Out‐of‐plane reinforcement of masonry walls using joint-embedded steel cables

The out-of-plane mechanism (rocking) of walls often causes fatalities and collapses of historic buildings during earthquakes. This paper addresses the problem of assessing the seismic resistance of walls subjected to out-of-plane bending, before and after reinforcement. A new retrofitting method, consisting in the use of high-strength steel cables fully embedded in the mortar bed joints was studied. An experimental investigation using full-scale brickwork specimens was therefore conducted in an attempt to assess the walls’ structural response when these are subject to out-of-plane loads. Test results demonstrated that it is possible to increase the out-of-plane capacity with the proposed method. A simplified macro-element procedure is also presented along with recommendations for the calculation of the walls’ capacity before and after the application of the steel cable reinforcement. Predictions of the magnitude of horizontal force required to cause out-of-plane failure using the proposed procedure and quasi-static analysis procedures are compared with the results of laboratory experiments

An Experimental Study on the Effect of Water on Historic Brickwork Masonry

Architectural heritage is deeply threatened by extreme weather events due to ongoing climatic change. Since these phenomena are becoming more and more serious, their effects cannot be neglected when a reliable assessment of a historic masonry structure is required. In this paper, the phenomenon of rising damp was studied, focusing on the influence of water on the unit weight of masonry walls made from fired clay bricks and lime mortar. This study consists of a basic experimental research on the variations in the unit weight of masonry undergoing an ageing treatment, which was simulated through some cycles of capillary water absorption and temperature changes. The experimental study proves that penetrating damp causes an increase in masonry unit weight of more than 20%. This basic result is significant in the structural assessment of historic masonry buildings. Subsequent papers will analyze the interaction with strengths parameters

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

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

Use of natural resins in repairing damaged timber beams – An experimental investigation

Different techniques including the application of steel elements, composite materials and polymeric resins have been used in the past to repair damaged timber beams. However, there is a growing need to replace these materials with those with minimal environmental impact. In addition, stringent requirements of conservation authorities on the compatibility between repair and parent materials have also necessitated search for innovative repair materials for timber beams. Therefore, an increasing shift of focus towards the use of materials derived from natural sources in repairing and reinforcing timber structures is currently experienced. This paper presents the results of an exploratory study on the use of natural resins (rosin and bone glue) in repairing oak timber beams. 15 oak timber beams with cross section dimensions of 67 x 67 mm and 1100 mm in length were tested in four-point bending to failure. Undamaged, damaged (unrepaired) and damaged but repaired timber beams (with rosin and bone glue) were tested. The effectiveness of the repair material and technique was analysed based on the bending capacity and mid span deflection at failure. The initial results show negligible effectiveness of rosin in repairing timber beams. In fact, about 16% reduction (average) in load carrying capacity with a corresponding 5% decrease (average) in maximum displacement was recorded. Relatively higher level of effectiveness was recorded with the use of bone glue (about 10 % average increase in load carrying capacity). However, over 30% corresponding average increase in the maximum displacement was also recorded. Further work investigating different repair techniques and other natural resins is presently underway

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

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)