Can I claim compensation from a builder for structural defects discovered after possession?

Yes, RERA specifically provides for a defect liability period (typically five years from the date of possession) during which the developer remains responsible for rectifying structural defects and other significant deficiencies in the construction, without additional charge to you, even after possession has already been handed over.

You should formally notify the builder in writing about the specific defects, giving them reasonable time to rectify the issues, and if they fail to respond or don't adequately fix the problem, you can escalate this through a RERA complaint, since failure to honour the defect liability obligation is itself a violation the authority can act on.

Document the defects thoroughly — photographs, dates you noticed them, and ideally an independent structural assessment if the issue is significant — since this evidence will support your complaint. Given that you're still well within the typical defect liability window, it would be worth pursuing this formally with the builder's help of a lawyer experienced in RERA matters rather than accepting the cost of repairs yourself.