Comprehensive analysis and design of brace frames using the Simpson Strong-Tie Yield-Link Brace Connection (YLBC) 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 brace frames. When assigning preliminary lateral brace sizes in RAM Modeler or in RAM Frame, it is important to keep in mind the connection is only valid for brace frames with W14 size I-shape braces in single diagonal, V-brace, or inverted V-brace configurations.
In RAM Frame, specify the Adjusted Fuse Strength using the Criteria – Yield-Link Brace Connection command.
Select the criteria for evaluation of the Adjusted Fuse Strength.
Use Calculated = YLBC frame design based on the applied loads onto the YLBC fuses. Use Maximum = YLBC frame design based on the maximum capacity of the YLBC fuses (PprC or PprT from ESR-4342).
In RAM Frame, assign the brace connection type using the Assign – Braces – Yield-Link Brace Connection command.
The Yield-Link Brace connection can be assigned to the Top, Bottom or both ends of the brace; select the desired option. Where structures are assigned a Seismic Design Category (SDC) of A, B, or C fuse configurations may be located on one end of a single brace member. Where structures are assigned a SDC of D, E, or F fuse configurations must be located at each of the brace unless the exceptions in ICC-ES ESR-4342 are met.
Select the Yield-Link brace connection size from the list of YLBC sizes. Select the assignment location for the connection, Top and Bottom, Top, or Bottom. The connection can be assigned selectively with the Single or Fence command, or to all of the Frame braces with the All command.
Once the brace ends have been assigned, RAM Frame will display the Yield-Link brace connection symbolically as shown:
The Yield-Link brace connection size assigned to a brace can be graphically viewed by invoking the View – Members command; select the lateral braces tab and check the Labels checkbox as shown below. Apply the options selected to display the assigned Yield-Link brace connection sizes.
The Yield-Link Brace Connection has been implemented for both R=8 and R=3. When creating the seismic load cases, specify the R value accordingly. Analysis
Perform the Analysis. When the Analysis is performed, the appropriate Yield-Link brace connection criteria properties are applied accordingly. Yield-Link brace connections are only permitted on W14 sized braces.
The Member Forces report for braces has been enhanced to identify that it has a Yield-Link brace connection, along with information about the effective axial stiffness:
A new section has been added to the Frame Takeoff report to include the Yield-Link brace connection sizes and 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 brace connection sizes as necessary.
Steel – Standard Provisions
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 including the Yield-Link brace connections, 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 brace will fail if the Yield-Link brace connection capacity is inadequate for the applied loads. Increasing the YLBC size will increase the load capacity.
Steel – Seismic Provisions
In the Steel – Seismic Provisions mode the seismic provision requirements for ESR-4342 and AISC 341-16 for both ASD and LRFD have been implemented for Yield-Link brace connections. Select the AISC 341-16 code in the Criteria – Codes command.
Input values for YLBC Cd/Ie and YLBC Sds. For R = 8, Cd = 5, Ωo = 2.5, and for R = 3, Cd = 3, Ωo = 3. The value of YLBC Sds should be consistent with the Sds value entry in the Seismic Provisions Load Combinations Generation dialog box.
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 Yield-Link Brace Connection (YLBC R=3) or Yield-Link Brace Connection (YLBC R=8) as appropriate. Remember that the value of R specified for the generation of the seismic forces must be consistent with the Frame Type selected here.
The Frame Type assignment on each member can be displayed by selecting the Frame Type labels option on the Frame Brace tab in the View – Members command.
Select the Process – Member Code Check command to have the code check performed on all of the members including braces with the Yield-Link brace connection 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. Any failed limit state check of the Yield-Link brace connection itself would require a resizing of the connection which can only be performed in Steel – Standard Provisions mode or Analysis mode.
The Seismic Provisions Member Code Check report show the results of all the member checks, including the check of the Yield-Link brace fuse configuration. Design of gusset plates, welds, and bolts in connection not performed in RAM.
Note: For new users of Yield-Link brace 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.