Questions on Moving Loads as per AASHTO

When I choose "HL93TRK" as shown in the following figure, will the program automatically adjust the distance between the two back wheels of the truck when performing the moving analysis?




Question 2. If I want to fix the distance between two wheels of the truck, how should I do?

Question 3: Also I have a technical comment, please correct me if I'm wrong.
I downloaded the example of "Curved Steel Composite I-Girder Bridge Design" from your website to study to build my model.





I noticed that in this example, you treated the moving loads the same for the Fatigue and other load combinations.




I don't think it is correct, because based on AASHTO, the moving truck used for Fatigue load case should have fixed distance between the two back wheels as 30'.




If we use the moving load results of other load cases for Fatigue load, we will end up with very big member sections to satisfy the fatigue check condition.
If you agree with my comments, I suggest adding a separate truck type for fatigue in the above "Define Standard Vehicular Load" so that it will be easier to use.


Question 1: When I choose "HL93TRK" as shown in the following figure, will the program automatically adjust the distance between the two back wheels of the truck when performing the moving analysis?
Answer: Yes.

Question 2. If I want to fix the distance between two wheels of the truck, how should I do?
Answer: If the purpose is to define a vehicle for fatigue, there is a separate vehicle called HS20-FTG for which the distance is fixed as 30 feet. You can use this vehicle for fatigue.


Question 3: Also I have a technical comment, please correct me if I'm wrong. I downloaded the example of "Curved Steel Composite I-Girder Bridge Design" from your website to study to build my model. I noticed that in this example, you treated the moving loads the same for the Fatigue and other load combinations. I don't think it is correct, because based on AASHTO, the moving truck used for Fatigue load case should have fixed distance between the two back wheels as 30'. If we use the moving load results of other load cases for Fatigue load, we will end up with very big member sections to satisfy the fatigue check condition. If you agree with my comments, I suggest adding a separate truck type for fatigue in the above "Define Standard Vehicular Load" so that it will be easier to use.
Answer: Thank you for you feedback. We will correct the tutorial accordingly. As mentioned in the answer to the question 2, you can use 'HS20-FTG' vehicle for fatigue.