14.2 Reading Beam Schedules, Stirrup Spacing Zones & Bar Cutoff Points

14.2 Reading Beam Schedules, Stirrup Spacing Zones & Bar Cutoff Points

Use the beam mark to locate the schedule entry. Check the direction used for left and right supports and follow each note to the applicable section. Read the first stirrup offset separately from the repeated spacing in an end zone.

Beam Schedule Architecture & Component Identification

Structural framing plans use alphanumeric tags to identify horizontal flexural members:

• Beam Marks: Designated as B1, B2, BM-101, or CB1 (cantilever beam).
• Girder Marks: Designated as G1, G2, or GIR-1. Girders are primary framing members that carry reactions from intersecting secondary beams and transfer them to columns.

The Beam Schedule translates these plan tags into exact steel configurations, detailing the member across its clear span ($l_n$) from the left support, through midspan, to the right support.

Sample Beam Schedule Layout

Longitudinal Reinforcement Breakdown

1. Member Dimensions ($b_w \times h$):
   • $b_w$ = Web width in inches (e.g., 16").
   • $h$ = Total member depth in inches (e.g., 28"). For cast-in-place slabs cast monolithically with beams, $h$ includes the slab thickness ($h_f$).
2. Top Continuous Bars: Extend the full span length along the top of the beam cage, with anchorage at supports as detailed. These provide structural continuity and support stirrup cages.
3. Top Support Add Bars (Negative Moment Steel): Added over supporting columns or girders where structural frames experience negative flexure (tension at top fibers). These bars are placed in the top layer or second layer beneath the continuous bars.
4. Bottom Continuous Bars: Run along the bottom soffit through the full span, extending into supports to resist positive moment and satisfy integrity requirements.
5. Bottom Midspan Add Bars (Positive Moment Steel): Placed in the bottom tension zone at the locations and lengths shown on the approved detail.
6. Skin reinforcement: For nonprestressed and Class C prestressed beams deeper than 36 inches, Section 9.7.2.3 requires longitudinal skin reinforcement distributed on both side faces for a distance of $h/2$ from the tension face. Check the required spacing under Section 24.3.2 and the approved detail.

Deciphering Stirrup Spacing Zones & Shear Detailing

End zones may have closely spaced stirrups to resist shear or provide confinement. Mark each change in spacing along the beam and check the count and distance from the specified datum.

In the example B1 schedule, the first No. 4 stirrup is 2 inches from each support face. The next ten are spaced 4 inches on center. Measured from the left support face, the last stirrup in that end zone is at $2+10(4)=42$ inches. Read the remainder and right end from the schedule. Verify the transitions so no spacing exceeds the specified value.

ACI 318-19 Table 9.7.6.2.2 addresses the maximum spacing of shear reinforcement along the length and across the width. The limits depend on the beam and required shear reinforcement. For a special moment frame beam, Section 18.6.4.4 limits the first hoop to 2 inches from the face of the supporting column. For an ordinary beam, read the first stirrup dimension on the approved detail.

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Flexural Bar Cutoff Points, Inflection Points & Development Extensions

At a bar cutoff, identify where the detail calls for a bar to end and what datum sets that point. ACI 318-19 Section 9.7.3.3 requires applicable flexural reinforcement to extend beyond the theoretical point where it is no longer needed by the greater of $d$ and $12d_b$. The section excepts the supports of simply supported spans and free ends of cantilevers. The design may impose additional development and cutoff requirements. Verify the approved physical bar length and end location.

Sections 9.7.3.8.1 and 9.7.3.8.2 require portions of the maximum positive moment reinforcement to extend along the beam bottom into the supports. For cast-in-place beams, at least one-third at simple supports and one-quarter at other supports extend at least 6 inches. Additional anchorage applies to beams in the primary lateral-load-resisting system under Section 9.7.3.8.2. Under Section 9.7.3.8.4, at least one-third of negative moment reinforcement at a support extends beyond the inflection point by at least the greatest of $d$, $12d_b$ and $\ell_n/16$. The inflection point is where the moment changes sign.

A span-fraction note can supply physical bar lengths for a particular project. If the detail specifies $0.25\ell_n$ measured from the support face into a 24-foot clear span, verify the shown 6-foot extension from that face. The detail and applicable development requirements determine the rest of the bar geometry.

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Torsion Detailing, Closed Stirrups & Beam-Column Joint Intersections

Where the design requires torsion reinforcement, ACI 318-19 Section 9.7.6.3.1 calls for closed stirrups satisfying Section 25.7.1.6 or hoops. Section 9.7.5.1 distributes longitudinal torsion reinforcement inside the perimeter of the stirrups or hoops, no more than 12 inches apart, with a bar or tendon at each corner. Verify the approved stirrup shape, hook detail and perimeter bars.

At a beam-column joint, use the approved section for ties through the joint, bar layering and anchorage. An extra bar in the wrong layer can alter cover and effective depth. ACI 318-19 Section 25.2.1 gives a minimum clear spacing of the greatest of 1 inch, $d_b$ and $4d_{agg}/3$ for parallel nonprestressed reinforcement in a horizontal layer, within its scope. Check the actual specified bar and aggregate sizes. Refer congestion that cannot be resolved within the approved details for review.

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Inspector Field Checklist for Beam Schedules