【正文】 EXPERIMENTAL RESEARCH OF REINFORCED CONCRETE COLUMN RETROFIT METHODS Introduction As the infrastructure of our country continues to age, the need for effective retrofittreatments has increased. Many building and bridge structural ponents no longerprovide capacity sufficient to meet the required code standards. Seismic upgrading andreinforcement protection are two of the major issues requiring retrofits. Additionally,many aging structural members no longer provide the load capacity of the original designbecause of concrete cracking, steel corrosion, or other damage. In this research, severalretrofit methods for increasing the axial load capacity of reinforced concrete columnswere tested and analyzed. Several currently applied methods for retrofitting columns include concrete jacketing,steel jacketing, and fiber reinforced polymer (FRP) jacketing. All three methods havebeen shown to effectively in increase the axial load capacity of columns. In addition, anew reinforcement product, Prefabricated Cage System (PCS) reinforcement, wasintroduced as a possible reinforcement option for concrete jacket retrofit applications. Project Scope Three retrofit reinforcement options, concrete jacketing, steel jacketing, and FRP wrapping, were experimentally analyzed in the research. Three different materials provided reinforcement for the concrete jackets: a rebar cage with spiral transverse reinforcement, welded wire fabric (WWF), and the aforementioned PCS. All specimenswere tested under axial pression loading only. Applied load and displacement weremeasured for all specimens throughout testing until failure. Additionally, response of theloaded specimens was observed and documented throughout the testing. Behavior of thenewly introduced PCS reinforcement was pared with traditionally used retrofitapplications already currently utilized in the structural engineering industry. Advantagesand disadvantages of each retrofit measure were identified. Additionally, model conceptswere presented for the response of concrete jacket retrofitted columns based on the workof Mander et al. (1988) and Cai (1987). Project Summary Seventeen circular columns were constructed and tested to failure in pression. First,similar reinforced concrete base columns were constructed with spiral transverse reinforcement. All base specimens had the same dimensions, transverse, and longitudinaleinforcement. The base specimens were then retrofitted with the different retrofitmethods previously discussed. One specimen, referred to as the base specimen, wastested without any retrofit applied. Three specimens were retrofitted with a spiral rebarreinforced concrete jacket. Two specimens were reinforced with a welded wire fabricreinforced concrete jacket. Three specimens were retrofitted with FRP wraps and twomore specimens were retrofitted with steel jackets. In addition, six specimens wereretrofitted with a PCS reinforced concrete jacket, including two different thicknesses ofPCS. Nine specimens had the entire cross section of the base column and retrofit area simulated a retrofit condition when the applied load is distributed across the entirecross section. Five specimens had the cross section of only the base column loaded,which simulated a condition when the load is only applied to the original member. Threeother specimens had increased lateral reinforcement spacing with similar transversereinforcement strength per spacing. These specimens also had the entire retrofit and basecolumn crosssection loaded. RETROFIT OF EXISTING STRUCTURES Many structures have historically been constructed using reinforced concrete. Typicalordinary concrete consists of fou