NAT'L INST. OF STAND & TECH

AlllDb 03^44 NBS

eference I . PROCEEDINGS

OF THE INTERNATIONAL WORKSHOP

ON THE PERFORMANCE OF OFFSHORE CONCRETE

STRUCTURES IN THE ARCTIC ENVIRONMENT

Held at the National Bureau of Standards, Washington, D.C.

MARCH 1 and 2, 1983
COVER PHOTO: Arctic oil drilling rig
PROCEEDINGS

NAVONAL BUREAU OP STANDARDS UBRARY OF THE INTERNATIONAL WORKSHOP

ON THE PERFORMANCE OF OFFSHORE CONCRETE

STRUCTURES IN THE ARCTIC ENVIRONMENT

Held at the National Bureau of Standards, Washington, D.C.

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use*

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MARCH 1 and 2, 1983

Nicholas J. Carino, Editor

Center for Building Technology

National Engineering Laboratory

National Bureau of Standards

U.S. Department of Commerce

Washington, D.C. 20234

July 1983

Sponsored by:

Technology Assessment and Research Branch

Minerals Management Service

U.S. Department of the Interior

Reston, VA 22091

and

Canada Centre for Mineral and

Energy Technology

Energy, Mines and Resources Canada

Ottawa, Canada KlA OGl

U.S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

NBSIR-83-2751

1 +

Energy, Mines and

Resources Canada

Energie, Mines et Ressources Canada

CANMET

Canada Centre

for Mineral

and Energy

Technology

Centre canadien

de la technologie

des mineraux

et de I'energie

MRP/MSL 83-128 (OP & J)

ABSTRACT

A workshop was held March 1 and 2, 1983 at the U.S. National Bureau of Standards. The objective was to bring together an international group of experts

for the purpose of information exchange on the subject of the performance of

Arctic offshore concrete structures. The workshop participants were divided

into four working groups to discuss the following subjects related to Arctic

offshore concrete structures: 1) design; 2) materials; 3) construction; and

4) inspection and repair. Each working group addressed the following topics

within their subject: past experiences, current projects, and recommended

research areas. The chairmen of each group prepared reports summarizing their

group's deliberations. These reports are incorporated into this workshop

summary.

Key words: Arctic; concrete; construction; design; inspection; offshore

structures; repair; research; structural engineering; technology

assessment; workshop.

1
RfiSUMfi

Les 2 et 3 mars 1983 a eu lieu l'atelier du U.S. National Bureau of Standards . Son but etait de reunir un groupe international d' experts pour favoriser un echange d ' information sur la performance des stations de haute mer en beton

dans l'Arctique. Les participants a l'atelier etaient divises en quatre

groupes pour discuter des sujets suivants, se rapportant aux stations de haute mer en beton: 1) conception; 2) materiaux; 3) construction; 4) inspection et

reparations. Chaque groupe de travail a traite des themes ci-apres a l'interieur de leur sujet: experiences passees, pro jets en cours, domaines de re- cherche recommandes. Le president de chaque groupe a prepare un rapport resu- mant leurs deliberations. Ces rapports sont inclus dans le present sommaire

de l'atelier.

Mots-cles: Arctique; beton; construction; conception; inspection; stations

de haute mer; reparation; recherche; genie mecanique; evaluation

de la technologie; atelier

ii
TABLE OF CONTENTS

Page

ABSTRACT i

RESUME ii

1. INTRODUCTION 1

2. REPORT OF DESIGN WORKING GROUP - By Ben C. Gerwick, Jr 4

2 . 1 Background 4

2.2 Summary of Discussions 8

2.3 Research Needs 17

3. REPORT OF MATERIALS WORKING GROUP - By Robert E. Philleo 19

3.1 Background 19

3.2 Summary of Discussions 19

3.3 Research Needs 24

4. REPORT OF CONSTRUCTION WORKING GROUP - By Peter Pullar-Strecker 26

4.1 Background 26

4.2 Summary of Discussions 28

4.3 Research Needs 30

5. REPORT OF INSPECTION/REPAIR WORKING GROUP - By Roger Browne 35

5.1 Background 35

5.2 Summary of Discussions 36

5.3 Research Needs 47

6. ACKNOWLEDGMENT 57

APPENDIX 58

iii

1.

INTRODUCTION

Construction of concrete offshore structures for mineral exploration in the

Arctic environment offers some of the most severe challenges to our technology. There are many unknown factors related to the design, materials selection, construction methods, and maintenance of such structures. New knowledge

must be sought in order to enhance our capabilities in each of the above

areas. But before research can be planned, it is necessary to know the latest

available information. To address these needs, an international workshop

dealing with offshore concrete structures in the Arctic environment was held

March 1 and 2, 1983 at the National Bureau of Standards (NBS). This report

summarizes the findings of the workshop.

The workshop was organized by the Center for Building Technology (CBT) and the

Canada Centre for Mineral and Energy Technology (CANMET). Funding was provided by the Technology Assessment and Research Branch, Minerals Management

Service (MMS), U.S. Department of the Interior. Additional support was provided by CANMET for publishing this report.

The workshop objective was to bring together an international group of experts

in the field of offshore concrete structures for the purpose of information

exchange in the following subject areas:

1. Past experiences in the design, construction, and performance of

Arctic offshore concrete structures.

2. Current projects and research programs related to Arctic offshore

structures

.

3. Recommended topics for research and development needed to enhance

our capability to construct viable Arctic offshore structures.

The workshop planning committee (composed of N.J. Carino (NBS), chairman; H.S.

Lew (NBS); V.M. Malhotra (CANMET); R.W. Revie (CANMET); and C.E. Smith (MMS)

identified a distinguished group of individuals who were invited to participate in the workshop. The participants were divided into four working groups

dealing with the following topics:
1. The DESIGN of Arctic offshore concrete structures.

2. Required characteristics of MATERIALS for Arctic offshore concrete .

3. Problems related to the CONSTRUCTION of Arctic offshore concrete

structures

.

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

The working groups were asked to discuss past experiences, ongoing projects,

and research needs in their specific area. The appendix includes the workshop

agenda.

Each working group was assigned a chairman who volunteered to perform the

following tasks: 1) prepare a position paper to initiate group discussion;

2) prepare a draft report of the group's discussion for presentation at the

plenary session; and 3) submit a final report to be incorporated into the

workshop proceedings. The Group Chairmen were as follows:

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

. Mr. Robert E. Philleo - Materials Group

. Mr. Peter Pullar-Strecker - Construction Group

. Dr. Roger Browne - Inspection/Repair Group

The reports of the Group Chairmen are presented in the following chapters.

Each report is organized into three sections: section 1 gives background

information; section 2 summarizes the current state of knowledge as derived

from each group discussion; and section 3 presents the recommended research

areas. Since the reports are contributions of the Chairmen, they are presented in their entirety as submitted to the editor, and only minor editorial

changes were made to keep the format uniform.

2
1.

INTRODUCTION

L’edification de stations de haute mer en beton pour 1 ’ exploration minerale

en milieu arctique represente l'un des plus grands defis pour notre technologie. II existe plusieurs facteurs inconnus relies a la conception, au choix

des materiaux, aux methodes de construction et a l'entretien de telles stations. Nous devons chercher a developper nos connaissances pour accroitre

nos competences dans chacun des domaines mentionnes ci-haut. Mais avant de

plaxifier de la recherche, nous devons etre au courant des toutes dernieres

informations. C'est en vue de ces besoins qu’a eu lieu les ler et 2 mars 1983

l'atelier international du National Bureau of Standards (NBS) sur les stations

de haute mer en beton en milieu arctique. Le presente rapport resume les con- clusions tirees de cet atelier.

Organise par le Center for Building Technology (CBT) et le Centre canadien de

la technologie des mineraux et de l’energie (CANMET), cet atelier fut subventionne par le Technology Assessment and Research Branch, Minerals Management

Service (MMS), U.S. Department of the Interior . Le CANMET a fourni un appui

financier additionnel pour la publication de ce rapport.

L’atelier visait a reunir un groupe international d’ experts dans le domaine

des stations de haute mer, afin d'echanger des informations sur les domaines

suivants

1. Experiences precedentes relatives a la conception, la construetion, et la performance des stations de haute mer en beton, dans

les eaux arctiques.

2. Pro jets en cours et programmes de recherche sur les stations de

haute mer dans les eaux artciques.

3. Sujets recommandes pour la recherche et le developpement necessaires a 1’ amelioration de nos competences pour construire des

stations en haute mer dans 1’ Arctique, qui soient valables.

3
Le comite responsable de la planification de l'atelier (compose de N.J. Carino

(NBS) , president; H.S. Lew (NBS) ; V.M. Malhotra (CANMET); R.W. Revie (CANMET);

et C.E. Smith (MMS) a identifie un groupe de personnes choisies pour participer a l'atelier. Les participants etaient divises comme suit, en quatre

groupes de travail:

1. La CONCEPTION des stations de haute mer en beton pour l'Arctique.

2. Les caracteristiques requises pour les MATErIAUX de construction

des stations de haute mer en beton pour l'Arctique.

3. Les problemes relies a la CONSTRUCTION des stations de haute mer

en beton pour l'Arctique.

4. Les problemes associes a 1' INSPECTION et a la REPARATION des stations de haute mer en beton de l'Arctique.

On avait demande a chaque groupe de travail de discuter de leurs experiences

precedentes, de leur pro jets en cours, ainsi que de leurs besoins de recherche

dans leur domaine particulier. L'ordre du jour parait dans l'annexe.

Pour chaque groupe, on avait designe un president charge des taches suivantes:

1) preparer un document de prise de position pour initier la discussion; 2)

preparer le premier jet d'un rapport sur les discussions du groupe, afin de

le presenter a la sceance pleniere; et 3) soumettre le rapport final destine

a etre inclus au proces-verbal de l'atelier. Voici les presidents de groupe:

• M. Ben C. Gerwick, Jr. - Conception

• M. Robert E. Philleo - Materiaux

• M. Peter Pullar-Strecker - Construction

• M. Roger Browne - Inspection/Reparation

3a
Les chapitres subsequents presentent les rapport des quatre presidents.

Chaque rapport comprend trois sections; la premiere donne les renseignements

preliminaires , la deuxieme resume l'etat actuel de nos connaissances , selon

chaque groupe de discussion, et la troisieme suggere des domaines de recherche. Les rapports etant la contribution des presidents, ils sont presentes

dans leur forme entiere, tels que soumis au redacteur, et on n’a effectue que

quelques changements minimes pour conserver l’uniformite du format.

3b
2. REPORT OF THE DESIGN WORKING GROUP - By Ben C. Gerwick, Jr.

2 . 1 BACKGROUND

The design of structures for the Arctic is dominated by the forces imposed by sea ice, both locally and globally. These can be quasi-static winter ice

conditions or highly dynamic actions occurring during break-up or summer pack

ice invasion, e.g., multi-year floes. The peripheral ice wall must resist

these intense local forces without "punching through" or "local holing" and

must have a ductile failure mode against such high intensity loads so as to

prevent progressive collapse.

Experience with ice breakers have shown that it is the relatively stiff frames

behind the exterior shell which are most subject to damage. Similarly, for

concrete structures, the internal structure must also transmit high global

forces through shear walls to the base and thence to the foundation. Ductility

and redundancy against progressive collapse should be incorporated into the

design of these walls. The base of the structure must resist "hard spot"

concentrated reaction loads, and must be capable of spanning uneven and

irregular sea floor profiles.

The impact effects of moving sea ice can develop a ratcheting effect, with

short-period peaks of force. Hence, low-cycle fatigue may be a design

consideration in some portions of a structure.

The harsh environment requires careful design to ensure durability against

freezing and thawing attack, especially in saturated zones: also against ice

abrasion, corrosion of reinforcement, and corrosion of prestressing steel and

anchorages. Local details must be designed to prevent damage from internal

freezing. Steel fittings may be subject to low temperatures, hence material

properties should be selected so as not to have brittle failure under impact

load

.

4
Severe thermal strains, both locally and globally, are imposed due to the

external extreme cold, and the internal heat from operations and produced oil.

Structures for the Arctic will normally be built in temperate climates and

towed to the Arctic. Designers therefore need to consider buoyancy, floating

stability (including damaged stability), and dynamic response during tow.

Structures must be capable of deployment through partially ice-covered waters.

To meet the shallow water conditions around Point Barrow and elsewhere,

structural lightweight concrete of special high strength may be required.

The interfaces with mechanical, instrumentation, and drilling systems must not

be overlooked, especially as they affect possible hydrostatic pressure differentials on the structure during ballasting, deballasting, and accidental rupture;

and also as they affect thermal strains, watertight integrity, and foundation

conditions

.

The utilization of concrete sea structures in the North Sea over the past

decade has led to the development of design rules and practices relevant to

the marine environment and high dynamic loads. The relevant guidelines which

are currently available include API Bulletin 2N, ACI 357R-78 (now being

revised), the FIP Recommendations for Concrete Sea Structures (4th edition in

preparation), the DNV Rules (1981 printing) with their appendices, the work of

the FIP subcommittees on Arctic Operations and Sea Operations, and the draft

rules of ABS.*

Important current technological developments to be addressed include the use of

condensed silica fume and other pozzolanic admixtures to increase strength and

impermeability, coatings to reduce friction and abrasion, multi-axial stress-

* API: American Petroleum Institute

ACI: American Concrete Institute

FIP: Federation Internationale de la Precontrainte

DNV: Det Norske Veritas

ABS: American Bureau of Shipping

5
strain effects and their implications for shear resistance, crack-width control

mechanisms, epoxy coated reinforcement, and mechanical anchorages and splices

for reinforcing steel (especially compression bars and stirrups).

Perhaps the most critical of all design-related matters is that of the

peripheral ice wall when subjected to extremely high local concentrated loads

with intensities in the range of 100 tons/ft^ (10 MPa). Slabs and shells are subjected to high flexural and membrane stresses as well as internal diagonal

tension and compression. Extremely heavy concentrations of reinforcement,

utilization of prestressing to increase shear capacity, and concentrated

stirrups are required to develop the necessary resistance.

Concrete structures offer great potential for the safe and economical

development of the Arctic but the environmental and operational demands are extremely severe, perhaps more severe than structural concrete has ever been

asked to face in the past. Hence, special care is required and suitable

research must be carried out on a continuing basis to develop and verify the means of improved performance.

The following is a list of items for special consideration in the design of

concrete structures for use in the Arctic:

1. Impact of ice features such as multi-year floes against structures;

energy dissipation.

2. High local ice loads ("punching shear" plus "flexure").

3. Failure modes of thick concrete walls, shells, and slabs, heavily

reinforced and/or prestressed, under intense local ice loads.

4. Improved stirrup details and/or use of headed stirrups.

5. Multi-axial stresses: potential for enhancement of compressive

and shear strengths, reduction of tensile strength on minor axes.

6
6. Shear: how to treat membrane and flexural shear under static, dynamic,

and cyclic action. Use of rational concepts of "diagonal tension" and

"diagonal compression" instead of artificial concept of "shear", in

order to avoid being trapped by empirical requirements of building

codes.

7. Fatigue aspects of concrete walls under ratcheting effects of

continuous crushing of ice.

8. Distribution of intense concentrated forces through structure:

peripheral walls, diaphragms, and shear walls.

9. Failure modes of diaphragm walls and shear walls under high compression

plus shear: means of increasing ductility.

10. Resistance of saturated concrete against freeze-thaw attack. Effect of

coatings. Migration of water vapor through concrete. Impermeability.

11. Resistance of concrete to ice abrasion. Friction of ice against

concrete. Adfreeze.*

12. Coatings for exposed concrete surfaces to reduce friction, adfreeze,

and abrasion.

13. Use of epoxy-coated reinforcement to reduce required cover, or to

enhance durability of concrete, especially when salt may be applied

to deck surfaces to prevent icing.

14. Concrete cover: effects on crack control, thermal strains, corrosion,

and performance under high concentrated loads.

* Adfreeze refers to the adhesion of ice to the concrete surface.

7
15. Long-term protection of prestressing anchorages from freeze-thaw attack

and corrosion.

16. Thermal gradients in thick-walled structures due to heated interior.

Global thermal deformations when lower or internal portions of the

structure are in water (0°C) and exposed portions are at temperatures

as low as -50°C. Producing wells may raise internal temperature to as high as 35°C.

17. Protection of internal compartments and voids, empty ducts, reentrant

angles, etc., against rupture from freezing water. Use of polyurethane

buffers

.

18. Use of structural lightweight concrete: considerations of freeze-thaw

resistance, tensile and shear strength, and abrasion resistance.

Should field tests be conducted at Treat Island (Corps of Engineers

Facility)

?

19. Use of condensed silica fume and other pozzolans: effects on strength,

failure modes (ductility), vapor impermeability, freeze-thaw resistance, and abrasion resistance. Proper design of reinforcement to ensure proper post-elastic behavior of the very high strength and high

modulus concrete obtained by use of silica fume.

20. Need for rugged, reliable, ice force sensor panels, which may be used

to determine local ice forces. Questions on how to interpret data from

intermittent seasons when applied to local and global load predictions.

2.2 SUMMARY OF DISCUSSIONS

The Design Group held three spirited and highly interesting sessions, covering

three topics: past experiences, current research and development projects, and areas of needed research.

8
The morning discussion addressed the past experiences in the design,

construction and performance of offshore concrete structures. Mr. S. Maxwell

of Gulf Canada Resources gave a detailed report on the Tarsiut caisson-retained

island, augmented by Mr. Tony Boyd of Swan and Wooster, the designer, and

Ben C. Gerwick, Jr., a consultant on the project.

The concrete structures themselves had performed well, with no apparent

freeze-thaw or ice abrasion damage. Some structural cracking had occurred

during initial set down on uneven support, due to a surveying error. Other

narrow cracks are apparently due to thermal strains during construction. The

cracking was not serious and had not led to further deterioration due to freeze-'-

thaw attack. This shows the effectiveness of the well-distributed reinforcement

in restraining crack growth. There was no evidence of damage due to local con- centrated ice loads or ice impact. Minor spalling has occurred due to impact

of large steel barges without fenders. In summary, these prestressed lightweight concrete caissons have given very satisfactory and predictable behavior.

Mr. Maxwell reported that global and local ice loadings during the winter of

1982-83 had been the most severe yet encountered. He also reported that industry now favored a concrete caisson or caissons for the Hibernia field, largely

because of the ability to resist small ice features (500 to 10,000 tons

(5 to 90 MN)) at wave-driven velocities, as well as large bergs of mass and

velocity appropriate to the 100-year recurrence.

Kurt Eriksson of VBB-SWECO reported on the 40 concrete lighthouses in the

Baltic Sea and their generally satisfactory behavior in the ice environment.

For up to 25 years, they have been subjected to moving annual ice sheets and

rubble pile build-up but have not shown any significant abrasion nor deterioration. Dynamic amplifications and resonance effects had occurred on a few

platforms. These have been well instrumented and documented and give valuable

information on ice-structure-foundation interaction. A paper was distributed

9
describing some ice load prediction methods against the background of Swedish

experiences .*

Mr. Sedillot of C. G. Doris reported on the design of concrete offshore platforms

for Texaco in the Baltic Sea.

The highly successful experiences of 15 concrete platforms in the North Sea were briefly presented and attention was directed to the current design and

construction of the shafts to resist supply boat and barge impact with con- centrated loads of comparable intensity to iceberg and ice floe impact loads.

The first afternoon session was devoted to a presentation of current research

and development projects. Many of these are proprietary: however it was pointed out that any responsible party, including the Government may buy into

these projects. Among the many current R & D projects are:

1 . High-strength lightweight concrete

• freezing and thawing behavior

o adfreeze

o friction of ice on surface

o heat of hydration

o abrasion by ice

Objective of future work is to develop design specifications plus a quality assurance/quality control program so as to enable an engineer

to design with confidence in this material.

2. Concrete elements subjected to high local forces imposed by ice

(commonly referred to as "punching shear"): elasto-plastic behavior;

* "Ice Force Design of Offshore Structures" by Alf Engelbrektson, prepared for an international conference: "Offshore Goteborg 83".

10
need to develop appropriate design criteria for shear in highly

reinforced concrete; progressive failure mechanisms. Behavior of

slabs and shells which have previously been cracked, repaired, and are then subjected to high loads. Ultimate load studies of the collapse mechanism and energy absorption under impact. Several participants agreed that "shear" was an inadequate concept for these cases

and that it was preferable to consider "diagonal tension" and "diagonal

compression". The importance of support conditions to the behavior

of peripheral ice walls was emphasized: these can significantly

influence the behavior under high local loading.

3. Composite-construction: "steel-concrete sandwich" construction,

also called "hybrid design". Utilization of internal supporting

structures of structural steel, connected by studs or similar means

to develop composite action with concrete slabs.

4. Impact of ice floes on structures: ice floe-structure-soil interaction

and compliance of the structure-soil system as well as crushing of the

ice and hydrodynamic dissipation of kinetic energy. Peak stresses are

of very short duration: hence, applicable concrete strength may be

30 percent or so higher than static cylinder strength.

5. Risk-reliability-consequences evaluation. Loading and Systems

Management as it affects risk. Consequence evaluation as it affects

safety factors and levels. Provision of redundancy to prevent

simultaneous or progressive collapse.

6. High strength normal weight concrete, with strengths in excess of

14,000 psi (100 MPa).

7. Ductility of highly compressed members, including compression members

subject to prestress. DNV is currently proposing a research program

in this area: other programs are underway in New Zealand and Japan.

11
8. A detailed inspection will be made this year of the Swedish concrete

lighthouses in the Baltic to ascertain their performance under up to

25 years of annual ice attack.

9. The U.S. Coast Guard is continuing tests with the Polar class ice

breakers to determine sea ice pressures, and the Minerals Management

Service is continuing with its program of ice forces against structures

and ice mechanics.

10. FIP has a Commission currently studying multi-axial stresses in

concrete structures.

11. There are a number of programs studying durability of concrete in the

Arcic environment. These include SOHIO's field tests, and joint

industry studies on durability, abrasion, friction, etc.

12. The University of California (Berkeley) has recently completed tests on the behavior of prestressed lightweight concrete under cyclic,

fully reversing membrane stresses at low temperatures and is now

commencing a program for testing cyclic, fully reversing shear effects.

Mr. Roger Stacey of NORDCO, Ltd. described a proposed program on a 1:10 scale

of a concrete platform subject to iceberg impact, to determine actual forces

and responses.

Several members directed attention to the current programs of AOGA, APOA, CIRIA

and C-CORE (Canada), also to current programs in Norway, Germany, The Netherlands,

£ France, and Japan.

AOGA: Alaska Oil and Gas Association

APOA: Arctic Petroleum Operators Association

CIRIA: Construction Industry Research and Information Association (U.K.).

12
Descriptions were presented of some of the structural concepts currently being

developed for use as exploratory drilling and production platforms in Arctic

and sub-Arctic waters. These include only those which have been publicly

reported:

1. Permanent caisson-retained production island at Tarsiut, (ATOLL),

using concrete caissons protecting a sand fill island.

2. Global Marine's Concrete Island Drilling Structure (CIDS), utilizing

concrete "honeycomb" modules, joined together at the site, both

transversely and vertically, in "brick" fashion.

3. SOHIO Petroleum's Arctic Module System, (SAMS), a prestressed lightweight

concrete caisson in which shear transfer of the ice forces to the sea floor is augmented by spuds.

4. The Arctic Cone Exploration System (ACES), a prestressed lightweight

concrete conical structure, being designed by Brian Watt Associates

for a consortium of companies including Shell, Exxon, and Chevron.

5. Brian Watts Arctic Caisson System (BWACS), a lightweight concrete

honeycomb caisson structure designed for Zapata, to improve shear

resistance in weak soils by drainage using the wick sand drain method.

6. Exxon's concrete production island caisson, with elevated deck, designed

by ABAM Engineers for 30 to 100 ft (10 to 30 meter) depths in Norton

sound

.

7. A concrete caisson for Norton Sound, designed for a nine-company

consortium headed by Chevron.

8. Norwegian Contractors TRIPOD 300 concrete caisson, designed originally

for 300 plus meters of water depth in the northern North Sea, now being considered for the southern Bering Sea.

13
9.

Exxon's concrete gravity-base MOHOTOWER, proposed for deep water in

the St. George Basin.

10. Fixed concrete caisson structures proposed by Norwegian Contractors

and by C. G. Doris for the Hibernia field, off Newfoundland, designed

to resist iceberg impact.

11. Floating caisson-shaped drilling, production, and storage structure

designed by Exxon for use in deep water. This features dynamic

downward breaking of ice to reduce mooring forces.

During the second afternoon session, members presented and discussed areas for

which they felt additional research and development are important. Some of

the most critical areas relate to ice loadings and the dynamic response of

structural systems, hence are not specific to concrete structures but apply to

all materials. Similarly, the matter of soil-structure interaction was judged

to be of great importance, especially for Arctic marine structures, due to the

high ratio of lateral to vertical loads and the special qualities of Arctic

sea floor soils.

Considerable discussion was directed to the complex phenomena associated with

the impact of a large multi-year ice floe or an iceberg with a structure, and

the need to consider elastic and inelastic responses of the entire system,

including soil, structure, water, and ice. The concept of permitting limited

local failure under extreme overload was presented and parallels were drawn to

current design practice for extreme earthquake action.

Probabilistic approaches to design for ice loads and structural responses were discussed. The current need for parametric or deterministic design values was strongly stated, in order to permit safe and rational designs pending the

acquisition of sufficient data upon which to base a probabilistic approach.

With deterministic and parametric loadings, it should then be possible to

prepare integrated design guidelines, with recommended load factors and safety

indices. There is also a need to develop appropriate serviceability criteria.

14
The ACI 318 Standard for design of reinforced concrete buildings may not be

fully applicable to the case of heavy concrete sections which have high

percentages of multi-axial reinforcement.

The dynamic nature of the continuous crushing of ice against a structure was noted. Cyclic peak stresses may be sufficiently close to the structure's

natural frequency to lead to dynamic amplification. In other cases, it is felt

that the structure's natural period of response may determine the crushing

period of the ice. These peak stresses, occurring at periods of 0.5 to 1.0

seconds, indicate the need to consider low-cyclic high-amplitude fatigue and

perhaps high-cycle fatigue as well.

Thermal strains may exist in an Arctic concrete structure on two scales: the

local through-wall thermal gradients, and the global strains between the lower

portion of the structure submerged in water at -2°C and the upper portion which

may be in air at -50°C. Meanwhile, oil production operations and waste heat

may have developed internal warm areas

.

The external surfaces of a concrete structure are subjected to a relatively few

cycles of intense freezing and subsequent thawing. Near the water line, there

may be many more cycles due to thawing by wave action. This zone also may be

subject to saturation and water vapor transmission. Tests on this phenomenon

have been carried out over many years at Treat Island, Maine, but do not include

the most recent concretes such as high-strength lightweight aggregate concretes

which include condensed silica fume.

Abrasion of the external concrete surface by ice is another research area. Near shore, the ice may have picked up silts, sands, and even gravel as a result

of ice gouging, and hence have greater abrasive effect.

Friction of ice on the surfaces of the structure may be important in determining

ice loads especially the clearing of ice over conical surfaces. These values

vary with relative temperatures and with surface roughness, which may be subject

to change with time as a result of abrasion and freeze-thaw action.

15
The behavior of concrete structural elements under multi-axial stress or strain

conditions was discussed. Under tri-axial compression, the apparent strength

in compression and shear is dramatically increased, whereas under biaxial com- pression, the tensile capacity along the third axis may be decreased, requiring

special reinforcement.

The joining and connecting of small and large precast segments of concrete

together present an opportunity for the development of innovative designs

to reduce time and costs of construction. They require attention to detail and

careful execution.

Deployment of large structures in a fragmented ice cover and the subsequent

relocation during periods of fast ice or fragmented cover is a feature which

could have major economical impact. It may be possible to shape the structure,

or one side of it, as an ice-breaking bow to facilitate operations in fast and

broken ice.

The group emphasized again the needs for parallel development in systems which

support concrete offshore structures of all types and the need to integrate

them into concrete structure systems. These include;

• Instrumentation

• Foundation engineering

o Mechanical systems (ballast, drainage, etc.)

9 Active and passive means of reducing or controlling ice forces.

Finally, the group briefly discussed hybrid designs, in which steel and concrete

work in composite structural action. Steel may permit a reduction in weight

and give added ductility, while prestressed reinforced concrete has excellent

performance at low temperatures, high durability, high fatigue resistance and

high redundancy and toughness.

16
2.3 RESEARCH NEEDS

1. Concrete slabs and shell subject to very high local concentrated loads

("punching shear") plus flexure plus membrane compression). Physical model

tests at large scale (to eliminate scale effects), realistic support

conditions and loadings representative of ice are needed to corroborate

nonlinear numerical analyses

.

Methods of reinforcing to ensure high resistance and a ductile (non-brittle)

mode of failure. Determine collapse mechanism and energy absorption after

passing peak resistance.

Examine acceptability of concept of permitting repairable local damage

under extreme and infrequent loadings, provided it does not lead to

progressive collapse.

Guidelines for evaluating resistance of very heavily reinforced thick

concrete sections to flexural and shear loads.

2. Shear walls and diaphragms supporting the peripheral ice wall are heavily

loaded in compression and shear. Means of enhancing resistance and ensuring

a ductile behavior under overload.

3. Determination of peak local forces generated during impact of large ice

feature against peripheral wall. Effects of hydrodynamic damping and energy

absorption and of compliance of structure-soil system in reducing peak

stresses

.

4. Low-cycle fatigue behavior and endurance of structural elements, especially

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

5. Establishment of deterministic and parametric (and eventually probabilistic)

ice loading criteria.

17
6. Abrasion of external walls by ice. Are sand and silt particles probable in sea ice at structure locations, and, if so, what is their effect on abrasion?

7. Adfreeze of ice on concrete surfaces. Friction under the probable range of

conditions.

8. Freezing and thawing behavior of concrete, especially in splash zone;

effect of coatings. Effectiveness of air entrainment and of condensed

silica fume.

9. Thermal strains, both through-wall gradients and global. Consideration of

recent research in USSR on thermal strains. Evaluation of effects of con- crete properties, reinforcement and prestressing details, and structural

configuration in limiting cracking due to thermal strains.

10. Performance and design basis for steel-concrete composite structural

elements. Methods of ensuring composite behavior. Effect of thermal

gradients and f reezing-thawing action.

11. Risk, reliability, and consequence evaluation principles for concrete

structures in the Arctic.

12. Optimum details for protection of post-tensioning anchorages in saturated

concrete subjected to freezing-thawing action in the Arctic.

13. Field durability tests on post-tensioned and conventionally reinforced

high strength lightweight concrete made with addition of condensed silica

fume. Use of Treat Island test facility.

14. Recommendations for load factors to be applied to ice loadings.

Determination of appropriate serviceability criteria. Guide as to load

combinations, e.g. , earthquake and ice, or waves and small ice features

(e.g. , "bergy bits") impelled at high velocity by the waves.

18
3. REPORT OF THE MATERIALS WORKING GROUP - By Robert E. Philleo

3 . 1 BACKGROUND

Concrete materials technology, developed over several generations, has

served the design profession well. Recent developments, however, require a re-examination of certain well established principles. The quality of concrete,

for example, has traditionally been designated by its water-cement ratio. A

variety of materials now being used as a part or all of the cementitious component of concrete may not lend themselves to treatment by normal water-cement

ratio criteria. Furthermore, some of the physical properties of both normal

weight and lightweight high-strength concrete may not be well understood, particularly when the concrete contains relatively new materials such as superplasticizers and condensed silica fume. Some of the design parameters are merely extrapolated from normal strength concrete. The important problem of

steel corrosion has been dealt with in specifications piece meal without

recognition of the several interrelated parameters.

3.2 SUMMARY OF DISCUSSIONS

There were two recurrent themes running throughout the discussions.

1. Impermeability is the most important property of concrete in the

offshore environment, particularly in the tidal and splash zone.

2. Existing criteria for steel cover and crack control in the permanently

submerged portions of offshore structures are too conservative. An understanding of all the factors necessary for corrosion suggests that corrosion

in this part of structures is highly unlikely. Yet for certain members

the crack control criterion is more critical in design than the wave criterion in establishing reinforcing steel quantities.

Much of the discussion may be summarized by relating it to the specific questions

propounded in the Materials Working Group position paper.

19
1. For seawater exposure, what composition of cement, particularly in regard

to tricalcium aluminate (C 3 A) content and alkali content, is optimum?

There is no evidence to support an upper limit on C3 A content of cement.

Sulfate attack is not a problem in high quality impermeable concrete. There

was not agreement on the need for a lower limit to protect the steel from

corrosion. This is still a fruitful area for research. Alkali content was not seen as a matter for serious consideration except where reactive aggregates

are used.

2. What pozzolans and slags used in what proportions are useful in the

exposures under consideration?

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

in that they reduce the permeability of concrete and retard the ingress of

chloride ions to the steel. The properties of silica fume were discussed at

length. An additional contribution it makes to corrosion protection is

increasing the electrical resistivity of concrete. Because pozzolan concrete

in general, and silica fume concrete in particular, may not be well characterized by water-cement ratio, interest was expressed in using permeability as a criterion of quality. To do so, permeability testing techniques must be

vastly improved, and in order to execute quality control there must be a means

for determining permeability of in situ concrete. Silica fume is commonly

restricted to a quantity equal to 5 percent of the weight of portland cement.

The quantity of fly ash generally exceeds 20 percent.

3. Should only non-chloride accelerators be used?

The question of whether to permit chloride-containing accelerators is part

of the larger problem of whether chlorides need to be limited if the steel is

protected by adequately impermeable concrete. High strength prestressed

concrete with extremely low permeability has been produced and has served

successfully with relatively high chloride contents. More work is needed.

20
4.

What is the applicability of high-range water reducers (superplasticizers)?

Superplasticizers were deemed to be necessary both to place concrete through

the maze of reinforcing steel existing in off-shore structures and to take

full advantage of silica fume, an extremely fine material with a high water

demand. The preponderance of evidence indicates that durable concrete can be

made with superplasticizers. However, existing criteria for air void systems

may need to be re-examined.

5. What are the proper admixtures, if any, for use in treraie concrete?

There is little underwater placement in offshore structures. Where it is

undertaken a workable cohesive concrete is required. No special admixtures

are needed although both superplasticizers and pozzolans promote cohesiveness.

Much of the discussion related to the fact that there are now available

proprietary systems which appear to do an adequate job of placing concrete

underwater without tremies . There is a need to develop non-proprietary methods

to impart adequate thixotropy to concrete to make these techniques generally

applicable

.

6. What precautions concerning reactive constituents should be observed in

selecting aggregates?

In important structures exposed to seawater, reactive aggregates should be

avoided

.

7. What is the role of lightweight aggregate, and what precautions should

be observed?

Lightweight concrete can be a useful material where weight reduction is an important factor. It is abrasion resistant because it is inherently a ceramic

material, but it is not resistant to percussive type impact because of its

porous structure. There is a need for further knowledge of thermal properties

in order to devise crack control measures during construction and a need for a

21
better understanding of the failure mechanism of reinforced lightweight

concrete

.

8. Is there a place for use of seawater as mixing water?

In important reinforced concrete structures, seawater should not be considered

as mixing water for concrete.

9. How do the permeability-water-cement ratio function and construction

tolerances interact to produce the optimum combination of water-cement

ratio and thickness of cover?

There are practical limits, having to do with placing tolerances and

construction operations, to using low permeability as a means to reduce the cover of reinforcing steel to very small values. The critical zone of a structure (tidal and splash zone) is relatively small and therefore not conducive

to generating large cost savings where a thick cover can be tolerated. One

benefit of thick cover is that it provides a space for placing concrete in

otherwise highly congested forms. Below the waterline cover is not critical

for durability. In the deliberations of the Working Group on Design, however,

it was pointed out that there are structures or portions of structures where

functional requirements demand as thin a cover as possible. These include

highly stressed regions where thick cover might be prone to spalling and where

highly impermeable concrete and epoxy-coated reinforcing bars should provide a practical solution. It had been the opinion of the Materials Working Group

that where there is no need for a thin cover there is likewise no need for

epoxy coated reinforcement since bare steel can be adequately protected by high

quality concrete. Other places where coated bars are probably cost effective

are exposed decks of offshore platforms where calcium chloride is likely to be

used for deicing. These surfaces are similar in exposure to bridge decks.

Other items not included in the original list of questions posed in the position

paper were discussed as follows:

22
In some exposures ice rubbing on structures produces abrasion which might

be counteracted by used abrasion-resistant aggregates. While the problem of

impact of large masses of ice is primarily a design problem, there is a need

for more information on ice abrasion, particularly when the ice carries as inclusions abrasive materials such as sand. It should also be noted that in some cases ice buildup on a structure may provide some resistance to abrasion.

Although there was difference of opinion in the final plenary session as to the

extent of the problem of galvanic corrosion in the submerged zone, it appears

that some existing criteria overestimate the problem of galvanic corrosion

produced by steel projecting from concrete because much less oxygen diffuses

to the steel than assumed. Some sacrificial anodes are superfluous.

The potential of steel fiber reinforced concrete is not being realized. The

literature is full of test results, but there is not much in the way of design

criteria. It is not inconceivable that in some structures fibers might replace

conventional reinforcing. In others they might be useful in end blocks of

prestressed concrete and in the cover of reinforcing bars. This is a fruitful

area for research.

There is a need for a better knowledge of early age properties of high-strength

concrete so that adequate crack-control procedures during construction may be

devised

.

Grouting of post-tensioning ducts can be critical in offshore structures

exposed to freezing. More information on the subject is needed.

During the final plenary session a question was raised about the low-temperature

behavior of ASTM A 706-steel. Floor discussion provided the information that

tests of reinforcement, presumably similar in composition to A 706-steel, had

been conducted at -140°C in Norway and at -163°C in the United Kingdom, and

they had demonstrated satisfactory behavior.

23
The Working Group on Design requested information on the applicability of

mechanical splices for large bars in compression. Substantial experience has

indicated that they may be used for all large bars in compression.

3.3 RESEARCH NEEDS

The following research needs were identified and are listed in priority order.

1. Establishment of permeability criteria with adequate test techniques

including means to test in situ concrete.

2. Establishment of realistic chloride limits when very low permeability

is attained.

3. A re-examination of air void spacing criteria for freezing and thawing

durability.

4. Properties of high-strength lightweight concrete made with condensed silica

fume and superplasticizer.

5. Early-age properties of high-strength concrete.

6. Methods of tests and criteria to determine whether grout in ducts is

effective

.

7. Development of suitable ice abrasion resistance criteria and tests.

8. Development of thixotropic concrete for underwater placing.

9. Design criteria for fiber-reinforced concrete.

10.

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

to replace those assumed properties extrapolated from normal strength

concrete.

24
11. Adequate design procedures for lightweight concrete.

12. Establishment, if necessary, of a minimum limit for C 3A content of

cement.

25
4. REPORT OF THE CONSTRUCTION WORKING GROUP - By Peter Pullar-Strecker

4.1 BACKGROUND

Methods of construction have to be chosen to suit what has been designed and

design must of course take account of what it is possible to construct.

Consideration of construction divorced from design has limited value, and the

intentions in design will become essential data for the construction process.

All Arctic concrete offshore structures are likely to be massive and those

intended for deep water will also be tall. Many of the construction problems

will be those common to any massive concrete constructions. For cast-in-place

construction, these include:

• Extraction and transportation of large quantities of aggregates,

probably at remote sites.

© Supply of cement, reinforcement materials, fuel, equipment, power,

accommodation and labor, in large quantities and over long distances.

© Continuous placing and compaction of high quality concrete in very

large pours.

While precast construction will require provision of facilities for lifting,

transporting and assembling large precast units.

The ability to cope with these general problems is the stock-in-trade of the

large contractor and is not peculiar to Arctic offshore structures. The

particular problems of constructing deep-water structures are within the recent

experience and expertise of British and European contractors who have built more than a dozen such structures for offshore oil and gas extraction in the

North Sea.

26
VThilst there are probably very few new problems that could require research

in construction, it is worth considering those familiar areas that are likely

to need more than ordinary care and attention in the case of Arctic offshore

structures. These include:

a Provision of quality control and testing of raw materials and concrete.

o Provision of batching facilities for a wide range of materials

including large aggregates, lightweight aggregates, concrete

admixtures, and cement replacement materials.

® Provision of back-up plant to allow uninterrupted pouring.

® Provision of means for transporting concrete from central mixing

plants to points of placing which may become more inaccessible as construction proceeds.

® Grouting pre-stressing cables in very long ducts.

© Assembling and connecting large units under difficult site conditions.

Finally, there are some special requirements that will be peculiar to

construction for Arctic works and that might give rise to a need for research

and development

© The scarcity of sheltered deep-water construction and assembly sites.

© The possibility of needing to renew structural units or fenders

destroyed by abrasion from floating ice.

© The provision of very large working platforms founded in shallow water

and transportable from one location to another.

27
4.2 SUMMARY OF DISCUSSIONS

The task of the group was to consider what new knowledge is needed for the

efficient and economical construction of offshore concrete structures for use

in Arctic waters. The definition of the task implied that certain related

topics need not be considered: firstly, construction in temperate latitudes of

units intended to be transported to the Arctic, since such construction was not

likely to give rise to fundamentally new problems; and secondly, the design of

structures, since this was to be considered by the Design Group.

The Construction Group therefore concentrated on that part of the construction

work that would have to be carried out in the Arctic, including the transportation of units to the installation site. The Group realized that the requirements of the designers would influence or even dictate some of the construction

problems, and that these problems would in turn have to be considered by the

Design Group. For this reason ideas were exchanged between the two Groups

during and after the working sessions. The Construction Group's view was that

any of the demands of designers could be met, at a price, and it was part of

good design to avoid excessive cost by designing for simple construction.

Not surprisingly, the special problems of construction in Arctic waters were seen primarily as those caused by the severe climate and remoteness. They can

be broadly grouped as the high cost of getting work done in the region, the

short time during which it is possible to move through the sea in the region,

and the difficulty of transporting units and equipment to the region from

temperate areas.

A separate cause of special problems was the need to avoid damage to the

exceptionally sensitive environment of the region.

The Group thought it right to consider problems that were economic or political

in origin, as well as those that were technical.

28
Sometimes it is better to avoid a problem than solve it. Many of the problems

and costs peculiar to Arctic regions might be avoided by ensuring that construction is as complete as possible before units are brought into the region.

Operations that really have to be done in the Arctic should not only be reduced

in number by this means , but should also be reduced to those that can be done

without expensive equipment. There is an obvious conflict to avoid: the more complete the unit is, the larger would be the equipment needed to handle it on

site.

Transportation to the region from the primary building site becomes an increasing

problem as units get more complete and therefore probably larger. A curious,

non-technical difficulty added to the technical problems is that the effect of

the Jones Act, intended to protect American trade, is actually to encourage the

construction of larger structures for Arctic waters at non-USA sites, since USregistered vessels (of which few are suitable) would not be needed to carry

them.

In any new venture, the assessment of risk must be based on theory and

calculation rather than experience, and correctly evaluating risk is crucial

to the economic success of the enterprise. Data and theory for this assessment,

whether it concerns risk to life, the environment or property, is sparse or at

any rate dispersed to an extent where it does little to create confidence. The

collection or creation of information in this area, and its independent assessment and validation, could help greatly in promoting a confident and positive

attitude towards the development of resources in the region.

These and more obvious technical considerations gave rise to a number of

recommendations for areas where more knowledge is needed. These are listed in

the following section together with recommendations that were passed to the

Construction Working Group during and after the workshop meetings, by other

working groups and by individuals

.

29
The Group made no specific recommendations on how the knowledge should be

collected or who should do the work, but it was agreed that since the information must be impartial and would be valuable to a large number of users, a professionally-managed program of projects, jointly funded by a numer of

interested parties, would be an efficient way of putting effect to the recom- mendations. The UK Concrete-in-the-Oceans program is an example of a very

successful program which was financed and managed in this way.

4.3 RESEARCH NEEDS

1 . Foundations for Structures

Structures which are to be founded on the sea-bed are usually designed without

any means of adjustment to suit an uneven installation site. Consequently, the

seabed has to be prepared in some way so that it provides an acceptable surface

to receive the structure. Often the preparation is the construction of a sand

or gravel mound which serves the function of partially leveling the surface

and also reduces the depth required for the structure.

The construction of the mounds and the final leveling of the surface, for

example by pumping sand to fill voids beneath structures, are areas where more knowledge could contribute to efficient, safe, and economical working.

Topics which should be investigated include:

© means of determining the relevant properties of potential fill materials

© methods of pumping and consolidating fill materials;

© the influence of ice particles in fill;

o means of protecting mounds from erosion; and

® grouting under cold sea water.

30
2

.

Berms for Protection From Floating Ice

A related problem is the construction of sand or gravel berms to protect

structures from floating ice. The research needs are probably the same as those noted under item 1.

3

.

Moving Platforms Through Ice-covered Waters

Drilling structures are normally useable at only one location per season because they can only be moved into position when the sea is sufficiently free

from ice. It if were possible to move structures through ice-covered waters, use at more than one location per season would become possible.

The possibility of designing structures so that they could be moved through icecovered waters, even if only very slowly, is considered to be a worthwhile area

of study.

Topics to be investigated might include:

o the design of structures as ice-breaking hulls;

• the power requirements for moving structures; and

o the economics of moving and re-using structures.

4

.

Poor Utilization of Equipment

The problem of being able to use drilling structures at only one location per

season applies also to other equipment, such as crane barges, which can only be

brought to the site when the sea is sufficiently free from ice. Under these

conditions equipment utilization is very poor and may be as little as 6 weeks

in a 3-year period.

It must be borne in mind that the high cost of doing any work in arctic sites

makes it desirable to complete structures as much as possible at temperate

construction sites and this could result in the production of units so large

31
that heavy lifting and installation equipment would normally be needed at the

working location.

By appropriate design it might, however, be possible to dispense with or reduce

the need for such equipment.

Topics to be investigated might include those in item 3 (but in relation to

equipment) and the design of structures that can be installed on site with a minimum of equipment.

5 . Transportation of Structures from Fabrication to Installation Sites

Structures for use in Arctic waters have to be built at sites in temperate

climates and must be towed or transported in vessels through seas which can be

stormy, ice-laden and, in places, shallow.

These conditions already impose many practical and technical problems, but, it

addition, a piece of legislation known as the Jones Act adds a problem which

appears to be quite unnecessary. The Jones Act restricts the use of non-USA

hulls to carry loads from one USA location to another. If, therefore, a suitable USA hull is not available to transport a structure to a USA installation

site, the structure must be built outside the USA, for example in Japan. Thus

legislation enacted to protect USA trade can have the opposite effect.

Transportation is a very major problem in developing the resources of the Arctic

waters and is an area where new knowledge could make an important contribution.

Topics that need consideration are:

• examination of the effects of the Jones Act and recommendations for

appropriate exemptions;

® collection of data on wind, wave, and currents in a Government-funded

program which would ensure the accessibility of the information; and

32
® collection and publication of data on ice movement, scour, and

hydrography in a similarly funded program.

6 . Assembly of Units on Site

It has already been said that structures should be as complete as possible

before they are brought to the installation site, but it is accepted that some assembly on site will continue to be needed.

Assembly operations should be quick and simple, and should need a minimum of

equipment

.

More knowledge is needed on:

© the tolerances required for interlocking units;

o materials and construction methods for load-distributing intermediate

layers

;

0 tolerance to local crushing;

© the design and construction of connections which can subsequently be

dismantled

;

o the protection of connectors from corrosion and accidental damage; and

moorings for use during assembly operations.

7 . Risk During Transportation and Installation

Risk from ice, wind, and currents while the structure is being transported or installed have to be assessed somewhat theoretically because of the limited

actual experience of construction operations. Such risks can be reduced both

by appropriate design and by suitable construction methods, but to do this

economically the risks and their consequences have to be evaluated.

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 their

consequences.

33
8 . Risks and Consequences of Accidental Spillage

Spillage of oil, grout or even mud could have an apparently large impact on the

unspoilt environment of the Arctic. The fear of such accidents may lead to very

strict requirements in an attempt to avoid them and the extra construction work

that arises directly from that strictness may itself be harmful to the environment. For example, the work of burying pipelines at great depth is likely to cause more environmental damage than burying them at shallow depths, though

the latter could be enough to protect them.

The risks and consequences of accidental spillage and the effects of

construction processes in creating pollution of air, land, and water need to

be evaluated in factual terms so that the control of construction and operation

can be appropriate in both method and degree.

Further study is needed of the impact of construction and of operation in the

environment of the region, and this study should be carried out under authoritative and independent control so that the facts it produces are acceptable to

all parties.

34
5. INSPECTION/REPAIR WORKING GROUP - By Roger Browne

5 . 1 BACKGROUND

In the last decade considerable effort has been put into the development

of inspection tools and repair methods for concrete structures. In the U.K.

much of this effort has been related to North Sea gravity structures, some of

which have now been in operation for 10 years. The rapid growth of construction in the Middle East with all of its inherent durability problems has also

necessitated the rapid development in inspection and repair technology. In

the U.S.A., the corrosion of over 200,000 highway bridges has similarly drawn

attention to the need for effective repair techniques.

Whilst for land based, coastal and offshore structures, inspection and repair

techniques have advanced considerably in recent years, the Arctic presents

additional problems by virtue of the extremely low temperatures which can occur, often as low as -50°C, and the presence of ice in varying forms. The

extreme cold influences the properties of not only the concrete and steel but

also repair materials which require particular properties for low temperature

curing; and inspection tools may not operate satisfactorily. In addition,

thermal stresses may be generated of sufficient magnitude to cause cracking.

The ice creates problems of access, particulary when flowing. Also the nature

of damage which can occur is unique, ranging from punching failure to severe abrasion. Ice also bonds well to concrete necessitating the use of coatings

to prevent adfreeze or design for increased lateral loading.

Existing procedures for inspection and repair must therefore be re-evaluated

in the light of these extreme environmental conditions, taking into account

the types of structures which are to be installed and the nature of damage

which can occur.

35
5.2 SUMMARY OF DISCUSSIONS

Arctic Structures

Various systems are currently being developed for offshore exploration and

production in the Arctic. These include tower structures, artificial islands,

ballasted caissons and berm islands, conical structures, and floating systems.

The type of structure to be used for a particular application will depend

to a large extent on tne water depth, the severity of the ice environment

and the rate of ice flow. The ice loads on an Arctic structure may include

flows and ice sheets, multiyear ridge plus flow, adfreeze, rubble pit, and summer impact.

In the severe ice conditions which can exist in the Beaufort Sea, conical

structures are proposed to induce flexural failure in the ice at loads

about an order of magnitude less than required to fail the ice by crushing.

When the ice environment is relativley light, with no multiyear ice, tower

structures may be used, such as those in Cook Inlet. When there is a reasonable

open water season, floating structures may be used.

The ways in which inspection and repair can be undertaken will be determined

by the type of structure in relation to its configuration, exposure conditions

and open water season. In particular, access may be difficult to large areas

of a structure. The nature of the damage which may occur will also be influence

by the configuration of the structure.

Environment

The term "Arctic" in the context of this chapter will be used to describe any area which encounters sea ice on an annual basis. This may comprise solely of

first year ice which may vary from 1 to 6 feet (0.3 to 2 m) in thickness,

36
or multiyear ice which has lasted through more than one season, is appreciably

harder than first year ice and can extend down to the seabed.

Below the water (or ice) level, inspection and repair may be extremely difficult

if not impossible to achieve during the winter freeze. Not only will the ice

layer prevent direct access to large areas of the structure, but also the

movement of the ice will create a serious hazard to divers and make the use of

remote control vehicles (RCVs) difficult. Similar problems are likely to

exist due to the severe currents below the ice. Above the ice or inside the

structure the problems will be less severe.

Fortunately, in most of the lease sale areas there is a period of open water

each season. This may be as little as 60 days in the Beaufort Sea to at least

6 months in the Bering Sea. During this period, inspection and repair methods

similar to those currently employed in the North Sea may be applicable.

However, it may not be possible to wait for a weather window and consideration

must therefore be given to means of inspection and repair during the winter

freeze when temperatures may be as low as -50°C.

Materials Performance

In addition to the normally aggressive exposure conditions in a marine

environment, Arctic structures are also required to withstand extreme freezethaw cycling, severe ice abrasion, impact loading, and differential thermal

gradients. For this reason, considerable effort has been put into the design

of high quality concretes with the current trend being towards the use of high

strength, air-entrained, lightweight concrete using superplasticizers and

alternative cementitious materials such as condensed silica fume. The aim is

to achieve:

• Low permeability which reduces the ingress of water

• Prevention of freezing and thawing damage when the small amount of

absorbed water freezes

o Reduced likelihood of steel corrosion

37
Extensive laboratory and field studies on concretes up to 80 years old have

highlighted the importance of low permeability in achieving durable structures.

However, whilst materials such as silica fume are currently being investigated

by numerous researchers, there is as yet only limited field performance data.

To assess in situ performance using conventional corrosion monitoring techniques

may require re-calibration of the equipment and perhaps a change in the

interpretation of results.

It must be noted that the properties of both the concrete and steel are influenced by temperature. Research has shown that:

o The compressive strength of a typical structural concrete will

increase, typically 30 percent when cooled from 20°C to -50°C.

o Concrete tensile strength, flexural strength and bond strength to rebar

will increase in proportion to the compressive strength.

o Deformation due to load is reduced and impact and crack resistance are increased

.

These changes in properties are related directly to the natural moisture content

of the concrete which is typically 4 to 5 percent. In this condition the voids

are not fully saturated and freezing need not present a problem.

The characteristics of reinforcing steel must also be considered. Steel tends

to embrittle at low temperatures. Conventional tests for Impact Transition

Temperature, such as the Charpy Notch Impact test, indicate that conventional

rebar may embrittle at temperatures as high as 0°C. On the other hand, tests

on full size bars have indicated that hot rolled steel may behave in a ductile

manner at temperatures below -50°C.

All these factors must be taken into account when undertaking damage analysis,

particularly when computer modelling is employed. The increased strength,

stiffness and crack resistance will all significantly influence predicted

performance.

38
Reasons for Inspection

In the North Sea there are statutory requirements to inspect concrete

structures, in order to provide a certificate of fitness. These are defined by:

o Offshore Minerals Working Act (U.K.)

© Dept, of Energy Guidance (U.K.)

o BS 6235 (U.K.)

o DNV Regulations

Each structure must be fully inspected within a 5 year period with a minimum

inspection requirement each year. Regular inspection enables potential problems

to be identified prior to serious defects occurring, and may avoid the need

for extensive repairs by the use of simple preventative measures. With the

level of understanding already achieved it may be possible to predict the life

of the structure prior to the need for repair.

Prudent construction inspection will minimize the extent of in service

inspection and aid the detailed location of rebar, prestressing steel and

hardware where damage occurs or modification to the construction is required.

Localized inspection is required in the event of damage and after the repair

is completed.

Survey Methods

Standard methods are available for in situ corrosion monitoring . These include:

® Potential measurements to identify activation of the steel

9 Concrete resistivity measurements to assess the rate of corrosion

o The use of resistance probes in conjunction with a Corrosometer to assess

the rate of corrosion

o Chloride diffusion measurement using the applied voltage technique

® Measurement of chloride ingress into drilled core samples

© The use of a covermeter to determine depth of steel

o Visual inspection (divers, RCVs)

39
Using these techniques it is possible to make a reasonable estimate of

the rate of corrosion and to predict the life of a structure before significant

maintenance is required.

Nondestructive tests can be made to assess the quality of concrete . These

include:

• Ultrasonic pulse velocity measurement

• Measurement of surface hardness by the Rebound Hammer test

Core samples have value in providing a more direct means of assessing

concrete strength and other properties such a permeability, resistivity, and

oxygen diffusion.

The following points should be noted:

o Many of these techniques have been used in the North Sea and some

have been adapted for use underwater.

9 Their performance at low temperature in unknown and modifications may

be necessary to enable satisfactory operation in Arctic conditions.

Various detection devices such as accelerometers, embedded strain gauges and

thermocouples can provide valuable information which can be used to assess in

service structural performance . Strain devices have been used extensively in

a range of nuclear structures and dams and have operated successfully at temperatures as low as -165°C. The use of embedded strain gauges also provides

the designer with full scale model test results against which to assess the

analytical techniques used in the design, enabling more rational design of

subsequent structures.

Many problems with instrumentation have resulted from fragmentation of

responsibility of installation through to data analysis. Lack of instrument

reliability, and over excessive data production can make data interpretation

extremely difficult.

40
Improvement in the value of instrumentation will be achieved by:

1) single part responsibility for design, installation, operation,

data processing and evaluation; and

2) better reliability of the instrumentation, particularly under low

temperature conditions.

Damage Analysis

Limited studies on damage caused by impact have been undertaken, leading to

the development of computer programs which can predict the mode of failure.

Experience with impact damage which has occurred to structures in the North Sea

has provided support to the theoretical studies.

Tests are being undertaken to establish the punching shear resistance of

typical concrete elements under ice load conditions as part of the development

of the ACES program in England. This can provide a basis for further investigation of the mode of failure of Arctic structures. Work has now been extended

to include repairs to the damaged elements to assess the post-repair

performance.

Analysis of inspection survey results also enables a potential damage assessment

to be made, predicting where problems are likely to arise. In this case preventative measures can be taken before the damage becomes either structurally

or aesthetically unacceptable.

Types of Damage

1. Corrosion of Rebar

In conventional marine structures, corrosion of the rebar presents the greatest

problems particularly in the splash zone. This area is subject to a build-up

of salts which diffuse into the concrete, activating the steel in the previously

41
passive alkaline environment. Once corrosion starts, oxygen, which may also

diffuse through the cover zone, fuels the corrosion process. In addition,

moisture in the concrete reduces the resistivity hence increasing the corrosion

current. Damage due to steel corrosion initiates as cracks which result from

the bursting stresses generated by the corroding steel. These enlarge until

the concrete spalls from the surface. Corrosion of steel in concrete may also

lead to loss of structural integrity as the uncorroded steel section reduces.

In addition, bond to concrete can be reduced.

2. Mechanical Damage

Mechanical damage may occur due to ice impact, abrasion, gouging, ship impact,

dropped objects, fire and explosion, and thermal shock from gradients (values

to 110°C can occur in the Arctic). Damage of this type may affect only the

surface of the concrete or induce severe structural damage with loss of concrete

and rupture of the rebar or prestressing steel. It is most likely that damage

due to impact will be local whether caused by ice, dropped objects, or supply

boats. Surface damage due to abrasion is likely to be more general.

3. Freezing and Thawing Distress

Freezing and thawing damage must also be considered, including the ratcheting

effect of ice in cracks.

4. Foundation Distress

Cracking distress of structures has resulted from differential settlement

or under-base scouring of soils.

In certain areas, seismic damage may also cause distress.

42
Repair Requirements

The need to undertake repairs must be assessed in relation to the significance

of damage as it affects the successful operation of the structure:

• Is immediate action required or can the repair be delayed?

• Can a temporary repair be carried out or is permanent reinstatement

necessary?

© The open water period may be the best time to undertake repairs when

there is no ice to hinder progress.

The significance of different types of damage must therefore be defined.

This already exists to some extent in current Codes of Practice which recommend

for example, maximum acceptable crack widths. Broadly, repair requirements

can be considered in the following categories:

© Structural/maintenance/ cosmetic

© Local or general

© Permanent or temporary

If a permanent structural repair is required, this may involve:

• Cutting out damaged concrete;

• splicing and protecting damaged rebar or prestressing steel;

© reinstating the prestress load; and

© replacing concrete and protecting the surface

Alternatively, a simple grouting operation may be sufficient.

If damage is in the form of surface abrasion or gouging, immediate repairs

may not be required. This would be assessed by considering the importance of

concrete cover and the rate of erosion in the prevailing environmental conditions.

43
Repair Methods and Materials

1 . Concrete

Currently, repairs to concrete in offshore structures are undertaken using

cement or resin based grouts, mortars, and concretes.

Specialized materials are used to overcome specific conditions related to a repair situation. These are generally acceptable for use at temperatures down

to about 0°C, but sub-zero temperatures may present problems with curing times

and viscosity. Little is known about the properties of some of these materials

at low temperature, particularly in the long term.

2. Rebar and Prestressing Steel

A range of methods are available for restoring damaged steel in the concrete.

These include the following:

• Epoxy materials are used in resin bonded couplers for the repair of

damaged rebar. In this case it is important that thermal compatability

exists between the epoxy and steel if bond is to be maintained.

o Reinstatement of prestress presents particular difficulties and a variety of schemes have been investigated. These include systems using

cast-in flat-jacks, external Macalloy bars and direct replacement of

tendons

.

® For corrosion protection it is possible to coat the rebar prior to

concreting and in some situations coatings are also applied to the

surface of the concrete. Such protection may be unnecessary if adequate

protection from the concrete cover exists. Fiber reinforcement may

provide a partial substitution for replacement reinforcing steel.

44
3.

Coatings to Concrete

The performance of low-friction, concrete coatings under Arctic conditions

is currently being evaluated as part of the ACES development program. The

materials examined are required to bond to concrete, reduce adfreeze and

provide abrasion resistance against ice. A range of materials are being

evaluated including polyurethane, epoxy and polyethylene. One criterion for

selection is the need for in-service repair.

A critical feature of any coating system is the practicality of adequate

adhesion in the long term and after damage repair.

4. Concrete Placement

Damaged areas can be repaired by installing concrete or steel panels,

mechanically attached to the structure. Placement of concrete repair materials

can be by pump, skip, tremie, shotcrete or hand trowel, depending on the size

and location of the damaged area. Techniques are developed to place special

concretes (e.g. Hydrocrete) to depths of 200 m in the North Sea.

5. Crack Sealing

A range of cementicious and resin-based products with suitable injection

techniques have been developed for marine crack repairs.

Special Repair Considerations

Repair materials used in an Arctic marine environment are required to

possess properties not always essential for land based repairs.

® They must be moisture tolerant in order to cure in the damp conditions.

Moisture presents no problem for cement-based materials but can impair

the performance of some of the epoxies and polyurethanes.

45
• They must also be stable under the severe exposure conditions if

continual maintenance is to be avoided.

o They must provide adhesion to frozen substrate.

In addition, the materials must be permited to cure adequately. For low

temperature applications some special epoxy materials have been developed which

will cure at temperatures as low as -20°C. For lower temperature application

either special materials must be developed, or heating must be provided to maintain a satisfactory temperature regime under the severe freezing environment.

The latter might be achieved by electrical heating of the rebar, by heated

formwork or enclosures, or perhaps by some form of microwave system. If this

should prove necessary, a thermal analysis must be carried out to establish the

likelihood of excessive thermal stresses with associated cracking or degradation

of the surrounding concrete.

Logistics

In the North Sea and Arctic, supply of equipment and materials is generally by

helicopter. The equipment used must therefore be suitable for this means of

transportation. For example, present UK regulations prohibit toxic/explosive/

poisonous materials being carried by helicopter.

The availability of materials and equipment must also be considered. Are they

locally available? If not, what is the transit time? Is there a justification

for keeping repair equipment on the rig or at base camp?

Access to the damaged area must be considered. For a conical structure, such

as ACES, there is a large surface area to be inspected perhaps in a relatively

short weather window. Cranage should preferably be available to all external

parts of the structure. If normal cranage is insufficient then provision for

installing special equipment should be made. Internal access to the structure

is also desirable to enable inspection and repair work to be undertaken

internally where possible.

46
If external work is required below sea levels, RCVs or divers must be employed.

Should this be required, it would be desirable to wait for the open water

period. Pre-placed identification marks on the concrete surface facilitate

underwater inspection.

During the winter freeze, access through the ice could be dangerous

particularly if the ice is moving. Exploding ice, breaking on the structure,

and large blocks of multiyear ice may present significant hazards for both

divers and equipment.

For safety reasons it is essential that all equipment complies with the

relevant petrochemical regulations.

5.3 RESEARCH NEEDS

In considering the current needs regarding inspection and repair of Arctic

structures, it was appreciated that a number of the topics listed below

overlapped with the activities of the other working groups.

The Inspection/Repair Working Group found that the subject matter is not easily

broken down into specific research items. In many cases, surveys, assessments

and studies need to be carried out to develop practical procedures as well as the further development of existing inspection, monitoring, and repair

techniques.

Inspection During Construction

The efforts involved in undertaking in-service inspection and in assessing the

need for repair are dependent on the structural detailing, the material selection

for "fitness for purpose", and the quality control exercised during construction.

The implications are as follows:

1. Tests need to be developed, if not available, to establish the fitness for

purpose of the materials as supplied, or in the case of concrete,

manufactured and cast on site. Such tests include:

47
• Brittleness of steel at low temperature, bearing in mind the need to

test full size bars or prestressing wires rather than smaller samples

of steel.

• Freezing and thawing resistance characteristics of the in situ concrete

(e.g., by testing cores).

® Permeability of the in situ concrete (e.g., by testing cores).

o Ice abrasion resistance of the in situ concrete with or without

coatings

.

Q Concrete cover measurement in relation to that specified.

o Effectiveness of prestressing steel grouting, and the freeze-thaw

resistance of the in situ grout.

2. Procedures need to be developed to record the actual location of

reinforcement, prestressing ducts, and other embedments in the structure,

to aid later identification in service where damage has occurred.

3. Further study is necessary to produce practical specifications for field

usage, covering relevant testing and control procedures.

Structure Integrity Monitoring

1 . It is essential to develop an integrated systems approach to the task of

strucutre integrity monitoring. All components of the structure must be

accorded the appropriate significance, e.g., foundations, marine response

characteristics (both static and dynamic), subsurface structure, and the

superstructure

.

2. Evaluation is required of equipment, installation procedures and data

handling, to produce meaningful results to the operator and the statutory

48
authority, and to avoid failure in service or difficulty in interpretation

of results.

3. Back-up testing of the systems, under simulated operating environments of

moisture and cold, is essential to minimize the risk of failure, hopefully

over the life of the structure.

4. Careful estimation of the magnitude and variation of possible data output

from sensing devices is essential, whether they be strain or stress gauges,

accelerometers, ice pressure transducers, seabed piezometers etc., to ensure

that the results are meaningful. For example, a low strain gauge result

can mean either a low strain or a high stress under restraint.

5. Back-up testing of the devices related to the materials in the structure is

essential to avoid errors in the conversion of strain gauge outputs into

corresponding stress values and to aid interpretation. Strain gauge results

for concrete need to be supplemented with data on the shrinkage, elastic

properties, creep, and thermal expansion of the in situ concrete, if stress

is to be determined. Alternatively, stress gauges, although less accurate,

can give a direct reading without the substantial errors of conversion of

strain values to stresses.

6. Study is required of the optimum approach for system design, installation

and monitoring, in association with the inspection requirements. Preferably

the same organization should be responsible for supervising and interpreting

the results as was involved during equipment selection, its installation

and the subsequent monitoring phases. There may well be an advantage to

link their responsibility with the regular inspection organization to

maximize the value from both.

Inspection Procedures

1. In view of the large surface areas of concrete involved, a scheme for

systematic recording needs development. The desired scheme should:

49
• be practical for inspectors to carry out;

• enable easy reference later onshore to evaluate possible defect

situations; and

9 be capable of being readily updated in subsequent inspections, to

highlight significant changes relative to previous inspections.

2. A practical system of coding visual defects such as cracks, staining,

and honeycoming needs urgent consideration, as visual inspection

is the primary method for global scanning of the structure.

Inspection Techniques

1. Existing techniques (such as visual and photographic defect recording, common NDT methods, and core sampling for subsequent analysis) need to

be investigated for their use:

9 above and below water;

o with and without freezing environments.

2. It may be necessary to modify the existing techniques and develop equipment

to operate underwater and at low temperatures. Equipment components may

not function reliably without modification, for example, electrical

components may need to be sealed against water vapor or be thermally

protected against extreme cold.

3. Novel techniques for inspecting the structure require detailed

investigation, since they may potentially provide greater information, or increase the scanning rate of the structure. Such techniques might include

o Tomography

9 Vibrational and ultrasound scanning

o Time domain ref lectometry , for scanning prestressing tendons for damage

along their length using end anchorage access

50
® Magnetic and other electrical responses to galvanic and local steel

corrosion, for example, as used for pipe line inspection

« Thermography, benefitting from the stable temperature conditions, to

identify local cold spots

Specialists in the specific technologies involved in the effective development

of such techniques need to work closely with inspection agencies to ensure the

practicality of the results.

4. For underwater inspection, design of equipment is required for operation by

divers or RCV's, preferably for recording at the surface.

5. Inspection from within structures with external walls, while having obvious

advantages, requires:

® study of suitable techniques, and

o consideration at the design stage for providing access under either wet

or dry conditions, preferably the latter. Many of the internal

inspection operating problems due to the cold and ice environment would

be avoided if internal inspection were made feasible.

Repair Procedures

Prior study is required to consider the total process involved in undertaking

a repair, particularly if major damage has occurred. Topics needing to be

assessed include:

® Methods for rapid early analysis of the damage from initial observations,

such as, for example, the size and construction details of a structure and

the ship where a collision has occurred, the velocity and shape of the ship

and extent of the cracked area.

51
• The availability of repair materials and equipment to undertake either a temporary or long terra repair.

• Repair methods and procedures to restore leak tightness or strength to the

structure. The former is of particular importance where oil pollution from

damaged storage tanks is important.

9 Inspection procedures and techniques for assessing the effectiveness of the

repair afterwards.

Repair Techniques for Types of Damge

Various levels and types of damage have been identified which will require

different methods for inspection and repair where immersed and cold conditions

exist

.

1. Abrasion

a. Inspection - methods of recording the nature and rate of abrasion need

investigation.

b. Repair -

o coatings - methods of repair need to be developed.

a concrete - thin overlay materials with adequate bond to existing

concrete need assessment and testing under simulated structural

conditions.

2. Spalling (due to impact from ice, vessels, or equipment)

a. Inspection - visual inspection may be sufficient

52
b. Repair - suitable cementitious/resin based products need evaluating

under simulated structural conditions.

3. Puncture (major damage due to impact from vessels or equipment)

a. Inspection - NDT methods need to be assessed to support visual

observation

.

b. Repair - techniques to restore the structure need development.

Restorations of the rebar, the prestress and the concrete need to be

considered as well as alternative restoration systems by, for example,

external patching or steel plating within or outside the structure.

4 . Cracking

a. Inspection - NDT methods need to be evaluated to assess extent and

nature of cracking.

b. Repair - suitable cementitious/resin based materials are required to

penetrate cracks under simulated site conditions.

5

.

Freezing and Thawing

a. Inspection - visual inspection may be sufficient.

b. Repair - the same requirements as for repairs of concrete damaged by

abrasion

.

6.

Corrosion

Corrosion of rebar may result in spalling, cracking, lamination of the concrete

cover, or loss of section of the bar. For prestressing steel, corrosion may

result eventually in tendon failure.

53
a. Inspection -

i. dry - techniques are already available which need modification for

on-site usage.

ii. wet - techniques need to be developed.

b. Repair - treatments of the steel need evaluation and simulation testing.

Consideration of further prevention techniques (e.g., cathodic protection,

surface coatings) may be necessary for avoiding similar damage to other

critical areas.

7 . Frozen Concrete

a. Inspection - existing techniques to inspect for concrete and steel damage

may not work for frozen concrete. Simulation testing is a priority need

in this area.

b. Repair - materials and equipment need evaluation and testing to identify

their suitability for placing and in service performance. For example,

injection equipment may block due to low temperature although the resins

may be suitable as regards, e.g., their bond to the frozen concrete.

Heating locally may be necessary and needs investigation.

8. Thermal Overload

Where a severe temperature difference occurs between oil in storage tanks and

the frozen external environment, damage to the relatively thin concrete walls

was not considered to be particularly onerous, so that neither inspection nor repair problems were identified.

54
9. Leakage (including seepage)

Leakage due to hydrostatic pressure may occur at poor construction joints,

porous concrete in the walls and local honeycombing, as well as at cracks.

Leakage paths along prestressing tendons have occurred in North Sea structures

and there has been great difficulty in identifying their source.

In other structures, leakage induced by hydrostatic pressure has resulted from

flow along embedments, due to settlement of fresh concrete below the rebar,

formwork ties, and other penetrations.

a. Inspection - novel techniques, such as radioactive tracer methods, need

development to track down the extent and source of leakage.

b. Repairs - sealing materials and techniques need development to withstand

the possible further build-up of hydrostatic pressure. Simulation testing

is essential.

Summary

With the likely large usage of concrete structures for Arctic oil and gas

exploration and production, it is considered essential to implement the

recommendations to ensure that inspeciton, monitoring, and repair proceduress

are developed to meet the special and demanding conditions likely in the Arctic

operating environment. Lack of suitable rapid and sound inspection and repair

techniques could well result in substantial increases in cost and production

time loss, subsequent deterioration of the structure in service or cessation

of platform operations after damage. The research requirements identified by

the Inspection/Repair Working Group are summarized in table 1.

55
Table 1. Research Needs Relative to Inspection and Repair

CATEGORY NEEDS

Test methods for assessing in situ

material performance.

1. INSPECTION DURING CONSTRUCTION 1.

2 .

3 .

2. STRUCTURE INTEGRITY MONITORING 1.

2 .

3 .

3. INSPECTION PROCEDURES 1.

2 .

4. INSPECTION TECHNIQUES 1.

2 .

3 .

4 .

Procedures for recording structural detailing

Practical specifications for testing and

control procedures.

Data processing for assuring the relevance

of results.

Optimization of control organization for

equipment design, installation, and monitoring in relation to inspection needs.

Observation recording systems.

Visual defect classification system.

Suitability of existing techniques for usage

underwater and/or in cold environments.

Development of novel alternative techniques

for faster and clearer scanning for possible

defects.

Assessment of inspection methods for RCV or diver usage.

Internal inspection techniques and needs for

structural design to facilitate their usage.

Evaluation of equipment and sensors performance regarding in-service

vulnerability.

5. REPAIR PROCEDURES

6. REPAIR TECHNIQUES

Evaluation and development of procedures for

damage analysis, repair, and after-repair

inspection.

Evaluation of the suitability of existing repair

materials and equipment used offshore to deal

with different potential types of damage (abraNOTES

i. Most of the above research must be dominantly related to underwater usage, as well as in low temperature, cold water environments and in frozen concrete.

ii. It is realized that in certain cases considerable development effort will be

required to make the technqiues effective under such field conditions.

iii. No order of priority has been given as each aspect is of equal significance.

56
6 . ACKNOWLEDGMENT

The planning committee wishes to express its thanks to the workshop participants

for giving their time to attend and actively participate in the workshop.

Special gratitude is extended to the Group Chairmen who volunteered so much of

their time to prepare their position papers and group reports. Appreciation

is extended also to Ms. Carol McKenzie for her extraordinary efforts in the

planning and execution of the workshop. Finally, we wish to thank Mrs. Sara R. Torrence for handling arrangements for the workshop, and Ms. Mary L. Ramsburg

and Ms. Ulesia B. Gray for typing the draft reports. It was the cooperation

of all these individuals that produced a successful workshop.

57
APPENDIX

I. WORKSHOP PARTICIPANTS

Mr. Gerry Bader, Swan Wooster Engineering, Inc., 500 N. E. Multnomah St.,

Portland, OR 97232

Mr. Robert Bea , PMB , Systems Engineering, Inc., 500 Sansome Street, Suite 400

San Francisco, CA 94111

Mr. Jal N. Birdy, Brian Watt Associates, Inc., 2350 E. North Belt Dr.,

Suite 450, Houston, TX 77032

Mr. Tony Boyd, Swan Wooster Engineering, Ltd., 1525 Robson St.,

Vancouver, B.C. CANADA

Dr. Theodore W. Bremmer, Department of Civil Engineering, University of New

Brunswick, Fredericton, New Brunswick, E3B 5A3 CANADA

Dr. Roger Browne, Manager, Research & Development Div . , Taylor Woodrow

Construction Ltd., 345 Ruislip Road, Southall, Middlesex

UB1 2QX, ENGLAND

Dr. M. S. Cheung, Public Works Canada, Civil Engineering Division, Room C45

,

Sir Charles Tupper Building, Riverside Drive, Ottawa,

Ontario K1K 0M2 CANADA

Dr. Nicholas J. Carino , Research Civil Engineer, National Bureau of Standards,

Building 226, Room B162, Washington, DC 20234

Mr. Reginald Clare, Sir Robert McAlpine & Sons, Ltd., P. 0. Box 74,

40 Bernard St., London WC1N 1LG ENGLAND

Mr. Edgar Curtis, Minerals Management Service, 800 "A" Street, Suite 201,

Anchorage, AK 99501

58
WORKSHOP PARTICIPANTS (Continued)

Mr. Felix Dyhrkopp, Platform Verification Section, Minerals Management Service,

3301 North Causeway Blvd . , P. 0. Box 7944, Metaire, LA

70010

Mr. Kurt Eriksson, Consulting Engineers, VBB-SWECO, Box 5038, 102 41 Stockholm,

SWEDEN

Mr. Edgars Ernstons, Engineer in Chief, Swedish National Administration of

Shipping and Navigation, Department of Works and Harbours,

Slottsgatan 82, Fack 601 78 Norrkoping, SWEDEN

Lt. Randall Fiebrandt, U.S. Coast Guard, G-MTH-4/ 13 , Washington, DC 20593

Dr. A. E. Fiorato, Construction Technology Laboratories, Portland Cement Ass.,

5420 Old Orchard Rd . , Skokie, IL 60077

Mr. Richard Giangerelli , Offshore Inspection & Enforcement Division, MS 647,

Minerals Management Service, Reston, VA 22091

Dr. Odd E. Gjorv, Professor of Civil Engineering, University of Trondheim,

N-7034 Trondheim, NORWAY

Mr. Ben Gerwick, Jr., 500 Sansome Street, San Francisco, CA 94111

Mr. John Gregory, Minerals Management Service, MS 647, 12203 Sunrise Valley Dr.,

Reston, VA 22091

Dr. David Haldane, Institute of Offshore Engineering, Heriot-Watt University,

Research Park, Riccarton, Edinburgh EH14 4AS UNITED KINGDOM

Mr. Harvey H. Haynes, 445 Bellevue Ave . , Suite 03, Oakland, CA 94610

59
WORKSHOP PARTICIPANTS (Continued)

Mr. Joseph I. Heneghan, Gunite Masonry Co., Inc., 1367 Bellraore Avenue,

North Bellmore, NY 11710

Dr. George C. Hoff, Mobile Research and Development Corp., Offshore Engineering,

P.0. Box 345100, Farmers Branch, TX 75234

Dr. Bernt Jakobsen, Norwegian Contractors, P.0. Box 40, Ankertorvet, Oslo 1,

NORWAY

Dr. Dag N. Jenssen, Det Norske Veritas, 16340 Park Ten Place, Suite 115,

Houston, TX 77084

Mr. Joseph F. Lamond , Office - Chief of Engineers, DAEN-CWE-DC , Washington, DC

20314

Dr. H. S. Lew, Leader, Construction Safety Group, National Bureau of Standards,

Building 226, Room B162, Washington, DC 20234

Dr. V. Mohan Malhotra, CANMET , Energy, Mines and Resources, 405 Rochester St,

Ottawa, CANADA K1A 0G1

Mr. Sam Maxwell, Gulf Canada Resources, P.0. Box 130, 401 9th Ave., SW,

Calgary, Alberta T2P 2H7 CANADA

Mr. James F. McNary, Senior Project Engineer, Global Marine Development Inc.,

P. 0. Box 3010, Newport Beach, CA 92663

Mr. Jan Moksnes , QA/ QC Manager, Norwegian Contractors, 4030 Hinna

,

P. 0. Box 115, Stavanger, NORWAY

Dr. Touraj Nasseri, Det Norske Veritas (Canada), Ltd., 8500 Macleod Trail SE

#210 S, Calgary, Alberta T2H 2N1 CANADA

60
WORKSHOP PARTICIPANTS (Continued)

Mr. Robert Philleo, Office - Chief of Engineers, Attn: DAEN-CWE-D,

Washington DC 20314

Mr. Robert E. Potter, Sohio Petroleum Co., 100 Pine St., San Francisco, CA

94111

Mr. Peter Pullar-Strecker , Director of Research, CIRIA, 6 Storey's Gate,

Westminster, London, ENGLAND SW1P 3AU

Mr. Gopal Rao , American Bureau of Shipping, 65 Broadway, New York, NY 10006

Dr. Winston Revie, Assistant Director, Materials Research Program Office,

CANMET, 555 Booth St., Ottawa, Ontario K1A 0G1 CANADA

Mr. John Roberts, Ove Arup and Partners, 13 Fitzroy St., London, ENGLAND

W1P 6BQ

Mr. Bjorn Roland, Det Norske Veritas, Veritasveien 1, Postboks 300,

N-1322 Hovik, Oslo, NORWAY

Mr. Karl Runge , Exxon Production Research Corp., P. 0. Box 2189, Houston, TX

77001

Mr. Ed. Sauve, Standard Oil Co. of California, P. 0. Box 7141, San Francisco,

CA 94120-7141

Mr. Phil T. Seabrook, B. H. Levelton & Associates, 8805 Osier Street, Vancouver,

British Columbia, CANADA V6P 4G1

Mr. F. Sedillot, C. G. Doris, 58A Rue Du Dessous Des Berges , Paris 75013 FRANCE

61
WORKSHOP PARTICIPANTS (Continued)

Dr. Robert G. Sexsmith, Buckland and Taylor Ltd., 1591 Bowser Avenue, North

Vancouver, B.C., CANADA V7P 2Y4

Mr. Morris Schupack, Schupack-Suarez Engineers, Inc., 225 Wilson Avenue,

South Norwalk, CT 06854

Dr. B. P. Malcora Sharpies, Noble Denton & Associates, Inc., 9575 Katy Freeway,

2 Bali Park Suite 400, Houston, TX 77024

Mr. Charles Smith, Minerals Management Service, MS 647, 12203 Sunrise Valley Dr.,

Reston, VA 22091

Dr. R. J. Smith, Canada Oil and Gas Lands Admin., 355 River Road, Ottawa,

Ontario, CANADA K1A 034

Dr. Roger Stacey, Director, Ocean Engineering Group, NORDCO, Ltd.,

P. 0. Box 8833, St. Johns, New Foundland , A1B 3T2 CANADA

Prof. S. M. Uzumeri, Department of Civil Engineering, University of Toronto,

35 St. George, Toronto, Ontario, CANADA M5S 1A4

Dr. Ian Weir-Jones, President, Weir-Jones Engineering Consultants, Inc.,

1574 West 2nd Ave . , Vancouver, B.C., CANADA V6J 1H2

62
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63
II. MEMBERS OF WORKING GROUPS

DESIGN CONSTRUCTION

BEN C. GERWICK, JR., CHAIRMAN PETER PULLAR-STRECKER, CHAIRMAN

Robert Bea Gerry Bader

Jal N. Birdy Edgar Curtis

Tony Boyd Dag Jenssen

William Cichanski (by correspondence) Robert E. Potter

Reginald Clare Robert G. Sexsmith

Felix Dyhrkopp

Kurt Eriksson

Edgar Ernstons

Lt. Randall Fiebrandt

David Haldane

R. J. S. Harris (by correspondence)

Bernt Jakobsen

Sam Maxwell

James F. McNary

Touraj Nasseri

John Roberts

Karl Runge

Ed Sauve

Francois Sedillot

Charles Vos (by correspondence)

B. P. Malcolm Sharpies

64
MEMBERS OF WORKING GROUPS (Continued)

MATERIALS

ROBERT PHILLEO, CHAIRMAN

Ted W. Bremner

M. S. Cheung

Tony Fiorato

Odd E. Gjorv

George C. Hoff

Jan Moksnes

Morris Schupak

Roger Stacey

S. Mike Uzumeri

INSPECTION

ROGER BROWNE, CHAIRMAN

Richard Giangerelli

Harvey H. Haynes

Joseph I. Heneghan

Joseph F. Lamond

Gopal Rao

Bjorn Roland, DNV , Oslo

Phil T. Seabrook

Ray J. Smith

Ian Weir-Jones

65
III. WORKSHOP AGENDA

Tuesday, March 1, 1983

9:00 - 9:25 a.m. Introduction and Welcome

Nicholas Carino, Chairman

Workshop Planning Committee

National Bureau of Standards

Samuel Kramer, Deputy Director for Programs

National Engineering Laboratory

National Bureau of Standards

Winston Revie, Assistant Director

Materials Research Program Office

Canada Centre for Mineral and Energy Technology

Charles Smith, Inspection Enforcement Division

Minerals Management Service

U.S. Department of Interior

9:25 - 10:00 a.m. Presentation of Position Papers (Plenary Session)

Introduction - Edward 0. Pfrang

Chief, Structures Division

National Bureau of Standards

Ben Gerwick - Chairman, Design Working Group

Robert Philleo - Chairman, Materials Working Group

Peter Pullar-Strecker - Chairman, Construction Working

Group

Roger Browne - Chairman, Inspection/Repair Working Group

66
WORKSHOP AGENDA (Continued)

10:30- 1:00 p.m. Working Group Meetings - Morning Sessions

2:00 - 3:30 p.m. Working Group Meetings - Afternoon Sessions

4 :00 - 5:00 p.m. Working Group Meetings - Afternoon Sessions

Wednesday, March 2, 1983

9:00 - 10:00 a.m. Working Group Meetings - Final Sessions

10 :30 - 1:00 p.m. Presentation of Group Reports (Plenary Session)

DESIGN - Ben Gerwick

MATERIALS - Robert Philleo

CONSTRUCTION - Peter Pullar-Strecker

2:00 - 3:00 p.m. Presentation of Group Reports and General Discussions

(Continued)

INSPECTION/REPAIR - Roger Browne

3:00- 3:30 p.m. Concluding Remarks and Adjournment

Mohan Malhotra

Canada Centre for Mineral and Energy Technology

Nicholas J. Carino

67

N BS-1 )4A rev. 2- m*t —' U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBSIR-83-2751

2. Performing Organ. Report No. S.'Puk'ITcation Date

July 1983

4. TITLE AND SUBTITLE

Proceedings of the International Workshop on the Performance of Offshore Concrete

Structures in the Arctic Environment

5. AUTHOR(S)

Nicholas J. Carino, Editor

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s) 7. Contract/Grant No. national bureau of standards

DEPARTMENT OF COMMERCE 8. Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

Technology Assessment and Research Branch Canada Centre for Mineral and Energy

Minerals Management Service Technology

U.S. Department of the Interior Energy, Mines and Resources Canada

Reston, Virginia 22091 Ottawa, Canada K1A 0G1

10. SUPPLEMENTARY NOTES

I

i 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

bi bl iogrophy or literature survey, mention it here)

A workshop was held March 1 and 2, 1983 at the U.S. National Bureau of Standards.

The objective was to bring together an international group of experts for the purpose

of information exchange on the subject of the performance of Arctic offshore concrete

structures. The workshop participants were divided into four working groups to

discuss the following subjects related to Arctic offshore concrete structures:

1) design; 2) materials; 3) construction; and 4) inspection and repair. Each working

group addressed the following topics within their subject: past experiences,

current projects, and recommended research areas. The chairmen of each group

prepared reports summarizing their group's deliberations. These reports are incorporated into this workshop summary.

12. KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key words by semi colon s) Arctic; concrete; construction; design; inspection; offshore structures; repair;

research; structural engineering; technology assessment; workshop.

13. AVAILABILITY

Uni imited

| | For Official Distribution. Do Not Release to NTIS

| 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

72

15. Price

USCOMM-DC 6043-P80