An algorithm for simulation of concrete cable-stayed bridges built on temporary supports and considering time dependent effects

摘要

The time-dependent phenomena effects might play an important role in the structural behavior of a cable-stayed bridge during construction and in service. In fact, because of these effects the target state of stresses (Objective Service Stage, OSS) can only be achieved at a certain target time. In the literature, a number of software have been presented to study creep and shrinkage effects during cantilever erection of cable-stayed bridges. Nevertheless, the effects of these phenomena in the alternative erection technique, the temporary support erection method, have received little attention. Furthermore, none of the presented software are able to: (1) Define a determined OSS for a given time including the time-dependent phenomena effects and the evolutionary erection of the superstructure. (2) Simulate the construction process assuring the achievement of a given OSS without the need of an overall iterative process taking into account time-dependent phenomena. (3) Provide the prestressing sequence in such a way that no additional tensioning operations are required to correct creep and shrinkage effects in service. To fill all these gaps, a new algorithm, the Forward-Direct Algorithm (FDA), is formally presented in this paper to simulate the construction process of cable-stayed bridges built on temporary supports. The main innovation of this algorithm consists of introducing the time-dependent phenomena effects into the unstressed length of the stays concept to calculate the prestressing strains to be introduced during the last re-tensioning operation. The application of the unstressed length concept has major advantages both in the simulation (as the OSS can be achieved without any overall iterative process) and in service (as re-tensioning operations to correct time-dependent phenomena effects can be avoided). To illustrate the creep and shrinkage effects during the construction and in service the FDA is applied to a real cable-stayed bridge. Furthermore, an analysis to define the optimum time to achieve the OSS is presented.