INTERREG IV(A) CHANNEL PROGRAMME FOSTERING … - Study 2... · Corrosion Survey & feasibility study...

INTERREG IV(A) CHANNEL PROGRAMME FOSTERING LONG TERM INITIATIVES IN

PORTS (FLIP) TOR BAY HARBOUR AUTHORITY

FLIP Study 2- Quay Resistance -

Corrosion Survey & feasibility study for

Cathodic Protection in Channel ports

(case study: Torquay Harbour Structures)

for sharing knowledge and best practice

with FLIP partners.

EU Interreg IVa Channel Programme FLIP project no.5675

Torbay Council:- ACTION (2.2.9) Engineering and Technical studies for Torquay,

Paignton & Brixham quays and corrosion resistance.

Study 2. Quay Resistance - Corrosion Survey, Torquay Harbour Structures

Introduction

The study is intended to address ongoing protection to existing unprotected steel and steel reinforced

structures at Torquay Harbour and forms one of three inter-related studies commissioned by Torbay

Council to examine the need to protect the infrastructure of the Tor Bay harbours and assessing their

value.

The studies are part funded under the EU Interreg IVa Channel Programme, FLIP (Fostering Long Term

Initiatives in Ports) project no.5675.The results from the studies provide an opportunity to share

knowledge with other FLIP port partners, to learn of common problems and identify technical

solutions. The FLIP project also disseminates the study results to small and medium sized ports and

harbours in the Channel area via the project website: http://www.flip-ports.eu/

_________________________________________________________________________________

FLIP Project .The Conseil General de Seine Maritime (SMCC), based in Rouen, France, is the lead partner of an

Interreg IVa Channel programme project bid called FLIP (Fostering Long Term Initiatives in Ports). The project

aims to promote a sustainable cooperation between small & medium sized ports in the Channel area. The project

brings together 9 partners from the UK and France.

________________________________________________________________________________

http://www.flip-ports.eu/

Executive Summary

In four of the six cases where Cathodic protection (CP) is feasible, galvanic anodes are recommended

to be installed in the near future. Of the remaining two cases, CP is not considered to be required at

the present time in one, and is not considered suitable in the other. An alternative solution is proposed

for the latter case.

In the remaining case where CP is not feasible, but where unprotected steel is present, at the

boardwalk sub frame at Princess Pier, suitable repair informed by truss load testing at the pier head

and followed by application of a protective coating system is recommended to be undertaken in the

near future.

At the pier head however, given the combination of the condition of the steelwork support to the

banjo, the cross ties to the circular piles, and the timber deck it may be more economically viable to

reduce the extent of the pier head structure, the majority of which is currently closed due not least to

the significantly defective condition of timber. For the purpose of informing some judgement on the

economy of options an estimate of cost of steelwork repair and coating will follow in due course.

Contents

1. Scope

2. Cathodic Protection (CP)

3. Princess Pier steelwork sub frame to boardwalk

3.1 Convention 3.2 Steel elements

3.2.1 Piles and connecting members, seaward side of the pier, chainage 2-147 3.2.2 Galvanised sub frame members ch. 28-152 3.2.3 Steel truss work concrete encased propping chainages 1-28

4. Conclusions and Recommendations

4.1 Cathodic Protection (CP) 4.2 Princess Pier steel sub frame to boardwalk

4.2.1 Piles and connecting members, seaward side of the pier, chainage 2-147 4.2.2 Galvanised sub frame members ch. 28-152 4.2.3 Steel truss work concrete encased propping chainages 1-28

4.3 Protective coating 4.4 Economic consideration

5. Photographs

Appendix A Torquay Harbour – Various Structures: Feasibility Study for Cathodic Protection 261/REP/01.

Corrosion Prevention March 2015

Appendix B Archive Drawings - Princess Pier

B1/1759/1 Princess Pier ‘Islander’ Area Structural Survey – Gen Arrangement Existing

Steelwork and Layouts at Deck Level and at Top of Sea Wall 1975

B1/1934/8 Princess Pier Reconstruction – Gen Arrangement of New Steel Supporting Deck

and Shelter 1978

B1/1934/9 Princess Pier Reconstruction – Typ Details of New Steelwork Supporting Deck and

Shelter 1978

B1/625/5 – Details of Existing Girders, Princess Pier 1968

1. Scope

This report is intended to address ongoing protection to existing unprotected steel and steel reinforced

harbour structures at Torquay Harbour.

Thus the potential for the installation of cathodic protection (CP) is examined – through a commissioned

specialist’s submission – and In line with the remit of ‘corrosion surveys’ described in the FLIP appendix

protective works to other steel elements of harbour structures not within the scope of CP are additionally

included.

Structures considered, and their steel elements are:

A. Princess Pier

steel box and circular piles

steel- framed support to the timber boardwalk

concrete encased propping to the suspended pier head widening B. Fish Quay

sheet piled quay wall C. South Pier

reinforced concrete (RC) slab extension to original masonry structure

driven steel box piles.

CP and non-CP solutions for the three structures, along with their design life expectancy and a guide range of

costs of detailed design and build/install are provided.

2. Cathodic Protection (CP)

CP can only be considered where structural steel exists within an electrolytic medium such as seawater (up to

around mid-tide), or concrete encasement. The appended report thus considers structural elements meeting

these criteria:

A. Princess Pier

steel box and circular piles

concrete encased propping to the suspended pier head widening B. Fish Quay

sheet piled quay wall C. South Pier

reinforced concrete (RC) slab extension to original masonry structure

driven steel box piles.

The report identifies viable CP solutions with cost estimates to all except the concrete encased propping at

Princess Pier, which may otherwise be protected by a coating system.

3. Princess Pier steelwork sub frame to boardwalk

3.1 Convention

Reference chainages and notations arise from, and align with those appearing in appended General

Arrangement drawings B1/1759/1 and B1/1934/8.

3.2 Steel elements

The steel elements below the timber boardwalk, indicated in arrangement drawings B1/1759/1 and

B1/1934/8 may be classified thus:

piles and their connecting members on the seaward side of the pier, supporting the castellated beams to the deck suspended over water, chainage 2-147. Piles double up width wise and are braced with tie rods below the pier head widening.

galvanised members installed 1970s through chainages 28-152

original/older steel truss work (anecdotally dated to 1950s/60s) and concrete encased propping below the widened pier head, in archive drawings is variously termed the ‘Banjo’ and ‘Islander’, chainages 1-28

3.2.1 Piles and connecting members, seaward side of the pier, chainage 2-147

Accelerated Low Water Corrosion (ALWC) is likely hidden by extensive marine growth to lower areas. As

recognised in the appended CP specific report these elements are recommended to be protected by CP, up to

mid tide.

Piles supporting the seaward side of the Pier were analysed by sample for section thickness. The newer piles

supporting the castellated beams were measured to be typically 15.5mm, aligning with the 14mm thickness

expected of Frodingham no 4 specified in archive drawings, whilst the thickness of the older ‘10” screw piles’

piles supporting the banjo structure was measured to average around 18mm. Such a section thickness is at

the heaviest end of circular steel sections currently available.

The 1½“ tie rod bracing to the screw piles supporting the Banjo structure is recognised by this and other

reports to be in such a deteriorated corroded condition that it cannot be repaired.

3.2.2 Galvanised sub frame members ch. 28-152

In many localised areas the zinc coating to members in this framing has deteriorated such that corrosion of

the host steel has commenced.

3.2.3 Steel truss work and concrete encased propping chainages 1-28

The existing arrangement at this location has replacement galvanised steel truss work extending through

gridline D2-28 and through C1-5.

Similar to a Structural Investigation Report, R01121S001/B, by Pell Frischmann in 2007 a sample of section

sizes was measured on ‘original’ steel at truss D2/C1, an exposed but easily accessible location. The condition

of the steel truss appeared to be typical of the more weathered truss and bracing units. Section thicknesses

measured:

Top chord 10mm Diagonal strut 8mm Lower chord 5mm

Archive drawing B1/625/5 indicates that original steel was ½” i.e. 13mm.

4. Conclusions and Recommendations

4.1 Cathodic Protection (CP)

Galvanic anodes are recommended to be installed to the sheet piled wall of the Fish Quay structure, to the

box piles of the South Quay structure, and to the box and screw piles of the Princess Pier structure in the near

future.

CP is not currently considered to be required to the suspended slab at South Pier, and is not considered

suitable for the concrete encased props to the pier head at Princess Pier.

4.2 Princess Pier steel sub frame to boardwalk

4.2.1 Piles and connecting members, seaward side of the pier, chainage 2-147

Since CP would only be effective to piles up to mid tide a protective coating is recommended to be applied

above this level.

The 1½“ tie rod bracing to the screw piles supporting the Banjo structure is beyond repair and should be

replaced.

4.2.2 Galvanised sub frame members ch. 28-152

Corrosion has not resulted in significant section loss and the life of this framework may be extended with the

application of a protective coating

4.2.3 Steel truss work concrete encased propping chainages 1-28 The degree of loss of section of the steel sub frame was considered sufficient to preclude crowd loading (of

5kN/sq m) in a 2007 Pell Frischmann report (Princess Pier, Torquay - Structural Investigation Report

R01121S001/B). The detail of this judgement, a 2D finite element model has been requested, but has thus far

not been forthcoming. Meanwhile, approximate analysis and bending moment/lever arm inspection suggest

there is residual capacity after section loss in the sampled truss members to approach crowd load capacity.

Trusses comprising similar angle and flat steel elements on gridlines B and D appear to have been designed to

support the ‘Islander’ building lost to fire in 1974. Having been required to support both imposed loading and

that of the dead load of the Islander building the capacity required of these trusses would have been greater

than that required at the pier head in its current open arrangement.

Since the degree of corrosion to the trusses makes an absolute judgement somewhat difficult to make, load

testing may be a suitable method of gaining confidence in truss capacity.

Agreement may simultaneously be reached on a reasoned likely loading, where standard crowd loading might

otherwise be applied in calculations. Similar circumstances gave rise to a reduced pedestrian loading being

tested and agreed to be a sufficiently appropriate degree of verification for public safety, to the Grand Parade

balustrade, Bath, an account of which features in The Structural Engineer, May 2015.

Load testing would be proposed to be undertaken on a sample bay between trusses C24/C20, and truss

D24/D20, thereby including the truss considered by the 2007 Pell Frischmann report to have the highest

amount of section loss. Being located over the original masonry pier structure, this bay affords the opportunity

for easier installation of a crash deck immediately below the bay under test. For ease, loading may be applied

and increased in a controlled manner by the filling of highway water barriers over support beams spanning

between the two trusses under test.

4.3 Protective coating

With the confirmation that trusses remain adequate, or may be repaired or enhanced to be rendered

adequate, this report and that of Pell Frischmann 2007 recommend the application of a coatings system.

Maker Coating Systems Ltd (ref AS8317) has recommended the Corroless EPF system for application to the

whole of the boardwalk sub frame and the piles above mid tide. The system can offer a 25 year life expectancy.

Preparation by blast cleaning may be possible, but the proximity of the marine and leisure environments may

permit only needle gunned surface preparation with its better guarantee of waste material

retrieval/enclosure. This may have an impact on the life expectancy of the system.

A guide price is to be received from Ian Williams Ltd for the application of the Corroless System to the

steelwork as existing, and to include some steel repair works.

4.4 Economic consideration

The majority of the pier head has been closed for several years, largely due to the condition of the timber

decking presenting a significant failure hazard.

Given the combination of conditions of the steelwork support to the banjo, the diagonal bracing, and the

timber deck it may, against the cost of repair be more economically viable to reduce the extent of the

boardwalk pier structure at the pier head.

The 2007 Pell Frischmann report offered three options to address the condition of the pier head (2007

estimated budget uplifted by 5% per annum to 2015):

option works estimated cost (£m)

1 rebuild as existing, including the estimated cost of timber deck replacement

1,640

2 rebuild, but only to a width aligned with that of the pier neck, including the estimated cost of timber deck replacement over the reduced width

1,303

3 remove the pier head and install ramped access from the end of the pier neck on to the original concrete surface

531

Further, the same report offered an estimate for the demolition of the banjo and landing stage, similarly

updated here, to £270k

5. Photographs – Princess Pier

Circular piles Concrete encased struts/props

Cross bracing Steel truss work

4.1 General view below steel trussed supported boardwalk at pier head, showing truss work and other

structural steel elements

4.2 General view of galvanised framing to boardwalk supported by octagonal piles

Appendix A Torquay Harbour – Various Structures: Feasibility Study for Cathodic Protection

261/REP/01. Corrosion Prevention March 2015

Appendix B Archive Drawings

Princess Pier

B1/1759/1 Princess Pier ‘Islander’ Area Structural Survey – Gen Arrangement Existing

Steelwork and Layouts at Deck Level and at Top of Sea Wall 1975

B1/1934/8 Princess Pier Reconstruction – Gen Arrangement of New Steel Supporting Deck

and Shelter 1978

B1/1934/9 Princess Pier Reconstruction – Typ Details of New Steelwork Supporting Deck and

Shelter 1978

B1/625/5 – Details of Existing Girders, Princess Pier 1968

Unit 2.01, Cannock Chase Enterprise Centre Tel: 01543 871808 Walkers Rise Hednesford e-mail: [email protected] Cannock Internet: www.corrosion-prevention.co.uk WS12 0QU Registered in England & Wales Co. Number 6208395 Registered Office

PROJECT NAME: FLIP Study 2- Quay Resistance - Corrosion Survey & feasibility

study for Cathodic Protection in Channel ports (case study:

Torquay Harbour Structures

DOCUMENT TITLE: FEASIBILITY STUDY FOR CATHODIC PROTECTION

DOCUMENT REF: 261/REP/01

CLIENT: TORBAY COUNCIL

Torquay Harbour 14 FLIP Study 2- Quay Resistance - Corrosion Survey & feasibility study for Cathodic Protection in Channel ports (case study: Torquay Harbour Structures © Corrosion Prevention Ltd. March 2015

0 Information I Spring J Preston 27/03/15

REV ISSUED FOR Prepared Checked Issue Date

Torquay Harbour 15 FLIP Study 2- Quay Resistance - Corrosion Survey & feasibility study for Cathodic Protection in Channel ports (case study: Torquay Harbour Structures © Corrosion Prevention Ltd. March 2015

CONTENTS

PAGE

SECTION 1 : INTRODUCTION 3

SECTION 2 : REFERENCE DOCUMENTATION 4

SECTION 3 : SCOPE OF REVIEW 6

SECTION 4 : FISH QUAY 7

SECTION 5 : SOUTH PIER 9

SECTION 6 : PRINCESS PIER 12

SECTION 7 : BUDGET SYSTEM COSTS 18

SECTION 8 : SUMMARY OF CONCLUSIONS &

RECOMMENDATIONS

20

APPENDIX 1 : LOCATION PLAN OF STRUCTURES

Torquay Harbour 16 Feasibility Study for Cathodic Protection © Corrosion Prevention Ltd. March 2015

SECTION 1

INTRODUCTION

Torbay Council have engaged Corrosion Prevention Limited (CPL) to undertake a feasibility study for the

possible application of cathodic protection systems to a number of steel and reinforced concrete structures

within Torquay Harbour.

CPL undertook a visual inspection of the structures on 23rd March 2015 to review the structures and collect

dimensional information to inform the study.

This report details the structures under consideration, presents information gathered during the survey,

presents commentary on the suitability of cathodic protection as a valid corrosion protection method,

outlines possible system types including limitations and constraints and provides budgetary guidelines for

the procurement of system designs, installation and operation.


SECTION 2

REFERENCE DOCUMENTATION

2.1 Standards

The advice given in this report is compliant with and based upon guidance contained in the following

reference documents:-

BS EN ISO 13174:2012 ‘Cathodic Protection of Harbour Installations’

BS EN 1504 ‘Products and systems for the protection and repair of concrete structures - Definitions, requirements, quality control and evaluation of conformity,’ in particular, BS EN 1504 Part 9, 2008: ‘General principles for the use of products and systems’;

Concrete Society Technical Report No. 69 ‘Repair of Concrete Structures with Reference to BS EN 1504’;

BS EN 12696:2012 ‘Cathodic protection of steel in concrete’; and

Concrete Society Technical Report No. 73 ‘Cathodic Protection of Reinforced Concrete’.

2.2 Information Provided by the Client

The following as-built structural drawings were provided by the client and reviewed by CPL prior to the site

visit:-

Construction Details:-

Drawing ‘Proposed Reconditioning of Fish Quay Wall’;

Borough of Torbay Drawing No. B1/1759/4 ‘General Arrangement of Transverse ‘A’ Frames’;

Borough of Torquay Drawing No. 3288 ‘Princess Pier Repairs’;

Borough of Torquay Drawing No. B1/625/4 ‘Renewal of Supporting Girders Princess Pier’;

Blythe and White Drawing No. W8177/L1 ‘Princess Pier Re-Construction’;

Borough of Torquay Drawing No. 7447 ‘Renewal of South Pier Widening; GA’;


Borough of Torquay Drawing No. 7448 ‘Renewal of South Pier Widening; Phase 1 Piling Fenders and Ladders’;

Borough of Torbay Drawing No. TCB/253 ‘Renewal of South Pier Widening; Slab Reinforcement Sheet No. 1’; and

Borough of Torbay Drawing No. TCB/254 ‘Renewal of South Pier Widening; Slab Reinforcement Sheet No. 2’.


SECTION 3

SCOPE OF REVIEW

3.1 Structures

The structures reviewed are as follows:-

Fish Quay o Sheet steel piled quay wall

South Pier o RC slab extension; and o Support steel box piles

Princess Pier o Driven steel piles to framed support to timber boardwalk; o Steel beam in concrete propping to suspended ‘Banjo/Islander’ widening; and. o Steel tubular piles supporting ‘Banjo/Islander’ widening.

A layout plan showing the location of the structures listed above is presented in Appendix 1 for reference.

3.2 General: Extent of Cathodic Protection

BS EN ISO 1317: 2012 (for steel piles in seawater), Section 1.4 it notes:-

For surfaces which are alternately immersed and exposed to the atmosphere, the cathodic protection is only

effective when the immersion time is long enough for the steel to become polarized. Typically, effective

cathodic protection is achieved for all surfaces below mid tide.

So, cathodic protection for steel piling is only achievable below mid tide level. This is not the case for

reinforced concrete or steel encased in concrete. The concrete acts the electrolyte and it is possible to

protect structures that are either immersed, in the tidal zones or atmospherically exposed.


SECTION 4

FISH QUAY

4.1 Structure Description & Survey Measurements

The outer sea facing wall of the fish quay is a steel sheet piled construction.

Photo showing view of Fish Quay Wall

The site survey confirmed the pile type used in the construction to be Larssen No. 3 piles. In some instances

this was visible as the original foundry stamp on the pile. A pile count was conducted showing there to be 67

No. out-pans around the two faces of the structure. The piles were observed to be free from corrosion

resistant coatings.


It was observed during the low water survey that there are numerous patches of the orange bloom typically

associated with Accelerated Low Water Corrosion (ALWC) on the sheet piling of this structure.

The bed level was surveyed at a sample number of locations and found to be consistent within a range of

approximately 0.5m except for the corner immediately adjacent to the Princess Promenade where the bed

level is higher. The bed level is at -1mCD, approximately 1m below LAT.

4.2 Cathodic Protection Feasibility

Cathodic protection would be a suitable method of applying corrosion protection to the sheet piles of the

Fish Quay up to the level of mid tide.

Cathodic protection systems for this type of structure are capable of providing full protection only up to mid

tide level. Should additional corrosion protection be required above this level coatings would be

recommended.

For structures of this nature cathodic protection systems can be either impressed current or galvanic anode

type systems. Due to the relatively small size of this structure and the practical problems related to installing

the cabling required, an impressed current systems is not recommended for the Fish Quay

A galvanic anode type system would be most suitable for this structure and could be designed to provide

protection up to 20 to 25 years.

4.3 Limitations to Cathodic Protection

To be fully compliant with the design codes for cathodic protection, anodes for such a system should be fully

submerged at all tides. However given the size of anodes required and the relatively shallow depths at low

water in front of this structure, it is unlikely that this could be fully achieved at the Fish Quay.

It is however possible to install anodes which would be partially exposed at low tide and still provide a

significant reduction in corrosion rate on the structure and combat ALWC. It is expected that the length of

anode still submerged at low water would be sufficient to provide the necessary protection current for the

amount of steel immersed at that time.

Anodes can be designed to be installed behind the line of the out-pan face and should not therefore interfere

with vessels moored alongside the quay.

4.4 Recommendations

Due to the extensive presence of ALWC on the sheet piling of this structure, we would recommend that a

cathodic protection system is installed in the near future.

We consider that a galvanic anode type cathodic protection system would be the most practical and cost

effective way of providing the necessary protection.


SECTION 5

SOUTH PIER


The South Pier is constructed from two main structural elements, a reinforced concrete deck slab supported

on a row of steel box piles.

Typical View of South Pier

Site measurements confirmed the as-built drawing detail identifying the supporting box piles as Larssen No.

2 box piles of which there are 22 No. No corrosion resistant coatings were evident on the piles.

A bed level survey was undertaken along the line of the box piles indicating that the bed level is consistent

within 0.5m over the length of the structure and at approximately -1.4mCD.

Areas of likely ALWC were noted on a number of piles in the low tide area.


Detailed construction details of the approximately 6m x 80m reinforced concrete deck slab have been

provided by the client, no further investigation was undertaken to ascertain the construction details of this

element of the structure.

A visual review of the condition of the concrete slab was undertaken form underneath the slab and, where

accessible, from the top side. From this general visual inspection, there were limited obviously visible areas

of spalling or damaged concrete on the soffit.


5.2.1 Larssen Box Piles

For the Larssen box piles supporting the deck, a galvanic anode cathodic protection system could be installed

with an anode provided for each individual pile to provide corrosion protection below mid tide.

As with the Fish Quay, impressed current solutions are not considered to be cost effective or practical for

such limited sections of steel piling.

5.2.2 Reinforced Concrete Deck Slab

Impressed current cathodic protection systems have been installed on the slab soffits of the nearby Princess

Promenade and similar systems would be suitable for the corrosion protection of this deck structure.

As stated in section 5.1 above however, the current level of corrosion damage to the slab does not visibly

appear extensive; it would therefore be advisable to undertake a more detailed concrete condition survey

prior to determining the requirement for active corrosion prevention methods being applied. If testing

demonstrates that the reinforcement is at risk from corrosion arising from chloride ingress then early

application of cathodic protection will prevent the requirement for extensive concrete repairs later.



For the Larssen box piles it would be practical to fit anodes to each individual pile such that they are fully

submerged at all tides and hence the systems would be fully compliant with the design codes. Anodes can

be orientated such as they are behind the seaward / mooring face.


Various different anode types could be considered for the cathodic protection of such a slab with differing

limitations to their use including changes to structural capacity due to additional mass or extensive drilling

of holes. Such limitations would be considered inr any detailed design process.

In general this slab would appear to be very suitable for the application of an impressed current cathodic

protection system.

5.4 Recommendations



As there is evidence of existing ALWC on a number of piles and this is likely to affect an increasing number of

piles if no action is taken, we would recommend that some form of corrosion protection system be installed

in the near future.

We consider that a galvanic anode type cathodic protection system would be the most cost effective way of

providing the necessary protection.


As the current damage from corrosion to the deck slab does not visually appear to be extensive, but noting

that the similarly aged and exposed deck slabs of the nearby Princess Promenade have been either replaced

or had cathodic protection applied due to corrosion damage, we would recommend a concrete condition

survey be undertaken to the deck slab to help establish the requirement or otherwise for active corrosion

protection systems such as cathodic protection.

Such a survey would also enable quantification of any concrete repairs that may be necessary which would

form a considerable cost element to any repair and cathodic protection programme of works planned for the

structure.


SECTION 6

PRINCESS PIER


Three separate structural sections of the Princess Pier have been included in the scope for this review:-

driven steel piles to framed support to timber boardwalk;

tubular steel piles supporting cantilever ‘Banjo/Islander’ widening; and

steel sections encased in concrete forming propping to the suspended ‘Banjo/Islander’ widening.

View of Steel Piles Supporting Timber Boardwalk

As shown on the as-built drawings, and observed on site, the 21 No. driven steel piles are octagonal in section

with each face being 180mm wide. Steel channel sections of approximately 100 x 150mm connect the piles

to the main pier wall at high level and at low water level.

A bed level survey was undertaken over the length of the section and the level was shown to vary between

circa LAT (0.0mCD) at the most shoreward pile to circa -3mCD at the opposite end of the structure.


There was no visual evidence of ALWC on the piles however there is extensive marine growth in the low

water range.

The 14 No. piles supporting the Banjo/Islander widening section are tubular with an approximately 1m

circumference and the local bed level is circa -3mCD.

Typical View of Tubular Support Piles and Heavily Corroded Cross Bracings


View of Concrete Propping (Inside Harbour)

The concrete props are in two sets, a set of 6 No. on the inner, harbour side of the Princess Pier and a further

7 No. on the outer, seaward side of the Pier.

Dimensional checks confirmed that the section sizes were consistent with the as-built detail drawing

provided. The props are fully exposed at low tide with the toe of the prop just above low water.

The general condition of the props on the harbour side of the wall appeared good with few notable defects

other than cracking and spalling of concrete in line with the embedded horizontal steel beams at the top of

the first and last prop and one longitudinal crack on one face of the most shoreward prop.

On the outer face extensive longitudinal cracking of all props is evident on the majority of faces. It is

anticipated that the greater extent of cracking on the outer props is due to an increased amount of chloride

ingress due to the more exposed environment outside of the harbour.

The cracking appears to be limited to the extent of the props above the line of marine growth. This is

consistent with a commonly observed phenomenon whereby concrete below the level of marine growth is

typically water saturated. This results in limited oxygen being available at the steel surfaces within the

concrete which limits the corrosion reactions and reduces the rate of corrosion.


View of Typical Prop on Seaward Side with extensive cracking


6.2.1 Steel Supporting Piles

As with the box piles of the south pier, a galvanic anode cathodic protection system with an anode installed

on each individual pile would be a suitable method of corrosion protection for these piles below mid-tide

level.

6.2.2 Steel Sections Encased in Concrete Props


As the lower extent of the concrete props are below mid tide, it would be possible to provide cathodic

protection to this extent of the props using similar galvanic system to those recommended for the immersed

steel piles detailed within this report. This would minimise the extent of works required below mid tide on

the concrete props.

For the sections above mid tide, an impressed current system could be designed to provide the necessary

protection. However, given the relatively small size and individual nature of the props we consider that an

impressed current cathodic protection system would have a relatively high cost for the benefit gained.

In addition impressed current systems that may be considered for the props require cables routed from the

protected structure back to a power supply unit in an accessible location. Any such cabling used for the

protection of the props would require to be run in cable management mounted on what appears to be

already severely corroded atmospherically exposed steel framework. This would mean that the cabling would

be vulnerable in the event of any further damage to the lattice steelwork and may be vulnerable to

wave/splash action on the outer side.

Given the extent of concrete repair that is likely to be required particularly on the outer harbour props, an

alternative approach may be to remove all of the concrete surround to the steel beam, providing this is does

not compromise the required structural capacity, and blast clean the steelwork prior to the application of a

high specification coating system.


6.3.1 Steel Supporting Piles

For the most shoreward piles, anodes may be partially or fully exposed at lowest tides. Whilst there may be

some underperformance in certain tidal conditions it is not expected that this would significantly reduce the

performance of any designed system.


Cathodic protection could be applied to the full extent of these elements that are concrete encased; although

as below there may be more efficient methods of providing corrosion protection.

6.4 Recommendations

6.4.1 Steel Tubular Supporting Piles

Given that ALWC has been identified on nearby structures within the harbour it is likely that these piles are

either already or will be effected at some point. It is recommended that a galvanic anode cathodic protection

system is installed to these piles.

For the piles supporting the Banjo/Islander widening section it is noted that the cross bracing and steel lattice

work supported by the piles is very heavily corroded above the level to which cathodic protection would be

effective. The decision as to whether cathodic protection is applied to these structures should be undertaken

as part of a wider consideration as to the future of the structures which they are supporting.



Whilst cathodic protection is feasible for these elements, we would recommend that other possible methods

of repairing and providing corrosion protection to these structures be considered in more detail.

It is our expectation that cathodic protection would prove to be both relatively expensive and possibly

vulnerable to damage and therefore would be less favourable compared to other possible approaches.

Cathodic protection should only be considered if it is structurally necessary to retain the concrete

encasement.


SECTION 7

BUDGET SYSTEM COSTS

7.1 Budget Outline

For guidance for each of the structures we present an outline budget cost for the design, supply and install

of the system types discussed in this document.

For the immersed steel in seawater structures pricing is based on the provision of a galvanic anode cathodic

protection system with a design life of 25 years.

The budget prices are based on previous experience of similar structures and present rates for aluminium

alloy anodes.

For the tidal/atmospherically exposed reinforced concrete structure, the budget pricing is based on the

guidance contained within the Corrosion Prevention Association Guidance Note. 12 ‘Budget Cost and Anode

Performance Information for Impressed Current Cathodic Protection of Reinforced Concrete Highway

Bridges’

7.2 Immersed Steel In Seawater

7.2.1 Fish Quay

To provide a galvanic anode cathodic protection system with a design life of 25 years for the sheet piled wall

of the Fish Quay, the following budgetary rates would apply:-

Design Fees: £2,500

Anode Material: 4200kg at £3/kg £12,600

Support Steelwork: 67 No. sets @ £35 each £2,345

Installation by Diver Team: 67 No. anodes @ £250 each £16,750

TOTAL £34,195

7.2.2 South Pier Box Piles

To provide a galvanic anode cathodic protection system with a design life of 25 years for the 22 No. box piles

supporting the South Pier deck, the following budgetary rates would apply:-



Support Steelwork 22 No. sets @ £80 each £1,760

Installation by Diver Team 22 No. anodes @ £250 each £5,500

TOTAL £14,710


7.2.3 Princess Pier Seaward Support Piles

To provide a galvanic anode cathodic protection system with a design life of 25 years for the 21 No. octagonal

piles supporting the cantilever timber walkway structure, the following budgetary rates would apply:



Support Steelwork 21 No. Sets @ £80 each £1,680


TOTAL £13,630

To provide a galvanic anode cathodic protection system with a design life of 25 years for the 14No. tubular

piles supporting the Banjo/Islander walkway structure, the following budgetary rates would apply:


Anode Material: 645kgs at £3/kg £1,935

Support Steelwork 14 No. Sets @ £80 each £1,120


TOTAL £8,055

7.3 Atmospherically Exposed Reinforced Concrete

7.3.1 South Pier Deck Slab

Based on the advice presented in CPA guidance note 12 a budget figure for the installation of an impressed

current cathodic protection system using a mesh overlay anode as used at the nearby Princess Promenade,

would be as follows:-

Slab Area = 80m x 6m = 480m2

Cost for cathodic protection @ £400/m2 = £192,00

A 30% uplift should be applied to this figure for fixed costs (mobilisation etc). This figure does not include for access nor any engineering and contract set up and administration. For this scheme access will be the major cost to be added to the comparative rates below; but this will be similar for any repair option. Costs for access should be sought from specialist contractors. Quoted rates do not include for restricted access or working hours. Any repair works will inevitably result in disruption to occupants/users of the pier. The above costings are based generally on published guidance, but in all instances we recommend the advice

of a specialist installation contractor is sought to confirm the costs on a particular structure.


SECTION 8

SUMMARY OF CONCLUSIONS AND RECOMMENDATIONS

STRUCTURE PILE TYPE CONCLUSIONS RECOMMENDATIONS

Fish Quay

Steel sheet piling

ALWC present. CP feasible using galvanic anodes.

Fit galvanic anodes.

South Pier

Steel box piles

ALWC present. CP feasible using galvanic anodes.


Reinforced concrete deck slab

CP feasible using impressed current. Requirement for CP not presently confirmed though.

Undertake a concrete condition survey.

Princess Pier

Octagonal piles supporting boardwalk

ALWC not seen but piles at high risk. CP feasible using galvanic anodes.


Steel sections encased in concrete props

Feasible to protect below mid-tide using galvanic anodes and above mid-tide using impressed current, but complex.

Seek alternative solution – remove concrete and apply protective coating system?

Steel piles supporting Banjo / Islander walkway.

CP feasible using galvanic anodes if structure to be retained.

Fit galvanic anodes if remainder of structure to be retained.


APPENDIX 1

STUCTURE LOCATION PLAN

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