Prevention Measures for Soft Storey Building

Reinforced concrete (RC) frame buildings are very common in the world. In such types of structure for functional requirements of parking space under the buildings no masonry in fill are provided resulting a construction with stilts. Wall buildings with vertically irregular configurations have been severely damaged or collapsed due to a story mechanism during severe earthquakes. This paper presents a criterion to prevent such failures. A story-safety factor is defined to represent the relative reserve strength against a story mechanism of the structure. The validity of this factor was examined by conducting dynamic response analyses of various analytical models of 7- and 11-story wall structures with an irregularity at the first story using two real earthquake records with long and short vibration periods and their numerous generated motions. The results show that the story-safety factor well controlled the failure mechanism of the structures. When the story-safety factor was larger than the corresponding dynamic shear magnification factor proposed by Paulay and Priestley [11] minus unity, a story mechanism of the structures did not occur in all cases. Practical procedure of using the story-safety factor for preventing a story mechanism at irregular stories is also presented.