返回知识库

1846x

001775

Cisca Tjoa, PE

2023-12-05

AISC 341 RFEM 6 中的支撑框架设计

普通异心支撑框架 (OCBF) 和特殊异心支撑框架 (SCBF) 可以在 RFEM 6 的钢结构设计模块中进行设计。按照 AISC 341-16 和 341-22，抗震设计结果分为两部分：杆件要求和连接要求。

有关地震配置输入的更多详细信息，请参见文章 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 341-16/22 [1].

Width-to-Thickness Limitations [Section D1.1 and F1.5a]
SCBF Stability Bracing of Beams – Required Strength & Stiffness [Sections F2.4b and D1.2a.1(b)]
SCBF Stability Bracing of Beams – Maximum Spacing [Sections F2.4b and D1.2a.1(c)]
Column Required Strength [Section D1.4a]
Brace Slenderness Ratio [Section F1.5b for OCBF and F2.5b(a) for SCBF]

Width-to-Thickness Limitations for Ductility Requirements

The braces in OCBF are designated as moderately ductile members according to Section F1.5a. All members (braces, beams, columns) in SCBF are designated as highly ductile members according to Section F2.5a.

The braces in OCBF must satisfy the requirements of AISC Seismic Provisions Section D1.1 for moderately ductile members. As an exception according to Section F1.5a, braces in tension-only frames with L_c/r greater than 200 do not need to satisfy the ductility requirement. This design check is shown as EQ 1300 in RFEM (Image 1).

知识库 001775 | AISC 341-16 RFEM 6 中的支撑框架设计

延展性检查

请注意： Tension-only frames are not permitted in SCBF as per Section F2.4d.

Stability Bracing of Beams in SCBF

The requirement for stability bracing is only applicable for beams in V- and inverted V-braced frames as per Section F2.4b [1]. The required strength and stiffness of the stability bracings are listed in the Stability Bracing by Member tab under “Seismic Requirements” (Image 2). 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).

梁的稳定性支撑

The required strength, Pbr, is defined in Equation A-6-7 of Appendix 6 of AISC 360-16/22 [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)

请注意： Pr is not applicable to braced frames.

The required stiffness, βbr, is defined in Equation A-6-8 of Appendix 6 of AISC 360-16/22 [3]:

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

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

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 341-16/22 Section F2.4b, which refers to Section D1.2a.1(c):

$L_{br} = \frac{0.19 \cdot r_{y} \cdot E}{R_{y} \cdot F_{y}} (AISC 341 - 16)$

$L_{br} = \frac{0.17 \cdot r_{y} \cdot E}{R_{y} \cdot F_{y}} (AISC 341 - 22)$

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

SCBF 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 in the Design Ratios on Members. The braced length, Lb, is the specified effective length for lateral-torsional buckling (LTB). The design check detail is shown in EQ 2100 (Image 3).

设计验算详情

Column Required Strength

All columns that are part of the seismic force-resisting system (SFRS) are required to be designed with 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 360-16/22 Chapter H.

For load combinations with overstrength seismic load, Chapter H is not applied when the option to neglect all bending moments, shear, and torsion in columns for overstrength limit state is activated. Example 4.3.2 of the Seismic Design Manual [2] demonstrates the design using the controlling case from both load combinations, standard and overstrength.

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 (Image 4).

柱所需强度

Brace Slenderness Ratio

For braces in V or Inverted V Frames in OCBF, the slenderness ratio L_c/r must be less than or equal to 4*√(E/F_y) according to Section F1.5b [1]. The intent is to limit the unbalanced forces that develop in framing members after brace buckling. This design check is shown as EQ 3300 in RFEM (Image 5).

For braces in X-configuration, the option to meet this requirement can be deactivated in the Seismic Configuration.

OCBF 支撑长细比验算

For braces in SCBF, the slenderness ratio L_c/r must be less than or equal to 200, according to Section F2.5b(a) [1]. This design check is shown as EQ 3310 in RFEM (Image 6).

SCBF 支撑长细比验算

Connection Requirements

The Seismic Requirements include the Required Connection Tensile Strength and the Required Connection Compressive Strength of the brace. They are listed in the Brace Connection by Member tab (Image 7). The design check details are not available for the connection strengths. However, the equations and standard references are listed in the table.

支撑连接(按杆件)

The symbols and definitions are shown in the following formulas:

$R_{y} \cdot F_{y} \cdot A_{g} / α_{s}$

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
[THESIS.TITEL]_g	支撑截面毛面积
α_s	LRFD-ASD 力水平调整系数 LRFD 为 1.0，ASD 为 1.5

支撑连接节点所需抗拉强度(OCBF & SCBF)

$1.1 \cdot F_{cre} \cdot A_{g} / α_{s} for OCBF (341 - 16)$

$1.14 \cdot F_{cre} \cdot A_{g} / α_{s} for SCBF (341 - 16 & 341 - 22)$

$F_{ne} \cdot A_{g} / α_{s} for OCBF (341 - 22)$

F_cre	AISC 360-16中截面E的临界屈曲应力，使用预期屈服应力，R_y F_y
[THESIS.TITEL]_g	支撑截面毛面积
α_s	LRFD-ASD 力水平调整系数 LRFD 为 1.0，ASD 为 1.5
_[F12]ne	根据 AISC 360-22 E 截面使用期望屈服应力的公称应力 R_y F_y

支撑连接点需配抗压强度

请注意： The capacity-limited design based on the expected braced strengths will be available in the future release.

知识库

知识库 001775 | AISC 341 RFEM 6 中的支撑框架设计

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。 (2016). AISC 341-16, Seismic Provisions for Structural Steel Buildings. 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。 (2016)钢结构规范, ANSI/AISC 360-16。芝加哥：AISC。
美国钢结构协会 (2022)。 Seismic Provisions for Structural Steel Buildings, AISC 341-22. Chicago: AISC.
美国钢结构协会 (2022)。 Specification for Structural Steel Buildings, ANSI/AISC 360-22. Chicago: AISC.

;