REHABCON IPS-2000-00063
ANNEX U
Application examples of RIM method
EC DG ENTR -C-2
Innovation and SME Programme
IPS-2000-0063
________________________________
REHABCON
Strategy for maintenance and
rehabilitation in concrete structures
________________________________
June 2004
ANNEX U Application examples of RIM method
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This annex includes two application examples of the Repair Index Method (RIM)
presented in Chapter 7 of the Manual between the case studies in the REHABCON
project:
Example 1: Strengthening and reparation of a reinforced concrete building using externally
bonded FRP and cathodic protection
Example 2: Strengthening and reparation of concrete piers at the Öland bridge
ANNEX U Application examples of RIM method
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Application example 1
STRENGTHENING AND REPARATION OF A REINFORCED
CONCRETE BUILDING USING EXTERNALLY BONDED FRP AND
CATHODIC PROTECTION
1
2
INTRODUCTION
JOB DESCRIPTION
2.1 Location and structural description
2.2 Initial situation: detected pathologies
3
SELECTED STRENGHTENING AND REPARATION SCHEME
4
PRESENT REPAIRED SITUATION
5
SELECTION OF THE BEST REPAIR OPTION FOLLOWING THE REPAIR INDEX
METHOD (RIM)
5.1 Aim
5.2 Reparation alternatives
5.3 Selection criteria
5.4 Evaluation of alternatives of solution
5.5 Conclusions
ANNEX U Application examples of RIM method
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1. INTRODUCTION
This case study is developed for the REHABCON project and the report describes the
inspection works, corrosion analysis and structural assessment carried out to determine the
extent of the structural pathologies of the building and the need of a strengthening and
reparation project.
Secondly, the selected reparation process is described and the present repaired situation of the
building is showed.
Finally, different reparation techniques are furtherly studied and compared in a normalised
evaluation matrix (following the Repair Index Method described in the paragraph 7.2. of the
Manual) in order to obtain which of the techniques is more suitable for this particular case.
2. JOB DESCRIPTION
2.1
LOCATION AND STRUCTURAL DESCRIPTION
The building is located in the city of San Sebastián in the north coast of Spain. The
construction belongs to the Public Administration Ministry and nowadays it is being used as
the seat of the Governmental Sub-delegation of Guipúzcoa.
The building was constructed in the mid 1950’s and designed for reinforced concrete.
Though no design drawings or schemes have been kept from that time. It holds four floors
plus the ground floor. And there is also a parking facility to be considered, placed in the
basement.
The core of the building is formed by a rectangular section (see Figure 1) of about 51 x 21 m,
while two irregular U-shaped bodies are attached to the main one at its edges. These lateral
bodies hold two floors each. (see Figure 2)
Figure 1
Building’s ground plan
ANNEX U Application examples of RIM method
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The main elements of the structure are square columns and beams which support an
unidirectional slab, formed by joists, ceramic cap vaults and a compression layer without any
wire mesh.
Figure 2
2.2
General views of the façade of the building
INITIAL SITUATION: DETECTED PATHOLOGIES
During the years 1997, 1998 and 2002 four different studies were carried out in the building.
The works undertaken comprised the following:
•
•
•
•
Detailed visual inspection of the building to determine current condition
Determination of the geometry and structural scheme
Corrosion study in order to detect active corrosion processes, register the corrosion
parameters and analyse the chloride content through chemical tests.
Structural assessment
All the studies followed the same scheme, but with different extensions and depths.
The first study was focused in the ceiling slab of the fourth floor, where important corrosion
damages in the steel reinforcement were detected, with the consequent loose of flexural
security. In this study, the presence of aggressive agents was highlighted and thus it was the
starting point for new studies. (see Figure 3)
ANNEX U Application examples of RIM method
Figure 3
5 (40)
Detected pathologies
The second one tried to determine the extent of the corrosion damages in the whole building,
especially in the areas exposed to high humidity levels.
The third and the four study completed the above ones and defined the rehabilitation
technique proposed for the fourth floor and assessed the whole structure to guarantee the
security level for new loads derived from the rehabilitation process, which included a new
heating system and a lift.
This case study is based on the results of the reparation works carried out after the
implementation of the recommendations of the four paper described.
The structural pathologies that were detected during the study period are summarized below:
1) Active corrosion processes
Corrosion damages in the steel reinforcement on the lower side were detected in a large
number of joists and beams. This damage was extended to the whole structure, but it was
mainly located in the slabs of the fourth floor.
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Corrosion was also detected in the columns in the basement and in the columns exposed to the
environment outside of the building.
In order to determine the origin of these phenomena some studies where taken in different
points of the structure. Chemical test to determine the content in chlorides and sulphates
revealed:
•
Most of the joists of the slabs were constructed using a concrete with high chloride
concentrations. These chlorides were added during the concreting phase.
•
Around 67 % of the beams presented also important chloride concentrations, which
were supposed to have the same origin as the one from the joists.
•
In spite of this, columns did not seem to contain chlorides from their execution
processes, moreover, it seemed that the chloride concentrations detected were caused
by the effect of the external conditions, like a high salinity rate.
The study of the carbonation depth (Figure 4) revealed that the concrete was not anymore
capable of passivating the steel, since the carbonation depth presented values around 45-50
mm. Therefore, these results indicated that the quality of the concrete of the structure was not
good, with a high porosity.
Figure 4
Carbonation depth
Those high chloride concentrations, added to water filtrations and high humidity detected in
some areas, showed a clear relation with corrosion processes in joists and beams. (Figure 5)
ANNEX U Application examples of RIM method
Figure 5
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Corrosion processes in joints and beams
To support this theory, it shall be stated that the steel bars placed on the lower side of the
joists presented much more widely spread corrosion processes than the bars placed on the
upper compression layer, being both parts exposed to the same levels of water filtrations. The
reason for this seems to be that the concrete of the joists presented a higher chloride
concentration, added to the effect of humidity condensation produced in the inner side of the
slab.
The primary cause for corrosion and humidity damages on the columns (Figure 6) in the
basements of the building were the frequent floodings.
Figure 6
Corrosion and humidity damages on the columns
The columns exposed to the environment outside of the building presented in some cases
active corrosion processes that lead to longitudinal cracks along the columns.
Those corrosion damages where acknowledged when corrosion measurements (Figure 7)
were carried out. Parameters as the corrosion intensity and electrical resistivity showed a clear
relation with active corrosion processes.
ANNEX U Application examples of RIM method
Figure 7
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Corrosion measurements
Therefore, those areas were suffering active corrosion of their steel reinforcement, which
caused a loose of bearing capability and threatened the durability and structural stability of the
building.
2) Cracking
A large amount of beams presented shrinkage cracks and also cracks caused by stresses
produced under service situations. Those cracks do not revealed a failure in the bearing
capability of the structure, but the lack of additional superficial steel bars for serviceability.
Figure 8
Cracks in beams
ANNEX U Application examples of RIM method
3. SELECTED
SCHEME
STRENGHTENING
9 (40)
AND
REPARATION
In the previous chapter, the damages of structure have been described. In the following lines,
the selected repair option is extensively described, indicating the materials used, processes of
execution and controls followed.
First of all, the structural elements subjected to reparation were determined. In the following
paragraphs the repair actions carried out in each element are listed:
Slabs:
The joists of the slabs presenting a loss of more than 1 mm in the diameter of their lower steel
reinforcement were strengthened with Carbon Fibre Reinforced Polymer (FRP) laminates,
bonded to their lower surface.
All the joists exposed to the environment outside of the building were furthermore protected
against corrosion with cathodic protection using a titanium wire mesh.
And all the areas presenting damages on the concrete surface were repaired with cementitious
mortar (H>25).
Beams:
Those reparation processes were also applied to some of the beams, mostly in order to
strengthen them against negative flexural stresses. Therefore the FRP laminates were mainly
bonded to the upper surface of the beams.
The cathodic protection using a titanium wire mesh was also applied to the beams exposed to
the environment outside of the building.
Columns:
Some of columns were strengthened, following the recommendations after the assessment,
with a concrete section enlargement.
The columns placed in the basement were also repaired using a concrete section enlargement.
This measure had nothing to do with strength problems, but was actually intended to avoid the
humidity caused by water filtrations from the ground, that lead to the corrosion of the steel
reinforcement of these columns. The new concrete surface was treated with a waterproof
material.
4. PRESENT REPAIRED SITUATION
After the execution of the works (Figure 9), the present situation is as follows, according to a
visual inspection:
ANNEX U Application examples of RIM method
•
•
10 (40)
No debonding of FRP sheets is detected. Nor in the edges neither in the middle any crack
can be visually appreciated.
Patching seems to be performing well. No crack between concrete surface and repair
mortar can be visually detected.
Figure 9
Situation after execution of works
5. SELECTION OF THE BEST REPAIR OPTION FOLLOWING
THE REPAIR INDEX METHOD (RIM)
5.1
AIM
The main objective is to select the best repair option following the alternative method in both
cases:
ƒ
Repair of the damages described in section 2.2, meaning the strengthening of the
structural elements that did not hold enough bearing capacity and the long term
protection against corrosion for the areas exposed to aggressive environmental
conditions.
ƒ
Protection of the concrete of the structure, meaning the application of techniques and
systems that prevent and delay the damages and maximize the service life with the
minimum cost.
ANNEX U Application examples of RIM method
5.2
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REPARATION ALTERNATIVES
The reparation alternatives are divided in two different groups according to the particular aim
they have: protection methods and reinforcement methods.
Therefore, the analysed techniques are:
1. Protection systems
Four different alternatives were considered to protect the concrete elements from corrosion
processes:
•
•
•
•
Patching
Cathodic protection
Chloride extraction
Anticarbonation coating
2. Strengthening scheme
Three different alternatives are considered to repair of the reinforced concrete damaged in
structural elements (beams, slabs and columns):
•
•
•
Section enlargement
Steel bonded plates
CFRP bonding
5.3
SELECTION CRITERIA
The selection criteria is applied to the methods described above and the evaluation matrixes
are presented in section 5.4 of this annex.
For an extensive description of the selection criteria please refer to section 7.2 of the Manual.
Here, the criteria used for the evaluation will just be listed:
Service life and durability
•
•
•
•
•
•
Normal service life of the repair
Accidental attacks
Exposure class
Feasibility of post-repair monitoring
Disturbance after repair
Compatibility with additional repair methods
Structural stability and safety
•
•
•
Structural consequences of failure
Failure type
Experience
ANNEX U Application examples of RIM method
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Execution of work
•
•
•
•
Execution control
Execution difficulty
Disturbance during repair
Safety of workers and users
Environmental, health and sustainabiliy
•
•
•
Environmental effects
Resources consumption
Safety of users
Economy
•
•
•
•
•
•
•
Direct cost
Maintenance cost
Preparation of substrate
Repair period
Access tools
Distribution of damages
Extension of damages
Aesthetics
•
•
Aesthetic contribution
Variability of aesthetics
5.4
EVALUATION OF ALTERNATIVES OF SOLUTION
Two main different groups of repairing methods that are considered, according to the detected
pathologies of the building.
On one hand, the active corrosion processes in beams and slabs, which require a specific
treatment and on the other hand the increasing of the bearing capacity of the whole structure
requires another kind of repairing methods. It should be remarked that both groups could
interact and thus a couple of solutions might be optimal in comparison with the rest.
Firstly, the best solution of each group will be chosen and afterwards it will be studied if the
interaction between those optimal alternatives is positive or not. This could lead to a change
of the selected repairing methods.
Finally, the possibility of analysing both groups globally will be pointed out, which means
studying in the evaluation matrixes all the possible couples as a single element. This way it
will be possible to obtain the optimal couple of repairing methods for this particular case.
ANNEX U Application examples of RIM method
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1. Protection system
Three different alternatives are considered to protect the concrete elements from corrosion
processes:
•
•
•
Patching
Cathodic protection (CP)
Chloride extraction (CE)
The anticarbonation coating is not evaluated because it would be impossible to achieve an
efficient corrosion protection in this particular case, due to the high content of chlorides in the
concrete mass, which could lead to inner corrosion.
SELECTION CRITERIA
SERVICE LIFE AND DURABILITY
The post-repair monitoring of cathodic protection is quite easy, thanks to a voltmeter that
registers all the relevant measures to control if the system is working properly. The failure of
patching or chloride extraction can only be discovered when the active corrosion processes
are visible on the concrete surface. On the whole, cathodic protection receives the higher
punctuation for this criteria.
Cathodic protection has a very good long term performance (around 100 years) while the
service life of chloride extraction is not entirely defined.
It shall be considered that the high chloride content in the concrete mass could lead to active
corrosion processes in spite of the patching repair under high humidity conditions. For this
reason the patching receives lower punctuations for the indicators of normal service life and
exposure class in this case.
The risk of an accidental attack is the same for all the alternatives.
Disturbances after repair are also minimum, even if cathodic protection involves periodical
inspections of a qualified worker to verify that the system is working properly.
It shall be stated that cathodic protection is incompatible with metallic reinforcements. Special
care shall be taken to select repair mortars that conduct electricity so that the circuit for the
cathodic protection may work without any interference.
All these issues remark the fact that the interaction between protection and reinforcing
methods is an important factor of decision.
STRUCTURAL STABILITY AND SAFETY
Structural consequences of failure are moderate for all the analysed cases, since the lack of an
protection against corrosion would have just mid or long term effects.
ANNEX U Application examples of RIM method
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Chloride extraction is a repair method that has been barely applied in Spain, therefore there
are few previous experiences recorded. Oppositely, previous experiences for CP and patching
are well known.
EXECUTION
Regarding execution difficulty CP and CE require experienced applicators.
Disturbances during the repair itself are equivalent (irrelevant) for the three methods, because
the building was closed till the works were over.
ECONOMY
Considering that the chloride extraction is a very specific method, only applied by a few
companies in Europe, this is the most expensive option.
Maintenance cost of patching and chloride extraction is low while cathodic protection
requires a continuous maintenance, but this maintenance is quite easy and not much cost
demanding.
The preparation of the substrate would be almost equivalent for all three methods, but for the
patching it is needed to reach the steel reinforcement and apply an anticorrosion coating on it.
The repair period is long for CP and Chloride extraction requires some extra time to work
appropriately. If the chloride extraction is carried out too fast, there is a risk of brittling the
steel reinforcement because of a H+ migration.
Access tools are the same for all of them but the distribution of damages has a much greater
influence for the patching since this is a applied at specific locations, depending on the
damaged areas. It is also important to remark that the amount of works to carry out on the
surfaces of the concrete elements is smaller for the chloride extraction which should lead to a
saving in the cost of access tools.
ENVIROMENT HEALTH AND SUSTAINABILITY
Cathodic protection is the best option according to this criteria. It has reduced environmental
effects, low resources consumption, and does not impose any threat to workers or users.
AESTHETICS
On one hand all the methods can be applied without changing the shape of the structural
elements and on the other none of them could improve the visual appearance of the mentioned
elements.
Therefore all the methods receive the same punctuation in this field.
WEIGHTS
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The weights applied to the different selection criteria to get the global repair index have been
changed for the evaluation of the best protection system.
Considering that the main aim of the protection system is the long term durability of the
structural elements, and not the reinforcement or bearing capacity of the structure, the criteria
of service life should have the bigger weight.
Following this idea, the weight for structural stability and safety has been reduced fro the 30
% to the 20 % (it will actually be considered as the most important criteria for the
reinforcement methods) and the weight for the economy has been reduced from the 20 % to
the 10 %, while the weight for service life was increased till the 40 % of the whole.
ANNEX U Application examples of RIM method
Table 1
16 (40)
RIM application for protection systems
Requirement
SERVICE LIFE &
DURABILITY
STRUCTURAL
STABILITY &
SAFETY
EXECUTION OF
WORK
Indicators
Normal service life of the repair
Accidental attacks
Exposure class
Feasibility of post-repair
monitoring
Disturbance (after repair)
Compatibility with additional
repair methods
Rser
Structural consequences of
failure
Failure type
Experience
Rstr
Execution control
Protection system
Cathodic
Chloride
Patching
Protection
extraction
4
4
3
2
4
2
3
4
3
4
2
2
3
4
4
3
4
4
3.5
3
3.3
3
3
3
4
3.5
4
4
3.5
3
1
2
1
Execution difficulty
2
3
1
Disturbance (during repair)
3
3
3
Safety of workers and users
4
4
4
3.2
3
3.5
3
2.5
3
2
3
3
4
3
2
3
3
2
4
3.3
4
3
4
3
4
3.3
1
3
3
1
2
2
3
4
2
2.6
1
4
2.5
2
4
3.1
1
4
2.5
1
2
2.4
1
4
2.5
3.21
3.20
2.73
Rexe
Environmental effects
ENVIRONMENT,
Resources consumption
HEALTH &
SUSTAINABILITY Safety of users
Renv
Direct costs
Maintenance cost
Preparation of substrate
Repair period
ECONOMY
Access tools (auxiliary
equipment)
Distribution of damages
Extension of damages
Reco
Aesthetic contribution
AESTHETICS
Variability of aesthetics
Raes
REPAIR INDEX (RI)
Repair index =( 0,3 x Service life) + ( 0,2 x Structural stability ) + ( 0,2 x Execution) +
( 0,1 x Environment) + (0,1 x economy ) + (0,1 x Aesthetics)
Results showed in the Table 1 confirm that PATCHNIG is the best protection system
option.
ANNEX U Application examples of RIM method
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2. Strengthening system for beams and slabs/ columns
Three different alternatives are considered to strengthen the structural elements with low
bearing capacity:
•
•
•
Section enlargement
Steel bonded plates
CFRP bonding
Those repair methods should be applied to strengthen slabs, beams and columns, but the
selection criteria for those diverse elements were different. Therefore two different evaluation
matrixes are shown, one is aimed to obtain the optimal repair method for the slabs and beams
and other one for the columns.
SELECTION CRITERIA
STRUCTURAL STABILITY AND SAFETY
It shall also be considered that this method has been barely used in Spain for this purpose,
therefore few experiences are known.
The failure type for the CFRP is brittle but since the laminates will be anchored to the
structural elements in the slabs and beams, the punctuation for this criteria is better for
slabs/beams than for columns.
SERVICE LIFE
The risk of accidental attacks is the same for the three analysed methods, since they will all be
protected against fire.
Considering the marine environment added to the presence of chlorides in the concrete mass
in this case study, the section enlargement and steel bonded plates may be problematic
because they involve the addition of steel, while the CFRP holds a very good performance
against chemical attacks.
It is important to consider that CFRP reinforcements could be vulnerable to fire if they would
not have a protecting cover.
The post-repair monitoring of the CFRP is quite difficult, because it will be covered by a
protection layer against fire damages, but it is possible to monitor it with NDT. This is the
reason why it receives the lower punctuation in this field.
Considering the disturbance after the repair works, it shall be remarked that the enlarging of
the section of the slabs and beams would lead to a lowering of the ceiling height.
Referring to the compatibility with additional repair methods it is important to consider that
the steel plates could conduct electricity and make the cathodic protection of the slabs and
beams fail. And it may also be stated that it is quite difficult to apply additional repair
ANNEX U Application examples of RIM method
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methods once the CFRP sheets are placed on the structural elements, since it would be
necessary to take them away first.
EXECUTION
It is easy to control the functioning of CFRP and repair it, if necessary.
Referred to the execution difficulty, the enlarging process comprises several phases and thus
it is quite complex. The weight of the steel bonded plates is also a factor to be taken into
account which makes the CFRP the most suitable method from this point of view. Problems
may arise when it comes to use it for the reinforcement of square columns, because the
corners of the columns could act as points with high stress concentrations. Therefore it is
recommended to round them.
The building was closed during the repair works, therefore the disturbance was irrelevant for
all the three methods.
ECONOMY
The direct cost for the CFRP differs clearly if it is applied for the slabs/beams or columns,
because the amount of materials needed is much bigger for the reinforcement of the columns
and the procedure is more difficult, for example corners should be rounded.
The maintenance cost for the steel bonded plates and the CFRP is bigger than the one for the
enlarging of the cross section, because it is needed to maintain the protection cover against
fire, while the enlarged concrete section will just need a cover painting.
It is also relevant to state that the preparation of the substrate has already been carried out
during the cathodic protection for the beams/slabs, therefore it will not cause additional costs
for the CFRP method. Oppositely, it will be quite difficult to achieve a smooth surface in the
columns to bond the CFRP sheets adequately.
Generally strengthening by means CFRP involves lower repair periods.
The extension and distribution of damages are not considered in these evaluation matrixes,
because these strengthening methods are not locally applied, moreover they will cover all the
damaged elements.
ENVIROMENTAL HEALTH AND SUSTAINBILITY
CFRP bonding causes none or little environmental impacts and the resources consumption is
small compared to the other alternatives. Furthermore it is safer for workers and users.
The steel plates are quite heavy, therefore the safety of the workers could be threatened while
placing the plates in the upper positions.
It is also remarkable that some of the resins and mortars used in all the studied methods are
extremely toxic and their disposals should be handled carefully.
ANNEX U Application examples of RIM method
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AESTHETICS
CFRP is hardly visible after application. So it does not deteriorate the aesthetics in any
aspects. The section enlargement is a very intrusive method as it greatly affects the structure
visually.
ANNEX U Application examples of RIM method
Table 2
20 (40)
RIM application for reinforcement systems in slabs and beams
Requirement
SERVICE LIFE &
DURABILITY
STRUCTURAL
STABILITY &
SAFETY
EXECUTION OF
WORK
Indicators
Normal service life of the repair
Accidental attacks
Exposure class
Feasibility of post-repair
monitoring
Disturbance (after repair)
Compatibility with additional
repair methods
Rser
Structural consequences of
failure
Failure type
Experience
Rstr
Execution control
Reinforcement systems
SLABS AND BEAMS
Steel bonded
Enlarging
Carbon
plates
cross section
fibre
3
4
2
3
4
2
2
4
4
3
3
2
4
2
4
2
4
3
3
3
3.1
1
1
1
2
4
2.3
3
4
4
3
3
2
4
2.3
3
Execution difficulty
Disturbance (during repair)
2
4
2
4
4
4
Safety of workers and users
2
4
4
2.7
2
3.2
2
3.75
2
3
3
4
3
2.6
2
2
3
2
3
2.6
3
3
3
2
3
2
2
3
2.2
1
3
2
2.6
1
2
1.5
3.4
1
4
2.5
2.4
2.7
3.0
Rexe
Environmental effects
ENVIRONMENT,
Resources consumption
HEALTH &
SUSTAINABILITY Safety of users
Renv
Direct costs
Maintenance cost
Preparation of substrate
Repair period
ECONOMY
Access tools (auxiliary
equipment)
Distribution of damages
Extension of damages
Reco
Aesthetic contribution
AESTHETICS
Variability of aesthetics
Raes
REPAIR INDEX (RI)
4
2
4
4
Repair index =( 0,2 x Service life) + ( 0,2 x Structural stability ) + ( 0,1 x Execution) +
( 0,1 x Environment) + (0,3 x economy ) + (0,1 x Aesthetics)
Results showed in the Table 2 confirm that CFRP BONDING is the best strengthening
system option for the SLABS & BEAMS.
ANNEX U Application examples of RIM method
Table 3
21 (40)
RIM application for reinforcement systems in columns
Requirement
SERVICE LIFE &
DURABILITY
STRUCTURAL
STABILITY &
SAFETY
EXECUTION OF
WORK
Indicators
Normal service life of the repair
Accidental attacks
Exposure class
Feasibility of post-repair
monitoring
Disturbance (after repair)
Compatibility with additional
repair methods
Rser
Structural consequences of
failure
Failure type
Experience
Rstr
Execution control
Reinforcement systems
COLUMNS
Steel bonded
Enlarging
Carbon
plates
cross section
fibre
3
4
2
3
4
2
2
4
4
3
3
2
4
4
4
2
4
3
3
3.3
3.1
1
1
1
2
4
2.3
3
4
4
3
3
1
2
1.3
3
Execution difficulty
2
2
3
Disturbance (during repair)
4
4
4
Safety of workers and users
Rexe
Environmental effects
ENVIRONMENT,
Resources consumption
HEALTH &
SUSTAINABILITY Safety of users
Renv
Direct costs
Maintenance cost
Preparation of substrate
Repair period
ECONOMY
Access tools (auxiliary
equipment)
Distribution of damages
Extension of damages
Reco
Aesthetic contribution
AESTHETICS
Variability of aesthetics
Raes
REPAIR INDEX (RI)
2
4
4
2.7
2
3.2
2
3.5
2
3
3
3
3
2.6
2
2
3
2
3
2.6
3
3
3
2
3
2.6
2
2
1
3
3
3
4
2.4
1
3
2
2.8
1
3
2
2.4
1
4
2.5
2.5
2.8
2.4
Repair index =( 0,2 x Service life) + ( 0,2 x Structural stability ) + ( 0,1 x Execution) +
( 0,1 x Environment) + (0,3 x economy ) + (0,1 x Aesthetics)
Results showed in the Table 3 confirm that SECTION ENLARGEMENT is the best
strengthening system option for the COLUMNS.
ANNEX U Application examples of RIM method
5.5
22 (40)
CONCLUSIONS
Following the Repair Index Method (RIM) described in section 7.2 of the Manual, the optimal
solutions for this specific case study are:
•
•
Protection system: Cathodic protection
Strengthening scheme: Section enlargement for the columns and CFRP bonding
for the slabs and beams.
This is the optimal couple considered, but special care should be taken to avoid any contact
between the titanium wire mesh of the cathodic protection and the CFRP laminates, cause the
laminates could conduct electricity and damage the functioning of the protection system. The
mortar that should be applied between both methods, could be therefore used to prepare the
regular surface (pore free) that is better for the CFRP laminates.
Since there are two different groups of repairing methods considered, it should be remarked
that both groups could interact or disturb each other, and thus a couple of solutions might be
optimal in comparison with the rest.
This could lead to a change of the selected repairing methods, taking into account that they
were chosen as best solutions inside of one single group, without considering the interaction
with the other.
It shall be pointed out the possibility of analysing both groups globally, which means studying
in the evaluation matrixes all the possible couples as a single element. This way it will be
possible to obtain the optimal couple.
As an example for this interactions it can be stated that cathodic protection is incompatible
with metallic reinforcements while surface coating may reduce the adherence between the
structure and future reinforcements.
It is also important to consider the structural element were the repair method is going to be
applied as a selection criteria. In this case study for instance, the optimal strengthening
scheme is different for the columns than for the joists and beams.
ANNEX U Application examples of RIM method
23 (40)
Application example 2
STRENGTHENING AND REPARATION OF CONCRETE PIERS AT
THE ÖLAND BRIDGE
1
INTRODUCTION
2
JOB DESCRIPTION
2.1 Location and structural description, (1) (2)
2.2 Damage situation, (3) (4)
2.3 Assessment, (3) (4) (7) (8) (10)
2.4 General Requirements, (5) (6)
2.5 Detailed requirements, (5) (6)
3.
SELECTED STRENGTHENING AND REPAIR SCHEME
3.1 Technical options, (7)
3.2 Repair Methods, (7) (9) (11) (12)
3.2.1. Method A
3.2.2. Method B
3.2.3. Method C
4.
SELECTION OF THE BEST REPAIR OPTION FOLLOWING THE REPAIR INDEX
METHOD (RIM)
4.1 Service life and durability
4.2 Structural stability and safety
4.3 Execution of work
4.4 Environment, health and sustainability
4.5 Economy
4.6 Aesthetics
4.7 Conclusions
REFERENCES
ANNEX U Application examples of RIM method
24 (40)
INTRODUCTION
This case study aims to exemplify the application of the Repair Index Method, RIM,
described in paragraph 7.2 of the Manual.
1. JOB DESCRIPTION
2.1
LOCATION AND STRUCTURAL DESCRIPTION, (1) (2)
The Öland Bridge is situated in the southeastern part of Sweden and is crossing the Kalmar
Sound between the mainland and the island of Öland. Since the 1920s there has been plans
and investigations about replacing the ferry services with a permanent bridge. The issue was
subject to a growing importance due to depopulation of the agricultural countryside and
increasing tourist traffic in summertime on the island of Öland. Every summer in recent years
close to a million tourists have visited Öland to spend their vacation in a beautiful landscape,
rich in sunshine and with little rain.
In November 1966 the Swedish Parliament decided to build the bridge. Construction work
started in 1968 and the bridge was completed and opened for traffic in September 1972.
With an overall length of 6 072 m and 156 piers, the Öland Bridge for many years was known
as the longest bridge in Europe. The bridge can be divided in three parts: the high-bridge over
the navigation channel and the two approach bridges on the mainland side and the Öland side.
The high-bridge is designed as a cantilever-built box girder bridge (freivorbau) of prestressed
concrete with spans 130 m. In the span over the navigation channel the clearance over the
water surface is 36 m on a width of 80 m.
The approach bridges have a length of 795 m on the mainland side and 4 355 m on the Öland
side. These bridges consist of non-tensioned reinforced concrete beams having 23 and 124
spans respectively. The spans are approx. 35 m long and the maximum distance between
expansion joints is approx. 560 m, equivalent to 16 spans. The beams are of I-section and 2.7
metres high. Roadway slab and beams were cast in place simultaneously with the aid of
travelling formwork. See Figure 1.
Most of the concrete was supplied from floating concrete mixing plants. Mainly dredgers
carried out excavation work for the piers. Working jack-up platforms were used for pile
works, sheet pile driving and casting. Roughly one-third of the piers rest on concrete piles and
the other on slap foundations on moraine. Most of the pier slab foundations are cast using
underwater concrete.
The piers have a solid cross section of concrete, 2.0*5.0 m with chamfered corners (0.5*0.5
m) and on the top a yoke-beam supporting the bearings and the loads from the bridge deck.
The height of the piers is varying. Maximum depth below the seawater surface is approx 8
metres and the height above the water surface varies from 3 to 15 metres.
This case-study report deals with the repair of 105 piers, during the period from 1990 to 1995,
located on the approach bridge on the Öland side.
ANNEX U Application examples of RIM method
25 (40)
ANNEX U Application examples of RIM method
2.2
26 (40)
DAMAGE SITUATION, (3) (4)
The first damages to the piers were observed already during the construction period. Cracks in
the top of the yoke-beams appeared as a result of inappropriate reinforcement design.
Afterwards, some of the piers have been repaired in a running restoration program.
At the beginning of the eighties damages to the pier columns were detected as well. These
damages were mostly concentrated to the area around the water surface in the splash zone.
The concrete surface had started to deteriorate, which could be seen as spalling of the
concrete cover and rusty reinforcement bars. In addition, mechanical wear from the icepressure had made the damages worse.
Later on, measurements showed very high chloride concentration in the splash zone and in
parts of the pier located as high as 3-4 metres above the water surface and a beginning
corrosion on the reinforcement bars.
But worse was to come, when severe corrosion on reinforcement bars close to the bottom slap
were detected. On some piers a great deal of the steel area was missing. These facts were
rather alarming and unexpected. At that time, it was thought that reinforcement deep below
the water surface and without access to oxygen would not be able to corrode to such a degree.
2.3
ASSESSMENT, (3) (4) (7) (8) (10)
Many different investigations have been executed to determine the cause of the damages.
The result of the investigations can be summarised as follows:
Primary cause of damage
The primary cause of the damage is supposed to be high porosity and insufficient
permeability in the concrete. The insufficient permeability has allowed water and chlorides to
penetrate the concrete cover and then released corrosion on the steel bars and subsequent
degradation. Laboratory tests have also indicated that repeated drying and drenching in the
splash zone cause capillary transport of chlorides. Therefore, high concentration of chlorides
is possible on areas located on a high level above the water surface as well.
The insufficient permeability is a consequence of many combined effects due to factors as
choice of material, concrete mixes and workmanship. In this case the following have been
stated:
•
Cement: In a comparative thick concrete structure as in this case, a low heat
generating type of cement would be preferable instead of ordinary Portland cement.
•
Aggregates: Laboratory tests have shown that aggregates delivered from Öland are
more porous than normal aggregates from the mainland.
•
Water: Brackish water from the Kalmar Sound has been used for concrete mixes.
ANNEX U Application examples of RIM method
27 (40)
•
Concrete mixes: The water-cement ratio has been too high. Cement content and the
test criteria of “watertight concrete” are insufficient. The weighing arrangement of
material in the concrete batching plant has been defective and unreliable.
•
Workmanship: Insufficient compaction by vibrators related to the rate of placing
concrete in the formwork. Early dismantling of formwork with subsequent
temperature shock to the concrete surface. Insufficient curing procedure and
protection.
Factors mentioned above have more or less influence to the permeability. The relative
significance of unfavourable influence is summarised in the list shown in Table 1.
Table 1. Significance of unfavourable influence
Factor
type of cement
type of aggregate
Cl-content in water for mixes
w/c radio
compaction
early dismantling of formwork
curing procedure
Relative significance
moderate
moderate
low
high
high
high
moderate
In addition to the primary causes (inappropriate material chose and workmanship), some
design criterions probably have influenced to the service life in a negative way:
2.4
•
The bridge deck ought to be placed at a higher level. Consequently, the yoke-beams
had not been exposed to salt-water splash.
•
The concrete cover ought to be thicker.
•
The detailed design of reinforcement in the yoke-beams is not very suitable. The
distribution of the reinforcement bars does not fit to the actual distribution of the
tensile stresses in the upper part of the beam.
GENERAL REQUIREMENTS, (5) (6)
General requirements for the repair work associated to the bridge can be summarised as
follows:
Service life:
Detailed requirements regarding formwork, concrete mix, concrete casting and curing etc are
given by the client. The intention is, that the requirements shall ensure the service life of the
structures during at least 75 to 100 years.
Strength:
General design loads for bridges shall be assumed.
The ice pressure design value shall be the same as for the original bridge (125 tons/m)
Detailed design shall fulfil requirements in valid official structural codes.
ANNEX U Application examples of RIM method
28 (40)
Execution:
During the almost 20 years that the Öland Bridge had been in service, it has become an
obvious necessity. The entire region is depending on a functional link between Öland and the
mainland and traffic obstacles have to be minimized. Ice, wave and wind conditions on the
site are well known as very severe and interruptions in the construction work have to be
considered. The seawater is normally frozen from January to Mars. As a consequence, the
client has set out the maximum construction time to five years.
Traffic lanes have to be centred to the middle of the bridge in order to decrease loads on the
yoke-beams during the repair work. Speed reduction during concrete casting and curing is
also prescribed. Boat traffic in the area around this part of the bridge is slight and limited
summertime to very small boats.
Accessibility to the piers from the bridge deck is restricted. Material has to be shipped to each
pier by boat. Exceptions are concrete deliveries, which can be pumped from the bridge deck
and personnel transports by bus. Temporary loads on the bearings from construction
equipment are limited to 20 tons.
Concrete mixes, reinforcement and workmanship shall fulfil requirements in valid official
codes.
Environment:
Safety and health are given priority to the workers on the working platforms and in the
cofferdams as well to the road-users on the bridge deck.
2.5
DETAILED REQUIREMENTS, (5) (6)
Concrete: K40, low heat generating cement, 420 kg cement per m3, w/c radio < 0.40,
aggregate size max 18 mm, air content 5.5 %.
Rate of placing concrete < 0.6 m/h
Reinforcement Ks40, concrete cover 60 mm.
Formwork shall be without any need of form-ties. Form panels shall be provided with a
special textile and tiny holes to let excess water and entrapped air bleeding out.
All concrete shall be compacted by use of internal vibrators during 500-600 sek/m3.
Curing shall continue until the temperature in the new concrete has fallen and is not more than
5 oC higher than the temperature of the old concrete or surrounding air. After dismantling of
the formwork, surfaces shall be protected and not exposed to seawater until the compression
strength has achieved 28 MPa.
Concrete surfaces above the water level shall be treated with a protective coating to avoid
chloride and water penetration.
ANNEX U Application examples of RIM method
3
SELECTED STRENGTHENING AND REPAIR SCHEME
3.1
TECHNICAL OPTIONS, (7)
29 (40)
Considering the facts about the damages, causes of damages and present structural strength
and safety of the piers, three main repair options can be outlined:
1. Reparation of damages in the splash zone and actions to stop or reduce further
degradation. (Structural strength is not crucial in this section of the piers).
2. Strengthening of the reinforcement in the lower parts of the pier columns, including
reinforcement in the construction joint to the foundation. (Applicable only on piers
with the upper side of the foundation lower than –4.0. Horizontal loads from the
bridge deck and ice pressure are dominating. As an assumption, the designer shall take
into account a reduction of 50% of the tensile strength capacity in the existing
reinforcement).
3. Strengthening of the yoke-beams. (This is a desirable option and has been established
gradually. Vertical loads from the bridge deck are dominating).
During the autumn of 1988, three construction companies performed test-repairs on four
piers. Experiences and results from this work (see Method A and B in section 3.2) have in the
time that followed been analysed and improved to the final solution (see Method C in section
3.2).
3.2
3.2.1.
REPAIR METHODS, (7) (9) (11) (12)
Method A
Method A is shown in Figure 2. In the initial stage, this method was applicable only on piers
with the upper side of the foundation higher than –4.0 and consequently complies only with
the requirement in option 1 above. Later, the method was revised and improved with
additional reinforcement to meet the requirements in option 2 and 3 as well. Method A is
tested on one pier only, nr 142.
Between the levels -2.0 and +2.0 (nevertheless up to that height, wherever the chloride
concentration is not higher than 0.5 % close to the reinforcement bars) all concrete are
removed by water-jet equipment. In this case, concrete removal had to be done to the full
height of the pier including the yoke-beam. The depth of the concrete removal shall be at least
100 mm but not more than 150 mm.
Existing undamaged reinforcement bars are left in place and corroded bars are cleaned and
supplemented to the same quantity as the original structure. Vertical reinforcement is
executed to fulfil the requirements in option 2. The reinforcement consists of unstressed VSLcables installed in bored holes from the top of the pier and anchored in the foundation.
Horizontal post-tensioned GEWI-bars in the yoke-beam fulfil the requirements in option 3.
Cathodic protection was established from –1.0 to the top of the pier and is separated in three
zones. The cathodic protection consists of Ferex-100-S flexible anode strands fasten in loops
to the rebar with standard plastic cleats and clips. The intention was to install an electrolytic
ANNEX U Application examples of RIM method
30 (40)
cathodic protection system for the lower parts of the pier as well, but this was abandoned on
this pier.
New concrete cover was cast in place in dry conditions (casting below the water surface was
not allowed) in such a way that the new surface is 50 mm enlarged. Concrete is cooled by
cold water circulating in steel pipes during the curing process.
ANNEX U Application examples of RIM method
3.2.2
31 (40)
Method B
Method B is shown in Figure 3. The method B complies with the requirements in option 1 and
2. Later on, the method was revised and improved with additional reinforcement to meet the
requirement in option 3 in same way as method A. The method B is tested on three piers, nr
134, 136, and 143.
A new concrete encasement is cast around the old pier. The encasement is cast in dry
conditions and designed to take care of all actual loads alone. The wall thickness is 400 mm.
The loads from the bearings on the yoke-beam are transformed to the encasement by means of
dowels. The dowels are placed on the pier-shaft in an area just below the yoke-beam. Above
and in the dowel area, concrete are removed by water-jet equipment (max 150 mm, but min
100 mm). Concrete surfaces below the dowel area are cleaned from loose and damaged
concrete.
Existing undamaged reinforcement bars are left in place and corroded bars are cleaned.
Additional reinforcement are erected and completed before casting work starts. Contact
between old rebars and reinforcement bars in the new encasement may not occur. Horizontal
post-tensioned reinforcement in the yoke-beam fulfils the requirements in option 3 and
consists of four threaded GEWI-bars (diameter 50 mm).
Cathodic protection systems were established from –1.0 to the top of the piers and are
separated in three zones. The cathodic protection consists of Ferex-100-S flexible anode
strands on two piers and a titanium anode wire mesh on the third. Cathodic protection systems
for the lower parts of the piers are arranged by use of inert magnetite anodes supplied with
continuous current and placed on the foundations.
Concrete is cooled by cold water circulating in steel pipes on one pier (nr 142). On the other
two, special cooling arrangement was not performed, because the temperature conditions were
favourable.
ANNEX U Application examples of RIM method
32 (40)
ANNEX U Application examples of RIM method
3.2.3
33 (40)
Method C
Method C is shown in Figure 4. Method C considers all aspects in the main repair options 1, 2
and 3. This is the final repair method and is executed on 105 piers.
Concrete surfaces are cleaned from loose and damage concrete as well as shells and sea-grass.
A manually operated water-jet nozzle executes cleaning and the water pressure is rather low.
A new concrete encasement is cast around the old pier. The encasement is cast in dry
conditions and designed to take care of all actual loads alone. The wall thickness is 400-500
mm. The loads from the bearings are transformed through the yoke-beam to the encasement
via two special supporting areas. The supporting areas are located underneath the yoke-beam
and are clearly defined inside a ring of injection-hoses. The supporting areas are injected by
epoxy resin half a year at the earliest after the encasement has been cast.
A soft and watertight sliding layer covers the whole surface of the old pier except the
supporting areas. The sliding layer allows small movements between the old pier and the new
encasement and prevents early-age cracking during cooling and harmful effects from creeping
and shrinking. In addition, concrete mixes before pouring are cooled down to 7-8 oC by liquid
nitrogen.
Anode systems for cathodic protection are not installed in method C.
ANNEX U Application examples of RIM method
34 (40)
ANNEX U Application examples of RIM method
35 (40)
4
SELECTION OF THE BEST REPAIR OPTION FOLLOWING THE
REPAIR INDEX METHOD (RIM)
In this chapter the best repair option is selected by means of the Repair Index Method (RIM)
given in paragraph 7.2 of the Manual.
Comments to indicators and adopted values for the Repair Performance Indexes (RPI) as
established in Table 7.1 and 7.2 according to paragraph 7.2 of the Manual are given in the
following.
4.1
SERVICE LIFE AND DURABILITY
Normal service life of the repair
Normal service life is more than 50 years for all methods regarding concrete works.
Later on, it has been observed that the cathodic anodes made of flexible strands have not
sufficient service life and are now out of order.
Accidental attacks
Method B and C are more robust and resistant to ice pressure overloads.
Exposure class
Vertical reinforcement in method A is more vulnerable to corrosion.
Feasibility of post-repair monitoring
Post-repair monitoring for method A and B is possible by means of NDT, i.e. measuring the
electric potential difference to confirm that the cathodic protection is in operation. The
monitoring of method C can be made by a visual inspection.
Disturbance (after repair)
Disturbance after repair is negligible for method A. The enlargement of the cross section in
method B and C may to some minor extent disturb the sea traffic.
Compatibility with additional repair methods
Compatibility with additional methods is high for method B and C and probably moderate for
method A. Method A involves various techniques.
4.2
STRUCTURAL STABILITY AND SAFETY
Structural consequences of failure
The consequences of failure are of course very severe and the same for all methods. However,
the probability of failure during the construction work is significant higher for methods A and
B. The risk is associated with the removal of concrete with the water-jet equipment. The
concrete was very soft and porous not only on the surfaces but also in deeper parts and it was
not possible to find any distinct dividing line between bad and good concrete. Consequently,
failure could occur if too much of the concrete section was removed. This was one of the
main reasons to the final choice of method C. No structural concrete is removed in method C.
Failure type
ANNEX U Application examples of RIM method
36 (40)
Failure type of the yoke-beam is ductile in methods A and B and very ductile in method C.
Method A and B are depending on a few heavy GEWI-bars and method C on a great number
of smaller and well distributed reinforcement bars.
Experience
Experiences are <10 years for all methods.
4.3
EXECUTION OF WORK
Execution control
Execution control is most comprehensive in method A, including work as water-jet, cathodic
protection, vertical and horizontal prestressed reinforcement. Method B has no vertical
reinforcement and method C has nothing of this.
Execution difficulty
Execution difficulty is most obvious regarding the erection of the cathodic protection. The
wire mesh anodes were more difficult to fix in place than the flexible strands. Furthermore the
mesh was damaged in connection with the erection of adjacent reinforcement bars.
Difficulties occurred to works related to the vertical reinforcement (method A) as well. Only
three out of eighteen reinforcement strands could be finished due to bad weather conditions.
Disturbance (during repair)
Disturbance (traffic disturbance) during repair is the same and moderate for all methods.
Safety of workers and users (during repair)
Safety of workers and users during repair is the same and high for all methods.
4.4
ENVIRONMENT, HEALTH AND SUSTAINABILITY
Environmental effects
Environmental effects are in this case evaluated regarding the obstacle to the water flow
through the Kalmar Sound (if any). Method A has kept the pier shaft slimmer and will thereby
not hinder the water flow to the same extent as method B and C.
Resources consumption
Resources consumption is evaluated regarding the consumption of concrete, which means that
method B and C will have a higher resource consumption than method A.
Safety of users (after repair)
Safety of users after repair is the same and high for all methods.
4.5
ECONOMY
Direct costs
It is not possible to compare the direct costs related to the different methods in an objective
way. Method A and B are only executed with simple measures during the test period, hence
the costs are relative high (approx 4.5 million SEK/ pier). The average cost for method C
ANNEX U Application examples of RIM method
37 (40)
during the final construction work is approx 2.5 million SEK/ pier. However, a great deal of
the costs is related to temporary equipment as cofferdams, jack-up platforms, scaffoldings etc.
A comprehensive conclusion is that the costs are very high (>1000 Euro/m2) for all methods.
Maintenance cost
Maintenance cost is negligible. However, the cost of electric power to the cathodic protection
(method A and B) can be estimated to approx <0.02 Euro/m2 and year. Other maintenance
cost for the cathodic protection system is not known.
Preparation of substrate
Preparation of substrate is more extensive in method A and B due to the water-jet works.
Repair period
Repair period is the same for all methods.
Access tools (auxiliary equipment)
Access tools (cofferdams) might, because it is smaller, be cheaper in method A.
Distribution of damages
Method A has the smallest repaired area.
Extent of damage
Method A has the smallest repaired area.
4.6
AESTHETICS
Aesthetic contribution
Aesthetic contribution is evaluated regarding the heavy look of the repair methods, which
means that method B and C will have the largest impact on the aesthetics.
Variability of aesthetics
Variability of aesthetic is related to variation in the moisture content and is the same and
moderate for all methods.
4.7
CONCLUSIONS
The results showed in Table 2 confirm that Method C is the best repair system.
In the case “The Öland Bridge” two alternatives of the Im-value, that indicates the weight of
each requirement, are tested. The first choice put weight on economy while the second instead
emphasise durability and execution of work as important requirements. The results will vary
and are strongly dependent on who is doing the evaluation (client, consultant, construction
company etc) and their choice of weighing the requirements.
ANNEX U Application examples of RIM method
Table 2
38 (40)
RIM application for repair systems
Repair system
Requirement
SERVICE LIFE &
DURABILITY
STRUCTURAL
STABILITY &
SAFETY
EXECUTION OF
WORK
Method
A
Method
B
Method
C
3
3
4
3
3
4
4
4
4
2
2
3
4
3
3
3
4
4
3.0
3.3
3.7
2
2
4
3
1
2.0
1
3
1
2.0
2
4
1
3.0
3
Execution difficulty
1
2
3
Disturbance (during repair)
2
2
2
Indicators
Normal service life of the
repair
Accidental attacks
Exposure class
Feasibility of post-repair
monitoring
Disturbance (after repair)
Compatibility with additional
repair methods
Rser
Structural consequences of
failure
Failure type
Experience
Rstr
Execution control
Safety of workers and users
Rexe
Environmental effects
ENVIRONMENT,
HEALTH &
SUSTAINABILITY
Resources consumption
Safety of users
Renv
Direct costs
Maintenance cost
Preparation of substrate
Repair period
ECONOMY
Access tools (auxiliary
equipment)
Distribution of damages
Extension of damages
Reco
Aesthetic contribution
AESTHETICS
Variability of aesthetics
Raes
REPAIR INDEX (RI)
Alternative 1:
REPAIR INDEX (RI)
Alternative 2:
4
4
4
2.0
4
2.5
3
3.0
3
2
1
1
4
3.3
1
3
2
1
4
2.7
1
3
2
1
4
2.7
1
4
3
1
2
1
1
2
2
1.9
2
2
2.0
1
1
1.4
1
2
1.5
1
1
1.7
1
2
1.5
2.7
2.8
2.5
2.9
3.0
3.5
Alternative
1
Alternative
2
x 0.2
x 0.25
x 0.1
x 0.1
x 0.1
x 0.25
x 0.1
x 0.1
x 0.4
x 0.2
x 0.1
x 0.1
ANNEX U Application examples of RIM method
39 (40)
REFERENCES
(1) Statens vägverk, Informationskontoret: “Ölandsleden”, Stockholm 1972
(2) Statens vägverk: ”Ölandsbron”, teknisk beskrivning, Stockholm 1972
(3) L Johansson, L Rombén, L Åberg: “Undersökning av skador på Ölandsbron”,
CBI-rapporter nr 8427 och 8616, 1984
(4) Stig Sällström: ”Utlåtande ang Ölandsbron”, febr 1986
(5) Vägverket, Kalmar län: ”BBR” vid utförande av provpelare, 1988-04-05
(6) NCC Öst: ”BBR” vid reparation av 105 st pelare, 1990-03-01
(7) W v Olnhausen: ”Vägreparationer i Sverige”, Väg- och Vattenbyggaren nr 3, 1990
(8) L Johansson, S Sällström: ”Ölandsbrons pelare - betongtekniska erfarenheter”,
Väg- och Vattenbyggaren nr 3, 1990
(9) W v Olnhausen: “Reparation av Ölandsbron”, Vägverket VB, mars 1990
(10) Olov Hildingson: ”Klorider i Ölandsbron”, Betong nr 2, juni 1991
(11) Vägverket/ NCC Öst: ”Ölandsbron i nya kläder”, Teknisk version, 1991
(12) Ingvar Nilsson: ”Sprickfri kringgjutning vid reparation av Ölandsbrons pelare”, maj
1995