Resolution: The setting, java.extended.properties=-verbose:gc in tra file will print out gc information on the standard output which is the console by default. However BW engine uses log4j and all its logs will be written the application log.
If you want to output those gc information to a temp file, you can edit .sh file and redirect the gc information to a file, for example, appending "> tmp.log" in the .sh file.
Applying -verbose:gc will produce huge amount of logs which should be mainly used for troubleshooting on production environment. As soon as you finish the testing, please reset it.