Fundamental aspects on the seismic vulnerability of ancient masonry towers and retrofitting techniques

Ancient masonry towers constitute a relevant part of the cultural heritage of humanity. Their earthquake protection is a topic of great concern among researchers due to the strong damage suffered by these brittle and massive structures through the history. The identification of the seismic behavior and failure of towers under seismic loading is complex. This strongly depends on many factors such as soil characteristics, geometry, mechanical properties of masonry and heavy mass, as well as the earthquake frequency content. A deep understanding of these aspects is the key for the correct seismic vulnerability evaluation of towers and to design the most suitable retrofitting measure. Recent tendencies on the seismic retrofitting of historical structures by means of prestressing are related to the use of smart materials. The most famous cases of application of prestressing in towers were discussed. Compared to horizontal prestressing, vertical post-tensioning is aimed at improving the seismic behavior of towers by reducing damage with the application of an overall distribution of compressive stresses at key locations.Technical University of BraunschweigUniversity of FlorencePolytechnical University of Guadalajar

The effect of parked wind turbines on wind flow and turbulence over a complex terrain

AbstractWind‐tunnel experiments were performed to study the wind characteristics on a parked wind turbine downwind of three types of hill and over a flat terrain. The focus of the study is on comparing wind characteristics on (a) a wind turbine standing alone and (b) this same type of wind turbine embedded in a wind farm. Particular emphasis is placed on the hill size and shape and the distance between the hill and the wind farm. The hill and wind‐farm models were subjected to an atmospheric boundary layer simulation to create realistic atmospheric conditions. Flow and turbulence were analyzed based on the measured mean flow velocity, Reynolds shear stress, turbulence intensity, and the power spectral density of velocity fluctuations. The experimental results reveal similar trends concerning (a) the wind characteristics obtained on a parked wind turbine embedded in a wind farm downwind of hills of various sizes and shapes and (b) the wind characteristics on this same type of parked wind turbine standing alone in the same position downwind of the same hills. In particular, the discrepancies in the mean flow velocity and turbulence intensity between these test cases are mostly below 5%, thus indicating that a complex terrain clearly has a dominant effect on the wind characteristics, while the effects of parked wind turbines on the wind characteristics are negligible. This important finding indicates that the structural loading of parked wind turbines situated on a complex terrain may be well calculated using the same procedures both for wind turbines standing alone and wind turbines embedded in wind farms if they are both placed at the same distance downwind of the same hills

The use of prestressing through time as seismic retrofitting of historical masonry constructions: past, present and future perspective

Unreinforced masonry is one of the oldest construction materials and main component of historical buildings. Masonry is a heterogeneous material with an anisotropic behavior and may fail quasi-brittle during earthquakes. This paper describes the main components and arrangements of historical masonry, seismic vulnerability and existing retrofitting techniques, especially prestressing. Based on the evolution of prestressing, it is developed a future perspective about the use of this technique on cultural heritage. Especial attention may be taken into account when using this technique because the compressive strength may be exceeded, leading to an explosive brittle failure. The correct application of prestressing requires the designing of a compatible device and optimal post-tensioning force that improves strength and ductility without endangering the structure.Technical University of BraunschweigUniversity of FlorencePolytechnical University of Guadalajar

Traffic-induced vibrations on a simple frame: Influence of external action coherence on structural response

The study of the traffic-induced response of a simple frame structure is presented. In particular, the effect of the spatial correlation, among the traffic-induced ground displacements, is discussed by means of a parametric study to achieve the purpose of outlining those configurations yielding the less-conservative structural response. Ground excitations are estimated by the model of Hunt (J. Sound Vib. 1991; 1:41–51; J. Sound Vib. 1991; 1:53–70) assuming a quarter-car vehicle model moving on an uneven roadway placed on the top of a homogeneous half-space. The structure consists of a rigid slab supported by four columns and subjected by traffic-induced forces suitably condensed in its center of mass. Copyright © 2008 John Wiley & Sons, Ltd