A rubber part for use as a structural component for incorporation into a brick or masonry wall structure in a reinforced concrete frame, to be located within the plane of the wall, has a length x and a stiffness along its length of Sx, a width y and a stiffness across its width of Sy, and a thickness z and a stiffness across its thickness of Sz, the stiffness of the part being anisotropic with Sy > Sx. The part is adapted such that, when in use, it is capable of controlling vibrations of the wall caused by seismic activity and also of having a damping effect thereby increasing the energy dissipation capacity of the structure. The rubber part is preferably in the form of a sheet and can be laminated on one or both major surfaces. The two major surfaces of the sheet may be contoured, for instance being corrugated across its width.