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Aim of this paper is the evaluation of the increasing of the load-carrying capacity of masonry arches strengthened at intrados extrados with poliparafenilenbenzobisoxazole (PBO) fabric reinforced cementitious mortar composite. An analytical procedure is proposed, in the Limit Analysis context, considering two schemes of load: a vertical load applied at the crown of the arch and a horizontal distribution proportional to the weight. The presence of the composite material is introduced by considering a plastic behaviour of the hinges defining the virtual kinematic mechanism compatible with the Limit Analysis hypotheses. Two assumptions on these mechanisms are made: a correct position of the hinges inside the cross-section of the masonry arch or a simplified location at the intrados or at the extrados of the structure. Finally, a parametric survey is carried out in order to understand the influence of the involved parameters on the load-carrying capacity of the strengthened masonry arches.

The determination of the seismic strength of masonry building is strictly connected to the in-plane strength of masonry walls under the action of horizontal forces. Simplified criteria are currently available in literature, based on modelling of the structure as loaded by dead loads and by a gradually increasing distribution of horizontal forces, proportional to the mass of the building. According to this approach, called push-over method, the seismic strength of the building corresponds to the intensity of these gradually increasing horizontal loads, leading the building to the failure condition. This paper moves in the framework of the Limit Analysis, based on the Heyman’s masonry model (1966), rigid in compression with no tensile strength. The resistant model refers to a multi-storey wall with openings arranged in regular patterns, along both vertical and horizontal directions, reinforced at floor levels by steel ties. The in-plane failure of the regular multi-storey walls can occur with the development of various kinematically admissible mechanisms, characterized by the attainment of the yielding state in the steel ties. The proposed methodology consists in the definition of the mechanism along which the failure effectively occurs and in a subsequent check of the statical admissibility of the internal stress state at the limit load. Only in this case, the corresponding kinematical multiplier is the effective collapse multiplier. The presence of the panels situated above the openings strongly conditions the in-plane failure of the wall, acting as diagonal struts, causing different horizontal displacements between the piers at the floor levels and consequently engaging the horizontal ties in the mechanism. In order to ensure the development of the global failure, avoiding local brittle failures, steel strengths of the ties have thus to be suitably defined. Finally, a parametric investigation is carried out considering different geometries of masonry walls and varying the position of the piers self-weights and the horizontal forces distribution, constant or proportional to the height of the masses from the foundation level.

The wall pier represents the vertical element of multi-storey walls with openings, the main resistant structural components of a masonry building. Structural systems of wall piers and spandrels are required to sustain the in-plane seismic actions acting on the wall, opposing with their weights to the action of horizontal forces. The behavior of masonry constructions results to be very far from the one characterizing ductile structures, because of the lack of energy dissipation during the deformation. A strength resource of masonry structures, properly reinforced in order to avoid early local failures, consists in exhibiting rocking behavior, until a failure condition is attained. An investigation on the dynamic behavior of masonry wall piers is carried out by following Housner’s studies and properly introducing the effect of diagonal cracks, shown by typical post-earthquake cracking patterns. As a consequence, the system is characterized by the detachment of a lower triangular region that becomes ineffective during the development of the mechanism and does not oppose with its weight to the overturning. Finally, it is shown that the occurrence of diagonal cracks can be prevented by the execution of suitable retrofit interventions.

The research of a failure criterion for concrete under multi-axial stresses is a very important task because of the numerous civil engineering applications. Nowadays several concrete failure tests are available in literature and various criteria have been proposed. A multi-axial failure criterion for the concrete founded on a simple physical basis, has been proposed by one of the authors. In this paper a sharper foundation of this criterion is given. The hardened cement paste (hcp), the binder of all the aggregate particles, is responsible of the concrete strength. Consequently, a preliminary average evaluation of the stresses, occurring, when the concrete is loaded, into the various phases components, and particularly in the hcp, is necessary to analyse the failure. To that end, the paper revolves around the analysis of the thermal behaviour of the concrete at its early stage of setting. It is shown that the heat production during the cement hydration process, is responsible to produce clearances among the various particles and the surrounding hcp that, in turn, the consequent statically determined structure of the concrete. Validation of this result comes out by analysing the elastic moduli and the thermal expansion coefficients. The micro-macro failure condition of Como & Luciano thus receives a sounder physical basis.

This paper gives a general formulation of the statics of the masonry continuum within the conceptual framework set up by J. Heyman in his fundamental and pioneering studies of masonry arches and vaults. Here the masonry body will be represented by an assemblage of rigid particles of stones, held together only by compressive forces, and liable to crack as soon as tensile stresses begin to develop. The very small size of the stones, compared to the overall dimensions of the body, permits a treatment in terms of a continuum.

Sommario Lo scopo del Lavoro è quello di fornire una valutazione approssimata della richiesta di duttilità e di resistenza necessaria affinichè una struttura possa assorbire l'azione di un terremoto di assegnata intensità. Per mezzo di un'opportuna equazione di bilancio è così mostrato che la capacità della struttura ad assorbire l'azione di terremoti violenti dipende da un particolare accoppiamento di resistenza e duttilità che viene definito come tenacità antisismica della struttura. Una prima valutazione dei rapposti di tenacità antisismica raggiungibili nelle strutture in cemento armato completa il Lavoro.

Sommario Vengono esaminate alcune difficoltà e problemi ancora aperti nella teoria della stabilità dei sistemi continui. Dopo aver approfondito il significato e l'importanza della scelta della “distanza” tra due configurazioni di un sistema continuo, il problema della stabilità dell'equilibrio delle strutture elastiche viene formulato in un opportuno spazio funzionale, nel quale è possibile dimostrare la validità del criterio dell'energia come condizione sufficiente di stabilità nel senso di Lyapunov.

Sommario Questo lavoro costituisce il proseguimento di uno studio sulle stabilità e comportamento postcritico delle strutture elastiche; nel precedente lavoro, pubblicato sul n. 4, vol. X, 1975 di questa rivista, è stato esaminato il problema della definizione dell'energia potenziale di un corpo elastico tridimensionale in un opportuno spazio funzionale delle configurazioni, e sono state esaminate le proprietà di regolarità di questo funzionale. Proseguendo il programma formulato nel lavoro precedente, viene ora innanzitutto completato lo studio del funzionale energia potenziale con riferimento a modelli strutturali mono e bidimensionali. Viene poi sviluppata la Parte II e cioè l'analisi della stabilità secondo Liapunov di una configurazione di equilibrio attraverso opportune formulazioni dei criteri dell'energia.

Sommario Con questa ricerca si intende fornire un contributo a una formulazione consistente della teoria della stabilità, dello stato critico e postcritico delle strutture elastiche.

In this note we study the stability of bending-torsional equilibrium of a cantilevered bar subjected at its end section to a follower force; this case may represent a wing subjected to the jet of a turbine-engine.

Sommario Sui fondamenti della teoria degli slip della plasticità dei metalli viene formulata in forma incrementale una teoria generale della deformazione dei mezzi continui soggetti all'azione di tensioni tangenziali. Vengono poi trattati, come casi particolari, il corpo elastico isotropo e incompressibile e il corpo plastico incrudente.

Sommario Si studia analiticamente l'evoluzione della superficie di plasticizzazione dei metalli in fase di incrudimento nel piano σ - τ. Il problema, che riveste notevole interesse teorico ed applicativo, viene risolto in forma completa nell'ambito della teoria degli slip e prendendo opportunamente in conto l'effetto Bauschinger.

Sommario In questa Nota viene studiato il comportamento plastico dei metalli prendendo in conto l'influenza dell'incrudimento e l'effetto Bauschinger.

Sommario In questa Nota viene formulata una consistente teoria lineare della stabilità dell'equilibrio delle strutture elastiche e si tratta il problema dell'equilibrio indifferente di un continuo costituito da un materiale elastico con elevata rigidità alla deformazione. Tutti i casi particolari di instabilità euleriana delle travi, piastre, gusci ecc., discendono come casi particolari e di questi viene fornita una classifica nei riguardi della loro importanza. Si fanno infine confronti con altre trattazioni.