The explanation of the failure to lift the Millennium Wheel was unconvincing (NCE 16 September). The proposed solution is also unlikely per se to overcome the problem.
The temporary cables and anchor plates will still sag initially and the moment induced in the anchor block heads when the cables are tensioned will remain as controlled by the diameter of the pins in the heads and the coefficient of friction. All traditional stay anchorage and stay ends suffer moments due to changes in sag or misalignment but seldom fail as a result.
The deficiency appears to be in the wedge collars (of which there is no mention of redesigning) and possibly in the absence of sufficient pre- tensioning.
AR Flint (F), 21 Dartmouth Street, London SW1H 9BP