ON THE SERVICE LIFE ASSESSMENT OF REINFORCED CONCRETE
ELEMENTS OF BRIDGE SPANS.
RADJABOV TOHIR YUSUPOVICH - TSTU department of “Artificial structures on highways”, acting associate
professor (90 986 23 89);
SHOJALILOV SHUKHRAT SHOMURODOVICH - TSTU department “Artificial structures on highways”,
acting associate professor (90 189 06 48);
SOBIROVA MAMURA MIRABDULLA QIZI – TSTU, department “Bridges and Tunnels”, doctoral student (97 713
23 10).
Annotatsiya.
Maqolada avtomobil yoʻllari va koʻpriklarning xalq xoʻjaligidagi oʻrni, tabiiy sharoiti, avtomobil
va temir yoʻl transportining unumdorligi, samaradorligi va xavfsizligini hisobga olgan holda, barcha yoʻl
elementlarining parametrlarini texnik-iqtisodiy asoslash tamoyillari, ularning qurilishdan keyingi umrboqiyligini
hisobga olingan.
Kalit so’zlar.
ko'priklar, yo'l o'tkazgichlar, ko'prik konstruktsiyalari, nuqsonlar va shikastlanishlar, yoriqlar,
rekonstruksiya, ekspluatatsiya ishonchliligi, umrboqiylik.
Аннотация.
В статье учтены роль автомобильных дорог и мостов в народном хозяйстве, их природные
условия, производительность, экономичность и безопасность автомобильного и железнодорожного
транспорта, принципы технико-экономического обоснования параметров всех элементов дорог, их
долговечность после строительство.
Ключевые слова:
мосты, эстакады, мостовые конструкции, дефекты и повреждения, трещины,
реконструкция, эксплуатационная надежность, долговечность.
Abstract.
The article takes into account the role of roads and bridges in the national economy, their natural
conditions, productivity, efficiency and safety of road and rail transport, the principles of feasibility study of the
parameters of all road elements, their durability after construction.
Keywords:
bridges, overpasses, bridge structures, defects and damage, cracks, reconstruction, operational
reliability, durability.
Introduction.
The Republic pays special attention to the development of the construction of
transport infrastructure both within and outside the Republic. From the first days of independence,
President Sh. M. Mirziyaev identified as one of his priorities the design and construction of the most
convenient and shortest roads and bridges with high capacity, which would ensure Uzbekistan’s
access to the world market. Currently, new projects are being implemented in the Republic of
Uzbekistan to ensure the development of transport and communication infrastructure. Over the past
years, such large-scale work has been carried out as the construction of main roads, the establishment
of transport links with foreign countries, the introduction of modern equipment and technologies into
the road sector, the training of specialists that meet the requirements of today and the improvement
of their qualifications.
Considering the role of highways and bridges in the national economy, natural conditions,
productivity, efficiency and safety of road and rail transportation, the principles of feasibility study
of the parameters of all road elements, as well as the choice of road direction and their construction,
are of great importance [1].
These features of their work must be taken into account by designers, builders, and maintenance
workers who are obliged to ensure normal year-round service of the road for a long time [2]. With
the current increase in traffic flow, bridge structures must develop accordingly. Naturally, the designs
of bridge abutments and intermediate supports had to meet the growing requirements for span
structures.
Figure 1. Total number of bridges in use in the republic
Methods.
Tasks
technical diagnostics
of any structures and structures is the development of
methods and tools intended for qualitative and quantitative assessment of indicators characterizing
the structural and operational properties and condition of functioning objects, their elements and
materials, as well as drawing up recommendations for their further operation in accordance with
technical requirements (Fig. 1.).
Figure 1. Technical diagnostics of bridge structures
Technical diagnostics of load-bearing structures of transport structures has the main goal - to
determine the actual technical condition of the structures, their ability to withstand the design loads
operating in a given period and ensure normal operation of the building. The objectives of the survey
may include searching for the best options for strengthening and rehabilitation of structures,
adaptability of the building to new loads and operating conditions during its proposed reconstruction.
If the survey is carried out after an accident, its causes, feasibility and the possibility of restoring the
building or its individual parts are analyzed. [3]
Results.
In real operating conditions, bridges are simultaneously exposed to several influences.
As a result, the intensity of damage accumulation increases, which can accelerate the failure of the
structure. The influence of several factors can be taken into account by introducing a multifactorial
measure of accumulated damage
D.
It is selected based on physical concepts of the operation of the
7 237
6191
1247
188
1 738
3326
390
96
0
1 000
2 000
3 000
4 000
5 000
6 000
7 000
8 000
Highway Committee
Local governments
Ministry of Water Economy
On commercial highways
Total number of bridges
Number of bridges under repair
structure under loads and environmental influences and is taken equal to zero for the initial state and
one at the moment of failure during operation [4]:
0
0
2
1
)
;
;
,...
,
(
k
t
t
x
x
x
D
,
(5)
here:
)
;
;
,...
,
(
2
1
t
x
x
x
t
- current values of the damage measure over time
t
depending on
stresses and variable factors of the loaded mode and operating conditions
x
1
,
x
2
,....,
x
t
;
Δ
k
is the
final value of the measure of accumulated damage at the moment of failure;
Δ
0
is the value of the
measure of accumulated damage in the initial period of operation (
t
= 0).
At time
t
= 0, the initial conditions are met :
)
0
;
;
,...
,
(
2
1
t
x
x
x
=
Δ
0
,
D =
0. Failure occurs
when the service life of the structure is equal to the service life:
)
;
;
,...
,
(
2
1
T
x
x
x
t
=
Δ
0
,
D
=
1, where
T is
the service life of the structure.
to choose a universal measure of damage that could reflect the full impact of all changes in a
material such as concrete. But, as experience shows, most external influences reduce the strength of
concrete, which affects the durability and reliability of the structure. [5]
The value of residual strength, which depends on the combined action of repeated load and
environment, duration of load application, chemical aggression in concrete, etc., can be obtained on
the basis of active experiments, allowing one to obtain the necessary multifactor correlations. Damage
measure
D
is a slowly changing function of the interactions of damaging factors. Increment of the
damage measure in the time interval Δ
t
:
t
D
j
j
)
(
, (6)
where
j
-
rate of increase in damage measure over time
t
in the stress range
σ - Δσ
/2<
σ
j
<
σ
+ Δσ
/2.
Variables
x
1
, x
2
,.... , x
i
, defining the measure of damage
D
according to formula (5), depend
on time:
x
1
= φ
1
(
t
),
x
2
= φ
2
(
t
) ...,
x
i
= φ
i
(
t
) . (7)
Damage measure speed
v
j
=
dD
j
/ dt
is a complex function of many variables
x
1
, x
2
,...., x
i
,
each of which in turn is a function of an independent variable time
t
according to expression (7):
i
i
i
j
i
xi
j
t
t
x
x
x
D
1
/
2
1
/
),
(
)
,
,
,...,
,
(
(8)
where
D '
xi
is
the derivative of the measure of accumulated damage with respect to the variable
x
i
;
φ'
(
t
) - derivative with respect to time
t
of the dependence of the factor
x
i
= φ
i
(
t
).
Mathematically, this means that the measure of accumulated damage is a non-linear function,
and the rate of accumulated damage depends
on D.
In equation (5) we replace the values
x
1
, x
2
,... .,
x
i
to their values according to expression (7):
,
)]
(
),...,
(
),
(
[
0
0
2
1
K
i
t
t
t
D
(9)
From equation (9) we express
t = f ( D
i
, σ
i
)
and substitute the values
of t
into equality (7):
x
1
= φ
1
(
D , σ
j
),
x
2
= φ
2
(
D , σ
j
) ...,
x
i
= φ
i
(
D , σ
j
) .
We express the rate of damage accumulation through
D by
substituting
x
i
= φ
i
(
D
i
, σ
i
) into
expression (8):
,
)
(
)]
,
(
[
1
/
/
i
i
i
j
i
xi
j
t
D
D
(10)
We replace the increment in equality (6) with a differential, taking into account the probabilistic
nature of the stress distribution and relation (10), we write:
dD =
0
]
)
;
(
)
(
)
,
(
[
1
/
/
dt
d
t
p
t
D
D
t
i
i
xi
(eleven)
where:
σ
0
–
voltage value below which damage does not occur;
р( σ; t
) - stress distribution
density at time
t .
Integrating expression (11) over the variable
D
ranging from
D
0
=
0 to
/
k
D
= 1, by variable
t
within the limits of
t
0
= 0 and
t
k
=
1, we obtain the condition under which the structure fails:
1
0
1
/
/
,
1
]
)
;
(
)
(
)
,
(
[
.
0
Dи
Е
t
i
i
xi
dt
d
t
p
t
D
D
dD
(12)
where
T is
the service life of the structure.
Condition (12) is
the basic equation for
calculating service life.
It establishes the relationship between the service life of the structure, the
value of stresses, their probabilistic distribution, and the intensity of exposure to damaging
environmental factors. From the solution of the basic equation the service life of the structure is
found[6].
A significant difference between service life calculations and traditional calculations of the
bearing capacity of a structure is the introduction into the calculation of the rate of rewarding
processes and changes in the internal properties of the structure. In a generalized form, the algorithm
for calculating the service life of load-bearing structures is:
,
,
,
)
,
,
,
(
агр
агр
R
P
a
P
R
D
T
(13)
Where
- an operator that converts the mathematical dependencies of the structural strength
reserve and the rate of damage accumulation into service life;
D ( R , σ, Р
R
, a
agr
) - a mathematical
representation of the strength reserve of a structure, depending on its strength
R ,
effective stresses
σ
,
probabilistic properties of strength
P
R
,
the degree of resistance of the aggressive environment
a
agr
;
h
(
σ
,
Р
σ
, and
agr
) - the rate of damage accumulation, depending on stresses, probabilistic properties
of the load
P
σ
,
indicators of the aggressiveness of environmental influences[7].
The operator in the simplest case is a division operation, however, if we take into account the
history of loaded structures together with the aggressive influence of the environment, then it is
necessary to solve the basic equation (12) to determine the service life, which in its structure
corresponds to expression (13) [8]. For the residual service life, the initial measure of accumulated
damage at the time of technical diagnosis is not equal to zero, and then the basic equation for
calculating the residual service life (12) takes the following form:
1
0
1
/
/
,
1
]
)
;
(
)
(
)
,
(
[
.
0
Dи
Е
t
i
i
xi
dt
d
t
p
t
D
D
dD
(14)
where
D
and
is a measure of accumulated damage after
t
and
years of operation;
T
'
is
the service
life at which the structure fails, taking into account its actual technical condition at time
t
and
.
Conclusion.
All initial data for determining the residual service life according to the formula
T
rest
=
T ' - t
and
are accepted in accordance with the operating conditions after the moment of monitoring
the technical condition: stress from the load
σ
, variable factors
i
that
determine the operating
conditions during the remaining period of operation from the moment
t
and
until the structure fails
T
The quantitative value of the measure of accumulated damage
D
and
is determined on the basis of
instrumental measurements of the characteristics of the stressed deformed state, the study of loading
modes and operating conditions of structures.
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