Experiences from the Northern Italy 2004 earthquake: Vulnerability assessment and strengthening of historic churches

This work is about the lesson learnt from the analysis of the damages caused to some churches by the strong earthquake, which struck Northern Italy in the year 2004. Focus is paid to some mechanisms which are not well known in the literature: the excessive and differential rocking of neighbouring transverse arches, the differential deflection of single leaf vault rings, the tie over-tension induced by the transverse arch rocking. In the paper, the structural solutions appositely studied to repair and to reduce the structure seismic vulnerability of these buildings are presented. Among these solutions: internal perimeter ties, lightweight wooden roof box structure, lightweight spandrel ribs are illustrated

Wooden Roof Box Structure for the Anti-Seismic Strengthening of HistoricBuildings

A wooden roof strengthening technique aimed at transforming the roof pitches into anti-seismic shear resisting diaphragms is presented in this paper. Shear diaphragms gather and transfer the seismic loads to the shear resisting walls. Diaphragms are built on top of the existing structures without significantly modifying the roof overall layout. The proposed strengthening technique is mainly reversible, minimally impairing the building integrity, and can be easily applied for the construction of anti-seismic wooden roofs in new buildings. A simplified design approach is presented, which allows to identify the static role of each element. An analytical method for the estimate of the box structure displacements, as well as a short digression on the displacement control requirements is also illustrated. The diaphragm technique was recently applied for the anti-seismic retrofit of some monumental buildings in Italy. A few case studies, as well as the basic design criteria for applying this technique are presented in this paper

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

Extrados Strengthening of Single-Leaf Vaults Against Seismic Actions

Single-leaf vaults are acknowledged among the most vulnerable components of historical masonry constructions with respect to earthquake loads, particularly when featuring large span to thickness ratios, as in the case of single leaf covering the main nave of churches. These elements often require structural strengthening against seismic actions. In this paper, two different extradostechniques are tested: lightweight plywood restraining elements and FRP laminates embedded in a lime mortar layer. The techniques are tested on single leaf vaults having a very unfavorable span to thickness ratio. A previous study on less slender vaults, showed that lightweight plywood centerings, applying passive confinement to the vault extrados, inhibit the onset of the typical four-hinges failure mechanism. This lightweight, dry solution can be easily prefabricated, transferred and assembled at the construction site. The technique is reversible and fully compliant with the major preservation principles. FRP is also effective against the onset of the failure mechanism but entails larger deformations of the retrofitted vault, which may be detrimental in the case of possible decorations. The solution requires special man labor to ensure correct smoothening and cleaning of the vault extrados and to trigger effective bond between the mortar and the vault extrados. Both solutions are shown to enable small relative displacements of the vault springing, which may follow the deformation of possible internal ties. The effectiveness of these retrofit techniques was comparatively verified through experimental tests on single-leaf barrel vault stripes at 1:2 scale subjected to cyclic distributed unsymmetrical loads and through comparison with the seismic response of a reference unreinforced single-leaf vault

Phosphorylation of Arabidopsis UVR8 photoreceptor modulates protein interactions and responses to UV-B radiation

Exposure of plants to ultraviolet-B (UV-B) radiation initiates transcriptional responses that modify metabolism, physiology and development to enhance viability in sunlight. Many of these regulatory responses to UV-B radiation are mediated by the photoreceptor UV RESISTANCE LOCUS 8 (UVR8). Following photoreception, UVR8 interacts directly with multiple proteins to regulate gene expression, but the mechanisms that control differential protein binding to initiate distinct responses are unknown. Here we show that UVR8 is phosphorylated at several sites and that UV-B stimulates phosphorylation at Serine 402. Site-directed mutagenesis to mimic Serine 402 phosphorylation promotes binding of UVR8 to REPRESSOR OF UV-B PHOTOMORPHOGENESIS (RUP) proteins, which negatively regulate UVR8 action. Complementation of the uvr8 mutant with phosphonull or phosphomimetic variants suggests that phosphorylation of Serine 402 modifies UVR8 activity and promotes flavonoid biosynthesis, a key UV-B-stimulated response that enhances plant protection and crop nutritional quality. This research provides a basis to understand how UVR8 interacts differentially with effector proteins to regulate plant responses to UV-B radiation.</p