major project - structural health monitoring using non-destructive techniques

I want to know what things should I keep in my mind while selecting the sites for the test 

The question is not clear. Do you want to know what all should be considered on some actual structure (building, bridge or whatever) or some different issue?

I want to know what things should I keep in my mind while selecting the sites for the test

What should be considered sir 

You haven’t answered the question asked.

Only a general answer is possible. Please check these sites. Maybe useful to clarify your ideas.

https://pdfs.semanticscholar.org/fc31/fa3c3ca0887fc27bdb980eb4f1696f7e84c4.pdf

https://s3.amazonaws.com/academia.edu.documents/32393251/An_introduction_to_structural_health_monitoring.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1539445698&Signature=AZKJr6J8FC1KzyVfqLAoryB5ock%3D&response-content-disposition=inline%3B%20filename%3DAn_introduction_to_structural_health_mon.pdf

https://s3.amazonaws.com/academia.edu.documents/35117476/VIBRATION-BASED_MODEL-DEPENDENT_DAMAGE.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1539445758&Signature=RG9NFJGSxs5emYKOtCpytpvQKzo%3D&response-content-disposition=inline%3B%20filename%3DVIBRATION-BASED_MODEL-DEPENDENT_DAMAGE_D.pdf