This page contains frequently asked questions related to moving load analysis.

General FAQ

How can I apply transverse moving load?

Moving loads can be applied only in the gravity direction. Response for lateral loads due to centrifugal, wind and braking forces would need to be evaluated by applying equivalent static forces in lateral direction.

If absolutely necessary, you could try evaluating lateral moving loads in a separate model by the following manipulation:

• Create a copy of your model and rotate the entire model by 90 deg about global x axis. This rotation will align the lateral direction of the actual structure with the gravity direction in the SAP2000 model.
• Apply and evaluate moving loads. I would recommend using zero width lanes, as this would enable you to reuse lane definition from the original model.
• Manually (outside of SAP2000) superimpose the response from the lateral moving load analysis with the results obtained from the original model.

How can I change speed of the moving truck?

You can define the speed of a moving truck for step-by-step moving load analysis by entering the desired value of speed on the the "Multi-Step Bridge Live Load Pattern Generation" form. Please note that you would first need to define a load pattern of type BRIDGE LIVE and then click modify bridge load button to access the "Multi Step Bridge Live Load Pattern Generation" form.

When we define a vehicle, which factor determines the direction of the movement of the vehicle? And how can we define a vehicle which can go in two directions?

For influence-based moving load analysis (load case type "Moving Load"), the vehicle is automatically moved in two directions. For step-by-step moving load analysis (load case type "Multi-step static"), you can specify the direction of vehicle movement as Forward or Backward on the "Multi Step Bridge Live Load Pattern Generation" form. To obtain multi step static response for a vehicle which can go in two directions, you could create an envelope of results for Forward and Backward motion of the vehicle.

Step-by-step FAQ

Why cannot I run the step-by-step moving load analysis when the vehicle defined using uniform load?

Vehicles defined uniform load can be used only in influence-based moving load analysis. To use the vehicle in the step-by-step moving load analysis, you would need to approximate the uniform load by a series of equivalent point loads.

Influence-based FAQ

How does the program place the vehicle to calculate maximum effect? What algorithm is used?

How exactly is each of the truck axle loads distributed over the adjacent shell elements in influence-based moving load analysis?

The effect of truck axle load is determined from interpolated influence surface. See Influence-based moving load analysis implementation page.

How exactly are the unit loads distributed from lane loading points to the model joints?

See Influence-based moving load analysis implementation and lane loading point connection pages.

The deflected shape for my moving load analysis does seem to look correct. Why?

The results of influence-based analysis are multivalued results (yielding min and max response components at each location). When deflected shape is plotted, the program determines the deflected shape from the deflections with maximum absolute values. This could be causing unexpected shape of the deformed shape when graphically reviewing the deflected shape. However, the minimum and maximum deflections for each joint can be found in the tabular output.

Why am I getting zero results for moving load analysis of a bridge object updated as solid model?

For solid models it is necessary to check the "Section Cuts" box on the "Moving Load Case Results Saved" form using command Analysis > Bridge Response. This is not needed for frame or shell models.