Course · lesson 5 of 6

Masonry under wind, and reinforced masonry

How a masonry panel carries wind on its face to SANS 10164-1 cl 5.5 as the STATIX masonry wall calculator does it: support conditions, the two flexural strengths and the orthogonal ratio, the moment coefficients, openings, cavity wall ties, and reinforced and bed-joint reinforced masonry as far as the page goes.

1. Learning outcomes

After this lesson you can:

describe a panel’s edges and find its moment coefficient;
use the two flexural strengths and the orthogonal ratio;
check a panel under wind, with its limiting dimensions;
see what openings and cavity ties do to the check;
know when to reinforce, and what the page checks for a reinforced wall.

2. Before you start

Loads 1, lesson 5 (zone pressures) and lesson 4 (f_k, units, cavity walls).
The free masonry wall calculator.
A pocket calculator and about 50 minutes.

3. Panels under wind

A panel under wind. Wind presses on (or sucks at) the face of a wall, and the panel carries it to whatever holds its edges: the floor or foundation below, a roof, ring beam or girt above, and columns, piers or return walls at the sides. SANS 10164-1 5.5.1 sorts each edge as free, simply supported or continuous.

Two flexural strengths. Masonry is much weaker when it cracks along a bed joint (bending about a horizontal axis, the panel spanning vertically) than when the crack has to cross the units (spanning horizontally). Table 4 gives both, by unit, mortar class and, for blocks, strength and thickness; their ratio μ enters the moment coefficients. On the page you enter both values.

Moment coefficients. Table 10 of SANS 10164-1 gives α for twelve panel types, A to L, by which edges are free, simply supported or continuous, for μ from 0.30 to 1.00 and h/L from 0.30 to 1.75. Outside that range the panel is taken as spanning one way. The calculator picks the type from the supports you give.

The resistance. The moment of resistance per metre is f_kx times the section modulus over γ_m. A dead load on the wall raises the weak-direction strength by g_d (5.5.3.1 b), which also raises μ. The page applies the load factor you choose to W_k: 1.6 from SANS 10160-1 by default, while SANS 10164-1 4.2.1.2 itself names 1.4; as STATIX applies them, check against your copy.

Limiting dimensions. Before any moment check, 5.5.2 limits how big a panel may be for its thickness; the smaller values apply with fewer continuous edges. The calculator checks the limit for the panel it has worked out and reports it as its own row.

4. The cl 5.5 route on the page

Two lateral methods on the page. The older one takes an α you enter (with a BS 5628 helper); the SANS 10164-1 cl 5.5 method finds the panel type, α, μ and the limits from the supports you describe, and handles cavity ties and openings. This lesson uses the cl 5.5 method on the SANS route only.

Openings. SANS 10164-1 Appendix F lets a wall with openings be split into sub-panels. The calculator makes the piers beside each opening full height, adds the panels below and above, gives each pier half of the wind on the opening, and treats every edge at an opening as free. A narrow pier with one free edge often ends up spanning vertically, on the weak strength.

Cavity walls under wind. Ties of the right type and number (Table 7: 2.5 per m² for leaves of 90 mm or more and a 50 to 75 mm cavity) let both leaves resist the wind together, the design strength being the sum of the leaves (5.5.3.4). The calculator asks for the tie type: butterfly and double triangle ties count only as far as they can carry the compression, and with no ties stated it takes the outer leaf alone.

5. Reinforced masonry

Reinforced masonry. Where a plain panel cannot carry the wind, bars in grouted block cores turn it into a reinforced wall to SANS 10164-2, which spans vertically between floor and roof. The calculator’s reinforced wall mode checks the bending, the bar spacing and the span-to-depth limit, and shows the detailing rows it leaves to you.

Bed-joint reinforcement. Light wire laid in the bed joints controls cracking and gives the horizontal (secondary) steel a reinforced wall needs, at least 0.05 % of b d. The page counts it as secondary steel in the reinforced wall mode; a panel designed to span horizontally on bed-joint steel (SANS 10164-2 Annex B) is not checked.

What the page leaves to you. The calculator reports what it does not check rather than passing it: detailing rows for reinforced walls, the forces the panel puts into its supports, and movement joints. A NOT CHECKED row is a job for the designer, not a pass.