Hi Poorima,
To use multiple files with the TIles plugin you have specify a comma-delimited list for the "definitions-config" parameter, as shown next.
<plug-in className="org.apache.struts.tiles.TilesPlugin">
<set-property property="definitions-config"
value="/WEB-INF/tiles-defs-crms.xml,
/WEB-INF/tiles-defs-embargo.xml"/>
<set-property property="moduleAware" value="true"/>
<set-property property="definitions-parser-validate" value="false"/>
</plug-in>
Hope that helps,
-James
http://www.jamesholmes.com/struts/