1、 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 components no longerprovide capacity sufficient to meet the required
2、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, severa
3、lretrofit 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 ef
4、fectively 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 j
5、acketing, 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 unde
6、r axial compression 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 compared with tradi
7、tionally 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
8、 al. (1988) and Cai (1987). Project Summary Seventeen circular columns were constructed and tested to failure in compression. First,similar reinforced concrete base columns were constructed with spiral transverse reinforcement. All base specimens had the same dimensions, transverse, and longitudinal
9、einforcement. 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 r
10、einforced 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
11、specimens had the entire cross section of the base column and retrofit area loaded.This 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
12、 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 cross-section loaded. RETROFIT OF EXISTING STRUCTURES Many structures have his
13、torically been constructed using reinforced concrete. Typicalordinary concrete consists of four constituents: gravel, sand, water, and cement.Reinforced concrete has some type of reinforcement, typically steel, combined withconcrete to produce a stronger system than plain concrete. Concrete is stron
14、g in compression but weak in tension. Tensile forces cause concrete to crack and eventuallyfail in a brittle manner at stresses significantly lower than the compression strength ofconcrete. Steel, or another type of reinforcement material, can be used to compensate forthe weak tensile strength of co
15、ncrete. This system is referred to as reinforced concrete. As reinforced concrete ages, a variety of detrimental effects can occur. These includespalling, flaking, or cracking of the concrete, and subsequent corrosion of the reinforcingsteel. These occurrences can significantly affect the strength o
16、f structural members.Members displaying these adverse affects may be rehabilitated using an appropriateretrofit method. Retrofitting is typically done for two reasons: rehabilitation or strengthening. As previously discussed, rehabilitation is fixing the structural deficiencies of a damaged structur
17、e or structural member. This may be necessary for aging members that no longerdisplay the strength of the original design. Strengthening increases the load-carryingcapacity of a structural member (Ersoy et al. 1993). This may be necessary if thesupported load is altered through the life of the struc
18、tural member, or if current designstandards have more stringent reinforcement requirements. Additionally, structuralmembers in seismic regions may need to be upgraded to current seismic requirements. Retrofitting can be applied to any structural members, including beams and columns.Several methods a
19、re traditionally utilized for retrofitting. These include concretejacketing, steel jacketing, and FRP strengthening (Wipf et al. 1997). Reinforcement forconcrete jackets can be provided by rebar reinforcement or welded wire fabric (WWF).Additionally, a relatively new product, Prefabricated Cage Syst
20、em reinforcement (PCS),is suggested as a possible reinforcement alternative for concrete jacket retrofits. PCS Benefits PCS reinforcement has some unique properties. The longitudinal and lateral reinforcement for PCS are located the same distance from the center of the member cross-section. This pro
21、vides increased flexural capacity, using the same amount of steelas a traditional rebar system, and results in more efficient use of the reinforcing steel.The monolithic action of PCS eliminates separation of longitudinal and transverseeinforcement. Additionally, PCS reinforcement is spread in a planar configurationwhich offers greater confinement than rebar reinforcement, as displayed
