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General
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General frequently asked questions are listed as follows:
How
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are transverse moving
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loads
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applied?
Answer: Transverse (horizontal) moving loads are available since CSiBridge V17.2.0. Braking, acceleration and centrifugal horizontal loads can be defined.
How is the speed of a moving truck changed?
Answer: For
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 -load analysis, once a load pattern of type BRIDGE LIVE and then click modify bridge load button Bridge Live type is defined, select Modify Bridge Load to access the "Multi-Step Bridge Live Load Pattern Generation" form form in which the speed of a moving truck may be specified.
When
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a vehicle
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is defined, how are two directions specified for its path of motion?
Answer: Depending upon analysis type, direction may be defined as follows:
- For influence-based moving-load analysis
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- , in which Moving Load is specified for load-case type, the vehicle
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- automatically
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- moves in two directions.
- For step-by-step moving-load analysis
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- , in which Multi-step Static is specified for load-case type, Forward or Backward vehicle direction may be specified on the Multi-Step Bridge Live Load Pattern Generation
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- form.
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- Multi-step
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- Static response for a vehicle which
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- may travel in either direction, results from Forward and Backward patterns may be enveloped.
Why are my bridge objects returning zero force during moving-load analysis?
Answer: The request for saving section forces should be made such that bridge objects return the proper response during moving-load analysis.
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Influence-based
Influence-based frequently asked questions are listed as follows:
How is the load from each truck axle distributed over shell objects?
Answer: During influence-based moving-load analysis, an interpolated influence surface determines the effect of loading from each truck axle. For additional details, please see the Influence-based moving-load analysis implementation article.
How are unit loads distributed from lane-load points to model joints?
Answer: For response, please see the Influence-based moving-load analysis implementation and Lane-load point connection articles.
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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?
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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.
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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.
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Why does deformed configuration from moving-load analysis not look correct?
See Deformed shape for moving load analysis.
Why are zero results generated for a bridge object which is updated as a solid model?
Answer: Analysis > Bridge Response > Moving Load Case Results Saved > Section Cuts must be selected for solid models, while it is not necessary for frame and shell models.
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| no | 23133 | comment | Enhancement for principal stresses in moving load analysis.
Step-by-step
Step-by-step frequently asked questions are listed as follows:
Why does step-by-step moving-load analysis not run when the vehicle is defined using a uniform load?
Answer: Vehicles defined using a uniform load may only be used during influence-based moving-load analysis. To use such a vehicle in step-by-step moving-load analysis, the uniform load would need to be approximated and modeled using a series of equivalent point loads.
Influence-line
Influence-line frequently asked questions are listed as follows:
Why is the influence line not displayed as a smooth line?
Answer: Influence lines will appear piecewise linear when discretization is more coarse. A similar effect occurs when output-station spacing is fairly large for moment-diagram plots. The effect of refining lane discretization (Figure 1) is apparent in the influence lines which follow (Figure 2):
Figure 1 - Lane data
Figure 2 - Influence line