  A combination of the searches for pair-produced vector-like partners of the
top and bottom quarks in various decay channels ($T$$\rightarrow$$Zt/Wb/Ht$,
$B$$\rightarrow$$Zb/Wt/Hb$) is performed using 36.1 fb$^{-1}$ of $pp$ collision
data at $\sqrt{s}$ = 13 TeV with the ATLAS detector at the Large Hadron
Collider. The observed data are found to be in good agreement with the Standard
Model background prediction in all individual searches. Therefore, combined 95%
confidence-level upper limits are set on the production cross-section for a
range of vector-like quark scenarios, significantly improving upon the reach of
the individual searches. Model-independent limits are set assuming the
vector-like quarks decay to Standard Model particles. A singlet $T$ is excluded
for masses below 1.31 TeV and a singlet $B$ is excluded for masses below 1.22
TeV. Assuming a weak isospin $(T,B)$ doublet and $|V_{Tb}| \ll |V_{tB}|$, $T$
and $B$ masses below 1.37 TeV are excluded.
