UNDERWATER INSPECTION OF BRIDGES
Kokodeev Artemy Vitalyevich
Saratov State technical
University Y.A. Gagarin
Student of 3 course special. SMT
Ovchinnikov Igor Georgievich
Saratov State technical
University Y.A. Gagarin
Doctor of technical Sciences, Professor
Keywords: The bridge; underwater inspection; damage; corrosion; diving;
sonar; bridge supports; safety exploitation.
Inspections of submerged elements of bridges over rivers are of great
importance to provide safety and long-term exploitation. However, in our
country very few attentions are paid to this problem.
And because of the low light of this serious question we decided to get
acquainted with the experience of specialists from the United States of America,
which frequently organize activities for the examination of elements of bridge
structures.
Security issues on the bridges were always relevant and important to the
government of the United States. But seriously the task of regulating the correct
operation of bridges puzzled only in the middle of the last century. The impetus
for the creation of a single national program of inspections of bridges to control
security has been a collapse 15 December 1967 on the Silver Bridge (Fig.1),
held over the Ohio River, and the connecting Point-Pleasant (West Virginia) and
Gallipolis (Ohio). The tragedy claimed the lives of 46 people. The destruction of
the bridge was caused by the deformation of
one of the pivotal suspension did not bear a
grown from the increased load before
Christmas transport stream. Followed the
chain сollapse of construction for only one
minute. Also the reason for the tragedy was
called fatigue of material from which
consisted bridge, and excessive corrosion.
After the accident at the Silver Bridge,
Fig.1 The consequences of the
the U.S. Congress has attended many
collapse of the Silver Bridge
questions, in particular, a complete database
of all the existing bridges. It was planned to
make a full assessment of their condition. The main mission was to prevent
incidents similar accident at the Silver Bridge. The U.S. Congress has initiated
the introduction of new state standards inspection of the condition of bridges in
1968, requiring periodic checks and inspections on all national bridges [6].
One of the main types of inspections of bridges become regular views
those parts of the buildings, which are under water. National standards have
defined a number of strict requirements:
1) Every state should carry out periodic inspections inspections on
bridges, in their territory, with a maximum interval between inspections in 24
months
2) Inspectors must have the necessary qualifications on this issue.
3) Should be developed and training of inspectors [7].
However, despite all the reforms, from time to time of the accident on the
bridge was. A vivid example of the consequences of a lack of interest in
forecasting the impact of watercourse to the bridge and the insufficient
protection of the bridge from scour was the accident on 5 April 1987 on the
Schoharie Creek Bridge in the state of New York (Fig.2), which killed 10
people. This sad event was preceded an abnormally large amount of
precipitation, which, combined with the factor of snowmelt, significantly
increased the level of water in the river. The official cause of the collapse was
called extensive scour in support number 3. It was recognized that protective
stone embankment was not fully served its purpose, and inspections and
maintenance of the bridge did not meet the necessary requirements. It was also
found that the supports of bridge are exposed to scour almost immediately after
passing the bridge in exploitation that was not calculated designers [9].
Fig.2 Collapse on the Schoharie Creek Bridge, New York, USA
Events on the bridge in the state of New York has exposed the problem of
insufficient reliability bridges the face of natural disasters such as flooding.
Became necessary improvements and advances in the design of bridge
constructions with regard to the influence of the factor of the waterway. And due
to this accelerated development of technologies and methods of underwater
inspections of bridges.
In the USA there are about 603 000 bridges of various types and
categories. And the vast majority, 502 000, cross the rivers and other waterways.
And all they require constant care, supervision and periodic inspection
inspections of underwater parts of bridges. [7]
The main objectives when underwater inspection bridge constructions are:
1) provision of necessary state supports (foundations, piers, pylons) for
safety operation of the bridge
2) detection of various defects of underwater bridge elements
3) prevent any possible damage of structural elements of constructions
with the help of timely action
Underwater inspections set ourselves purposes to gather information on a
number of important questions:
1. Checking the existence of cavities (cracks) in stone / concrete masonry
2. Detection of damaged / missing elements of masonry
3. Detection of weathering of masonry
4. Checking the condition of joints and seams
5. Assessment to exposure of reinforcement and rebar
6. Traces of rust, chips, abrasive wear, crushing in concrete elements
7. Assessment of ground deformation in support parts bridge construction
8. Checking the status of the steel constructions (pipes, steel caisson and
screw piles, steel caissons) [3].
Fig.3 Examples of failures and defects of elements of the bridge
In order to avoid serious accidents on the bridges, it is extremely
important that after the inspection of the underwater parts of constructions, to
detect and assess accurately identified damage and defects (Fig.3). The reasons
for such violations can be of rules of manufacture of works, violations of
operating facilities and design errors [1].
Only highly skilled specialists should carry underwater inspections of
bridges. However, in practice there is a problem - when such events just need
the team of divers, who, however, have insufficient knowledge and experience
in civil engineering.
Diving works on the river is recommended in low-water period with a low
level of environmental pollution, and in good visibility.
Different methodology is used diving operations, depending on the
purposes set. In cases when must a large number of short dives and the main
requirement is the speed of action is applied, so-called, scuba diving: the diver is
equipped with autonomous device for air supply (Fig.4). Under adverse
conditions for inspections - high speed of flow of the river, pollution/water
turbidity, and if necessary, a long and detailed inspection, apply such
technologies diving, in which the diver is connected with a special cable with
equipment on the surface. They provide the diver with necessary quantity of air,
and also communication with his band [8].
There are norm and safety for divers:
1. The minimum age diver 18 years of age, maximum age of 45 years
(sometimes allowed to dive on small depth)
2. Fitness by doctor in last six months
3. Good physical condition, ability to withstand stress
4. Free from cardiac and ear problem
5. Not addicted to alcohol and excess smoking
6. Going special tests to work at the depth
7. Knowledge of special signals when diving
8. Ability to work in zero visibility conditions [3].
When underwater inspections of bridges divers always the issue of safety
of their life. And often limited to only team of divers is not possible, for
example, large depth of research, or
when environmental conditions when
it is impossible to adequately conduct
the underwater inspection of the
bridge. In such cases, it is logical to
use such special technology, as
different sonar and devices ROV
(remotely operated vehicle).
Also, these technologies in
Fig.4 Inspection diver of element of
some cases can apply well in advance
bridge support
of diving divers to collect information
on defects structures, the formation of
scour, acting on the support, and also
about the clusters of construction and other debris, which will facilitate and
ensure the safety of the divers. ROV’s devices can serve as a navigator, guiding
divers to certain areas.
One of the kinds of
technologies
of
underwater
inspections, available to inspectors
are hydroacoustic systems, or sonar
(Fig.5). Sonar (SOund Navigational
And Ranging - sound navigation
and ranging) uses sent and reflected
sound waves to detect underwater
objects and distance measurement.
Fig.5 Sonar device in action
This technology began to use a
fairly long time to determine the
depth of the watercourse, the
discovery of an object under water [8].
An example of the application and use of sonar technology is the situation
in may 2008 in the U.S. Midwest. In the same period fell significant
precipitation, which caused the rise level of a large number of rivers and
subsequent flooding. One of the most suffered from the flood was Iowa state.
The Government are seriously worried about the condition of the bridges on the
territory of the state in which the consequences of floods could be catastrophic.
With the rise of water level in the reservoir water penetrates through the gaps
between elements of the walls and saturates soil backfill, which increases its
disposal and may lead to irreversible deformation structures. Also at fluctuations
of water level in the reservoir occurs alternate wetting and drying of the surface
of the elements of the bridge that leads to the development of the corrosion
processes [2].
The use of divers at inspection of bridge supports, foundations and piers
in Iowa was excluded. The solution was found in the use of technology
«scanning sonar for underwater images areas near the bridge during the peak of
the flood, and further modeling of possible negative impacts of floods on the
construction of the bridge.
Ultimately, produced very good data and images for every bridge, the
scan was conducted with the use of sonar equipment «Kongberg Mesotech»
(Fig.6).
Fig.6 Images of underwater parts of the supports, received with the use of sonar
«Kongberg Mesotech».
It was confirmed that no bridge demanded immediate measures to
strengthen the security constructions, although in some cases, surveys require
further monitoring of the situation. [5]
Procedure underwater inspections require careful thorough planning. For
the choice of the appropriate method and necessary equipment is determined by
the place of inspection. The analysis of existing records from previous
inspections. Selection of team of divers.
Technology of underwater inspections of bridges is quite varied.
Depending on the need, apply sounding methods to control scour. To get an
overall picture of the status of concrete helps sclerometer. To determine rebar
location uses a magnetic recognizer rebar. When to the check uniformity of
filling and compaction of the concrete used ultrasound system. To measure the
thickness of the steel bridge elements often use ultrasonic thickness gauge.
Detection of cracks on the surface of parts of supports produced in the
framework of magnetic particle research. And for detection of internal defects
using radiography.
Anticipating the beginning of underwater inspection of bridge is
determined by the plan audits and inspections. Most often studied traces of the
consequences of scour the actions of the waterway on supports, the examination
of presence of cracks and other defects. Also check the general condition of
concrete to report significant chips, their size and location, they produce photo and video surveillance.
Based on the analysis of the survey results is constituted of the report of
the inspectors and divers, and after make decisions on elimination of defects, if
any, have been recorded.
For example. In the underwater inspection of the bridge has detected the
presence of defects of concrete piles (fatigue concrete composition or
deterioration frost resistance). The tender is announced for underwater works on
micro- concreting piles of the bridge.
The sequence of works can be divided into several stages:
1) initial inspection, filming future work places;
2) cleaning and surface preparation processed elements of bridge support;
3) evaluation of terms and cost of works;
4) getting work start, formwork/fixing worksheets;
5) micro-concreting [3].
In conclusion, would like to note that in our country were made first
major step in-depth studies and compilation of methods for the inspections of
bridges, including their underwater parts. This is largely due to the fact that the
age of some constructions calculated already many decades of years. Operators
began not only to monitoring to the bridges, and to fix the time, place, character
education, and development of a defect that had not been done [2]. And to
speed up this process, it is reasonable to get acquainted with methods of foreign
scientists and specialists on this issue.
Systematic and scientific aimed underwater exploration is very important
for the safe operation and management of bridge construction. Because a
considerable number of collapses and accidents occurring on bridges can be
avoided by timely conducting underwater inspection and examinations.
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