The present invention discloses a device for dissipating mechanical energy of a frame structure which is under a lateral force comprises a base plate for attachment to the frame structure, having a pair of vertically extending flanges on one side; a centre plate having one end connected between the pair of flanges by a first pivotal connection; a pair of elongate plate members extending perpendicular to the base member, one plate member being connected on each side of the other end of the centre plate by a second pivotal connection such that the pair of plate members can execute a seesaw movement about the second pivotal connection and the assembly of the centre plate and the pair of plate members can execute a swinging movement about the first pivotal connection; characterised in that a pair of elastic members are disposed between the flanges of the base plate, one on each side of the centre plate, and a second pair of elastic members are disposed one between each of the pair of elongate members and the centre plate.