Comprehensive analysis and design of moment frames using DuraFuse connection technology are now available in the RAM Structural System. This document describes the use of this feature.

Modeling

Create the model as customary for any project using steel moment frames.  When assigning preliminary lateral beam and columns sizes in RAM Modeler or in RAM Frame, it is important to keep in mind the following rules:

1. For a two-sided DuraFuse connection, beam depths must be equal or have a difference in depth greater than 6” to accommodate installation of plates and bolts. This is required because for beams of equal depth, the continuity plates extend across both sides of the column. For beams of different depths, the continuity plates are separate. If there is not a large enough difference between the beam depths the plates will run into each other or the bolts can’t be installed. Minor differences in depth can be accommodated with shims, contact DuraFuse to verify.
2. To allow the placement of the cover plate on the column, the relationship of the width of the beam and the width of the column is governed by the following equation:

b_bf  +  0.25 in  ≤  b_cf  +  2t_cp

where:

            b_bf = width of the beam flange

            b_cf = width of the column flange

            t_cp = thickness of the cover plates

If the beam width exceeds this value it will be necessary to cope the beam flanges.

Criteria

In RAM Frame, the Criteria for these moment connections can be specified using the Criteria – DuraFuse command.

      

  

The connection properties are different for high seismic (inelastic) applications versus wind (elastic) and low seismic applications. Select the criteria that is appropriate for the moment frames.

Note that DuraFuse panel zone properties are built-in automatically and accounted for when DuraFuse is assigned as a moment connection; the options for Rigid End Zones in the Criteria – General command are ignored.

Assign

In RAM Frame, assign the moment connection type using the Assign – Beams – Frame Beam Connection Types command.

 

The DuraFuse connection can be assigned to one or both ends of the beam; select the desired option. Generally, the Frame beams will have the DuraFuse connection on both ends, but in some cases it might be desired to pin one end of the beam and assign the DuraFuse moment connection on the other.

The connection can be assigned selectively with the Single or Fence command, or to all of the Frame beams with the All command.

The DuraFuse connection can be assigned to cantilever members when the cantilevers are modeled as Stub cantilevers. The DuraFuse connection is incompatible with cantilevers modeled as Extensions.

Once the beam ends have been assigned, RAM Frame will display the DuraFuse moment connection symbolically as shown:

 

The Assign – Columns – DuraFuse Parameters command can be used to assign cover plate dimensions and beam stiffness modifiers and stiffened regions. This command is not necessary, the program will automatically determine the appropriate values, and should only be used if directed by the engineers at DuraFuse. There may be circumstances where a nonstandard configuration results in a more economical design; this is unusual, but this command gives DuraFuse the ability to instruct engineers to change those parameters.

Analysis

When the Analysis is performed, the appropriate DuraFuse connection criteria properties are applied accordingly. Certain checks on sizes are performed to ensure compatible sizes are assigned to the frames. Some sizes are not permitted; if such a size has been assigned the program will display the following error:

Note that the analysis will proceed, but it should not be considered valid.

If the beams on either side of a joint are close in depth but not the same depth, a warning is displayed indicating that shims will be required. This condition is allowed but should be avoided if possible:

If the beam width exceeds the relationship defined previously, a warning is displayed indicating that the beam flange will need to be coped. This condition should be avoided if possible:

The Member Forces report for beams has been enhanced to identify that it has a DuraFuse connection, along with information about the member stiffness:

 

The report for columns includes the cover plate information, the panel zone spring stiffness, and the column stiffness multiplier:

 

A new section has been added to the Frame Takeoff report to include the cover plate weight of the DuraFuse connection:

 

Steel – Standard Provisions

The design moment and shear for the beams are taken at the face of the column. The unbraced length of the beam is measured from face of column to face of column.

The design moment and shear for the columns are taken at the face (top and bottom edges) of the cover plate.  The unbraced length (both x and y) is taken as the column height, not reduced by the connection depth.

For the connection itself, only the cover plate is designed; the design of the fuse plates, top plates, continuity plates and shear tabs are provided by DuraFuse Frames (https://durafuseframes.com). No Joint checks are performed in Standard Provisions mode.

Steel – Seismic Provisions

In the Steel – Seismic Provisions mode the seismic provision requirements for AISC 341-10 and -16 ASD and LRFD have been implemented for DuraFuse connections. Select one of those codes in the Criteria – Codes command.

It is necessary to assign a frame type to each member, used by the program to determine which seismic provisions are pertinent. This is done using the Assign – Frame Type command. Select either Special Moment Resisting Frame or Ordinary Moment Resisting Frame as appropriate. This assignment must be consistent with the methodology selected in the Criteria – DuraFuse command, as explained above. If the frame type is not consistent with the methodology the members will be indicated as failing; the following error message will be given in the View/Update command:

The Frame Type assignment on each member can be displayed by selecting the Frame Type labels option on the Frame Beam and Frame Column tabs in the View – Members command. The text on the display should show SMRF or OMRF.

Select the Process – Member Code Check command to have the code check performed on all of the members, and select the Process – Member View/Update command to select and view the results for an individual member.

Select the Process – Joint Code Check command to have the code check performed on all of the joints and select the Process – Joint View/Update command to select and view the results for an individual member.

The Seismic Provisions Member Code Check and Joint Code Check reports show the results of all the checks:

Note: Designs using the DuraFuse connection should be reviewed and verified by DuraFuse Frames. To assist in this process, upon completion of preliminary and/or final lateral designs using DuraFuse connection technology, users should send their RAM model (e.g. “filename.rss” file), including any customized beam, column or deck tables, to DuraFuse Frames (801-727-4060) at contact@durafuseframes.com for verification and validation of the computer model.  Upon completion of model review, DuraFuse Frames will provide structural drawings (notes and details), including stamped/signed calculations for each DuraFuse moment connection for the specific project.