§9.[E3] Special Moment Frames (SMF)

§9.2 Beam-to-Column Joints and Connections

Connections in Special moment frames require pre-qualification according to Section 9.2b achieving the performance requirements of §9.2a. The engineer is referred to §9.2b which references AISC 358-05 as a source for several connections that are considered pre-qualified.

When calculating the required shear strength per §9.2a (9-1) all standard provision load combinations with seismic load cases are considered, replacing the seismic load case and factor with the force produced from a term 1.0E where E = 2.0 [1.1 Ry Mpr] / L. The 1.0 load factor will replace the load factor associated with the seismic load case in the underlying load combination. L is taken as the distance between reduced beam sections, if they exist, otherwise L is the distance between the face of the columns supporting the beams. Mpr is the ultimate strength of the beam in bending at the reduced beam section, if it exists, otherwise it is from the full beam section.

Note: For ASD the Mpr term is not divided by Ω (1.5) as is typically performed in other similar calculations such as §9.3a. This may produce conservative shear forces for ASD design if the Ω factor is then assigned to the capacity calculations. All SidePlate^® and DuraFuse^® beam-to-column joints demonstrate conformance with 9.2a as indicated in 9.2b per ICC-ES ESR-1275

All AISC 341-10 beam-to-column joints demonstrate conformance with §9.2a as indicated in §9.2b per ICC-ES ESR-1275

§358-05 5.8-6 [358-10 5.8-6, 358-16 5.8-6] Moment force at Column Face

Where AISC 358-05 Section 5.8-6 RBS Connection is designated in the Codes dialog box the maximum force at the column face is calculated and checked relative to equation 5.8-6. If this check fails the RBS dimensions can be adjusted or section size changed to meet this requirement. The load applied between the face of the column and the RBS is not considered in the calculation of the maximum moment on the face of the column.

§9.3 [E3.6e] Panel-Zone of Beam-to-Column Connections

Only connections parallel to the column web are considered and checked by the program.

The required shear strength of the panel-zone is determined from the summation of moments at the column faces as determined by projecting the expected moments at the plastic hinge locations (RBS if they exist) to the column faces. The material factor ϕv = 1.0 (LRFD) and Ωv = 1.50 (ASD) in all cases.

Note: For the determination of the panel zone forces the moment at the face of the column is calculated as described above but for ASD the Mpr term is calculated as ( 1.1 / 1.5 ) Ry Fy (note the 1.5). This produces equivalent level of design for ASD and LRFD panel zones.

If AISC 358-05 RBS Moment Frame Connections are designated in the Code Dialog then the 1.1 factor on the Mpr calculation is replaced with the Cpr value provided by the user for Special Moment Frame joints.

Pu and Pa (for panel zone capacity calculation) is taken as the maximum axial load on the column at the joint from all standard provision load combinations.

If the beams frame into the flange of the column at some angle other than parallel to the column web, then the component of the beam force parallel to the column web is used. No torsion force in the beam, should it exist, is resolved into a force on the face of the column if the beam is not parallel to the column web.

Panel Zone shear is calculated as the moment divided by the distance between the center of the beam flanges.

Note: The requirements of 9.3b are irrespective of the magnitude of the panel shear force. The program can consider the use of plug-welds to reduce the required web plate thickness, refer to the Criteria > Joints menu command to select this plug weld option.

§9.4 Beam and Column Limitations

Refer to the requirements of 8.2b [D1.1b].

Per Table I-8-1 footnote 3, SMF columns will be checked to comply with λps in Table I-8-1 when Equation 9-3 is less than 2.0, else they will be checked against AISC 360 Table B4.1.

If AISC 358-05 RBS Connections are designated by the engineer in the Codes dialog then the beam b_f / 2 x t_f value is performed based on the dimensions of the RBS per AISC 358-05 (6). The value bf shall not be taken as less than the flange width at the ends of the center two-thirds of the reduced section.

§358-05 5.3.1 [358-10 5.3.1, 358-16 5.3.1] Beam Limitations

If AISC 358-05 Section 5.3.1 RBS Moment Connections are designated in the Codes dialog box then all the additional Beam Limitation requirements of this section, beyond those of AISC 341-05, will be performed. For 5.3.1(2) the beam depth will be used to assess if the section size exceeds the largest W36 section depth. It may be possible however that a beam with greater depth is appropriate (or shallower depth inappropriate) if they are not pre-qualified.

§358-05 5.3.2 [358-10 5.3.2, 358-16 5.3.2] Column Limitations

If AISC358-05 Section 5.3.2 RBS Moment Connections are designated in the Codes dialog box then all the additional Column Limitation requirements of this section, beyond those of AISC 341-05, will be performed.

§9.5 [E3.6f] Continuity Plates

If AISC358-05 RBS Connections are designated by the engineer in the Codes dialog then the AISC 358-05 2.4.4 requirements will be performed. In this check the program will assess the column dimensions and indicate when stiffeners are required to be provided.

Continuity plates are not required for DuraFuse connections per pre-qualified documents.

§9.6 [E3.4a] Column-Beam Moment Ratio

The calculation of ΣM×pb is determined by summing the projections of the expected beam flexural strength(s). The applied loads between the RBS (if it exists) and the column face is not considered.

If the beams frame into the flange of the column at some angle other than parallel to the column web, then the component of the beam force parallel to the column web is used to calculate M×pb

If no reduced beam section is specified on a member than the capacity of the full member is utilized.

If AISC 358-05 RBS Moment Frame Connections are designated in the code selection dialog, a 1.1 factor on the Mpr calculation is replaced with the Cpr value provided by the user for Special Moment Frame joints.

For SidePlate connections,the factor on the Mpr calculation is 1.21 and the Strong Column – Weak Beam check is performed as follows:

\frac{Σ Z_{c} (f_{y} - \frac{P_{u}}{A_{g}}) (\frac{h}{h - d_{p l} - d_{c} / 2})}{Σ 1.21 f_{y} Z_{b}} > 1.0

\frac{Σ Z_{c} (\frac{f_{y}}{1.5} - \frac{P_{a}}{A_{g}}) (\frac{h}{h - d_{p l} - d_{c} / 2})}{Σ \frac{1.21}{1.5} f_{y} Z_{b}} > 1.0

where

dpl	=	depth of SidePlate
d_c	=	depth of column
h	=	average story height

For DuraFuse connections, the factor on the M_pr calculation is 1.0 and the Strong Column – Weak Beam check is performed as follows:

\frac{Σ Z_{c} [\frac{H}{H - (d_{b} / 2 + C 6 + d_{c} / 4)}] (F_{y c} - \frac{P_{u}}{A_{g}})}{Σ (Z_{b} F_{y b} + M_{v})} > 1.0

\frac{Σ Z_{c} [\frac{H}{H - (d_{b} / 2 + C 6 + d_{c} / 4)}] (F_{y c} - \frac{P_{u}}{A_{g}})}{Σ (\frac{Z_{b} F_{y b}}{1.5} + M_{v})} > 1.0

where

H	=	Half of the story height, in (mm)
C6	=	Cover plate extension above or below adjacent beam depths.
M_v	=	Additional moment due to shear amplification from the centerline of the column to the plastic hinge location (face of column).

For Yield-Link^® connections, the factor on the M_pr calculation and Strong Column – Weak Beam check is performed as follows:

M_pr = P_r - Link (Beam Depth + t-stem)

\frac{Σ Z_{c} (f_{y} - \frac{P_{u}}{A_{g}})}{Σ f_{y} Z_{b}} > 1.0 for LRFD, and

\frac{Σ Z_{c} (\frac{f_{y}}{1.5} - \frac{P_{a}}{A_{g}})}{\frac{Σ f_{y} Z_{b}}{1.5}} > 1.0 for ASD

For the exception (if necessary) the design shear strength of a story is calculated as the component of the major axis shear strength, of all the columns in the direction of the column under consideration, added together. All columns, not only those columns of the special moment frame type, are considered. The exception requiring consideration of only exempt columns is not considered.

§9.7 [E3.4c(2)] Beam-To-Column Connection Restraint

A column will be assumed to remain elastic only if the ratio from Equation 9-3 is greater than 2.0.

A joint is considered restrained if contained within a deck, is a beam frames into the weak axis of the column, or by the user specifying that the column is braced.

If the user indicates that the minor axis of the joint column is unbraced then the physical bracing (deck or beams) is ignored and the joint is considered unrestrained.

The deck is only considered to brace the joint at the elevation of the top flange of the beams framing into the flanges of the column.

If a beam (not a joist) is determined to frame into the minor axis of the column at the joint, then RAM Frame assumes that the joint is restrained at the elevation of both the top and bottom flanges of the framing beams.

§9.8 [E3.4b] Lateral Support of Beams

Pertinent detailing information regarding stiffness and spacing of lateral bracing required of beams is provided.

Beams framing into the side of a lateral girder are assumed to brace both the top and bottom flange of the girder.

Joists framing into the side of a lateral girder are assumed to brace only the top flange of the girder.

If required the engineer can assign user brace points to all lateral beams to meet this provision. The user brace points should represent actual physical bracing to be provided on the constructed beam.