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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 3
P. T. C. MENDES | M. L. T. MOREIRA
|
P. M. PIMENTA
2.3 Variation in the geometric reinforcement ratio
The geometric ratio of the longitudinal reinforcement of the
beams was considered with the values of ρ
1
= 3,78%, ρ
2
=
3,22%, ρ
3
= 2,68% and ρ
4
= 1,63%, corresponding to the pos-
sibility of details with the CA24 and the CA50 steel to various
processes of design, according to Figure 9.
2.4 Configurations of corrosion
Taking into account the most frequently configuration of corrosion of
the longitudinal reinforcement corresponds to the corrosion of the low-
er level of the bars, one opted to admit the reduction of the section of
the bars in this layer in 40%and 100% according to Figures 10 and 11.
2.5 Loads
To analyze the designed bridges for the 240 KN standard ve-
hicle-load (TB240), it was considered the dead loads and the
360 KN standard vehicle-load (TB360) of NB6 [ 4 ] and 450 KN
standard vehicle-load (TB450) of NB6 [ 5 ], including the effect
of the impact through the coefficient of impact φ.
3. Results of the analysis
3.1 Compressive stresses on
the concrete – cracking effect
For the models with elements of bar and shell (B-S), the maxi-
mum stress on the concrete , considered uniform along the
width and the tensile stress in the reinforcement, determined in
its center of gravity and both varying linearly along the height
were obtained from the maximum bending moment and the geo-
metric characteristics of the cross section [ 6 ].
In the model with solid elements, the longitudinal compression
stress on the top of the flange varies considerably along the
width of the flange, in the center of the elements from 1 to 12
indicated in Figure 12, depending on the type of applied load, as
indicated in Figures 13 and 14 for load situations {DEAD} and
{DEAD + φ.TB450} in uncracked section and Figures 15 and 16
in cracked section.
It is observed for the load {DEAD} that the maximum value of
longitudinal compression stress on the top of the flange is 2,897
KN/m
2
or 2.90 MPa (Figure 13), obtained with the uncracked
section, and that in the most unfavorable load type, correspond-
ing to the load combination {DEAD + φ.TB450}, the maximum
value of longitudinal compression stress on the top of the flange
is 6,790 KN/m
2
or 6.79 MPa (figure 16), obtained with the
cracked section. Therefore the maximum longitudinal compres-
sion stress varies between 2.90MPa and 6.79 MPa, with a sec-
tion considered uncracked and cracked respectively.
It seems that the maximum compressive stress suffers an in-
crease of 134.1% among the two extreme situations analyzed
– only load {DEAD} and uncracked section and load {DEAD +
φ.TB450} with cracked section. However, considering the con-
crete with f
ck
= 18.0 MPa the compressive stress varies from
16.1% to 37.7% of the characteristic compressive strength of
concrete and from 22.6% to 52.8% of the design compressive
strength of concrete. Considering the medium value on the top
of the flange these percentages become from 13.6% to 25.9%
of the characteristic compressive strength of concrete and from
19.0% to 36.3% of the design compressive strength of concrete,
little significant take in account the strength of the material.
3.2 Compressive stress in
concrete – corrosion effect
Figures 17 and 18 present stress values of minimum, medium
and maximum compressive stress on the top of the flange for
each of the following situations:
Figure 12 – Compressed-elements of bridge slab