricks are presented. Experimental failure load results were compared with predictive bond strength models proposed in literature for concrete substrates. On the basis of measured strengths and local deformations, interface fracture energies were calibrated and an analytical function was proposed as bond stress-slip law. Finally, a bilinear law was calibrated for practical design applications.

Structural investigations and analyses for the conservation of the ‘Arsenale’ of Venice

Abstract Systematic interventions are being planned and progressively designed on most buildings of the Arsenale of Venice, the Venetian republic’s shipyard, a very large complex of docks and sheds of peculiar construction characteristics. These renovation interventions are required in view of new uses for the revitalizing of that area, which is currently almost completely neglected. In the paper, after a general presentation of the main properties and of the most relevant deterioration phenomena of the principal parts of the monumental area, the methodology that is being used for the structural diagnosis, for the implementation of guidelines for the future interventions and for the maintenance of the restored conditions are presented. Some preliminary results, given by experimental tests performed both in situ and in laboratory on materials and structural elements, and by FE simulations, are discussed.

Seismic Vulnerability of Historical Structures: Damage State of the Abruzzo (Italy) Churches in the Sequence of the April 2009 Earthquake

Each earthquake represents a particular moment in the history of the affected region. The seismicity in Italy reaches frequently high values, what makes it a country particularly affected by this kind of natural disasters. Historical constructions (in particular masonry ones) are structures that show a high vulnerability to the type of loads introduced in the sequence of a seismic event. This paper focus on the effects of the 6th of April 2009 earthquake, that affected the region of Abruzzo (Italy), over the historical buildings of the region, in particular churches, by establishing a set of different objectives directed to the understanding of their structural behavior and to the assessment of the extent of post seismic damage in this structures. During the emergency period that followed the earthquake, many churches and other historical constructions (towers, walls, palaces, etc…) were surveyed, according to the official 1st level damage survey forms for Cultural Heritage (C.H.), by the workgroup of the University of Padova (UNIPD). The information collected from these surveys was later inserted and organized in a database. A statistical work is presented, illustrating the referred information and focusing on the data related with the damage assessment of the considered monuments. This work presents an intuitive overview of the seismic effects over the surveyed churches, allowing not only to better understand the response of these structures to this particular action, but also correlating the earthquake data with its effects on the churches.

Out-of-plane shake-table tests of strengthened multi-leaf stone masonry walls

Existing unreinforced multi-leaf stone masonry (URM) buildings are one of the most earthquake prone types of construction. Failure typically occurs even at low levels of earthquake-induced loads, with the out-of-plane delamination of masonry leaves and consequent collapse of the whole façade. Although this issue has been tackled by several researchers, dynamic tests reproducing the earthquake behaviour of as-built and strengthened multi-leaf stone URM walls are very limited in the literature. In response to this lack, shake-table testing of eight full-scale multi-leaf stone masonry walls followed by dynamic modal identification was performed. The application of steel tie-rods in the wall cross-section, the injection of the inner-core using hydraulic lime-based grout, and a combination of the two techniques are presented herein as suitable interventions to enhance the monolithic behaviour of multi-leaf stone URM walls. Tying the outer masonry leaves together increased the seismic capacity by a factor of 1.8 compared to unreinforced condition, while injecting grout into the inner-core of the wall provided resistance to peak ground acceleration (PGA) that were 2.3–3.6 times the PGA resisted by as-built walls, depending on the quality in the execution of the intervention. The results obtained in the walls strengthened with both techniques were significantly related to the grout injection only.

Experimental Study of the Bond of FRP Applied to Natural Stones and Masonry Prisms

Compared to more traditional techniques, the application of Externally Bonded-Fibre Reinforced Polymers (EB-FRP) represents a viable alternative for the strengthening of masonry structures, also in case of Cultural Heritage buildings where strict requirements need to be met, aimed at minimizing the impact of the intervention. Since the FRP-to-masonry bond behaviour strongly affects design and effectiveness of such interventions, several investigations have been carried out in recent years to study this phenomenon, generally based on the longer experience developed for concrete substrates. Mortar joints, which are geometrical and mechanical discontinuities, distinguish and characterize masonry substrates from concrete ones, and therefore deserve a special attention as far as their role in the bond behaviour is not clarified yet. This paper, aimed at giving a contribution also from a methodological point of view, presents the main experimental results of shear tests carried out on glass composites (GFRP) applied to natural calcareous stones (pietra leccese), to lime mortar blocks and to masonry prisms made by coupling stones and lime mortar. Overall 22 shear tests were performed, keeping a bonded length of 200 mm for stones and mortar specimens while it was changed from 65 mm (corresponding to one stone and one mortar joint) to 195 mm (three stones and three mortar joints) in the case of masonry prisms. The effect of the FRP end anchorage on the test development was investigated as well, and results of the experimental tests are herein discussed in detail.

Shaking Table Tests on Multi-Leaf Stone Masonry Structures: Analysis of Stiffness Decay

The influence of the natural hydraulic lime-based grout on the dynamic behaviour of injected multi-leaf stone masonry elements is discussed in the paper. Shaking table experiments on two stone masonry buildings, tested before and after grout injection, have been performed. The paper focuses on the analysis of both the recorded accelerations and related displacements, at the bottom and at each further storey. This leads to evaluate the stiffness of the unstrengthened and injected structures. The input at increasing PGA allowed the stiffness decay to be studied, simulating a gradual damaging of the structures. These results were also interpreted in the light of both computed frequencies and mode shapes. Finally, the comparison among these results, obtained from all the models, allows to deepen the knowledge concerning the effects induced by the lime-based grout injection and on its capability to modify the dynamic behaviour, when intervening on a damaged (repairing) or on an undamaged (strengthening) structure.