In one embodiment, a reinforced fiber cement article comprising a fiber cement piece and a reinforcing fixture bonded to a portion of the fiber cement piece for improving the performance, strength and durability of the fiber cement piece. The reinforcing fiber cement article could be used as or in conjunction with a siding plank assembly, which further comprises an interlocking feature that allows the siding plank to be stacked with other siding planks in a manner such that a uniform and deep shadow line is created. The interlocking feature sets the gauge of the exposed plank face and allows for leveling of the plank during installation. The reinforcing fixture could also serve as a thick butt piece or a plastic spline that produces a deep shadow line. A cementitious adhesive is used to bond the reinforcing fixture to the fiber cement piece.