building frame at the first floor level. These col-
lars and sway bolts serve to stiffen the columns
at the lower building level.
STRUCTURAL INFLUENCES
There were several factors that could affect the
structure of the ice cap DYE sites. They can be
grouped into two broad categories: dynamic and
static. Dynamic factors, such as wind loading
and vibrations (Haynes 1988), will not be dis-
cussed in this report. Our concern was strictly
with the static performance of the building sup-
port system. Four of the more important static
factors were (1) differential settlement of the
Figure 8. Truss collars.
footings beneath the columns, (2) tilting of these
1collar, 2support channel, 3side-acting bolt, 4end-acting
footings, (3) column plumbness or tilt, and (4)
sway bolt, and 5column half.
horizontal forces on the columns within the truss
system. Technical considerations for each of
The truss systems serve to stiffen the eight col-
these factors and how they could affect the
umns by bracing the columns horizontally. This
stresses within the supporting columns will be
was necessary because of the length of the col-
discussed in this section.
umns and their associated weakness to large hor-
Differential settlement of the column footings
izontal loads, such as wind loads. The collars
is caused by differences in densification rates of
surrounding the columns contain 12 adjustable
the foundation snow beneath each column foot-
sway bolts each. These sway bolts transmitted
ing. At DYE-2, the snow was not of uniform con-
the forces through the columns to the collars and
sistency because of the presence of ice lenses of
vice versa. The whole system acted to distribute
various sizes and thicknesses imbedded in the
loads throughout the four columns contained
matrix of the snow. These "defects" were formed
within each of the two truss systems. Static forces
by snow melting and refreezing during the
between the trusses and columns were measured
warm summer months and subsequent burial
at the sway bolt locations.
beneath drifted or fallen snow. Matrix density ir-
A similar arrangement exists at the building
regularities cause differences in the densification
level. In this case, the collars were built into the
rate for a given load, and thus settlement irregu-
Figure 9. Column footings.
4
Previous Page
