The use of transverse connectors as reinforcement of multi-leaf walls

The need for new retrofitting techniques is the consequence of an increasing interest in the conservation of historic construction. The global behavior of a stone masonry structure is often governed by the level of connection between masonry wall leaves and the overall quality of the masonry material. This paper presents the results of an investigation carried out on site and in the laboratory on multi-leaf stone masonry panels strengthened using stainless steel rod inserted in a grouted fabric sleeve. The aim is to increase the collaboration between weakly connected masonry leaves. Pull-out tests were conducted on site on full-scale stone masonry wall panels, with the aim of studying the force required to pull out a connector under uniaxial tension. Several wall panels were assembled in the laboratory using solid calcareous stones and weak mortar and the effectiveness of the connectors was tested in shear and compression on both virgin and damaged panels. The experimental tests allowed the analysis of the behavior of the multi-leaf panels. Experimental results show that a substantial improvement of the wall panels' mechanical behavior can be achieved by applying transverse connectors

Static consolidation of a renaissance palace by resins, pins and connecting rods

The paper reports the results of a research on the static consolidation of an important XV century tower by Bramante belonging to an important monumental complex located in the Po Valley which was showing worrying structural conditions . The tower, 19 m high, very thin, lacking connections in the highest part, showed overturnings of the four façades not in plumb by over 150mm; Due to the presence of architectural terracotta elements, it was not possible to intervene on the external facades. This is why the authors decided to create a sort of hoop from inside using a U (120 mm) steel profile fastened to the walls by means of steel pins anchored with epoxy resins. The pins (12 mm, 350 mm length) have been positioned at a distance of 50 cm inclined by 30° alternatively downwards and upwards in order to get at minimum of 2+2 courses of bricks. Then, by a series of steel tie rods it was possible to tie the opposite walls. Finally, triangular frames have been positioned on the 4 corners in order to avoid teething collapse in case of great stress. Before starting with the strengthening work, as described above, experimental tests, supported by the Bossong company, were conducted to verify tensile stress resistance of each pin. The tests studied different solutions in terms of diameter and anchoring material. The tensile tests , carried out by using a specific hydraulic puller equipped with a dynamometer and a displacement transducer, showed very high allowable loads , between 20 and 60 kN/pin depending on the pin and fastening type. According to data obtained, the most suitable solution was chosen; it was also used in other parts of the castle. The behavior of the reinforced structure , which withstood the February 2012 earthquake without any problem demonstrated the validity of the proposed technique which is an interesting, non invasive solution for historical buildings

Injected Anchors For The Seismic Retrofit Of Historical Masonry Buildings: Experimental Study On Brick Masonry

The paper reports the results of a research on the behaviour of injected anchors in historical masonry under cyclic loads. Tests in laboratory with masonry specimens (bricks and mortar with low characteristics to replicate a real historical masonry) were conducted to analyse the response of steel anchors injected with a special sock and with different sorts of mortar (cement and lime based). The test benches replicate the real condition of the use of these anchors: to connect masonry panels (T and L connections) or to anchor steel ties to contrast the arch thrust. Monotone and cyclic pull out tests were conducted on short and long anchors (injected orthogonally and lengthwise to the masonry main plane) to compare the results and to define the loss of strength under cyclic loads for different situations. The results allowed to obtain: 1) construction of load-displacement graphs, up to the maxi- mum load value (maximum strength) of each anchor and the related displacement; 2) steel bar deformation graphs on the length of the anchors (thanks to the strain gauges installed on steel bars) at different values of load and under cyclic loads; 3) qualitative bond stress curve derived from the steel bar strains, which allowed to investigate the behavior of the anchors along the bar length under cyclic loads

Injected Anchors For The Seismic Retrofit Of Historical Stone Masonry Buildings: In Situ Experimental Tests

The paper reports the results of a research on the behaviour of injected anchors in historical masonry under cyclic loads. Monotonic and cyclic pull-out in situ tests were conducted on historical stone masonry to analyse the response of anchors injected orthogonally to the masonry main plane and at different heights to evaluate also the effect of different values of normal confinement on the anchor behaviour. Moreover the tests were conducted on anchors of different length, instrumented with strain-gauges. The aim was to investigate the loss of strength under cyclic loads. The results allowed: 1) construction of load-displacement graphs, up to the maximum load value (maximum strength); 2) steel bar deformation graphs on the length of the anchors at different values of load, under cyclic loads; 3) qualitative bond stress curve, derived from the steel bar strains, to investigate bond behavior along the bar length

Pre-stressed vertical injected anchors on historical masonry: a case study, the Bell Tower of Botta di Sotto il Monte Papa Giovanni XXIII

The Bell Tower of the Church "Sacro Cuore Gesù e S. Egidio Abate" in Sotto il Monte (Bergamo, Italy), represents a case study of the research programme "ANIMUS", funded by the European Programme FESR-2007-2013. The necessity of building a steel belfry on top of the bell tower required a detailed study of its connection with the supporting masonry structure. This connection has been realized by means of deep vertical anchors, obtained by grouting steel bars by injecting the grout in special socks, such that any dispersion of the mortar in the masonry is avoided. By this technique, a "bulb" creating an effective interlock with the masonry structure is created. The behaviour of the system has been studied by means of a finite element model, allowing to assess the performance of the connection under wind and seismic loads both at service and ultimate limit states. The results have highlighted the opportunity to design vertical anchors with a double bulb of mortar. This way, by grouting the deeper bulb soon after installation, the anchor could be pre-stressed to avoid any decompression of the connection between the superstructure and the masonry tower under service loads. The upper bulb, grouted at a later time, has the role of transferring the loads exceeding serviceability limit state to the masonry structure. After the installation of vertical anchors, an experimental phase started with the execution of cyclic tests, thus allowing to evaluate the effectiveness of the intervention and to compare experimental and numerical results