Design Research Of Anchors For Prestressing Carbon Fiber Reinforced Plastics Tendons

During the past half century ,the use of prestressing members has increased tremendously in a various of structure. However, like general reinforcement concrete structure ,a main problem in prestressed concrete is the poor corrosion resistance of steel tendon which may lead to the lower durability construction . This make a number of prestressed structures need to be strengthened , which cause vast economic losses . Many researcher began to pay attention to steel tendon corrosion and provided some useful measurements .More recently , a effective idea is the way to replacing steel tendon or prestressing strands with the fibre reinforced plastics or polymer in reinforcement concrete.Fibre reinforced plastics (FRP) is composed of fiber filament and a resin matrix. The fiber of high tensile strength and high modulus of elasticity is used as reinforcing material . The synthetic resin is used as matrix material and is mixed with adequate auxiliaries . The fiber reinforced plastic rebar is manufactured using a pultrusion method and necessary surface process . It offers significant advantages over conventional reinforcing , namely , high tensile strength to weight ratio , excellent corrosion resistance , high fatigue strength and electro -magnetic neutrality . As a result , replacing steel bar with FRP in reinforcement concrete may effectively overcome corrosion of steel tendon and increase structural durability.Conventional anchors for steel tendon are inadequate to FRP due to the relative weakness of FRP tendon in the transverse direction . The key problem facing the application of FRP tendons in prestressed concrete is the development of an appropriate anchorage system . At present , two main types of anchors are usually used with FRP tendons : mechanical gripping anchors and bond type anchors . These anchors may essentially satisfy the engineering needs . But there are still some shortcomings in these anchors : 1.Excessive radial pressure on FRP tendon exerted by wedge result in premature failure in anchorage zone . 2.The creep of resin as boned material results hi the losses of prestressing stress and the long -term stability is poor . hi words , available anchors are not perfect and can not satisfy all the technical requirements of a post- tensioning anchorage -tendon assembly . This dissertation try to design adequate anchorage for CFRP to eliminate such defect hi available anchors .This dissertation consists of seven parts . A brief description of the key problem existed in reinforcement concrete , the historical development , the production process and the advantages of FRP tendon is given in Chapter 1 and chapter 2 . The short- term and long- term mechanical properties of the common types of FRP reinforcement are also summarized . In chapter 3 , the common anchors for steel tendon are outlined and the wedge anchor is preliminary analysed . In chapter 4 , some current available anchors for FRP tendon at home and abroad are introduced and the performances , the failure mode and the problem needed to be solved of various anchors are dealt with . In chapter 5 , the technical requirements of FRP anchors are summarized . Two concepts are presented to reduce stress peak in anchorage zone : the soft zone concept and the differential angle concept, and a dedicated numerical method using the theory of elasticity has been developed . Then , using the differential angle concept, a new stainless steel anchorage for CFRP has been developed according to comparing the stress distribution on CFRP in different angle of anchor .There are relative uniform stresses on CFRP tendon in this new anchor. On the basis of steel anchor , a new type of concrete anchor is designed , followed by brief introduction of the properties of ultra -high performance concrete . In chapter 6 , the bond mechanisms and influential factors to FRP and concrete , mortar , resin are discussed . The bond stress, the stress of FRP and embedment length are also dealt with . A complex anchorage system, which may get over the default in long- term perfo...