174 research outputs found
Experimental tests on existing RC beams strengthened in flexure and retrofitted for shear by C-FRP in presence of negative moments
Abstract The shear strength of reinforced concrete beams extracted from existing buildings often reveals insufficient transversal steel reinforcement, mainly due to design or construction defects or increased design load requirements. FRP wrapping is one of the best solutions to improve beam shear strength as the retrofitting intervention is fast and the cost is modest. Design codes provide clear indication about the retrofitting design of simply supported beams, while the case of a beam with negative moments at the end is not considered, although this is in the case of a beam in a framed structure. One of the main uncertainties lies in the effectiveness of the FRP U sheet anchorage behavior in the area of negative bending moments with cracked concrete. This may limit the shear strength of the retrofitted beam. In this study, two beams extracted from an existing building constructed in the 1930s in Rome and retrofitted by carbon fiber-reinforced polymer (C-FRP) U strips placed at beam ends, where also negative bending moments were present, and have been evaluated with experimental tests at the laboratory of the Department of Architecture of Roma Tre University. Beam steel and concrete characteristics were evaluated by means of different tests. The experimental results are discussed considering the final results in terms of maximum shear resistance in the presence of negative bending moments. Load deflections at different points along the beam, shear-C-FRP deformation along the reinforcement strips and the damage state for different load levels, are presented. The importance of avoiding possible fragile mechanisms in the sections retrofitted with FRP is clearly shown
Asynchronous earthquake strong motion and RC bridges response
The dynamic response of long structures (e.g., bridges) is sensitive to the spatial variability of strong ground motion (asynchronous motion). Ground motion differences increase from point to point with increasing foundation distance. This latter is due to two physical phenomena: soil-wave interaction, that causes the loss of coherence and local amplification; wave traveling with finite velocity, that causes signals time lag. This ground motion variability produces a different structural demand compared to the synchronous one, which is the only one considered by designers in the majority of cases. A few codes consider this type of actions, therefore further research efforts are necessary. In this study, asynchronous ground motions are generated by means of a new generation procedure implemented in the software GAS 2.0 using as input the simultaneous strong motion records from the April 6th, 2009, L'Aquila (Italy) at the seismic stations AQA and AQV, located in the Aterno River valley. These records are used to calibrate the generation model and to produce sets of asynchronous earthquake sampling. The asynchronous earthquake sets are applied on a typical highway reinforced concrete bridge to study its dynamic response considering two different configurations: non-isolated with traditional supports and isolated bridge with lead rubber bearings. The bridge is placed in two positions along the wave propagation direction: a position near one recording station and a position between the two stations to consider local soil effects. The response parameters investigated are the maximum relative displacements of soil and deck. The results show that there is an important variation of relative displacement along the direction of wave propagation due to asynchronous motion with effects that designer should consider for the structural details design of isolated and non-isolated bridges. Keywords: Asynchronous motion, Bridges, Seismic response, Earthquake spatial variabilit
Damage patterns in the town of Amatrice after August 24th 2016 Central Italy earthquakes
The impact of the two seismic events of August 24th 2016 on the municipality of Amatrice was highly destructive. There were 298 victims, 386 injured, about 5000 homeless, and the historical center of the town suffered a great number of partial and total collapses. The 260 strong motion records obtained for the first event were analyzed and plotted in a shakemap, comparing them with the macroseismic damage surveys made in 305 localities. On the basis of an inspection survey made in September 2016, a map of the damage patterns of the buildings in the historical center was elaborated according to the EMS 98 classification. The damage level resulted very high with more than 60% of the inspected buildings showing partial or total collapse. The elevated level of destruction was mainly caused by the high vulnerability of the masonry buildings, mostly due to specific vulnerability factors such as the poor quality of masonry, the lack of connections between walls and the poor connection between external walls and floors
Numerical and experimental analysis of the leaning Tower of Pisa under earthquake
Twenty years have passed from the most recent studies about the dynamic behavior of the leaning Tower of Pisa. Significant changes have occurred in the meantime, the most important ones concerning the soil-structure interaction. From 1999 to 2001, the foundation of the monument was consolidated through under-excavation, and the "Catino" at the basement was rigidly connected to the foundation. Moreover, in light of the recent advances in the field of earthquake engineering, past studies about the Tower must be revised. Therefore, the present research aims at providing new data and results about the structural response of the Tower under earthquake. As regards the experimental assessment of the Tower, the dynamic response of the structure recorded during some earthquakes has been analyzed in the time- and frequency-domain. An Array 2D test has been performed in the Square of Miracles to identify a soil profile suitable for site response analyses, thus allowing the definition of the free-field seismic inputs at the base of the Tower. On the other hand, a synthetic evaluation of the seismic input in terms of response spectra has been done by means of a hybrid approach that combines Probabilistic and Deterministic Seismic Hazard Assessment methods. Furthermore, natural accelerograms have been selected and scaled properly. A finite element model that takes into account the inclination of the structure has been elaborated, and it has been updated taking into account the available experimental results. Finally, current numerical and experimental efforts for enhancing the seismic characterization of the Tower have been illustrated
Time-dependent cyclic behavior of reinforced concretebridge columns under chlorides-induced corrosion andrebars buckling
This study presents the results of a refined numerical investigation meant at understanding the time-dependent cyclic behavior of reinforced concrete (RC) bridge columns under chlorides-induced corrosion. The chloride ingress in the cross-section of the bridge column is simulated, taking into account the effects of temperature, humidity, aging, and corrosion-induced cover cracking. Once the partial differential equations governing such multiphysics problem are solved through the finite-element method, the loss of reinforcement steel bars cross-section is calculated based on the estimated corrosion current density. The nonlinear cyclic response of the RC bridge column under corrosion is, thus, determined by discretizing its cross-sections into several unidirectional fibers. In particular, the nonlinear modeling of the corroded longitudinal rebars exploits a novel proposal for the estimation of the ultimate strain in tension
and also accounts for buckling under compression. A parametric numerical
study is finally conducted for a real case study to unfold the role of
corrosion pattern and buckling mode of the longitudinal rebars on the time
variation of capacity and ductility of RC bridge columns
Effect of different soil treatments on production and chemical composition of essential oils extracted from Foeniculum vulgare Mill., Origanum vulgare L. and Thymus vulgaris L
The aim of the present study was to investigate how essential oil production and associated chemical composition and related biological activity could be influenced by different cultivation treatments and distillation method. Foeniculum vulgare Mill. (fennel), Origanum vulgare L. (oregano), and Thymus vulgaris L. (thyme) were cultivated in absence of any fertilizer (control) and in presence of three different fertilizers: a chemical one with augmented of mineral phosphorus and potassium, a second added with hydrolysed organic substance and mineral phosphorus and potassium (organic-mineral) and a third one treated with high content of organic nitrogen of protein origin (organic). The plants were subjected to steam distillation using two modalities: recycled and continuous to obtain 32 essential oil samples. Chemical composition analysis was performed by gas chromatography-mass spectrometry; in vitro antimicrobial activity was evaluated by broth microdilution method. In general, the recycled distillation method appeared to have a slightly higher yield than the continuous method. The "mineral" and "organic-mineral" treatments resulted in the higher yield compared to the "organic" or "control" treatments, and this was particularly evident in the recycled method. The "control" plants had a lower yield of essential oils. Anethole (13.9-59.5%) and estragole (13.4-52.2%) were the main constituents of fennel oils, p-cymene and its derivatives carvacrol and thymol were the main constituents of oregano and thyme samples. The antimicrobial activity of thyme oils on Staphylococcus aureus ranged from 0.31 to 0.16% (v/v); a lower effect of oregano samples and no activity of fennel samples were observed. The essential oils failed to inhibit the growth of Pseudomonas aeruginosa strains
Integral abutment bridges:Investigation of seismic soil-structure interaction effects by shaking table testing
Leaning Tower of Pisa:recent advances on dynamic response and soil structure interaction
The Leaning Bell Tower of Pisa has been included in the list of the World Heritage Sites by UNESCO since 1987.
Over the last 20 years, the Tower has successfully undergone a number of interventions to reduce its inclination.
The Tower has also been equipped with a sensor network for seismic monitoring. In this study, preliminary results
on the dynamic behavior of the monument are presented, including a review of historical seismicity in the region,
identification of vibrational modes, definition of seismic input, site response analysis, and seismic response
accounting for soil-structure interaction. This includes calibration of the dynamic impedances of the foundation to
match the measured natural frequencies. The study highlights the importance of soil-structure interaction in the
survival of the Tower during a number of strong seismic events since the middle ages
- …