ENGINEERING ANALYSIS OF A TYPICAL PRE-CODE URM BUILDING IN ZAGREB

This paper evaluates the seismic resistance and vulnerability of an existing unreinforced masonry (URM) building in Zagreb's Folnegovićevo neighborhood. The building with potentially low seismic resistance was erected in the 60s, a period characterized by the introduction of the first seismic code in practice. It has a rectangular plan 36.9 m x 10.7 m and consists of a basement, a ground floor and four floors totaling 17 m in height. The solid brick walls with variable thickness are evenly distributed in both directions and they run continuously from the foundation to the top. The reinforced concrete slabs are 14 cm thick rigid diaphragms made of MB 20 concrete class with smooth rebars GA 240/360.Two structural variants were analyzed: one with reinforced tie-beams and one without. Equivalent Static Analysis was conducted manually and , a Time-History Linear Dynamic Analysis was performed with the Tower Radimpex software for preliminary assessment. This method provided a basic assessment of the building’s seismic resistance, while also comparing manual and numerical results. Two advanced methods, Nonlinear Time-History Analysis (NLTH) and Pushover Analysis, were conducted with Diana FEA software employing Engineering masonry constitutive law to describe the highly nonlinear behavior of masonry walls which can crush, crack, or fail in shear. NLTH simulated the building's response to the 2020 earthquake, identifying critical structural components and potential damage. The Pushover Analysis evaluated how the building responded to increasing lateral loads, focusing on seismic resilience and collapse mechanisms.This research provides an in-depth comparison of different analytical approaches, contributing to the methodology for assessing and strengthening existing buildings. Conclusions drawn from these analyses emphasize recommendations for modifications to improve structural performance and safety.