After the installation of libaio i686 rpms , i also installed each package given in the document.
After installation of the packages relink the grid binaries with below document.
How To Relink The Oracle Grid Infrastructure Standalone (Restart) Installation Or Oracle Grid Infrastructure RAC/Cluster Installation (11.2 or 12c). (Doc ID 1536057.1)
After relinking of grid binaries, I relinked the oracle database binaries as well, but dbca didn't work then also. Then I uninstalled the oracle binaries and reinstalled.
The dbca run well now ... Happiness after frustating 24 hrs.