AN UNUSUAL MODE OF
TRANSPORTATION
IN A CONGESTED CITY:
A CASE STUDY - EL MARIOTTIA BRIDGE - EGYPT
Dr. Hussein Abbas
INTRODUCTION
UShaped steel segments were
2.40 m deep, each having an inner
Transporting oversize overweight
temporarily braced until the concrete
vertical web and a steeply inclined
bridge components on wheels is
slab was cast. The box shape
outer one of a slope of about 60° to the
generally a difficult task to achieve.
provides in addition improved aesthet-
horizontal (1:1.75). These two boxes
But transporting, lifting, fitting and
ics value and smooth external lines
are connected together with a lower
adjusting eight pieces each measures
with the elimination of the bottom
stiffened plate field welded longitudi-
58 m and weighing 130 tons in the old
flange overhangs and the location of
nally to the lower boxes' flanges. The
city of Cairo through its 18 million
web stiffeners hidden inside the box.
three components form an open three
inhabitants is a real challenge. Not
The bridge U-shape sections consist
cell cross section. The top four flanges
only that but also delivered on site for a
of a series of longitudinal and trans-
of the large box were temporarily
long distance of 22 km that separates
verse stiffened welded plates. The top
connected laterally by means of an
the fabrication yard to the final bridge
flanges are fabricated from 40 to 50
adequate Warren type truss bracing
position located few kilometers away
mm thick plates which are connected
that has been kept during the critical
from the pyramids plateau in Giza, the
to an inclined outer web forming an
construction stage until the concrete
unique site of historical importance.
angle of approximately 30o from verti-
slab was cast and hardened.
Although the transfer of the moving
loads occurs with a substantial safety,
failure may occur due to fatigue in the
welds connecting the upper flanges to
the web plates especially for
orthotropic plates with trapezoidal
stiffeners subjected to heavy and
repeated road traffic.
ERECTION SEQUENCE
Prior to casting the concrete deck, the
side by side U-shape steel girders are
considered in a critical stage. At this
stage, the non composite steel must
support the entire construction load
including the wet concrete action.
During this period the top flanges are
BRIDGE DESCRIPTION
cal and an inner vertical one, by
in compression and susceptible to
The box shape proved to be most
continuous longitudinal deep penetra-
lateral torsional buckling. During
appropriate for this type of construc-
tion welds.
construction, the trussed box U-girder
tion because of its high torsional stiff-
The steel bridge structure spanning
is quasi-closed without the deck slab,
ness. However due to concerns about
58m rests at the end points of two
but once the concrete has cured, it
distortion of the steel plates constitut-
concrete corbels. This drop-in-span
acts a continuous lateral bracing for
ing the box during construction, the
consists of two identical open U-boxes
the top flanges of the girder.
12
Issue 72 March 2014
2014
72

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