Hi Arun,
Are you sure, adding of required fields to extract structure thru append?
Directly you can go SE11, give the extract structure name and display. see the last row, your added fields may appear. if not then add properly. by using append structure button on tool bar.
Append required field to your extract structure and go to RSA6, select your data source and change mode, added field may be hided, so un hide it and save it.
Go to RSA3 and see whether added field was visible or not. its visible with null records. later try to activate your logic and see.
Thanks