Structures lifecycle plan - for highway bridges, footbridges and retaining walls

The Highways Asset Management Plan (HAMP), implemented in April 2017, is the overarching document that provides a framework for highway asset management in South Tyneside. It clearly sets out what highway and structure asset management means to the Council and outlines the procedures, processes and systems available that we have, or will be in place, to help ensure that South Tyneside’s highway and transport assets are maintained in a condition that is considered fit and safe for reasonable use.

Lifecycle planning is an important aspect of asset management and involves drawing up long-term plans for managing an asset grouping with the aim of providing the required levels of service at the lowest whole life cost. Lifecycle plans capture all information relating to the inventory, its condition and performance. They identify both the short-term routine maintenance needs and long-term capital costs and enable annual spend profiles per asset to be produced. In addition they enable long-term predictions about the deterioration of various assets and their maintenance needs to be forecast. Lifecycle plans provide secondary benefits in enabling the knowledge and judgement of key personnel, to be captured and documented, thereby enabling it to be shared and further developed. They also enable the Council to gather information on the costs for each treatment option and the effect that this expenditure has on performance improvement year on year. Once these are known, benchmarking can then take place with other authorities / treatments etc.

Lifecycle Planning recognises that there are key stages in the life of each asset type and that investment options need to be considered at each of these stages to ensure that each part of the asset achieves its full expected life, at minimum cost. Structures assets go through the following stages during their lifecycle:

Identification and Feasibility

• A need for a new asset is identified in order to facilitate new development, to increase existing capacity or to improve performance.

Planning and Design

• The detailed design of the new asset including securing the necessary permissions and consents.

Construction

• Execution of the design and creation of a new asset on site.

Operate Maintain and Improve

• Routine maintenance on a cyclical basis in order to sustain an asset in a serviceable condition, including vegetation clearance, drainage maintenance, in channel watercourse clearance etc.
• Programmed maintenance works including component renewal and preventative maintenance, including joint replacement, waterproofing membrane renewal, renewal of corrosion protection systems etc.
• Component upgrade including safety fences, bridge deck bearings etc.
• Improvements to existing stock in order to accommodate the requirements of current or new standards

Disposal

• Decommissioning and recycling of an asset at end of its useful service life.

The structures asset group includes a number of diverse items, which are outlined in the list below:

1. Highway bridges (32 No)
2. Footbridges which either carry footways adjacent to road bridges or span over roads
3. Culverts with a span 0.9m or more within the roads network
4. Subways within the roads network
5. Retaining walls (50 No currently identified)
6. River structures including quay walls etc.
7. High mast lighting columns 20 metres or more in height
8. Structural aspects of sign and signal gantries as defined in HA Standard BD63/17 ‘Inspection of Highway Structures’
9. Structural aspects of traffic signal mast arm assemblies as described in HA Standard BD94/17 ‘Highway Structures: Design (sub-structures and special structures) materials Special Structures. Design of minor structures’.

This document describes the outline approach to be adopted with regard to lifecycle planning for highway bridges, footbridges and retaining walls. For the purpose of this document, highway bridges also includes culverts with a span of 0.9m or greater and subways carrying the public highway.

The requirement for further lifecycle plans will be assessed for the additional assets defined in the above list.

It is intended that the lifecycle planning process detailed herein will satisfy the requirements outlined within the ‘Well Managed Highway Infrastructure’ Code of Practice.

With regard to highway bridges, footbridges and retaining walls, this document provides information with regard to the following:

• The context of the lifecycle plan.
• A description of lifecycle modelling approach.
• The use of lifecycle planning in whole life costing.
• The use of lifecycle planning in determining progress towards meeting HAMP Service Standards.
• Future years work programmes.
• Management of risk.
• Changes and improvements.

The South Tyneside Highways Asset Management Plan 2015-2019 sets out the overall policy aims and objectives for the management of the highways asset. The plan identifies the key strategic priorities of South Tyneside Council as the responsible Highway Authority. The objective of the HAMP is to manage the maintenance demands over a period of years through the adoption of a risk based approach to the delivery of highway’s asset maintenance. This will ultimately lead to the adoption of a preventative approach which will deliver considerable long term financial benefit through the reduction in future funding requirements associated with the maintenance of existing assets in a more sustainable condition.

To implement this strategy will require a long term commitment which recognises that a suitable asset prioritisation system is necessary, based upon the relative importance attributed to each asset portfolio in delivering an effective and safe transport system.

A suitable time frame can range from 10 to perhaps 60 years, however, no matter the overall proposed lifespan, it should be considered in more manageable sections comprising discreet 5 year periods.

All of the information required in order to deliver an appropriate lifecycle plan for highway bridges, footbridges and retaining walls should be stored within a Bridge Management System. The BridgeStation Advanced Bridge Management System can be employed to fulfil this requirement. South Tyneside currently utilise BridgeStation software in order to achieve this aim. The Bridgestation system is managed and operated by Northumberland County Council on behalf of South Tyneside Council.

Currently only highway and footbridges are contained within the database, moving forward, it is proposed that retaining walls will be included within the bridge management system and incorporated into the programme of biennial General Inspections. This will be undertaken during Financial Year 2019 to 2020. Once retaining structures are incorporated, consideration will then be given to prioritising STC’s other structures asset groups for inclusion within the system.

The BridgeStation system comprises individual data for each structure which allows the development of maintenance strategies that incorporate preventative measures and promote a Whole Life Costing approach. The system is based upon component level; information for each structure, all of which is incorporated within the database. The information is collated from archive material and is supplemented by additional data as it becomes available, including results from general and principal bridge inspections.

The ‘Well Managed Highways Infrastructure’ Code of Practice introduced in October 2016 states the following:

‘Lifecycle planning principles should be used to review the level of funding, support investment decisions and substantiate the need for appropriate and substantial long term investment’.

A robust inspection regime is the basis upon which the whole lifecycle planning process depends. The process should categorise each structure by its constituent elements and record their condition. Each element is assessed and given a score based upon the severity and extent of any defects noted during the inspection process. This process is necessary since it allows different lifespans of individual components to be accommodated, for instance, a bridge deck waterproofing system may have a design life of 25 years, whereas deck bearings may require replacement at differing intervals and certain elements may perform adequately indefinitely.

Unfortunately the required data is not always available, under such circumstances the Structures Asset Management Planning Toolkit (SAMPT) produced on behalf of the UK Bridges Board, can be employed to predict the lifespan of each individual element. This is achieved through the use of complex deterioration profiles to predict the lifespan of each element. Also of influence are the environmental conditions to which each element is subject, these can be categorised as mild, moderate or severe and incorporated into the model. The element score determined during the inspection process can then be used in order to predict the remaining lifespan of the element in question. This function is undertaken by the BridgeStation system, based upon the principles detailed within the SAMPT.

The output from this exercise can then be used to populate the appropriate module within BridgeStation to provide scenario planning over the short to long term period. This in turn allows the prediction of preventative maintenance requirements over the chosen time period. The results of this process are then used to quantify future financial commitments required in order to maintain stock at an appropriate condition level, in accordance with the requirements of the Well Managed Highway Infrastructure Code of Practice.

BridgeStation stores the condition data for each structure at element level. The software package can then be used to report in accordance with the four main strategies detailed within the SAMPT, those being Planned Preventative, Planned Targeted, Planned Do Minimum and Unplanned Reactive. Definitions are given in the table below:

Severity and Extent definitions are presented in Appendix A of this document. Example BridgeStation BCI pro-forma are presented in Appendix B.

It is recommended that these strategies are adopted in order to evaluate which best suits the needs and available budget of South Tyneside Council. A combination of the above based upon STC’s priorities linked to the Resilient Route network hierarchy will form the basis of an appropriate lifecycle plan. This would allow the targeting of limited resources to ensure that preventative maintenance is prioritised to support network hierarchy requirements.

Two scenarios will be considered to allow detailed life cycle planning, with a gap analysis undertaken in order to determine the most appropriate time to carry out treatment work to maintain stock at an appropriate level:

1. 30 year life cycle plan to maintain current stock condition levels
2. 30 year life cycle plan based upon current budget predictions over the 30 year period

These two scenarios will provide the basis to decide appropriate interventions and the point at which these should be undertaken. They will also highlight any shortfall in funds required and allow the preparation of long term financial plans to be undertaken.

The use of new technology based around an integrated, customer focused solution which supports agile working will assist in the delivery of an asset management system for structures that is easily incorporated into an overall Highways Asset Management Plan compliant with the requirements outlined in the Code of Practice for Well Managed Highway Infrastructure. BridgeStation provides a complete asset management tool for bridges and highway structures that when utilised to its full potential will facilitate this process.

The processes detailed will support the principles of Value Management and Value Engineering with the provision of potential work banks with associated cost information allowing the prioritisation of maintenance works into a programme of defined duration, in the first instance a three year duration should be considered and compared with available budgets.

Value management can be incorporated by grouping specific work types together for multiple bridges or by grouping different work types together for a single structure. Consideration could also be given to targeting works required across structures in a specific location. Applying Value Management principles would also allow consideration to be given to prioritising across asset groups as well as within them wherever possible – this approach is likely to save traffic management costs, minimise traffic disruption, reduce congestion and travel times. It should also bring about environmental benefits; the integration of bridges and structures schemes with other asset maintenance programmes will ensure best value of the investment is achieved, for example, co-ordinating maintenance on structures to coincide with resurfacing and drainage maintenance projects.

Value Engineering options for the prioritised schemes can then be proposed for final budget approval. Options for maintenance; renewal or upgrading of each component within the scheme will be considered to ensure the investment will deliver the best value for money within the whole lifecycle of the asset.

Central to the Lifecycle Planning approach is the use of Whole Life Costing (WLC), which seeks to determine the total cost of ownership of an asset. It involves a structured approach to identify the direct and indirect costs that may occur during its lifecycle. It provides a basis for comparing alternative maintenance strategies in order to identify the most advantageous option over a defined period.

A whole life cost approach ensures that consideration is given to the maintenance requirements throughout the asset’s lifecycle. Alternative maintenance strategies can be evaluated in terms of future cost and asset performance.

Whole life costing for maintenance strategy option appraisal ensures that the most beneficial treatments are applied at the most opportune time, enabling informed maintenance planning decisions to be made, to maximise cost benefit and value.

At scheme level, whole life costing may be used as one of the criteria upon which maintenance decisions are made and the preferred option selected. However, it is not the only factor, other factors such as engineering judgement, network operations, buildability, affordability and risk management also require consideration.

Well Managed Highway Infrastructure Code of Practice describes how whole life costing may be incorporated into a value management process that considers a range of issues and influences to be considered during the development of a prioritised programme of schemes that is aligned with South Tyneside’s objectives and which delivers value for money. Whole Life Costing for Structures will be incorporated into the Value Management and Value Engineering processes above using the Well Managed Highway Infrastructure Code guidance.

Risk Management is an important part of both corporate governance and performance management. It allows the Council to avoid problems and failures, rather than just reacting to them when they arise. It helps the Council to identify where it needs to focus its efforts and resources, to exploit more opportunities and suffer fewer failures. As part of the risk management process in the Council, these risks and opportunities should be formalised and recorded.

The adoption of the four strategies identified in Section 3.0 of this document represents a risk based approach to the management of the highway structures asset stock in South Tyneside and as such, demonstrates compliance with the relevant aspects of the code of practice.

The following consideration should be taken into account to ensure implementation and on-going compliance with the Code of Practice.

The South Tyneside Council Highway Structures Inspection Programme (HSIP) represents the means by which the element condition data for highways structures assets is collated. This data comprises the principal source of the information that feeds into the lifecycle planning process through its interpretation with the context of the BridgeStation asset management tool. All inspections shall take account of recommendations 7, 14, 16 and 17 of the Well Managed Highway Infrastructure Code of Practice. The following inspection types require incorporation into the HSIP.

• General Inspections are undertaken for all highway bridges at a 2 year interval, the frequency may be increased in certain circumstances, such as for structures with a low BCI (Critical) score, or for those frequently affected by flood events. The GI’s are currently carried out by Northumberland County Council’s Bridge Inspectors on behalf of South Tyneside Council. All BCI element data is input into the BridgeStation asset management tool once the inspection has been undertaken.
• Commencing with Financial Year 2019 to 2020, retaining structures will be incorporated into the BridgeStation management system and the General Inspection programme detailed above.
• Principal Inspections should generally be undertaken at six year intervals in accordance with the requirements of BD63/17 Inspection of Highway Structures, however, there is scope to increase the interval subject to a risk based assessment. Currently, PI’s are undertaken on an ad-hoc basis when required to inform maintenance requirements. Going forward an appropriate interval for PI’s to be undertaken will be determined on a structure by structure basis in accordance with the requirements set out in BD63/17 Chapter 8 ‘Risk Based Principal Inspection Intervals’. A risk rating shall be calculated for each structure, the rating should take into account the likelihood of an event occurring and its potential consequences. For England, these parameters are defined in Annex A of BD63/17. Once risk ratings for each structure have been evaluated, a programme of inspection intervals shall be prepared.
• Special Inspections provide detailed information on a particular part, area or defect that is causing concern, or which the inspection of falls outside of the normal GI/PI inspection regime and should be undertaken as required when due cause arises. Examples of when a Special Inspection may be required include in the aftermath of any flooding where bridge supports may be susceptible to scour, or when a particular issue is identified with implications for a certain structure type such as the case with post-tensioned bridges, or for bridges constructed from certain material types such as cast iron. Any Special inspections undertaken shall have the results recorded within BridgeStation to allow any developing trends to be identified.
• Confined spaces and underwater inspection requirements are detailed within the BridgeStation system in order to ensure that these requirements can be planned into the inspection programme.
• Structural reviews are normally undertaken when a significant change occurs, such as a change in usage, loading, condition or revision to assessment standards. The procedure to be followed in order to establish whether a review is required is detailed in BD101/11 ‘Structural Review and Assessment of Highway Structures’, the flow chart presented below gives a graphic representation of the process involved.

An assessment programme was undertaken within South Tyneside during the 1990’s, however, much of the information, including assessment reports and calculations has been lost. As a result, existing assessed capacity ratings cannot be substantiated. Referring to the flow chart above, a programme of structural reviews should be identified in order to inform an assessment programme. This will be established on an individual structure by structure basis taking into account network hierarchy and the level of risk presented by each highway bridge. The results of this exercise will form the basis for the development of a risk based assessment programme. Once an initial round of reviews have been undertaken, trigger points based upon structural deterioration should be determined at which further reviews are required.

• The Bridge Inspector Certification Scheme provides a means of demonstrating the competency of Bridge Inspector’s, discussion with Northumberland County Council, South Tyneside’s inspection partner should be undertaken in order to evaluate what competency requirements are in place or whether further implementation is required.
• The risks of not undertaking works should also be recorded as part of value management arrangements. Hard issues such as condition and assessed capacity should be considered alongside soft issues such as local importance, synergies with other work and structures with low BCI (Critical) scores. A review will also be required for future introduction of Risk Management to the Retaining Wall Inspection regime.
• Consideration is required in order to determine whether alternative budget sources, such as the Challenge Fund would be appropriate to deliver improvements across STC’s highway structures stock.
• Any sub-standard structure should be considered to represent a risk to the public, lifecycle planning should identify appropriate remedial actions. Until such time that these actions are implemented, a risk based approach to the management of sub-standard highway structures should be introduced. Adoption of an interim measures regime, such as that detailed in BD79/13 ‘The Management of Sub-Standard Highway Structures’, will assist in the management of this high risk until such time as remedial treatments are implemented.

Should the recommendations and procedures set out within this document be adopted and incorporated into the Highways Asset Management Plan, it is considered that South Tyneside Council will have in place a robust lifecycle management procedure for highway bridges, footbridges and retaining structures, that is in accordance with the recommendations set out in the Well Managed Highway Infrastructure Code of Practice. In order to ensure compliance for all structure assets, the complete asset portfolio should be subject to the similar procedures.

The above BCI scores are based on critical element score with the worst condition used to calculate the BCI value

For the BCI Average score each element has different Weighted Condition Scores to produce an overall condition of the Bridge