1,721,461 research outputs found
Ground Penetrating Radar (GPR) for bridge inspection
No full textBridge inspection plays a crucial role in providing bridge operators with an overview of their infrastructure’s current condition, enabling them to extend their service life. This is even more important since a significant number of bridges were constructed after World War II with few comprehensive documents regarding their construction, for example blueprints. In such cases, non-destructive testing (NDT) methods can be employed to investi-gate the structure without causing damage. Among the widely utilized NDT methods, Ground Penetrating Radar (GPR) stands as one of the most widely used methods to localize reinforcement and prestressing strands, thanks to its efficient acquisition capabilities that are characterized by the speed in performing the acquisition and the instantaneous visualization of results. However, due to the inherent complexity, the use of GPR requires qualified and experienced users to obtain high-quality survey data. To assess the capabilities and limitations of GPR, experimental reinforced concrete beams were casted to simulate real-life scenarios. Plastic and metallic tendon ducts were used, and variable spacing between stirrups was adopted. Surveys were conducted using 2GHz bipolar GPR unit, and grid scans were used to maximize the benefit of the GPR. This study presents interesting results in terms of determining the concrete cover, rebar spacings, and the position of tendon ducts accurately. These findings hold significant value for structural engineers who would like to use GPR, especially for bridge inspection applications
Identificazione strutturale di una struttura metallica mediante prove di vibrazione forzata
No full textNella presente nota si riporta un esempio applicativo di una metodologia di identificazione basata su prove di vibrazione forzata. Vengono descritti i risultati di una prova dinamica con vibrodina effetuata su una porzione dell’ampliamento del Politecnico di Torino a struttura metallica: dai dati sperimentali si sono calcolate le funzioni di risposta in frequenza che hanno fornito frequenze proprie e deformate modali. Successivamente si è confrontata la risposta con un modello agli elementi finiti correlando modi propri e frequenze
Evaluation of the residual prestressing force in reinforced concrete elements by means of prestress release tests
No full textPrestressed reinforced concrete elements can be subjected to relevant stress variations over time because of steel stress relaxation and concrete time- dependent deformation, often amplified in case of possible steel strands failure, caused by progressive material degradation. This will lead to a significant reduction of the overall prestressing force. The age of the majority of Italian bridges, originally designed without particular attention to durability, is quickly approaching their design service life. In this framework, the need to periodically evaluate the deterioration level of the materials becomes of paramount importance, in particular for prestressed steel strands; this will allow the attainment of a reliable estimation of the residual prestressing force in prestressed reinforced concrete beams (common in bridges and viaducts). The present paper aims at evaluating the reliability of a semi-destructive technique which can be used for performing prestress release tests on reinforced concrete elements by means of the removal of small portions of concrete, often involving only a portion of the concrete cover. Tests were performed on reinforced concrete columns subjected to a predefined compressive axial load, in order to have a direct comparison between the experimental deformation, measured by means of strain gauges, and the effective axial stress, applied through the experimental set-up. Different parameters have been considered during the tests, such as the geometric sawing configuration and the order of the steps performed before the removal of the concrete sample, evaluating their effect on the strain release, with the aim of proposing a reliable procedure easily applicable during in-situ tests
A Standardized Approach for the Early Restorative Phase After Esthetic Crown-Lengthening Surgery
No full textThe aim of the present case series article was to provide a standardized approach for the early restorative phase after a crown-lengthening surgical procedure. Different advantages can be ascribed to this approach: the clinician can prepare a definitive prosthetic finishing line in the supragingival location; the early postsurgical temporization allows the conditioning of soft tissues, especially the interdental papillae, during their maximum growing phase; and the clinician can choose the time for the definitive prosthetic rehabilitation in a patient-specific manner according to the individual potential and duration of the soft tissue rebound. In this study, this standardized approach was applied to the treatment of two esthetic cases requiring crown-lengthening procedures
VALUTAZIONE DEL FATTORE DI STRUTTURA DI EDIFICI PREFABBRICATI ESISTENTI COMPLETATI CON UN SISTEMA DI CONNESSIONE DISSIPATIVA NEI NODI
No full textOne of the most important seismic vulnerability of existing precast structures, widely used in Italy for one-storey industrial buildings, is due to the lack of mechanical connection between structural elements, as highlighted by the earthquakes that struck the Emilia region (northern Italy) in May 2012. The realization of dissipative connections is proposed as a solution for seismic rehabilitation of structures designed without anti-seismic standards, in particular for the beam-column joints. This work investigates the behavior of dissipative evices composed by carbon-wrapped steel tubes, able to guarantee a dissipative fuse effect. The aim of the study is to determine the effectiveness of the introduction of such devices in the beam-column connections. Incremental dynamic analyses have been performed on different case studies, in order to evaluate the behavior factor for structures with dissipative beam-column connections. The results of the numerical study show how the introduction of the dissipative devices produces, as expected, a significant reduction of forces transmitted to the structure, comparing the seismic response of simple structures equipped with dissipative devices with the response of the equivalent elastic systems
Experimental and numerical evaluation of fiber-matrix interface behaviour of different FRCM systems
Full text linkFiber Reinforced Cementitious Matrix (FRCM) composites are a relatively new strengthening system family, whose mechanical behavior is strongly affected by the wide array of possible inorganic matrices and composites fabrics that can be used and coupled together. Structural tests highlighted that global capacity of the system is strongly affected by fabric-matrix adhesion mechanism. In the present paper, the experimental results of tensile and single-lap shear tests, aimed to define mechanical properties of four FRCM types, are discussed and compared. For each system type, the failure modes for both types of test have been physically identified and clarified. The following development of detailed finite element models, carefully reproducing the mechanical behavior of the different layers of the strengthening system, allowed for the proposal of a reliable shear stress-slip relation for the fiber-matrix interface. The experimental outcomes showed the relevant dispersion of the results in terms of performance, effectiveness and failure mechanisms exhibited by the different FRCM types while the numerical interpretation allowed for a better understanding of the reasons and the parameters behind them
FRCM strengthening systems efficiency on the shear behavior of pre-damaged masonry panels: an experimental study
No full textExisting masonry constructions are highly vulnerable to seismic actions, as demonstrated by the severe earthquakes which stroke the Italian territory in recent years, causing great damages, especially in old masonry buildings. Therefore, restoring damaged buildings, with the aim to recover or improve their structural capacity, is a key aspect in the post-seismic interventions. Fiber reinforced composite materials could be effectively used to this purpose. One aspect which is worth to investigate is the application of these reinforcement typologies on damaged structural elements. Even though many experimental campaigns are available concerning the mechanical improvement given by composite materials applied on undamaged structural elements, only few can be found considering strengthening of already damaged masonry walls. The objective of the work here presented is to evaluate the shear response of damaged masonry panels strengthened using fiber reinforced cementitious matrix (FRCM). Two unreinforced brick masonry walls were subjected to diagonal compression tests, producing an extended state of damage. Afterwards, the same walls were strengthened with FRCM and diagonal compression tests were again performed. Comparisons were done between the results of the unreinforced samples and the pre-damaged strengthened ones, in terms of shear strength and post-peak behavior. The FRCM retrofitting system was also used to strengthen an undamaged masonry panel, which was tested in order to analyze similarities and differences with respect to results obtained for pre-damaged samples. The experimental campaign allowed to study the sole contribution of the reinforcement to the shear capacity of the wall panels. Results showed that the presence of FRCM reinforcements on damaged masonry panels influenced the shear behavior of the samples, which experienced a more ductile failure
SEISMIC BEHAVOIUR OF GROUTED SLEEVE CONNECTIONS BETWEEN FOUNDATIONS AND PRECAST COLUMNS
No full textThe paper presents the results of experimental tests on the cyclic behaviour of a column-foundation for precast concrete elements. The tested connection is built using steel tubes embedded in the footing, in which the column rebars are grouted. In particular the rebars are grouted with high strength mortar, in order to guarantee structural continuity between connected elements. The experimental results from the test carried out on the precast column footing joint were compared to the response of a reference cast in place specimen that was tested in the same experimental campaign. The behaviour of the tested specimens was analysed from different points of view: stiffness, strength, ductility and energy dissipation. On the basis of experimental data, numerical models were developed to simulate the behaviour of elements tested
Simulazioni numeriche di prove di aderenza su rinforzi FRCM con rete di carbonio
No full textI materiali compositi fibrorinforzati a matrice inorganica (FRCM) sono materiali innovativi che possono essere
utilizzati per il rinforzo di strutture murarie al fine di migliorare il loro comportamento in presenza di azioni
orizzontali. Il loro utilizzo si sta progressivamente diffondendo grazie alla buona compatibilità di questi materiali
con il substrato murario e alle buone prestazioni in termini di permeabilità, sostenibilità e facilità di applicazione.
L’impiego di compositi FRCM può influenzare il comportamento a taglio della muratura sia in termini di capacità
che di modalità di rottura. Infatti, la presenza dei rinforzi generalmente determina un aumento della resistenza a taglio
e un meccanismo di rottura meno fragile. Uno degli aspetti più importanti da analizzare, determinante nel garantire
l’efficacia o meno di un sistema di rinforzo, è l’aderenza tra il substrato murario e il composito FRCM. Per questo
motivo, la caratterizzazione meccanica dei materiali compositi prevede l’esecuzione sia di prove di trazione che di
prove di aderenza. Nel presente lavoro, sono state condotte simulazioni numeriche di prove di aderenza su rinforzi FRCM con rete di carbonio applicati su substrato murario con l’obiettivo di calibrare un appropriato legame bondslip. In particolare, si adotta una strategia di micro-modellazione del rinforzo FRCM, nel quale le fibre di carbonio sono modellate singolarmente e viene considerato il possibile scorrimento all’interfaccia tra fibre e matrice, tramite elementi di interfaccia, al fine di riprodurre le modalità di rottura tipicamente riscontrate in prove sperimentali. I risultati numerici sono confrontati con quelli provenienti da alcune campagne sperimentali precedentemente condotte sullo stesso sistema FRCM, arrivando così alla calibrazione di una legge di bond-slip che potrà essere implementata nella modellazione numerica di prove sperimentali su elementi strutturali rinforzati in vera grandezza
Shear-Compression Test on Masonry Walls with an Innovative Experimental Setup
Full text linkThe behavior and failure mechanism of a masonry wall subject to in-plane shear depends on several factors,
such as the wall geometry, the boundary conditions, the acting stresses, and the masonry mechanical parameters. The
objective of this research was the study of the in-plane shear behavior of full-scale masonry panels through an innovative
experimental setup, purposely designed to reproduce a double fixed boundary condition in order to induce a diagonal
cracking failure mode. Such a boundary condition was ensured by the presence of an upper horizontal rigid steel beam,
combined with the possibility of modulating the compressive load applied to the masonry panel, while increasing the
horizontal displacement. Nonlinear numerical simulations were carried out to analyze the capability of the experimental
setup of reproducing the desired loading and restraint conditions and to predict the shear behavior of a clay brick masonry
panel. A finite element model was realized, in which all the components of the experimental setup were included to
account for all possible failure modes, and the masonry panel was modelled according to a macro-modelling approach.
The results of the numerical predictions were compared with the results of a shear-compression test on a masonry panel,
which will be presented in the paper. The good agreement obtained between the numerical and the experimental results,
both in terms of load vs displacement curve and development of the cracking process, confirmed the suitability of the
setup in reproducing the assumed boundary conditions and shear failure mode
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