SAMCO Final Report 2006 F09 Report on Bridge Management
as those linked to the type of environment or to the presence of aggressive factors may be considered only indirectly, by recurring to specific adequate design solutions, to specific construction techniques and maintenance policies. For instance, the in- crease in cover in reinforced or pre-stressed concrete structures to be built in coastal areas, or the adoption of special concrete mix with entrained air in cold countries are solutions that may slow down the process of deterioration of structures. Even the choice of a particular structural scheme, which allows the reduction or the elimination of the expansion joints, may lead to an increase of the durability of the structure over time.
Apart from a correct design and an attentive construction, the activities of monitoring and assessment are decisive for the long duration of bridges when carried out during the operation of the structure. For example, sometimes simple problems and defects, if not reported, and let free to deteriorate in an uncontrolled way, may lead to severe damage as e.g. in the case of:
Chloride-induced corrosion, which may lead to very concentrated and local corrosion near a joint and no spalling, but where e.g. 50 % of the reinforce- ments cross-section may disappear and lead to unexpected structural col- lapse.
Prestressed cables in ducts, which may also corrode without visible signs and lead to unexpected failures.
Alkali-silica reactions and the carbonation-induced corrosion, which may lead to crack formations or spalling, which may not damage the structures safety, but where the debris may fall from the structure on to the road or railway and cause accidents.
Moreover, it may be said that the factors that influence the long-term performance of a bridge are difficult to be described theoretically. Their influence on the durability of structures may be assessed only on the basis of the information derived from experi- ence.
For this objective, surveillance and monitoring of structures over time allow to derive structural and functional information on the process of deterioration. This information is useful at every stage into the life of a bridge.
First of all they are used to control and to assess the conditions of the structures dur- ing their service life. In this way it is possible for the road responsible to guarantee an adequate, at least sufficient, level of safety to traffic.
Second, as a consequence of the evaluation of safety, of the assessment of the ex- tension of damage and of its evolution, on the basis of the results of surveillance and monitoring, it is possible to prioritise the interventions of repair and to choose the
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