An important item which concerns moving-load analysis is that certain vehicle types, including the AASHTO double truck (HL-93S), apply only for negative moment at supports and for interior reactions. These response quantities are defined under Usage on the General Vehicle Data form shown in Figure 1:
Figure 1 - General Vehicle Data
Next, structural objects which exhibit negative moment at supports or interior reactions should be designated using vehicle response components, as described in the CSI Analysis Reference Manual (Vehicle Response Components, page 446) and the attached PDF.
To satisfy AASHTO requirements, HL-93S vehicles should be applied using either of the following two methods:
- Coordinate these response components with the HL-93S vehicle by assigning vehicle-response-component overwrites through Assign > Frame Loads or Area Loads > Vehicle Response Components. For complex models, however, this process may require significant effort.
- Generate conservative results by modifying the vehicle definition to include Usage > All Other Responses. As a result, the HL-93S vehicle is used for all response measures, which is appropriate when the positive moments induced by HL-93S vehicles are similar to those of HL-93K vehicles.
