Two Span Composite Steel Girder Moving Load Analysis

Question:

Question 1:
When defining a Moving Load Case there is a Sub-Load Case input box for each vehicle class. There is a "Scale Factor" input box. What does the scale factor represent?

Question 2:
As Per 2012 AASHTO LRFD Sec. 3.6.1.3.1 the extreme force effect due to vehicle live load for negative moment between points of contraflexure under a uniform load on all spans at interior piers shall be taken as 90% of the effect of two design trucks (HL-93 Truck) placed a minimum of 50ft. apart (lead axle of one truck and rear axle of the other truck) in the same lane and having 14ft. spacing between the two 32kips axles. Does Midas run this scenario? and if so how can I achieve that? It also states that the two design trucks shall be placed in adjacent spans to produce the maximum force effects.

Also is there a way to run the moving load cases with two HL-93 Truck Vehicles loaded in the same lane at the same time?

Thank you

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Answer:Hi,

1. Program will consider the value of wheel load which is multiplied with the scale factor. You can use the scale factor for 2-D plane analysis to apply distribution factor which is specified in the design code. It is not used for 3-D analysis.
2. If you intend to design in AASHTO LRFD, there are functions to consider about negative moment in the code named “Lane Supports-Nagative Moments at Interior Piers” and “Lane Supports-Reactions at Interior Piers”.
Please refer to the following path of functions and link to the online manual.
Main Menu > Load > Moving Load > Lane Supports - Negative Moments at Interior Piers.
http://manual.midasuser.com/EN_Common/Civil/856/Start/05_Load/07_Moving_Load_Analysis_Data/Lane_Supports-Negative_Moments_at_Interior_Piers.htm
Main Menu > Moving Load > Lane Supports - Reactions at Interior Piers.
http://manual.midasuser.com/EN_Common/Civil/856/Start/05_Load/07_Moving_Load_Analysis_Data/Lane_Supports-Reactions_at_Interior_Piers.htm
And you should check on “Span start” where supports are defined on “Traffic Line Lanes” dialog.
Then you can view two trucks.

Thanks & Regards,
Jihoon kang