NAT'L INST. OF STAND & TECH

A111DS T7M3bT

1 NBS

REFERENCE Publications

./

^ 0F Co,

\

*&

\I"*

1/1 a*

^ffAU O* *

NBS TECHNICAL NOTE 1192

U.S. DEPARTMENT OF COMMERCE/National Bureau of Standards

Offshore Concrete

Structures in the Arctic:

Research Needs

-QC —

100

. U5753

1192

1934

J
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau's technical work is per- formed by the National Measurement Laboratory, the National Engineering Laboratory, and

the Institute for Computer Sciences and Technology.

THE NATIONAL MEASUREMENT LABORATORY provides the national system of

physical and chemical and materials measurement; coordinates the system with measurement

systems of other nations and furnishes essential services leading to accurate and uniform

physical and chemical measurement throughout the Nation's scientific community, industry,

and commerce; conducts materials research leading to improved methods of measurement,

standards, and data on the properties of materials needed by industry, commerce, educational

institutions, and Government; provides advisory and research services to other Government

agencies; develops, produces, and distributes Standard Reference Materials; and provides

calibration services. The Laboratory consists of the following centers:

Absolute Physical Quantities2 — Radiation Research — Chemical Physics —

Analytical Chemistry — Materials Science

THE NATIONAL ENGINEERING LABORATORY provides technology and technical ser- vices to the public and private sectors to address national needs and to solve national problems; conducts research in engineering and applied science in support of these efforts; builds and maintains competence in the necessary disciplines required to carry out this research and technical service; develops engineering data and measurement capabilities;

provides engineering measurement traceability services; develops test methods and proposes

engineering standards and code changes; develops and proposes new engineering practices;

and develops and improves mechanisms to transfer results of its research to the ultimate user. The Laboratory consists of the following centers:

Applied Mathematics — Electronics and Electrical Engineering2 — Manufacturing

Engineering — Building Technology — Fire Research — Chemical Engineering2

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts

research and provides scientific and technical services to aid Federal agencies in the selection, acquisition, application, and use of computer technology to improve effectiveness and

economy in Government operations in accordance with Public Law 89-306 (40 U.S.C. 759), relevant Executive Orders, and other directives; carries out this mission by managing the Federal Information Processing Standards Program, developing Federal ADP standards

guidelines, and managing Federal participation in ADP voluntary standardization activities; provides scientific and technological advisory services and assistance to Federal agencies; and

provides the technical foundation for computer-related policies of the Federal Government.

The Institute consists of the following centers:

Programming Science and Technology — Computer Systems Engineering.

'Headquarters and Laboratories at Gaithersburg, MD, unless otherwise noted; mailing address Washington, DC 20234. 'Some divisions within the center are located at Boulder, CO 80303.
JJATIOH/iL EUREAU OF 3T3KDASDS

LIBRARY Offshore Concrete Structures

in the Arctic: Research Needs

^

Nicholas J. Carino

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

Washington, DC 20234

Sponsored by:

Technology Assessment and Research Branch

Minerals Management Service

U.S. Department of the Interior

Reston, VA 22091

U.S. DEPARTMENT OF COMMERCE, Malcolm Baldrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued April 1984
National Bureau of Standards Technical Note 1 192

Natl. Bur. Stand. (U.S.), Tech. Note 11 92, 52 pages (Apr. 1984)

CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1984

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
OFFSHORE CONCRETE STRUCTURES IN THE ARCTIC:

RESEARCH NEEDS

by

Nicholas J. Carino

ABSTRACT

A study of research needs to enhance the capability to design, maintain, and

approve concrete offshore structures for the Arctic was carried out by the

National Bureau of Standards on behalf of the Minerals Management Service,

Department of the Interior. The study was composed of three activities: a letter survey of key individuals in the field; an international workshop on the subject; and a review of available literature. Data gathered from these

activities were used to develop a comprehensive list of research needs in the

fol lowing areas: design, materials, construction, inspection and repair.

Key words: Arctic environment ; concrete; construction; design;

durability; inspection; marine; offshore structures;

repair; research.

i i i
TABLE OF CONTENTS

Page

ABSTRACT i i i

1.0 I NTRODUCTION 1

1 .

Purpose 1 1.2 Structures in the Arctic 1

1 .

Scope 5

2.0 RESPONSE TO SURVEY 8

2.

Questionnaire 8

2.2 Summary of Responses 8

3.0 NBS WORKSHOP ON THE PERFORMANCE OF ARCTIC

OFFSHORE CONCRETE STRUCTURES 10

3.

Workshop Format 10

3.2 Design Group 11 3 .

Mater la I s Group 14

3.4 Construction Group 17

3.5 Inspection/Repair Group 19

4.0 ANNOTATED BIBLIOGRAPHY 21

5.0 RECOMMENDED AREAS OF RESEARCH 23

5.1 Research Areas Related to Design 23

5.2 Research Areas Related to Materials 24

5.3 Research Areas Related to Construction 26

5.4 Research Areas Related to Inspection

and Repa i r 26

6.0 ACKNOWLEDGMENT 28

7.0 REFERENCES 29

APPEND IX 31

A.1 Annotated Bibliography 31

A. 2 Research Projects on Offshore Concrete

Structures 46

IV
1.0 INTRODUCTION

1.1 PURPOSE

It has been reported that the Beaufort Sea has the greatest potential of any

region In North America in terms of oil and gas production [1]. To tap these

reserves will require the construction of permanent offshore exploration,

production and storage structures so that year round operations can be performed. Many of these structures will be constructed of concrete [2,3,4]. It has been shown that properly constructed concrete structures can be extremely

durable and maintenance-free when exposed to marine environments [5-10].

In addition, concrete structures can provide the mass and rigidity that may

be required to survive the extreme loading conditions of the Arctic.

The offshore Arctic environment represents a frontier in terms of the design

and construction of permanent structures. There are very few case histories

of structures in Arctic waters by which to judge the appropriateness of proposed materials and methods of design, construction, inspection and repair.

These unknown factors make it difficult to assess, with a high degree of confidence, the expected performance of proposed structures.

Within the last decade, a considerable amount of resources have been expended

to answer some of the questions, and research results have appeared in a variety

of symposia, conferences and journals dealing with offshore structures. In order to make efficient use of additional resources, it is necessary to assess the current state of knowledge, and thereafter identify in which direction

future efforts should be directed. Recognizing this need, the Minerals

Management Service(MMS), Department of the Interior, contracted with the

National Bureau of Standards to perform such a study and identify fruitful areas of research. This report summarizes the results of the study.

1.2 STRUCTURES IN THE ARCTIC

Within the 1970's, 14 large structures have been constructed in the North

Sea [11 #12], and their successful performance up to now has confirmed the

adequacies of their design and construction [5]. While much of this experience

can assist in predicting performance of structures in the Arctic, there is one factor that still has many unknowns associated with it, namely, the severe

ice loading conditions. The proposed locations of many of the offshore Arctic

structures will expose them to a wide variety of ice forms, ranging from small

floating fragments to pack ice four or more meters thick [13,14], Some data

have been gathered from the performance of concrete I ighthouses exposed to

ice [15], but these experiences have not included conditions of Arctic severity. A considerable amount of research effort has been devoted to the subject

of ice mechanics, ice loading of structures and ice movement in the sea. The American Bureau of Shipping has recently completed an extensive literature

review of this topic [16], and it was concluded that much additional research

Is required on this complex subject.

The North Sea structures have been placed in water depths of around 150 meters

and have been designed to resist wind and wave loadings. The structures pro1
posed for the Arctic will be founded in shallower water, typically less than

60 meters, and will be required to resist tremendous ice pressures [13].

Various design concepts have been proposed for different site conditions

C2-4,17-20D. In order to acquaint readers unfamiliar with these proposals,

a brief review of the basic concepts is presented. The review follows the

ideas in ref. \J>~], which summarizes the main attractions and limitations of

each concept.

The structures proposed for the Arctic can be divided into four generic categories:

- Artificial islands

- Caisson-retained islands

- Conical gravity structures

- Caisson gravity structures

Figure 1 provides schematic cross-sections of these types of structures.

The possibility exists for hybrid structures which combine one or more features

of the above concepts.

Artificial Islands:

In shallow waters, a working platform may be constructed by simply building

a gravel mound projecting above the water surface (Fig. 1a). The artificial

island achieves its strength to resist ice forces by its large mass, and ice

rubble build-up around the perimeter enhances the structure's resistance.

Advantages:

-Large production capacity due to large deck area and weight capacity

-Can accommodate large number of wells

-Separation of production, drilling and accommodation platforms

-Can resist all ice formations expected in the Arctic

Limitations:

-Requires readily available source of materials

-Sensitive to weather window (Ice free period) and environmental

conditions during construction of upper portion of island

-Oil storage would have to be accommodated on top of island

-Permanent ice rubble around island during winter may hamper access

by supply and maintenance vessels

-Feasibility in deep waters restricted by ability to construct steep

slopes with dredged sand

Caisson Retained Islands:

With increasing water depth, an excessive quantity of material would be re- quired for artificial islands. An alternative approach is to construct a rigid peripheral wall and place earthfill within the wall (Fig. 1b). The

wall can be constructed from concrete segments, which are precast at a temperate location, towed to the installation site and joined together. Ice

forces are resisted by the large mass of the combined wal l-earthf i I I structure.
Advantages:

-Substantial production capacity due to large deck area and weight

capacity

-Relatively inexpensive structure depending on water depth and ice

features

-Scouring and erosion around the structure is expected to be moderate

within its design I ife

-Can be designed to avoid substantial grounding of ice rubble, thereby

allowing vessel access to structure

Limitations:

-Installation, hook-up and commissioning works require significant

on-site operations

-While some oil storage can be accommodated by hollow wall elements,

large volumes would have to be stored on top of the structure

-Installations of wall segments and earthfill are sensitive to weather

conditions

Conical Gravity Structures:

This type of structure is composed of a large diameter base, a cone section

and the deck section (Fig. 1c). The large base serves to provide stability

against sliding and overturning and provides buoyancy during towing of the

structure from its fabrication point to the installation site. The conical

section is intended to cause flexural failure of the ice rather than crushing,

as in the caisson retained island. The cone section is of a relatively small

diameter so as to reduce the total ice load on the structure. In a variation

of the basic concept, the conical section is an adjustable collar to permit

use of the same structure in different water depths. The basic principle

of this concept is to permit the moving ice to flow past the structure with

minimum resistance.

Advantages:

-The entire structure can be fabricated at a moderate climate location

-Significantly lower costs than other concepts for water depths

in the range of 40 to 70 meters

-Adaptable to a range of foundation conditions

-Shallow draft requirements

-Fabrication period is relatively short

-Permanent ice pile-up all around the structure is not expected,

so vessel access should be feasible most of the time

Limitations:

-Limited production capacity due to deck and well restraints

-Minimum oil storage capacity in structure

-Mating of deck system and lower structure must be performed in the

Arctic

-Large ice island invasion will probably require temporary relocation
of the structure

-Concept relies on good understanding of ice environment and

ice/structure interaction

-Upper part of structure will require reliable corrosion protection

and maintenance approach

-Direct tanker loading probably not feasible

Caisson Gravity Structures;

This concept differs from the conical structure in that a very large polygonal

caisson is used; the walls may be vertical or sloped (Fig. 1d). The caisson

relies on its great mass and strength to resist ice loads.

Advantages:

-Platform is constructed and fully integrated in a moderate climate

-Substantial oil storage capacity can be incorporated in the structure

-Large production capacity due to its large size and strength

-Minimal construction operations required in Arctic

-Minimal structure maintenance requirements

-Can be designed to avoid substantial grounding of ice rubble,

permitting vessel access downstream of ice movement

-Concrete shell will have low sensitivity to high local ice pressures

Limitations:

-Good foundation materials required

-Requires substantial draft during towing to Arctic, will probably

require ice breaking assistance during tow

-Feasibility of direct tanker loading not proven

-Not certain that structure can survive worst possible ice features

with adequate integrity

In addition to the above generic concepts, hybrid structures have been proposed

that combine the advantages of the individual concepts and attempt to minimize

the limitations. Other proposals include floating caisson structures tethered

to the sea bed.

As of this writing (1983), most of the completed Arctic structures have been

artificial gravel islands. The only exception is the Tarsiut caisson retained

island completed in October 1981, in 21 meters of water [20. The peripheral

wall is constructed of four lightweight concrete caissons resting on about

a 15-meter thick sand berm. The structure has been extensively instrumented

to monitor its performance during ice loading L~22H. The data gathered from

this pioneering structure will provide valuable information to assist in the

design of future platforms.

Another significant structure is scheduled for installation in the U.S.

Beaufort Sea in August 1984. The structure is called a concrete island drilling system (CIDS), and is a submersible drilling unit for use in water depths

between 9 and 15 meters. The structure will be 29 meters high and is built
in three sections: a steel mud base to sit on the sea bed; a concrete caisson

structure to rest on the steel base; and an upper steel deck for equipment

and living modules [23]. Plans are to produce an artificial grounded ice

rubble on the windward side of the structure to reduce ice loadings. An extensive monitoring system will be installed to monitor forces on the structure

as well as its displacements.

1.3 SCOPE

As previously stated, the purposes of this study were to assess the state

of knowledge relative to the performance of offshore concrete structures in

the Arctic environment, and to identify the research needed to enhance the

present capability to design, maintain and approve such structures. Since

the subject of offshore technology is quite extensive, the study was limited

to concrete structures, and to the following aspects:

-Design

-Materials

-Construction

-Inspection

-Repair

To meet the stated objectives, the project consisted of three tasks:

-Conducting a letter survey of key individuals knowledgeable in the subject

-Organizing and sponsoring an international workshop

-Performing a review of the available literature

The next three chapters summarize the results of each task. Based on the

acquired information, recommendations for future research were developed,

and these are reported in chapter 5.
T3C

_cg

CO

"co "o<

CO

CO

LLJ o

-Q

CO

CO

CD

CO

+-* CD ' / n

co CO

4-> O

S- <

CD

+->

s-o

-a

<u

too

CLo

s-CL

co

a>j- -po

S- +J

co

a>

s-o

_c

CO H4-O

4-O

CO

a>Q-

>>

cu

a> CD

CD

cn
c) Conical

gravity

structure

Concrete

shell

d) Caisson

gravity

structure

Concrete

shell

7—?—r~? > "/ / /

l> s > ?" / ? / > ; /> /

Seabed

Figure 1 Generic types of offshore structures proposed for the Arctic

7
2.0 RESPONSE TO SURVEY

2.1 QUESTIONNAIRE

In order to gain preliminary Information on needed research related to offshore

concrete structure, a questionnaire was sent to a number of Individuals knowledgeable in this subject. The questionnaire requested four responses:

1) Which areas related to the design, construction or service ability

of concrete structures are lacking the Information you would require

if you were Involved in a project in Arctic regions?

2) What are the names and addresses of other persons who could provide

additional information?

3) What recent research on this subject are you aware of? Who is conducting the research and will the results be made public?

4) Do you have any additional comments that may be of assistance?

The responses to question #2 assisted in developing the list of invited participants for the NBS Arctic Workshop, which is discussed in Chapter 3. The

answers to question #3 were incorporated Into the list of research projects

presented in the Appendix. The following section summarizes the responses

to questions #1 and #4.

2.2 SUMMARY OF RESPONSES

The following topics were identified as areas of needed research:

Ice Loading:

A coherent approach Is needed to relate Arctic structures to structures

in other areas with respect to overall level of reliability, taking

account of service life, return periods of ice features, level of

expected safety, etc.

Analysis of ice statistics is needed in order to arrive at load levels

for checking the ultimate, serviceability and fatigue limit states.

There might be a need to consider a "survivability" limit state, similar

to that used for design of structures In seismic regions.

There is a need for establishing magnitudes and distributions of local

pressures on structures due to various ice features.

Structure:

There is a need for a rational approach for designing against punching

shear failure of norma I weight and lightweight reinforced concrete

sections subjected to local ice pressures.

There is a need to enhance our understanding of I ce-water-structu resoil Interactions during earthquakes.

8
Criteria need to be established to safeguard structures against degradation due to freezing and thawing of water within cracks.

The applicability of lightweight concrete and high-strength concrete

to Arctic structures should be studied.

Materials;

Establish the long-term performance characteristics of the following

in the Arctic environment, especially in the near sea surface zone:

-Concrete, both normalweight and lightweight

-Reinforcing steel, prestressing tendons and anchorages with

particular reference to brittle fracture

-Abrasion resistance of concrete surfaces, and the application

of fiber-reinforcement to improve abrasion resistance

-Coatings for reducing ice adhesion forces (adfreeze)

-Polymer- impregnated concrete for increasing strength and reducing

permeabi I ity

Operation:

Effective Ice management methods need to be identified for keeping

the structure ice free and accessible.

Waste heat management should be studied to reduce Ice adhesion bond

with concrete surfaces.

Inspection and Repair:

Improved inspection methods need to be developed.

Methods need to be developed to repair the following:

-Damaged concrete surfaces

-Ruptured concrete sections

-Reinforcing steel and prestressing tendons

-Damaged coatings

As will be seen in the following chapter, many of the above research areas were also identified in the NBS Arctic Workshop.
3.0 NBS WORKSHOP ON THE PERFORMANCE OF ARCTIC OFFSHORE CONCRETE STRUCTURES

3.1 WORKSHOP FORMAT

In order to bring about an exchange of information on the subject of offshore

concrete structures, an international workshop was held at the NBS on March 1 and 2, 1983. The workshop was organized by NBS, MMS and the Canada Centre for

Mineral and Energy Technology (CANMET). Funding was provided by MMS and CANMET

contributed by publishing the workshop report.

The objective of the workshop was to bring about an exchange of information in

the following areas:

-Past experiences in the design, construction and performance of Arctic

offshore concrete structures.

-Current projects and research programs related to Arctic offshore structures.

-Recommended areas for further research and development in order to enhance

the capability to construct viable Arctic offshore concrete structures.

The workshop planning committee invited a recognized group of international

experts in various areas related to offshore concrete structures. A total of

51 individuals participated in the workshop. The participants were divided into

four working groups each deal ing with one of the fol lowing subjects:

-The DESIGN of Arctic concrete structures.

-Required characteristics of MATERIALS for Arctic offshore structures.

-Problems related to the CONSTRUCTION of Arctic offshore structures.

-Problems associated with the INSPECTION and REPAIR of Arctic offshore structures.

Each working group had a chairman who volunteered to prepare a position paper

to initiate group discussion and a final report of the discussions. The chairmen

were as fol lows:

-Mr. Ben C. Gerwick, Jr. - Design

-Mr. Robert E. Phllleo - Materials

-Mr. Peter Pul lar-Strecker - Construction

-Dr. Roger Browne - Inspection/Repair

The chairmen's reports have been incorporated into the workshop proceedings

C24H. Each group's report was organized into three sections: background;

summary of discussions; and recommendations for future research. The following

sections summarize the group reports Including recommended areas of research.

10
3.2 DESIGN GROUP

A highlight of the workshop discussions was a presentation on the performance

of the Tarsiut caisson retained island. It was reported that the concrete

structures had performed well. Some structural cracking had occurred during

initial set-down of the caissons because of uneven support resulting from

a surveying error. The cracking was not considered serious and had not led

to further deterioration due to cyclic freezing and thawing. Additional damage,

in the form of minor spa I ling, had occurred due to impact of steel barges

without fenders. The measured global and local ice loadings during the winter

of 1982-83 were reported to have been the most severe yet encountered. In summary, it was concluded that the prestressed, lightweight concrete caissons

have displayed satisfactory and predictable behavior.

There was discussion about the generally satisfactory behavior of Swedish

lighthouses exposed to Ice environments. For up to 25 years, these concrete

structures have been exposed to moving ice sheets and rubble pile build-up

without showing significant abrasion or deterioration. Some lighthouses have

been well Instrumented and documented, providing valuable information on icestructure-foundatlon interaction.

The highly successful experiences of 15 North Sea structures were discussed.

Attention was directed to the current design of the shafts to resist boat

Impacts of Intensity comparable to ice loadings expected in the Arctic.

One of the discussion sessions was devoted to presentations of current research

and development projects. While many of the projects are proprietary, it was pointed out that any responsible party may buy into them. The following

projects were noted:

-The mechanical and durability properties of high-strength lightweight

concrete under Arctic conditions.

-The behavior of reinforced and prestressed concrete elements under the

action of concentrated loads, including the behavior of repaired elements.

-The behavior of steel -concrete composite elements.

-The response of structures to Impact of ice floes, considering the Icestructure-foundatlon Interaction, which includes the compliance of the

structure-foundation system and energy dissipation due to ice crushing

and hydrodynamics.

-The evaluation of risk and rel Iabi I ity,and the consequences of local failure

on overall safety levels.

-The properties of high-strength normalwelght concrete, with strength In excess of 14,000 psl (100 MPa).

-The ductility of highly compressed members.

-Detailed inspection of Swedish concrete lighthouses in the Baltic Sea

11
to ascertain their performance under up to 25 years of annual Ice loading.

-Ice pressures on Polar class Icebreakers, Ice forces against structures

and Ice mechanics.

-Multiaxial stresses in concrete structures.

-Various studies on the performance of concrete in the Arctic environment,

such as durability, abrasion resistance, friction forces, etc.

-Behavior of prestressed lightweight concrete under cyclic, fully reversing

membrane and shear stresses at low temperatures.

-Study of a model platform subjected to iceberg impact.

The above projects, plus those listed in the Appendix, give a good indication

of the scope of recent and current research efforts related to concrete structures.

In addition to research projects, the following examples of concepts being

developed for use as exploratory and production platforms in Arctic and subArctic waters were presented:

-Global Marine's Concrete Island Drilling Structure (CIDS), utilizing con- crete "honeycomb" modules which are joined together horizontally and

vertically at the site to complete the structure.

-SOHIO's Arctic Module System (SAMS), a prestressed lightweight concrete

caisson in which shear transfer of Ice forces to the foundation Is augmented

by spuds.

-The Arctic Cone Exploration System (ACES), a prestressed conical structure

being designed for a consortium of oil companies Including Shell, Exxon

and Chevron.

-Brian Watts Arctic Caisson System (BWACS), a lightweight concrete honeycomb

caisson employing the wick and drain method to improve the shear resistance

of weak sol Is.

-Exxon's concrete production Island caisson with elevated deck, designed

for 30 to 100 ft (10 to 30 m) water depths In Norton Sound.

-A concrete caisson for Norton Sound designed by a nine-company consortium

headed by Chevron.

-The TRIPOD 300 concrete caisson, originally designed for 300 plus meters

in the North Sea, now being considered for the Southern Bearing Sea.

-Exxon's concrete gravity base M0N0T0WER proposed for deep water In the

St. George Basin.

-Fixed concrete caisson for the Hlbernla field, off Newfoundland, designed

12
to resist iceberg Impact.

-Floating caisson drilling, production and storage structure designed for use in deep water and featuring dynamic downward breaking of ice.

In the discussions of research needs, the problems of ice loading, dynamic

structural response and soil-structure Interaction were identified to be of

great Importance for all structures in the Arctic. Other general needs include

probabilistic approaches to design for ice loads and appropriate serviceability

criteria. The point was raised that the standard design criteria for reinforced concrete buildings may not be applicable to thick concrete sections

having high percentages of multi-axial reinforcement. Additional discussion

dealt with some of the severe environmental conditions that must be endured

by concrete structures, such as large thermal gradients, ice abrasion, and

cyclic freezing and thawing.

The following specific research areas were identified by the Design Working

Group:

-The behavior of concrete slab and shell elements subject to concentrated

out of plane forces plus the simultaneous action of membrane stresses.

Investigations should address the following:

Tests of large scale and reduced scale specimens to identify any

"scale effects".

Use of realistic support conditions and loadings characteristic of

ice in order to corroborate non-linear numerical analyses.

Methods of reinforcing to ensure high load resistance and high energy

absorption capacity.

Acceptability of the concept permitting repairable local damage under

extreme loadings provided damage does not result in progressive collapse of entire structure.

Guidelines for evaluating the resistance of heavily reinforced thick

sections subjected to concentrated loads and membrane stresses.

-Investigate means for enhancing the resistance and energy absorption of

shear walls and diaphragms subjected to high compressive and shearing

stresses.

-Determination of peak local forces generated during the impact of large

Ice features against the peripheral wall. The effects of hydrodynamic

damping, Ice fracture energy absorption and soil-structure compliance

on the peak loads should be considered.

-Low-cycle fatigue behavior of structural elements, especially peripheral

walls, under the "ratcheting" effects of continuous ice crushing.

-Establishment of deterministic and parametric (and eventually probabilistic) Ice loading criteria.

-Recommendations for load factors for ice loadings. Determination of appropriate serviceability criteria. Guidelines for appropriate load comblna13
tions to be considered in design; e.g., earthquake and ice, or waves and

small ice features ("bergy bits") impelled at high velocity by waves.

-The abrasion of external walls by ice, and the effects (if any) of sand

and silt particles in sea ice contacting the structure.

-The adhesive bond of ice to concrete and the probable range of friction

forces.

-The freezing and thawing behavior of concrete, especially in the splash

zone. The effectiveness of air entrainment and silica fume.

-Evaluation of the effects of thermal gradients, both through wall and

global. Evaluation of the effects of concrete properties, reinforcement

and prestressing details, and structural configurations on limiting the

cracking due to thermal strains.

-Performance and design criteria of steel -concrete composite elements.

Investigation of methods for assuring effective composite action, effects

of thermal gradients and effects of freezing and thawing.

-Risk, reliability and consequence evaluation principles for Arctic concrete

structures.

-Details for protecting post-tens ion ing anchorages against freezing and

thawing action.

-Field durability tests of post-tens ioned and reinforced high strength,

lightweight concrete incorporating condensed silica fume.

3.3 MATERIALS GROUP

The majority of the discussions dealt with questions of concrete durability

under the extreme Arctic conditions. There were two recurrent ideas during

the discussions:

-For improved durability, impermeability is the most important property

for concrete exposed to seawater, particularly in the tidal and splash

zones.

-Existing criteria for concrete cover and crack control in permanently

submerged structures are too conservative. Consideration of the factors

necessary for steel corrosion suggests that active corrosion in these

areas is highly unlikely. Yet for certain members the crack control

criterion for corrosion protection is reported to be more critical than

the wave criterion in designing the quantity of reinforcement.

Much of the discussion dealt with the points addressed in Chairman Philleo's

position paper, and is summarized in the following paragraphs.

14
There Is no evidence to support an upper limit of trlcalcium-alumlnate content

for cement exposed to seawater. Sulfate attack Is not a problem In high quality, impermeable concrete. Alkali content of cement was not seen as a problem

except where reactive aggregates are used. It was further mentioned that

for important structures exposed to sea water, reactive aggregates should

not be used.

Pozzolans, such as fly ash and condensed silica fume, and slags are useful

for concrete In sea water because they reduce permeability, and thereby reduce

the ingress of chloride Ions. Since the traditional concepts of water-cement

ratio may not fully characterize concrete with pozzolans, interest was expressed

in using permeability as a criterion for quality. This would require Improvements In permeability testing of concrete and the development of methods for

measuring in-place permeabi I Ity.

More work is needed to answer the question of whether or not accelerators

containing chlorides should be permitted In offshore structures. It was men- tioned that high strength, prestressed concrete has served successfully in

the presence of high chloride content. The basic question is whether chlorides

need to be limited if steel is protected by high quality, impermeable concrete.

The use of high-range water reducers (superplasticizers) was deemed to be

necessary both for placing concrete In the heavily reinforced sections and

for allowing the use of condensed silica fume, which is extremely fine and

requires high water content for workability. The evidence indicates that

durable concrete can be made with high-range water reducers, but there are some questions about the existing criteria for the necessary air void system.

Concerning the need for proper admixtures for use with tremie concrete, it was mentioned that there probably will be little underwater placement in Arctic

offshore structures. In addition, there are available proprietary systems

which permit underwater placement without using tremies.

Lightweight aggregates can be useful materials where weight reduction is an important consideration. Further knowledge is needed about the thermal properties and failure mechanisms of lightweight concrete.

In important offshore structures, sea water should not be used for the mixing

water.

It was noted that there are practical limits to using low permeability concrete

as a means of reducing concrete cover. For example, a minimum amount of cover

is required for proper concrete placement between formwork and reinforcing

bars. In addition, the critical zone of a structure (tidal and splash zone)

may be a relatively small portion of the total, and reduced cover may not

generate large cost savings. Below the water line, cover is not critical

for durability. However, when design requirements call for limited cover

in the critical zone, highly impermeable concrete and epoxy-coated reinforcing

steel is a practical solution. Where there is no need for thin cover, there

is likewise no need for epoxy-coated reinforcement as steel can be adequately

protected by sufficient cover of high quality concrete. The use of epoxy-coated

bars may be cost effective In the exposed working platforms, where calcium

15
chloride is likely to be used for delclng.

Additional discussion covered topics not mentioned In the position paper.

For example, the subject of Ice abrasion was addressed, and it was concluded

that more Information is needed In this area. The potential of fiber reinforced

concrete has yet to be realized In offshore structures. There Is a need for

structural design criteria to supplement the wealth of test data on this material .

During the plenary session two topics related to materials were brought up.

One dealt with cathodic protection. While differences of opinion were noted,

It appears that some of the existing criteria may overestimate the problem

of galvanic corrosion of steel projecting from concrete in the submerged zone. The other question dealt with the low temperature behavior of ASTM A 706

reinforcing steel (60 ksl, weldeable deformed bars). However, It was noted

that tests conducted In Norway and the United Kingdom on steels with presumably

similar composition Indicated adequate performance at low temperatures.

The following research needs were Identified by the Materials Group and are

listed In the priority order suggested by the Group:

-Establishment of permeability criteria with adequate test techniques Including means to test In-situ concrete.

-Establishment of realistic chloride limits when very low permeability

concrete is employed.

-Re-exam I nation of air void spacing criteria for freezing and thawing durability.

-Properties of high-strength, lightweight concrete made with condensed

silica fume and superplastlclzer.

-Early age properties of high strength concrete.

-Methods of test and criteria to determine whether or not tendon ducts

have been effectively grouted.

-Development of suitable test methods and criteria for ice abrasion resist- ance of concrete.

-Development of thixotroplc concrete for underwater placement.

-Design criteria for fiber reinforced concrete.

-Mechanical properties of high-strength concrete, such as shear resistance,

to replace those assumed values extrapolated from normal strength concrete.

-Adequate design procedures for lightweight concrete.

-Establishment, If necessary, of a minimum limit for tricalclum alumlnate

content of cement.

16
3.4 CONSTRUCTION GROUP

One of the key points in the Construction Group's discussions was that many

of the construction problems arise from the design requirements. While the

demands of designers can usually be met (at a price), a good designer will

avoid excessive construction costs by keeping the design simple. The special

problems associated with Arctic offshore construction are the difficulties

in transporting units and equipment from temperate areas to the site, and

the short time period during which the site is accessible through the water.

These problems arise because of the generally shallow water and ice infestation associated with the Beaufort Sea.

It was suggested that many of the construction problems can be avoided by

ensuring that the units are as complete as possible before being shipped to

the site. Construction operations at the site should be minimized, and those

that are required should be kept simple. However, transportation problems

increase as the size of the units increase.

The Group addressed the problems that may arise because of the Jones Act.

The law is intended to protect American trade but may actually encourage

construction of large structures at non-USA sites, since US-registered vessels

(few of which are suitable) would not be needed for transport to the final

destination.

The following areas of needed research were identified by the Construction

Group:

Foundations for structures:

Gravity structures will usually be required to rest on fill material.

Techniques for construction of the mounds and the final leveling of the

surface are areas where additional knowledge is needed. In addition, the

following topics should also be investigated:

-means of determining the relevant properties of potential fill materials

-methods of pumping and consolidating fill materials

-the influence of ice particles in the fill -means of protecting mounds from erosion

-grouting under cold sea water

Berms for protection from floating ice:

Sand and gravel berms may be required to protect the structure from floating

ice. Research needs are similar to those above for foundations.

Moving platforms through ice-covered waters:

Moveable drilling structures would normally be useable at only one location

per season because they can only be moved when the sea is sufficiently

free from ice. In order to permit drilling at more than one location

per season, it is necessary to consider techniques for moving structures

through ice-covered waters. Topics to be investigated might include:

-the design of structures as ice-breaking hulls

17
-the power requirements for moving structures

-the economics of moving and re-using structures

Efficient utilization of equipment:

At the construction site, lifting equipment such as crane barges will be

needed to assemble prefabricated units. To minimize the size of the required

equipment and to reduce the time when the equipment is needed, novel designs

and installation techniques should be investigated.

Transportation of structures from fabrication to Installation sites:

Structures destined for the Arctic will have to be prefabricated in temperate climates and towed or transported to their final destination through

seas which can be stormy, Ice- laden and, in places, shallow. These conditions

pose technical and practical problems, but the Jones Act poses additional

problems. The Act restricts the use of non-U. S. hulls to carry loads from one U.S. location to another. Therefore, if a suitable U.S. -hull is not

available to transport a structure from a U.S. -fabrication point to a U.S.- instal lation, the structure will have to be fabricated outside the

U.S. Thus, legislation enacted to protect U.S. -trade can have opposite

effects. Research topics related to transportation of structures might

include:

-Examination of the effects of the Jones Act, and recommendations

for appropriate exemptions

-Collection of data on wind, wave and currents In a publicly funded

program which would ensure accessibility to the Information

-Collection of data on Ice movement, scour and hydrography in a similarly funded program

Assembly of units on site:

Assembly operations should be quick and simple, and should require a minimum

of equipment. Research areas include the following:

-Required tolerances for interlocking units

-Materials and construction methods for load-distributing Intermediate

layers

-Tolerances to local crushing

-Design and construction of connections which can be subsequently

dismantled

-Protection techniques for connectors subject to corrosion or accidental

damage

-Mooring systems for use during assembly operations

Risk during transportation and installation:

A topic for further study Is the loading that can arise from Ice, wind, waves and current during transportation and installation, and an evaluation

of the consequences of the loading.

Risks and consequences of accidental spillage:

Spillage of oil, grout or even mud may have a large Impact on the Arctic

environment. The fear of such accidents may lead to very strict requirements

18
in an attempt to avoid them. The extra construction work that arises from

that strictness may itself be harmful to the environment. The risks and

consequences of accidental spillage and the effects of the construction

process on the environment need to be evaluated in factual terms so that

the required controls can be appropriate in both method and degree. Further

study is needed on the impact of construction and operation in this region,

and this study should be performed under authoritative and independent

control so that the results are acceptable to all parties.

3.5 INSPECTION/REPAIR GROUP

While advances in inspection and repair technology have occurred for offshore

structures, the Arctic poses additional problems by virtue of the extremely

low temperatures (down to -50°C) that can occur and the presence of ice in

varying forms. In addition, the nature of the damage which may be sustained

is varied, ranging from punching failure to ice abrasion of peripheral walls.

The discussions of the Inspection/Repair Group dealt with re-evaluation of

the existing inspection and repair procedures for offshore structures in light

of the extreme environmental conditions of the Arctic.

The first topic of discussion was materials performance. A thorough understanding of the mechanical and durability characteristics under Arctic conditions

is required when undertaking damage analysis and developing repair strategies.

The available inspection methods for monitoring steel corrosion, concrete

quality and structural performance were reviewed. It was noted that many

of these techniques will have to re-evaluated in light of the operating conditions encountered in Arctic structures.

The Group reviewed the various forms of damage that can be expected: steel

corrosion, mechanical damage, freezing/thawing damage and foundation distress.

The need to undertake repairs must be assessed in terms of the significance

of the damage on the successful operation of the structure. Some damage may

require immediate action while in other cases repair may be delayed until

suitable conditions arise.

The techniques and materials currently available for repairing offshore structures were discussed and the special requirements for Arctic applications

were addressed. The primary need is for durable materials that can be applied

under very cold conditions.

In developing a list of research needs, the Group found that the subject matter

is not easily broken down into specific research items. The Group felt that

in many cases, surveys, assessments and studies need to be performed to develop

new and practical procedures as well as to further develop existing technology.

The following research needs were identified for different categories:

19
Inspection during construction:

-Development of test methods for assessing In-sltu material performance

-Procedures for recording structural detailing of the as-built structure

-Development of practical specifications for field use, including relevant

testing and control procedures

Structure integrity monitoring:

-Evaluation of sensor and monitoring equipment performance under in-service

conditions to ensure meaningful output data

-Development of efficient and reliable data processing techniques to ensure correct Interpretation

-Development of optimum approaches for system design, installation monitoring

and data interpretation

Inspection procedures:

-Development of systematic and practical recording systems to permit easy

reference and updating during subsequent Inspections

-Development of a practical system for coding and classifying visual defects

Inspection techniques:

-Evaluation of existing techniques for use underwater and/or In cold temperatures

-Development of alternatives to visual Inspection for faster and more accural e scanning of the structure

-Development of equipment for use underwater with remote controlled vehicles

-Development of techniques and designs to permit Inspection from within

structures having walls

Repair p rocedures:

-Development and evaluation of procedures for damage-analysis, repair and

after-repair Inspection and evaluation

Repair techniques:

-Evaluation of the suitability of existing technology to deal with the

various types of damage anticipated In the Arctic

-Development of materials and techniques for repairs that cannot be performed

with existing technology

20
4.0 ANNOTATED BIBLIOGRAPHY

To supplement the information obtained from the NBS Arctic Workshop, a review

was carried out of the available literature In order to better formulate the

state-of-the-art of concrete structures in the Arctic. It must be realized

that the published data may not necessarily represent the actual state of

knowledge as there are many proprietary research projects whose results have

not yet been publicly released. The majority of the available literature

has appeared in the proceedings of numerous symposia and conferences dedicated

to offshore structures, which is Indicative of the rapidly changing level

of knowledge In this field.

The appendix contains an annotated bibliography of the publications found

to be relevant to the subject of concrete structures in the Arctic. The refer- ences have been grouped Into four categories, paralleling the four working

groups In the NBS Arctic Workshop.

The selected references In the design category can be grouped into the following

topic areas:

-Descriptions of various conceptual designs for platforms intended for

different Arctic conditions

-Designs of specific platforms

-Structural performance of reinforced and prestressed concrete

elements

-State-of-the-art reviews and suggested areas of needed research

Several articles dealing with ice forces have been included In the design

category. These are either of a general nature to acquaint the reader with

the magnitude of the problem posed by ice, or they present some of the practical

aspects of designing structures to resist the effects of ice loading. As

stated in the introduction, the scope of this report does not deal in detail

with Ice forces and Ice mechanics. The American Bureau of Shipping report covers the state-of-the-art in this area D6U.

The majority of papers in the materials category deal with the durability

of concrete structures In the marine environment. The following aspects are addressed:

-Corrosion of embedded steel

-Deterioration due to cyclic freezing and thawing

-Deterioration due to chemical attack

-Fatigue behavior In the presence of sea water

A recurrent conclusion in many of the articles Is that concrete can be a highly

durable material In the marine environment if the following guidelines are

fol lowed:

-Use materials with a proven performance record

-Proportion concrete mixtures so as to minimize permeability

-Use appropriate design details

-Exercise quality control in construction

21
However, there appears to be one topic on which there is not widespread agreement, namely, the interrelation between cracking and corrosion.

The majority of the articles in the construction category review the construction of specific structures. There are some general references on construction

techniques, and some discuss the series of Arctic projects that have been

planned by U.S. and Canadian firms. As a result of the construction of North

Sea platforms and concrete lighthouses, a sophisticated technology has evolved

for constructing offshore structures under difficult conditions. Much of

this experience can probably be applied to the construction of structures

in the Arctic. A noteable reference deals with the construction of the Tarsiut

caisson retained island [_2\~}. Completed in the fall of 1981, it is the first

significant concrete structure in the Beaufort Sea, and is expected to provide

essential feedback on the suitability of current design criteria.

In the inspection/repair category, the following topics are covered:

-Reviews of existing technology for inspecting offshore concrete structures

-Suggested inspection programs for offshore concrete structures

-Inspection reports of in-service structures

-Reviews of the causes of damage to concrete structures in a marine environment

-Reviews of repair techniques for different types of damage

As is the case for construction, experiences gained In inspecting North Sea

structures have produced systematic inspection procedures for dealing with

a marine environment and the large surface areas that need to be inspected.

Some of this technology can be applied directly to Arctic structures. However,

the low temperature conditions and the limited time period during which inspections can be performed, will clearly require new approaches in the Arctic.

Two of the references dealt with the inspection and monitoring programs employed

on the Tarsiut island [21, 22], The experiences gained from these programs

will identify specific problems in carrying out inspections of Arctic structures.

22
5.0 RECOMMENDED AREAS OF RESEARCH

The information obtained from the letter survey, the NBS Arctic Workshop,

and the literature review were utilized to Identify areas of needed research

related to concrete offshore structures. In the course of this study, recent

and ongoing research projects were also identified and these are listed In Appendix A. 2. The recommendations of the Workshop were the primary sources

for developing the list of research needs. The information from the literature survey gave an Indication of the existing available data related to

some of these topics. Areas of needed research are grouped In the same categories as used in the annotated bibliography.

5.1 RESEARCH AREAS RELATED TO DESIGN

The presence of ice, in its varying forms, poses critical problems in designing

Arctic offshore structures. As a result, the critical research needs are

related to Ice.

Resistance of concrete structures to punching failure:

Any permanent structure In the Arctic will have to be designed to resist Ice

loading. The loadings have to be considered on both global and local scales.

It has been estimated that local pressures as high as 10 MPa may have to be

resisted by the external concrete walls, and the walls must be designed to

resist local punching failure. If the design criteria In the existing standards

for concrete buildings are used to design the walls, the resulting thicknesses

are very large. This presents problems In designing a structure with low

draft requirements. The punching resistance criteria for building slabs have

been derived from tests on thin and lightly reinforced specimens, whereas

offshore structures are expected to be thick and heavily reinforced. The

presence of a large amount of reinforcement can Increase the confinement of

the concrete, which can increase Its load capacity as occurs In spirally reinforced columns. In addition, the walls can be prestressed which can also

enhance punching resistance. Thus, there Is a need to Investigate the punching

resistance of heavily reinforced and thick slab and shell elements. The

research might Include the following tasks:

-Review of literature, especially that related to design of nuclear structures

-Physical tests on model and full-scale elements, both slabs and shells,

with and without prestresslng

-Analytical studies Incorporating non-linear material models and failure

criteria under multi-axial stresses

-Punching resistance of repaired elements

Ice loading:

A structure In the Arctic will be exposed to a variety of ice forms, ranging

from small floating fragments to multi-year floes, each subjecting the structure

to different load intensities. While there has been extensive research addressing the subjects of Ice mechanics and ice-structure interactions, there are

23
still unknown factors. Most of the work on fee-structure Interactions has

involved models and there are questions about extrapolating the model results

to the full-scale conditions. Information is also lacking on the statistical

properties of ice loadings, which are required to carry out a design having

a known reliability. Possible research subjects include the following:

-Studies of the distribution and local peak values of pressure generated

by Ice Impact on the structure; the effects of hydrodynamic damping, energy

absorption due to ice fracture and so i

I -structure compliance on the peak

values should be included

-Studies of the ice-adhesion bond to concrete and the associated friction

coefficients

-Analysis of ice loading statistics In order to arrive at load levels to

consider for different design limit states

-Development of load factors and load combinations to be considered in

design

Ductility enhancement:

The large global Ice forces on a structure will be transferred to the foundation

by means of internal structural elements, which have to be strong and relatively

ductile. The lack of ductility makes the structure susceptible to progressive

failure in the case of an unforseen local overload. The high variability

of Ice loading increases the probability of local overloads, and it is essential

that the structure be able to survive such conditions. Hence, Information

Is needed on how to achieve high strength and ductility for structural elements

subjected to the simultaneous action of compression and shear. Possible re- search topics might include:

-The development of novel reinforcement details

-The utilization of steel -concrete composite construction

5.2 RESEARCH AREAS RELATED TO MATERIALS

It has been demonstrated that reinforced concrete structures can be highly

durable in a marine environment provided that the materials and design details

are carefully chosen and executed. However, the severe environmental conditions of the Arctic pose new questions about the performance of concrete structures.

Permeability criteria for durability:

It is generally agreed that exposed concrete requires low permeability for

durability. Typically, low permeability has been achieved by specifying the

use of low water-cement ratios. However, with the widespread use of cement

replacements and additives (such as fly ash, slag and condensed silica fume),

water-cement ratio may no longer characterize the resultant permeability.

Hence, it Is logical to switch from water-cement ratio criteria to permeability criteria in order to assure durable concrete. Research should address

the fol lowing:

-Correlation between permeability and resistance to degradation by various

24
disruptive actions, such as sulfate attack, steel corrosion, freezing

and thawing, etc.

-Development of test methods to measure permeability, Including In-place

methods for acceptance testing

-Investigation of optimum mixture proportions in terms of strength, impermeability and economy

High-strength lightweight concrete:

Due to the shallow waters along towing routes from fabrication to installation

points, prefabricated structures must be capable of floating with low draft.

The use of lightweight concrete can help to satisfy this need, but for efficiency the concrete must also be of high strength. There are questions about

the mechanical and durability properties, and their Interrelationships, of

this new material. Areas to be investigated might include:

-Mechanical and thermal properties

-Resistance to freezing and thawing damage under saturated conditions,

including a re-exam i nation of the air-void system criteria to ensure adequate resistance against freezing and thawing

-Resistance to Ice abrasion, which would Include need to develop appropriate test methods

-Optimum mixture proportions

-Design criteria for structural elements

Corrosion of reinforcement:

An extensive amount of data have been accumulated on this subject, and it

Is generally agreed that corrosion Is not a problem In the permanently submerged

portion of an offshore structure. The problem Is severe where concrete Is exposed to alternating wetting and drying. Despite the wealth of research

data, there are still unresolved Issues such as the significance of cracking

on corrosion rate and allowable levels of chloride Ions. Conflicting conclusions have often been reported because of differences In testing conditions,

or because of unforseen Interactions among the factors affecting corrosion

rate. There Is a need to re-examine previous Investigations In the light

of our current understanding of steel corrosion In concrete, and develop practical and effective criteria for minimizing the probability of corrosion.

The following points should be studied:

-Allowable chloride Ion concentration, with due consideration to other

factors such as concrete permeability and depth of cover -The significance of cracking In relation to corrosion of reinforcing and

prestresslng steel

Other areas:

There are additional subjects that merit further study:

-Utilization of f Iber-relnforced concrete to enhance the energy absorption capabilities of structural members

-Utilization of polymer- Impregnated concrete to enhance strength and reduce

permeabl I Ity

-Coatings to reduce Ice adhesion

-Establish criteria to safeguard against degradation from freezing and

25
thawing action on water-filled cracks

5.3 RESEARCH AREAS RELATED TO CONSTRUCTION

The construction of large North Sea structures has resulted In the technology

required to successfully build and Install concrete offshore facilities.

The primary hinderances to direct utilization of this technology In Arctic

construction are the shallow waters over which the structures must be towed

and the short open water season. Identification of research areas related

to construction is not a simple task, because we are often dealing with the

developmenf of techniques to solve a particular problem rather than trying

to gain fundamental understanding about the nature of the problem. In addition,

many construction problems can be avoided during the design stage by giving

proper consideration to constructabl I Ity. Areas requiring new approaches might

Include:

-Techniques for rapid preparation of subsea foundations and protective

berms for gravity structures

-Techniques for towing structures through ice-covered waters

-Techniques for rapid joining of precast units at the Installation site

As pointed out in the Workshop, the Implications of the Jones Act should be

carefully re-examined. If It Is found that the Act will effectively eliminate

the possibility of construction of structures at U.S. locations, means of

permitting exemptions from the Act should be considered.

5.4 RESEARCH AREAS RELATED TO INSPECTION AND REPAIR

As In the case of construction, the inspection programs of North Sea structures

have produced orderly procedures for surveying large surface areas and for

efficient presentation of large amounts of data. In inspecting Arctic structures, consideration must be given to the fact that the structure will be

ice-bound for the major part of the year. To assist In future Inspections,

consideration should be given during design for providing access into the

structure so that some of the Inspection can be performed without having to

deal with the Icy environment. Identification of research needs related to

inspection is also difficult, because generally we are dealing with the development of new Inspection methods, the modification of existing methods, or the

evaluation of the applicability of existing methods In the Arctic environment. The following areas need investigation:

-Development of novel alternative techniques for rapid scanning of the

structure, techniques such as infra-red thermography or radar are promising

candidates

-Development of Inspection techniques utilizing remote controlled vehicles

with monitoring facilities on top of the structure

-Evaluation of performance of existing nondestructive test methods on frozen

concrete

26
Repair techniques will be dictated by the nature of the damage. Some forms

of damage will be unique to Arctic structures, such as abrasion by Ice or punching failure due to unusually large local Ice pressures. For these kinds

of damage, new repair techniques need to be developed. For typical damage

such as cracking or spalllng, existing techniques may be used. However, the

repair materials require careful evaluation to ensure that they will function

as desired under cold temperature conditions. The following topics should

be Investigated:

-Development of methods for repairing puncture damage, which would include

methods of repairing damaged reinforcement and restoring prestresslng

If necessary

-Development of techniques for evaluating the adequacy of repairs

-Development of appropriate repair materials for the types of damage and

environmental conditions unique to Arctic structures

27
6.0 ACKNOWLEDGMENT

Gratitude Is extended to Mr. Bruce Giza of the NBS Structures Division for

assistance In performing the literature search and arranging for acquisition

of the documents. Appreciation Is expressed to Mr. Charles E. Smith of the

Minerals Management Service for his help in providing publications and the

names of key Individuals In the subject area. Finally, thanks Is expressed

to the chairmen of the working groups and to the participants In the NBS Arctic

Workshop; their efforts played a major role in the successful completion of

this study.

28
7.0 REFERENCES

1) Anon., Encouraging Strikes Spur Search in U.S., Canadian Beaufort Sea Oil

and Gas Journal, Dec 21, 1981, pp 21-26

2) Anon., Other Platforms Show Possibilities, Offshore and Gulf Coast Oil

Reporter, V40, No 5, May 1980, pp 173-177

3) Fretheim, I.B., Offshore Structures for the Canadian Arctic, Proc of the

Canadian Structural Concrete Conference, University of Toronto, Sept 17-18,

1981, pp 19-55

4) Jahns, H.O., Arctic Platforms, Proc. Symposium on Outer Continental Shelf

Frontier Technology, Marine Board Assembly of Engineering, Nat Res Council,

Nat. Academy of Sciences, Wash. D.C., 1980, pp 41-71

5) Faulds, E.C., Structural Inspection and Maintainance In a North Sea

Environment, Proc 1982 Offshore Technology Conf, May 3-6, 1982, Houston,

TX, Vol. 3, OTC 4360, pp 713-724

6) Fjeld, S. and Roland, B., In-Service Experiences with Eleven Offshore

Concrete Structures, Proc 1982 Offshore Technology Conf, May 3-6, 1982,

Houston, TX, Vol. 3, OTC 4358, pp 687-693

7) Wlebenga, J.G., Durability of Concrete Structures Along the North Sea Coast

of the Netherlands, In AC I SP-65 Performance of Concrete In Marine

Environment, American Concrete Institute, Detroit, 1980, pp 437-452

8) Gjorv, O.E., Durability of Marine Concrete Structures Under Arctic

Conditions, Proc 1st Int Conf on Port and Ocean Engineering Under Arctic

Conditions, Trondhelm, Norway, 1971, pp 934-943

9) Mehta, P.K., Durability of Concrete In Marine Environment — A Review,

In AC I SP-65 Performance of Concrete In Marine Environment, American Concrete

Institute, Detroit, 1980, pp 1-20

10) Browne, R.D. and Domone, P.L.J., The Long-Term Performance of Concrete

In the Marine Environment Proc Conf Off-Shore Structures, ICE, London,

Oct 7-8, 1974, pp 49-59

11) Furnes, 0., Concrete and Other Alternative Platform Designs, Proc Int

Petroleum Exhibition and Technical Symposium (SPE), Bejlng, China,

March 18-26, 1982, SPE 10001, 31 pp

12) Moksnes, J., Quality Assurance for Concrete Platforms In North Sea Oil

Fields, Concrete International, V 4, No 9, September 1982, pp 13-19

13) Klvislld, H.R., Offshore Structures In Arctic Ice, Proc Int Conf on The

Behavior of Off-Shore Structures (BOSS '76), Trondhelm, Aug 2-5, 1976,

V 2, pp 249-266

29
14) Pal I lster,A.E. and Pal lister, J., Ice Covered Waters — A New Offshore

Petroleum Environment, APOA Review, V 1, No 2, May 1978, pp 12-17

15) Engelbrektson, A., Ice Force Design In the Light of Experiences from the

Baltic Paper prepared for International Conference "Offshore Goteborg-83",

VRM 057-003, 16 pp

16) Tunik, A., Miller, D.N. and Chen, Y.K., Literature Review on Ice Loadings, American Bureau of Shipping Technical Report 0ED-83006/TD-8301

,

Feb. 1983, 153 pp.

17) Anon., Review of APOA Project 110 - Conical and Cylindrical Gravity

Structures for Southern Beaufort Sea, APOA Review, V 6, No 1 , Spring/Summer

1983, pp 28-29

18) Jarlan, C.E., Hibernia Oilfield Development of a Prestressed Concrete

Drilling and Production Platform, Proc Symposium on Production and

Transportation Systems for Hibernia Discovery, St. Johns NF, Feb 16-18,

1981, pp 18-26

19) Gerwick, B.C.,, Prestressed Concrete Floating Terminal for Arctic Ocean

Service, Proc 3rd Int Conf on Port and Ocean Engineering Under Arctic

Conditions, Fairbanks, AK, Aug 11-15, 1975, pp 581-595

20) Gerwick, B.C., Utilization of Prestressed Concrete In Arctic Ocean

Structures, Proc 1st Int Conf on Port and Ocean Engineering Under Arctic

Conditions, Trondhelm, Norway, 1971, pp 917-933

21) Fitzpatrlck, J. and Stennlng, D.G., Design and Construction of Tarsiut

Island In the Canadian Beaufort Sea, Proc 1983 Offshore Technology Conf,

May 2-5, 1983, Houston, TX, Vol. 2, OTC 4517, pp 51-60

22) Weaver, J.S. and Berzlnis, W., The Tarsiut Island Monitoring Program,

Proc 1983 Offshore Technology Conf, May 2-5, 1983, Houston, TX, Vol. 2,

OTC 4519, pp 67-74

23) Anon., Exxon to Use Concrete Island to Drill In Beaufort, Oil and Gas

Journal, Sept. 19, 1983, pp 82-83

24) Carino, N.J., Editor, Proceedings of the International Workshop on the

Performance of Offshore Concrete Structures in the Arctic Environment,

March 1 and 2, 1983, National Bureau of Standards, NBSIR 83-2751, July

1983, 69 pp (also CANMET Report MRP/MSL 83-128 (OP & J))

30
APPENDIX

A.1 ANNOTATED BIBLIOGRAPHY

DESIGN

Anon., Review of APOA Project 110 - Conical and Cylindrical Gravity Structures

for Southern Beaufort Sea, APOA Review, V6, No 1, Spring/Summer 1983, pp 28-29

Reviews research project by Esso Resources Canada Ltd on design of monocone

gravity structure. Important questions that require further investigation

include the long-term water absorption properties and the shear and tensile

strength of the proposed I ightweight reinforced concrete. It is stated that

the combination of cost and engineering difficulties of the monocone concept

have led to suspension of work on bottom-founded gravity structures.

Engelbrektson, A., Ice Force Design In the Light of Experiences from the Baltic,

Paper prepared for International Conference "Offshore Goteborg 83",

VRM 057-003, 16 pp

Describes ice load prediction methods against the background of experiences

gained from Swedish lighthouse structures In the Baltic. Discusses factors

affecting Ice forces on structures and the dynamic effects of ice forces.

Design equations for predicting ice forces are presented, and it is suggested

that they would be applicable in Arctic sites having similar Ice characteristics

to the Baltic Sea.

Almazov, V.O. and Kopalgorodski, E.M., Bearing Capacity of a Reinforced Concrete

Shell in an Arctic Environment, Cold Regions Science and Technology, 6(1982)

pp 89-98

Discusses design requirements for offshore Arctic Structures in order to prevent

cracking of concrete under external loads plus stresses due to temperature

gradients. Describes research studies In USSR of model shell structures subjected to external forces plus stresses due to temperature gradients (0 to

-50°C). Also describes tests on beam and compression members.

Furnes, 0., Concrete and Other Alternative Platform Designs, Proc Int Petroleum

Exhibition and Technical Symposium (SPE), Bejing, China, March 18-26, 1982,

SPE 10001, 31 pp

Reviews the design and construction of North Sea platforms. Design principles

and analytical procedures are outlined. Alternatives to concrete gravity

platforms are discussed. It Is concluded that concrete structures designed

In accordance with current criteria are durable and maintenance-free even

in the harsh North Sea environment.

31
Waagaard, K., Fatigue Strength Evaluation of Offshore Concrete Structures,

In ACS SP-75 Fatigue of Concrete Structures, American Concrete Institute,

Detroit, 1982, pp 373-397

Presents a summary of recommendations for fatigue strength evaluations of

offshore concrete structures. The fatigue provisions of AC I, DNV, FIP, NPD

and TNO are reviewed and compared. Cites the need to develop simplified evaluation methods to Indicate whether fatigue will control structural design.

Yee, A. A., The Superiority of Concrete Honeycomb Construction for Marine

Structures, Proc Arctic Offshore Drilling Platform Symposium, Los Angeles

CA, October 7, 1982, pp 7-1 - 7-16

Discusses structural concept for concrete offshore structures composed of

a honeycomb cellular core with composite top and bottom slabs. The design

Is claimed to result In economical use of materials, has material storage

areas and low draft requirements. Concepts for use of such structures In the

Arctic are described.

Frethelm, I.B., Offshore Structures for the Canadian Arctic, Proc of the

Canadian Structural Concrete Conference, University of Toronto, Sept 17-18,

1981, pp 19-55

Discusses considerations and concept solutions to the design of production

platforms. The main concepts Include: conical gravity structures, caisson

gravity structures, earth-filled caisson retained structures and earthflll

structures. The positive and negative features of each concept are discussed.

In addition, hybrid concepts which combine the strengths of Individual concepts

are presented.

Gerwlck, B.C., Concrete Offshore Structures — A State of the Art, Proc of

the Canadian Structural Concrete Conference, University of Toronto, Sept 17-18,

1981, pp 3-17

Identifies problem areas for concrete structures in the Arctic: the properties

and behavior of lightweight concrete; coatings for concrete; punching shear

resistance of walls; fatigue properties In a marine environment; thermal

strains; freezing and thawing; steel corrosion; stability of structures during

towing and Installation; earthquake response; freezing of water In confined

spaces; grouting of ducts; connection of deck to substructure; and repair

of damaqe.

32
Gerwick, B.C., Litton, R.W. and Reimer, R.B., Resistance of Concrete Walls

to High Concentrated Ice Loads, Proc 1981 Offshore Technology Conf, May 4-7,

1981, Houston, TX, Vol. 3, OTC 4111, pp 425-436

Addresses the resistance of walls to local concentrated ice forces. Design

of walls according to current building code practice results in excessively

thick walls that present flotation problems. A finite element analysis of

a wall segment was performed to gain insight into the structural performance

under high local loading. It is suggested that the required punching resistance

may be achieved by prestressing through the thickness. For ductility, stirrups

should be anchored.

Jarlan, C.E., Hibernia Oilfield Development of a Prestressed Concrete Drilling

and Production Platform, Proc Symposium on Production and Transportation Systems

for Hibernia Discovery, St. Johns NF, Feb 16-18, 1981, pp 18-26

Presents a design concept for a prestressed gravity platform for the Hibernia

field. Features of the structure are derived from previous concepts and knowledge related to installations in ice infested waters. The structure is similar

to the Ekofisk tank in the North Sea except that it is adapted to resist ice

impact. The hydrodynamics of moving icebergs are presented. A rubble mound

is suggested to dampen iceberg impact forces. Suggestions are given for hydrauI ic model studies.

Letourneur, 0. and Falcimaigne, J., Concrete Production Floating Platforms,

Proc Symposium on Production and Transportation Systems for Hibernia Discovery,

St. Johns NF, Feb 16-18, 1981, pp 122-133

Discusses the design of a floating concrete production platform for use in

the Hibernia field. The structure is patterned after similar platforms used

in the North Sea. Upon the approach of a large iceberg, the platform would

be disconnected and moved away from the approaching ice.

Lundrigan, H. and Lindgren, J., Potential Concrete Structures for Hibernia,

Proc Symposium on Production and Transportation Systems for Hibernia Discovery,

St. Johns NF, Feb 16-18, 1981, pp 27-38

Discusses in general terms the construction schemes for structures off of

Newfoundland; the methodology is patterned after proven techniques in North

Sea construction. Three design approaches for fixed platforms to withstand

iceberg impact are discussed. The fixed structure may be surrounded by protective berms or fendering to absorb impact energy of the icebergs, or the structure is designed to resist impact by elastic energy absorption.

33
Anon., Other Platforms Show Possibilities, Offshore and Gulf Coast Oil Reporter,

V40, No 5, May 1980, pp 173-177

Describes different platform concepts for the Arctic. Concrete structures

include conical hull structures that are gravity or pile supported and are

intended for water depths up to 250 ft. For deeper waters, a floating concrete

caisson has been proposed.

Jahns, H.O., Arctic Platforms, Proc Symposium on Outer Continental Shelf

Frontier Technology, Marine Board Assembly of Engineering, Nat Res Council,

Nat. Academy of Sciences, Wash. D.C., 1980, pp 41-71

Presents a survey of existing and proposed platforms for use in areas where

resistance to Ice forces Is major design consideration. Man-made islands identified as being the most technically and economically attractive structures

In shallow waters with large ice forces. Gravel and ice Islands are discussed.

Concepts for use In deeper Arctic waters are presented. Extensive reference

I 1st.

Allan, A. and Pal lister, J., The Mechanical Properties of Ice: The Second

Step, APOA Review, V 2, No 2, June 1979, pp 7-11

Reviews research programs on the properties of ice. Various test methods

developed for in-place testing are described.

Bercha, F.G. and Stenning, D.G., Arctic Offshore Deepwater Ice-Structure

Interactions, Proc 1979 Offshore Technology Conf, April 30-May 3, 1979,

Houston, TX, Vol. 4, OTC 3632, pp 2377-2386

Interactions of ice formations with monocone gravity structure are described.

Authors conclude that design loads can be predicted by judicious application

of modern and classical ice mechanics. However, there are still unanswered

questions about: scale effects; the statistical descriptions of input data;

extension of interaction analyses to other processes; and a comprehensive

probabilistic analysis of all interactions.

Pal I lster,A.E. and Pal lister, J., Ice Covered Waters — A New Offshore Petroleum

Environment, APOA Review, V 1, No 2, May 1978, pp 12-17

Provides a general description of the various ice forms that are encountered

in the Arctic. A glossary of Ice terms Is provided, and two research projects

on ice conditions In the Arctic are reviewed.

34
de Long, J. J. A. and Bruce, J.C., Design and Construction of a Caisson Retained

Island Drilling Platform for the Beaufort Sea, Proc 1978 Offshore Technology

Conf, May 8-10, 1978, Houston, TX, Vol. 4, OTC 3294, pp 2111-2120

Describes design of a set of caissons for construction of retained island

in the Beaufort Sea. While the specific design Is steel, the economics and

operational principles apply equally to a concrete structure. The justification

for such structures is the reduction in fill material to create an artificial

island. .—--.-

Jazrawi, W. and Khanna, J., Monocone - A Mobile Gravity Platform for the Arctic

Offshore, Proc 4th Int Conf on Port and Ocean Engineering Under Arctic

Conditions, St. Johns, NF, Sept 26-30, 1977, pp 170-184

Discusses the "monocone" concept— a single column gravity structure resting

on a large circular base and fitted with a moveable conical collar Intended

to cause downward flexural failure of the Ice. Design criteria are discussed

and it Is stated that the monocone is an efficient and versatile structure

capable of being set down in water up to 41 m deep. The structure is intended

to provide year-round operation.

Gerwick, B.C., The Future of Offshore Concrete Structures, Proc Int Conf on The Behavior of Off-Shore Structures (BOSS '76), Trondheim, Aug 2-5, 1976,

V 1, pp 978-1000

Future developments in the field of offshore concrete structures are described.

The following areas are addressed: new design concepts for new environments;

advances In design procedures; Improved construction methods; development

of new concrete materials; and Improvements In management and contractual

capabilities to carry out large and complex projects.

Kivlsild, H.R., Offshore Structures In Arctic Ice, Proc Int Conf on The Behavior

of Off-Shore Structures (BOSS '76), Trondheim, Aug 2-5, 1976, V 2, pp 249-266

A general treatment of the problems associated with structures In the Arctic.

The main features of the Ice environment are presented, and the various design

concepts for coping with ice forces are described. The possible interactions

between different Ice formations and platform structures are discussed. The

magnitude of the ice forces depend on the nature of the Ice formation and

the structure's geometry.

Gerwick, B.C., Prestressed Concrete Floating Terminal for Arctic Ocean Service,

Proc 3rd Int Conf on Port and Ocean Engineering Under Arctic Conditions,

Fairbanks, AK, Aug 11-15, 1975, pp 581-595

Describes conceptual design of large prestressed concrete floating terminal,

which would be designed for downward breaking of the Ice. Advancements in

concrete materials technology and In the understanding of shear-resistant

mechanisms are cited as factors that will further the application of prestressed

35
concrete In the Arctic.

Gerwick, B.C., Utilization of Prestressed Concrete In Arctic Ocean Structures,

Proc 1st Int Conf on Port and Ocean Engineering Under Arctic Conditions,

Trondheim, Norway, 1971,pp 917-933

Discusses ways In which prestressed concrete can be effectively used In Arctic

offshore construction. Conceptual designs of prestressed concrete drilling

and production platforms In shallow and deep waters are described.

MATERIALS

Ivanov, F.M., Vinogradova, E.A., Gladkov, V.S., and Usachev, I.N,, Frost

Resistant Concrete for Offshore Structures, Operational Life (In Russian),

691.327:666.972.53, pp 40-41

Discusses requirements to assure concrete capable of withstanding many cycles

of freezing and thawing: use materials with proven service records, optimize

concrete mixture Including appropriate admixtures; maintain correct curing

conditions to assure durable hardened paste and minimize thermal stresses;

and use proper consolidation procedures. Service record of 15 years shows

that when properly made concrete can withstand severe exposure to freezing

and thawing In the Arctic environment.

Arthur, P.D., Earl, J.C. and Hodkiess, T., Corrosion Fatigue In Concrete for

Marine Applications, In ACI SP-75 Fatigue of Concrete Structures, American

Concrete Institute, Detroit, 1982, pp 1-24

Reports on studies of the fatigue life of reinforced concrete beams exposed

to sea water. Under low cycle fatigue (ocean wave frequency), found that

fatigue life In sea water is better than in air; this is explained by deposition

of solid material In the cracks (crack blocking). At higher frequencies (3

to 5 Hz), crack blocking did not occur and fatigue life In sea water was reduced. Data on reversed bending and with prestressed concrete are being

obtained.

Mehta, P.K. and Gerwick, B.C., Cracking-Corrosion Interaction in Concrete

Exposed to Marine Environment, Concrete International, V 4, No 10, October

1982, pp 45-51

Physical and chemical processes which lead to enlargement of microcracklng

in concrete are classified, and the chemical processes of corrosion are reviewed. A necessary factor for active corrosion is the presence of an adequate

supply of oxygen. Increasing concrete permeability Increases the access of

oxygen to steel. The primary effect of Increased microcracklng Is to Increase

concrete permeability.

36
Browne, R., Mechanisms of Corrosion of Steel in Concrete In Relation to Design,

Inspection and Repair of Offshore and Coastal Structures, In AC I SP-65

Performance of Concrete in Marine Environment, American Concrete Institute,

Detroit, 1980, pp 169-204

Reviews research carried out in the UK and other countries to answer questions

about the expected performance of North Sea structures. Discusses 4 key factors

related to steel corrosion: chloride Ion penetration, loss of concrete resistivity, availability of oxygen and concrete cover. Unanswered questions relative

to these factors are presented. Different levels of repair are suggested

based on the level of chloride ions and deterioration.

FIdjestol, P. and Nil sen, N., Field Test of Reinforcement Corrosion in Concrete,

In AC I SP-65 Performance of Concrete In Marine Environment, American Concrete

Institute, Detroit, 1980, pp 205-221

Reports on the results of research aimed at answering questions about the

relationship between crack width and corrosion. Precracked beams were placed

in sea water, and electrochemical measurements were made along with examination

of the reinforcment at periodic Intervals. The conclusions were that the

corrosion rate in saturated concrete is very low due to a low oxygen concentration and that crack widths within the normal range and under static load have

minor Importance.

Gerwlck, B.C., Research Requirements for Concrete In Marine Environment, in

AC I SP-65 Performance of Concrete In Marine Environment, American Concrete

Institute, Detroit, 1980, pp 577-587

Reviews recent research projects aimed at answering questions about the performance of concrete structures in hostile marine environments. Future research

should be performed In the areas of structural response, environmental degradation, new materials, methods of construction and repair, and new design concepts. It Is suggested that joint Industry-government research programs are

a means for undertaking large and expensive research projects.

Haynes, H., Permeability of Concrete In Sea Water, In ACI SP-65 Performance

of Concrete in Marine Environment, American Concrete Institute, Detroit, 1980,

pp 21-38

Discusses relationship between porosity In concrete and permeability. It Is the capillary pores In hardened paste that controls permeability. Tests Indicate that the permeability of concrete exposed to sea water decreases with

time, which Is postulated to be due to chemical reactions that produce solid

products that block pores in the paste.

37
Holm, T.A., Performance of Structural Lightweight Concrete In a Marine

Environment, In ACI SP-65 Performance of Concrete In Marine Environment,

American Concrete Institute, Detroit, 1980, pp 589-608

Reviews performance of I Ightwelght concrete structures exposed to sea water.

Laboratory freezing and thawing tests are reviewed, as well as tests on cores recovered from a concrete ship built In 1919. It was concluded that properly

proportioned lightweight concrete can provide excellent performance In marine

appl Icatlons.

Maklta, M., Mori, Y. and KatawakI, «., Performance of Typical Protection Methods

for Reinforced Concrete In Marine Environment, In ACI SP-65 Performance of

Concrete In Marine Environment, American Concrete Institute, Detroit, 1980,

pp 453-471

Discusses the use of resin coatings, galvanizing, cathodlc protection, concrete

coatings and inhibitors as possible means of protecting steel In concrete.

Powder epoxy coatings gave best protection. Urethane concrete coatings proved

to offer no protection, likewise for sodium sulfite based Inhibitors. Galvanizing was found to not always be satisfactory In the splash zone.

Mehta, P.K., Durability of Concrete In Marine Environment — A Review, In ACI SP-65 Performance of Concrete In Marine Environment, American Concrete

Institute, Detroit, 1980, pp 1-20

Reviews Investigations of the durability of concrete exposed to sea water.

Presents chemical reactions associated with the deterioration of concrete

and steel corrosion. It is concluded that Impermeability Is the most important

property governing the durability of concrete. In addition, Individual processes of deterioration tend to limit themselves to different parts of the structure. The tidal zone Is the most vulnerable part of a marine structure.

C'Nell E.F., Study of Reinforced Concrete Beams Exposed to Marine Environment,

In ACI SP-65 Performance of Concrete In Marine Environment, American Concrete

Institute, Detroit, 1980, pp 113-132

Reports on long-term study of reinforced beams exposed to sea water in the

tidal zone and to freezing and thawing. Major conclusions were that with

air entrained concrete the years of exposure did not lower the f lexural strength

below design values, and that larger crack widths Increased the amount of

corrosion. Crack widths less than 0.4 mm did not result in corrosion.
Okada, K. and Miyagawa, T., Chloride Corrosion of Reinforcing Steel In Cracked

Concrete, In AC I SP-65 Performance of Concrete In Marine Environment, American

Concrete Institute, Detroit, 1980, pp 237-254

Examines the influence of cracks on the mechanism and rate of corrosion of

reinforcing steel. It was concluded that the corrosion rates decreased with

time, and under conditions of wetting and drying the corrosion rate increased

during drying. A clear relationship between crack width and corrosion rate

was not established.

Paterson, W.S., Fatigue of Reinforced Concrete in Sea Water, in ACI SP-65

Performance of Concrete In Marine Environment, American Concrete Institute,

Detroit, 1980, pp 419-436

Reports on results of research to study the fatigue life of cold worked reinforcement (Torbar) In sea water. Found that cracks In reinforced concrete

beams filled up with deposits during tests. Tests did not Identify a fatigue

limit for the steel reinforcement.

Sharp, J.V. and Pu I lar-Strecker, P., The United Kingdom Concrete- in-the Oceans

Program, In ACI SP-65 Performance of Concrete In Marine Environment, American

Concrete Institute, Detroit, 1980, pp 397-417

Reviews UK research program. Seven projects are discussed; three of them deal

with corrosion, three deal with siructural aspects and one deals with inspection

of existing offshore structures. Findings of the corrosion projects are summarized: cracking affects initiation of corrosion bui other factors affect its

rate; there will be little or no corrosion in permanently submerged structures;

in the splash zone adequate concrete cover is required to prevent corrosion.

Vanden Bosch, V.D., Performance of Mortar Specimens In Chemical Accelerated

Marine Exposure, In ACI SP-65 Performance of Concrete In Marine Environment,

American Concrete Institute, Detroit, 1980, pp 487-507

Reports results of tests on the chemical resistance of portland and blast

furnace slag cement. Concluded that 10% slag addition results in concrete

with high resistance to sea water attack. Excellent performance of marine

structures In the Netherlands Is cited as demonstration of the durability

of slag cement concrete.

Gjorv, 0., Vennesland, 0. and El-Busaidy, A.H.S., Electrical Resistivity of

Concrete In Oceans, Proc 1977 Offshore Technology Conf, May 2-5, 1977, Houston,

TX, Vol. 1, 0TC 2803, pp 581-588

Reports on laboratory experiments aimed at providing information on the electrical resistivity of concrete. The degree of saturation was found to have

the greatest effect on the resistivity value. In general, the same factors

39
that affect permeability were found to influence resistivity, such as degree

of hydration, water/cement ratio, and maximum aggregate size. Cracking tended

to reduce resistivity.

Matsuishi, M., Nishimaki, K., Takeshita, H, Iwata, S. and Suhara, T., On the

Strength of New Composite Steel -Concrete Material for Offshore Structure,

Proc 1977 Offshore Technology Conf, May 2-5, 1977, Houston, TX, Vol. 1, OTC

2804, pp 589-594

Describes composite material composed of concrete placed between steel plates.

Beams were made and tested in center-point loading. The composite material

is reported to provide large energy absorption capacity. A method for computing

the ultimate strength of the composite material Is presented. Test results

are compared with non-linear finite element analysis.

Browne, R.D. and Domone, P.L.J. , The Long-Term Performance of Concrete in

the Marine Environment, Proc Conf Off-Shore Structures, ICE, London, Oct 7-8,

1974, pp 49-59

Reviews previous studies on the durability of concrete in marine environments.

It Is concluded that in order to produce durable concrete: use materials

with proven history, especially cement composition; use correct mixture proportions to permit low permeability along with ease of placement; use proper

design details, such as cover, especially In the splash zone; and adopt proper

quality control procedures during construction.

Gjorv, O.E., Durability of Marine Concrete Structures Under Arctic Conditions,

Proc 1st Int Conf on Port and Ocean Engineering Under Arctic Conditions,

Trondhelm, Norway, 1971, pp 934-943

Reviews the results of Inspections of marine structures along the Norwegian

Coast. The most serious durability problems were associated with chemical

deterioration of concrete and steel corrosion. The tidal zone was identified

as being most vulnerable to environmental attack, and deterioration appears

to result from Interactions of several processes. In general, the inspected

structures were in good condition even after 50 years of service.

40
CONSTRUCTION

Fitzpatrick, J. and Stennlng, D.G., Design and Construction of Tarsiut Island

In the Canadian Beaufort Sea, Proc 1983 Offshore Technology Conf, May 2-5,

1983, Houston, TX, Vol. 2, OTC 4517, pp 51-60

Presents a summary of the design and construction considerations for the Tarsiut

Island. The Island Is constructed of four concrete caissons arranged In a square, backfilled and resting upon a submerged sand berm. The advantage

of lightweight concrete Is highlighted. The structure was completed In Oct.

1981 and has survived two winters. The construction process Is outlined.

Anon., E&P Spending in Canadian Frontier Areas to Hit $1.2 Billion in 1982,

Oil and Gas Journal, July 12, 1982, pp 84-93

Discusses status of Canadian oil exploration in the Arctic regions. The Tarsiut

Island project Is highlighted as the first step In planning for a series of

larger islands.

Anon., Operator Interest Keen in U.S. Beaufort Sea, Oil and Gas Journal, July

12, 1982, pp 71-77

Discusses status of US oil exploration In the Alsaka region.

Mcksnes, J., Quality Assurance for Concrete Platforms In North Sea Oil Fields,

Concrete International, V 4, No 9, September 1982, pp 13-19

Describes the quality assurance program employed in the construction of North

Sea oil platforms. The quality control procedures employed during construction

are also described. It is reported that rigorous requirements for these structures have resulted in a general Improvement In project management, construction

procedures and concrete technology.

Anon., Encouraging Strikes Spur Search in U.S., Canadian Beaufort Sea, Oil

and Gas Journal, Dec 21, 1981, pp 21-26

Discusses results and future plans for exploration and production drilling

In the Beaufort Sea. The Canadian development plan Is described, and It calls

for the construction of a significant number of artificial Islands.

MacLeod, N.R. and Butler, J.H., The Evaluation of Dredging Materials for

Island Construction In the Beaufort Sea, Proc 1979 Offshore Technology Conf,

April 30-May 3, 1979, Houston, TX, Vol. 4, OTC 3633, pp 2387-2397

Describes three-phase program to obtain suitable materials for construction

of the Issungnak gravel Island In 20 m of water. The phases Included: a reflection seismic survey to locate prime borrow areas; sampling of sediments; and

41
dredging tests to verify that required production rates could be achieved.

Long, J.E., Experience In Prestresslng and Grouting Concrete Offshore

Structures, Proc Conf Design and Construction of Offshore Structures, ICE,

London, Oct 27-28, 1976, pp 115-119

Reviews experiences gained during construction of North Sea platforms. Most

pioneering work has been In the area of grouting very tall vertical ducts.

Procedures are suggested for successful grouting of vertical ducts.

Werensklold, K., Maritime Operations Relative to Construction of Large Concrete

Offshore Structures, Proc Conf Design and Construction of Offshore Structures,

ICE, London, Oct 27-28, 1976, pp 97-105

Describes the tasks of maritime operations related to the construction of

offshore structures towed to their final locations. It is emphasized that

careful planning and consideration of many details Is essential for a successful

operation. Back-up systems must be available and all participants must be

properly briefed.

Doughty, S.C., Deep Sea Construction, ASCE Journal of the Construction Division,

V101, No 3, Sept 1975, pp 607-622

Discusses the complexity of deep sea construction; the special problems associated with Arctic structures ere mentioned.

Eriksson, K., Concrete Caissons for Offshore Lighthouses, Proc FIP Symposium

on Concrete Sea Structures, Tbilisi, 1972, pp 79-83

Describes construction techniques of Swedish lighthouses and suggests that

techniques are applicable to offshore arctic structures. Experiences Indicate

that as little construction as possible should be performed at sea. At sea the most difficult work encountered was the preparation of the seabed.

42
INSPECTION/REPAIR

Weaver, J.S. and Berzinis, W., The Tarsiut Island Monitoring Program, Proc

1983 Offshore Technology Conf, May 2-5, 1983, Houston, TX, Vol. 2, OTC 4519,

pp 67-74

Presents a description of the monitoring programs used during the construction

of Tarsiut Island and during drilling of exploration well. A quality assurance

program was used to assure that the structure was built as required. Procedures

are described for controlling the grain size of the berm fill material, for

assessing the shear strength of the seabed, and for monitoring the sandfill

densities. The Instrumentation for the operational monitoring program Is discussed.

Wright, B.D. and Weaver, J.S., Tarsiut Winter Alert Warning, Proc 1983 Offshore

Technology Conf, May 2-5, 1983, Houston, TX, Vol. 2, OTC 4518, pp 61-66

Describes methodology, procedures and experiences associated with the Tarsiut

Island monitoring program. The Ice conditions surrounding the island are

discussed. Instrumentation was installed to measure ice loads and the island's

response. The objectives were to provide real time monitoring of structural

performance and to provide data for Improved design criteria. Observed Ice

forces during the 1981-82 winter were less than the design values.

Faulds, E.C., Structural Inspection and Ma intai nance in a North Sea Environment,

Proc 1982 Offshore Technology Conf, May 3-6, 1982, Houston, TX, Vol. 3, OTC

4360, pp 713-724

Reviews experiences and lessons (technical and financial) learned from Inspections of North Sea structures. Statutory requirements and Inspection philosophy

are reviewed. Inspection plans are presented and the application of inspection

equipment and techniques are described. The superiority of concrete over steel structures in terms of less frequent inspections and maintenance is

mentioned. Repair procedures are described for damages Incurred by some structures.

Fjeld, S. and Roland, B., In-Service Experiences with Eleven Offshore Concrete

Structures, Proc 1982 Offshore Technology Conf, May 3-6, 1982, Houston, TX,

Vol. 3, OTC 4358, pp 687-693

Discusses possible deterioration sources of concrete structures: overloads;

concrete degradation; steel corrosion; and foundation scouring. Presents

general considerations in planning an Inspection program. Visual Inspection

Is the most feasible and reliable method for underwater inspection of concrete

structures. Results of inspection of 11 structures In the North Sea revealed

excellent performance. The only significant damages were due to accidental

local impact loads.

43
Browne, R.D., Doyle, V.J. and Papworth, F., Inspection of Concrete Offshore

Structures, Journal of Petroleum Technology, V 33, No 1

1 , Nov 1981, pp 2243-2251

Discusses the inspection philosophy and procedures used to inspect an offshore

concrete structure. Critical areas are defined for detailed inspection.

Procedures are presented for dealing with the vast data collected during an inspection. Areas of research related to repair are discussed. The development

of underwater NDT methods to locate defects covered by marine growth, to assess

and monitor corrosion, and to evaluate the effectiveness of repairs are critical areas of needed research.

Geymayr, G.W., Repair of Concrete in Tropical Marine Environment, in AC I SP-65

Performance of Concrete in Marine Environment, American Concrete Institute,

Detroit, 1980, pp 527-556

Corrosion mechanisms for reinforced concrete in sea water are reviewed. Various

repair techniques are discussed. Use of epoxy mortar for underwater repairs

on actual structures is described. The proper use of vapor barriers is discussed.

Heneghan, J. I., Shotcrete Repairs of Concrete Structures in Marine Environment,

in AC I SP-65 Performance of Concrete in Marine Environment, American Concrete

Institute, Detroit, 1980, pp 509-526

Presents discussion of causes of damage to marine structures. Proper proportioning of shotcrete mixtures including use of accelerators and latex emulsions.

Procedures for surface preparation, anchoring of reinforcing steel and shotcrete placement are presented. Case studies of successful shotcrete repairs

are discussed.

Schrader, E., Dikeou, J. and Gill, D., Deterioration and Repairs of Navigation

Lock Concrete, in AC I SP-65 Performance of Concrete in Marine Environment,

American Concrete Institute, Detroit, 1980, pp 557-576

Reports on test program to evaluate alternative materials and methods to repair

damaged walls of navigation lock. A thin coat of glass fiber reinforced and

latex modified shotcrete was chosen as the most cost effective repair method.

Wiebenga, J.G., Durability of Concrete Structures Along the North Sea Coast

of the Netherlands, in AC I SP-65 Performance of Concrete in Marine

Environment, American Concrete Institute, Detroit, 1980, pp 437-452

Reports on inspection of 64 North Sea structures ranging in ages from 3 to

63 years. Most were built with blast furnace slag cement. Depth of carbonation

in splash zone was found to be low. Fifty-six structures did not have evidence

of corrosion. Where corrosion was found, it was associated with a long period

of exposure and insufficient concrete cover.

44
Browne, R.D., Domone, P.L. and Geoghegan, M.P., Inspection and Monitoring

of Concrete Structures for Steel Corrosion, Proc 1977 Offshore Technology

Conf, May 2-5, 1977, Houston, TX, Vol. 1, OTC 2802, pp 571-580

Reviews existing inspection methods for embedded steel, such as: visual; reinforcement location with covermeter; chloride content determination of cored

samples; electrochemical potential of in-place steel; and measurement of con- crete resistivity. None of existing methods are totally adequate, and development of new approaches Is needed. A possibility Is to develop a method which

continuously monitors embedded steel.

45
A. 2 RESEARCH PROJECTS ON OFFSHORE CONCRETE STRUCTURES

ALASKA OIL AND GAS ASSOCIATION

#10 Arctic Marine Terminal Facilities, Chukchi Sea

#11 Offshore Oil Terminal Structure Facilities In the Chukchi Sea

#22 Investigation of Ice Forces on Cylindrical and Conical Offshore

Structures

#61 Conical Structure Test Program

#75 Sea and Subsea Floor Properties

#77 Superstructure Icing

#83 Seismic Risk Analysis for the Gulf of Alaska

#106 Arctic Cone Test Strucuture - Phase I #113 Conical Structure Test Program, 1979-80

#121 Preliminary Design of an Arctic Cone Test Structure with Indirect

Load Measurement

#124 Beaufort Sea Multi-year Ice Ridges and Land-fast Ice Crystal

Orientation

#152 Punching Shear Resistance of Concrete Structures

#155 Evaluation of Artificial Islands for Norton Sound

#156 Ice Interaction with Sloping Barriers

#162 Norton Sound Production Structure

#174 Design of an Arctic Cone Exploration Structure— Phase I

ARCTIC P ETROLEUM OPERATORS ASSOCIATION

#57 Adfreeze Study

#85 Adfreeze on Conical Structures

#86 Study of Pressure Ridge/Cone Interaction

#103 Interaction Between Ice Sheets & Wide Structures

#104 Measurement of Ice Pressures on Artificial Islands (Phase I)

#105 In-Situ Ice Pressure Measurements Around Artificial Islands

(Phase I I)

#110 Conical and Cylindrical Gravity Structures for Southern Beaufort

Sea

#122 In-Situ Ice Pressure Measurements 1976/77

#125 Experimental Ridge-Caisson Retained Island Interaction 1976/77

#143 Model Experiments to Determine the Forces and Behavior of Moving

Ice Fields Against a Concrete Drilling Caisson

#145 Caisson Retained Island Design

#197 Tarsiut Caisson Island Data Acquisition 1981/82

#197 Tarsiut Caisson Island Data Acquisition 1982/83

#204 Arctic Offshore Production Platform Evaluation

#205 Environmental Design Criteria for Arctic Offshore Platforms

46
PET NORSKE VERITAS

Behavior of Concrete Structures in Deep Water

Ductility Performance of Offshore Concrete Structures

Impacts and Collisions Against Offshore Platforms

Ice-Structure Interaction

Dynamic Response of Fixed Structures Under Impulsive and Cyclic Ice

Loading

STUDIES FOR OFFSHORE NEWFOUNDLAND

Fixed Platform Feasibility Study

Offshore Storage and Loading Facilities Feasibility Study

Ice Protection Studies

Gravity Base Structure — Feasibility Design

Gravity Base Structure — Gectechntcal Studies

Gravity Base Structure — Concrete Punching Shear Analysis

Risk Assessment Study

NETHERLANDS INDUSTRIAL COUNCIL FOR OCEANOLOGY

Concrete Mechanics

Durability of Concrete Offshore Structures

Fatigue of Concrete

Probabilistic Safety of Offshore Structures

UK CONCRETE- I N-THE-OCEANS PROGRAM

Fundamental Mechanisms of Corrosion of Steel Reinforcement in Concrete

Immersed in Sea Water

Designing Against Corrosion in Offshore Structures

Exposure Tests on Concrete Samples Under Different

Exposure Conditions

Effects of Temperature Gradients on Walls of Oil Storage Structures

Survey of Existing Reinforced Concrete Marine Structures

Strength of Large Prestressed Concrete Members in Shear

Fatigue Strength of Reinforced and Prestressed Concrete In Seawater

Modes of Failure of Concrete Platforms

Fatigue Analysis of Reinforced Concrete Marine Structures

Review of Punching Shear and Impact Resistance of Concrete Slabs

Location of Potential Areas of Corrosion in Concrete Offshore Structures

Corrosion Under Water Undetectable by Visual Inspection

Criteria for Cover and Control of Cracking

Classification of Typical Visible Defects

Fatigue Strength of Repaired Beams

Impact Damage to Cell Roofs

47
NBS-114A (REV. 2-8C) U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS TN 1192

2. Performing Organ. Report No. 3. Publication Date

April 1984

4. TITLE AND SUBTITLE

Offshore Concrete Structures in the Arctic: Research Needs

5. AUTHOR(S)

Nicholas J. Carino

6. PERFORMING ORGANIZATION (If joint or other than NBS. see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

Final

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City, State. ZIP)

Technology Assessment and Research Branch

Minerals Management Service

U.S. Department of the Interior

Reston, VA 22091

10. SUPPLEMENTARY NOTES

"2 Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

A study of research needs to enhance the capability to design, maintain,

and approve concrete offshore structures for the Arctic was carried out by

the National Bureau of Standards on behalf of the Minerals Management

Service, Department of the Interior. The study was composed of three

activities: a letter survey of key individuals in the field; an international workshop on the subject; and a review of available literature.

Data gathered from these activities were used to develop a comprehensive

list of research needs in the following areas: design, materials,

construction, inspection and repair.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

Arctic environment; concrete; construction; design; durability;

inspection; marine; offshore structures; repair; research.

13. AVAILABILITY

|KX] Unlimited

Q For Official Distribution. Do Not Release to NTIS

^CX) Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402.

]] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

52

15. Price

USCOMM-DC 6043-P80
NBS TECHNICAL PUBLICATIONS

PERIODICALS

JOURNAL OF RESEARCH—The Journal of Research of the National Bureau of Standards reports NBS research and develop- ment in those disciplines of the physical and engineering sciences in which the Bureau is active. These include physics, chemistry,

engineering, mathematics, and computer sciences. Papers cover a broad range of subjects, with major emphasis on measurement

methodology and the basic technology underlying standardization. Also included from time to lime are survey articles on topics

closely related to the Bureau's technical and scientific programs. As a special service to subscribers each issue contains complete

citations to all recent Bureau publications in both NBS and non- NBS media. Issued six times a year. Annual subscription: domestic

$18; foreign $22.50. Single copy, $550 domestic; $6.90 foreign.

NONPERIODICALS

Monographs—Major contributions to the technical literature on

various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and industrial practice (including safety codes) developed in cooperation with in- terested industries, professional organizations, and regulatory

bodies. Special Publications—Include proceedings of conferences sponsored by NBS, NBS annual reports, and other special publications

appropriate to this grouping such as wall charts, pocket cards, and

bibliographies. Applied Mathematics Series—Mathematical tables, manuals, and

studies of special interest to physicists, engineers, chemists,

biologists, mathematicians, computer programmers, and others engaged in scientific and technical work.

National Standard Reference Data Series—Provides quantitative data on the physical and chemical properties of materials, compiled from the world's literature and critically evaluated. Developed under a worldwide program coordinated by NBS under

the authority of the National Standard Data Act (Public Law

90-396).

NOTE; The principal publication outlet for the foregoing data is the Journal of Physical and Chemical Reference Data (JPCRD)

published quarterly for NBS by the American Chemical Society

(ACS) and the American Institute of Physics (AIP). Subscriptions,

reprints, and supplements available from ACS, 1 155 Sixteenth St., NW, Washington, DC 20056.

Building Science Series—Disseminates technical information developed at the Bureau on building materials, components,

systems, and whole structures. The series presents research results,

test methods, and performance criteria related to the structural and

environmental functions and the durability and safety characteristics of building elements and systems.

Technical Notes—Studies or reports which are complete in themselves but restrictive in their treatment of a subject. Analogous to monographs but not so comprehensive in scope or definitive in treatment of the subject area. Often serve as a vehicle for final reports of work performed at NBS under the sponsorship of other government agencies.

Voluntary Product Standards—Developed under procedures

published by the Department of Commerce in Part 10, Title 15, of

the Code of Federal Regulations. The standards establish nationally recognized requirements for products, and provide all concerned interests with a basis for common understanding of the

characteristics of the products. NBS administers this program as a supplement to the activities of the private sector standardizing

organizations. Consumer Information Series—Practical information, based on N BS research and experience, covering areas of interest to the con- sumer. Easily understandable language and illustrations provide

useful background knowledge for shopping in today's tech- nological marketplace. Order the above NBS publications from: Superintendent of Documents. Government Printing Office, Washington, DC 20402. Order the following NBS publications—FIPS and NBSIR's—from

the National Technical Information Service, Springfield. VA 22161

.

Federal Information Processing Standards Publications (FIPS

PUB)—Publications in this series collectively constitute the Federal Information Processing Standards Register. The Register

serves as the official source of information in the Federal Govern- ment regarding standards issued by NBS pursuant to the Federal Property and Administrative Services Act of 1949 as amended,

Public Law 89-306 (79 Stat. 1127), and as implemented by Executive Order 11717(38 FR 12315, dated May 11, 1973) and Part 6 of Title 15 CFR (Code of Federal Regulations).

NBS Interagency Reports (NBSIR)—A special series of interim or

final reports on work performed by NBS for outside sponsors

(both government and non-government). In general, initial dis- tribution is handled by the sponsor; public distribution is by the National Technical Information Service , Springfield, VA 22161,

in paper copy or microfiche form.
U.S. Department of Commerce

National Bureau of Standards

Washington, D.C. 20234

Official Business

Penalty for Private Use $300