29-17

Special Moment Frames Intermediate and Ordinary CIP Moment Frames

Flexural frame members shall satisfy the followingconditions:

Factored axial compressive force Ag f c / 10 Clear span ln 4 effective depth Width to depth ratio bw/h 0.3 Width bw 10 in. Width bw width of supporting member c2 +

distances on each side of the supportingmember equal to the smaller of the width of the supporting member c2 or three-fourths of the overall dimension of supporting member c1

21.5.1

Minimum reinforcement shall not be less than

3 f c bw dfy

and200 bw d

fyat any section, top and bottom, unless provisionsin 10.5.3 are satisfied.

21.5.2.1

The reinforcement ratio () shall not exceed 0.025.

21.5.2.1

At least two bars shall be provided continuously atboth top and bottom of section.

21.5.2.1

Positive moment strength at joint face 1/2negative moment strength at that face of the joint.

21.5.2.2

Neither the negative nor the positive momentstrength at any section along the member shall beless than 1/4 the maximum moment strengthprovided at the face of either joint.

21.5.2.2

Intermediate Factored axial compressive force Agf'c / 10

21.3.2

Ordinary No similar requirements.

Same requirement, except as provided in 10.5.2, 10.5.3, and 10.5.4, although minimum reinforcement need only be provided at sections where tensile reinforcement is required by analysis.

10.5

The net tensile strain at nominal strength shallt not be less than 0.004.

10.3.5

Provide minimum structural integrity reinforcement.

7.13

Intermediate Positive moment strength at joint face 1/3 negative moment strength at that face of the joint.

21.3.4.1 Ordinary No similar requirement.

Intermediate Same requirement, except it is needed to provide only 1/5 of the maximum moment strength at the face of either joint at every section along the member.

21.3.4.1Ordinary No similar requirement.

continued on next page

Fle

xura

l Req

uir

emen

tsG

ener

al

Table 29-3 Flexural Members of Frames

Prestressing steel, where used, shall satisfy the following:

The average prestress fpc shall not exceed the smaller of 500 psi and f'c/10.

Prestressing steel shall be unbonded in potential plastic hinge regions and the calculated strains in the prestressing steel under the design displace- ment shall be less than 0.01.

Prestressing steel shall not contribute to more than 0.25 of the positive or negative flexural strength at the critical section in a plastic hinge region and shall be anchored at or beyond the exterior face of the joint.

Anchorages of the post-tensioning tendons resisting earthquake-induce forces shall be capable of allowing tendons to withstand 50 cycles of loading, bounded by 0.40 and 0.85 of the specified tensile strength of the prestressing steel.

21.5.2.5

No similar requirements.

29-18

Table 29-3 Flexural Members of Frames (contd)

Lap splices of fl exural reinforcement are permitted only ifhoop or spiral reinforcement is provided over the lap length.Hoop and spiral reinforcement spacing shall not exceed d/4 or4 in. Mechanical splices shall conform to 21.1.6 and weldedsplices shall conform to 21.1.7.

21.5.2.3, 21.5.2.4

Lap splices are not to be used: Within joints. Within a distance of twice the member depth from the face of the joint. At locations where analysis indicates fl exural yeilding caused by inelastic lateral displacements of the frame.

21.5.2.3

Hoops are required over a length equal to twice the memberdepth from the face of the supporting member towardmidspan at both ends of the fl exual member.

21.5.3.1

Hoops are required over lengths equal to twice the memberdepth on both sides of a section where fl exural yielding mayoccur in connection with inelastic lateral displacements of theframe.

21.5.3.1

Where hoops are required, the spacing shall not exceed:

d/4 8 diameter of smallest longitudinal bar 24 diameter of hoop bars 12 in.

The fi rst hoop shall be located not more than 2 in. from theface of the supporting member.

21.5.3.2

Where hoops are required, longitudinal bars on the perimetershall have lateral support conforming to 7.10.5.3.

21.5.3.3

Where hoops are not required, strrups with seismic hooks atboth ends shall be spaced at a distance not more than d/2throughout the length of the member.

21.5.3.4

Transverse reinforcement must also be proportioned to resistthe entire design shear force, neglecting the contribution ofconcrete to shear strength, if certain conditions are met.

21.5.4

There is no requirement that splices be enclosedin hoops.

No similar requirement.

IntermediateSame requirement.

21.3.4.2

OrdinaryNo similar requirement.

Reinforcement for fl exural members subject tostress reversals shall consist of closed stirrupsextending around fl exural reinforcement. Also,provide minimum structural integrity reinforcement.

7.11.2, 7.13

IntermediateSame requirement

21.3.4.2

OrdinaryNo similar requirement.

No similar requirement.

IntermediateSimilar requirement except thatseismic hooks are not required.

21.13.4.3

IntermediateTransverse reinforcement mustalso be proportioned to resist the design shearforce.

21.13.3OrdinaryProvide suffi cient transverse reinforce-ment for shear and torsion.

11.4, 11.5

Special Moment Frames Intermediate and Ordinary CIP Moment Frames

Tran

sver

se R

ein

forc

emen

t

S

plic

es

Ag = gross area of section, bw = width of web, d = effective depth of section

f c = specified compressive strength of concrete, fy = specified yield strength of reinforcement

29-23

Table 29-4 Frame Members Subjected to Bending and Axial Loads

Special Moment Frames Intermediate and Ordinary CIP Moment Frames

Gen

eral

Fle

xura

l Req

uir

emen

tsFrame members under this classifi cation must meet the following requirements: Factored axial compressive force > Ag f c / 10 . Shortest cross-sectional dimension 12 in. Ratio of shortest cross-sectional dimension to per-

pendicular dimension 0.4.

21.6.1

The fl exural strengths of columns shall satisfy the following:Mnc (6/5) Mnb

where Mnc = sum of moments at the faces of the joint, corresponding to the nominal fl exural strengths of the columns.

Mnb = sum of moments at the faces of the joint, corresponding to the nominal fl exural strengths of the beams. In T-beam costruct-ion, slab reinforcement within an effective slab width defi ned in 8.12 shall be consid-ered as contributing to fl exural strength.

If this requirement is not satisfi ed, the lateral strength and stiffness of the column shall not be considered when determining the strength and stiffness of the structure, and the column shall conform to 21.13.

21.6.2

The reinforcement ratio (g) shall not be less than 0.01 and shall not exceed 0.06.

21.6.3.1

Mechanical splices shall conform to 21.1.6 and welded splices shall conform to 21.1.7. Lap splices are permit-ted only within the center half of the member length, must be tension lap splices, and shall be enclosed within transverse reinforcement conforming to 21.6.4.2 and 21.6.4.3.

21.6.3.2

The transverse reinforcement requirements discussed in the following fi ve items on the next page need only be provided over a length (lo) from each joint face and on both sides of any section where fl exural yielding is likely to occur. The length (lo) shall not be less than: depth of member 1/6 clear span 18 in.

21.6.4.1

Sp

lices

Intermediate Factored axial compressive force > Ag f c / 10 .21.3.2

Ordinary No similar requirements.

No similar requirements.

The reinforcement ratio (g) shall not be less than 0.01 and shall not exceed 0.08. For a compression member with a cross section larger than required by consider-ations of loading, the reinforcement ratio (g)can be reduced below 0.01, but never below 0.005 (10.8.4).

10.9

There is no restriction on the location of splices which are typically located just above the fl oor for ease of construction.

Intermediate The length (lo) is the same as for special moment frames.

21.3.5.2

Ordinary No similar requirements.

Tran

sver

se R

ein

forc

emen

t

continued on next page Ach = cross-sectional area of member measured out-to-out

of transverse reinforcement

Ag = gross area of section

f'c= specifi ed compressive strength of concrete

fyt = specifi ed yield stress of transverse reinforcement

bc = cross-sectional dimension of column core measured center-to-center

of outer legs of the transverse reinforcement comprising area Ashhx = maximum horizontal spacing of hoop or crosstie legs on all faces of

the column

s = spacing of transverse reinforcement

so = longitudinal spacing of transverse reinforcement within the length lo.

29-24

Ratio of spiral reinforcement (s) shall not be less than the value given by:

s = 0.45 AgAch

1

fc'

fytand shall conform to the provisions in 7.10.4.

10.9.3

Transverse reinforcement must be provided to satisfy both shear and lateral support requirements for longitudinal bars.

7.10.5, 11.1

No similar requirements.

Intermediate Maximum spacing so is 8 smallest longitudinal bar diameter, 24 hoop bar diameter, 1/2 smallest cross-sectional dimension, or 12 in. First hoop to be located no further than so/2 from the joint face. 21.3.5.2

Ordinary No similar requirement.

Vertical bars shall not be farther than 6 in. clear from a laterally supported bar.

7.10.5.3

Intermediate Outside the length lo, spacing oftransverse reinforcement shall conform to 7.10 and 11.4.5.1.

21.3.5.4

Ordinary Transverse reinforcement to conformto 7.10 and 11.4.5.1.

Intermediate Transverse reinforcement must also be proportioned to resist the design shear forces specifi ed in 21.3.3.

Ordinary Provide suffi cient transverse reinforce-ment for shear. 11.5.4, 11.5.6

Intermediate Similar to 21.6.4.6

21.3.5.6

Ordinary No similar requirements.

Table 29-4 Frame Members Subjected to Bending and Axial Loads (contd)

Ratio of spiral reinforcement (s) shall not be less than the value given by:

s = 0.12 fc'

fyt0.45 Ag

Ach1

fc'

fyt

21.6.4.4

Total cross-sectional area of rectangular hoop reinforcement for confi nement (Ash) shall not be less than that given by the follow-ing two equations:

Ash = 0.3 sbc fc' / fyt( ) Ag / Ach( )1[ ]

Ash = 0.09 sbc fc' / fyt( ) 21.6.4.4

If the thickness of the concrete outside the confi ning transverse reinforcement exceeds 4 in., additional transverse reinforcement shall be provided at a spacing 12 in. Concrete cover on the additional reinforcement shall not exceed 4 in.

21.6.4.7

Transverse reinforcement shall be spaced at distances not ex-ceeding 1/4 minimum member dimension, 6 longitudinal bar diameter, 4 in. so = 4 + [(14 - hx)/3] 6 in.

21.6.4.3

Cross ties or legs of overlapping hoops shall not be spaced more than 14 in. on center in the direction perpendicular to the longitudi-nal axis of the member. Vertical bars shall not be farther than 6 in. clear from a laterally supported bar.

21.6.4.2, 7.10.5.3

Where the transverse reinforcement as discussed above is no longer required, the remainder of the column shall contain spiral or hoop reinforcement satisfying 7.10 spaced at distances not to exceed 6 longitudinal bar diameter 6 in.unless a larger amount of transverse reinforcement is required by 21.6.3.2 or 21.6.5

21.6.4.5

Transverse reinforcement must also be proportioned to resist the design shear force (Ve).

21.6.5

Columns supporting reactions from discontinued stiff members,such as walls, shall have transverse reinforcement as specifi ed in 21.6.4.2 through 21.6.4.4 over their full height, if the factored axial compressive force, related to earthquake effects exceeds (Agfc / 10).Where design forces have been magnifi ed to account for the overstrength of the vertical elements of the seismic-force-resisting system, the limit of Agfc / 10 shall be increased to Agfc / 4. This transverse reinforcement shall extend into the discontinued mem-ber for at least the development length of the largest longitudinal reinforcement in the column in accordance with 21.7.4.If the column terminates on a footing or mat, the transverse rein-forcement shall extend at least 12 in. into the footing or mat.

21.6.4.6

Special Moment Frame Intermediate and Ordinary CIP Moment FramesTr

ansv

erse

Rei

nfo

rcem

ent

(co

nti

nu

ed)