Seismic Moment Connections

Design for seismic moment connection detailing is done per the AISC Seismic Design Manual, 3rd Edition (2016) &2nd Edition (2010) contains two documents: the AISC 341-16/10 Seismic Provisions for Structural Steel Buildings and the AISC 358-16/10 Prequalified Connections for Special and Intermediate Steel Moment Frames for Seismic Applications. These documents contain common design standards for seismic systems, including seismic connection design criteria.

The following seismic moment connections are available:

Moment Frame Systems:
- Column/Beam Direct Weld Moment Connection
  - Reduced Beam Section Moment Connection (OMF, IMF, SMF)
  - Welded Un-reinforced Flange-Welded Web Moment Connection (OMF, IMF, SMF)
- Column/Beam Extended End Plate Moment Connection
  - Bolted Un-stiffened Extended End Plate Moment Connection (OMF, IMF, SMF)
  - Bolted Stiffened Extended End Plate Moment Connection (OMF, IMF, SMF)
- Column/Beam Flange Plate Moment Connection
  - Bolted Flange Plate Moment Connection (OMF, IMF, SMF)
Braced Frame Systems:
- See the Seismic Vertical Brace Connections topic for information on which seismic braced connections are available.

Note:

Unless otherwise specified, all code references below are to AISC 341-16 and AISC 358-16.
Seismic moment connection design in RISAConnection is limited to the current edition of the US design code. No results will be given if you select any other design code.
Per section 1.3 of the AISC 358-16/10, the all pre-qualified IMF and SMF connection types must be designed according to the Load and Resistance Factor (LRFD) provisions. Therefore, only the OMF, OCBF, and SCBF connection types are allowed to be designed per ASD provisions.

How to Create a Seismic Moment Connection

Starting from Scratch in the Stand-Alone Version

If you are using RISAConnection as a stand-alone program, then you can define your seismic moment connection as follows:

Start a new model and select your Column/Beam Moment connection type. Applicable connection types are:
1. Column/Beam Direct Weld Moment Connection
2. Column/Beam Extended End Plate Moment Connection
3. Column/Beam Flange Plate Moment Connection
Select your Seismic System.

Enter the appropriate Seismic Moment Connection Input Values.

Importing a Connection from a RISAFloor or RISA-3D Model

If you are using the integration between RISA-3D and RISAConnection to create your model, then you can define your seismic connection as follows:

RISA-3D:

If you are using RISA-3D on its own, then you must apply both a "Column/Beam Seismic Moment" Connection Rule and a Seismic Design Rule to the member.

Make sure to solve in RISA-3D for your seismic detailing results. If you do not have seismic detailing results in RISA-3D, then the information cannot be exported to RISAConnection. For more information about seismic detailing results, see the RISA-3D Help file topic "Seismic Detailing".

When exported into RISAConnection, the program will determine the Connection Type, Seismic System , and seismic input values based on the applied Seismic Design Rule and the RISA-3D solution results. Once in RISAConnection, these cannot be changed.

RISAFloor:

If you are using RISAFloor, you can apply the "Seismic Moment" Connection Rule within RISAFloor or in RISA-3D.
1. You may only apply the "Seismic Moment" Connection Rule to Lateral members.
Use the Director tool to take the model into RISA-3D in order to apply the Seismic Design Rule. Solve your lateral load combinations in RISA-3D in order to get your Seismic Detailing results.
1. If you have not done this, the connection will not export to RISAConnection.
When exported into RISAConnection, the program will determine the Connection Type, Seismic System , and seismic input values based on the applied Seismic Design Rule and the RISA-3D solution results. Once in RISAConnection, these cannot be changed.

Determining the Seismic System

The integration between programs uses the following "translation" to determine the Seismic System for moment connections:

Seismic Moment Connection Input Values

The following seismic input values are available for moment connections:

Shear due to Gravity, V_g - Beam shear due to gravity loads, V_gravity. This is used to determine the required shear strength, V_h, of the beam and beam web-to-column connection.
Clear Span, L - Clear length of the beam between supporting column flanges.
Sh - Plastic Hinge Location, distance from face of column flange. (Only for RBS connections imported from RISA-3D, otherwise this value is calculated based on the RBS dimensions.)
Z Factor - Ratio of the reduced plastic section modulus of the RBS to the full plastic section modulus of the beam. This value comes from RISA-3D, so it is only available for RBS connections that were imported from RISA-3D.
R*Mu - Required moment for OMF connections. See OMF Required Strength for more information. (Only for OMF connections.)
R*Vu - Required shear for OMF connections. See OMF Required Strength for more information. (Only for OMF connections.)

Seismic Moment Connection Limitations

Below is a list of limitations regarding the seismic design:

Seismic design is not supported under the Canadian design code.
Seismic design is not supported under the AISC 341-05 (1st edition) Seismic Design Manual.
IMF and SMF connection types must use the LRFD design method.
OMF, OCBF, & SCBF connection types can use either ASD or LRFD design.
Seismic Design will not apply to splice connections at this time.
RISAConnection will not design stability bracing, however these requirements are addressed in RISA-3D.
Code provisions for steel backing on welds are not checked at this time.
Strong Column-Weak Beam checks can only consider a single story column at this time.

Reduced Beam Section (RBS) Moment Connection

A Reduced Beam Section moment connection may be defined in RISAConnection as the "RBS" Seismic System within the Column/Beam Direct Weld Moment Connection. Depending on the ductility of your system, you may assign the RBS as an OMF, IMF, or SMF. The design of this type of connection is done per AISC 341-16 and AISC 358-16, chapter 5. Please see the Seismic Moment Connection Checks section for more information.

When you use this connection type, the following changes to geometry and assembly apply:

Web Weld Entry

In addition to the existing welding/bolting requirements of the moment connections, the Column/Beam Direct Weld Moment Connection includes the "Web Weld". This weld is between the beam web and the column flange. It is required per AISC 358-16 chapter 5, section 5.6 (2) (a) (for RBS) and per AISC 358-16 chapter 7, section 8.6 (5) (for WUF-W). This weld must be a CJP with an electrode type of either E70 , E80, or E90.

Weld Access Holes

RISAConnection will automatically modify the geometry of the RBS and WUF-W seismic connections to include the Weld Access Hole Requirements of the AISC 358-16. This manual refers to the AWS D1.8/D1.8M 2009 section 6.10.1.2. RISAConnection uses the limits of this code to determine the geometry of the Weld Access Holes:

Note:

Currently these are not editable.

RBS Dimensions

RISAConnection will apply default dimensions to the reduced beam section. But you may edit these at any time in the Assembly section of the Connection Properties.

RISA-3D Integrated Models

When a seismic moment RBS connection is imported from RISA-3D, the a, b, and c dimensions are predetermined from the RISA-3D Seismic Design Rules data. In the RISA-3D Seismic Design rule, you are required to input a Z Factor (ratio of reduced section Z to full section Z) and a Hinge Location ( distance from face of column flange to the center of the reduced section.

Seismic Design Rule spreadsheet from RISA-3D:

In order to assure that the RISA-3D results are consistent with the RISAConnection results, RISAConnection will then automatically calculate these dimensions.

The a and b values are dependent on the Hinge Location: a + 0.5*b = Hinge Location. If you change one of these values, the other will also update based on this equation.
The c value is back-calculated from AISC 358-16 equation 5.8-4 using the Z Factor. This value cannot be edited.

RBS Limitations

The beam connection must be bolted.
The shear plate depth is required to extend the full distance between the weld access holes (per AISC 358-16 section 5.6 (2) (a).

Welded Un-reinforced Flange Welded Web (WUF-W) Moment Connection

A Welded Unreinforced Flange- Welded Web moment connection may be defined in RISAConnection as the "WUF-W" Seismic System within the Column/Beam Direct Weld Moment Connection. Depending on the ductility of your system, you may assign the WUF-W as an OMF, IMF, or SMF. The design of this type of connection is done per AISC 341-16 and AISC 358-16, chapter 8. Please see the Seismic Moment Connection Checks section for more information.

When you use this connection type, the following changes to geometry and assembly apply:

Web Weld Entry

In addition to the existing welding/bolting requirements of the moment connections, the Column/Beam Direct Weld Moment Connection includes the "Web Weld". See the discussion above for more information.

Weld Access Holes

RISAConnection will automatically modify the geometry of the RBS and WUF-W seismic connections to include the Weld Access Hole Requirements of the AISC 358-16. See the discussion above for more information.

WUF-W Dimensions

RISAConnection will apply default dimensions to the WUF-W shear plate. But you may edit these at any time in the Assembly section of the Connection Properties.

WUF-W Limitations

The beam connection must be welded.

Bolted Stiffened/Un-stiffened Extended End Plate (BEEP) Moment Connection

A Bolted Unstiffened or Stiffened Extended End-Plate moment connection may be defined in RISAConnection as the "BEEP" Seismic System within the Column/Beam Extended End Plate Moment Connection. The end plate can be stiffened of unstiffened depending on if you have applied a stiffener plate in the Connection Category input of Connection Properties (this is required for 8 bolt layouts).

Depending on the ductility of your system, you may assign the BEEP as an OMF, IMF, or SMF.

The design of this type of connection is done per AISC 341-16 and AISC 358-16, chapter 6. Please see the Seismic Moment Connection Checks section for more information.

Bolted Flange Plate (BFP) Moment Connection

A Bolted Flange Plate moment connection may be defined in RISAConnection as the "BFP" Seismic System within the Column/Beam Flange Plate Moment Connection. Depending on the ductility of your system, you may assign the BFP as an OMF, IMF, or SMF.

The design of this type of connection is done per AISC 341-16 and AISC 358-16, chapter 7. Please see the Seismic Moment Connection Checks section for more information.

Ordinary Moment Frame (OMF) Connections

The AISC 358-16 is specifically for the design of seismic IMF & SMF connections. However, you are allowed to define your connection as an Ordinary Moment Frame (OMF) using any of the AISC 358-16 pre-qualified connection types. In this case, many of the checks will be for reference only as they are not specifically required by the design code.

OMF Required Strength

Per AISC 341-16 section E1.6b, the flexural strength of an OMF shall be the lesser of:

1.1*Ry*Mp (LRFD) / (1.1/1.5)*Ry*Mp (ASD)
R*Mu (For minimally ductile moment frames, the required moment need not exceed R*Mu based on discussion in the AISC 341 commentary)

Per AISC 341-16 section E1.6b, the required shear strength of an OMF is computed using the AISC 360-16 (15th edition) load combinations.

When a model is imported from RISA-3D, these values are brought over from the RISA-3D seismic detailing calculations. When a model is created using the stand-alone version of RISAConnection, the user is expected to enter these values.

Seismic Moment Connection Checks

The following checks are included with the regular (AISC 360-16, 15th edition) checks for seismic moment connections. The seismic checks will always be shown at the bottom of the results report fpr seismic moment connections.

If you are using a RISA-3D integrated model, these checks do not depend on the loads from the load combinations. The seismic checks design to a probable maximum moment which is independent of the actual applied forces.

Seismic Material and Geometry Limitations -

This check includes material geometry limits from the AISC 341-16 and from the applicable chapter in the AISC 358-16. Specific code section references are presented in the output report.

Seismic Width to Thickness Ratios-

This check includes width to thickness ratio checks per AISC 341-16, Table D1.1.

For OMF connections, this check is for reference only.

Seismic Moment at Face of Column-

This section calculates the probable maximum moment at the face of the column, M_f and the design flange force, F. This is required by all connection types per the AISC 358-16. Specific code section references are presented in the output report.

For OMF connections, this check is for reference only. RISAConnection will check to see which is the minimum design moment (R*M_u or M_pr) and which is the minimum design shear (R*V_u or V_h) and then use that to calculate the design flange force. Based on the AISC 341-16 commentary, the required moment of minimally ductile moment frames need not exceed R*Mu.

Seismic Parametric Limitations-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It includes geometry limitation checks based on AISC 358-16, Table 6.1.

Seismic Weld Limitations-

This checks the requirements of AISC 341-16, section A4 and the specific weld requirements of each chapter in the AISC 358-16. Specific code section references are presented in the output report.

Seismic Flange Bolt Limitations-

This check is only applicable to Bolted Flange Plate Moment Connections (BFP). It checks the bolt size and spacing requirements of AISC 358-16 chapter 7. Specific code section references are presented in the output report.

Seismic Flange Plate Limitations-

This check is only applicable to Bolted Flange Plate Moment Connections (BFP). It checks the beam flange plate thickness and connection limitations of AISC 358-16 chapter 7. Specific code section references are presented in the output report.

Seismic Bolt Limitations-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It checks the bolt material and size requirements of AISC 358-16 chapter 6. Specific code section references are presented in the output report.

Seismic Plate / Misc Limitations-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). This checks the end plate width limitation as well as the end plate and the column flange for "thick" plate behavior. The "thick plate" check is covered in the AISC Design Guide #4 "Extended End-Plate Moment Connections", 2nd edition, Section 3.3. This is the same as the regular Verify Bolt Prying Assumption check.

Seismic End Plate Limitations-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It checks the end plate thickness and width requirements of AISC 358-16 chapter 6. Specific code section references are presented in the output report.

Seismic RBS Connection Detail Limitations-

This check is only applicable to Direct Weld - Reduced Beam Section Moment Connections (RBS). It checks the reduced beam section geometry requirements of AISC 358-16 chapter 5. Specific code section references are presented in the output report.

Seismic WUF-W Connection Detail Limitations-

This check is only applicable to Direct Weld - Welded Unreinforced Flange-Welded Web Moment Connections (WUF-W). It checks the WUF-W shear plate geometry requirements of AISC 358-16 chapter 8. Specific code section references are presented in the output report.

Seismic Column-Beam Moment Ratio-

This section calculates the column-beam moment ratio. This is required for all SMF connection types per AISC 341-16, section E3.4a. Specific code section references are presented in the output report. Because RISAConnection only has column and loading information for the one column, only a single story height column will be considered in the calculation of M*pc (projected flexural strength of the column).

For OMF and IMF connections, this check is for reference only.

Seismic Flexural Strength of Beam-

This check is only applicable to Direct Weld - Reduced Beam Section Moment Connections (RBS). It checks the flexural strength of the beam at the face of the column per AISC 358-16, equation (5.8-8).

Seismic Flange Strength-

This check is only applicable to Bolted Flange Plate Moment Connections (BFP). It checks the beam flange tensile rupture, block shear, and compression buckling per AISC 358-16 section 7.6. Specific code section references are presented in the output report.

Seismic Beam Web Checks-

This checks the beam web shear limit states per AISC 358-16. Specific code section references are presented in the output report.

Seismic End Plate Shear-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It checks the end plate shear limit states of AISC 358-16 chapter 6. Specific code section references are presented in the output report.

Seismic End Plate Flexural Yielding-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It checks the end plate design strength per AISC 358-16, equation (6.8-5) (AISC 358-10, equation (6.10-5)).

Seismic Bolt Strength-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It checks the bolt shear and bearing limit states of AISC 358-16 chapter 6. Specific code section references are presented in the output report.

Seismic Bolt Moment Strength-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It checks the bolt moment strength against the probable seismic design flange force per AISC 358-16, equation (6.8-3) (AISC 358-10, equation (6.10-3)).

Seismic Flange Bolt Shear Strength-

This check is only applicable to Bolted Flange Plate Moment Connections (BFP). It checks the flange bolt shear strength per AISC 358-16, equation (7.6-8).

Seismic Beam Web Bolt Checks-

This check is only applicable to Bolted Flange Plate Moment Connections (BFP). It checks the beam web bolt bearing and shear limit states per AISC 358-16, chapter 7. Specific code section references are presented in the output report.

Seismic Vert. Plate Checks-

This check is only applicable to Bolted Flange Plate Moment Connections (BFP). It checks the beam web shear plate (vertical plate) shear limit states per AISC 358-16, chapter 7. Specific code section references are presented in the output report.

Seismic Column Weld Strength-

This check is only applicable to Direct Weld - Welded Unreinforced Flange-Welded Web Moment Connections (WUF-W).It checks the column weld shear strength per AISC 358-16, section 8.6 (2).

Seismic Column Strength-

This check is only applicable to ordinary moment frames (OMF). It checks the column limit states per AISC 341-16, section E1.6b.

Seismic Column Web Strength-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It checks the column web limit states per AISC 341-16 section E1.6b.

Seismic Column Flexural Yielding-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It checks the column flange design strength per AISC 358-16, equations (6.8-14 & 6.8-15) (AISC 358-10, equations (6.10-14 & 6.10-15)).

Seismic Stiffener Plate Limitations-

This checks the transverse stiffeners (continuity plate) requirements per AISC 341-16, section E3.6f (2). If this check fails, then continuity plates are required.

Seismic Stiffener Strength-

This check is only applicable to Extended End Plate Moment Connections (BSEEP, BUEEP). It is only included when transverse stiffeners (continuity plates) are included in the model. This will check the transverse stiffener strength per AISC 358-16, section 6.8.2 step 6 (AISC 358-10, section 6.10.2 step 6). Specific code section references are presented in the output report.

Seismic Panel Zone Limitations-

This check only applies to special moment frames (SMF). It checks the panel zone thickness requirements per AISC 341-16, section E3.6e (2). If this check fails, then web doubler plates are required.

Seismic Panel Zone Shear-

This checks the shear strength of the panel zone per the requirements of the AISC 358-16. Specific code section references are presented in the output report. If this check fails, then web doubler plates are required.

For OMF connections, this check is per the regular AISC 360-16 (15th edition) section J10.6.

For OMF and IMF connections, this check is for reference only.

Seismic Doubler Plate Strength-

This checks the yield strength and weld strength of the doubler plate against the required doubler plate shear force due to seismic forces. Specific code section references are presented in the output report.

Because Seismic Panel Zone shear is only applicable to SMF connections, this check is not applicable to OMF or IMF connections.

Seismic Moment Connection DXF Output

In addition to the regular DXF output, the seismic moment connections will include:

Identification of the seismic system
Identification of the demand critical welds
Identification of the protected zone (only applicable to IMF & SMF seismic systems)