1,720,970 research outputs found
VAULT-FILL INTERACTION IN MASONRY BRIDGES: AN EXPERIMENTAL APPROACH - 2: DYNAMICS
No full textThis paper is the continuation of a companion paper presented in this conference by the same authors. It is first demonstrated that scaled models may reproduce the dynamic response of masonry bridges if proper scaling criteria are set. The comparison of the natural frequencies of the real bridge to the ones expected on the basis of structural models may provide important information on the inner structure of the bridge, which is often known only approximately or is unknown at all and is only postulated. A series of laboratory tests are discussed to identify and quantify the contributions to the natural modes, shapes and frequencies of the different elements of a masonry bridge. 1:4 prototypes have been used; dynamic tests have been performed at different levels of load-induced damage and in different settings: bare arch and arch + fill. It is showed that the structural elements, and their effective contribution to the load bearing structure, may actually be identified by means of dynamic identification techniques. Damages, mainly due to material degradation or overload, instead, may be identified on the basis of dynamic testing only if their extent is large enough to be detected also visuall
VAULT-FILL INTERACTION IN MASONRY BRIDGES: AN EXPERIMENTAL APPROACH - 1: STATICS
No full textMasonry bridges are usually considered as an arch to which non-structural elements (spandrels, fill, etc.) are added. Experimental and theoretical evidences show, instead, that spandrels and fill take part in the load carrying mechanism accounting for a large part of the load carrying capacity. If this is neglected, the structural models may turn out to be unreliable and their outcomes strongly non-correlated with the real response of the bridge. In this paper, the arch-fil and arch-spanrel interaction is demonstrated and quantified by means of experimental tests on reduced scale models set on proper scaling rules. Woth deep and shallow arches are considered
Masonry bridges: validation of structural models through dynamic testing
No full textLaboratory tests are used to identify the contributions of the different elements to
the dynamic response of a masonry bridge. 1:3 prototypes have been used retaining the
similarity to the real bridges by reducing not only the geometric quantities but also the material
properties. The arches have been tested dynamically at different levels of load-induced damage
and in different settings: bare arch and arch + fill. The structural elements, and their effective
contribution in terms of stiffness to the load bearing structure, may be identified on the basis of
dynamic identification techniques. Damages, on the contrary, may be recognized only if their
extent is large enough to be detected also visually. Therefore, at present, the condition state of a
masonry bridge should not entirely rely on dynamic identification procedures, while dynamic
testing appears to be a crucial technique to assess the reliability of structural models and to
identify the actual load bearing structure of the bridge
Reliability of dynamic identification techniques connected to structural monitoring of monumental buildings
No full text
Calibration and Reliability of the Rebound (Schmidt) Hammer Test
No full textOne of the most widely spread techniques to estimate the compressive strength of concrete is the rebound hammer test, also known as Schmidt Hammer test. In spite of a large number of scientific works trying to calibrate the test, to identify the parameters affecting its results and to estimate its reliability, the original Schmidt curve is still provided by the producers along with the hammer and is used in Structural Engineering Applications. This paper discussed an extensive research, and application, of this technique to a large number of cubes provided by the Laboratory for Building Materials of the University of Genoa, Italy, showing that several phenomena strongly affect the test: moisture content, maturity, stress state among the others. Strength estimates may differ as much as 70% if these parameters are not taken into account. Besides, several in situ investigations on existing buildings were affected by a large dispersion of data, so that we should conclude that the Rebound Hammer is unable of giving a reliable estimate of the concrete strength. This is probably due to the very limited area of the material on which the test is performed that allows also small local inhomogeneity to affect quite strongly the test. Therefore, the rebound hammer seems to be useless in the estimation of concrete compressive strength, being only a rough tool for estimating material homogeneity inside a specific concrete typ
CAROTAGGIO E CLASSIFICAZIONE DEL CALCESTRUZZO: INCERTEZZA ED AFFIDABILITA’
No full textIl carotaggio viene tipicamente considerato come la prova per eccellenza nella definizione della resistenza del calcestruzzo di strutture esistenti. Oltre che per una valutazione diretta della resistenza, è spesso utilizzata per calibrare i risultati forniti da altri tipi di prove, come le prove di pull out o le prove che si riferiscono a metodi combinati (SONREB e SONREB-WIN).
La letteratura scientifica, particolarmente quella classica statunitense, ha evidenziato come la resistenza di una carota sia alquanto diversa da quella di un campione cilindrico confezionato durante il getto, e come la resistenza dei due tipi di cilindri sia difficilmente correlabile. Alcuni lavori recenti forniscono relazioni empiriche per valutare l’influenza sulla stima della resistenza di alcuni fattori, come il disturbo del campione dovuto alla modalità di estrazione, il suo diametro, la presenza di armature, la direzione di carotaggio rispetto a quella di getto.
In questo lavoro vengono presentati i risultati di un’ampia indagine sperimentale finalizzata ad individuare meglio l’effetto di diversi fattori sulla resistenza di una carota.
L’analisi è stata eseguita su campioni di calcestruzzo appartenenti a 6 distinte classi di calcestruzzo assieme ai quali sono stati confezionati provini cubici e cilindrici.
Sono stati eseguiti carotaggi con 4 diversi diametri sia in direzione ortogonale che longitudinale al getto, e sono state eseguite successivamente prove di compressione. I risultati delle prove di compressione su carota, anche in termini di rigidezza, evidenziano come anche i carotaggi conservino significativi margini di variabilità del dato sperimentale e forniscono una prima quantificazione dell’effetto di alcuni parametri sulla stima della resistenza del calcestruzzo. A differenza di altri lavori, alcuni di questi parametri risultano funzione della resistenza del calcestruzzo
A new pull-out technique for in-place estimation of concrete compressive strength
No full textA new type of post-installed wedge anchor (B15G) is presented. A refined geometry of the anchor bolt and a careful choice of all the technical details, allow the insert to work also in tensile stress states and to avoid much of the practical uncertainties that affect the commonly used procedures.
The calibration of the procedure has been performed on 3 classes of concrete and for 5 stress distributions (medium and low compression, vanishing stress states, inhomogeneous compressive stresses and inhomogeneous tensile stresses). It has been found that the correlation curves, pull-out force vs. compressive strength, are not linear and depend on the stress state; besides, the statistical scattering of the calibration tests never exceeds 7-8% of the average value
- …
