The bridge is erected in two halves
lifting up the bridge boxes in position.
with the remainder strip of the bottom
Also, the middle strip of the lower plate
flange to be installed after erection by
whose clear width measures 1370
field welding. For this reason, a
mm was welded to the two box girders
system of temporary bracing was posi-
taking into consideration the effect of
tioned and bolted in-field to connect
shrinkage and distortion resulting
the pair of upper chord plates together
from welding. The longitudinal welded
and to stabilize the flanges of the U-
joints at the junction of the two boxes
shaped girders. The end cross girders
were completed on site after every two
lines with the elimination of the bottom
were welded to connect the two boxes
boxes have been raised into position.
flange overhangs and the location of
together. This erection bracing is
CONCRETE DECK
web stiffeners inside the boxes.
usually removed from the completed
The bridge deck is made out of a cast-
Lateral and torsional rigidity of the box
bridge.
in-place reinforced concrete slab of
girders permit elimination of span
In this project, the contract included
250 mm thick, acting in a composite
lateral bracing that typically clutters
both fabrication and erection of the
fashion with the top steel flanges by
the span underside. The box girders
structure. The erector is the sub-
means of shear connectors. The deck
also offer improved serviceability with
contractor to the fabricator. This
is provided with 2 long overhangs of
the elimination of numerous external
current type of contract in Egypt elimi-
horizontal surface where moisture
nates the conflict between the fabrica-
retaining debris collects. Finally the
tor and erector. This also allows the
box girders provide the advantage of
fabricator to choose where shop
improved load distribution when used
assembly is required and determine
in conjunction with moment resistant
the most efficient method of erection.
floor beam connections. The geome-
Each 130 ton single box was lifted by
try analysis and the design of practical
two cranes and each end was posi-
details of this bridge posed a series of
tioned over three bearing pads, two
2800 mm each giving a total deck
unique problems. These challenges
temporary the other permanent. The
width of 15.80 m sufficient to accom-
were met by the joint effort of all those
completed bridge rests on four type
modate three traffic lanes, in one
who participated in the design. El
direction and two emergency walk-
Mariottia Infrastructure project is a
ways and one shoulder.
successful example for a large civil
The decision of transporting and
structure located in an environmen-
trucking by road complete boxes was
tally constraint and highly urbanized
taken to cope with the tight delivery
area in the mega city of Cairo.
time schedule and the client's require-
ments. No traffic interruption was
allowed except for a few hours by
2B permanent reinforced elastomeric
might over the weekend. The route of
bearings of dimensions 700x600x115
the convoys was traced then reported
each. To minimize traffic disruptions,
to the local Authorities for their prior
the lifting operations were restricted to
approval and issuing permit.
five hours during the night time on
CONCLUDING REMARKS
weekends; no closures were permit-
Steel box was selected in the main
ted.
Two track mounted cranes
girder of El Mariottia Bridge largely
equipped with 7 axles of 400 meter
because of improved aesthetics. The
tons capacity each have been used for
box girder provides smooth external
13
Issue 72 March 2014
2014
72

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