1,721,146 research outputs found
Shear strength of an anchor post-installed into a hardened concrete member
Full text linkLiterature has recently provided the analytical model that predicts the shear strength of the anchor embedded into masonry. It is apparent that this model does not apply to the anchor embedded into concrete, as the ultimate contact pressures are different. A gap in the literature was hence filled, but there existed a remaining gap. In order to fill that last gap, further research was done. This paper is herein an account of that work. The paper deals with the anchor post-installed by drilling into an already compact concrete structure, used to transmit applied loads from an attachment to the concrete, subjected to a force acting at the end that emerges from the concrete and orthogonal to the anchor (shear force with no axial force), with large clearance from the edges, either alone or with large clearance from other anchors. Being post-installed, the embedded part of the anchor is a straight shaft with no hook at the embedded end, and with no nuts, washers, or plates attached to the shaft. The paper presents an analytical model absent in literature prior to this study that predicts the maximum shear force the anchor can carry, thus called “shear strength” of the anchor. The assumptions of the analytical model were established from the results of a non-linear numerical model specifically constructed by the author. The predictive capacity of the analytical model and accuracy of its results were assessed and verified by experimental tests of real anchorages specifically designed and performed by the author. This paper also presents the numerical model and the comparisons of the analytical predictions to those experimental results, as well as com parisons to experimental results borrowed from literature and code provisions
Structural layout that takes full advantage of the capabilities and opportunities afforded by two-way RC floors, coupled with the selection of the best technique, to avoid serviceability failures
No full textA recently cast two-way rectangular reinforced concrete floor with a span-to-thickness ratio equal to 34.1, which constituted the two stories above ground of an office building under construction, exhibited a totally unsatisfactory deflection performance. The static loading test performed at the end of the construction work demonstrated that the stiffness of the floor was too low. Furthermore, not only the floor that had been loaded for the test, but also the other floor, exhibited excessive increases in deflections with time.
The author was entrusted with the task of redesigning the floor, which had to constitute the stories of a further nine buildings of the construction lot, whose floors had been designed equal to the floor that had failed, and neither the spans nor the thickness could be changed. The author designed and constructed a test building whose story was made up of a floor with perimeter, spans and thickness equal to those of the floors that had failed, but with different structural conformation, boundary conditions, and both amount and configuration of steel reinforcement. The new floor was built using a different construction method as well. The loading test carried out on this floor measured very low immediate deflections. The load was left on the floor for three years and the deflections increased only moderately. The test results substantiated all the theoretical analyses that had been previously carried out and confirmed that the structural performance was adequate. On that account, the proposed floor was eventually employed for the nine buildings of the complex that remained to be built.
This paper – which is directed at analyzing a structural failure, helping reduce the incidence of serviceability failures, and extending the operating horizons of thin RC floors – explains why the original version of the floor failed, describes the new version of the floor, including the loading test on the prototype and on the nine new buildings, and provides a useable and reproducible recipe for designing and assessing high span-to-thickness ratio rectangular RC floors
Appunti per una inedita epistemologia dell’ingegneria strutturale = Suggestions for a New Epistemology of Structural Engineering
No full textIl criterio che maggiormente caratterizza la scienza moderna è la probabilità, ampiamente introdotto con mirabile chiarezza da Jakob Bernoulli e Pierre-Simon Laplace attorno al 1712, colpendo e contraddicendo l’ordine rigidamente deterministico della fisica e meccanica classiche. La probabilità ha introdotto l’incertezza: anche ammettendo l’esistenza della causalità naturale non si può parlare di certezza di un evento ma soltanto di una più o meno grande probabilità del suo verificarsi. Tale osservazione è sintetizzata dalla lapidaria affermazione di Bernoulli nella sua storica opera Ars Conjectandi del 1713 (postuma): “La probabilità è un grado della certezza” (“probabilitas enim est gradus certitudinis”).---The tutorial makes a parallelism between structural engineering of today and in the past. First, the article analyz-es how the most important principles that have characterized modern physics affect structural engineering. Then, the author questions how the great structural engineers would be if they lived and worked now and attempts at offering an answer. Finally, the author gives his suggestion about what changes must be made in the relationship between society and engineers of today in order for the latter to have the same tremendous impact on the world as they did in the past
Seismic upgrading of masonry churches
No full textThe paper is proposed for the topic Conceptual Design, in particular as regards existing buildings.
The masonry churches are usually highly vulnerably to the horizontal transverse seismic action, since the bearing vertical structures (masonry columns along with the supported wall and the arch systems), which are isolated and slender, have to carry the seismic action only by mass. The seismic upgrading can be obtained only by transforming the transverse load-carrying capacity of the vertical bearing structures from mass strength to material strength.
To this objective, the basis of the columns can be fixed at the soil, but this options is usually to onerous. Moreover, to this objective, external reinforcement can be epoxy bonded onto the masonry surfaces, but this option is usually prevented by evident aesthetic reasons.
An alternative solution is obtainable by fixing the top of the vertical bearing structures to the edges of the horizontal structures that form the covering of the churches, and by inserting the reinforcement in the vertical masonry structures. The top joint transforms the isolated vertical structure in framed structure, hinged at the basis. The internal reinforcement provides the vertical bearing structures with the capacity of transmit high bending moment.
Nevertheless, a special device has to be adopted to transfer longitudinally the top moment, otherwise the pillar and the beam of the ideal frame do not lay on the same vertical plane.
Such system may upgrade the ultimate seismic capacity (severe damage). Conversely, such system does not upgrade the service limit state (limited damage), since does not enhance the stiffness. In order to upgrade also the stiffness of the structures, the reinforcement has to be pre-tensioned. In so doing, the seismic upgrading can be reached for a masonry church.
The proposed conceptual approach to seismic upgrading has been applied to the case of the parish complex of San Giuliano di Puglia (in Molise; Italy). This building — compounded by church, parish house, parish school, belfry and civic tower — was severely damaged by the notorious earthquakes of October, 31, 2002 (when the elementary school collapsed, causing the death of 26 pupils and 3 teachers, and the hurting of many others people).
Since the church, along with the major part of the building complex, were about to collapse, first-aiders decided to support arches and vaults with wood centrings, to wrap the columns by post-tensioned wood centrings, and to constrain the walls by external steel tendons. Although the extended and deep state of damage seemed to suggest the demolition of the building, the city administration and the historical overseers expected its restoration, because of its cultural and social value.
The Italian Ministry of “Infrastrutture and Trasporti” bestowed the amount for recuperating the parish complex (3.7 million of euro) and the author was entrusted of the structural design of the repair, rehabilitation, and seismic upgrading of the whole building. The seismic upgrading was obtained by the above mentioned conceptual approach
Three-layered sandwich plate: Exact mathematical model
No full textThe subject of this paper is the plate composed of two relatively stiff outer layers (skins) and a more compliant inner layer (soft interlayer, called core), i.e., three-layered (sandwich) plate. This system may represent composite and laminated plates, e.g., sandwich panels and decks. This paper presents a model that describes the behavior of three-layered plate by a system of exact analytical (explicit) equations,
derived from the Kirchhoff–Love plate assumptions. Accordingly, this system of equations corresponds
to the Kirchhoff–Love equation of the plate.
The pie-chart of research on sandwiches allots only a slight slice to analytical modeling, while it allots the largest slice to approximate prediction methods. In particular, the three-layered plate lacked the two-dimensional governing equations. Empirical or semi-empirical formulations, finite element models,
a priori formulas based on simplified or rough theories may represent more accessible research topics; however, they suffer from high layer-to-interlayer stiffness ratios, which impinge on their results. Thus, these approximate prediction methods provide unsatisfactory results for the continuously increasing ratios that the industry is developing, and will be developing, to increase ever more the stiffness-todensity
and strength-to-density ratios of the sandwiches. Conversely, this model, whose formulation is exact, does not suffer whatsoever from high skin-to-core elastic modulus ratios, and therefore it is specifically dedicated to modern, advanced, and innovative sandwich plates.
To apply this exact model is less time consuming than to generate any finite element mesh or to apply any approximate method. Consequently, approximate methods become completely unnecessary for the three-layered plates that comply with Kirchhoff–Love plate assumptions. On the contrary, for the threelayered plates that do not comply with these assumptions, the finite element models continue to represent a viable means, provided that beforehand their reliability is checked and their free parameters are calibrated. To facilitate check and calibration, exact results from the model are provided in the paper, which finite element results can be compared to
Strengthening of Masonry Arches with Fiber - Reinforced - Polymer Strips
No full textThis paper deals with masonry arches and vaults strengthened with surface fiber-reinforced polymer (FRP) reinforcement in the form of strips bonded at the extrados and/or intrados, considering strip arrangements that prevent hinged mode failure, so the possible failure modes are: (1) crushing, (2) sliding, (3) debonding, and (4) FRP rupture.
Mathematical models are presented for predicting the ultimate load associated with each of such failure modes.
This study has shown that the reinforced arch is particularly susceptible to failure by crushing, as a result of an ultimate compressive force being collected by a small fraction of the cross section. Failure by debonding at the intrados may also be an issue, especially in the case of weak masonry blocks or multiring brickwork arches. Failure by sliding has to be considered if the reinforcement is at the extrados and loading is considerably nonsymmetric
Church of San Giuliano di Puglia: Seismic repair and upgrading
No full textThe notorious October-31-2002 earthquake threatened the collapse of the church of San Giuliano di Puglia (Campobasso, Italy). This paper describes the main points of the repair and seismic retrofitting of the town church, San Giuliano Martire. The seismic retrofitting had to meet the new Italian seismic code that was issued immediately after this earthquake (seismic upgrading). The structural rehabilitation was limited because of the requirements to stay true to the original aspect (conservation of the bare-surface stone masonry, without plaster). To this end, the design considered recent scientific advancements and developed innovative methods, rather than just referring to technical practice.
The rehabilitation work, in particular the technical innovation, has been tested by two earthquakes, both of them with an epicenter within close proximity to the building. The first one struck in 2007, with a magnitude of 3.1; the second one in 2011, with a magnitude of 3.7 and a Peak Ground Acceleration of 0.19⋅g. Whilst the sacral furniture resting on the ground suffered from significant damage, none of the earthquakes caused any structural damage to the building. In particular, no cracks opened in the masonry structures. The PGA and seismic forces of the 2011-earthquake were 1.7 and 2.5 times greater than the values prescribed by the present Italian code for the damage limitation and no-collapse requirements, respectively. This proves the effectiveness of applying post-tensioned bonded tendons to masonry structures, in order to significantly increase both the stiffness and the lateral load-carrying capacity of a masonry building
Lateral load-carrying capacity of steel columns with fixed-roller end supports
No full textThe subject matter of this paper is the interaction of flexure and compression in steel beam-columns with fixed-roller boundary conditions. It is shown that, for those end restraints, the effective length factor approach is inaccurate to account for geometric non-linearity. The paper then presents a formula to predict the strength of steel members subjected to simultaneous axial compression and transverse load, allowing for the formation of plastic hinges one following the other with a considerable gap. The formula is devoted to quantitative safety assessment, as it is more accurate than conventional formulas, and also to the design phase, as it is simple to use. The paper gives a detailed account of the formulation and provides some examples that show differences from the results obtained from conventional and code formulas
Predictive multiscale model of delayed debonding for concrete members with adhesively bonded external reinforcement
No full textThe research described in this paper relates to flexural concrete members strengthened by means
of external reinforcement bonded adhesively onto the surface, in particular, by fiber-reinforced
polymeric strips, sheets, or laminates. The research is specifically devoted to external reinforce-
ment being already in tension under a dead load or a low fraction of live load. The concrete
cover exhibits initial flaws, which were unimportant when a member was not externally rein-
forced, but that may give rise to slow crack propagation up to delayed debonding when the
member is externally reinforced. This paper presents a model for predicting the delayed de-
bonding. The common debonding models, including code provisions, focus mainly on the struc-
tural and material scales, and thus ignore delayed failure. On the contrary, this new model
focusses on the mesoscale, which considers the velocity of crack growth that leads to debonding.
While on the nanoscale and microscale the crack velocity depends on the microstructure, on the
mesoscale the crack velocity depends on the interfacial bond shear stresses and crack length. This
dependence can be synthetized by the ratio between the mode II stress intensity factor, KII, and
its critical value KIIC. The model describes the delayed debonding in terms of interaction between
bond shear stress and time (ultimate domain maximum bond shear stress versus delayed time)
Consolidamento statico e adeguamento sismico delle costruzioni in muratura: annotazioni. - I parte
No full textEditore: Associazione Ingegneri ed Architetti della Provincia di Bologna. Articolo revisionato dal Comitato scientifico della rivista nel dicembre 2004. Stampata a Bologna; anno LX
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