No abstract

The first part of this paper sets the scene for the growth of the road programme in the UK since 1950 and new additions to the existing stock of bridges. The second part describes the events that gave concern for the preservation of those bridges and the attention given to the policy and inspection procedures to safeguard the nation's existing stock. Tables describing the bridge stock, the principal factors influencing maintenance expenditure and the principal tasks are provided, together with concluding observations and acknowledgement of the great efforts of the bridge engineering community over the half-century covered.

Measurements of earth pressures on four standard motorway bridge abutments backtilled with different materials and in different ways, suggest that the geometrical shape of the abutment is important in determining the backfill pressure. The earth pressures recorded showed little correlation, either in magnitude or distribution, with the earth pressures assumed in the design which was based upon an equivalent fluid concept. The results of a three dimensional finite element analysis compare favourably with the field measurements of earth pressures, and this method may represent a more valid design approach for this type of structure. Les mesures des pressions des terres sur quatre culées de pont d'autoroute classique, remblayés avec des matériaux différents et de différentes façons, suggérent que la forme géométrique de la culée est importante dans la détermination de la pression du remblayage. Les pressions des terres enregistées ont montré peu de corrélation, soit en grandeur, soit en distribution, avec les pressions des terres admises, dans le projet qui était basé sur le concept du fluide équivalent. Les résultats d'une analyse aux éléments finis à trois dimensions, se comparent favorablement avec les mesures des pressions des terres faites en chantier, et cette méhode peut représenter un projet d'approche plus valable pour ce genre de structure.

No 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.