How to consider different notional size for creep calculations for plate elements in orthogonal directions?
Question:
The plate deck elements will be experiencing creep and shrinkage in two directions. The notational thickness under CEB-FIP considers the perimeter around the plane perpendicular to the expected effect. In the case of prestressing/post-tensioning in two directions, that perimeter and area will be different and therefore the creep and shrinkage effects will be different. The Midas input appears to only allow for a single notational thickness to be entered and therefore the effect is applied equally in both directions.
Answer:
This is more of an engineering limitation of this method of applying the creep. However, there is a simple solution to this.
Generally, what engineers do in this situation is a bit of approximation, and the notional size for a deck is considered as its thickness, the justification for which is as below.
The plate deck elements will be experiencing creep and shrinkage in two directions. The notational thickness under CEB-FIP considers the perimeter around the plane perpendicular to the expected effect. In the case of prestressing/post-tensioning in two directions, that perimeter and area will be different and therefore the creep and shrinkage effects will be different. The Midas input appears to only allow for a single notational thickness to be entered and therefore the effect is applied equally in both directions.
How can I accurately model different C&S effects in each direction in Midas?
Answer:
This is more of an engineering limitation of this method of applying the creep. However, there is a simple solution to this.
Generally, what engineers do in this situation is a bit of approximation, and the notional size for a deck is considered as its thickness, the justification for which is as below.
A sample calculation for a deck that is 200ft long and 20 ft wide with a thickness of 6 inches could be referred to below.
So, this justification holds true for both longitudinal as well as transverse directions.
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