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Transverse reinforcement determined in ■ accordance with AC I 318-02 Section 21.10.3 at both ends

Figure 4.21. Intermediate moment-resisting frame (IMRF); transverse reinforcement requirements for frame beams.

Figure 4.22. Intermediate moment-resisting frame; transverse reinforcement requirements for frame columns.

4.2.3.4. Detailing Requirements for Two-Way Slab Systems Without Beams

Detailing requirements given in Sections 21.12.6.1 through 21.12.6.7 may be summarized as follows:

• All reinforcement provided to resist Ms shall be placed within the column strip defined in Section 13.2.1.

• Reinforcement to resist yrMs shall be placed within the effective slab width defined in Section 13.5.3.2.

• Not less than one-half of column strip reinforcement at the support shall be placed within the effective slab width defined in Section 13.5.3.2.

• Not less than one-quarter of top reinforcement at the support in the column strip shall be continuous throughout the span.

• All bottom reinforcement in the column strip shall be continuous or spliced with class A splices. At least two of the column strip bottom bars shall pass within the column core and shall be anchored at exterior supports.

• Not less than one-half of all bottom reinforcement at midspan shall be continuous and shall develop its yield strength at the face of the support as defined in Section 13.6.2.5.

Figure 4.23. Seismic detailing requirements for two-way slabs in areas of moderate seismic risk; flat slab-beams not permitted in UBC zones 3 and 4, or for buildings assigned to SDC C, D, E, or F.

• At discontinuous edges of the slab, all top and bottom reinforcement at the support shall be developed at the face of the support as defined in Section 13.6.2.5.

Refer to Figs. 4.23, 4.24, and 4.25 for pictorial representations of these items.

4.2.4. Special Moment-Resisting Frames

4.2.4.1. General Requirements: Frame Beams

General requirements for the design and detailing of special moment-resisting frames (SMRF) given in Sections 21.3.1.1 through 21.3.1.4 are summarized as follows:

Figure 4.24. Seismic detailing requirements for two-way slabs in areas of moderate seismic risk; column strip.
Figure 4.25. Seismic detailing requirements for two-way slabs in areas of moderate seismic risk; middle strip.

• Factored axial compressive force < Af'10.

• Width < width of supporting member (measured on a plane perpendicular to the longitudinal axis of the flexural member) + distances on each side of the supporting member not exceeding three-fourths of the depth of the flexural member.

See Fig. 4.26 for schematics of general requirements.

4.2.4.2. Flexural Reinforcement: Frame Beams

This last requirement, referring to the width limitation, effectively eliminates the use of flat slabs as frame beams in areas of high seismicity or for buildings assigned to SDC D, E, or F.

Figure 4.26. Frame beam; general requirements, special moment frame.

Structural requirements for flexural reinforcements and their splices given in Sections 21.3.2.1 through 21.3.2.4 for frame beams are as follows:

• Minimum reinforcement shall not be less than at any section, top and bottom, unless provisions of Section 10.5.3 are satisfied.

• The reinforcement ratio p shall not exceed 0.025.

• At least two bars must be provided continuously at both top and bottom of section.

• Positive moment strength at joint face shall be >1h negative moment strength provided at that face of the joint.

• Neither the negative nor the positive moment strength at any section along the member length shall be less than 1/4 the maximum moment strength provided at the face of either joint.

• Lap splices of flexural reinforcement are permitted only if hoop or spiral reinforcement is provided over the lap length. Hoop and spiral reinforcement spacing shall not exceed

• Lap splices are not permitted

• Within a distance of 2h from the face of the joint.

• At locations where analysis indicates flexural yielding caused by inelastic lateral displacements of the frame.

• Mechanical splices shall conform to Section 21.2.6 and welded splices shall conform to Section 21.2.7.1.

4.2.4.3. Transverse Reinforcement: Frame Beams

Requirements for transverse reinforcement (hoops and stirrups) in frame beams given in Sections 21.3.3.1 through 21.3.3.6 and Section 21.3.4 are summarized as follows:

• Hoops are required in the following regions of frame members:

• Over a length equal to 2h from the face of the supporting member toward midspan at both ends of the flexural member.

• Over lengths equal to 2h on both sides of a section where flexural yielding may occur in connection with inelastic lateral displacements of the frame.

• Where hoops are required, the spacing shall not exceed:

• 8 x diameter of smallest longitudinal bar.

• The first hoop shall be located no more than 2 in. from the face of the supporting member.

• Where hoops are required, longitudinal bars on the perimeter shall have lateral support conforming to Section 7.10.5.3.

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

and and

200 bwd fy

• Stirrups or ties required to resist shear shall be hoops over lengths of members in Sections 21.3.3, 21.4.4, and 21.5.2.

• Hoops in flexural members shall be permitted to be made up of two pieces of reinforcement: a stirrup having seismic hooks at both ends and closed by a crosstie. Consecutive crossties engaging the same longitudinal bar shall have their 90-degree hooks at opposite sides of the flexural member. If the longitudinal bars secured by the crossties are confined by a slab on only one side of the flexural frame member, the 90-degree hooks of the crossties shall be placed on that side.

• Transverse reinforcement must also be proportioned to resist the design shear forces.

Figures 4.27 and 4.28 show transverse reinforcement schematics for frame beams.

4.2.4.4. General Requirements: Frame Columns

The requirements given in Section 21.4 are summarized as follows:

• Factored axial compressive force > Af/10.

• Shortest cross-sectional dimension measured on a straight line passing through the geometric centroid >12 in.

• Ratio of the shortest cross-sectional dimension to the perpendicular dimension >0.4.

Figure 4.27. Frame beam; transverse reinforcement requirements, special moment frame.
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