0000000000425967
AUTHOR
Granata M. F.
La variazione di schema statico nei ponti in cemento armato precompresso durante le fasi costruttive e l’influenza dei fenomeni lenti
The construction of prestressed concrete bridges often presents different construction stages in which the structural static scheme changes many times, together with the characteristics of the construction elements. In fact, prefabrication and in situ assembly involve a multiple variation of the scheme with the introduction and removal of restraints, especially when temporary sup-ports are used. These transitional phases can strongly modify the structural behavior, in relation also to the deformations due to shrinkage and creep. In this study an evaluation of the effects of time-dependent phenomena is presented, for the case of complex sequences in which delayed restraints and removal of pr…
Seismic assessment and retrofit of a concrete building highly damaged by reinforcement corrosion
In existing concrete structures damaged by corrosion, the limited quantity and poor distribution of reinforcements as well as a lack of seismic details are common to many cases because they are built before the advent of seismic codes. In this paper the seismic assessment and retrofit of a concrete building sited in Sicily is presented in order to show a case-study of a corroded reinforced concrete structure to be trans-formed with new structural elements for functional reasons linked to Civil Protection. After many decades of complete abandonment, the structure was strengthened with different strategies, allied to the construction of new steel-concrete composite floors: concrete and steel …
Prevenzione del degrado dei ponti in c.a.p. con la precompressione bilanciata. Il ponte funicolare
La trave e l'arco hanno comportamenti strutturali completamente differenti. La trave infatti, sotto l'effetto dei carichi applicati, ha un comportamento tipicamente flessionale mentre l'arco, grazie alla spinta e alla sua sua curvatura geometrica, può essere progettato con un comportamento funicolare a prevalenza assiale. Le strutture precompresse possono combinare intelligentemente questi due diversi comportamenti e la precompressione può essere favorevolmente utilizzata per trasformare la trave in una struttura funicolare, analoga ad un arco, con comportamento prevalentemente assiale. In questa nota viene presentata una filosofia di progetto per lo studio dei ponti a piastra precompressi,…
Safety assessment in N-M-V interaction of prestressed concrete elements subject to degradation of the reinforcements
The estimation of residual life of viaducts and bridges is urgently topical, due to the age of Italian infrastructure network. Among the causes of reduced life of prestressed concrete structures, the role played by corrosion in prestressed reinforcements is fundamental. In fact, the reduction of the reinforcement cross-section with the formation of the outer layer of iron oxides and hydroxides and the bad filling of the ducts, induces an intermediate behaviour between that of external (unbonded) and internal (bonded) prestressing. For these reasons, the evaluation of degradation and its influence on structural safety cannot be neglected in the assessment of sections of existing structures c…
Effect of degradation on the structural behaviour of an existing cantilever reinforced concrete bridge in Southern Italy
The performance of cantilever reinforced concrete bridges is fundamental topic in assessment and retrofit of Italian infrastructures, because the static scheme of the so-called “Gerber bridges” was very popular between 50’s and 70’s of XX Century. Many of them present severe damage due to the drainage of the deck waters inside the joint and to the consequent degradation of Gerber saddles. Furthermore, the state of corrosion of the reinforcements together with the actual degree of freedom of internal constraints, often partially blocked due to degradation and subsequent maintenance over time, modify the structural behaviour and the performance both in terms of service and ultimate limit stat…
THE REHABILITATION THROUGH EXTERNAL PRESTRESSING OF HISTORICAL REINFORCED CONCRETE BRIDGES WITH REDUCED PERFORMANCE: A CASE STUDY
Many existing reinforced concrete bridges exhibit behaviour at the Service Limit State and the Ultimate Limit State which can be considered unsatisfactory with respect to the current provisions of Codes, but which are actually deficiencies deriving from obsolete calculation methods, structure age, material degradation, diffuse or localized corrosion and increased loads. Among these, cantilever bridges with half-joints may present a decrease in global safety coefficients for the most stressed current sections of the deck or in the local ones, that affect the performance of elements sensitive to degradation, such as Gerber saddles. In these cases, simple strengthening interventions through ex…