the rock to carry the full weight of the structure. Later, when the weight
of the structure was carried on the permanent bents, this blocking was
knocked out, but the bents were left in to carry the weight of the column
itself, which was swinging more or less from the structure above. The
weight of the structure was placed on these bents directly beneath the
columns by jacking up the temporary girders again, putting blocking between
the bents and the base of the columns, and taking out the blocking which
had been put in previously under the temporary shoring girders. The 24-in.
water main was carried over the excavation on cables from the temporary
shoring girders, except when they were being jacked up, at which time posts
were placed beneath it.

Anchor-bolts were put in place between the column bases and the bents
directly beneath, in order to increase the lateral stiffness, and raker
braces were also used. This having been done, the temporary shoring girders
were moved south to the next column, where the process was repeated. The
timber bents, shown in detail by Fig. 2, were then put in place as shown by
Figs. 4 and 5, and by Fig. 3, Plate XLVII. These bents were framed as
tightly as possible, using generally a 20-ton jack, and they were erected
simultaneously at each pair of columns. The weight was taken on these
columns by jacking up directly beneath the column base and taking out the
blocking between this base and the bent directly beneath the column. On
releasing the jack the weight was transferred to the permanent timber
bents, and the east and west columns of each pair were transferred on the
same day. One 80-ton jack was used on the easterly columns and two were
necessary on the westerly columns, one on each side of the 24-in. water
main. The raker braces of these permanent bents were not framed as tightly
as the main posts, in order that the main post should carry the entire
weight and the raker braces merely steady the structure.