Within the presented research, model tests were performed in 1-g conditions to investigate the liquefaction potential of Skopje sand as a representative soil from the Vardar River’s terraces in N. Macedonia. A series of shaking table tests were performed on a fully saturated, homogeneous model of Skopje sand in the newly designed and constructed laminar container in the Institute of Earthquake Engineering and Engineering Seismology (IZIIS), Skopje, N. Macedonia. The liquefaction depth in each shaking test was estimated based on the measured acceleration and pore water pressure as well as the frame movements of the laminar container. The surface settlement measurements indicated that the relative density increased by ~12% after each test. The observations from the tests confirmed that liquefaction was initiated along the depth at approximately the same time. The number of cycles required for liquefaction increased as the relative density increased. As the pore water pressure rose and reached the value of the effective stresses, the acceleration decreased, thus the period of the soil started to elongate. The results showed that the investigated Skopje sand was highly sensitive to void parameters and, under specific stress conditions, the liquefaction that occurred could be associated with large deformations. The presented experimental setup and soil material represent a well-proven example of a facility for continuous and sustainable research in earthquake geotechnical engineering.

This paper presents the outcomes of an extensive experimental investigation on the seismic performance of an innovative exoskeleton retrofitting system, developed as part of the ERIES-RESUME project. The proposed system integrates laminated timber and aluminium components to enhance the structural resilience of existing reinforced concrete (RC) buildings, while also offering the potential for thermal upgrading. Two identical 1:3 scale RC models, representing typical non-ductile structures, were tested on a shaking table at the IZIIS Laboratory of the Institute of Earthquake Engineering and Engineering Seismology in Skopje. The first model, initially unstrengthened, was subjected to seismic loads until significant structural and infill-wall damage was reached. Following appropriate repairs, the exoskeleton was applied, and the model was retested. The second model was equipped with an exoskeleton from the outset. Test results demonstrate significant improvements in seismic performance, including increased stiffness, reduced interstory drifts, reduced acceleration amplification, and reduced infill wall damage. The study confirms the feasibility and effectiveness of the proposed exoskeleton system as a practical solution for retrofitting vulnerable reinforced concrete buildings.