(a) Direct design method in 8.10
(b) Equivalent frame method in 8.11
(a) For columns not braced against sidesway
(b) For columns braced against sidesway
where M1/M2 is negative if the column is bent in single curvature, and positive for double curvature.
If bracing elements resisting lateral movement of a story have a total stiffness of at least 12 times the gross lateral stiffness of the columns in the direction considered, it shall be permitted to consider columns within the story to be braced against sidesway.
|Flange location||Effective overhanging flange width, beyond face of web|
|Each side of web||Least of:||8h|
|One side of web||Least of:||6h|
(a) Maximum positive Mu near midspan occurs with factored L on the span and on alternate spans
(b) Maximum negative Mu at a support occurs with factored L on adjacent spans only
(a) Maximum positive Mu near midspan of panel occurs with 75 percent of factored L on the panel and alternate panels
(b) Maximum negative Mu at a support occurs with 75 percent of factored L on adjacent panels only
(a) Members are prismatic
(b) Loads are uniformly distributed
(c) L ≤ 3D
(d) There are at least two spans
(e) The longer of two adjacent spans does not exceed the shorter by more than 20 percent
|Positive||End span||Discontinuous end integral with support||wuℓn2/14|
|Discontinuous end unrestrained||wuℓn2/11|
|Negative||Interior face of exterior support||Member built integrally with supporting spandrel beam||wuℓn2/24|
|Member built integrally with supporting column||wuℓn2/16|
|Exterior face of first interior support||Two spans||wuℓn2/9|
|More than two spans||wuℓn2/10|
|Face of other supports||All||wuℓn2/11|
|Face of all supports satisfying(a) or (b)||(a) slabs with spans not exceeding 10 ft (b) beams where ratio of sum of column stiffnesses to beam stiffness exceeds 8 at each end of span||wuℓn2/12|
To calculate negative moments, ℓn shall be the average of the adjacent clear span lengths.
(a) Solid slabs or one-way joist systems built integrally with supports, with clear spans not more than 10 ft, shall be permitted to be analyzed as continuous members on knife-edge supports with spans equal to the clear spans of the member and width of support beams otherwise neglected.
(b) For frames or continuous construction, it shall be permitted to assume the intersecting member regions are rigid.
|Member and condition||Moment of Inertia||Cross-sectional area|
|Flat plates and flat slabs||0.25Ig|
|Member||Alternative value of I for elastic analysis|
|Columns and walls||0.35Ig||0.875Ig|
|Beams, flat plates, and flat slabs||0.25Ig||0.5Ig|
Notes: For continuous flexural members, I shall be permitted to be taken as the average of values obtained for the critical positive and negative moment sections. Pu and Mu shall be calculated from the load combination under consideration, or the combination of Pu and Mu that produces the least value of I.
where ∑Pu and Vus are the total factored vertical load and horizontal story shear, respectively, in the story being evaluated, and Δo is the first-order relative lateral deflection between the top and the bottom of that story due to Vus.
where βdns shall be the ratio of maximum factored sustained axial load to maximum factored axial load associated with the same load combination and I in Eq. (184.108.40.206.4c) is calculated according to Table 220.127.116.11.1(b) for columns and walls.
where M1/M2 is negative if the column is bent in single curvature, and positive if bent in double curvature. M1 corresponds to the end moment with the lesser absolute value.
|Cm = 1.0||(18.104.22.168.3b)|
|(a) M1 = M1ns+ δsM1s||(22.214.171.124.1a)|
|(b) M2 = M2ns+ δsM2s||(126.96.36.199.1b)|
|(c) Second-order elastic analysis|
where ∑Pu is the summation of all the factored vertical loads in a story and ∑Pc is the summation for all sway-resisting columns in a story. Pc is calculated using Eq. (188.8.131.52.2) with k determined for sway members from 184.108.40.206.3 and (EI)eff from 220.127.116.11.4 or 18.104.22.168.5 as appropriate with βds substituted for βdns.
(a) Flexural members are continuous
(b) εt ≥ 0.0075 at the section at which moment is reduced