Simona Coccia

Slender masonry structures, in the absence of disintegration phenomena, can be idealized as rigid bodies subjected to seismic excitation. In this study, a closed-form expression for the behavior factor (q-factor) associated with overturning collapse under out-of-plane seismic loading is derived. The analysis considers five-step pulse seismic inputs. In the proposed approach, valid for slender masonry structures, sliding failure is neglected, and collapse is assumed to occur when, at the end of the seismic excitation, the rotation of the structure reaches a value equal to its slenderness. Based on this criterion, it is possible to derive a formulation for the q-factor as a function of a dimensionless parameter that combines the geometric characteristics of the slender structure and the period of the applied accelerogram. To validate the proposed formulation, a comparative analysis is conducted against the results obtained from a numerical integration of the motion equation using a set of 20 natural accelerograms recorded in Italy. The characteristic period of each accelerogram is evaluated through different methodologies, with the aim of identifying the most suitable approach for application in simplified seismic assessment procedures.

The paper presents the main lines of a new theory of the seismic dynamics of masonry structures in the context of the masonry Heyman model. The seismic action is represented by a sequence of horizontal acceleration pulses of rectangular shape, alternating in sign, of given intensity and wavelength. The central point of the proposed new theory is the definition of the way in which the dynamical collapse takes place, occurring during the motion of the no-tension structure, excited by the seismic shaking. Two new aspects play a fundamental role in this definition. The first is the configuration of zero strength, in which the potential energy of the weights reaches its maximum and where the structure has completely lost its strength. The second is the occurrence of the gradual accumulation of deformation of the structure that takes place under the pulse sequence, in spite of the alternating pulse action. Collapse thus takes place under the simultaneous achievement of the configuration of zero strength and the arrival of the acceleration pulse that pushes the structure to go beyond this configuration. By increasing the pulse number of the sequence, collapse takes place under smaller values of horizontal acceleration intensity. Finally, an asymptotic sequence of pulses allows an equation to be formulated for the behaviour factor (the ratio of collapse horizontal acceleration intensity to the static acceleration) for safe seismic design.

Impacts analysis in the rocking of masonry circular arches Paolo Bisegna, Simona Coccia, Mario Como, Nicola Nodargi [button link="https://www.mrforum.com/wp

The elasto-plastic oscillator, representing the basic model for reinforced concrete and steel structures, shows its inadequacy when dealing with masonry structures. The column, resting on a rigid plane with friction, is shown to be particularly appropriate to model the dynamic behaviour of masonry structures. At this aim, this paper investigates the motion of a slender rigid block (SRB), initially resting in its vertical configuration and hit by a seismic input, represented through a single impulse constituted by a rectangular or sinusoidal half-wave or a simplified sequence of horizontal acceleration pulses, having rectangular or sinusoidal shapes. An accumulation of the rotation of the SRB exists under the action of sequences of opposite acceleration pulses. The dynamic collapse is shown to take place when the column is led to its critical configuration – where the restoring moment of the weight is lost – so that the last pulse can further increase the rotation of the column. Expressing the behaviour of the SRB by means of the force reduction factor, the ratio between the magnitude of the collapse horizontal acceleration and the static strength of the column, the difference between the responses of the column decreases with increasing the number of the pulses of the sequence. A simple definition of the asymptotic failure domain can be obtained with a good approximation with a limited number of pulses. It is possible to evaluate the minimum collapse acceleration intensity of seismic sequences of pulses of any assigned duration able to produce the collapse of the rigid block, representing the seismic strength of the SRB. Finally, the results obtained in the theoretical analysis are compared with the outcomes of more accurate and time-consuming non-linear dynamic or incremental analyses (IDA).

The out-of-plane behaviour of the walls as a consequence of an earthquake is the main vulnerability of existing masonry structures. In the case of rigid in compression not tensile resistant material, incremental dynamic analyses may be employed to evaluate the effective strength of a rocking element. When the seismic capacity of the wall is inadequate, retrofit interventions are required to assure an acceptable safety level. Conventional seismic retrofitting techniques on masonry walls influence the seismic performance of the element, which typically is modified in an out-of-plane bending behaviour. In this paper, analytical investigations are presented to investigate the possibility of a seismic retrofitting intervention able to increase the seismic strength of the wall without modifying its seismic behaviour. The analysed retrofitting technique consists in the application of composite vertical bars either in the middle section of the wall or at its external surfaces. The seismic behaviour of the retrofitted masonry wall is analytically evaluated by means of a parametric incremental dynamic analysis, carried out with an ad hoc in-house software. The effectiveness of the intervention is analysed in terms of level of seismic improvement, defined as the ratio between the seismic capacity of the reinforced and unreinforced walls.

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.