Comprehensive analysis and design of moment frames using the Simpson Strong-Tie Yield-Link moment frame connection is now available in the RAM Structural System. This document describes the use of this feature.
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:
In RAM Frame, specify the moment frame type – SMF, IMF, or MF – using the Criteria – Yield-Link 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 Yield-Link panel zone properties are built-in automatically and accounted for when Yield-Link is assigned as a moment connection. In the Criteria – General command, the option to Ignore Effects for Rigid End Zones should be selected.
In RAM Frame, assign the moment connection type using the Assign – Beams – Frame Beam Connection Types command.
Select the Yield-Link tab. The Yield-Link connection can be assigned to one or both ends of the beam; select the desired option. Generally, the Frame beams will have the Yield-Link connection on both ends, but in some cases it might be desired to pin one end of the beam and assign the Yield-Link moment connection on the other.
Link sizes can be assigned to the beam using a selected default size. If the Default option is used the program will automatically select the Yield-Link size. However, this command can also be used to assign explicit Yield-Link sizes to the beams by selecting the Use option and specifying the desired connection size from the list. The default Yield-Link size selected by the program won’t necessarily work, but is a good starting point; if it is determined that the size is inadequate, the Assign command can be used to assign a different size.
If default sizes aren’t working, explicit sizes can be selected using the Use option:
Or it may be easier to modify the Default sizes by selecting the Change Defaults button and specifying larger default sizes:
The connection and Yield-Link sizes can be assigned selectively with the Single or Fence command, or to all of the Frame beams with the All command.
The Yield-Link connection can be assigned to cantilever members when the cantilevers are modeled as Stub cantilevers. The Yield-Link connection is incompatible with cantilevers modeled as Extensions.
Once the beam ends have been assigned, RAM Frame will display the Yield-Link moment connection symbolically as shown:
The Yield-Link size assigned to a beam can be graphically viewed by invoking the Assign – Beams – Frame Beam Connection Types command; if the size is a user-specified size, the size will be listed with an asterisk.
Perform the Analysis. When the Analysis is performed, the appropriate Yield-Link connection criteria properties are applied accordingly. Certain checks on sizes are performed to ensure compatible sizes are assigned to the frames. Beam flanges must be at least 0.4 in. thick. Some combinations of beam size, column size, and Yield-Link size are not permitted. The beam flange and column flange must be sufficiently wide for the Yield-Link connector. If either is insufficient, a warning will be given when the Analysis is performed. It will then be necessary to assign a wider beam or wider column (or use a smaller Yield-Link connector). In some cases, the Analysis will be terminated, in which case the condition must be resolved before continuing. In other cases the Analysis will proceed, but the engineer must remember to go back and resolve the warning conditions, or to make special accommodations for the configuration (which would involve coordinating with the engineers at Simpson Strong-Tie to verify that the condition is acceptable, or to design a custom connection).
The Member Forces report for beams has been enhanced to identify that it has a Yield-Link connection, along with information about the joint stiffness:
A new section has been added to the Frame Takeoff report to include the Yield-Link sizes and the weight of the plates in the connections:
Verify that the drifts do not exceed the drift limits given by the building code. The drift values can be obtained using the Process – Results – Drift command. Adjust the member sizes and Yield-Link sizes as necessary.
Go to the Steel – Standard Provisions mode to determine the adequacy of the members and connections according to the standard steel specifications (i.e., AISC 360, not AISC 341).
To investigate the adequacy of the member sizes, invoke the Process – Member Code Check command. Use the Process – Member View/Update command to investigate individual members. Resize any failing members as necessary.
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 of the beam. The unbraced length (both x and y) is taken as the column height, not reduced by the beam depth.
To investigate the adequacy of the Yield-Link connections, invoke the Process – Joint Code Check command. Joints that are adequate will show a green sphere symbol, joints that are adequate but require stiffener plates will be shown with a blue plate symbol, joints that are adequate but require a web doubler plate will be shown with a blue sphere symbol, and joints that fail will be shown with a red sphere symbol.
Use the Process – Joint View/Update command to investigate individual joints.
The joint will fail if the maximum size of web plate and stiffeners are inadequate to make the joint work, but the most common cause of joint failure will be a Yield-Link connector with inadequate area:
It may be able to resolve this by assigning a larger Yield-Link size. However, in some cases it may be necessary to assign deeper beam sizes. With deeper beams the distance between the Yield-Link connectors above the top flange and below the bottom flange increase, so the axial load in the connectors decrease (Axial Force = Moment / Distance between connector centroids).
The Joint View/Update dialog allows you to investigate increasing the column size to eliminate web plates and stiffeners, and to investigate different connector sizes to eliminate Yield Link Axial Capacity failures.
In the Steel – Seismic Provisions mode the seismic provision requirements for AISC 341-16 and AISC 341-10, for both ASD and LRFD, have been implemented for Yield- Link connections. Select one of those codes in the Criteria – Codes command.
The Yield-Link tab of the Criteria – Joints command has settings for how the bracing of the top and bottom flange of the beams is to be considered per AISC 341 Section 12.3.2(7), the shear plate grade and thickness and bolt information, and the intended detail for the web plates.
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 (for Yield-Link SMF (R=8)), Intermediate Moment Resisting Frame (for Yield-Link IMF (R=4.5)), or Ordinary Moment Resisting Frame (for Yield-Link MF (R=3)) as appropriate. This assignment must be consistent with the methodology selected in the Criteria – Yield-Link 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.
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. Modify the member sizes as necessary to eliminate the member design failures.
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 joint.
The plates, bolts, and welds for the Yield-Link connection are designed when the Joint Code Check is performed. The shear plate and bolt information can be viewed and modified using the Shear Plate Properties button on the Joint View/Update dialog:
The Seismic Provisions Member Code Check and Joint Code Check reports show the results of all the checks, including the design of the Yield-Link connection plates.
CAD drawings can be generated using the File – Export Yield-Link DXF command in RAM Frame. The drawings include Frame elevations, joint details, and all the associated tables of Yield-Link sizes, shear plate, stiffener plate (if required), doubler plate (if required), connection bolts and connection welds. The information presented can be used for pricing and detailing by the contractor.
Note: For new users of Yield-Link moment connection, Simpson Strong-Tie will provide assistance to review the design file. Users should send their RAM model (e.g. “filename.rss” file), to Simpson Strong-Tie at email@example.com. A Simpson Strong-Tie representative will contact you within 48 hours to discuss your project.