Discussion. The Design and Construction of the Calder Bridge on the M1 Motorway.

Abstract

It is indicated in 5 19 that the end blocks are prestressed in three directions. I took this to mean the transverse stressing of the end beam on which the precast planks stand; nothing, however, appears on Fig. 8. Can the Authors clarify? 81. I was interested in the toothed surfaces between the units 'precast', as it were, on the falsework. I would like to know why they were toothed. Did the Authors carry out any tests? This cannot have been an inexpensive construction, and it seems to me that some justification should be given for having such detail. 82. The Authors say later that any jointed construction in the beams over the piers would be inadequate in strength. Can they give the grounds for this statement? 83. The Authors, in 5 36, state that the relaxation of the wire did not exceed 7%. I may be mistaken in my dates, but I would have thought that wire with 3% relaxation was available at that time. 84. The encasement of tendons was one of the points which for some time exercised the minds of those who sit on CP 11 5 as to whether it was necessary to have any further protection, as clearly the casing of the tendons must be unstressed. Although one Author has said that there were no visible cracks, this does not mean that there were no cracks. Have the Authors given any thought to this matter, and what is their view? There are not enough case histories of this type of construction to formulate the right sort of guidance in a code of practice. 85. I was most interested in the various analyses done for the prestressing of the end blocks vertically. It would be useful to know which of the values of the envelope, found from all the various work done, was used.