Limitations and realistic application of equivalent load methods in pre-stressed concrete structures

The purpose of this paper is to investigate several important methods of obtaining the equivalent loads in pre-stressed concrete structures, and to compare the advantages and limitations of each method. The methods devised in this study include the use of curvature of tendon, characteristics of primary moment, self-equilibrium condition and linear segments approximation of tendon. Several important numerical examples, including simple and continuous beams, are presented to show the differences among the methods. It is shown that the equivalent loading system is not uniquely determined depending on the approach adopted to calculate the equivalent loads, which results in different section forces even from the same pre-stressed concrete structure. The self-equilibrium conditions of the equivalent loading system are discussed, which indicates that some parasitic reactions may arise by some approximate equivalent loads even for the determinate structures. The present study indicates that the equivalent load method can be applied to various types of pre-stressed concrete members in a rational and efficient manner by carefully obtaining the equivalent loads.