An improved joint edge assembly, of the type used in the construction of concrete slabs, is disclosed. The device also includes a current confinement layer including a sequence of doped n-p-n-p semiconductor layers to produce a n-p-n-p blocking structure and a semi-insulating semiconductor material deposited over the n-p-n-p blocking structure. It safely holds the post in position when pounding is commenced. When an earthquake strikes, the steel ball drops and contacts the magnet.