Nuovi arrivi

The response of masonry walls subjected to out-of-plane seismic actions is one of the most challenging topics in masonry mechanics. Experimental testing in support of  theoretical models is quite limited, and even when approaching the problem from a simpler static point of view (lateral resistance of  walls subjected to mass-proportional out-of-plane static forces) the need for clear experimental references is strongly felt. In the case of dry stone masonry, reduced scale static testing can be carried out with quite simple and economical methods.
This research report  presents the design, the execution, the results and the analyses of a series of static tests performed on several configurations of 1:5 scaled wall specimens made of regular dry stone masonry, focusing on their lateral strength capacity.
The tests have been performed at the University of Pavia, with the main objective of verifying existing analytical expression for the computation of the static collapse multiplier of the out-of-plane failure mechanisms.
A testing method already applied by other researchers has been followed. The testing device for the static tests was a tilting platform. No mortar was used in the models, which means that the shear strength along the joints was given purely by friction. The collapse multiplier was calculated from the inclination angle of the platform. 
In total, 42 configurations have been tested, varying the length of the walls, the presence and position of openings, the staggering ratio, the quality of the connection between walls, the existence of vertical overburden loads in the out-of-plane and in the in-plane walls, and the number of stories.

In the analysis and design of buildings, concrete floors are generally considered to be infinitely rigid in their plane. This idealisation affords the simplification of computer models used for analysis, as well as the overall seismic design of the vertical lateral force resisting elements. However, the poor performance of a multitude of buildings in recent earthquakes revealed that the rigid diaphragm assumption may not be appropriate for the design of certain floor geometries and floor systems. In fact, the damage and collapse of several buildings was largely attributed to deficient diaphragm designs. Precast concrete floor systems were observed to be quite flexible; and measured floor accelerations were several times larger than those prescribed by building codes for the design of diaphragms. These findings led to the development of improved floor acceleration estimation methods by researchers. However, these methods are only applicable to either elastically responding structures, or those modelled with rigid diaphragms. Noting that all diaphragms are flexible to some degree, and that this flexibility can lead to “unconventional” force and displacement patterns in a building during seismic excitation, there still exists a need to thoroughly characterise the seismic response of buildings with very flexible diaphragms for their proper design. A comprehensive study on the seismic response of flexible diaphragm RC wall buildings was undertaken. An extensive number of non-linear dynamic response simulations were performed on buildings of various heights that incorporated diaphragms with differing degrees of in-plane flexibility. The intensity level of the seismic input was incrementally increased, resulting in clear trends between the wall displacement ductility demands and the recorded diaphragm inertia forces.