In moving load analysis, there is one important item that you should be aware of. Certain types of vehicles, such as the AASHTO "double truck" (HL-93S), apply only for negative moments at supports and for interior reactions. This is defined by checking the appropriate items in the Usage data set as shown below:

Now, SAP2000 does not "know" what elements and their internal forces represent negative moments at supports or interior reactions, unless we designate these elements for SAP2000 as such. For this purpose, the program uses the concept of vehicle response components, which is described in CSI Analysis Reference Manual, chapter "Bridge Analysis", section "Vehicle Response Components" and further explained in the attached note.

Depending on the particular model, you may consider the following two approaches apply the HL-93S vehicle to satisfy the AASHTO requirements:

(1) You could assign vehicle response component overwrites using "Assign > Frame Loads (or Area Loads) > Vehicle Response Components" menu command to designate the response components which should be used for the HL-93S vehicle. However, for certain types of complex models, this may require significant effort.

(2) You could simply obtain conservative results by modifying the vehicle definition to include "All Other Responses" in the vehicle usage. This way the HL-93S vehicle would be used for all responses. This may be appropriate when the positive moments due to HL-93S vehicle are expected to be similar to positive moments due to HL-93K vehicle.

Attachements

• Vehicle Response Components (PDF File, 122 KB)