In Memory Member Splitting and Node Merging
Description:
In Bentley Structural V8i, the ability to export to STAAD.Pro without creating an analysis model in Bentley Structural was introduced. This is achieved with the new "Physical Only" option on the export dialog. The analysis model is said to be created "in memory" upon export to STAAD. This topic describes how the analytical elements are split and nodes merged "in memory".
To correctly model connections between the end of one member and the end of another it is necessary to connect the respective analytical elements by a common node. Similarly, to correctly model connections between the end of one member and another at some arbitrary point along its length where no node exists, it is necessary to divide a segment into two by inserting a node. When synthesizing an analysis model from a physical model, differences in member cross-sections cause the ends of the resulting wireframe elements to be disconnected. To determine where connections should exist in the wireframe analysis model, a tolerance value is used. Any two member ends (nodes) which have a distance less than the tolerance value will be merged. Similarly, any node, within the tolerance distance from a member, will be projected onto the member and the member will be split into two.
Member Splitting - The process of dividing a member's analytical representation in multiple segments by inserting nodes between the two end nodes. Node Merging - The process of replacing the end node of a member with a nearby node which is connected by another member such that a common joint is created and the total number of nodes is reduced.
Figure 1 - Node Merging
Figure 2 - Member Splitting
Figure 3 - Combined Merging and Splitting
Figure 4 - Setting the node tolerance
Example:
Figure 5 - Small building model with node tolerance set to zero; members 5 and 6 are NOT split and there are disconnected nodes at the tops of columns
Figure 6 - Same small building model as in Figure 5 above exported with node tolerance set to three (3) inches; members five(5) and six (6) have been split and all members connect to a single node at the top of each column.