PSI - Issue 62

Marco Menegotto et al. / Procedia Structural Integrity 62 (2024) 1014–1019 Menegotto, M.,. Fieno, L., Rocchi, M.C.

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Analogous detections are performed all along the works and worked out in graphs, referring to various types and degrees of damage, for planning the remedial interventions. Actual concrete properties are determined by tests on drilled cores. Reinforcing steel bars are sampled by cutting, then tested. Prestressed reinforcement and the grouting in its ducts are examined by means of endoscopy and sonic tests, exceptionally by extracting samples. The corresponding typical remedial provisions, falling into ordinary maintenance, are: cleaning surface and rebars, adding reinforcement with anchors, restoring/upgrading the sections by refilling special concrete or mortar according to the degree of damage; where this one is severe, possibly removing and replacing the whole element or part of it. The provisions basically tend to restore the initial capacity and improve the durability. Another typical source of damage are earthquakes. The induced damages are treated case by case, by means of extraordinary maintenance. Generally, they require strengthening or upgrading measures, that take priority over ordinary maintenance and incorporate its provisions, too. In April 2009, the strong L’Aquila quake hit some structures, that were not designed for. A huge campaign of repair and retrofitting was engaged where possible (i.e. where replacement was not the main option), especially on bridge piers and foundations. However, a particular serviceability damage occurred on several decks, which underwent a partial loss of support where rollers ran out of place. The structures as such didn’t suffer due to that but dangerous vertical gaps appeared on the road and traffic had to be stopped immediately. Supports were then replaced, dimensioned for grater displacements.

Fig. 5 a) roller support, undamaged

b) support having lost its roller due to seismic displacement

That earthquake marked a turning point in the concept of repair provisions. In fact, after that event, the modern seismic standards were implemented, becoming mandatory. Before, obsolete standards based only on the permissible stresses’ criterion were still in use, although in 2003 new criteria were introduced aside and in 2008, for the first time, the National Code NTC 2008 made them official, although optional, and allowed also for the use of the Seismic Structural Eurocode. After L’Aquila event, only the Limit States analysis is to be used in structural verifications, also in seismic areas, together with a very accurate zoning for the determination of the actions on a specific site. The opportunity, offered by the indispensable repairs, led not only to consider heavy retrofitting to comply with the new structural standards but also to update other features, like road geometry, guardrails and barriers, environmental issues, etc. Therefore, in many cases the final decision was that the involved structures would be better dismissed and rebuilt, rather than retrofitted, with a new design satisfying all the new functional requirements and its aesthetic impact.