  We experimentally measure the static stress at the bottom of a granular
chains column with a precise and reproducible method. The relation, between the
filling mass and the apparent mass converted from the bottom stress, is
investigated on various chain lengths. Our measurements reconfirm that the
scaling behavior of the stress saturation curves is in accord with the
theoretical expectation of the Janssen model. Additionally, the saturation mass
is displayed as a nonmonotonic function of the chain length, where a
distinguishing transition of the saturation mass is found at the persistence
length of the granular chain. We repeat the measurement with another measuring
methodology and a silo with different size, respectively, the position of the
peak maintains robust. In order to understand the transition of the saturation
mass, the friction coefficient and the volume fraction of granular chains are
also measured, from which Janssen parameter can be calculated. Finally, we
preliminarily measure the bottom stress for two distinct packing structures of
long chains, find the effect of the entanglements on the bottom stress, and
argue that the entanglements might be responsible for the transition of the
saturation mass.
