3rd Croatian Conference on Earthquake Engineering 3CroCEE

One of the largest districts, known for its replicated building typologies, has been selected for this study, focusing on six-story reinforced concrete frame structures with infill masonry walls typical of 1960s construction. At the time of construction, building codes did not emphasize seismic activity to the extent that modern standards do, and the construction technology differed significantly from current practices. These buildings were often constructed using a combination of in situ concrete techniques and prefabricated slab decks, with materials classified according to outdated standards. Moreover, the design of these structures was based on older codes, which lacked the rigorous considerations of seismic resilience found in contemporary regulations. To address these discrepancies, extensive material testing and ambient vibration tests were conducted to assess the current properties and dynamic characteristics of the buildings, including natural frequencies and modal shapes. Based on in situ data, a validated structural model was used to simulate the building’s behavior. The Modulus of Elasticity of the infill masonry walls was measured using the Flat Jack method, providing insights into their contribution to lateral load resistance. Results indicate that the building can withstand moderate seismic events without immediate structural intervention, though retrofitting may be required to meet current seismic standards. Additionally, advanced structural models have been developed and calibrated to simulate the effects of common private interventions, such as modifications for commercial or residential use. These models offer a detailed analysis of how such alterations affect the building’s structural integrity and seismic performance, highlighting potential vulnerabilities and areas that may require further reinforcement.