Experimental testing of engineered masonry infill walls for post-earthquake structural damage control

The paper presents the results of an experimental campaign on the behaviour of engineered masonry infill walls subjected to both in- and out-of-plane loading. The aim of the research was to develop a design approach for masonry infill walls capable of solving their vulnerability and detrimental interaction with the frame structure when exposed to seismic excitation. Tests on two large-scale specimens and sub-assemblies were performed in order to evaluate the infill deformation capacity, the damage associated with different drift levels, and the mechanical properties of the components. A design solution with sliding joints to reduce the infill-frame interaction and ensure out-of-plane stability, which was proposed in a previous study, was developed and refined with focus on construction details. The aim of sliding joints is to ensure a predetermined mechanism in the infill wall, which is governed by hierarchy of strength and is capable of ensuring ductility and energy dissipation that can be taken into account in the design practice, thanks to the predictability of the response. The two infill wall specimens, one of them including an opening, reached up to 3 % in-plane drift with very little damage and supported an out-of-plane force equivalent to a horizontal acceleration four times the acceleration of gravity. The force-displacement hysteretic curve, sliding at the joints and crack pattern show the efficiency of the construction technique, based on affordable and tradition-like construction processes and materials. The technique, presented here for hollow fired-clay masonry units, can be extended to different masonry infill typologies

Indagine sperimentale su diaframmi di piano antisismici realizzati con doppio assito

Il presente lavoro di ricerca ha lo scopo di analizzare la tecnica del doppio assito ligneo mediante uno studio sperimentale finalizzato a fare chiarezza sui meccanismi caratteristici di questa tecnica di rinforzo sismico. Si sviluppa in tre diverse fasi: la ricerca bibliografica, il dimensionamento iniziale e le prove sperimentali, sia locali che su scala reale

Analysis of a scaled stone masonry facade subjected to differential settlements

Historical masonry structures are vulnerable to differential settlements of the ground. This vulnerability is potentially higher for historic buildings on wooden pile foundations, which can have their bearing capacity reduced by material deterioration. In order to protect such buildings from the effect of soil subsidence it is therefore essential assessing their response to settlements. The aim of this paper is to investigate the settlement-induced damage on a stone masonry façade. For the first time, experimental testing and computational analyses were performed on a scaled model of a specific existing historic structure, the Loggia palace in Brescia, Italy. Differential settlements were applied to dry blocks and mortar joints models of the façade. Experimental results showed the capability of the façade to reach a new equilibrium configuration following the subsidence of two adjacent columns. This approach can be used to assess the behaviour of similar structures. The validated numerical model confirms the interpretation of the failure mechanism and has the potential to allow extending the approach to a wider range of settlement and structural scenarios, as well as to different buildings

Lightweight ribs for the strengthening of single leaf vaults undergoing seismic actions.

In this paper the behavior and the collapse mechanism of single leaf vaulted structures undergoing seismic loads are discussed, and an innovative technique based on the use of lightweight ribs is proposed. The efficiency of the solution is verified by means of non linear numerical analyses on a strengthened single leaf vaulted structure. The numeric model is validated through comparison with the results of experimental tests performed on lightweight ribs subjected to cyclic, unsymmetrical load conditions

Critical aspects and stress redistribution in historical multi-leaf masonry walls

Massive masonry structures, like historical high towers and large pillars of churches, can be subjected to critical static situation, due to heavy persistent compressive stress, associated with vertical dead load. In the case of multi-leaf walls, the assessment can be difficult in regards to both, evaluation of the compression strength of masonry, and analysis of the state of stress. This research is motivated by the problem of the medieval bell-tower of the Church of S. Maria Assunta on Torcello Island in Venetian Lagoon; the aim is to quantify the redistribution of stress during the centuries across the wall, caused by non-uniformity of creep. Particularly, this study analyses the gradual increase of compression stress in the masonry cladding that could reach critical values. Due to little information about experimental data, long-term tests on reproduced ancient lime mortar have been started in order to define the creep behaviour of different mixtures. Another purpose is to investigate the advantages in terms of stress reduction due to partial and limited rebuilding technique (“scuci-cuci”), frequently used in the past, for the substitution of heavily damaged parts of masonry

The role of sapwood plasticity in the delamination phenomenon of repaired timber beams

For the repair of ancient wooden floors, the employment of steel plates glued by epoxy-adhesive into longitudinal grooves is a non-invasive technique which appears appropriate for the restoration of precious wooden beams. This technique requires particular attention to the delamination of the glued reinforcement due to the shear and normal stress concentration which occurs at the end of the repairing element. The peeling phenomenon is governed by the peak stress that depends on the capability of the sapwood to develop plastic strain. The aim of the present study is to evaluate the shear behaviour of the wood by means of a specific test focused on the plastic local resource of sapwood. Three small sapwood specimens were tested, providing an accurate shear-stress strain constitutive law which showed a significant plastic deformation. The experimental results were also adopted for nonlinear finite element analysis showing the importance of this plasticity on the delamination collapse of a repaired timber beam