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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
Fatigue lifetime of a RC bridge along the Carajás railroad
nent loading and is under great stress variations when the moving
loads act. Because of this, the lifetime of the section is 1.33E +07
years approximately, for the operational train, and 7.05E +05 for
the future train type.
Must be remarked that these lifetimes were estimated using the
specified characteristic strength of concrete in the project (f
ck
=
18 MPa). The other sections were also analyzed for fatigue and
the results regarding lifetime are presented in Figure 29 (semi
log scale), considering also the f
ck
specified in the project for both
operational and future trains. Figure 29 shows that occurs a re-
duction in the fatigue lifetime of the sections with the change of
loading from operational to future train type. It is also observed
that the lifetime of the sections located on the first support is very
high (support at the abutment E1, section S1, x = 0 m) which did
not occur in the third support sections (section S21, x = 40 m). In
section S21 the critical element (suffering greater fatigue damage)
is the concrete on the bottom surface. Therefore, based on the
results obtained for other bridges already analyzed (bridges over
the rivers Mearim, Cajuapara and Rio Vermelho), it is known that
the real compressive strength of concrete is much higher than the
value specified in the project. Thus, one must be considered the
Figure 28 � �oncrete rectified stress and limit
fatigue stress according to NBR 6118 : 2003 [11]
Ta�le � � �atigue analysis �or stringer�s cross section S21 under operational train type loads
Element
Damage
Loaded train
Unloaded train
Total (pair)
Bottom surface reinforcement
1.09 E-11
5.02 E-13
1.14 E-11
Top surface reinforcement
1.45 E-12
6.46 E-14
1.51 E-12
Bottom surface concrete
5.83 E-13
1.58 E-19
5.83 E-13
Top surface concrete
0.00 E+00
0.00 E+00
0.00 E+00
Section maximum damage
1.14 E-11
Section lifetime in pair of trains
8.77 E+10
Section lifetime in years
1.33 E+07
Ta�le � � �atigue analysis for stringer�s cross section S21 under future train type loads
Element
Damage
Loaded train
Loaded train
Loaded train
Bottom surface reinforcement
9.26 E-11
5.02 E-13
9.31 E-11
Top surface reinforcement
1.32 E-11
6.46 E-14
1.33 E-11
Bottom surface concrete
2.16 E-10
1.58 E-19
2.16 E-10
Top surface concrete
0.00 E+00
0.00 E+00
0.00 E+00
Section maximum damage
2.16 E-10
Section lifetime in pair of trains
4.63 E+09
Section lifetime in years
7.05 E+05