Heritage Masonry Buildings in Urban Settlements and the Requirements of Eurocodes: Experience of Slovenia

With rare exceptions, masonry buildings in historic urban settlements have been conceived only for gravity loads. Because their resistance to earthquakes is generally not adequate, seismic retrofitting is needed if the buildings are located in seismic-prone areas. As in the case of the new construction, no collapse and damage limitation criteria determine the basic parameters for retrofit and redesign of heritage buildings. Based on the results of experimental research, damage at story drifts within the range of 0.4% to 0.6% and 1.0% to 1.2% of story height has been found as acceptable at maximum resistance and at ultimate design-limit states, respectively. If the design ground acceleration values do not exceed 0.25 g and the number of stories is limited to two to three, practically the same level of seismic safety as required for the new construction can be attained by only improving the integrity of the structure and resistance of existing masonry walls. Because the effectiveness of economically acceptable retrofitting measures is limited, a reduction of design seismic loads, not exceeding 33 % of the code required value, is proposed in the zones of high seismic intensity. As the experimental results indicate, a moderately increased amount of damage to structural walls may be expected in such a case, without risking collapse of the building.