Vehicle Class - AASHTO Moving Load Analysis

Question:

MIDAS tech,
I have a few questions regarding the HS20-44 lane loading.
1. I’m looking at the LL tracer for element 1014 for maximum shear. The moving load case 2 includes the program default for the 0.64 klf and 26 kips moving shear load. When I tried to pull this out of the model and separately add the 0.64 klf and 26 kips moving shear, the results are very different and the placement of the loads are very different. Why might this be? It appears that only the lane load is applied in 1 lane and only the point loads in one lane.
Figure 1: HS20-44 Lane C for shear (Vxx) LL tracer results
Figure 2: HS20-44L for shear (Vxx) LL tracer results
Note that I did change the impact to 10% on HS20-44L and only want the 10% impact on the point loads for HS20-44 Lane C. So the results should be a little different, but not this extreme. Definitely should be seeing the same pattern of LL positioning.
2. Also, why isn’t there another lane load and point loads for the next adjacent span when I separate this out?
Thanks,

---

Answer: Hello User,

There is a difference between combined and independent option when using with same vehicle.
We have two different things here,
1) Vehicle or Vehicle Class.
2) Combined or Independent option
It took some time for me to make trial runs, and I compared in the attached spreadsheet. Please check it out.
Combined or Independent option works with different vehicle classes but not for same vehicle. If we use one same vehicle in different sub-load cases, then combined and independent will give same result.

So correct comparison can be done when 'HS20-44 Lane Point Loads' and 'HS20-44 Lane only' should be made under vehicle classes, and then used for making combined loading effect in moving load cases.




kindly reply back if you have any further issues.
Regards,