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Redundancy factor, ρ, is automatically obtained horizontal seismic forces according to ASCE 7-16 Section 12.3.4. |
A redundancy factor, ρ, shall be assigned to SYMBOLS
Eh = Horizontal seismic load effect
hwall = height of shear wall
hwp = height of wall pier
Lwall = length of shear wall
Lwp = length of wall pier
ρ = Redundancy factor
QE = Effects of horizontal seismic forces from V or Fp
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The Redundancy factor, ρ, is used for the seismic force-resisting system in each of two orthogonal directions for all structures in accordance with Eq. 12.4-3.
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According to 12.3.4.1
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The value of - ρ is permitted to equal 1.0 for the following:
Structures assigned to Seismic Design Category B or C
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P-delta effects and story drift calculation
Design of
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Design of nonbuilding structures that are not similar to buildings
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collector elements, splices, and their connections
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using the seismic load effects
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with the overstrength factor of Section 12.4.3
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Design of members or connections where the seismic load effects, including overstrength
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factor
Diaphragm loads determined using Eq. (12.10-1), including the limits imposed by Eqs. (12.10-2) and (12.10-3)
Structures with damping systems designed
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per ASCE Chapter 18
Design of structural walls for out-of-plane forces, including their anchorage
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Redundancy Factor, ρ, for Seismic Design Categories D through F
For structures assigned to Seismic Design Category D and having with extreme torsional irregularity as defined in Table 12.3-1, Type 1b, ρ shall equal equals 1.3.
For other structures assigned to Seismic Design Category D and for structures assigned to Seismic Design Categories E or F, ρ shall equal is controlled automatically. Moreover, the software uses 1.3 unless one of the following two conditions is met, whereby ρ is permitted to be taken as 1.0. A reduction in the value of ρ from 1.3 is not permitted for structures assigned to Seismic Design Category D that have an extreme torsional irregularity (Type 1b). conditions occurs.
Seismic Design Categories E and F are not also specified allowed to use because extreme torsional irregularities are prohibited (see Section 12.3.3.1).a.
Each story resisting more than 35% of the base shear in the direction of interest
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according to Table 12.3-3.
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Structures are regular in plan at all levels provided that the seismic force-resisting systems consist of at least two bays of seismic force-resisting perimeter framing on each side of the structure in each orthogonal direction at each story resisting more than 35% of the base shear.
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Topics covered in this section:
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Lateral Force-Resisting Element | Requirement |
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Braced frames | Removal of an individual brace, or connection thereto, would not result in more than a 33% reduction in story strength, nor does the resulting system have an extreme torsional irregularity (horizontal structural irregularity Type 1b). |
Moment frames | Loss of moment resistance at the beam-to-column connections at both ends of a single beam would not result in more than a 33% reduction in story strength; nor does the resulting system have an extreme torsional irregularity (horizontal structural irregularity Type 1b). |
Shear walls or wall piers with a height-to-length ratio greater than 1.0 | Removal of a shear wall or wall pier with a height-to-length ratio greater than 1.0 within any story, or collector connections thereto, would not result in more than a 33% reduction in story strength; nor does the resulting system have an extreme torsional irregularity (horizontal structural irregularity Type 1b). The shear wall and wall pier height-to-length ratios are determined as shown in Figure. |
Cantilever columns | Loss of moment resistance at the base connections of any single cantilever column would not result in more than a 33% reduction in story strength; nor does the resulting system have an extreme torsional irregularity (horizontal structural irregularity Type 1b). |
Other | No requirements. |
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