SAP2000 - RAMPTH Function in "Bridge Live"

Hallo everyone,

I have a question to SAP and the RAMPTH function and was hoping that somebody might be able to help me. I am trying to calculate the dynamic response of a multi-span Bridge.
In my calculations in excel I have used a triangular function to define the impact of a truck wheel on the bridge deck.

The displacements are similar to those in SAP2000. However, the values and the graphs for velocity and acceleration in SAP2000 do not match those in excel. I have used Newmarks direct integration method for both calculations (SAP2000 and Excel).

I am aware that where the load pattern type “Bridge Live” is selected, a separate time function (RAMPTH) is automatically created to apply the truck loads.
Does anyone know what analytical basis is applied in SAP2000 when this function is used? Is the basis of this function triangular?
Many thanks in advance.

Donna