  In this article, goal-oriented a posteriori error estimation for the
biharmonic plate bending problem is considered. The error for approximation of
goal functional is represented by an estimator which combines dual-weighted
residual method and equilibrated moment tensor. An abstract unified framework
for the goal-oriented a posteriori error estimation is derived. In particular,
$C^0$ interior penalty and discontinuous Galerkin finite element methods are
employed for practical realization. The abstract estimation is based on
equilibrated moment tensor and potential reconstruction that provides a
guaranteed upper bound for the goal error. Numerical experiments are performed
to illustrate the effectivity of the estimators.
