Discussion on Papers 12 and 13

Mr Long (Paper 12) The prestressing systems being employed to date in gravity platforms seem very small, both in relation to the size of the platforms and in comparison with current practice in bridges. The tendons are almost always grouped in families and so, as an exercise, my organization recently repriced a platform pre-stressing and grouting sub-contract on the basis of a simple 2 for 3 tendon substitution using a larger system. This showed almost 20% saving in the sub-contract sum, principally due to the fact that many of the activities take roughly the same manpower and time, regardless of the system in use. Obviously, this is an oversimplification because there are consequential problems, for example, in scaffolding needed to support heavier jacks and tendons which would cause additional expense to the main contractor. But with fewer sub-contract operations to perform to achieve the same level of prestress, the overall programme time should be reduced, and broadly speaking this is the critical factor.