1、原文 Construction and Building Materials Volume 21, Issue 5 , May 2007, Pages 1052-1060 An approach to determine long-term behavior of concrete members prestressed with FRP tendons Abstract The combined effects of creep and shrinkage of concrete and relaxation of prestressing tendons cause gradual cha
2、nges in the stresses in both concrete and prestressing tendons. A simple method is presented to calculate the long-term prestress loss and the long-term change in concrete stresses in continuous prestressed concrete members with either carbon fiber reinforced polymer (CFRP) or aramid fiber reinforce
3、d polymer (AFRP) tendons. The method satisfies the requirements of equilibrium and compatibility and avoids the use of any empirical multipliers. A simple graph is proposed to evaluate the reduced relaxation in AFRP tendons. It is shown that the prestress loss in FRP tendons is significantly less th
4、an that when using prestressing steel, mainly because of the lower moduli of elasticity of FRP tendons. The long-term changes in concrete stresses and deflection can be either smaller or greater than those of comparable girders prestressed with steel tendons, depending on the type of FRP tendons and
5、 the initial stress profile of the cross-section under consideration. Keywords: Creep； FRP； Long-term； Prestress loss； Prestressed concrete； Relaxation； Shrinkage Nomenclature A area of cross section d vertical distance measured from top fiber of cross section E modulus of elasticity age-adjusted el
6、asticity modulus of concrete fpu ultimate strength of prestressing tendon - 2 - h total thickness of concrete cross section I second moment of area O centroid of age-adjusted transformed section t final time (end of service life of concrete member) t0 concrete age at prestressing y coordinate of any
7、 fiber measured downward from O aging coefficient r reduced relaxation coefficient ratio of modulus of elasticity of FRP or steel to that of concrete c(t,t0) change in concrete strain between time t0 and t O change in axial strain at the centroid of age-adjusted transformed section O c(t,t0) stress
8、applied gradually from time t0 to its full amount at time t pr intrinsic relaxation reduced relaxation p total long-term prestress loss change in curvature cs shrinkage strain of concrete between t0 and t c(t0) instantaneous strain at time t0 (t, t0) creep coefficient between t0 and t c(t0) stress a
9、pplied at time t0 and sustained to a later time t p0 initial stress of prestressing tendon reinforcement ratio curvature the ratio of the difference between the total prestress loss and intrinsic relaxation to the initial stress Subscripts 1 transformed section at t0 c concrete cc net concrete secti
10、on - 3 - f FRP reinforcement or flange p prestressing FRP tendon ps prestressing steel tendon s steel reinforcement Article Outline Nomenclature 1. Introduction 2. Relaxation of FRP prestressing tendons 3. Proposed method of analysis 3.1. Initial steps 3.2. Time-dependent change in concrete stress 3
11、.3. Long-term deflection 4. Application to continuous girders 5. Development of design aids 6. Illustrative example 7. Summary Acknowledgements References 1. Introduction The use of fiber reinforced polymer (FRP) tendons as prestressing reinforcements have been proposed in the past decade and a few
12、concrete bridges have already been constructed utilizing fiber reinforced polymer (FRP) tendons. Compared to conventional steel prestressing tendons, FRP tendons have many advantages, including their noncorrosive and nonconductive properties, lightweight, and high tensile strength. Most of the resea
13、rch conducted on concrete girders prestressed with FRP tendons has focused on the short-term behavior of prestressed members； research findings on the long-term behavior of concrete members with FRP tendons are scarce in the literature. The recent ACI Committee report on prestressing concrete structures
