what is percentage of total score we need to score to get into IIT THIRUPATI in a fair branch?

Firstly before answerig your request, I would like to mention their is nothing a fair branch. Every branch is good and have enough scope for you to do well provided you have related interest in it and also hardworking to it.

Well if have told me your category I would be able to more accurate answer. So I would answer it according to Gen category.

For IIT Tirupati you must be getting a minium of 8k rank to stand a chance of grabbing it's seat.

For getting 8k rank, though JEE advanced varies but you can safely assume you have to score 40% of the total marks.

Also since now ownwards the JEE advanced has become subjective, so percentage score will further depriciate. Hence the safe score would be around 30-33% . This approximation I've given from the best of my knowledge.