Exercise set
Civil Infrastructure Rehabilitation Prioritization and Life-Cycle Planning Exercises
Solved civil infrastructure rehabilitation exercises for RPN, benefit-cost ranking, backlog funding, lifecycle cost, handover, residual risk and closeout.
These exercises focus on civil infrastructure rehabilitation prioritization and life-cycle planning: risk scores, benefit-cost ranking, backlog clearance, annual funding, timing, life-cycle cost, post-repair acceptance, handover records, residual risk and closeout gates. Field inspection and condition-assessment calculations are handled in a separate specialist exercise set.
Use these calculations as decision screens. Real rehabilitation programs require owner objectives, consequence classes, traffic or occupancy effects, constructability, permit constraints, procurement rules, stakeholder impacts, uncertainty budgets and responsible engineering approval.
Release Evidence Notes
Rehabilitation evidence should connect the selected intervention to the original failure mode. A completed work order is not enough; closeout should show repaired element, residual risk, acceptance measurements, record updates, future trigger, cost basis, schedule effect and accountable reviewer.
Engineering Boundary Notes
The simplified economic and risk screens below do not replace formal asset-management policy, code-based design, probabilistic risk assessment or public-sector funding governance. They teach how to make prioritization assumptions visible.
Common Release Mistakes
Common mistakes include ranking only by visible damage, ignoring consequence, double-counting benefits, accepting repairs without mechanism-specific measurements, clearing backlog on paper while deferring high-risk assets, and treating life-cycle cost as a single deterministic number.
Scenario Map
| Scenario | Exercises | Primary check | Engineering decision |
|---|---|---|---|
| Risk and priority | 1, 2, 10, 15, 18 | RPN, weighted priority and risk reduction per cost | Rank the work and identify release blockers. |
| Funding and timing | 3, 4, 5, 6, 11, 14 | Backlog clearance, NPV, LCC, disruption and contingency | Choose a fundable intervention plan. |
| Repair acceptance and closeout | 7, 8, 9, 12, 13, 16, 17 | Readings, records, residual risk, schedule and post-repair interval | Accept, hold or extend monitoring. |
Exercise 1: Risk Priority Number
An asset defect has severity 8, occurrence 5 and detection score 4. Compute the RPN.
Solution
Engineering Comment
RPN is a ranking screen. It does not prove absolute risk because the scales are ordinal.
Plausibility Check
The maximum on a 1-to-10 scale is 1000, so 160 is a moderate-high screen.
Exercise 2: Risk Reduction After Rehabilitation
After repair, occurrence drops from 5 to 2 and detection improves from 4 to 3 while severity remains 8. Find the RPN reduction.
Solution
Engineering Comment
Severity often remains high because consequence does not disappear even when probability and detectability improve.
Plausibility Check
Both occurrence and detection scores improve, so RPN must decrease.
Exercise 3: Rehabilitation Benefit-Cost Ratio
A repair avoids expected annual losses of 85,000 dollars for 6 years. The repair costs 310,000 dollars. Ignore discounting. Find benefit-cost ratio.
Solution
Engineering Comment
A ratio above 1 supports the repair economically, but safety-critical work may be mandatory regardless of BCR.
Plausibility Check
Total avoided loss is 510,000 dollars, larger than cost, so BCR is above 1.
Exercise 4: Backlog Funding Clearance
The rehabilitation backlog is 4.8 million dollars. Annual funding is 0.9 million dollars and new deterioration adds 0.3 million dollars per year. Estimate net clearance time.
Solution
Engineering Comment
The program is reducing backlog, but eight years may be too slow for high-consequence assets.
Plausibility Check
If only 0.6 million dollars is cleared each year, several years are required for a 4.8 million dollar backlog.
Exercise 5: Annual Funding Gap
To clear the same 4.8 million dollar backlog in 5 years while new deterioration adds 0.3 million dollars per year, find required annual funding.
Solution
Engineering Comment
Funding targets should include new deterioration, otherwise the backlog plan is structurally underfunded.
Plausibility Check
The required amount is greater than 0.96 million dollars per year because new deterioration is added.
Exercise 6: Life-Cycle Cost Comparison
Option A costs 500,000 dollars now and 40,000 dollars per year for 10 years. Option B costs 720,000 dollars now and 15,000 dollars per year for 10 years. Ignore discounting. Which is cheaper?
Solution
Option B is cheaper by 30,000 dollars.
Engineering Comment
A higher capital repair can be justified if it reduces recurring maintenance enough.
Plausibility Check
Option B costs 220,000 dollars more initially but saves 250,000 dollars in maintenance.
Exercise 7: Post-Repair Crack Acceptance
Acceptance requires average crack width below 0.20 mm. Readings after repair are 0.16, 0.19, 0.21 and 0.18 mm. Find the average and decision.
Solution
The average passes, but the 0.21 mm local reading should be reviewed against the local limit.
Engineering Comment
Average acceptance can hide a localized active crack. Closeout should state both average and maximum.
Plausibility Check
Most readings are below 0.20 mm, so an average below 0.20 mm is plausible.
Exercise 8: Handover Record Hold
A rehabilitation package requires 18 closeout records. The contractor submits 15, and 2 of those are incomplete. Find usable record completion.
Solution
Engineering Comment
The asset should remain on handover hold if missing records affect inspection intervals, warranties or future load decisions.
Plausibility Check
Only 13 usable records exist out of 18, so completion near 70 percent is reasonable.
Exercise 9: Residual Risk Screen
Initial annual failure probability is 0.020. Rehabilitation reduces it by 70 percent. Consequence is 2.5 million dollars. Find residual expected annual loss.
Solution
Engineering Comment
Residual risk is not zero. It should be linked to monitoring and future inspection triggers.
Plausibility Check
The probability is less than one percent after repair, so expected annual loss is much less than consequence.
Exercise 10: Weighted Priority Score
Three projects have condition, consequence and cost scores. Project A: 80, 60, 50. Project B: 60, 90, 40. Project C: 70, 70, 80. Weights are 0.4, 0.4 and 0.2. Rank by weighted score.
Solution
Rank: C, B, A.
Engineering Comment
The cost score must be defined consistently. If higher cost should reduce priority, the score must already be inverted.
Plausibility Check
Project C is balanced and has the highest cost score, so it leads under these weights.
Exercise 11: User Disruption Cost
A lane closure affects 18,000 vehicles per day, adds 4 minutes per vehicle and lasts 12 days. Value of time is 18 dollars per hour. Estimate disruption cost.
Solution
Engineering Comment
User cost can change the preferred construction window or staging strategy.
Plausibility Check
The total delay is 14,400 vehicle-hours, and 14,400 times 18 dollars is 259,200 dollars.
Exercise 12: Work Package Critical Path
Design review takes 3 weeks, procurement 6 weeks, repair 4 weeks and acceptance testing 2 weeks in sequence. Find total duration.
Solution
Engineering Comment
If tasks are truly sequential, procurement often controls the release date more than field repair duration.
Plausibility Check
All four durations are positive, so the total must exceed the largest single task.
Exercise 13: Post-Repair Inspection Interval
Baseline inspection interval is 24 months. Residual risk factor is 1.5. Use interval equal to baseline divided by risk factor.
Solution
Engineering Comment
Shortening the interval is appropriate when residual uncertainty remains after repair.
Plausibility Check
A factor greater than 1 reduces the interval below 24 months.
Exercise 14: Contingency Allowance
Base rehabilitation cost is 1.2 million dollars. Design uncertainty contingency is 12 percent and access contingency is 8 percent. Estimate total with additive contingencies.
Solution
Engineering Comment
Separate contingencies help explain whether the uncertainty is technical, access-related or market-related.
Plausibility Check
The total contingency is 20 percent, and 20 percent of 1.2 million is 0.24 million.
Exercise 15: Risk Reduction per Dollar
Project A reduces RPN by 112 at a cost of 310,000 dollars. Project B reduces RPN by 150 at a cost of 600,000 dollars. Compare RPN reduction per 100,000 dollars.
Solution
Project A gives more RPN reduction per 100,000 dollars.
Engineering Comment
Efficiency is useful for portfolios, but high-consequence mandatory work may still outrank efficient low-cost work.
Plausibility Check
Project B reduces more total RPN but costs almost twice as much, so lower efficiency is plausible.
Exercise 16: Pavement Treatment Timing
If IRI grows from 2.6 to a trigger of 3.4 m/km at 0.20 m/km per year, estimate years to treatment.
Solution
Engineering Comment
Treatment can be planned before the trigger if mobilization, traffic control or budget cycles require lead time.
Plausibility Check
The required increase is 0.8 m/km, and four increments of 0.20 reach it.
Exercise 17: Drainage Retrofit Benefit
A drainage retrofit costs 180,000 dollars and reduces expected flood-damage loss from 70,000 dollars per year to 25,000 dollars per year. Estimate simple payback.
Solution
Engineering Comment
Payback is useful, but hydraulic safety and road closure risk may justify action even with longer payback.
Plausibility Check
Four years of 45,000 dollar savings equals the 180,000 dollar cost.
Exercise 18: Rehabilitation Closeout Gate
A closeout gate requires acceptance testing pass, records at least 95 percent complete and residual high-risk items equal to zero. Results are pass, 92 percent and one high-risk item. Decide the gate.
Solution
The gate fails because records are incomplete and one high-risk residual item remains.
Engineering Comment
Passing field tests cannot close the rehabilitation if records and residual risk do not support future asset management.
Plausibility Check
Two of the three criteria fail, so the decision must be hold.
Validation Package Checklist
- intervention is linked to the original failure mode and consequence class;
- risk score, benefit basis, cost basis and uncertainty are stated;
- user disruption, funding constraints and schedule drivers are visible;
- post-repair measurements include acceptance threshold and maximum value where relevant;
- handover records are complete enough for future inspection and maintenance;
- residual risk, future trigger and accountable owner decision are documented.