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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
Fatigue lifetime of a RC bridge along the Carajás railroad
1. Introduction
The bridge over the river Mãe Maria is located in the city of Marabá,
Pará state, and is part of the Carajás Railroad (EFC). It is used to
allow iron ore transport from Carajás, a city in Pará yet, to Itaqui
harbor in São Luis city, state of Maranhão. Due to the need for load
increasing, which currently is 320 kN to 400 kN per axle, studies
focused on the new behavior of the structure are of extreme impor-
tance for the service life of this bridge.
1.1 Structural system description
The studied bridge is a straight line structure located along the
Carajás Railroad crossing the river Mãe Maria, identified as OAE
50A. Built in reinforced concrete, cast “in situ”, the OAE has two
hyperstatic spans, totaling 64.20m, crossing the bed of the river
with two spans of 20.00 m providing a cross section width of 5.85
m. On the deck slab is the rail
line superstructure for passage
of trains. Safety on the OAE is
guaranteed with the presence
of refuges and metal railings as
shown in Figure 1.
The superstructure is slab on
beams type. The deck consists
of four spans of continuous
stringers of “pi” cross section,
with linear variation of the web
thickness from 0.35mto 0.70 m
near the supports and block B2,
as shown in Figure 2, stiffened
by transversal beams (second-
ary) on charted neoprene sup-
port devices at the abutmentE1
and block B2. The beams are
embedded in the abutment E2.
Figure 3 shows the overall structural system with beams, abut-
ments, blocks and reinforced concrete caissons cast “in situ”.
1.2 Dynamic loads
The fleet of locomotives and wagons currently in operation for
transporting ore in the EFC is composed mostly of locomotives
DASH9 which represents almost 30% of the total fleet, as shown
in Table 1, and GDT wagons that represent about90% of the fleet.
Basically two types of compositions are applied, being one com-
posed by two front locomotives followed by 104 wagons, plus
one intermediate locomotive and more 104 wagons, which corre-
sponds to 80% of the fleet in operation. There are situations where
the position of the intermediate locomotive varies and may stay at
the end of the composition. The other composition uses three front
locomotives pulling 208 wagons. Figure 4 shows the longitudinal
distances considered for locomotives and wagons.
In the future, the EFC will be
loaded by new trains-types,
with a greater number of wag-
ons and individual load higher
than the present. It is intended
to work with two models, where
the basic difference is the num-
ber of locomotives between the
wagons. In the first situation
there are
2 locomotives + 110
wagons + 1 locomotive + 110
wagons + 1 locomotive + 110
wagons
. On the second, the
configuration is
2 locomotives
+110 wagons + 2 locomotives
+ 220 wagons
. Table 2 shows
the loads for the current and
future operational trains-types
considering GDT wagons and
DASH9 locomotives.
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Figure � � (a) bridge's cross section (meters); (b) linear variation of the stringers' width close to supports
A
B