Experimental evaluation of shear and compression strength of masonry wall before and after reinforcement: Deep repointing

Masonry presents some inadequacies due to its almost total lack of tensile strength. Typical damage to multiple leaf walls during earthquakes is the loss of bond between the leaves with consequent collapse of the external leaf. Retrofitting or repair of this damage is a very difficult task. In many cases grout injection or wall jacketing fail due to incompatibility with the construction technique of the walls. A complementary technique to the grouting has been proposed by the authors. Experimental results and applications of the technique on site have shown positive characteristics and the results of tests carried out on site show, in some cases, increases in shear strength and stiffness of the masonry walls

Calibration of a visual method for the analysis of the mechanical properties of historic masonry

The conservation and preservation of historic buildings affords many challenges to those who aim to retain our building heritage. In this area, the knowledge of the mechanical characteristics of the masonry material is fundamental. However, mechanical destructive testing is always expensive and time-consuming, especially when applied to masonry historic structures. In order to overcome such kind of problems, the authors of this article, proposed in 2014 a visual method for the estimation of some critical mechanical parameters of the masonry material. Based on the fact that the mechanical behavior of masonry material depends on many factors, such as compressive or shear strength of components (mortar and masonry units), unit shape, volumetric ratio between components and stone arrangement, that is the result of applying a series of construction solutions which form the "rule of art". Taking into account the complexity of the problem due to the great number of variables, and being on-site testing a not-always viable solution, a visual estimate of the mechanical parameters of the walls can be made on the basis of a qualitative criteria evaluation. A revision of this visual method is proposed in this paper. The draft version of new Italian Building Code have been used to re-calibrate this visual method and more tests results have been also considered for a better estimation of the mechanical properties of masonry

Masonry wall panels retrofitted with thermal-insulating GFRP-reinforced jacketing

Today there is a need to provide thermally efficient walls, while at the same time to increase the mechanical properties of old unreinforced masonry walls that will not require large amounts of energy in the retrofitting or deconstruction processes. To address this problem, this paper gives the results of shear tests carried out on masonry panels made of solid bricks retrofitted with a new technique based on the use of glass fiber-reinforced polymers (GFRP) grids inserted into a thermal insulating jacketing. This was made of different low-strength lime-based mortars. Tests were carried out in laboratory and results were used for the determination of the shear modulus and strength of the wall panels before and after the application of the GFRP reinforcement. Retrofitted panels exhibited a significant enhancement in the lateral capacity when compared to the control panels. The thermal performance of the proposed mortars was also investigated both with and without GFRP. Low values of thermal conductivity were found, especially for the samples with GFRP; a reduction of the thermal transmittance value in the 34–45 % range was also obtained by applying 45 mm layer of coating in conventional masonry walls

Sustainable Strengthening Techniques for Masonry Structures

Reducing the energy consumption is an important objective of the construction industry and this also applies for renovation, retrofit and refurbishment of existing buildings. Masonry buildings often need to be retrofitted and the use of Fibre Reinforced Polymeric (FRP) materials has proven to be a viable solution. With the inevitable declining of fossil fuels, carbon fibres and epoxy resins must be substituted with greener materials. This paper reports the results of several experimental investigations recently conducted by the authors using glass fibre meshes embedded into an inorganic matrix (known as FRCM: Fibre Reinforced Cementitious Matrix) to reinforce historic masonry constructions. This strengthening technique has been applied in laboratory to reinforce masonry wall panels, tile brickwork vaults and to construct masonry ring-beams at eaves level of existing buildings. The mechanical behaviour of the reinforced masonry elements have been significantly enhanced and test results demonstrate that is possible to avoid the use of more traditional composite reinforcements like high-strength carbon fibres and epoxy resins to bond the reinforcing materials to the masonry substrate

Shear resistance of screwed timber connections with parallel to grain FRP reinforcements

Several applications involving the use of Fibre Reinforced Polymers (FRP) glued on the tension side of timber beams are available in literature. However, some drawbacks (durability, product cost and health and safety restrictions, difficulties in removal) have limited an intensive use of organic adhesives (i.e. epoxy resins, etc). A possible solution could be the use of metal screws, changing the nature of the connection from chemical to mechanical. This paper describes an experimental investigation on the mechanical behaviour of externally bonded FRP composites using steel screws. Two different composite materials have been considered: Carbon Fibre Reinforced Polymer (CFRP) and Glass Fibre Reinforced Polymer (GFRP) and three different metal screw types have been used. FRP strengthening was then applied to timber blocks and shear tested conducted to study the performance of the screwed connection. The response of the screwed connection was recorded: catastrophic collapse did not occur, as the connection failed gradually for slippage phenomena produced by screw yielding and wood displacement. The slippage between timber and FRP plate has been recorded and tests described in this paper demonstrated that the effectiveness of screwed FRP strengthening could be compromised by these phenomena

Fiberglass Grids as Sustainable Reinforcement of Historic Masonry

Fiber-reinforced composite (FRP) materials have gained an increasing success, mostly for strengthening, retrofitting and repair of existing historic masonry structures and may cause a significant enhancement of the mechanical properties of the reinforced members. This article summarizes the results of previous experimental activities aimed at investigating the effectiveness of GFRP (Glass Fiber Reinforced Polymers) grids embedded into an inorganic mortar to reinforce historic masonry. The paper also presents innovative results on the relationship between the durability and the governing material properties of GFRP grids. Measurements of the tensile strength were made using specimens cut off from GFRP grids before and after ageing in aqueous solution. The tensile strength of a commercially available GFRP grid has been tested after up to 450 days of storage in deionized water and NaCl solution. A degradation in tensile strength and Young’s modulus up to 30.2% and 13.2% was recorded, respectively. This degradation indicated that extended storage in a wet environment may cause a decrease in the mechanical properties

The Failure of Masonry Walls by Disaggregation and the Masonry Quality Index

The visual method for assessment of the structural behaviour of historic masonry walls, known by the acronym MQI (Masonry Quality Index) was introduced in 2002 by a team of researchers from the University of Perugia, Italy. This is based on a visual survey of the faces and the cross section of a wall panel, and it aims at verifying if a wall complies with the “rules of the art”. Based on this analysis, it is possible to calculate a numerical index: numerous tests, carried out on site by the authors to validate the method, have demonstrated that the index is able to provide useful information about the mechanical characteristics and structural response, in general, of the analysed wall panel. The failure mode of a wall panel under the action of an earthquake is a critical aspect. In general, the failure modes can be categorized in two classes: masonry disaggregation and the development of a local or global mechanism of wall elements (macroelements). Several theoretical models and numerical simulations only consider the latter. In this paper, application of the MQI method is further investigated, with particular emphasis to those masonry typologies which are more prone to collapse by disaggregation during a seismic event. Under the action of an earthquake, some types of masonry are typically unable to deform and to split in macroelements, and another type of failure occurs: this is the so-called “masonry disaggregation” or “masonry crumbling”. This type of failure anticipates the ones resulting from macroelement methods or stress analysis. As a conclusion, these latter methods become completely inappropriate and potentially hazardous, as they overestimate the seismic capacity of the building under investigation. The MQI method has been adapted to assess the structural response of different types of masonry under the action of an earthquake. In detail, the aim was to verify when the phenomenon of masonry disaggregation is likely to occur

Effect of transversal steel connectors on the behaviour of rubble stone-masonry walls: two case studies in Italy

Multi-leaf masonry walls are very common in historical constructions and have been primarily designed to resist vertical static loads. Recent earthquakes have shown their high vulnerability against dynam-ic horizontal and static compression loads which can easily produce the detachment of the different leaves and determine important damage and catastrophic consequences. An increasing interest in the conservation of his-toric masonry constructions has produced a need for new consolidation and retrofitting methods. With the aim of increasing the mechanical characteristics, the overall structural behaviour and ultimately the safety of mul-ti-leaf masonry wall panels against out-of-plane collapse mechanisms, several reinforced techniques have been investigated. In this paper, a new strengthening system which consists in the application of a pre-loaded steel bar enclosed into a fabric protective bag-case, is investigated. The steel-bar connector is inserted into a pre-drilled hole made in the masonry in order to bond the masonry leaves and to prevent the detachment dur-ing seismic events; finally cement-based grout is injected at high pressure inside the fabric bag-case. The aim is to increase the collaboration between masonry leaves and increase the wall-capacity. The paper initially de-scribes the reinforcement technique and its fields of application and expected benefits. In the second part, the paper addresses two case studies where this reinforcing method has been recently applied: the medieval castle of Laurenzana, located in the southern Italian region of Basilicata and a coeval 18th-century annex building nearby the Royal Palace of Capodimonte (Naples)

Experimental analysis of masonry ring beams reinforced with composite materials

It is known that the application of a ring beam is an effective method to prevent an out-of-plane collapse mechanism of perimeter wall panels. However this effective reinforcing method presents some problems. In order to address this, this paper describes the problems associated with this reinforcing method and studies a new technique for reinforcing historic masonry buildings by realizing a new type of ring beam made of recycled old stones or bricks reinforced at the bed joints with glass-fibre sheets, GFRP (Glass Fiber Reinforced Polymer) grids or/and PBO (polybenzoxazole: poly-p-phenylene benzobisoxazole) cords. An experimental investigation has been carried out on 8 full-scale rubble-stone or brickwork masonry ring beams tested in bending. The testing included the use of composite materials inserted into the mortar joints during the fabrication phase of the beams and pinned end conditions (four-point bending configuration). Beams were reinforced with different reinforcement layout

Uncertainty analysis of FRP reinforced timber beams

Timber has been a popular building material for centuries and offers significant sustainable credentials, high mechanical and durability properties. Availability, ease to use, convenience and economy have made timber the most used construction material in history but, as it is a natural material, uncertainty in its mechanical characteristics is considerably higher than man made structural materials. National codes and engineers usually employ high factor of safety to incorporate timber strength uncertainty in design of new structures and reinforcement of existing ones. This paper presents the results of 221 bending tests carried out on unreinforced and reinforced soft- and hardwood beams (fir and oakwood) and illustrates the reinforcement effect on timber capacity and strength uncertainty. Both firwood and oakwood beams have been tested in flexure before and after the application of a composite reinforcement made of FRP (Fiber Reinforced Polymer) unidirectional sheet. The uncertainty in the strength of reinforced timber is also quantified and modelled. Test results show that the FRP reinforcement is effective for both enhancing the beam load carrying capacity and for reducing strength uncertainties