although thread is old, but it might be helpful for those who are needing an answer for this question
if you want to export a structure you specify TABL,
after a nugget gets created you can differentiate a table from a structure based on TABCLASS="INTTAB"
if you exported several objects from a Package than this helps you differentiate the structure from table
<TABL TABNAME="ZST_AUSWERTUNGOUTPUT" DDLANGUAGE="D" TABCLASS="INTTAB" .../>
for tables tabclass has value of TABCLASS="TRANSP"