The Studies On The Vibration And Working Performance Of Externally Prestressed Concrete Beams

The prestressing technique using external tendons is considered as an important part of unbonded prestressing system,has been used more and more in the new building and old ones, the relevant research has been progressed greatly, but most of the studies are on the static performance, and the stuies of dynamic performance are not enough, many relevant problems are still unsolved. In the structure dynamic performance, nature frequency is a very important parameter, the in-depth analysis on nature frequency is the research base of external prestressing concrete structure.The formulae for calculating frequency are derived from classical frequency equation with the influence of axial force and bending moment. The formula raised by Ayaho Miyamoto is improved and extended, some formulae for frequency calculation have been given when external tendons are arranged in three different configuration, many factors have been considered in the analysis of the beam vibration frequency, the unconstrained length of externally prestressed tendon is determined in reason, and some effective antivibration measures are provided in the end. The frequency change regulation of external prestressing beam is discussed in the paper, then the feasibility of detecting prestressing loss using vibration method is studied. Other problems of calculating frequency are analyzed in the paper, including the difference from the usual concrete structures prestressed with unbonded and bonded tendons, taking no account of stress increment and so on.The working performace of external prestressing concrete beam is studied in the paper, the calculatation methods of stiffness and crack are summarized and analyzed. The recommended value of the equivalent reduced coefficient of external tendon is 0.20, considering the contributions to stiffness and restraint to crack are smaller than those of bonded ones, and the results show good coincidence. Further analysis indicates the calculation of deflection and crack shall take into account many factors, such as second order effect,stress increment,concrete shrinkage and creep, temperature and so on.