The need to improve the ability of an existing building to withstand seismic forces arises usually from the evidence of dam-age and poor behaviour during a recent earthquake. It can arise also from calculations or by comparisons with similar buildings that have been damaged in other places. While in the first case the owner can be rather easily convinced to take measures to improve the strength of his building, in the second case dwellers that have much more stringent day-to-day needs are usually reluctant to invest money in the improvement of seismic safety.