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This page 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 are transverse moving loads applied?
Answer: Moving loads are only applied in the gravity direction. Equivalent static forces may be applied in the lateral direction to evaluate response from centrifugal, wind, or braking forces.
If necessary, lateral moving loads may be evaluated in a separate model using the following approach:
- Create a copy of the model, then rotate the entire model, about the global x-axis, by 90 degrees. The lateral direction of the actual structure will then align with the gravity direction of the computational model.
- Next, apply and evaluate moving loads. Use zero-width lanes such that lane definition from the original model may be used again.
- Use a post-processing procedure in Excel or by another means to superimpose response from lateral moving-load analysis with that from the original model.
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 step-by-step moving-load analysis, once a load pattern of Bridge Live type is defined, select Modify Bridge Load to access the Multi-Step Bridge Live Load Pattern Generation form , where in which the speed of a moving truck may be specified.
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- For influence-based moving-load analysis, where in which Moving Load is specified for load-case type, the vehicle automatically moves in two directions.
- For step-by-step moving-load analysis, where 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 form.
- To obtain Multi-step Static response for a vehicle which 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
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Influence-based frequently asked questions are listed as follows:
How is the load from each truck axle distributed over shell objects?
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Answer: For response, please see the Influence-based moving-load analysis implementation and Lane-load point connection articles.
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Why does
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deformed configuration
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from moving-load analysis not look correct?
Answer: Influence-based analysis results are multi-valued, meaning that minimum and maximum response values are generated for each location of measurement. Both positive and negative displacement values are plotted, depending on which has the greatest absolute value. To see only the minimum or maximum deflection set, data may be reviewed in tabular output.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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Related IncidentIncidents: Principal stresses in moving load analysis:
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Question 1: How does the program place the vehicle to calculate maximum effect? What algorithm is used? open-questionAnswer 1: OPEN QUESTION |
Step-by-step
Step-by-step
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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