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Cisca Tjoa, PE

2024-02-27

AISC 341-22 RFEM 6 中可弯矩性系杆件设计

在 RFEM 6 的钢结构设计模块中提供了三种类型的弯矩框架（普通、中间和特殊）。按照 AISC 341-22 进行抗震设计结果，分为两部分：杆件要求和连接要求。

关于地震配置输入的更多详细信息将在另一篇文章中介绍， KB | AISC 341 RFEM 6 中的抗震设计 .

Member Requirements

The following design checks for members that are part of the seismic force-resisting system (SFRS) are available in RFEM. The sections listed refer to Seismic Provisions AISC 341-22 [1].

Width-to-Thickness Limitations [Section D1.1]
Stability Bracing of Beams – Required Strength & Stiffness [Section D1.2a.1(b) for IMF and D1.2b for SMF]
Stability Bracing of Beams – Maximum Spacing [Section D1.2a.1(c) for IMF and D1.2b for SMF]
Stability Bracing of Beams at Hinge Locations – Required Strength [Section D1.2c.1(b)]
Column Required Strength [Section D1.4a]
Column Slenderness Ratio for Unbraced Connection [Section E3.4c.2b]

Width-to-Thickness Limitations for Ductility Requirements

Members in IMF are designated as moderately ductile members according to Section E2.5a. Members in SMF are designated as highly ductile members according to Section E3.5a.

柱子翼缘

The column flange of SMF must satisfy the requirements of AISC Seismic Provisions Section D1.1 [1] for highly ductile members. This design check is shown as EQ 1200 in RFEM (Image 1).

知识库 001875 | AISC 341-22 RFEM 6 中可弯矩性系杆件设计

1 翼缘延性要求

柱子腹板

The limiting width-to-thickness ratio for webs of highly ductile members is determined using the governing load case for axial load, as stipulated in Section D1.4a [1]. The governing load case is based on all load combinations, including gravity only CO, CO with standard seismic load, and CO with overstrength seismic load. This check is shown in EQ 1100 in RFEM (Image 2).

2 腹板延性要求

Similar to the columns, the width-to-thickness checks are also done for the beams.

Stability Bracing of Beams

The required strength and stiffness of the stability bracings are listed in the Stability Bracing by Member tab under “Seismic Requirements” (Image 3). These values can be compared to the calculated available strength and stiffness when designing the bracing members that frame into the beam. There are no design check details available (only references).

3 杆件的稳定性支撑

There are two different values listed for the required strengths. The first value, P_br, is applicable for the stability bracings that are located outside the plastic hinge location. P_br is defined in Equation A-6-7 of Appendix 6 of AISC 360 [3]:

P_{br} = 0.02 \cdot (\frac{M_{r} \cdot C_{d}}{h_{o}})

P_br	稳定梁的支撑所需强度
M_r	梁的所需抗弯强度。 M_r = R_y F_y Z/ α_s [AISC 341 公式 D1-1]
C_d	倍曲率系数 = 1.0 [AISC 341 章节 D1.2a(b)]
h_o	翼缘中心距离 h_o = d - t_f

梁的稳定性支撑 (所需强度)

The second, larger value, P_r, is specifically for the stability bracings at the plastic hinge location. It is defined in Equation D1-4 of AISC 341 [1]:

P_{r} = 0.06 \cdot R_{y} \cdot F_{y} \cdot Z / (α_{s} \cdot h_{o})

P_r	塑性铰位置处稳定梁的所需支撑强度
R_y	预期屈服应力与最小屈服应力之比
F_y	规定的最小屈服应力
Z	截面（或连接）在塑性铰位置的有效塑性截面模量
α_s	LRFD-ASD 力大小调整系数 = 1.0 (LRFD) 和 1.5 (ASD)
h_o	翼缘重心之间的距离

梁的稳定性支撑 (塑性铰所需强度)

The required stiffness, β_br, is defined in Equation A-6-8 of Appendix 6:

β_{br} = \frac{1}{Φ} \cdot (\frac{10 \cdot M_{r} \cdot C_{d}}{L_{br} \cdot h_{o}}) (LRFD)

β_{br} = Ω \cdot (\frac{10 \cdot M_{r} \cdot C_{d}}{L_{br} \cdot h_{o}}) (ASD)

d	有效高度
[SCHOOLTRAINING.NUMBEROFSTUDENTS]	有效高度
[SCHOOLTRAINING.NUMBEROFSTUDENTS]	有效高度
[F12]_y	钢筋屈服强度
[SCHOOLTRAINING.NUMBEROFSTUDENTS]	有效高度

梁的稳定性支撑（所需刚度）

The maximum spacing of the stability bracing must satisfy the requirements of AISC 341-22 Section D1.2a.1(c) for IMF and Section D1.2b for SMF.

L_{br} = \frac{0.17 \cdot r_{y} \cdot E}{R_{y} \cdot F_{y}} for IMF

L_{br} = \frac{0.086 \cdot r_{y} \cdot E}{R_{y} \cdot F_{y}} for SMF

L_br	稳定梁支撑的最大间距
r_y	绕弱轴回转半径
E	弹性模量
R_y	预期屈服应力与最小屈服应力之比
F_y	指定的最小屈服应力

梁的稳定性支撑(最大间距)

The design check for the maximum spacing is presented together with the other member requirements under “Design Ratios of Members”. The design check detail is shown in EQ 2100 (Image 4). The braced length, L_b, is the specified effective length for lateral-torsional buckling (LTB).

4 稳定梁的最大间距

Column Required Strength

All columns that are part of the seismic force-resisting system (SFRS) are required to be designed with the overstrength loads. In many cases, the amplified axial force does not need to be combined with the concurrent bending moments. The option to neglect all bending moments, shear, and torsion in columns for overstrength limit state is activated by default. This option can be deactivated in the Seismic Configuration.

For standard load combinations without overstrength from seismic load effect, the combined loading is checked according to AISC 360-22, Chapter H.

For load combinations with overstrength seismic load, Chapters F and H are not checked when the option to neglect all bending moments, shear, and torsion in columns for overstrength limit state is activated.
In Example 4.3.2 of the seismic manual [2], the controlling case from both load combinations, standard and overstrength, needs to be considered.

Bending moments resulting from a load applied between points of lateral support can contribute to column buckling. Therefore, they are required to be considered concurrently with the axial loads by deactivating the option to neglect the moments.

5 柱所需强度

Column Slenderness Ratio for Unbraced Connection

For columns in SMF with no transverse member bracing at the connection, the potential for out-of-plane buckling at the connection shall be minimized by limiting the slenderness ratio L/r to be equal to or less than 60, according to Section E3.4c.2b [1]. Unbraced connections occur in special cases, such as in a two-story frame without an intermediate floor.

In all other cases, the option to meet this requirement can be deactivated in the Seismic Configuration.

6 柱长细比

The connection requirements are covered in the article KB | RFEM 6 中的 AISC 341-16 弯矩结构连接强度 .

知识库

知识库 001875 | AISC 341-22 RFEM 6 中可弯矩性系杆件设计

作者

Cisca 负责北美市场的客户技术支持和持续的程序开发。

链接

KB | AISC 341 RFEM 6 中的抗震设计

参考

美国钢结构协会 (2022)。 Seismic Provisions for Structural Steel Buildings, AISC 341-22. Chicago: AISC.
AISC。 (2018)。抗震设计手册（第 3 版）。美国钢结构研究所，Chicago。
美国钢结构协会 (2022)。 Specification for Structural Steel Buildings, ANSI/AISC 360-22. Chicago: AISC.

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