The graceful lines of the White Bird
Bridge on north Idaho's US 95 belie the challenge presented in its construction.
Begun in 1974, the bridge was the last link in a 10 year improvement effort
to widen Idaho's north-south highway. Opening of this section
eliminated the torturous 23 switchbacks in 7 miles that previously dropped
the roadway 3000 feet into the Salmon River canyon from Camas Prairie.
Passing 205 feet above White Bird Creek, the bridge is 810 feet long and
includes an imperceptible arch which is more concerned with compensating
for thermal expansion than imparting strength. The steel structure
consists of 2 parallel sets of 11 girder sections. The knee braces
are fully boxed while the horizontal sections are open topped "bath tub"
girders. The steel was placed by Ironworkers from local 14
in the employ of Fought Erection and Operating Engineers from locals 370
and 702 working for Gray's Crane and Rigging.
Staging for the project was done
from the south approach, where construction began.
The steel was shipped cross country
by rail and trucked to the job
from the south. There was a closer railhead
to the north, but the north side of the canyon is too steep to provide
good work space, and the girders would not negotiate the switchbacks north
of town. The main girders average 100 feet in length and weigh 42
to 48 tons each, while the knee braces are 52 tons apiece, and the short
haunch girders a mere 32 tons. Transport over the highway was accomplished
with the front end on a dolly and the rear end on a steer trailer.
Pilot cars were required fore and aft.
||Looking across the canyon to the
south abutment and the turn off to the town of White Bird. The old highway
is in the bottom of the canyon. The Salmon River is just beyond the
||Falsework bents were erected prior
to placing the bridge steel as the bridge would not be self supporting
until the final connection was made. The falsework towers are of
a "Tinker Toy" design consisting of identical sets of bolt together components
with only the top cap being a custom fixture. The vertical members
are about 8" square and the bracing is 2" tubing.
|The head block already
has a sling on one side of the sister hook. The girder on the right is
about to be moved closer to the edge of the abutment. The crane will
then be repositioned before putting the girder into place.
||The crane in the foreground
will set the girder down overhanging the edge. The 2 cranes will
then each lift 1 end and move the girder into place.
The first girder goes into
||Getting ready to move the second
girder to the edge.
|Moving the second girder
||The crane is backing
up carrying 1 end of the knee brace.
|Two cranes lift the
knee brace clear of the ground, then the left end will be raised and the
right lowered until it is upright.
||With the beam upright,
the lower crane will slack off, transferring the load entirely to the higher
rig. The lines draped over the boom pendants will be used to temporarily
guy the brace while the cranes are repositioned.
|The lower crane has
completely slacked off and the beam is supported entirely by the upper
||Two men are climbing
down the beam after unhooking the lower crane.
|Now suspended by a
single crane, the knee brace is being set on its foundation bolts, while
the other crane is moved back up to the abutment where it will be set up
for the luffing operation.
||The knee brace is now bolted to
its foundation and tied off in a near vertical position. The
crane on the lower landing has moved to the right. Its jib has been
installed for handling men, tools and rigging. The whip line of the
crane on the roadway is being taken off the boom and will be reeved horizontally
to luff the brace into position.
|The first knee brace is in position,
and the luffing reeve is down and the fixtures are being removed from the
|The 32 ton haunch girder
is the first piece to be lifted the full height of the bridge. The
scaffolds on the side of the girder are for the connectors to work from
while bolting the haunch onto the knee brace.
||The "sidewalk superintendents"
on the old highway are enjoying their last good view. The road will
be closed when the work progresses past this point.
|The foreman checks the load as
he climbs to join the connectors
Next, the second haunch goes up.
The inside men are waiting at the top to begin bolting. Note the
angle in the fixture at the top of the falsework. This allows for
the slope and arch in the bridge.
|Once a girder is in
place, the cranes are required to hold it 'til 55% of the bolts are torqued.
The cranes are then cut loose to set up for the next pick while the bolting
||Here is where we find
out how well the surveyors did their job. The first intermediate
girder goes up. It fits into the other parts and the bolt holes line
up. The attachment is made with fishplates. There are about 850 bolts
in each end.
|Placement of the second
intermediate girder completes the south third of the structure. The
cranes will be partially dismantled and moved into the canyon where
they will be reassembled and moved onto the north slope to begin work on
the other end.
||Assembling the crane
boom on the old highway. Note the 22% slope of the access road going
to the north end work landings.
|Booming up after assembly
||The knee braces were
the first parts put up on the north end. Here, the luffing lines
are being attached.
|With 1 knee brace set,
the cranes have moved out to make way for bringing up the next girder.
The dozer is pulling a sulky derrick which carries one end of the girder;
the other end is on a steer trailer. The girder will be backed onto
a switchback and the dozer & sulky will move out to give the cranes
||Next, the haunch girders
were placed atop the knee braces.
|The abutment girders
have been placed and the intermediate girder is being brought up slope
to the cranes. Another girder can be seen at the far right.
||When the north third of the steel
was hung, the cranes moved down to the canyon floor where they were reconfigured
to set the 3 interconnecting center sections. Here, the first south
end cantilever is being placed. The crane on the left has replaced
its short throat boom tip with a long taper tip.
|The second cantilever
on the south end. The rig in the foreground has added mid-point suspension
lines on the boom.
As the intervening
gap narrowed, the surveyors became quite busy. There could be no
room for error when the last girder was put in place. The bridge
was going to be 6 inches too long due to ground movement at the north side
of the canyon. The slow southerly creep had accumulated in the months
after construction of the north approach road. There had been numerous
delays in getting the steel, and the abutment had crept south a sixty-fourth
of an inch every 2 or 3 days. The solution was to trim 3 inches off
the end of a pair of girders, and re-drill all the bolt holes. The
adjusting screws in the falsework fixtures were used to increase the arch
of the bridge to obtain the additional space.
The view from the skip on the way up
to the bridge.
||One of the reconfigured
cantilever girders goes up on the north end.
The first center span goes up. The 2 cranes paired on the right are
lifting with an equalizer bar between their hooks.
The second center span went up the
following day, completing 5 month's steel work. A reinforced concrete
roadway was built atop the structure and the bridge was opened for traffic
in early 1975. Within a year, work was done to relieve accumulating
southward pressure against the north abutment.
This page ©2002 by M. Huntington
Opening photograph by Will Hawkins.
All other photos ©1974 by M. Huntington
questions & comments are welcome
This page has been accessed