Load Point selection in Moving Load Analysis Control

Question:

Hello,

I have a question regarding my grillage model. I’m doing a check for Vmax on member 66 (a member near the support) under the FLS load case. The FLS load case runs a vehicle concentrically along girder line 3 and uses the cross beam method to distribute the load. Using the moving load tracer, it indicates that two of the vehicle axles are located on span 1 resulting in a positive shear (or uplift) of approximately 40 kN. Could you please indicate how this vehicle position results in a positive shear in the model? Please let me know if there is something wrong with my model because this result does not make sense. The shear force diagram provided is not equivalent to the vehicle position for element 66 MVmax case. I would expect two sets of axles with each axle multiplied by the respective DLA value.



Answer:Hello,

When the moving load tracer feature is used, the max and min moving load cases represent the positive and negative output respectively. Now, we were checking the MVmax case. Hence, the output was positive at i end of element no. 66. If this particular position is converted into a static load case and then its shear diagram is checked, the results are as below.

To create the static load case, follow the steps as shown in the image below.


Actually, its the moving load analysis control options that is causing only 1 axle to act. Kindly refer the image below for the option being used in the model that was sent to us.


When the influence line dependent option is selected, if the result being checked is for Maximum, only the positive Influence zone loads are converted into static loads. The loads reducing the worst effects are not converted into static load. For element 66 at I end and for shear due to max moving load case, the worst effect is caused only by second last axle of the vehicle while the last axle relieves this effect. Hence when converting into static load case, only 1 axle loads are added. The last axle is ignored.

If this is not the way it is required, kindly use the other option (All Points) in the Load point selection. Once this is done, the results would be as per your expectations. More details on these options could be referred to in the online help manual (Link).
Creation date: 10/27/2017 5:31 AM ()      Updated: 10/27/2017 3:10 PM ()
Files
DataImage97.png
resend