## 1 Introduction  
Multi-story structure is one of the major structural systems in many countries. From past earthquakes it has been suggested that this structure type is relevant to a large proportion of seismic damage and collapse, e.g., the 1994 Ms 6.6 Northridge earthquake in the US [1], the 1995 Ms 7.3 Kobe earthquake in Japan [2],the 2008 Ms 8.0 Wenchuan earthquake, and the 2010 Ms 7.1 Yushu earthquake in China [3; 4; 5], as well as earthquakes in New Zealand (2010 Ms = 7.0 and 2011 Ms = 6.1) [6], and Italy (2012 Ms = 5.9) [7; 8; 9]. For multi-story buildings, reinforced concrete (RC) frames and masonry structures are the two main structural systems. In traditional understanding, RC frames have a better seismic performance than the masonry buildings. However, the investigation of two epicenters of the Wenchuan earthquake, i.e., the towns of Beichuan and Yingxiu, shows the collapse ratio of RC frames (63%) is higher than that of masonry buildings (48%) [10]. Huge loss of life was caused due to the collapse of RC frames. Furthermore, the failure modes observed during the Wenchuan earthquake were inconsistent with the seismic design desire. Mechanisms of 'weak story collapse' and'strong beam-weak column' were observed in abundance [11]. Lessons learned from the past earthquakes highlighted that the seismic collapse resistance of RC frames needs to be improved urgently.  
Numerous studies have been conducted in two fields: collapse mechanisms and collapse resistance measures for RC frames. In the former aspect, the conducted experimental work, including static and shake table tests, could be classified into three levels: the component level [12; 13; 14], the structural level [15; 16; 17] and the level of overall structure with non-structural elements, such as infill, panel, etc. [18; 19]. As the collapse is a global behavior containing an incessant force redistribution during the collapse process, tests of the overall structures are generally regarded as the most reliable research method. Actually, the structural members and nonstructural members both influence the collapse mechanism of the RC frames. As the infill-frame interaction in RC buildings is varied, masonry infills, always present in RC frames, change the structural collapse mechanisms [20]. Meanwhile, research to date also indicates that numerical simulation has also become an effective way to study structural collapse mechanisms [21; 22; 23; 24; 25]. The advanced component models for structural members and the calibration test are the key issues to obtaining reasonable simulation results. Similarly, it is more persuasive for the experimental work to have an actual damaged building in the earthquake as a comparison. Meanwhile, methods to improve the seismic collapse resistance of RC frames including theoretical design methods [26] and practical retrofit measures [27; 28] were also conducted by many researchers.  
This study thus performed a shake table collapse test of a typical multi-story RC frame, and the prototype building almost collapsed in the 2010 Ms 7.1 Yushu earthquake in China. The structural collapse mode and mechanism were analyzed, and the corresponding remedy measures were also discussed. The research outcome of this study provides some understanding of the inherent collapse mechanisms of similar RC frames during strong earthquakes, and also offers a practical design method to improve the seismic collapse resistance of RC frames.