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

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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

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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