Corrosion protection

When designing tiebacks as a part of permanent structures, where they have to last as long as the structures, we must rely on good engineering judgment. The oldest corrosion-protected tieback we know of has been in service for only 60 years and most structures are designed to last longer. It must be recognized that we are dealing with a new technology which has great apparent advantages, but cannot have its long-term efficacy proven by citing many examples. We can cite some similarities to other types of projects, but are ultimately forced to make an engineering evaluation of the resistance of the tiebacks to corrosion. Corrosion mechanisms, corrosion rates, the effects of the earth on the corrosion, and methods of preventing corrosion by coatings or encapsulation are the topics which we have to study. Reasonable judgments are being made of these factors and tiebacks are being used as vital parts of permanent structures. Figure 7.1 is a photograph of the cable-suspended roof of the Olympic Stadium in Munich, which is one of the most spectacular uses of this technique. The ends of the roof cables were anchored with tiebacks in sand.