Dear Mohammad Masfiqul Alam Bhuiyan and Ahmed Hamma

I read your paper:

A Hybrid Multi-Criteria Decision Support System for Selecting the Most Sustainable Structural Material for a Multistory Building Construction

And these are my comments:

1- My comments do not refer to structural engineering but to MCDM procedures. There is no doubt that you have made extensive research for this article. I think that you took good care in selecting experts in construction engineering, but I am afraid that the same care weas not taken in the application of the MCDM methods. There are some incongruencies as well as inaccuracies.

You want to select the most sustainable material for a building construction, which implies considering at the same time and jointly the economics, the environment and the social field. However, you selected a method, AHP, which works opposite, since it analyzes separately and in a linear hierarchy, each of the four main criteria. I am not blaming the method; it was designed for that purpose; it is the incorrect use of a method that I understand is incorrect.

For instance, in Figure 2, the four criteria are not connected, which is not real.

Criteria like Technical and Economics are normally strongly related. For example, the technical department decides to use radiant flooring for heating (a technical system), which has a cost different of using a hot-water system (a different technical system). Technical is also related to environment, as in the case that technical decides to recycle waste water produced in the building, by treating it, it involves technical issues, economics and environment. They are not isolated.

As another example, suppose that engineering proposes to use radiant flooring, and the financial guys say that they don’t agree because there is no money for that, so they ask engineering to look for a less expensive heating. As you can see, considering individual aspects and solving them linearly, and then, adding them up, does not make sense.

This is the real-world.

2- In page 4 you say “The remarkable contributions of this research comprise the integration of technical aspects with the commonly used three pillars (economic, social, and environmental)”

Not so remarkable or new; this integration has been done for decades before your paper.

3- In page 5 you say “. Subjective (qualitative) methodsand objective (quantitative) methods are the two types of weighing techniques”

This is inexact. There are not qualitative and objective methods. That denomination applies to criteria. Normally, a MCDM handles both.

4- In reality, I don’t think that you can address a problem like this with four main criteria. What about risk, legal issues, topography, access to the site, material supply, constructors’ expertise, etc.?

5- In page 1o you say “3.6. Fuzzy AHP”

According to Saaty, the AHP creator, AHP never should be used with fuzzy logic, because AHP is already fuzzy.

6- In page 11 you speak about consistency. Yes, there is a FORCED consistency regarding the DM values.

This consistency indicates that the DM was more or less articulate; remember that there is a formula that forces him to be coherente, like it or not, and that the coherence or transitivity is his, andnot related with the real world, which is normally intransitive.

7- In page 21 you say “Steps 1 and 2: A pairwise comparison matrix was developed for each user to compute the relative priorities of criteria from the user’s point of view”

Suppose that you need to pair-compare criterion Stress, that is, the force applied in the middle of a beam, and Strain, which is its deformation regrading its central axis. Sincerely, I don’t imagine an engineer doing this comparison and deciding for instance, that stress is three times more important than strain. In my opinion, it is absurd; however, this is what pair-wise comparison is about. How can anybody trust the result of this comparison, and don’t forget that there can be ‘n’ engineers giving different values.

Considering this aspect, which is the object in performing fuzzy with arbitrary data?

8- In page 24 you say “The owner’s opinion was given a higher weightage of 40%, while the rest of the team received 30%”

Why? Because he is the owner and, in this condition, he knows better than other experts? This does not look very professional.

9- In page 26 you determine that RC is the best option. I wonder how you can reach that conclusion without considering the structural characteristics of the four alternatives.

It suggests that in this study all modulus of elasticity are the same, when it is known than this is different between different options, and even in different kind of timber.

10- What I still don’t understand is why you compute two different kinds of weights, objective and objective. Of course, the first is useful to consider the experience and know-how of the DMs, but how do you use both?

It is necesario to remember that both types of weights do not have the same meaning. Weights from entropy or using statistics, represent quantity of information of each criterion and they are capital to evaluate alternatives.

Weights from AHP are simply a relative measure of criteria importance and have no relation to alternatives evaluation.

11- In page 28 you say “In the end, this application generated several outputs for the users”

If at the end the users have several outputs, it appears that they came back to square one. In my opinion, what they need is one solution, not several.

I hope these comments may help you

Nolberto Munier