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Integral Analyses Model (IAM)

In this page basic strategies of IAM's are discussed. Furthermore, examples are displayed. 

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An Integral Analysis Model (IAM), is a model where a structure is analyzed on both structure and detail level. In this page basic strategies needed to develop an IAM are discussed. On the bottom of the page links to IAM examples can be found.

From structure level to connection level

In most cases, steel structures are modeled in finite element method software packages by using 1D elements. In these FEM-models the structure is analyzed on a structural level.  When all criteria of the structural model are satisfied, information can be extracted to do the analysis on a detail level. This can be a steel connection or a steel joint. In the following paragraph, a strategy will be explained how to extract the information needed for a connection from the FEM-model.

As mentioned before, 1D elements are used when modeling steel structures in FEM software packages. A steel structure will be therefore modeled as a wire frame. Within this wire frame, 1D elements are displayed as lines. Each line has a starting point and an ending point, see figures below. 

The information needed to analyze a connection, can be extracted by setting up a rule of logic based on the start and end points of these lines. The lines that occur in the model are stored in a list. To extract the lines from this list that are connected to a desired point, the following rule of logic can be coded: 

Rule of logic:
Every line that has a start or end point equal to the desired point is an attached line of the joint.

This rule of logic iterates over the list of lines and will collect attached lines. In the figure below the attached lines of the top left corner are highlighted.

 

Information needed for detail analysis:

  • Attached lines
  • Cross-section
  • Material (Steelgrade)
  • Loads per load case (N, Vz, Vy, Mt, My, Mz)
  • Hierarchy

Hierarchy of steel structures

Information needed for the detail analysis, which cannot be extracted from the FEM model is the hierarchy. Steel structures contain a particular hierarchy. The hierarchy determines if a beam is a primary, secondary or tertiary beam and whether a beam is continuous or ended. In the figure below, the joint in the top left corner is displayed. Three beams are attached to this joint, therefore 3! = 3*2*1 = 6 combinations in hierarchy are possible, see figure below. To make sure a joint is built up as desired, a hierarchy number can be included. The beam with a hierarchy of 1 has the highest hierarchy and will be continuous. The beams with a lower hierarchy (2 and 3) will be cut by beams with a higher hierarchy.

 

On a structural level, groups of elements can be created. These groups are defined based on their function, the topchord elements, the diagonals, etc. The hierarchy of a structure can be assigned to the groups. Using this method, the IAM will build up the joints in the desired sequence.    

Example of hierarchy:

Hierarchy Groupname
1 Column
2 Topchord
3 Bottomchord
4 Post 
8 Diagonal

Examples of IAM's

In the following links, examples of integral analyses models can be found.

Steel truss with welded connections

Steel truss with bolted connections

Steel Dome structure