No archives located in the jenkins jobs folder when building with uploadArchives

I have a bunch of jenkins freestyle projects that builds java projects using gradle 1.5 and the gradle jenkins plugin.

On the jenkins master each job has a ‘builds’ folder, eg:

/var/lib/jenkins/jobs/sample_job_01/builds

I have configured each job to only keep 10 builds including artifacts. In the builds folder there are 10 folders named by date but they only contain :

build.xml
changelog.xml
log

No artifacts are stored in these folders. Why are the artifacts not stored in the Jenkins jobs builds folders? They are uploaded just fine to Artifactory.