Model Merge

Model Merge is a feature located on the Modify ribbon that scans through your model and automatically merges elements in the model. Model Merge detects unconnected nodes along member spans, unconnected crossing members and duplicate nodes, members and plates. You can use Model Merge to build models faster, as well as to detect and fix modeling errors.

Click on image to enlarge it

Knowing what Model Merge does allows you to skip modeling steps as you build your model and let the software perform these steps for you.  You can take advantage of Model Merge in modeling your structure in many ways, some of which are discussed in the following links.

What do you want to do?

• Perform a model merge

What do you want to know?

• What are the limitations of Model Merge?
• How can I control Model Merge?
• What are some examples of Model Merge?
• What is the Model Merge process?

Model Merge Options

There are four main options for the model merge.

• If the Merge Crossing Members box is checked then as part of the merge process, all members will be scanned along their lengths for crossing members. Crossing members will be merged together at their intersection points. If you have cross bracing you may or may not want them to be merged. A finite element crossing a physical member will cause only  the finite element to be broken up at the point of intersection. If two physical members are crossing, a node will be placed at the intersection point.

• Merge Inactive Members if left unchecked allows you to limit the merge process to the parts of your model that are selected. This allows you to prevent the program from merging portions of your model where you may have intentionally put nodes at the same location or have two members next to each other.

• Trim/Extend Crossing Beams can help connect member ends that are within the merge tolerance from an adjacent beam. Checking this box will move the end node of that member so that it lies on the adjacent beam.

• Trim/Extend Crossing Wall Panels can help when you have two wall panels that are overlapping or intersecting by a distance smaller than the merge tolerance. This allows you to easily correct minor modeling flaws. This will also correct the condition where a defined wall panel is non-coplanar.

A ‘Merge Tolerance’ feature that defines the maximum distance 2 nodes can be apart and still be merged together, affects the overall Model Merge feature. It is also used when scanning for crossing members and for unattached nodes along the spans of members. See Merge Tolerance under ‘Model Settings’ for more information.

Model Merge Examples

Looking at this frame, consider the column line on the right side, members 1-7 and 7-13. If you did not use Physical Members you would define this just that way, as two separate members. With the model merge capability you could instead enter a single member definition, 1-13, and let the model merge function break it up for you.

Other convenient uses of the model merge function are laying out floor plans and being able to draw all the nodes right over the main girders or defining truss chords as full length rather than specifying each panel point. The model merge will take care of breaking up the members at all the intersecting points. Of course the Physical Member feature goes a step farther for these situations because these members never need to be split to model a connection – allowing you to make edits and understand results more readily. See Physical Members to learn more.

Model Merge Limitations

Certain types of shape types and certain load types can cause members to not get broken up by the model merge function. In particular, members that are Tapered WF shapes will not get broken up by the model merge. Even if such members have intermediate unattached nodes, or crossing members within their spans, they will not be broken up.

Model Merge Process

1. Duplicate nodes are merged together.
2. All the members are scanned for other members crossing along their span. If a crossing member is found, a nodes is created at the intersection point.
3. All the members are scanned for nodes along their span. If found, the member is broken up into pieces to incorporate the nodes.
4. Duplicate members are merged together. Physical members take precedence over finite element members. Longer members take precedence over shorter members that are fully coincident with the longer member. When duplicate members with different section sets are merged, the set listed first in the Sections Sets spreadsheet are used.
5. Duplicate plates are merged together. 

To better understand how the model merge function works, please refer to this figure:

Diagram A shows the model before a merge. The two column lines are separated in diagrams A and B strictly for ease of viewing, they should be considered to be right on top of each other. Nodes 1 and 5 (in diagram A) have exactly the same coordinates, as do nodes 3 and 10.  None of these members are Physical Members.

Step 1 of the merge eliminates duplicate joints changing the model from diagram A to diagram B. On diagram A, nodes 1 and 5 are duplicates (same coordinates), as are nodes 3 and 10. Nodes 5 and 10 are merged into nodes 1 and 3 respectively. This means any loads applied to nodes 5 and 10 are now applied to nodes 1 and 3. Any members connected to 5 and 10 are now connected to nodes 1 and 3 (these members are shown with the inclined lines in diagram B).

Step 2 looks for crossing members, however, there aren't any for this particular example. Members that are parallel to each other aren't treated as "crossing" since the end nodes of overlapping members will be merged in Step 3.

Step 3 is where the members are scanned for intermediate span nodes. This takes us from diagram B to diagram C.  Referring to diagram B, member 1-2 has two intermediate nodes (5 and 6), member 6-7 has one intermediate node (node 2), and so on. The members with intermediate joints are broken up, shown in diagram C.

Step 4 eliminates duplicate members, in this case those that were created in step 2. This takes us from diagram C to diagram D. Looking at diagram C, the duplicate members are shown as the double lines.  The first member listed on the Member spreadsheet is maintained and the other member is deleted. Any loads applied to the deleted member are transferred to the remaining member.

The final merged model is shown in diagram D. The column line is now comprised of 8 members, 1-5, 5-6, 6-2, etc. up to member 9-4.

Perform a Model Merge

To perform a Model Merge:

1. In the current model view window, select the items you wish to merge.

   Typically you will want everything to be selected.

2. Go to the Modify ribbon.
3. Click on the Model Merge icon to bring up the model merge parameter window.

4. Set the parameters for the new merge.

   For help on an item, click the Help icon and then click the item.

5. Click Apply All or Apply Selected to apply the model merge to the entire model or items you selected.