# Load Combinations

**Question:**

Good afternoon,

I have a model and I want to obtain the results under permanent state.

In order to do that, I have created two artificial construction stages CS1 and CS2. CS1 is for time equal to zero, and CS2 is after 10000 days in order to account the effects of creep and shrinkage in the long term.

In the results, I want to obtain the internal forces and deflections under deal loads, superimposed dead loads and prestress after all time dependent effects.

However, it is not clear to me what is the difference in obtaining these results, (1) using dead loads from CS or (2) the summation of dead and superimposed dead load from Post-CS.

In my model the results from these two load combinations are different, whereas I would excepted them to be the same.

Could you please explain me why? Could you please also let me know which is the right way to obtain the required results, for example for deflections?

or

I have attached my model.

Thank you

**Answer:**

Hello,

Greetings.

Thanks for reaching us.

The difference between construction stage results and static load results is due to the value of E (Elastic Modulus).

The static load case results uses elastic modulus as defined in material properties.

But the construction stage uses elastic modulus as per compressive strength gain function and activation age. For CS1, elements are activated at 28 days and E value is different from the material inputted as shown below.

So, if we remove the compressive strength gain function, the results obtained are similar as shown below.

Similarly, if we change the material input elastic modulus to value of compressive strength gain function as shown below, it will also yield same deflection in this case.

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Grillage_Model_ULS_Spring_LL_Opt_Tend.mcb 1 MB |