Masonry bearing

Bearing of a beam or other concentrated load on the top of a concrete masonry wall, by strength design to TMS 402-22: the bearing area under the loaded area (4.4.4), the 2:1 spread along the wall (5.1.1), bearing on the masonry under a bond beam and the nominal bearing strength Bn = 0.8 f'm Abr with φ = 0.60 (9.1.8). It also gives the length of wall that carries the load at half the height and the load per foot, to copy into the wall calculation.

The calculation is by strength design only, so the LRFD / ASD switch is not shown.

Edition. The design basis is TMS 402-22 / TMS 602-22. The text of the 2022 code is not on hand. Section numbers come from TMS's cross-reference and the wording was read in TMS 402-13 (4.3.4 p. C-43, 5.1.3 pp. C-51 to C-52, 9.1.8 p. C-127).

Inputs of the masonry bearing #

• Wall: thickness; the masonry under the load (a bond beam, a fully grouted wall, or hollow units on their face shells); for a bond beam, its courses and the wall under it (hollow, partially grouted with an equivalent solid thickness you enter, or fully grouted); running bond or not; f'm.
• Loaded area: length along the wall and width across it, offset from the wall centre line. The load is taken as concentric on this area: for a beam end that rotates or sits off centre, enter the part of the area concentric with the load. That is your judgment; the code gives no rule.
• Along the wall: the wall each side of the loaded area, to the nearest end, opening or movement joint; the height below the load; the spacing of concentrated loads.
• Loads: by load type, P the concentrated load and w a line load on the wall at the same level. w is added at the section under a bond beam, over the spread length; it does not bear on the loaded area.

Auto-design (editor toolbar) varies loaded length, loaded width and bond beam courses. Objective: the smallest loaded area, with a bond beam course counted as 40 in.². Every other input is kept.

Checks performed #

The wall's axial and flexural strength is not checked here. It depends on the wall's moments and slenderness, which are not inputs, and a bare axial check at this level would suggest a precision it does not have. The key results give the load per foot of wall: check the wall with it in the masonry wall calculation.

The drawings (on screen, in the report and on the PDF / DXF drawing sheet) are the wall elevation with the load, the bond beam courses and the 2:1 lines, and the plan on the wall with A1 and A2.

Limitations #

Not covered: allowable stress design; clay masonry; the bearing plate or beam; anchorage and uplift; the wall's strength; the bond beam as a flexural member; a load pocketed into the side of a wall; grout strength (f'g ≥ f'm).

Simplifications: the bond beam course is 8 in. nominal less the 3/8 in. joint. A2 in a wall not in running bond is taken as A1 (conservative). In partially grouted masonry the equivalent thickness averages grouted and hollow cells: your judgment if grouted cells sit directly under the load.

Still to verify in TMS 402-22 / 602-22 (marked (to confirm against the code text) in the check references): the section number 4.4.4 (the cross-reference row is blank and the number is inferred), the numbering of the bearing φ in 9.1.4, the number of Commentary Figure CC-5.1-5, and that the provisions are unchanged from 402-13.

Verification examples #

Verification status: 25 values compared in 9 examples (0 published, 9 hand calculations from the cited equations): 25 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: written from an older edition, with the differences noted. Not yet compared line by line with the target edition.

No published numeric example of masonry bearing is available free. The Masonry Designers' Guide 2022 examples 7.5-1 to 7.5-3 are paid. Every value below is a hand calculation from the equations above, not a published result; they will be replaced or joined by those examples when the guide is on hand.