Stiffness of the base plate
ETAG 001, Annex C and TR 029 contain no detailed information on the verification of a stiff base plate. Nevertheless, this verification is very important. In case of a non-rigid base plate and acting bending moment(s) the resultant of the compression forces below the base plate moves into direction of the welded profile, the lever arm of the internal forces is smaller than assumed in the calculation and the tension forces on the individual anchors of a group are higher than assumed in the theory of elasticity.
The design of the base plate is carried out in DesignFiX using a Finite Element Program for the determination of the plate thickness. It is explicitly pointed out that the anchor plate design is based on a proof of stresses and allows no direct statement about the stiffness of the base plate. The proof of the necessary stiffness in order to fulfil the requirements of the theory of elasticity has to be done separately or it must be ensured by suitable measures (e. g., by welded stiffeners) that the conditions of the theory of elasticity are met.