外文翻译：RETROFIT OF EXISTING STRUCTURES2.1 IntroductionMany structures have historically been constructed using reinforced concrete. Typical ordinary concrete consists of four constituents: gravel, sand, water, and cement. Reinforced concrete has some type of reinforcement, typically steel, combined with concrete to produce a stronger system than plain concrete. Concrete is strong in compression but weak in tension. Tensile forces cause concrete to crack and eventually fail in a brittle manner at stresses significantly lower than the compression strength of concrete. Steel, or another type of reinforcement material, can be used to compensate for the weak tensile strength of concrete. This system is referred to as reinforced concrete.As reinforced concrete ages, a variety of detrimental effects can occur. These include spalling, flaking, or cracking of the concrete, and subsequent corrosion of the reinforcing steel. These occurrences can significantly affect the strength of structural members. Members displaying these adverse affects may be rehabilitated using an appropriate retrofit method.Retrofitting is typically done for two reasons: rehabilitation or strengthening. As previously discussed, rehabilitation is fixing the structural deficiencies of a damaged structure or structural member. This may be necessary for aging members that no longer display the strength of the original design. Strengthening increases the load-carrying capacity of a structural member (Ersoy et al. 1993). This may be necessary if the supported load is altered through the life of the structural member, or if current design standards have more stringent reinforcement requirements. Additionally, structural members 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 are traditionally utilized for retrofitting. These include concrete jacketing, steel jacketing, and FRP strengthening (Wipf et al. 1997). Reinforcement for concrete jackets can be provided by rebar reinforcement or welded wire fabric (WWF). Additionally, a relatively new product, Prefabricated Cage System reinforcement (PCS), is suggested as a possible reinforcement alternative for concrete jacket retrofits.2.2 Prefabricated Cage System (PCS) ReinforcementPCS reinforcement, as shown in Figure 2.1, is essentially a continuous steel section with holes applied as a secondary process. The PCS reinforcement provides longitudinal and transverse reinforcement simultaneously and can be used in circular or rectangular sections. This monolithic connection reduces the need for separate longitudinal and transverse reinforcement. PCS can be used as reinforcement in columns, shear walls, foundations or beams. PCS reinforcement can be concentrically layered if large reinforcement ratios are required (Figure 2.2). For a column, vertical steel strips provide longitudinal reinforcement while the horizontal steel strips provide transverse reinforcement. Tests have shown that PCS provides higher confinement capacities than traditional rebar reinforcement systems (Shamsai and Sezen 2005).2.2.1 PCS ProductionPCS reinforcement is produced from steel tubes or plates. Standard steel tubes or plates are punched or cut to provide holes with the desired dimensions. In lieu of tubes, steel plates can be bent into the required shape and then welded. Casting of PCS reinforcement has also been suggested as a method of production.Cutting of holes in the PCS can be performed with a variety of methods including laser (as shown in Figure 2.3), plasma, flame, and abrasive water jet cutting. Additional suggested methods include milling, electrochemical machining, electrical discharge machining, and chemical etching. Precision, time, cost, availability, and thickness limitations vary among the different cutting methods (Shamsai 2006).Punching holes to form the PCS reinforcement is suggested for mass production. Computer numerical control (CNC) machines can program the punching spaces and dimensions for PCS reinforcement. Three suggested CNC punching machines include a single station press, a mechanical turret punch press, and a hydraulic turret punch press. Punching also has disadvantages including steel thickness restrictions and possible steel deformations (Shamsai 2006).2.2.2 PCS BenefitsPCS 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 provides increased flexural capacity, using the same amount of steel as a traditional rebar system, and results in more efficient use of the reinforcing steel. The monolithic action of PCS eliminates separation of longitudinal and transverse reinforcement. Additionally, PCS reinforcement is spread in a planar configuration which offers greater confinement than re