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1. Introduction
The research developed by Mendes [ 1 ] with information about
5.619 Brazilian bridges belong to Brazilian Federal Roads net-
work allowed them to be characterized by age, dimension and
the number of spans, structural systems, standard vehicle-load
and the stability and durability conditions. The majority of these
bridges are more than 30 years old, with no or little informa-
tion about the mechanical characteristics of their materials. The
changes occurred over time in the capacity and the geometry of
the loads in the fleet of vehicles circulating, as well as the find-
ing of the perceptible signs of the deterioration, both concrete
as well as reinforcement of the bridges, conducted to an evalu-
ation of the distribution of the stresses in the cross sections of
the reinforced concrete bridges considering the effects of the
variation of the module of elasticity of concrete and of the rein-
forcement corrosion.
The aim of this work is to contribute for structural evaluation in the
reinforced concrete bridge through the analysis of the variation in
the distribution of stresses in the concrete and in the reinforce-
ment, resulting from the variation of the module of the elasticity
of the concrete and of the reduction in the geometric longitudinal
reinforcement ratio from corrosion, in a representative bridge from
the stock of existing bridges.
In this work, a bridge with representative span and cross sec-
tion existent on the Brazilian Federal Roads were analyzed,
supposing different longitudinal reinforcement ratios, different
configurations of reinforcement corrosion in each case and two
values for the module of the elasticity of the concrete, E
c
and
0.5E
c
. The value of E
c
was determined with the expression
of NBR6118 [ 3 ] supposing a concrete with f
ck
= 18.0 MPa.
Due to the unknown real value of the strength characteristics
of the older bridges and to consider the effect of the long-term
deformation, opted to also consider the module of elasticity as
half of E
c
.
1.1 Justification of the adopted model
In Mendes [ 1 ] the distribution of bridges on the Federal roads by
age group was obtained, highlighting the high number of bridges
(41.2%) with unknown ages (Figure 1). Admitting that this sample
is representative to the set, 70% of the bridges is more than 30
years old, from which naturally exists a significant growth in the
pathologies [ 2 ]. It should be noted, however, that the bridges with
unknown ages are probably the oldest ones, which will increase
the percentage with more than 30 years old.
The large number of bridges for which are unknown (or not aware)
the year of the construction constitutes only one sample of the dif-
ficulties found for a more detailed analysis of the existent situation
and an evidence of little importance given to the register and treat-
ment of the information.
Of the existing bridges on the Brazilian Federal Roads, 1,588
bridges had their structural systems not informed. Excluded bridg-
es for which the structural system was not informed, 98% of the
bridges are made of reinforced or prestressed concrete, in beam,
slab or arc model (Figure 2).
From the total of bridges registered, 3,153 of them the vehicle-load
adopted in the structural analysis is unknown (corresponding to
56% of the total number of bridges). Among the bridges which the
vehicle-load is known, 642 were projected with standard vehicle-
load of 240 KN (corresponding to 64%) and 237 were projected
with standard vehicle-load of 450 KN (corresponding to 9.6%) (Fig-
ure 3). Probably most of non-informed bridges were analyzed with
a 240 KN standard vehicle-load.
389
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 3
P. T. C. MENDES | M. L. T. MOREIRA
|
P. M. PIMENTA
Figure 1 – Distribution of the number of bridges by age, excluding the ones where the age is not known