Una nueva especie de Gutierrezia (Asteraceae, Astereae) de Argentina

Ratto, Francisco. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente. Cátedra de Botánica Sistemática. Buenos Aires, Argentina.Bartoli, Adolfo. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Recursos Naturales y Ambiente. Cátedra de Botánica Sistemática. Buenos Aires, Argentina.e004, 5 p.Gutierrezia tortosae Ratto & Adr. Bartoli, a new species from Argentina, is described and illustrated. The new species resembles Gutierrezia mandonii (Sch. Bip.) Solbrig, in having xylopodium, similar shaped leaves, and yellow ray florets, but differs by having erect and rigid stems, erect leaves and smaller heads. A key to differentiate it from the allied species which inhabit in the northwest of Argentina is provided

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 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

Earthquake protection of colonial bell-towers in Colima, Mexico with externally prestressed FRPs

A methodology for the seismic vulnerability reduction of old masonry towers with external prestressing is presented. It is applied at the Colonial bell-towers of the Cathedral of Colima, Mexico, characterized for being a high seismic area (M>7.5). The 3D FE models are calibrated with experimental data and assessed through nonlinear static approaches including the seismic demand and an accurate validated masonry model. Based on an extensive parametric study on different configurations of old masonry towers, it is selected an optimal prestressing force and device. The Colonial towers are retrofitted with four prestressing devices of FRPs to convert them into a high energy-dissipative reinforced masonry. The external vertical prestressing is included at key points identified in the seismic vulnerability assessment. This technique is in compliance with the demand for architectural conservation and may be located without drilling and unbounded in order to be fully removable. The seismic performance is enhanced by increasing force, displacement, and internal confinement. It is observed an upgrading of 35% and 20% of displacement capacity. With these results it is corroborated that external vertical prestressing allows a substantial increment of ductility for seismic energy dissipation purposes

Earthquake protection of colonial bell towers in Colima, Mexico with externally prestressed FRPs

A methodology for the seismic vulnerability reduction of old masonry towers with external prestressing is presented. It is applied at the Colonial bell-towers of the Cathedral of Colima, Mexico, characterized for being a high seismic area (M>7.5). The 3D FE models are calibrated with experimental data and assessed through nonlinear static approaches including the seismic demand and an accurate validated masonry model. Based on an extensive parametric study on different configurations of old masonry towers, it is selected an optimal prestressing force and device. The Colonial towers are retrofitted with four prestressing devices of FRPs to convert them into a high energy-dissipative reinforced masonry. The external vertical prestressing is included at key points identified in the seismic vulnerability assessment. This technique is in compliance with the demand for architectural conservation and may be located without drilling and unbounded in order to be fully removable. The seismic performance is enhanced by increasing force, displacement, and internal confinement. It is observed an upgrading of 35% and 20% of displacement capacity. With these results it is corroborated that external vertical prestressing allows a substantial increment of ductility for seismic energy dissipation purposes.ITESO, A.C.Technical University of BraunschweigUniversity of Florenc

Seismic Behavior and Failure Mechanisms Identification of Ancient Masonry Towers

Strong damage or complete loss suffered by the cultural patrimony when subjected to considerable earthquake ground shaking has been occurring through the history of humanity. The occurrence of these unexpected and unavoidable events has demonstrated that ancient masonry towers are one of the most vulnerable structural types to suffer strong damage or collapse. There are certain relevant aspects determining the seismic vulnerability of towers in terms of behavior and failure mechanisms that differentiate these vertical structures from most of compact historical constructions. This is the first stage of an international scientific research between the University of Braunschweig and the University of Florence, aimed to develop a methodology to mitigate the seismic risk of ancient masonry towers located in seismic zones with the use of prestressing devices of smart materials. Therefore results quite important a deep understanding and identification of all the most important aspects that determine the seismic vulnerability of ancient masonry towers in terms of behavior and failure mechanisms. For achieving this, it is considered the relevant literature, observed damage after real earthquakes and mainly engineering experience.Technical University of Braunschwei

Seismic risk mitigation of historical masonry towers by means of prestressing devices

This work presents the investigation of the efficiency of different prestressing devices as a rehabilitation measure for the seismic risk mitigation of historical masonry towers. As a first phase, the seismic vulnerability of theoretical masonry towers was assessed by means of numerical models validated with information from the literature, observed damage and behavior of these structures due to passed earthquakes (crack pattern and failure mechanisms), and mainly taking into account the engineering experience. Afterwards, the validated models were rehabilitated with different prestressing devices; analyzing the results and concluding which device or the combination of them improved in a better way the seismic performance of the masonry towers. Finally, the methodology will be applied in two historical masonry towers located in seismic areas; the medieval tower “Torre Grossa” of San Gimignano, Italy, and one of the bell towers of the Cathedral of Colima, Mexico.Technical University of BraunschweigUniversity of Florenc