  A search for a charged Higgs boson, $H^\pm$, decaying to a $W^\pm$ boson and
a $Z$ boson is presented. The search is based on 20.3 fb$^{-1}$ of
proton-proton collision data at a center-of-mass energy of 8 TeV recorded with
the ATLAS detector at the LHC. The $H^\pm$ boson is assumed to be produced via
vector-boson fusion and the decays $W^\pm \to q\bar{q^\prime}$ and
$Z\rightarrow e^+e^-/\mu^+\mu^-$ are considered. The search is performed in a
range of charged Higgs boson masses from 200 to 1000 GeV. No evidence for the
production of an $H^\pm$ boson is observed. Upper limits of 31-1020 fb at 95%
CL are placed on the cross section for vector-boson fusion production of an
$H^\pm$ boson times its branching fraction to $W^\pm Z$. The limits are
compared with predictions from the Georgi-Machacek Higgs Triplet Model.
