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The *layout line* is used to define horizontal and vertical bridge alignment.

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h1. FAQ

h2. For curve definition, both radius and end bearing need to be entered. What type of curve is being defined by this?

*Extended Question:* For circular curve, either radius or end bearing would be sufficient. Similar applies to transition curve. What curve is being defined and where is the radius measured? Related form: [Bridge layout line - horizontal layout data|migration1d:Bridge layout line - horizontal layout data-form]

*Answer*: An arc of specified constant specified is centered within the specified station range. If this arc length is less than the difference in stations, transitions are created of where the curvature varies linearly from 1/R at each end of the arc to zero at the corresponding station end point.

h2. What Z elevation should I use for my layout line definition?

*Extended Question:* Usually we prefer defining a [layout line|kb:layout line] to specify the lanes as it is so much convenient and elegant. However I wish to know where should the actual layout line Z level exist? For example in case of a straight deck with crown at center and sloping out if we choose the layout line Z coordinate same as the Z coordinate of crown of deck, then away from the centre line the Z coordinate of deck will be lower than the crown Z coordinate while lane Z will remain same as the Z coordinate of crown of deck. It is not clear to me whether this can affect the analysis and loading of deck?

*Answer:* The elevation of the layout line does not need to match the elevation of the riding surface. The Z elevation for the layout line should be above the elevation of the riding surface. The program will then distribute the lane loads to the joints immediately below the lane Z elevation. Therefore, the key is to define the layout line in the correct location in plan and _above_ the riding surface. After you define the lane from the layout line, you can check that the load is getting applied to the the correct joints via the ["Display > Show Lanes > Show All Points and Connections"|kb:Lane loading point connection] menu command. If the [lane loading points|kb:Lane loading point] are getting connected to joints below the riding surface you can further restrict the objects that should get loaded by the lane via the "Objects Loaded by Lane" option on the lane definition form.

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Related Incidents:

* {incident:no=32262|comments=Question on the significance of layout line Z elevation}
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h1. See Also

* [Baseline geometry tutorial|tutorials:Layout line geometry]