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Composite bridge deck design

Question:

Hi,

We are currently working on a twin girder composite bridge using a grillage model.

I would like to model the longitudinal beam element as composite section including the steel section and equivalent width of the deck slab. 

I wanted to understand if I will need 2 separate model for modelling the short term and long term load or whether Midas can distinguish between short term and long term load and apply the modular ratio accordingly.


Answer:

Hello,

Actually, construction stage analysis is generally used where time dependent properties (compressive strength gain, creep and shrinkage) are defined and based on that time dependent properties, the effects for long term load are observed.  
Post CS stage (after construction stage), concrete would have gained strength and short term loads are applied generally after construction stages as modular ratio is observed accordingly.

But if construction stage analysis is not to be performed, short term and long term modular ratio can be defined while defining the composite section property as shown below.
Note: These modular ratios are overridden if construction stage analysis is performed. 


A separate boundary group will be created which has updated section stiffness scale factor for long term (Es/Ec creep) which needs to be activated for long term loads in the "boundary Change Assignment" option under Analysis control as shown below.


A short video has been attached for reference where application of modular ratio and results for SW using long term modular ratio and short term modular ratio is compared for non-construction stage process.

Question: Hi,
Thanks for the clarification. 

I am assuming Midas will take Creep into account for any loadcase we include in the construction stage (i.e. Super Imposed Dead Loads etc.)?
 
Answer:
Hello,

Yes, creep and other time dependent effects will be taken care in construction stage analysis itself and we need not define short term and long term loading and corresponding modular ratio in that process.  The whole process and sequence is simulated by the midas in construction stage analysis.
Creation date: 5/31/2021 5:13 PM (jatin2010)      Updated: 5/31/2021 5:13 PM ()
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long-short term.mp4
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Steel Composite Bridge_Postcs.mcb
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