Bond beam chord and collector
A reinforced concrete masonry bond beam at a roof or floor diaphragm: as the chord it carries the diaphragm's bending moment as a tension and compression couple, as the collector (drag strut) it delivers the diaphragm reaction of a wall line to a shear wall shorter than the line. Wind and seismic, strength or allowable stress design (the switch in the toolbar), with the overstrength factor Ω0 on collectors where ASCE 7-22 12.10.2.1 requires it. US and metric units.
Edition. TMS 402-22 is not on hand: the masonry uses the shared library (the 402-16 text read in the library scan, with the 402-22 numbering of the TMS cross-reference list; to confirm against the code text). ASCE 7-22 12.10 was read in the library copy.
Inputs of the bond beam #
- Bond beam: what it acts as (chord, collector or both); the wall thickness; 1 or 2 courses, each with 1 or 2 bars of one size; Grade 60 or 40; f′m; coarse or fine grout (the clearance around the bars, TMS 402 6.1.4); epoxy coating (150 % development length); the lap length provided; corner bars and their leg length.
- Diaphragm: span L along the chord and depth b between chords; the wind and seismic loads per foot of span at strength level. The seismic load is the diaphragm force Fpx of ASCE 7-22 12.10.1.1 (Eq. 12.10-1, not less than 0.2 SDS Ie wpx).
- Collector: the reaction of the wall line, from the same diaphragm (R = w L / 2 on the end wall line, whose length is then the diaphragm depth) or entered with the line length; the shear wall length and whether it sits at one end of the line or in the middle. The diaphragm shear is taken uniform along the line.
- Seismic: the seismic design category (Ω0 applies in SDC C to F), Ω0 of ASCE 7-22 Table 12.2-1 for the system (2.5 prefilled, reinforced masonry shear walls), and SDS, Ie and the weight wpx when you want the minimum of Eq. 12.10-2 checked (wpx = 0 skips it).
Auto-design (editor toolbar) varies the courses, bars per course, bar size, lap and corner bar legs. Objective: the least bond beam steel, then one course before two. The diaphragm, loads, wall line, f′m, wall thickness and seismic factors are kept.
Checks performed #
| Check | Basis |
|---|---|
| Chord tension and compression | T = C = w L² / (8 b) for each load type, ASCE 7-22 2.3.1 / 2.3.6 or 2.4.1 / 2.4.5 (1.0W, 1.0E or 0.6W, 0.7E); no Ω0 on chords (12.10.1) |
| Collector tension and compression | F = R (Lc − Lw) / Lc (wall at one end) or half of it (wall centred); seismic × Ω0 in SDC C to F (12.10.2.1) |
| Tension on the bars | Strength: φ As fy, φ = 0.90 (TMS 402 Table 9.1.4); allowable stress: As Fs (8.3.3.1) |
| Compression on the bond beam | Strength: φ 0.80 (0.80 f′m An), φ = 0.65 (9.3.3.1.1, Table 9.1.4); allowable stress: 0.25 f′m An (8.3.4.2.1). Braced continuously by the wall and diaphragm (no slenderness reduction); the bars are not tied and are not counted (9.3.2) |
| Minimum diaphragm force | Seismic load × L ≥ 0.2 SDS Ie wpx (Eq. 12.10-2), when wpx is entered |
| Bar size and area | Diameter ≤ t/8 and ≤ 1/3 of the grout space; area at a lap ≤ 8 % of the grout space (6.1.3) |
| Lap splices and corner bars | ld = 0.13 db² fy γ / (K √f′m) ≥ 12 in. (Eq. 6-1; 402-22 6.1.6.3.1, 6.1.7.1.2), K the least of cover, clear spacing and 9 db; without corner bars an advisory says the force cannot pass the corner |
The drawings are the diaphragm plan (chords, the wall line with its shear wall and collector, dimensions) and the bond beam section with its bars.
Limitations #
- A simply supported diaphragm under a uniform load; continuous, cantilevered or flexible-rigid diaphragm analyses are yours (enter the reaction of the line instead).
- The bond beam under the chord or collector force only: its action as a lintel, or with the out-of-plane wall bending at the same time, is not combined.
- The diaphragm-to-bond-beam connection (ledger and anchor bolts: use the masonry anchor calculation), the shear wall, transfer forces of irregularities (12.10.1.1) and the 25 % increase of 12.3.3.4 for connections of irregular structures in SDC D to F are not designed.
- The overstrength combinations are applied to the force you enter; the three cases (a) to (c) of 12.10.2.1 are covered when that force is the largest Fpx-based force.
Verification examples #
Verification status: 8 values compared in 3 examples (0 published, 3 hand calculations from the cited equations): 8 within tolerance, 0 recorded deviations. No published example: every value is a hand calculation. That checks the program against this reading of the code, not the reading itself. Code basis: not yet recorded for this module.
No published example is on hand: hand calculations of the chord and collector forces, the bar and masonry strengths and the development length of the default bond beam. TMS 402-22 itself is to be read for the final numbering; the equations are from the 402-16 text (Eq. 6-1, 8.3, 9.3).