COMPARATIVE NUMERICAL INVESTIGATION OF TIMBER ADDED FLOORS ON EXISTING RC STRUCTURES

As urban areas become increasingly dense, the vertical extension of existing structures has gained importance, especially in seismically active regions. The challenge is more pronounced for older buildings designed with minimal or no seismic provisions. Light frame timber systems are often preferred for vertical extensions due to their low mass, which minimizes additional seismic forces on the existing structure. At the Institute of Earthquake Engineering and Engineering Seismology (IZIIS) in Skopje, experimental shaking-table tests were performed on two-story reinforced concrete (RC) structures with timber-added floors to assess their structural performance. The goal of these tests was to examine the impact of vertical extension on the structural behavior under seismic loads. To validate the experimental findings, numerical analyses using OpenSees software were conducted. Initially, modal (eigen) analyses were performed to determine the natural frequencies and vibration mode shapes of the structure. This was followed by pushover analyses using a nonlinear static procedure in both the transverse and longitudinal directions. Modal force patterns based on the first mode of vibration were applied to simulate the loading conditions. Lastly, dynamic analyses under seismic ground motion were performed to further assess the behavior of the structure with timber-added floors. The comparative study highlights the effectiveness of using timber for vertical extensions, providing insight into its impact on the seismic performance of existing RC structures.