A new strategy for analysis of erection stages including an efficient method for creep analysis

The paper presents an efficient numerical procedure for materially and geometrically nonlinear FE analysis of segmentally erected structures, including time dependent effects due to load history, creep, shrinkage and aging of the concrete. The main attribute of this procedure is its generality: the procedure is applicable to any kind of structure and does not require heavy coding. Modification of structure topology is carried out using an efficient procedure for creating/removing elements. The problem data are the reference configuration of the structure and the construction stages represented by an adding and removal time for each element. This procedure, presented here for beam elements, can be extended to any kind of finite element and allows the transforming of any standard FE code to deal with evolutionary structures.Besides, time effects have a strong influence, especially for concrete structures. These effects must be taken into account in the design process. To meet the demand of design offices, the model must be simple, efficient and scientifically sound. The approach presented in this article, is a good balance between these two objectives. This method is based on the fictitious loading age method with improvements to take into account recovery and to yield back the same final strain as superposition. The method requires only six variables at each Gauss point. At intermediate stages, the maximum discrepancy in strain observed is 5%. This method is applied to a complex stress history and compares favourably with results obtained by superposition.Application to the erection of a two-span cable stayed bridge is discussed at the end of the paper.