رفتار لرزه ای ستون های فولادی کامپوزیتی آسیب دیده از زلزله ژاکت تقویت شده با روکش فولادی Study on seismic behavior of encased steel jacket-strengthened earthquake-damaged composite steel-concrete columns

1．Introduction As a kind of attractive composite structure, steel reinforced concrete structure has the advantages such as high carrying capacity, high rigidity and good seismic performance. Steel reinforced concrete has been widely used in large-span structures and high-rise buildings in earthquake-prone areas around the world [1,2]. The recent earthquake survey of China’s Wenchuan earthquake (2008), Iranian-Pakistani boundary earthquake (2013) and China’s Ludian earthquake in Yunnan Province (2014) shows that a large number of damaged frame structures need damage grade identification and corresponding reinforcement & repair measures with the exception of critically damaged frames demanding turnover and reconstruction [3,4,5,6]. According to the principle, steel reinforced concrete frame composite column is an important load-bearing member of frame structure, therefore it is necessary to study restoration and reinforcement of steel reinforced concrete column as well as its anti-seismic property [7,8]. At present, “Standard for earthquake-resistant evaluation of buildings” (GB50023-2009), “Regulation of building seismic strengthening technique” (JGJ116-2009) and “Technical guide for post-earthquake building identification and reinforcement” have never focused on seismic identification and reinforcement of steel reinforced concrete structure. In particular, buildings designed in accordance with China’s earthquake resistant code can still meet the requirement of “being modifiable in moderate earthquake and not falling in strong earthquake”. For buildings that can be repaired, “reinforcement and repair” should be more reasonable than “turnover and reconstruction” either from the point of view of solving the urgency of settlement problem of the masses in the disaster areas or from the economic point of view of post-disaster reconstruction. Therefore, the study of seismic damage degree, reinforcement method and seismic performance of reinforced structure means very important engineering significance for improving its seismic capacity and post-disaster recovery and reconstruction. Repair & reinforcement of seismic damage structure mainly involves three issues: (1) Repair seismic performance of the reinforced structure. (2) Influence and law of different degrees of earthquake damages on structural restoration and reinforcement. (3) The specific advantages of repaired and reinforced of structure over unreinforced structure. (4) Impact of different axial compression ratios [9], different reinforcement heights on structure seismic [10].