Question
During the construction stage analysis of PSC BOX, the moment significantly increases due to creep.
The current construction stage analysis for the PSC BOX bridge is as follows:
1. Girder construction begins after the completion of the pier construction.
2. Tendon tensioning on the 7th day after girder construction for tendons 3-3' and tensioning of the remaining tendons on the 28th day.
3. Application of secondary loads 200 days after girder construction and general loads after 5000 days.
Here, at the 28th day when all tendons are tensioned (CS2-First Step) and 200 days later (CS2-Last Step), I observe a significant increase in the moment at the last pier and girder in the Creep Secondary results, and I am unsure of the cause.
It's been 172 days, and I am uncertain if such an increase is normal.
Answer
During construction stage analysis, the age of concrete elements when activated should be input as the age when the concrete serves as a structural element after the removal of shoring and formwork.
If the age is input as 0, it may affect the results as the concrete does not function structurally.
In such cases, it is advised to modify the age to a value that corresponds to the actual situation.
For example, if the age is adjusted to 7 days considering the strength development of concrete, it is observed that the creep member forces also decrease.