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is devoted to frequently asked questions (FAQ) related to moving-load analysis. |
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General
General
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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 replace 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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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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Question 1: How does the program place the vehicle to calculate maximum effect? What algorithm is used? Answer 1: OPEN QUESTION |
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