Develop interventions programs

Estimation of financial needs and condition of infrastructure assets

Hamed Mehranfar

Yushu An

2024-04-29

Intervention Strategies vs Intervention Programs

Intervention strategies

• Include all interventions to be executed on an item taking into consideration of all possible conditions of the item
• Are developed without consideration of other sub-items, items or super-items

Intervention programs

• Include the interventions to be executed on items taking into consideration the specific conditions of the items
• Are developed with or without consideration of the other sub-items, items, or super-items

• The interventions on an item include all interventions on the sub-items of the item.
• The conditions of the item include the conditions of the sub-items of the item.

Programs are also dealing with interventions, but they are different that it tells when things are done.

How to construct a maintenance intervention program

The construction of a maintenance intervention program can be:

• Derived directly from the maintenance intervention strategy
• Based directly on expert opinion
• Done by using agency rules

Example agency rules

• If less than 5% of the surface area of a bridge requires an intervention according to the intervention strategy to be followed, no intervention is performed (to ensure interventions are not performed on very small parts of bridges).

• If more than 5% of the surface area of a structure requires an intervention according to the intervention strategy to be followed, than interventions for all parts of the bridge that are in states 3, 4 and 5 are performed (to ensure a sufficient return period between interventions)

Take each strategy and each asset, put together with the actual condition, to generate first a list of assets that should have intervention, a good place to start Could be based on expert opinion, which evolve into agency rules, such as 5% threshold.

How to construct a maintenance intervention program

Step	Description
1	Determine the time intervals and time period in which maintenance interventions are to be executed.
2	Estimate the percentage of each item in each state at \(t=0\).
3	Determine the probable maintenance interventions to be executed at t in which a maintenance intervention is to be executed without consideration of other items (based on actual or expected state of items).
4	Determine the maintenance interventions to be executed at each t in which a maintenance intervention is to be executed with consideration of other items (based on actual or expected state of items and agency rules). (Attention: Not covered in Excel spread sheet explicitly)
5	Estimate probable costs of maintenance interventions to be executed at time \(t\).
6	Estimate the probable state of each item at \(t= t+1\).
7	Repeat steps 2 to 7 (with t= t+ 1) until the probable states of all items, the maintenance interventions to be executed, and maintenance intervention costs are determined over the specified time period (a first intervention program exists).
8	Verify all constraints at time t, e.g., budget limit in each time interval.
9	Determine the maintenance interventions to be included in the maintenance intervention program so that all constraints are satisfied.

At least one constraint to distribute resource if you can’t do everything you’d like to do.

Example of intervention program that correspond to different intervention strategies

Bridge identifier	Intervention program	intervention program
	1	1
B1	7,29	22
B2	1,24	10
B3	1,23	9
\(\cdots\)	\(\cdots\)	\(\cdots\)
\(\cdots\)	\(\cdots\)	\(\cdots\)

There’s uncertainty with respect to the future, but the result for year 23/24 generated from the mathematics Program 2 is delayed perhaps based on agency rule

How to evaluate a maintenance intervention program

Intervention Program 1

Intervention Program 2

Compare costs and effects on service overtime

How to evaluate a maintenance intervention program

Intervention Program 1

Intervention Program 2

Compare the condition evolution overtime

How do we decide which intervention to postpone if we can’t do all the ones we want?

\[ B/C = \frac{(C_{IS-R}^l-C_{IS-O}^l)+C_t}{C_{IS-O}^l} \]

How do we decide which intervention to postpone if we can’t do all the ones we want?

\[ B/C = \frac{(C_{IS-R}^l-C_{IS-O}^l)+C_t}{C_{IS-O}^l} \]

The benefit could be taken as the difference between the long term costs if the reference maintenance intervention strategy was followed and the long term costs if the optimal maintenance intervention strategy was followed

This would lead to all objects of the same type in the same state having the same B/C ratio.
It would be nice, perhaps, to have the larger objects prioritised before the smaller objects.

This can be done by adding the cost of the intervention on the object to the benefit. I agree it is not strictly a benefit but it is a way of prioritizing the large objects that will bring us the most benefit over the small objects – There are many other ways.
I challenge you to use a better one!

The cost could be taken as the long term costs if the optimal maintenance intervention strategy was followed

\(C_t\) : Cost in year \(t\)
\(C_{IS-O}^l\) : long term costs if selected maintenance intervention strategy followed

If we can’t do everything we’d like to do, how can we decide what to do? This is also explained in the paper

Cost is in the benefit because, to give an indication of which one would be best to do, this is proxy to prioritize large object, otherwise all the objects with the same state and same cost wouldn’t be very helpful

Example of intervention program that correspond to different intervention strategies

Bridge identifier	Intervention program 1	Maintenance cost	B/C
B1	7, 29	100, 100	2.8, 2.8
B2	1, 24	100, 100	3.1, 3.1
B3	1, 23	100, 100	2.7, 2.7

Budget limit = 150 CHF per year

Means we can’t do B2 and B3 in year 1

The B/C tells us it is more beneficial to us to do B2, so we postpone B3

Example of intervention program that correspond to different intervention strategies

Bridge identifier	Intervention program 1	Maintenance cost	B/C
B1	7, 29	100, 100	2.8, 2.8
B2	1, 24	100, 100	3.1, 3.1
B3	1, 23	100, 100	2.7, 2.7

Bridge identifier	Intervention program 1	Maintenance cost	B/C
B1	7, 29	100, 100	2.8, 2.8
B2	1, 24	100, 100	3.1, 3.1
B3	2, 23	105, 100	2.8, 2.7

Budget limit = 150 CHF per year

Means we can’t do B2 and B3 in year 1

The B/C tells us it is more beneficial to us to do B2, so we postpone B3

How to evaluate a maintenance intervention program (with constraint)

Without constraint

With constraint

Compare the costs and effects on service overtime

How to evaluate a maintenance intervention program (with constraint)

Without constraint

With constraint

Compare the condition evolution overtime

Next steps

• Next sessions:
  • Finalize determining optimal intervention strategy for every asset category (you can build on this template!)
  • Develop intervention programs
• Submission of all materials
  • PolyBox
  • Friday 31/05/2024

Thank you for your attention!

Questions?

Hamed Mehranfar
Doctoral student
hmehranfar@ethz.ch

ETH Zürich
Institute of Construction and Infrastructure Management (IBI)
Chair of Infrastructure Management
HIL G 32.2, Stefano-Franscini-Platz 5
8093 Zürich

www.ibi.ethz.ch