Course · lesson 6 of 6

Lintels

How the STATIX lintel calculator loads and designs a lintel over a wall opening: arching and the load triangle of SANS 10400-K Annex B, floors and beams inside it, precast, masonry and RC lintels, the bearing under the ends to SANS 10164-1 5.4.3, and what the calculator leaves out.

1. Learning outcomes

After this lesson you can:

decide whether the masonry over an opening can arch;
find the load on a lintel from the triangle, floors and beams;
choose between precast, masonry and RC lintels and read the calculator’s answer;
check the bearing under the lintel ends;
know what the calculator does not cover.

2. Before you start

Lesson 4 (f_k, β, concentrated loads) and Loads 1 (the take-down).
The free lintel calculator.
A pocket calculator and about 50 minutes.

3. The load on a lintel

Arching. Bonded masonry over an opening does not simply rest on the lintel: once there is enough of it above and beside the opening, it arches over and carries most of the wall load to the sides. The lintel then carries only the masonry below the arch and the loads that reach it. SANS 10400-K Annex B turns this into a design rule.

The load triangle. Annex B gives the lintel the masonry inside an equilateral (60°) triangle on a base of 1.1 times the clear span, and takes the span as 1.1 times the clear span. The calculator analyses over the larger of that and the clear span plus one bearing, so its moments are on the safe side.

When the masonry can arch. Annex B needs enough masonry above the lintel at mid-span (at least 0.6 times the clear span and 600 mm, B.3.4) and beside the opening (at least 600 mm and 0.2 times the span, B.3.5). If either is missing, the calculator gives the lintel the whole rectangle of masonry above it and every load at 100 %, which is conservative.

Loads from floors and beams. A slab or a beam end that lands inside the triangle goes onto the lintel in full, spread at 45° on the way down (B.3.6 b); one in the interaction zone beside and above it counts at 50 % (B.3.6 c); higher up the arch carries it. Annex B draws the zone but does not dimension it: the calculator takes it 1.1 times the base high, as established practice does, and says so.

Combinations. Lintels carry mostly permanent load, so the STR-P combination often governs. The calculator runs both ultimate combinations and the service one, and designs for the envelope.

4. Kinds of lintel

Three kinds of lintel. The calculator designs a reinforced masonry lintel to SANS 10164-2 and an in-situ RC lintel with the STATIX beam engine to SANS 10100-1. A precast prestressed lintel is not designed there: the page gives its design load and checks it against the safe load you read from the maker’s table. Steel lintels are not offered; design them as steel beams.

Precast lintels and their bearing. SANS 10400-K sets the least bearing of a precast lintel by what it carries and how far it spans; tick “supports roof trusses” on the page and it applies the longer bearings. Only units made to SANS 1504 count as structural.

5. Bearings, bars and what is left out

Bearing under the lintel ends. Each end puts a concentrated load on the pier beside the opening. SANS 10164-1 5.4.3 checks it twice: right under the bearing, against an enhanced local strength set by the bearing type of Figure 2, and lower down at 0.4 times the wall height, where it has spread at 45° and adds to the wall’s own load. The calculator does both for every lintel type; give the wall height for the second.

Anchoring the bars. In a short lintel the bottom bars have little room past the support. SANS 10164-2 7.6.9.2 asks for 12 bar diameters beyond the centre line of the bearing, or 12 diameters plus half the depth from its face. The calculator checks it for a masonry lintel and suggests a longer bearing or hooked bars.

Composite action. A lintel built into the masonry above it can act with that masonry as one deep wall-beam (SANS 10164-1 5.4.4), which allows lighter lintels. The calculator does not use it; it uses the load-triangle method of Annex B, which is simpler and conservative.

What the page gives. The free calculator shows the verdict and each check’s utilisation; with an account, the calc sheet shows the load model step by step and a bending schedule for masonry and RC lintels. It can also take one lintel over several openings with piers between, as a continuous beam. This lesson uses the SANS route throughout.