The enhancements to the CIS/2 exporter include expanded export of the end reactions for structural linear members. Previously, only the major shear force (Vz) was exported for each end of a linear member. Now, the export file contains the other components of the end reaction force (Vx, Vy). The moments are included as well.
Note: This overview includes the original documentation for the export of Analysis Data though CIS/2. It has been updated to reflect the current Structural UI such as the new Analysis Data tab of the element Information dialog box.
The only changes to the CIS/2 exporter were:
There have been no changes to the structure of the CIS/2 export entities.
The CIS/2 export translator includes camber information for structural members when it is defined for a member. Camber values are included for both the Design and Manufacturing export options.
CIS/2 Export File
The camber is assumed to be measured at the midpoint of the linear member. The camber is expressed as an “absolute” (not relative) value in the CIS/2 export file. The camber is also assumed to have only a component in the Z axis (not the Y axis). RAM does not assign a Y component of camber.
The units of the camber are given in master units.
In both Design and Manufacturing models a part_prismatic_simple_cambered_absolute entity is created.
In a Design model, an assembly_design_structural_member_linear_cambered_absolute is also created.
The NIST CIS/2->VRML translator can be used to view the export file. For the Manufacturing model (only) it will list camber values in the HTML report and display the camber in flyover text in the VRML viewer such as Cortona .
In the flyover text camber is given as three values. The first value is the offset along the member at which the camber is measured. This should be the midpoint of the beam. The second value is the Y (lateral) displacement. The third value is the Z displacement. Units are in master units.
The CIS/2 export translator includes information about shear studs for structural members. Shear stud values are included for both the Design and Manufacturing export options.
The benefit of shear stud support in the CIS/2 exporter is that it preserves the information for downstream applications such as structural steel detailing packages. This allows the shear stud counts calculated by an analysis application to be efficiently passed through the Bentley design model to detailing applications. The shear stud information does not need to be re-entered and this saves time and promotes accuracy.
Shear stud values are typically imported from analysis applications such as RAM.
The Shear Studs field contains the number of shear studs associated with a member. There is no other information (currently) imported from RAM about the shear stud configuration. Only the shear stud counts are imported.
In the case of multiple groups of studs the stud counts are represented by a series of integer values: For example, “3, 2, 3” denotes three groups of studs having counts of 3, 2 and 3 respectively. Multiple stud counts may be present when a member has other members connected to it and the stud counts are divided along the member. Each group represents the number of studs that appear in a particular segment.
In a typical workflow the size of the studs and the specific layout positions along a member (single, double, staggered) are provided by a structural steel detailing application downstream.
Shear studs are exported to both the Design and the Manufacturing models.
In a Design model a group of studs are represented by the following entities:
Overall joint system
1 per shear stud group
Describes the fastener mechanism used in the joint and the layout positions of each fastener.
The layout positions are approximated. A uniform distribution of studs in a single row is assumed.
A list of fasteners
The shear stud is the only fastener in the list.
The stud diameter and length are set to 0.5” and 1.0” These values are placeholders.
In a Manufacturing model a group of studs are represented by the following entities:
The stud diameter and length are set to 0.75” and 3.5”. These values are placeholders.
In the case of multiple stud groups in a member, each group is represented as a separate joint. For example, there are 3 joints written for a stud configuration of “3, 2, 3”. Applications importing the CIS/2 file can determine the total number of studs associated with a particular member by totaling the stud counts for each shear stud joint associated with a member.
Each group has a separate coordinate system with the origin at the 1st stud in the group.
Shear Stud Coordinates
Detailing applications such as Tekla or SDS will calculate the actual positions of the shear studs for manufacturing. Consequently, by default, no coordinates of the individual shear studs are calculated and all the shear studs for a particular joint are placed at the origin of the joint.
There is a setting in the export dialog box to generate approximate coordinates of the shear studs in the joint. The coordinates are calculated based on the assumption that there is a single row of studs evenly spaced along the member. The coordinates are approximated so that the shear stud joints may be visualized in tools such as the NIST CIS/2 -> VRML translator. Please note that turning on the generation of the shear stud coordinates can have significant performance impacts for models with a large number of shear studs.
There are few commercial detailing applications that import shear studs from CIS/2 Design models but this is an area of planned development for several vendors.
In the meantime, the NIST CIS/2->VRML translator can be used to view the export file and visualize the shear stud connections for each member.
Version CTV 7.50 and later is necessary to view Design model shear stud connections.
This is a good VRML plug-in for a web browser. It is necessary for the NIST translator.
This is an example of a Design model with a member that has a “2, 2, 2, 2” stud configuration.
The reaction forces are optionally exported in a CIS/2 Analysis model that is packaged in the same export file with the Design model. The CIS/2 schema allows multiple models to be present in a file; the importing application determines which one(s) to process.
In a typical workflow, the reaction forces will be calculated by an analysis application such as RAM and then imported with the geometry into a Bentley Structural design model. In this case the resulting design model does not have an explicit analysis model because the RAM import does not create one. When the CIS/2 export file is created a default analysis model is synthesized that represents the members, their intersections and the end nodes. This analysis model is expressed as CIS/2 entities and exported to the output file.
In a later version of the CIS/2 export tool any existing Bentley Structural analysis model will be exported instead of the synthesized model.
Reaction forces are associated with members in the Structural Data of an element. The End1 Forces and End2 Forces fields are used to hold the reaction forces for the respective ends.
The units of a reaction force are kips for imperial models and kN (kiloNewtons) for metric models.
The units of a reaction moment are kip-ft for imperial models and kN-m (kiloNewtons-meters) for metric models.
The CIS/2 Export dialog box has a new checkbox “Include Reaction Forces”. When checked, this will add the Analysis model (with the reaction forces) to the Design model in the CIS/2 export file. The Manufacturing model does not support the export of reaction forces so when the primary export model is set to Manufacturing the “Include Reaction Forces” checkbox is disabled.
The Analysis model is not automatically included because it does increase the export time. Typically, adding the Analysis model will approximately double the export time and the size of the resulting CIS/2 file.
If the “Include Reaction Forces” option is checked, the resulting CIS/2 export file will contain both the CIS/2 Design and the Analysis model. The downstream application that imports the CIS/2 file will determine which models are imported.
When the analysis model is synthesized, analysis elements and nodes are added to the export model that represents the analytical view of the structural model. Every linear member will have analysis nodes at its endpoints. In addition, if a member is intersected by other members then the member will be subdivided into sub-elements and nodes will be added at the points of intersection.
The Bentley Structural user preference “Node Tolerance” is used as the effective range to determine when members intersect and nodes can be merged into a single node. Make sure that the Node Tolerance setting is set to a reasonable value because it is a critical setting in determining the resulting topology of the analysis model.
For example, the following configuration of structural members will be subdivided as shown:
These are the primary CIS/2 entities that are used to describe the analysis model and the reaction forces.
Vx, Vy, Vz
Mx, My, Mz
associates a reaction force with an element node
analysis element of linear member
associates a node with an element
associates an analysis element with a design assembly (part)
The NIST CIS/2->VRML translator can be used to view the export file. For the Analysis model it will display the reaction forces in flyover text in the browser. When the cursor hovers over an element the flyover text will be displayed. Any reaction force that is present will be at the end of the flyover text such as “..Gravity end reactions: 0. 0. 18.”.
This capability is enabled only when the output browser is set to Firefox in the NIST translator. This is due to a limitation in Internet Explorer with respect to the size of flyover messages.
The NIST CTV translator and a VRML plug-in are available from these web sites:
NIST CTV: http://cic.nist.gov/vrml/cis2.html
VRML Plugin: http://www.parallelgraphics.com/products/cortona/
You may view either the Design model or the Analysis model (or both) by using the on-screen display buttons “Design Model” and “Analysis Model”. If the button is green the corresponding model is shown; if it is red the model is hidden.
The Analysis Model display mode has options to show any combination of the structural elements, nodes or wireframes that represent the analysis model.
The NIST translator does not report the moment components but the values may be found by inspecting the STEP file. Using selection sets, individual elements can be exported to CIS/2 and the properties examined in the resulting output file.