sh25 pepe stream bridge - present value end of life (pveol

SH25 BSN1720 Pepe Stream Bridge - Present Value End of Life (PVEoL) Analysis Report | 1

SH25: Pepe Stream Bridge

Present Value End of Life (PVEoL) Analysis Report

21 December 2020

This example of a PVEOL Analysis has been adapted from an original report to highlight some of the principal issues that need to be addressed. Much of the report is abbreviated.

The agreement of Beca Ltd to use their original report is acknowledged.

SH25 BSN1720 Pepe Stream Bridge - Present Value End of Life (PVEoL) Analysis Report

SH25 BSN1720 Pepe Stream Bridge - Present Value End of Life (PVEoL) Analysis Report | i

Contents

1 Introduction ........................................................................................................ 1

2 Economic Evaluation Procedure...................................................................... 1

3 Existing Bridge Performance, Condition, and Maintenance Requirements ..................................................................................................... 2

3.1 Balustrades ...................................................................................................................................... 2

3.2 Deck ................................................................................................................................................. 3

3.3 Beams .............................................................................................................................................. 2

3.4 Abutments ........................................................................................................................................ 2

3.5 Piers ................................................................................................................................................. 2

3.6 Piles ................................................................................................................................................. 2

4 Maintenance Strategies ..................................................................................... 2

Option 1: No Further Maintenance and Replace Bridge in 2022/23 .......................................................... 2

Option 2: Undertake Maintenance and Replace Bridge in 2031/32 .......................................................... 3

5 Replacement Bridge .......................................................................................... 3

6 Inspection and Maintenance Costs ................................................................. 4

6.1 Inspection Activities ......................................................................................................................... 4

6.2 Ongoing Repair and Maintenance ................................................................................................... 4

7 PVEoL Analysis ................................................................................................. 5

8 Summary ............................................................................................................ 5

9 Recommendations ............................................................................................. 5

Appendices

Appendix A – Cost Estimate Breakdown For Bridge Replacement

Appendix B – PVEoL Analysis

Appendix C – Reference Material

| Introduction |


1 Introduction

Pepe Stream Bridge is located immediately south of Tairua on SH25 RS/RP 172/0 over a narrow tidal estuary.

The record drawings indicate that the bridge was designed and constructed circa 1942. The bridge is a three

span single lane structure with a 3.66m (12’) lane width between kerbs. It is constructed as three 13.4m (44’)

long simply supported spans. Each span comprises a two beam in-situ reinforced concrete T beam deck. The

deck spans are supported on reinforced concrete piers and abutments, which are in turn supported on precast

concrete piles. The original concrete balustrade panels remain.

Visual site inspections and concrete condition testing have identified the bridge to be in very poor condition.

Spalling and cracking are widespread on the concrete deck and beams. The concrete balustrades are also in

poor condition with spalled concrete exposing corroded reinforcement on a number of panels.

Due to the poor condition of the bridge, a Present Value End of Life (PVEoL) analysis is required to determine

the optimum timing for bridge replacement and the appropriate interim management strategy.

Figure 1-1 View from downstream side along bridge

2 Economic Evaluation Procedure

Waka Kotahi’s Investment Assessment Framework (IAF) requires improvement projects to be evaluated

against the following assessment factors to determine the project’s Priority Order;

● Cost-Benefit Appraisal, and

● Results Alignment, and how the proposed works align with the outcomes sought by the Government Policy

Statement (GPS). Results Alignment falls outside of the scope of this report.

For projects such as bridges approaching end-of-life, a Benefit Cost Ratio is not applicable and a Present

Value End of Life Analysis (PVEoL) assessment shall be used. The PVEoL assessment is used to determine

the NPV least whole-of-life cost option which maintains the current level of service. The assessment identifies

the optimal timing for construction of a hypothetical replacement bridge providing a like-for-like level of

| Existing Bridge Performance, Condition, and Maintenance Requirements |


service. For this site, the hypothetical like-for-like structure is a single lane bridge constructed to the same

width and length as the existing bridge.

The PVEoL procedure is used to determine when replacement of the bridge will be economically justifiable, on

the basis that like-for-like replacement of the bridge would be of lesser NPV cost than maintaining service

levels through maintenance and refurbishment (followed by bridge replacement in the future). Once economic

justification has been demonstrated, the new bridge will be designed to meet current design standards. Cost-

benefit appraisal would be used to consider further incremental improvements over and above minimum

design requirements.

3 Existing Bridge Performance, Condition, and Maintenance

Requirements

The following previous investigations have been referred to as preparation of this PVEoL Report.

● Live load evaluation report by Beca, September 2018, refer Appendix C

● Concrete condition assessment report by WSP, August 2018, refer Appendix C

● Defect locations and dimensions to prepare VPR10 (2018 Maintenance Contract), September 2019

Critical section capacities were assessed and reported in SH25 Pepe Stream Bridge BSN1720 - Live Load

Evaluation Report, 13 September 2018. Based on assumed condition factor of 0.90, critical results were 74%

and 89% of General Access flexural and shear capacities respectively. The bridge is also deficient in

longitudinal shear along the beam-slab interface, when assessed to NZS3101.

The existing bridge is in poor condition. There have been extensive previous concrete repairs undertaken to

address reinforcing steel corrosion and concrete spalling. Chloride contamination has been found to be high in

both the original concrete and in the repair material, especially at locations with shallow concrete cover.

Substantial volumes of concrete repairs are required. Replacement of some damaged balustrades is also

required.

Representative defects have been included in the following subsections of this report. The estimated costs of

future maintenance and inspections have been provided in Section 6.

3.1 Balustrades

Severe reinforcement corrosion and concrete spalling. Concrete has spalled from portions of most balustrade

infill panels.



Replacement of the damaged sections of the balustrade within the next 2 years is recommended, to mitigate

the safety hazard to bridge users.

3.2 Deck

Cracks and spalling have been observed on the deck soffit, both between the beams and on the deck

cantilever. All spalled areas exhibit exposed and corroded reinforcement.

Figure 3-2 Spalling on deck soffit exposing corroded reinforcement

Concrete repairs are required to delay further reinforcement corrosion and loss of load bearing capacity. Deck

concrete repair within the next year is recommended to mitigate the risk of deterioration.

Figure 3-1 Severe corrosion and loss of concrete on most handrail panels.



3.3 Beams

There are widespread areas of spalling up to 3m long mainly on the soffit and the side faces of the beams.

Most spalled areas exhibit exposed and corroded reinforcement.

Figure 3-3 Spalling of concrete and corrosion to reinforcement widespread on beams.

Figure 3-4 Spall cracking showing reinforcement bleeding on beam at a previous patch repair

Concrete repairs are required to delay further reinforcement corrosion and loss of load bearing capacity.

Concrete repair volumes are estimated to be 5.4m3, representing nominally 8% of the bridge superstructure.

3.4 Abutments

Concrete spalling has been observed at both abutments, adjacent to the end of the main beams. Some

spalled areas exhibit exposed and corroded reinforcement.

Figure 3-5 Spalling and corrosion to reinforcement on face of abutment

Figure 3-6 Spall cracking on abutment face directly under beam

Since the spalled areas on the abutment face are immediately below or adjacent to the end of the main

beams, further spalling may result in loss of support and hence affect the structural integrity of the bridge.

Abutment concrete repairs are required to delay further reinforcement corrosion.

3.5 Piers

Spalling have been observed on the LHS side face of Pier B near the top, exhibiting exposed and corroded

reinforcement.


Figure 3-7 Spalling and corrosion to reinforcement on side face of pier

Figure 3-8 Cracking on side face of pier

Concrete repairs are required to delay further reinforcement corrosion and loss of load bearing capacity.

3.6 Piles

The piles have not been inspected during previous inspections as they were fully submerged under water.

Low tide inspection (possibly requiring a professional diver) is recommended to establish the condition of the

piles under water.

4 Maintenance Strategies

Two maintenance strategies have been identified for the bridge as follows.

Option 1: No Further Maintenance and Replace Bridge in 2022/23. Option 2: Undertake Maintenance and Replace Bridge in 2031/32.

Option 1: No Further Maintenance and Replace Bridge in 2022/23

This bridge has had extensive previous concrete repairs. These repairs are now deteriorating, and in

conjunction with extensive new areas of concrete spalling and corrosion reinforcement, further extensive and

imminent maintenance will be required. This option assumes no further significant maintenance to the

existing bridge, aside from ongoing inspection activities and attending to any life-safety issues prior to a

replacement bridge being completed.

This option attempts to minimise ongoing maintenance expenditure and prolong as far as possible the timing

of bridge replacement (minimise the discounted bridge replacement cost). It is assessed that without further

maintenance, the replacement bridge will need to be completed within about 3 years. It is anticipated that by

this point in time, based on the past rate of deterioration, the loss of strength resulting from corrosion of

flexural and shear reinforcement will require unacceptable load restrictions.

This option carries a reasonable likelihood of unplanned interventions and/or level of service reductions,

unless further investigations are undertaken to assess reinforcement corrosion and the appropriateness of

condition factor currently used in the posting analysis.

If this strategy is adopted, the existing bridge will no longer be able to be cost-effectively maintained in the

event of replacement being deferred. Should deferral occur, the bridge is expected to require a posting


weight restriction, and the cost of repairs and major reconstruction of elements is expected to escalate

considerably.

In conjunction with a regular programme of special inspections to identify distress, the structure is likely to

perform adequately until 2022/23. However, Waka Kotahi should be cognisant that this structure carries a

heightened level of risk and accordingly increased likelihood of requirements for intervention or weight

restrictions to maintain appropriate safety margins.

Option 2: Undertake Maintenance and Replace Bridge in 2031/32

This option involves a further tranch of extensive concrete repairs with the aim of extending as far as

practicable the timing of bridge replacement. Maintenance activities include;

● 2019/20: 5.4m3 of concrete repairs, representing nominally 8% of the bridge superstructure.

● 2021/22: Repairs to bridge barriers

● 2022/23: Repairs to substructure.

For bridges such as this in a marine environment, experience indicates that typically as a concrete bridge

deteriorates, two or three tranches at most, of major concrete spall repairs can be undertaken at about 8-12

year cycles. For this bridge, due to its history of deterioration (previous extensive repairs having been

undertaken) and the general state of the structure, a further round of repairs beyond about 2032 is

considered to be non-viable due to the anticipated condition, with repairs to repairs and corrosion of

reinforcing such that load capacity will be affected. By that stage, the existing bridge will be about 90 years

old and will be simply uneconomic to maintain further.

This option addresses maintenance requirements as they become necessary to support the ongoing use of

the bridge until about 2032. However, due to the deteriorated condition of the bridge, leaving it in service

until 2032 carries a significant risk of unplanned interventions and/or level of service reductions being

required.

The assessed cost and timing of inspections and maintenance is covered in Section 6.

5 Replacement Bridge

Assumptions for the evaluation of the cost of a new hypothetical ‘like-for-like’ bridge are as follows.

• The design life of the new bridge shall be 100 years.

• Dimensions of the replacement bridge shall be like for like to the existing bridge, i.e. single lane,

same length and width. It has been assumed that the replacement bridge comprises two spans,

which is considered more cost effective than replacement with a three span structure to match the

existing. Further refinement of options, such as a single span bridge and potential for shallow

foundations at the southern abutment may lead to reductions in the cost of the replacement bridge.

• Superstructure is assumed to be prestressed single hollow core beams.

• Substructure is assumed to be in-situ abutments and pier supported on bored piles.

• The new bridge is to be built immediately upstream of the existing bridge. The existing bridge shall

remain open to traffic during construction for replacement.

• The replacement cost is $1,640,000, based on the scope described above.

• The professional fee is $200,000 for the design and $75,000 for MSQA, based on the scope

described above.


• A contingency allowance of 25% has been included within the cost estimate, recognising the design

solution’s conceptual status.

• The replacement bridge adopted for the PVEoL analysis provides ‘like for like’ level of service as the

existing bridge. This a hypothetical scenario for economic comparison purposes only. Any new

bridge will be designed to current standards.

6 Inspection and Maintenance Costs

6.1 Inspection Activities

● General Inspections: $300 per inspection every two years. Not affected by bridge replacement work.

● Principal Inspections of existing structure: $8,000 at six-yearly intervals.

● Principal Inspections of replacement structure: $500 per inspection every six years for the first two rounds

following replacement of bridge; $8,000 per inspection thereafter.

6.2 Ongoing Repair and Maintenance

6.2.1 Superstructure Concrete Repair

$560,000 in year 1. Based on a tendered price to carryout deck and beams spall and crack repairs, under

the Bridge Maintenance Contract 2019/20. This estimated cost includes contingency allowance of nominally

40% for the physical works. A large contingency is adopted due to the high likelihood that additional repair

quantities will be discovered as works progress.

6.2.2 Substructure Concrete Repair

$170,000 in year 3. Proportion of concrete requiring repair is assumed to be the same as that for the

superstructure, with an additional allowance for scaffolding around piers. This estimated cost includes

contingency allowance of nominally 40% for the physical works. A large contingency is adopted due to the

high likelihood that additional repair quantities will be discovered as works progress.

6.2.3 Barrier Concrete Repair

$50,000 in year 2. Based on cost of $28,815.26 + GST for the repair carried out in November 2017. This

estimated cost includes contingency allowance of nominally 40% for the physical works. A large contingency

is adopted due to the high likelihood that additional repair quantities will be discovered as works progress.


7 PVEoL Analysis

The following options have been assessed in accordance with PVEoL procedures and are presented below.

Option 1: No further maintenance and replace bridge 2022/23. Option 2: Undertake maintenance and replace bridge in 2031/32. Refer to Appendix B for details. Option 1: NPV = $1.63m Option 2: NPV = $1.82m The analysis therefore shows that the lowest NPV whole-of-life cost is Option 1. This therefore indicates that no further maintenance should be undertaken and that the bridge replacement should be completed in 2023.

8 Summary

This bridge is almost 80 years old and is nearing the end of its design life. It is located within an estuarine

environment which has had a detrimental effect on its condition and necessitated significant previous

maintenance. Based on inspections and recent investigations, it is apparent that further imminent and

significant maintenance will be required. The PVEOL analysis indicates that continuing maintenance is not

economically justified and that the bridge should be replaced by 2023.

9 Recommendations

We recommend that Waka Kotahi;

● Confirms the decision to replace the bridge within not greater than 3 years (2023). The PVEoL

assessment demonstrates that further maintenance is not economical, and therefore the replacement

bridge should advance as quickly as practicable.

● Initiates a business case for bridge replacement along with an options study to identify potential options

for replacement.

● Continues to regularly monitor the bridge, until replacement is completed.

It should be noted that in selecting this deferred maintenance approach, it is critical that the bridge

replacement proceeds in accordance with the above programme to avoid service level reductions and more

costly maintenance activities.


Appendix A – Cost Estimate Breakdown For Bridge Replacement

A


Appendix B – PVEoL Analysis

B

PVEoL Analysis Graphs for Pepe Stream Bridge

Figure B1 - 6% Discounted Rate

Simplified General Procedure for carrying out a PVEoL Analysis

PVEoL - Present Value End of Life Analysis Example

Formula to calculate NPV:

NPV = Net present value

IC = Initial construction cost (material, fabrication, erection, etc)

T = Design life in years (usually 100 years for bridges)

t = Operation time in years

OC = Operating maintenance cost

DR = Discount rate

Project: SH25 Pepe Bridge - Example

Prepared by: Beca Ltd Date: May 2020

INPUT DATA

Year 0 2020 Enter Current Year Here

Discount Rate 6.0% Enter Discount Rate (Real for constant dollars or Nominal if using inflation)

Economic Assessment Period 40 Enter economic assessment period of project

Cost of General Inspection(including report) 300 Enter Cost of General inspection

Cost of Principal Inspection (including report) 8000 Enter Cost of Principal Inspection

Year Ending 2020 2021 2022 2023 2024 2025 2026 2027 2028 2029 2030 2031

Financial Year 2019/20 2020/21 2021/22 2022/23 2023/24 2024/25 2025/26 2026/27 2027/28 2028/29 2029/30 2030/31

Period 0 1 2 3 4 5 6 7 8 9 10 11

Discount Factor 1.0000 0.9434 0.8900 0.8396 0.7921 0.7473 0.7050 0.6651 0.6274 0.5919 0.5584 0.5268

(6% Discount) Option 1 – Replace bridge in 2022/23

Cost $300 $100,000 $100,300 $1,715,000 $300 $0 $300 $0 $300 $0 $300 $0

Cummulative cost $300 $100,300 $200,600 $1,915,600 $1,915,900 $1,915,900 $1,916,200 $1,916,200 $1,916,500 $1,916,500 $1,916,800 $1,916,800

Total Cost $2,038,600

Discounted Cost $300 $94,340 $89,267 $1,439,947 $238 $0 $211 $0 $188 $0 $168 $0

Cummulative discounted cost $300 $94,640 $183,906 $1,623,853 $1,624,091 $1,624,091 $1,624,302 $1,624,302 $1,624,491 $1,624,491 $1,624,658 $1,624,658

PVEOL Value $1,632,762


Cost $585,000 $50,000 $170,300 $0 $300 $20,000 $8,000 $0 $300 $0 $200,300 $1,715,000

Cummulative cost $585,000 $635,000 $805,300 $805,300 $805,600 $825,600 $833,600 $833,600 $833,900 $833,900 $1,034,200 $2,749,200

Total Cost $2,855,800

Discounted Cost $585,000 $47,170 $151,566 $0 $238 $14,945 $5,640 $0 $188 $0 $111,846 $903,441

Cummulative discounted cost $585,000 $632,170 $783,736 $783,736 $783,974 $798,919 $804,559 $804,559 $804,747 $804,747 $916,593 $1,820,034

PVEOL Value $1,823,559


General Inspections 300$ 300$ 300$ 300$ 300$ 300$

Principal Inspections

Replacement professional service fees 100,000$ 100,000$ 75,000$

Replacement physical works 1,640,000$

300$ 100,000$ 100,300$ 1,715,000$ 300$ -$ 300$ -$ 300$ -$ 300$ -$


General Inspections 300$ 300$ 300$ 300$

Principal Inspections 8,000$

Superstructure concrete repairs 560,000$

Substructure concrete repairs 170,000$

Barrier repair 50,000$

Replacement professional service fees 25,000$ 20,000$ 200,000$ 75,000$

Replacement physical works 1,640,000$

585,000$ 50,000$ 170,300$ -$ 300$ 20,000$ 8,000$ -$ 300$ -$ 200,300$ 1,715,000$

Appendix C – Reference Material

• Principal Inspection Report, Beca, 3 March 2018

• Live Load Evaluation Report, Beca, September 2018

• Concrete Condition Assessment Report, WSP, August 2018

C

sh25 pepe stream bridge - present value end of life (pveol

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