Px ∆

θ=

(Eq C-30)

Vxh sx C d

Where:

Px = the total vertical design load at and above Level x (kN or kip). When calculating the vertical

design load for purposes of determining P-delta, the individual load factors need not exceed

1.0.

∆ = the design story drift occurring simultaneously with Vx (mm or in).

Vx = the seismic shear force acting between Level x and x-1 (kN or kip).

The stability coefficient, θ shall not exceed θmax determined as follows:

0.5

θmax =

≤ 0.25

(Eq C-31)

βC d

Where:

β = the ratio of shear demand to shear capacity for the story between Level x and x - 1. This

ratio may conservatively be taken as 1.0.

When the stability coefficient, θ is greater than 0.10 but less than or equal to θ max the incremental factor

related to P-delta effects, ad shall be determined by rational analysis (see FEMA 303, Commentary,

5.3.7). To obtain the story drift for including the P-delta effects, the design story drift, ∆ shall be

multiplied by 1.0/(1 - θ). When θ is greater than θ max the structure is potentially unstable and shall be

redesigned.

C12. DIAGONAL STRAP DESIGN. From the values of seismic story shear, Vx and additional shear

force due to torsion, the shear panel dimensions are defined and diagonal straps designed. The straps

are tension only members and their design strength is defined by the following equation (AISI, C2, p. V

45):

φt A nFsy = φt ∑ (b s t s )Fsy

(Eq C-32)

Where:

φ = the resistance factor for tensile members (0.95).

t

An = the cross-sectional area of the all diagonal straps in tension (bsts).

bs= the width of an individual diagonal strap.

ts = the thickness of an individual strap.

Fsy = the design yield strength of the strap.

The shear panel lateral yield capacity, Qsy when the diagonal straps are the sole lateral-load-resisting

element is calculated as follows:

W

= nsb s t sFsy

Q sy

(Eq C-33)

2

H + W

2

Where:

W = the width of a trial shear panel.

H = the height of a trial shear panel.

C-9

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