Cyclic shear-compression tests on masonry walls strengthened with alternative configurations of CFRP strips

This work reports the results of an experimental programme aimed at investigating the in-plane behaviour of clay-brick masonry walls externally strengthened by carbon fiber reinforced polymer (CFRP) strips. Particularly, four different geometrical layouts were considered for the CFRP strips, though keeping unchanged the quantity of composites employed in each wall. Firstly, a preliminary experimental work was carried out on samples of the constitutive materials for quantifying their key mechanical properties and evaluating the bond behaviour of FRP strips on the masonry substrates. Then, eleven cyclic shear-compression tests were performed to observe the response of strengthened walls and the influence of the strengthening layouts under investigation. The proposed experimental report is intended as a contribution to the current state of knowledge about the behaviour of FRP-strengthened masonry walls: it is available to assess the accuracy and possibly improve the predictive capacity of design-oriented capacity models. Finally, the comparison of the reported experimental results with the predictions obtained by applying the analytical relationships proposed by a recently issued guideline for FRP strengthening of masonry structures is proposed.     

Detecting short-term evolution of Etnean scoria cones: a LIDAR-based approach

The 2001 and 2002–2003 flank eruptions on Mount Etna (Italy) were characterized by intense explosive activity which led to the formation of two large monogenetic scoria cones (one from each eruption) on the upper southern flank of the volcano. Continuous monitoring of Etna, especially during flank eruptions, has provided detailed information on the growth of these cones. They differ in genesis, shape, and size. A set of high resolution (1 m) digital elevation models (DEMs) derived from light detection and ranging (LIDAR) data collected during four different surveys (2004, 2005, 2006, and 2007) has been used to map morphology and to extract the morphometric parameters of the scoria cones. By comparing LIDAR-derived DEMs with a pre-eruption (1998) 10 m DEM, the volume of the two scoria cones was calculated for the first time. Comparison of the LIDAR-derived DEMs revealed in unprecedented detail morphological changes during scoria cone degradation. In particular, the morphologically more exposed and structurally weaker 2002–2003 cone was eroded rapidly during the first few years after its emplacement mainly due to gravitational instability of slopes and wind erosion.     

First-order corrections to the radiation patterns of P-and S-waves in a prestressed medium

Summary. The long wavelength radiation patterns of P - and S -waves are determined for an elastic prestressed earth model. The prestress is treated as a perturbation of an isotropic medium. Non-zero first-order corrections are found to the eigenvalues and eigenvectors of the deviatoric seismic moment tensor. The radiation pattern given by a purely tangential dislocation is equivalent to a double couple contaminated by a dipolar term linear in the perturbation.     

A dislocation model of microplate boundary ruptures n the presence of a viscoelastic asthenosphere

Summary. A microplate is modelled as an elastic plate with two long strike-slip boundaries, lying over a Maxwell-type viscoelastic asthenosphere. The microplate is subjected to a constant and uniform shear strain rate by the opposite motions of two adjoining larger plates. After the occurrence of an earthquake at one of the microplate boundaries, the time evolution of shear stress at the other boundary is studied. It is found that stress build-up at the second boundary is delayed due to stress diffusion governed by the asthenosphere relaxation. Earthquake occurrence at this latter boundary would be delayed depending upon both the microplate width and the ratio between the Maxwell relaxation time of the asthenosphere and a characteristic time required for tectonic strain to recover rupture conditions. It turns out that the parameters which determine the occurrence of seismic activity along the microplate boundaries are more strictly constrained in the presence of a viscoelastic asthenosphere than in the case of an elastic half-pace model.     

Experimental study of fracture at geological scale velocities

Summary. It is well-known that the chemical environment and the thermodynamical conditions play a fundamental role in the physics of the fracture properties of solids which in turn appear relevant in the understanding of the earthquake mechanism and related precursory phenomena. We designed and built an experimental apparatus capable of measuring the fracture velocities with control of the physical and chemical environment as well as of the applied stress. The apparatus consists of a chamber where both the total pressure and the partial pressure of gases can be controlled. The stress is applied in mode I (tension) configuration. The crack is detected optically on the surface of the sample with an ordinary microscope and the velocity of propagation is directly measured by the increase in length in the elapsed time. The very good stability of the system over very long periods allows us to measure crack velocities down to 10⁻¹² ms⁻¹. The propagation under such low-velocity regimes appears interesting from a geological standpoint since it implies extremely low stress values, which are generally assumed to have no effect on crustal rocks. The first results obtained will be discussed, with particular regard to the apparent dramatic influence of the partial pressure of water vapour in the crack propagation velocity.     

On the mechanism of formation of the tyrrhenian sea

We investigated some of the existing hypotheses on the formation of the Tyrrhenian Sea basin, and we found that none of them appears satisfactory. By quantitative considerations we show that proposed mechanisms, such as those based on oceanization or back-arc spreading, cannot explain the origin of this basin. We suggest an alternative mechanism, consisting on the gabbro-eclogite transition, which occurs in the basaltic layer of the continental crust when anomalous mantle contacts the crustal basement. This leads to the formation of eclogite, which tears off the crust, sinks into the astenosphere, and accumulates at its base. As a consequence of the destruction of the basaltic layer the crust is strongly reduced and a deep basin is formed. We also suggest that the processes of crustal thinning and subsidence developed as proposed here at different times in different regions.