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001767

Cisca Tjoa, PE

2023-12-05

AISC 341-16 Diseño de barra de momento en RFEM 6

Los tres tipos de pórticos resistentes a momento (Ordinario, Intermedio, Especial) están disponibles en el complemento Cálculo de estructuras de acero de RFEM 6. El resultado del cálculo sísmico según AISC 341-16 se clasifica en dos secciones: requisitos de barras y requisitos de conexión.

Los detalles más detallados sobre la entrada de configuración sísmica se tratan en un artículo separado, Kb | Cálculo sísmico AISC 341 en RFEM 6 .

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 [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.

Ala del pilar

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).

KB 001767 | AISC 341-16 Diseño de barra de momento en RFEM 6

Requisito de ductilidad de la brida

Alma del pilar

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).

Requisito de ductilidad del alma

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).

Arriostramiento de estabilidad por barra

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 360-16 [3]:

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

P_br	Resistencia necesaria del arriostramiento de la viga de estabilidad
M_r	Resistencia necesaria a flexión de la viga. M_r = R_y F_y Z/ α_s [AISC 341 Ecuación D1-1]
C_d	Factor de doble curvatura = 1,0 [AISC 341, sección D1.2a(b)]
h_o	Distancia entre el centro de gravedad del ala h_o = d - t_f

Arriostramiento de estabilidad de vigas (resistencia necesaria)

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 341-16 [1]:

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

P_r	Resistencia necesaria del arriostramiento de la viga de estabilidad en la posición de la articulación plástica
R_y	Relación entre el límite elástico esperado y el límite elástico mínimo especificado
F_y	Mínima tensión de fluencia especificada
Z	Módulo resistente plástico eficaz de una sección (o una conexión) en la posición de la articulación plástica
α_s	Factor de ajuste del nivel de fuerza LRFD-ASD = 1,0 para LRFD y 1,5 para ASD
h_o	Distancia entre el centro de gravedad del ala

Refuerzo de estabilidad de las vigas (resistencia necesaria en la articulación plástica)

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	Canto útil
d	Profundidad estática eficaz
d	Profundidad estática eficaz
f_y	Límite elástico del acero de refuerzo
d	Profundidad estática eficaz

Arriostramiento de estabilidad de las vigas (rigidez necesaria)

The maximum spacing of the stability bracing must satisfy the requirements of AISC 341-16 Section D1.2a.1(c) for IMF and Section D1.2b for SMF.

$L_{br} = \frac{0.19 \cdot r_{y} \cdot E}{R_{y} \cdot F_{y}} for IMF$

$L_{br} = \frac{0.095 \cdot r_{y} \cdot E}{R_{y} \cdot F_{y}} for SMF$

L_br	Separación máxima del arriostramiento de la viga de estabilidad
h_o	Distancia entre centros de gravedad de alas
U	Deformación
S(T_a)	Aceleración de respuesta espectral de cálculo para el período lateral fundamental de la estructura en la dirección considerada
û	desplazamiento en nudo

Arriostramiento de estabilidad de vigas (separación máxima)

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).

Separación máxima de la viga de estabilidad

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 360-16, 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.

Resistencia requerida de la columna

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.

Relación de esbeltez de la columna

The connection requirements are covered in the article Kb | Resistencia de la conexión del pórtico resistente a momentos según AISC 341-16 en RFEM 6 .

Base de datos de conocimientos

KB 001767 | AISC 341-16 Diseño de barra de momento en RFEM 6

Autor

Cisca es responsable del soporte técnico al cliente y el desarrollo continuo de los programas para el mercado norteamericano.

Enlaces

Referencias

Instituto Americano de Construcción de Acero. (2016). AISC 341-16, Seismic Provisions for Structural Steel Buildings. Chicago: AISC.
AISC. (2018). Manual de diseño sísmico , (3ª ed.). Instituto Americano de Construcción de Acero, Chicago.
Instituto Americano de Construcción de Acero. (2016) Especificación para edificios de acero estructural , ANSI/AISC 360-16. Chicago: AISC.

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