FAQ: 3D Bridge

What defines the stake-out line, and is it related to the CL primary lane?

The stake-out line serves as the reference point for defining lane alignments, which represent various lane configurations achievable over the bridge deck. These alignments run parallel to the stake-out line, and users determine the left/right boundaries relative to this line.

How can Traffic load patterns be deleted?

Traffic load patterns can be deleted like any other load case: simply right-click on the object and select "Erase."

Are the "factor" values referring to “alpha factors” for lanes according to national annex standards?

The “factor” value serves multiple purposes. When a vehicle is defined with unit loads, it acts as a load factor. Alternatively, if the vehicle is defined with a characteristic load model, the "factor" represents the code-defined alpha value.

Regarding load modifiers and dynamic factors, is the dynamic factor specific to certain types of loads, like Type Vehicle, and already included in LM1 and LM2?

Load modifiers have versatile applications, including dynamic amplification or adherence to national annex-defined factors. This flexibility ensures adaptability across various load scenarios.

Why is the “wheel load ratio” locked in Carriageway loading?

The wheel load ratio feature, reflecting the ratio between tracks for trains, adheres to the specifications outlined in EN 1991-2 6.3.5 (1).

How does the lane alignment relate to the CL stake-out line, and can this be visually demonstrated during the definition process?

Lane alignment is measured with respect to the stake-out line: a negative number denotes the left-hand side, 0 represents the stake-out line, and positive values indicate the right-hand side.

Is mass generation the most intuitive and efficient workflow for managing multiple vehicles?

Currently, mass generation offers the most efficient workflow for managing multiple vehicles, simplifying the process of ordering results and combining vehicles into groups.

Could you provide a step-by-step procedure for understanding the workflow, possibly covered in the User guide?

Utilizing the Traffic load item involves high computational demand; thus, a prototype calculation is recommended before mass generation. This involves iterative adjustments to prototype load items to refine settings and inspect significant results. Subsequently, the Wizard and Mass generation tools facilitate the creation of load items for other result components.

What is the difference between Brute-force and Multistart optimization?

The Brute-force method systematically tests all discrete positions and values of vehicle parameters, whereas Multistart optimization employs an optimization algorithm for convex functions. Each method offers advantages and disadvantages in terms of speed and precision.

Why does the traffic load pattern feature create unit-moving loads instead of directly applying loads based on certain geometrical requirements?

Traffic load patterns generate moving loads associated with Moving loads, allowing for flexible positioning and editing of load configurations.

What is the purpose of "U resultset" and "Uclone" as mentioned in the guide?

"U resultset" and "Uclone" facilitate calculations in models with limit-state dependent materials, reducing computational time by offering options for selected result components.

How are priority ratings understood and applied?

Priority ratings influence geometrically exclusive vehicles in traffic load models, determining the order of vehicles in the maximization process.

Can vehicles with different psi-factors, such as LM1 TS and UDL, be in the same load pattern?

Yes, vehicles with different psi-factors can be included in the same load pattern, provided they share the same psi-factor in the load combination.

Is it possible to not run certain load cases (traffic load pattern) like load combinations?

Currently, all lane alignments can be disabled to avoid calculations for specific load cases.

Can the position of a load be frozen to observe its effect without generating a load case?

Presently, load case generation is limited to creating load cases without re-visualization or documentation capabilities.

Is it feasible to run load patterns on closed portal frame bridges with traffic on the bottom plate?

Yes, multiple traffic load patterns can be defined and coupled in load groups to accommodate closed portal frame bridges with traffic on the bottom plate.

How can the size of the influence graph be adjusted in moving loads?

The size of influence areas in moving loads can be adjusted within line/surface-moving load settings.

How are security class values (SK1, SK2, SK3 and SK4) determined through manual factors in Excel tables for custom load combination factors?

Certain values can be determined through manual factors in Excel tables within the custom setup for load combinations.

Is there a way to disregard vehicle loads that are outside the structure without affecting those partially inside?

Currently, there is no control mechanism in place to disregard vehicle loads outside the structure.

Can the visibility of all unit loads created as separate load cases be toggled off?

This feature is not available at present.

Why are there no reaction forces for line support and traffic load patterns?

Reaction forces are currently only developed for support groups.

Can the equilibrium be shown for different traffic load patterns to gauge the weight distribution on the bridge?

The ability to display equilibrium for different traffic load patterns is a feature request and poses challenges due to the variability of load scenarios and calculations within the FEM core.

Why is the load group for influence loads (TLC) not being disallowed when selecting a custom setup in load combinations?


When selecting a custom setup in load combinations, the grey color in the load group panel indicates that the load group for influence loads (TLC) is not considered in the "Max. of load group" calculation. As a result, regardless of the load group combination settings, this load group behaves as if it were deactivated for all load group combinations.


However, it's important to note that for load combination generation, checking or unchecking this checkbox has no effect. Therefore, unchecking this checkbox should not automatically deactivate the entire column. If users wish to completely disregard this load group (including for load combination generation), they should manually deactivate the cells in the column.

How does “transversal load positioning” effects my calculations?

The transversal load positioning is activated if the nominal width of the vehicle is smaller than the width of the designated lane in the “lane alignment”. An example can be the load model 2 (LM2) in EN 1991-2, 4.3.3 (1) which should be applied at any location on the carriageway. In FEM-Design only one lane can be applied in the “lane alignment” and the transversal load positioning will be tested on multiple positions within the lane during the maximum search since the default vehicle has a notional lane of 3 m.


Shaho is the author of this solution article.

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