At what stage of the work were the archaeological discoveries made? Presumably there were discussions between the Iraqi Ministry of Construction and the organization responsible for archaeological preservation. It would be of interest to know whether the Engineer was consulted on this matter and, for example, if he was allowed to give consideration to the possible redesigning of the bridge, perhaps by increasing the spans, to avoid destruction of the ancient brickwork. M r P. L. Martin, Rendel, Palmer & TrittonThe foundation design for the bridge was dominated by consideration of the extraordinary scour conditions. Design studies therefore centred on pile capacity under both vertical and lateral load at times of flood. This discussion contribution enlarges on the pile testing which was camed out. 45.The first two pile tests did not confirm either that the permanent piles would have adequate bearing capacity or that settlements under working load would be within acceptable limits. A further test was made. The test had two objectives. The first was to prove the effectiveness of the unorthodox procedure for cleaning the base of the pile shaft. The second was to determine the relationship between end bearing capacity and the standard penetration test data obtained from the site investigations. An extrapolation could then be made to determine base capacity under scour conditions. Ideally this test would have been made on a pile founded at -9.0 m, but, even if skin friction could have been eliminated entirely, it would have been necessary to increase the test load to compensate for the increased overburden pressure (from +5.0 m to river-bed level) over that occurring at maximum scour. Furthermore, a test pile could not by then

No abstract

DiscussionMr A. J. Harris (Consulting Engineer) commented first on the question of safety.He had always hesitated t,o design on the basis of ultimate load and whilst he was becoming persuaded of the soundness of that principle for small structures, he was still very doubtful if the ultimate load was the right basis of design for heavy large-span bridges where the live load quite commonly represented little more than one-quarter of the tota load. Was it right to design on the ultimate limit in such structures? Considerations of the basis of design had led him to ask one or two questions. For example in 9 24 the Author had stated that it was necessary to have a very good bond between cable and concrete and went so far as to say "experience shows" that the rupture load might be reduced by 30% or even more for large spans, if the bond was not efficient. Was there in fact any such experience of large spans 4 There was much experience of testing very small spans, but could one call on experience of large spans to justify that view 9 221. The Author had further referred to the possibility of using cables of parabolic form which were completely free of the beam. How was that to be reconciled with the Author's remarks on bond, sincc with fiee cables there would be very little bond at all? On the ultimate basis of design such cables would be rejected, but many such had been successfilly used. Equally, on the question of factor of safety, the footnote to 5 121 Downloaded by [] on [11/09/16].

No abstract