Effects Of Steel Brace On RC Frame Structural Progressive Collapse

The global stability of building space has always been one of the most essential topics of building structural design. In recent years, an even greater attention has been paid to this topic by many researchers and structural engineers. The current structural design specifications model focuses on how to ensure the working performance of the complete structure under normal loads, however abnormal loads effect has been less concerned. Nowadays with a more and more complicated structure and a higher possibility of occurring abnormal events, the flaws of traditional building design system have been exposed gradually. The traditional building design is not able to clearly consider the collapse resistant capacity when the building is under abnormal loads. In addition, steel bracing of RC buildings has been applied as a retrofitting technique to increase the lateral stiffness and load resisting capacity of existing buildings so as to limit earthquake damage to buildings. Although there were many papers of seismic performance of this dual system for the past three decades, how to obtain improved progressive collapse performance, by arranging steel braces into a structure, has yet to be investigated and it is the focus of this thesis.Based on the alternate path method, the dynamic response and progressive collapse resistance mechanism of RC frames in which steel braces in different vertical form were arranged and in different floors were studied. Elastical-plastical dynamic time-history analysis under large earthquake of RC frames which steel braces were arranged in different floors was also considered. The result showed that:1. the "Λ"-shaped/"V"-shaped and inverted "Y"-shaped braces that were considered in this thesis, can improve the resistance of progressive collapse. Where whether the end of braces were directly connected to the joint which is the up end of the sudden removed column is one of the key factors for RC frame to improve its collapse resistance, while the continuity of braces in the internal frames is not that essential.2. The anti-progressive collapse ability of a frame will not change acutely with the arranging direction shifted in horizontal plane. 3. Braces fixed up in different stories, can prevent progressive collapse effectively that was caused by the sudden remove of a bottom column. But with the rising of the strengthen floor the collapse resistance will decrease and the residual upper column will changed from a compression member into a tension one. So when we adopt the upper strengthen measures, the tensile property of columns should be investigated reasonably.4. Steel braces in partial story in the frames that designed to GB specifications, will lead the adjacent floor to be an unsubstantial layer. But this unsubstantial layer will not lead to collapse of building under the action of the rarely met earthquake. This thesis point out, arrangement of steel braces in the2nd layer of a RC frame could be a effective measure to prevent progressive collapse, meanwhile this measure can make people ensure structural safety when the rarely met earthquake is arriving.