## 1 Introduction  
The seismic vulnerability of multi-story reinforced concrete (RC)-framed structures built according to relatively old seismic code provisions increases significantly when their ground floor pays are left open to function as parking spaces, whereas the bays of the upper stories are infilled with unreinforced masonry infill panels (UMI). It was demonstrated by extensive past research that the dynamic behaviour of such structures, with a relatively flexible ground floor (\"soft story\") and stiff upper stories due to the presence of UMI, results in increased earthquake demands on the ground floor columns and shear walls, which are not designed to withstand such force levels. This is due to the interaction of the UMI with the surrounding RC frames, which contributes to a substantial increase of the upper story stiffness compared to the story stiffness of the ground floor. This, in turn, leads to structural damage (Figures 1-3), unless the RC structural elements at the ground floor are properly designed [1, 2, 3, 4, 5, 6, 7]. Current revised seismic codes include provisions against such unfavourable seismic responses [4, 5, 6, 7]. However, there are many existing old RC structures with such a soft-story seismic deficiency. This undesired stiffness irregularity in elevation, due to the presence of UMI, could also be detected in plans in which UMI are placed irregularly, thus introducing a significant torsional response. It is well known that, apart from the masonry infills, the geometry of an RC building in plan and the location of the vertical structural elements (shear walls and columns) are among the primary causes of torsional response, thus contributing to a further increase in the vulnerability of such buildings [4, 8, 9]. Current seismic design includes provisions against such unfavourable torsional seismic responses [5, 6, 7]. The formation of short columns by constructing UMI within the bays of RC frames also leads to severe structural damage of such RC columns (Figure 4). Retrofit schemes should try to introduce specific countermeasures to effectively address these causes of severe structural damage. During post-earthquake activity, further damage accumulation or even collapse can be prevented by temporary sharing schemes, as depicted in Figures 1-3, where either wooden or steel structural members are employed. Such effective temporary countermeasures, being part of a prompt post-earthquake preparedness plan, could save damaged buildings from total collapse. For buildings with a soft story the objectives of a permanent retrofitting scheme usually are an extension of the temporary countermeasures, e.g., to provide the ground floor story with an increased stiffness, shear capacity, and possibly ductility. In the provisions of relevant guidelines [4], the designer is provided with a number of distinct choices for a retrofitting technique denoted as reinforced concrete infill, whereby reinforced concrete infill panels (RC-IP) are cast in place, filling selected bays of an RC-framed structure. It is also important to identify the irregular placing of UMI within a story or UMI which could trigger the short column failure mechanism and try to introduce effective countermeasures. [PERSON] and [PERSON] [10] by an extensive experimental and numerical study investigate the effectiveness of a number of alternative retrofitting strategies to prevent the failure of existing underdesigned reinforced concrete frames potentially vulnerable to horizontal earthquake loads. They investigated retrofitting schemes with FRP composites or RC jacketing of the columns, eccentric steel bracing, or  
Figure 1: Damaged columns at the soft story. Figure 3: Damaged columns at the soft-story and temporary steel shoring. Figure 2: Temporary wooden story. Damaged shear wall at the soft story. RC infill walls spread along the height of a building in order to compare the effectiveness of such retrofitting schemes.