We are currently working on a RC garage model (11” slab thickness, max span ≈34’). We are noticing that our load history deflections are much larger than we are expecting.
When we run load history deflections we get a Final Instantaneous Deflection of 3.257” in our worst span.
We created a load combination based off of ACI 318-9.5.2.5 to compare this to. The load combination we created essential takes sustained loads (DL + 10%LL + 50%ParkingLL), multiplies them by the long-term multiplier from ACI, and then adds in Service loads (DL+LL). Using 2.0 as a conservative value for the long-term multiplier, our resulting load combination is as follows:
Using this formulation, we get a maximum deflection of 1.044" from the 'Max Deflection' plot under the load combination.
We are aware of some of the reasons stated in Section 65 of the Concept Manual as to why some deflection results are lower than those calculated in Load History deflections, but we are having a difficult time making sense of the difference being 3x what ACI predicts.
Are there any other reasons that could explain the large discrepancy?
I have attached the model in question for reference.
Thanks