Seismic risk in regions with moderate seismicity, such as Switzerland, was largely underestimated. A vast majority of existing buildings have been built without specific earthquake resistant features and do not meet modern requirements. Although several projects tackle this issue, there is a lack of knowledge in unreinforced masonry (URM) structures, especially in countries with moderate seismicity. Fragility curves proposed by HAZUS and RISK-UE represent a common method to carry out a seismic assessment, even if these methodologies are rough. This paper describes the results obtained with an analytical displacement-based methodology to assess the seismic risk in existing buildings through fragility functions. Since fundamental period, ultimate drift, damage grades and torsional behaviour have significantly influenced fragility curves, new formulations are proposed. A 15-storey URM existing building with plan-irregularities is analyzed. Impact and accuracy of main parameters are addressed in this shear-wall building. The obtained fragility curves are compared to those obtained using HAZUS and RISK-UE approaches. The seismic behaviour of this building is also estimated with ambient vibration measurements. Main results of these experimental measurements are briefly described.