673,039 research outputs found
Carte di S. Fedele in Como
No full text"Dalla Raccolta storica della Società storica comense, volume VI."Mode of access: Internet
Dynamical collapse of masonry arches under sequences of impulses of horizontal acceleration
No full textA new formulation of the seismic response of the masonry arch hit by sequences of impulses of horizontal acceleration, of assigned intensity and duration, is the subject of the paper. After a preliminary evaluation of the static limit acceleration intensity AL, under which the arch starts to move, the central point of the paper is the determination of the equation of the motion of the arch, considering the gradual changes of mechanism's geometry. It is shown that the arch, under the hammering sequence of impulses of suitable intensity and duration, can reach, without oscillations, a resonance condition with a consequent build-up of progressively accumulating deformation up to the configuration of zero strength and the consequent dynamic failure. The ratio qN = AN/AL - between the impulse collapse acceleration AN and the limit static acceleration AL - is achieved by considering the gradual increase in the impulse number N of the sequences. The minimum value of the collapse acceleration ratios qN, which is the real behavior factor q, is then obtained by considering the PGA and the period TE of the expected earthquake. A discussion on the differences existing between the static and the dynamic collapse of the arch, with the development of many examples, concludes the paper
Influence of epibenthic predators on activity of a burrowing shrimp, Upogebia pusilla (Petagna), in a mediterranean intertidal mudflat
No full textDynamical assessment of the performance factor "Q" for the masonry wall under the out of plane seismic action
No full textThe non-linear out of plane dynamical response of the masonry wall, suitably reinforced at the top and hit by sequences of acceleration pulses, alternating in sign and with different intensity and duration, is the subject of the paper. The wall moves out of its plane with a gradually changing failure mechanism and two relevant aspects characterize this motion: the occurrence of a rotational build up under the action of the pulse sequence, in spite of their alternating in sign and the occurrence of the dynamical collapse. This last takes place when, under the second last pulse of the sequence, the increasing mechanism has reached the critical configuration in which all resistance of the wall is lost. The arriving of the last pulse, pushing the wall to further increase its rotation, yields the collapse. The ratio between the dynamical and the statical collapse accelerations – the so-called strength reduction or performance factors – is thus directly determined following the dynamical response of the wall to the pulse sequences. The paper, which is part of an ongoing research (Coccia et al. 2022) reveals how the wall, so vulnerable under the out of plane seismic actions, can mobilize collapse mechanisms capable of defending it by the destructive action of the quakes
Out-of-plane dynamical strength of masonry walls under seismic actions
No full textThe dynamic analysis of the out-of-plane response of masonry walls, with different reinforcing systems and hit by sequences of pulses alternating in sign, representative of the seismic action, is the aim of the paper. The analysis is done in the context of the Heyman model of the no tension masonry structures. We consider the wall of the last story of a simple masonry house, commonly reinforced at its head by a ring beam, usually in a reinforced concrete. It has also been considered the retrofitting of the wall by applying, on both its sides, vertical bands in FRP, or similar. The dynamics of the wall, activated by sequences of pulses, is analyzed in detail, considering the change of geometry occurring in the mechanism during the motion. The corresponding differential equation is integrated in a closed form. It is shown that, under the alternating sequence of shocks, the dynamical collapse of the wall takes place immediately after the occurrence of an accumulation of out-of-plane deformation of the wall that drags it into the configuration of zero strength, where any resistance, due to the weight, has been lost. The collapse takes place right after when the subsequent incoming pulse pushes the wall to go further beyond this configuration. The check of the seismic safety of the masonry wall concludes the paper. The smallest limit static strength of the wall required in order the wall, having pulsation p, could be able to sustain, at the limit of the dynamical collapse, the action of the asymptotic pulse sequence with acceleration intensity PGA and specific duration p T-E/2 of the expected earthquake. It is shown that the wall, reinforced by a top ring beam, with the addition of vertical bands of glass or similar, of suitable length, pasted with lime mortar, can reach the required level of seismic safety
Resistenza del pilastro in c.a. caricato assialmente da un azione eccentrica
No full textThe paper aims to study the equilibrium configurations of the reinforced concrete column under the action of an eccentric axial load. The classical example of the column hinged at its side sections is analysed taking into account the cracks growing. The gradual stiffness reduction due to cracking yields a strong interaction among mechanical and geometrical non linearity. The column fails when the plastic state is reached at the critical section. The tension stiffening occurring among the cracks, corresponding to a suitable shear-slip equation, is the main effect that controls the behaviour of the column. The critical load is obtained as a function of its eccentricity and of the mechanical properties of concrete and reinforcing bars. Comparisons of the results predicted by the proposed model with some experimental tests show good agreement
Comportamento di strutture a telaio in c.a. progettate in classe di duttilità alta
No full textAim of the paper is the evaluation of the global ductility demand for a plane reinforced concrete frame designed with the prescription of the recent Italian guidelines.
The outcomes of the analyses are judged in the framework of a performance based approach, and the global ductility demand of the examined scheme is evaluated through the application of assessed methods and compared with the ductility capacity of the structure. The result of the analyses is the inadequacy of the designed frame to sustain the seismic action.
Finally a new method for the design of the plane frames is proposed
Effects of taxonomic resolution in analysis of macrobenthic communities of a mediterranean coastal lagoon (Orbetello, Italy)
No full textA reformulation of a multi-axial failure criterion for the concrete
No full textThe 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
On the error exponent of Markov channels with ISI and feedback
No full textWe extend Burnashev's [5] classic result for the error exponent of discrete memoryless channels with feedback to the case of Markov channels with ISI and feedback. This is a nontrivial extension of our previous work [6] where we treated the case of Markov channels with feedback but without ISI. Tools from stochastic control theory are used to treat the case with ISI
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