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*NOTE:* While created for [SAP2000|sap2000:home], this article also applies to [CSiBridge|csibridge:home].
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An important item which concerns [moving-load|kb:Moving-load analysis] 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:

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!Vehicle_definition_usage_selection.png|align=center,border=0!

{center-text}Figure 1 - General Vehicle Data{center-text}

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Next, structural objects which exhibit negative moment at supports or interior reactions should be designated using vehicle response components, as described in the {new-tab-link:http://www.csiberkeley.com/}CSI{new-tab-link} [_Analysis Reference Manual_|doc: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.
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* 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.


h1. Attachments

* [Vehicle Response Components |^Vehicle_Response_Components.pdf] (PDF)