E1Ordinary moment frames (OMF)

E1.5a Basic Requirements

There are no limitations on width-to-thickness ratios of members for OMF beyond those in the Specification. There are no requirements for stability bracing of beams or joints in OMF beyond those in the Specification. Structural steel beams in OMF are permitted to be composite with a reinforced concrete slab to resist gravity loads. OMF composed of structural steel trusses and columns shall satisfy the additional requirements of Section E1.7.

E1.5b Protected Zones

There are no designated protected zones for OMF members.

E1.6a Demand Critical Welds

Complete-joint-penetration (CJP) groove welds of beam flanges to columns are demand critical welds and shall satisfy the requirements of Sections A3.4b and I2.3.

E1.6b FR Moment Connections

FR moment connections that are part of the seismic force-resisting system (SFRS) shall satisfy one of the following requirements:

• (a) FR moment connections shall be designed for a required flexural strength that is equal to the expected beam flexural strength, $R_{y} M_{p}$, multiplied by 1.1 and divided by $\alpha_{s}$, where $\alpha_{s}=\mathrm{LRFD}-\mathrm{ASD}$ force level adjustment factor $=1.0$ for LRFD and 1.5 for ASD.

The required shear strength of the connection, $V_{r}$, shall be determined using the capacity-limited seismic load effect. The capacity-limited horizontal seismic load effect, $E_{c l}$, shall be determined as follows:

where

$L_{c f}=$ clear length of beam, in. (mm)

$M_{p}=$ plastic moment, kip-in. (N-mm)

$R_{y}=$ ratio of expected yield stress to the specified minimum yield stress, $F_{y}$

Continuity plates shall be provided as required by Specification Section J10.

User Note: The permitted welds for the welded joints of the continuity plates to the column flanges include CJP groove welds, two-sided partial-

joint-penetration (PJP) groove welds with reinforcing fillet welds, two-sided fillet welds, and combinations of PJP groove welds and fillet welds.

• (b) FR moment connections shall be designed for a required flexural strength and a required shear strength equal to the maximum moment and corresponding shear that can be transferred to the connection by the system, including the effects of material overstrength and strain hardening.

The continuity plate requirements in Section E1.6b(a) shall apply, except that the required flexural strength used to check for continuity plates shall be the maximum moment that can be transferred to the connection by the system.

User Note: Factors that may limit the maximum moment and corresponding shear that can be transferred to the connection include column yielding, panel-zone yielding, the development of the flexural strength of the beam at some distance away from the connection when web-tapered members are used, and others. Further discussion is provided in the Commentary.

• (c) FR moment connections between wide-flange beams and the flange of wide-flange columns shall either satisfy the requirements of Section E2.6 or E3.6, or shall meet the following requirements:
• (1) All welds at the beam-to-column connection shall satisfy the requirements of Chapter 3 of ANSI/AISC 358.
• (2) Beam flanges shall be connected to column flanges using CJP groove welds.
• (3) The shape of weld access holes shall be in accordance with AWS D1.8/D1.8M, clause 6.11.1.2. Weld access hole quality requirements shall be in accordance with AWS D1.8/D1.8M, clause 6.11.2.
• (4) The required strength of the welded joint of the continuity plate to the column flange shall not be less than the available strength of the contact area of the plate with the column flange. Alternatively, continuity plates shall satisfy the requirements of Section E3.6f.2.

User Note: The permitted welds for these welded joints include CJP groove welds, two-sided partial-joint-penetration (PJP) groove welds with reinforcing fillet welds, two-sided fillet welds, and combinations of PJP groove welds and fillet welds.

• (5) The beam web shall be connected to the column flange using either a CJP groove weld extending between weld access holes, or using a bolted single-plate shear connection designed for the required shear strength given in Section E1.6b(a).

User Note: For FR moment connections, panel-zone shear strength should be checked in accordance with Specification Section J10.6. The required shear strength of the panel zone should be based on the beam end moments computed from the load combinations stipulated by the applicable building code, not including the overstrength seismic load.

E1.6c PR Moment Connections

PR moment connections between beams and columns shall satisfy the following requirements:

• (a) Connections shall be designed for the maximum moment and shear from the applicable load combinations as described in Sections B2 and B3.
• (b) The stiffness, strength, and deformation capacity of PR moment connections shall be considered in the design, including the effect on overall frame stability.
• (c) The nominal flexural strength of the PR connection, $M_{n, P R}$, shall be no less than $50 \%$ of $M_{p}$ of the connected beam.

Exception: For one-story structures, $M_{n, P R}$ shall be no less than $50 \%$ of $M_{p}$ of the connected column.

• (d) $V_{r}$ shall be determined in accordance with Section E1.6b(a) with $M_{p}$ in Equation E1-1 taken as $M_{n, P R}$.

E1.7a Analysis Requirements

The truss members and their connections shall be designed for the capacity-limited horizontal seismic load effect, $E_{c l}$, defined by the truss end connection forces prescribed in Section E1.7d.

E1.7b Basis of Design

OMF composed of structural steel trusses and columns are limited to one-story structures.

E1.7c System Requirements

Columns shall be braced out-of-plane at both the top and bottom chord elevations of the moment-connected truss. Stability forces shall be based on the column bracing requirements for panel bracing from Specification Appendix 6, Section 6.2.1. Bracing shall be designed to meet beam-column bracing requirements of Specification

Appendix 6, Section 6.4, using column axial loads and bending moments consistent with connection design forces prescribed in Section E1.7d.

E1.7d Truss-to-Column Connections

Truss-to-column connections shall be designed to transfer top and bottom chord axial forces equal to or greater than the minimum of the following:

• (a) The expected yield strength in tension of the truss chord section, determined as $R_{y} F_{y} A_{g} / \alpha_{s}$
• (b) The chord force associated with the expected flexural strength of the column, determined as $1.1 R_{y} M_{p} / \alpha_{s}$
• (c) The chord force associated with the moment based on the expected shear strength of the column between the top and bottom chord of the connected truss

where

$A_{g}=\text { gross area, in. }^{2}\left(\mathrm{~mm}^{2}\right)$

$F_{y}=$ specified minimum yield stress, ksi (MPa)

OMF truss-to-column connections shall be designed to transfer the vertical shear force generated from end moments consistent with these chord forces.