Masonry parapet
A concrete masonry parapet cantilevered above the roof line: components-and-cladding wind on parapets or the seismic force on a cantilevered parapet, the parapet designed at the roof line (reinforced or unreinforced, strength or allowable stress with the switch in the toolbar), and the anchorage of the wall to the roof at that line. US and metric units.
Edition. TMS 402-22 is not on hand: the parapet uses the shared masonry library (the 402-13 text with the 402-22 numbering where confirmed), as the freestanding wall does. ASCE 7-22 is on hand and read for 30.6 (parapets), 13.3 and Table 13.5-1, 12.11.2.1 and 1.4.4.
Inputs of the parapet #
- Parapet: height above the roof line; wall thickness; reinforced or unreinforced; grouting; f′m; the mortar (unreinforced); the bar, spacing and grade (bars at the centre); the wall weight with its grout; the wall below from the floor to the roof (for the anchorage reaction and the tributary weight); the mean roof height.
- Wind: from the basic wind speed, exposure, Kzt, Ke and Kd (0.85), the wall zone (4 or 5, Figure 30.3-1) and the roof zone behind the parapet (2 or 3, Figure 30.3-2A), and GCpi for the wall below (0.18 enclosed); or the net parapet pressure and the wall pressure entered at strength level. The effective wind area of the parapet is its height times a third of it.
- Seismic: SDS, Ip, and the building's R, Ω0 and Ie (for Rμ); the flexible diaphragm span Lf for ka (0 for a rigid diaphragm).
- Anchorage: the anchor spacing along the wall and the design strength of one anchor at strength level (φRn: the masonry anchor type, or the connector's listing).
Auto-design varies the wall thickness, the bar and spacing and the anchor spacing. Objective: the least masonry and steel, then the fewest anchors. The height, loads, f′m, the anchor's strength and the building data are kept.
Checks performed #
| Check | Basis |
|---|---|
| Wind on the parapet | ASCE 7-22 30.6, Eq. 30.6-1: case A (wall positive, roof edge or corner negative) and case B (wall positive and negative); zone 3 takes zone 2 with a parapet of 3 ft or more (Figure 30.3-2A note 5); Figure 30.4-1 above 60 ft |
| Seismic on the parapet | ASCE 7-22 13.3.1: Fp = 0.4 SDS Ip Wp (Hf/Rμ)(CAR/Rpo), CAR = 2.2, Rpo = 1.5, Hf = 3.5 at the roof, between 0.3 and 1.6 SDS Ip Wp; Ev = 0.2 SDS D |
| Parapet flexure, reinforced | Strength: stress block, φ by Table 9.1.4 (9.3.2). Allowable stress: cracked transformed section (8.3) |
| Parapet flexure, unreinforced | M/S − P/A at most φ fr (Table 9.1.9.1) or Table 8.2.4.2 |
| Parapet shear | 9.3.3.1.2 / 8.3.5 (reinforced), 9.2.6 / 8.2.6 (unreinforced) |
| Anchorage at the roof line | Wind reactions inward and outward of the wall below and the parapet; 12.11.2.1 Fp = 0.4 SDS ka Ie Wp (at least 0.2 ka Ie Wp and 5 psf); 1.4.4 (0.2 Wp, at least 5 psf); times the spacing against the anchor's design strength |
The anchorage is at strength level whatever the method of the parapet. A solid masonry parapet carries the difference of the pressures on its two faces, so the GCpi of Eq. 30.6-1 cancels across it; GCpi is used on the wall below. The drawing is a section through the parapet and the top of the wall at the roof.
Limitations #
- Low-slope roofs only (Figure 30.3-2A); sloped roofs, return corners and braced parapets are not covered.
- The roof diaphragm, its continuous ties (12.11.2.2), the 1.4 factor on steel anchorage elements (12.11.2.2.2), the anchor hardware, coping and flashing are not designed.
- The wall below is not designed in its own span (masonry wall or slender wall types).
- Second-order effects in the parapet are neglected (short cantilevers).
Verification examples #
Verification status: 13 values compared in 5 examples (0 published, 5 hand calculations from the cited equations): 13 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 masonry parapet example to ASCE 7-22 is on hand: hand calculations of the parapet wind pressures (cases A and B), the seismic force, the moment and strength at the roof line, and the anchorage reactions, from the cited equations.