1,300 research outputs found
Stima della resistenza del calcestruzzo attraverso il consumo di energia
No full textNella pratica dell’ingegneria la stima della resistenza del calcestruzzo su strutture esistenti è da sempre un aspetto molto delicato inoltre i vari metodi di indagine hanno la necessità di avere come riferimento i valori ottenuti dal carotaggio. In quest’ottica è stata condotta una campagna sperimentale per valutare l’applicabilità di un metodo, per la stima preliminare della resistenza del cls, ba-sato sulla misura dell’energia consumata per praticare un foro. In questo lavoro vengono presentati i risultati delle prove di taratura condotta calcestruzzi con resistenze da 20 a 90 MPa caratterizzati con prove su campioni standard e carote. L’analisi dei diversi fattori che possono alterare il risultato della prova, il basso impatto economico unito ad un danno limitato hanno permesso di evi-denziare le potenzialità del metodo
A NEW RETROFITTING TECHNIQUE FOR MASONRY BRIDGES
No full textRetrofitting of masonry bridges usually applies the basic concepts of r.c. to this kind of masonry structure. The results are that often that the retrofitting works are almost ineffective and, always, the historical value of the bridge is largely lost. A series of tests on reduced properly scaled models (see other papers in this Conference) show that the actual load carrying structure is an arch with reduced span in comparison with its geometric appearance. The actual span depends on the fill material (stiffness and strength) at the springing. Besides, the fill does not distribute the load, applied on its surface, on the arch extrados close to the ultimate load. Based on these two issues, a new retrofitting technique is discussed: selective injection of the fill, limited to the part close to the springing, may reduce the effective arch span, thus increasing the l.c.c. of the bridge as a whole. This issue is discussed through a test on a 4m-span model
Effetto dello stato tensionale sulla prova di pull out
No full textLa prova di pull-out è riconosciuta come una delle tecniche più affidabili per la stima della resistenza del calcestruzzo in opera. In questo lavoro vengono presentati e discussi i dati delle campagne sperimentali svolte dai laboratori DICCA nell’ottica di analizzare i limiti di affidabilità della prova. Individuando i fattori di vulnerabilità delle attuali tecnologie si è potuti arrivare alla definizione di un nuovo sistema caratterizzato da: i) rididuzione delle incertezze legate alla fase applicativa della prova; ii) materiali di alto livel-lo che consentono di eseguire la prova con su calcestruzzi da 5 a 90 MPa. La nuova tecnologia B15G è stata calibrata su 5 miscele di calcestruzzo, e per 5 distinti stati tensionali. Le curve di correlazione tra forza di estrazione e resistenza a compressione del mate-riale così ottenute: i) sono marcatamente non lineari; ii) dipendono significativamente dallo stato tensionale; iii) presentano una di-spersione statistica inferiore al 15%
LOAD BEARING STRUCTURE OF MASONRY BRIDGES
No full textMasonry bridges are often considered arches to which the fill, retained by the spandrels, contributes as a stabilizing dead load. Recent research demonstrated that the arch-fill interaction is a fundamental contribution to the load carrying capacity of these bridges. To highlight this aspect, several tests on reduced scale models were performed but improper scaling rules introduced a bias on the results making them often unreliable. In this paper, test results on reduced scale models, according to proper scaling rules, are discussed providing an estimation of the amount of load carrying capacity increase due to the arch-fill interaction. Up to now, only a deep arch model has been tested, showing also that the classic assumption of hinge-mechanism is not fulfilled, being anticipated by compressive crushing of the materials. This raises some questions on the standard procedures for the bridge assessmen
Core-to-Cubic Strength Ratio for Historical-Like Concrete
No full textCoring is considered to provide the best estimate of concrete compressive strength in existing structures and is common-ly used to calibrate Non-Destructive and Moderately Destructive Techniques. Historical concrete, produced in the pre-code period until the ‘20s, significantly differs from modern concrete due to lack of standardization, improper rules of thumbs and to aggregate shape (round, smooth and often excessively large aggregates) and proportioning. Therefore, the applicability of the procedures calibrated on modern concrete to an historical one, also coring, is an issue that needs to be discussed. In this paper, an experimental campaign on historical-like concrete, i.e. with the same defects as histor-ical concrete, aims at identifying the reliability of drilled cores due to the effect of round aggregates. The results show that standard procedures commonly used on modern concrete cannot be directly applied to historical concrete: drilled cores suffer from scale effects (core diameter) and from cutting damage of the material much more than modern con-crete. In detail, the core-to-cubic ratio, that modern codes assume in the range 0.70-0.85, due to the dimension and shape of the aggregates is found inside a larger range, 0.70-1.00, and, as opposed to modern concrete, is found to be decreasing as concrete strength increases. Besides, the diameter of the core is found to have a relevant effect on the estimate of the material compressive strength and on the core-to-cubic strength ratio, pointing out that the dimension of the core affects the results much more than for modern concrete. This latter result, that needs further research, points out that historical concretes may be rather different from modern ones and probably need larger cores to be drilled than modern concrete due to the larger dimension of aggregates that is often found in pre-code concrete
Rebound Hammer Test: An Investigation into Its Reliability in Applications on Concrete Structures
No full textThe issue of concrete strength often arises in civil engineering practice, either due to quality control of new constructions or due to the assessment of existing structures. To this aim, one of the most widely spread techniques is the rebound hammer (Schmidt hammer) test, for which calibration is still related to the original Schmidt curve dating back to the early 50’s. In spite of the large amount of research work performed in the last decades, the uncertainties of the rebound test are still not clearly quantified and open to further insight. This paper presents and discusses a wide research campaign on laboratory specimens and on third-party specimens delivered to the Laboratory for Building Materials of the University of Genoa, Italy, for standard quality controls. While it is well known that moisture content, surface finishing, and concrete maturity strongly affect the test result, the effect of the stress state has not yet been studied and is found in this research to be a further parameter affecting the test reliability. The final outcome of all the uncertainties is variability in estimated concrete strength as large as ±70%; additionally, some issues are discussed on the intrinsic uncertainty of this test. As already demonstrated by many authors, the results of this research also show that a universal calibration curve to be used for any concrete, in any condition, conceptually does not exist
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
Trace contaminants in biogas: Biomass sources, variability and implications for technology applications
No full textBiogas represents a renewable and controllable energy source. Although predominantly composed of methane and carbon dioxide, it also contains various trace contaminants that can be detrimental to the technologies used for its conversion.
The aim of this work is to comprehensively explore trace contaminants in biogas. The assessment employs a two-level approach: an extensive literature review on biogas trace contaminants, complemented with on-site analyses from real-scale biogas plants to enhance and validate the literature findings. The biogas contaminants – sulphur compounds, siloxanes, halocarbons and aromatic compounds – are quantified and categorised into four distinct groups: landfill gas, agricultural gas, gas derived from the organic fraction of municipal solid
waste (OFMSW), and gas from wastewater (WWTP). This study also provides contaminant effects and required thresholds for different biogas conversion technologies, including internal combustion engines, upgrading to biomethane, and innovative solid oxide fuel cells (SOFCs).
The two-level analysis reveals significant variability in contaminant levels across different biogas sources, with H2S being the most prevalent contaminant, averaging between 181 (WWTP) and 901 ppm (landfill gas). Other sulphur compounds show the highest average concentration in biogas from OFMSW (98 ppm), followed by agricultural and landfill gases. Siloxanes are typically more abundant in biogas from WWTP (2.55 ppm), while landfill gas exhibits the highest average concentrations of halocarbons and aromatic compounds (6 ppm and 109 ppm, respectively). Moreover, this study highlights the need for in-depth measurements of contaminants for highly sensitive technologies, such as SOFCs, to properly design tailored contaminant removal solutions
Correction to: When terminology hinders research: the colloquialisms of transitions of control in automated driving (Cognition, Technology & Work, (2022), 10.1007/s10111-022-00705-3)
No full textIn the original article, author affiliation published with error. The correct affiliations are: Davide Maggi—Institute for Transport Studies, Leeds, UK. Richard Romano—Institute for Transport Studies, Leeds, UK. Oliver Carsten—Institute for Transport Studies, Leeds, UK. Joost C. F. De Winter—Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Delft, The Netherlands. The original article has been corrected.Human-Robot Interactio
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