Non-Ductile Internal Forces per ASCE 7-16 with ideCAD
How ideCAD defines non-ductile internal forces according to ASCE 7-16?
The design internal forces corresponding to the non-ductile behavior are automatically increased by the overstrength factor Ωo selected from Table 12.2-1.
In structural systems with high ductility, the internal forces increased by the Overstrength factor Ωo coefficient cannot be taken higher than those compatible with the yield state defined based on the principle of capacity design.
Structural system selection, Response modification coefficient R, Deflection amplification factor Cd and Overstrength factor Ωo are defined by the user.
Symbols
Ωo = Overstrength factor
Some elements of properly detailed structures are not capable of safely resisting ground-shaking demands through inelastic behavior. These elements must be designed with sufficient strength to remain elastic. The load effect is approximated by the use of an overstrength factor, Ω0, which approximates the inherent overstrength in typical structures based on the structure’s seismic force-resisting systems.
For reduced internal forces corresponding to the non-ductile behavior of the structural system elements, the Overstrength factor is used as the multiplier (Ωo > 1). These internal forces are internal forces that cause brittle collapse, such as shear force in reinforced concrete elements and forces acting on joints in steel elements.
For example, in a reinforced concrete column, the shear forces caused by earthquake effects are obtained by multiplying with the overstrength factor, Ωo. Since the shear force shows brittle collapse behavior, internal forces caused by earthquake effects must be multiplied by the overstrength factor, Ωo, according to 12.4.3.
Structural System Type | Response Modification Coefficient, R | Overstrengh Factor, Ωo | Deflection Amplification Factor, Cd | Structural System Limitations Including Structural Height, hn (ft) Limits | ||||
|---|---|---|---|---|---|---|---|---|
Seismic Design Category | ||||||||
B | C | D | E | F | ||||
A. Bearing Wall Systems | ||||||||
A1 - Special reinforced concrete shear walls | 5 | 21/2 | 5 | NL | NL | 160 | 160 | 100 |
A2 - Ordinary reinforced concrete shear walls | 4 | 21/2 | 4 | NL | NL | NP | NP | NP |
A3 - Detailed plain concrete shear walls | 2 | 21/2 | 2 | NL | NP | NP | NP | NP |
A4 - Ordinary plain concrete shear walls | 11/2 | 21/2 | 11/2 | NL | NP | NP | NP | NP |
B. Building Frame Systems | ||||||||
B1 - Steel eccentrically braced frames | 8 | 2 | 4 | NL | NL | 160 | 160 | 100 |
B2 - Steel special concentrically braced frames | 6 | 2 | 5 | NL | NL | 160 | 160 | 100 |
B3 - Steel ordinary concentrically braced frames | 31/4 | 2 | 31/4 | NL | NL | 35 | 35 | NP |
B4 - Special reinforced concrete shear walls | 6 | 21/2 | 5 | NL | NL | 160 | 160 | 100 |
B5 - Ordinary reinforced concrete shear walls | 5 | 21/2 | 41/2 | NL | NL | NP | NP | NP |
B6 - Detailed plain concrete shear walls | 2 | 21/2 | 2 | NL | NP | NP | NP | NP |
B7 - Ordinary plain concrete shear walls | 11/2 | 21/2 | 11/2 | NL | NP | NP | NP | NP |
C. Moment-Resisting Frame Systems | ||||||||
C1 - Steel special moment frames | 8 | 3 | 51/2 | NL | NL | NL | NL | NL |
C2 - Steel special truss moment frames | 7 | 3 | 51/2 | NL | NL | 160 | 100 | NP |
C3 - Steel intermediate moment frames | 41/2 | 3 | 4 | NL | NL | 35 | NP | NP |
C4 - Steel ordinary moment frames | 31/2 | 3 | 3 | NL | NL | NP | NP | NP |
C5 - Special reinforced concrete moment frames | 8 | 3 | 51/2 | NL | NL | NL | NL | NL |
C6 - Intermediate reinforced concrete moment frames | 5 | 3 | 41/2 | NL | NL | NP | NP | NP |
C7 - Ordinary reinforced concrete moment frames | 3 | 3 | 21/2 | NL | NP | NP | NP | NP |
D. Dual Systems with Special Moment Frames Capable of Resisting at Least 25% of Prescribed Seismic Foces | ||||||||
D1 - Steel eccentrically braced frames | 8 | 21/2 | 4 | NL | NL | NL | NL | NL |
D2 - Steel special concentrically braced frames | 7 | 21/2 | 51/2 | NL | NL | NL | NL | NL |
D3 - Special reinforced concrete shear walls | 7 | 21/2 | 51/2 | NL | NL | NL | NL | NL |
D4 - Ordinary reinforced concrete shear walls | 6 | 21/2 | 5 | NL | NL | NP | NP | NP |
E. Dual Systems with Intermediate Moment Frames Capable of Resisting at Least 25% of Prescribed Seismic Foces | ||||||||
E1 - Steel special concentrically braced frames | 6 | 21/2 | 5 | NL | NL | 35 | NP | NP |
E2 - Special reinforced concrete shear walls | 61/2 | 21/2 | 5 | NL | NL | 160 | 100 | 100 |
E8 - Ordinary reinforced concrete shear walls | 51/2 | 21/2 | 41/2 | NL | NL | NP | NP | NP |
F. Shear Wall-Frame Interactive System with Ordinary Reinforced Concrete Moment Frames And Ordinary Reinforced Concrete Shear Walls | ||||||||
F1 - Shear wall-frame interactive system | 41/2 | 21/2 | 4 | NL | NP | NP | NP | NP |
G. Cantilevered Column Systems Detailed to Conform to the Requirement for | ||||||||
G1 - Steel special cantilever column systems | 21/2 | 11/4 | 21/2 | 35 | 35 | 35 | 35 | 35 |
G2 - Steel ordinary cantilever column systems | 11/4 | 11/4 | 11/4 | 35 | 35 | NP | NP | NP |
G3 - Special reinforced concrete moment frames | 21/2 | 11/4 | 21/2 | 35 | 35 | 35 | 35 | 35 |
G4 - Intermediate reinforced concrete moment frames | 11/2 | 11/4 | 11/2 | 35 | 35 | NP | NP | NP |
G5 - Ordinary reinforced concrete moment frames | 1 | 11/4 | 1 | 35 | NP | NP | NP | NP |
H. Steel Systems not Specifically Detailed for Seismic Resistance, Excluding Cantilever Column Systems | ||||||||
H - Steel Systems not Specifically Detailed for Seismic Resistance | 3 | 3 | 3 | NL | NL | NP | NP | NP |
