EDS 02-1001 Cable Bridge Design Requirementslibrary.ukpowernetworks.co.uk/library/asset/a56d8880-4a4c-4340-b097-0... · cable-bridge design aspects is preferable, it is accepted that

Document Number: EDS 02-1001

Version: 1.0

Date: 01/03/2018

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ENGINEERING DESIGN STANDARD

EDS 02-1001

CABLE BRIDGE DESIGN REQUIREMENTS

Network(s): EPN, LPN, SPN

Summary: This standard details the design principles for cable bridges at all voltages.

Author: Uriel Arias Date: 01/03/2018

Approver: Barry Hatton Date: 13/03/2018

This document forms part of the Company’s Integrated Business System and its requirements are mandatory throughout UK Power Networks. Departure from these requirements may only be taken with the written approval of the Director of Asset Management. If you have any queries about this document please contact the author or owner of the current issue.

Applicable To

UK Power Networks External

☒ Asset Management ☒ G81 Website

☒ Capital Programme ☐ UK Power Networks Services

☐ Connections ☐ Contractors

☐ Health & Safety ☐ ICPs/IDNOs

☐ Legal ☐ Meter Operators

☒ Network Operations

☐ Procurement

☐ Strategy & Regulation

☐ Technical Training

Cable Bridge Design Requirements Document Number: EDS 02-1001

Version: 1.0

Date: 01/03/2018

© UK Power Networks 2018 All rights reserved 2 of 12

Revision Record

Version 1.0 Review Date 13/03/2023

Date 01/03/2018 Author Uriel Arias

New standard to cover cable bridge design


Version: 1.0

Date: 01/03/2018


Contents

1 Introduction ............................................................................................................. 4

2 Scope ....................................................................................................................... 4

3 Glossary and Abbreviations ................................................................................... 4

4 Pre-Design Considerations ..................................................................................... 5

4.1 Legislation ................................................................................................................. 5

4.2 Design Life and Future Maintenance ......................................................................... 5

4.3 New Cables in Existing Cable Bridges ....................................................................... 5

4.4 Location Assessment ................................................................................................ 5

4.5 Flood risk ................................................................................................................... 6

4.6 Fire Risk .................................................................................................................... 6

4.7 Security ..................................................................................................................... 6

4.8 Appearance ............................................................................................................... 7

5 Design Requirements .............................................................................................. 8

5.1 General ..................................................................................................................... 8

5.2 Cable Bridge Dimensions .......................................................................................... 8

5.3 Access ....................................................................................................................... 8

5.4 Cable Entries and Routes .......................................................................................... 9

5.5 Vibration and Dynamic Response .............................................................................. 9

5.6 Structural Considerations .......................................................................................... 9

5.7 Cables ..................................................................................................................... 10

5.8 Bridge Types ........................................................................................................... 10

5.8.1 Standard Cable Bridge ............................................................................................ 10

5.8.2 Major Cable Bridge .................................................................................................. 11

6 Records .................................................................................................................. 11

6.1 Handover ................................................................................................................. 11

7 References ............................................................................................................. 11

7.1 UK Power Networks Standards ............................................................................... 11

7.2 National and International Standards ....................................................................... 11

Appendix A – Examples of Existing Cable Bridges ........................................................ 12

Tables

Table 4-1 – Cable Bridge Soffit Height .................................................................................. 6

Table 5-1 – Cable Bending Radii .......................................................................................... 9


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1 Introduction

This standard details the design requirements for cable bridges. Whilst standardisation of cable-bridge design aspects is preferable, it is accepted that each project is specific. It is essential therefore that the cable bridge design, whilst incorporating the requirements of this document, assesses each project design on its merits.

The principal function of the design is to provide structures to support the electrical cables and ensure a safe environment for operational/maintenance staff and general public safety.

Design aspects such as strength and properties of materials are covered within the Design Manual for Road and Bridges (Highways England).

UK Power Networks cable bridge assets are strategically important to the continuity of the electricity supply. The risk of damaging more than one circuit should be minimised as the consequences of damage to more than one circuit are considerable.

2 Scope

This standard applies to the design of cable bridges in LPN, EPN, SPN.

3 Glossary and Abbreviations

Term Definition

CDM Construction and Design Management

DMRB Design Manual for Roads and Bridges

Major Cable Bridge Diversion

A cable diversion requiring more than a one 500mm diameter steel pipe and supporting structure.

SAP PM UK Power Networks asset register (formerly known as Ellipse)

Standard Cable Bridge Diversion

A cable diversion that can be accommodate inside a self-supporting 500mm steel pipe

UK Power Networks UK Power Networks (Operations) Ltd consists of three electricity distribution networks:

Eastern Power Networks plc (EPN).

London Power Network plc (LPN).

South Eastern Power Networks plc (SPN).


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4 Pre-Design Considerations

4.1 Legislation

Cable bridges shall be designed to the following the Local Planning Authority recommendations and relevant British and European Standards such as BS EN 1990:2002+A1:2005.

Where appropriate and/or applicable the design shall comply with current Building Regulations and the Town & Country Planning Act.

The design shall comply with the CDM and all Health, Safety & Environmental legislation.

4.2 Design Life and Future Maintenance

The main fabric of the cable bridge shall have a design life of not less than 120 years with internal and ancillary structures designed for a minimum 40-year life. Careful consideration shall be given to minimum maintenance throughout.

Maintenance requirements together with additions and alterations to the installed cables shall be considered at the design stage. Therefore, the design shall:

Provide adequate access to and around the cables.

Require minimum maintenance.

Minimise risks to operational engineers.

Allow for future removal and replacement of all cables.

Include consideration for maintaining wayleaves and access agreements throughout the life of the asset.

4.3 New Cables in Existing Cable Bridges

Before any plans to install cables in new or existing cable bridges are finalised consent for the scheme shall be obtained from UK Power Networks Asset Management.

Consent is conditional upon a review of the risk to the existing assets from the installation and will consider, among other things, cable sizing and spacing, cable type, loading, security and fire risk.

4.4 Location Assessment

The cable bridge location shall be assessed relative to the number of circuits carried, the potential loss of supplies following a catastrophic failure and the level of unrecoverable demand.

The impact of damage to all circuits at each location shall identify:

Initial demand at risk.

Customers at risk.

Recoverable demand through network switching.

Residual unrecoverable demand.

Residual customers at risk.

Likelihood of unauthorised access (security of site, isolated location).

Health and Safety impact (proximity to road, railway etc.).

Environmental impact (fluid filled cables, proximity to watercourses).

Demand lost for repair time.

Customers lost for repair time.


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Wherever practicable, electrical connections shall be made where the risk from interruption or damage by flood water is minimised.

Where a bridge crosses a dual carriageway carrying traffic with permitted speeds in excess of 30mph, both carriageways should be crossed with a single span to avoid the need for a support in the central reserve.

The position of a bridge should be chosen to maximise the use of the topography and to avoid or minimise the need for stairs and ramps.

4.5 Flood risk

When considering the location of a new cable bridge it is essential that the risk from future flooding is assessed. In the case of cable bridges the primary sources of risk is associated with the level of the water stream during extreme weather events. If it is found that the proposed location is affected by flooding, then ideally an alternative site should be sourced. This cannot always be achieved and it therefore becomes essential that measures are put in place to provide mitigation against the effects of flooding.

The height of the soffit will be determined by the maximum cable rating carried by the bridge, as shown in Table 4-1. Information regarding flood risk and levels can be obtained from the local Environment Agency office.

Table 4-1 – Cable Bridge Soffit Height

Cable Rating Minimum Soffit Height

132kV cables Flood depth associated with a 1000-years return period event plus 500mm



Control cables Flood depth associated with a 100-years return period event plus 500mm

4.6 Fire Risk

A competent person shall carry out a fire risk assessment in compliance with the Regulatory Reform (Fire Safety) Order 2005.

A risk assessment of the network shall also be carried out to establish the risk to the network and need for mitigation/reconfiguration should circuits be affected by fire.

4.7 Security

Security provision shall be advised by UK Power Networks Company Security and following an Electricity Supply Quality and Continuity Regulations (ESQCR) based security risk assessment.

Cable bridges can be subject to various forms of damage, misuse and vandalism. Where there is a history of vandalism and/or graffiti, the designer shall ensure that the design reduces or mitigates the opportunity and likely impact of vandalism and graffiti on the structure and the visual aspect of the bridge.

The security rating requirements shall be established for any installation before design commences, this shall be reviewed on every occasion that new cables are installed.


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For high-risk areas the following measures may be required following a site specific security risk assessment:

Dome cameras covering the approach to the cable bridge.

Security lighting with infra-red lamps for night vision.

Appropriate signage.

UK Power Networks Company Security shall confirm the specification of the security measures required, following EDS 07-0101 ‘Security Specification for Operational Sites’.

4.8 Appearance

The aesthetics of cable bridges should be sympathetic with the local environment and is subject to approval from the Local Authority in most of the cases.

The appearance of cable bridges shall follow the advice given in the Highways Agency publication “The Appearance of Bridges and Other Highway Structures” and “The Design and Appearance of Bridges” (DMRB) .


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5 Design Requirements

5.1 General

Cable bridges shall be constructed of steel, aluminium alloy, reinforced or pre-stressed concrete.

The full range of considerations such as safety, aesthetics, environmental impact, cost, robustness, sustainability, buildability, operation and maintenance should be balanced when producing the design.

Given the location of bridges, it is likely that they will be pre-fabricated solutions that are lifted into place. It is often the case that this requires detailed planning and organisation due to the vicinity of the public infrastructure.

5.2 Cable Bridge Dimensions

The number of cables will determine the dimensions of the cable bridge. The minimum clearances between each circuit -and between each circuit and the cable bridge walls, shall be in the same as specified in EDS 02-0041 ‘Cable Tunnel Design Manual’. For design purposes, the minimum spacing for 33kV and 11kV circuits shall be considered the same as for 132kV cables.

If the cable bridge is to accommodate multiple voltages then consideration of fire separation shall be a factor in the cable bridge size.

5.3 Access

Either temporary ramps or stairs shall provide access to the deck of the bridge. Access is only required for inspection and maintenance purposes carried out by competent personnel.

Access shall be as short and direct as practicable and follow the line of the circuits, avoiding detours and unnecessary climbing.

Cable bridge access stairs and ramps can have an adverse visual impact that should be minimised. Opportunities to build access into contours of the landscape should be taken.

The design shall discourage any users other than UK Power Networks Personnel; suitable guardrails, fencing or appropriate planting may be used to achieve this.


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5.4 Cable Entries and Routes

The design shall provide for the co-ordination of cable entries from outside circuits and for power and control cable routes in the cable bridge. Design guidance for typical cable bending radii for copper cable is given in Table 5-1.

Table 5-1 – Cable Bending Radii

Cable Type Bending Radius

132kV 3m

33kV 1.6m

11kV 1.2m

Control 0.6m

Actual cable bending radii shall be confirmed with Asset Management prior to the finalisation of the design.

The cable entries shall be sealed at the completion of construction to prevent water ingress. The sealing arrangement shall be removable to enable the cables to be installed and the cables entries resealed.

5.5 Vibration and Dynamic Response

Due consideration shall be given to the susceptibility of the bridge to vibrations induced by bridge users. Particularly the possibility that vandals may deliberately attempt to excite the structure into motion.

All bridges shall satisfy the vibration serviceability requirements set out in BS EN 1991-2 its National Annex and PD 6688-2.

5.6 Structural Considerations

Where cable bridge sub-structures are sited on railway or waterway property, the appropriate Authority’s requirements shall be satisfied.

For new bridges over existing roads, the foundation design shall take into account the effects of traffic during construction. This should include, but not be limited to, the safety of the travelling public, the safety of the workforce, any disruption to traffic and future inspection and maintenance requirements.

For design purposes, a combination case of design loads shall accommodate the self-weight of cables, the supporting structure weight, wind, snow and personnel/equipment loads.

Cable support steelworks shall be designed and specified to accommodate the weight of the cables and imposed short circuit loads of 20kN of which 10% (2kN) is transmitted into the support and structure.


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5.7 Cables

Cables on the cable bridge shall be protected against mechanical damage, fire and water both during installation and in operation.

Before any plans to install cables in new or existing cable bridges are finalised a technical brief outlining the following design parameters shall be produced:

Cable bridge width (mm).

Cable bridge length (mm).

Design Flood depth.

Cable bridge height to soffit.

Required ratings for cable circuits along the route (circuits to be installed and circuits that

are existing).

Voltage, size and type of any existing cables.

Cables in cable bridges shall have the following design parameters:

Fluid filled cables or cables which increase the risk of fire shall not be installed.

Cable joints shall not be installed.

Cables shall be adequately supported for both installation and operation and secured in

order to accommodate the dynamic operational forces and thermal expansion.

Cable entries and unused ducts shall be sealed against ingress of water, dust and other

materials.

Cables shall be specified and supplied in accordance with document EAS 02-0000

‘Approved Materials List – Cables’.

5.8 Bridge Types

The types of bridges described in this this section are recommended for their simplicity, but changes may be required according to site conditions. Examples of existing standard and major bridges are shown in Appendix A.

5.8.1 Standard Cable Bridge

For 11kV diversions or smaller, a 500mm diameter steel tube filled with foam concrete shall be used. The cable cluster layout shall allow no less than 25mm of foam concrete between ducts. This can accept ducts in different configurations subject to the scheme requirements (e.g. three 160mm diameter cables, three 125mm diameter cables and one 90mm diameter cable).

The foundations will typically be reinforced concrete footings at either end. The ground condition will determine the size and depth required as well as the need for piles.

The span of the cable bridge is limited by the structural capacity of the steel pipe; the maximum span shall be limited to 10m for this type of bridge.

All steelwork shall be protected with two coats of corrosion protective paint to BS EN ISO 12944-5:2007.


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5.8.2 Major Cable Bridge

A major cable bridge is required when the number of circuits or the span requires a more robust structure than the one provided by a steel tube in Section 5.8.1.

A major diversion bridge will consist of 500mm steel tubes in parallel on a supporting structure. The design considerations for standard diversion cable bridges apply to each tube on a major diversion cable bridge.

6 Records

Project and as-built drawings and structural details shall be stored on ProjectWise. Cable records shall be stored with Netmap. Details of all civils assets shall be stored on the Asset Register.

6.1 Handover

User manuals and action to be taken in the event of emergency shall be summarised and documented on site in order to provide guidance in future years.

7 References

7.1 UK Power Networks Standards

EAS 02-0000 Approved Equipment List - Cables

EDS 02-0041 Cable Tunnel Design Manual

EDS 07-0101 Security Specification for UK Power Networks Operational Sites

7.2 National and International Standards

BS EN 1991-2:2003 Eurocode 1 Actions on Structures. Traffic loads on bridges

BS EN ISO 12944-5:2007 Corrosion protection of steel structures by protective paint systems. Protective paint systems.

Design Manual for Roads and Bridges, Volume 2, Highways England.

The Appearance of Bridges and Other Highway Structures, NR37, The Highways Agency.

The Electricity Safety, Quality and Continuity Regulations (ESQC) 2002 as amended (2006).

Regulatory Reform (Fire Safety) Order 2005.


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Appendix A – Examples of Existing Cable Bridges

Standard Cable Bridge

Major Cable Bridge

Documents

EDS 02-1001 Cable Bridge Design Requirementslibrary.ukpowernetworks.co.uk/library/asset/a56d8880-4a4c-4340-b097-0... · cable-bridge design aspects is preferable, it is accepted that