# 121

Dear J. A. N. N. Jayakody, M. C. M. Nasvi , D. J. Robert , S. K. Navaratnarajah , L. C. Kurukulasuriya , F. Giustozzi , C. Gunasekara , S. Setunge

I read your paper

Development of a Cross-Asset Model for the Maintenance of Road and Water Pipe Assets using AHP Method

My comments:

In my opinion your case is naïve, because it appears that the only assets are the pavement and the water trunks. Normally, under the pavement of a city street there are many assets like: Water mains and trunks, sewerage trunks, gas pipelines, electric wires, trunks for rain water drains and storage, communications fibre, sometimes steam conduits, piping for compressed air, non-longer working utilities, etc., therefore, every time you break the pavement you have to deal with different utilities and at a different depth. In https://www.pinterest.ca/pin/186969822016032051/ you can see a cross-section of a New York Street.

I- In page 1 you say “the system as a whole (cross-assets) since the maintenance of one asset will trigger the degradation of another asset.”

I am afraid that this assertion is inexact. Why the maintenance of one asset will trigger the degradation of another. Do you have a mathematical support for this?

Assume you have to renew an old pavement. Why this fact should bring degradation of water trunks, that by the way, are buried many meters underneath the road?

However, when it is decided to resurface a road, it is necessary to find out what utilities are underneath. It is very common to see that a new pavement scarcely three months old must be destroyed because a utility underneath it needs immediate attention.

2- “The major challenge in developing such a framework for cross-asset systems consisting of road and water pipe assets is the unavailability of a set of reliable relative weights derived considering multiple criteria for the maintenance of these assets. This is mainly because the maintenance planning of roads and water pipes is usually performed by two independent authorities”

I fail to understand the relatiuonshion with weights here. Yes, there could be differences in coordination, needs and execution times but normally, it is not related to weights, but due to the lack of appropriated planning.

3- In page 3 “multi-attribute utility theory and analytical hierarchy process (AHP) can be used to analyze and quantify multiple alternatives based on the preference of the decision maker”

I do not think that both, the utility theory and AHP, both descriptive methods, can be used to solve a problem like this. These methods work on the basis of personal preferences and then reflect what the DM wants to be. This is good for selecting a movie or a vacation place but not for serious problems, where the aim is to consider what should be done not what the DM wants or wishes. Most of MCDM methods, are normative, in the sense that they adjust to data, norms and positions, and where personal wishes are secondary or inexistent. Of course, the opinion and experience of the DM is important, and should be considered, but not conditioning the whole problem to it; you also confirm this in your next paragraph.

4- In page 3 “Among all the available multi-criteria decision-making methods, the AHP is one of the most straightforward and widely adopted approaches”

True, it is the most used method, and the reason is because it does not demand analysis or thinking, only put a value as per your intuition. After that, you push the start button and you get a result that gives a weight for each criterion. Which is the relation of this with real life? None

5- In page 3 “The goal is for the problem to be solved. The measures of performance used to judge the options for the goal are considered the criteria, where options are the alternatives available to achieve the goal. In the AHP method, the top-down approach of prioritization is used [18]. Accordingly, first, the criteria are prioritized. Subsequently, the sub-criteria (if available), options, and sub-options (if available)”

I am afraid that this is incorrect.

The general objective of a problem, say to decrease poverty, does not have a goal. It is only a wish, and very valid indeed.

The performance values are not measures, for they are not metrics, they are real or subjective values, that denote the degree of participation of each alternative in pursuing an objective

Criteria have goals or targets, expressed in quantities, as for instance amount of funds available, (Euros) availability of water (m3/day) or maximum limits for contamination (%). These are the targets, and converts the criteria in objectives with a clear target to fulfill.

It is true that in AHP the top-down approach is used, and thus permitting the DM to alter real data using invented weights, without knowing what effect they may produce.

This is illogical, just consider this simple example, how can you alter the ingredients of a cake if you do not know which will be the result? Wouldn’t be better using the prescribed components, get a result, and if you do not like it, or you want to improve a particular aspect say, to be sweeter, adding a little more sugar? This is the bottom-up approach.

Do you know that this is the system used for instance in designing and building planes, automobiles, medical drugs, hydro electric dams, writing literary works and music, designing the best routes to be used by international truck transportation? They work on a mock up or physical model, subject to similar conditions, as for instance intensity of the wind in an airplane or a car,

Experiment on them and extract conclusions that are applied in the final design of the car. In MCDM that mock up is the initial decision matrix.

That is, the DM corrects data, following his experience and know-how, considering his/her ideas to improve something, AFTER, not BEFORE getting results, exactly the opposite of what AHP does.

6- “while there are a very limited number of studies focusing on the use of AHP for cross-asset maintenance combining more than one asset”

Why? Because if you are dealing with several assets that intercross you cannot use the lineal hierarchy established by AHP. Consider this real example:

Assume than in Main Street you have to change the water trunk because it is corroded. The City Hall have plots of the different underground services in that street, like electricity, telephone (at least in the old days), wires for lighting poles that must be replaced because of age or capacity, expanding rain drainage, inspect sewerage trunks, etc., therefore, you have several independent projects but that are linked for technical and commercial reasons. On top of that another project is restoring pavement.

Do you think that you can change the corroded water trunks without considering the others projects? Obviously not, all different projects are linked by precedence.

That is, there is also a technical and engineering precedence, since normally, the water truck is the deepest service (to avoid freezing), followed by sewerage, followed by wires, etc., which means that it will be the first, and only after it is repaired and buried again, it is possible to commence with the second deepest, and so on. This is real-life, not a black board example.

You cannot establish this precedence in AHP, nor can you treat the different criteria in isolation, and you cannot do this with a lineal hierarchy structure. This is the reason, by which, AHP is no longer applicable to real life projects, although it was, back in the 50s, when social and environment issues did not participate in projects.

7- Page 3 “All the results from the decision-making process were subsequently subjected to sensitivity analysis, and the most significant factors based on cost and service life were determined”

Sensitivity analysis (SA) has no relation with what you assert. SA is used to determine the strength of a selected alternativewhen there are changes in some criteria that affect it. On what grounds can you assert that cost and service life are the most significant factors?

8- In page 8 “When conducting several comparisons one after the other, it is possible that illogical judgments are made by making the pair-wise comparison matrix inconsistent [41, 18]. For instance, when item A is preferred over item B and item B is preferred over item C, item A should be given a higher preference compared to item C to ensure consistency. Therefore, consistency ratio (CR) is used to evaluate the level of consistency”

Should be given? Mandatorily? Therefore, the DM must correct something that he did?

Why? To allow using the Eigen Value method? Don’t you think that this is absurd? Is the DM a robot that must follow orders from an algorithm? Hard to understand indeed

I can continue with my comments, but I think that in my opinion, at least, it is not worth analyzing something that started in the wrong way.

Hope this can help

Nolberto Munier