Dynamic assessment of the axial force in the tie-rods of the Milan Cathedral

The Milan Cathedral, constructed over a period of more than 400 years, is one of the few Gothic cathedrals where permanent metallic tie-rods are installed under all naves to support a portion of the lateral thrust exerted by vaults and arches. After the recent failure of one tie-rod, an extensive research program was carried out to characterize the metallic material and to evaluate the axial forces and the tensile stresses of the tie-rods through dynamic testing and system identification. After a description of the methodology adopted in the dynamic assessment of tie-rods in the Milan Cathedral, the paper presents the main results of the investigation, in terms of fundamental frequencies and axial forces in the tie-rods

Procedure di Calcolo per l’Uso di EB FRP nel Rinforzo a Taglio di Travi in Cemento Armato

The aim of this work is assessment and analysis of the reliability of the most well-known design models, available for the prediction of the contribution of fiber reinforced polymer (FRP) systems to the shear capacity of strengthened reinforced concrete beams. In this study, current analytical formulations for basic shear design and shear strengthening design are presented in detail and main problems and lacks, being the motivation of this work, are highlighted. The research is based on the comparison of previous experimental studies with both current design guidelines and design models recently proposed by several authors, considering also various recommendations for the angle of inclination of shear cracks. Assessment of design procedures was done using probabilistic aproach, and several descriptive statistical measures, such as the average (AVG) and the coefficient of variation (CoV), have been obtained from database, regarding different strengthening schemes. A more detailed analysis of reduced database was made, considering only Ujacketed configurations with transversal steel. Because of its good performance, a detailed investigation on Pellegrino and Modena (2008) model has been made and in order to predict better results, modification of this model has been proposed

Assessment of design procedures for the use of externally bonded FRP composites in shear strengthening of reinforced concrete beams

Shear strengthening of reinforced concrete (RC) elements with fibre reinforced polymer (FRP) composites is actually a research topic far to be completely solved. Existing shear strength models lead sometimes to overly non-conservative results and need to be validated with a sufficient number of experimental tests. The aim of this work is to assess some common design models for the prediction of the shear capacity of RC beams strengthened with externally bonded FRP composites. The research is based on a wide database collected from recent literature and is mainly focused on the combination of the basic codes for RC structures (without strengthening) with current models for FRP shear strengthened structures. The research significance of this work is due to the lack of information on the performance of the above models when combined with basic codes. Particular attention was dedicated on the consistency of the models for FRP strengthened structures with Eurocode 2, since it assumes a method based on the truss model with variable inclination of the compressed strut. Lastly, some improvements of the model proposed by Pellegrino and Modena, which takes into account the interaction between steel and FRP contributions to the shear capacity, are proposed

Frequency splitting in the tie-rods of the Cathedral of Milan

During experimental investigations on the dynamic behavior of the tie-rods of the Cathedral of Milan, a frequency splitting phenomenon, also known as "dispersive phenomenon", was detected in the structural response of 4 ties. The present paper reports on the techniques adopted to investigate the observed behavior. The recorded data were first analyzed by estimating the Frequency Response Functions, then by applying classic Operational Modal Analysis techniques to confirm the presence of the phenomenon. Subsequently, the possibility of reproducing the frequency splitting was verified by implementing a linear model which takes into account an imaginary dispersion matrix D. Since, according to the literature, dispersive phenomena are supposed to be associated to the response of damaged structural elements, accurate visual inspections and further dynamic tests (hammer and ambient vibration tests) of the ties exhibiting the mentioned behavior have been scheduled in the near future

The Effect of Ginkgo Biloba (EGb 761) on Epileptic Activity in Rabbits

Different animal models are used to evaluate the process of epileptogenesis. In this investigation the kindling model of epilepsy was used. The epileptic focus was induced in Chinchilla rabbits by stimulation of the hippocampus with electric stimuli. We presumed that the extracts of Ginkgo biloba affect the formation of kindling epilepsy. Bioelectric activity of the brain was registered throughout the development of kindling with and without standardized extracts from dried ginkgo leaves (EGb 761). For each animal the following has been determined: the values of the minimum current strength necessary for the origination of threshold after-discharge (AD) – discharges appearing after the cessation of stimulation; duration of the threshold AD; number of stimulations necessary for the origination of full kindling; time latency for the development of full kindling; number of spontaneous epileptogenic discharges manifested in EEG two days following the formation of full kindling during 60-minute registration. The results show that the process of epileptogenesis was influenced by EGb 761. It has been established that if the animals received EGb 761, significantly weaker minimum current strength was necessary for the development of the epileptogenic focus and the AD were longer, while the number of necessary electrostimulations for the appearance of full kindling was less and the latency was shorter

Exchange-Bias and Grain-Surface Relaxations in Nanostructured NiO/Ni Induced by a Particle Size Reduction

Transition-metal-oxide/transition-metal nanocomposites, such as NiO/Ni, FeO/Fe, and CoO/Co, have been the subject of much recent investigation (i) because of their potential applications and (ii) because they are good model systems for studies of some effects on the nanoscale. They are used, for example, as catalysts, fuel-cell electrodes, magnetic memories, etc. When a nanocomposite is composed of both ferromagnetic (FM) and antiferromagnetic (AFM) nanoparticles, interesting physical properties can occur, such as the phenomenon of exchange bias (EB). A Ni/NiO nanocomposite obtained by the thermal decomposition of nickel(II) acetate tetrahydrate, Ni(CH3COO)(2)center dot 4H(2)O, at 300 degrees C, is composed of NiO (62%) and Ni (38%) with crystallite sizes of 11 and 278 nm, respectively. We observed an increase in the crystallite size for NiO and decrease of crystallite size for Ni, a decrease in the microstrain for both and an increase in the NiO phase content with thermal annealing in air, while high-energy ball milling leads to a decrease of the crystallite size, an increase in the size of the agglomerates, and microstrain as well as reduction, NiO - GT Ni. The lattice parameters of the nanosized NiO and Ni show a deviation from the value for the bulk counterparts as a consequence of crystallite size reduction and the grain-surface relaxation effect. The exchange bias found in a milled sample with particles of 10 nm (NiO) and 11 nm (Ni) disappears for larger particles as a consequence of a coupling-area decrease between the antiferromagnetic and ferromagnetic particles. Due to reduction/oxidation (NiO LT - GT Ni) and size as well as surface-relaxation effects the saturation magnetization value increases/decreases with milling/annealing, respectively. Having in mind the effect of size on the exchange bias, coercivity, and magnetization values, it is possible, by annealing/milling, to tailor the composition and particle size and then control the exchange bias and improve the other magnetic properties of the Ni/NiO