Learn · worked example

Masonry lintel design to SANS 10164

Masonry over an opening does not all sit on the lintel. Once the mortar has set, the brickwork arches over the opening, so the lintel carries only a triangle of masonry above it, plus any floor or point load that lands inside that triangle's zone. Loads higher up go round the opening into the walls. That is why a lintel can be much smaller than the wall above suggests, as long as there is enough masonry above and beside the opening for the arch to form. Every number below comes from the free STATIX lintel calculator with the inputs in step 1.

1. The problem

Input	Value
Lintel type	Reinforced masonry lintel (SANS 10164-2)
Clear opening Lc	1800 mm
Wall thickness	230 mm
Bearing each end	350 mm
Masonry above to the floor / roof	2400 mm
Beside shorter side	600 mm
Unit	Brick
Material	Burnt clay
Unit strength nominal	14 MPa
Mortar class	II
Category manufacturing / construction	B / I
Slab / roof G / Q, characteristic	8 kN/m
Slab or roof imposed line load kN per m	2 kN/m
Slab bears	On the wall above
Cover to the bar	40 mm
Infill concrete	Grade 25
Exposure Table 17	E1
Steel corrosion rating Table 15, checked against Table 16	C1 uncoated

2. Effective span and the arch

The effective span runs a little past each face of the opening into the bearing. The masonry can only arch if there is enough height of wall above the opening and enough wall beside it (a pier); otherwise the whole height must be carried.

clear opening 1,800 mm → effective span 1,980 mm (lintel 2,150 mm long) masonry above needed for the arch: 1,080 mm → OK pier beside the opening needed: 600 mm → OK arching: yes, the load triangle applies

3. Loads on the lintel

The lintel carries its own weight, the masonry triangle (zero at the ends, largest at midspan) and any floor load or point load inside the load zone. The worst load combination gives the bending moment and the shear.

masonry triangle: 0.00 → 7.49 kN/m from 85 to 1,075 mm masonry triangle: 7.49 → 0.00 kN/m from 1,075 to 2,065 mm lintel self-weight: 1.49 → 1.49 kN/m from 0 to 2,150 mm governing 1,35G + 1,0Q (STR-P): M = 4.89 kNm, V = 7.16 kN

4. Bending

The lintel (with the masonry or concrete above it working with it, for a reinforced masonry lintel) must resist the moment. A deep lintel has a lower limit on span over depth.

Span/depth >= 1,5 (7.2.4.1 f): [SANS 10164-2 7.2.4.1 f, 7.2.4.2.2] 6.16 ≥ 1.50 OK Flexure: [SANS 10164-2 7.2.4.1, 7.2.4.2] 4.89 ≤ 13.95 kNm OK Minimum area of main steel: [SANS 10164-2 7.6.1] INFO

5. Shear

Near the supports the shear stress must stay within what the masonry or concrete can carry.

Shear: [SANS 10164-2 7.2.5.1, 6.2.4.1] 7.16 ≤ 25.46 kN OK

6. Deflection and lateral stability

A lintel that sags cracks the masonry above, so span over effective depth is limited. A long, slender lintel must also not buckle sideways.

Deflection: span/d (Table 12): [SANS 10164-2 7.2.6, 7.2.3.3, Table 12] 7.1 ≤ 20.0 OK Lateral stability: [SANS 10164-2 7.2.3.3] 1,800.0 ≤ 13,800.0 mm OK

7. Bearing at the ends

The end reactions bear on the walls each side. The stress right under the lintel, and spread down to a depth below it, must stay within what the masonry can take.

Bearing left (on unreinforced masonry): [SANS 10164-1 5.4.3.1 a, Fig. 2] 0.089 ≤ 1.992 MPa OK Bearing right (on unreinforced masonry): [SANS 10164-1 5.4.3.1 a, Fig. 2] 0.089 ≤ 1.992 MPa OK Bearing: stress at 0,4h below: [SANS 10164-1 5.4.3.1 b, Fig. 3a, Table 8] 0.191 ≤ 1.574 MPa OK

8. Steel, cover and materials

Bar size and spacing, laps, anchorage at the ends, cover and corrosion protection, the infill grade and the masonry strength itself.

Construction control category I: [SANS 10164-2 6.4.1.1, Table 9] PASS Mortar class I or II: [SANS 10164-2 5.4.1 a, 6.2.2.1] PASS Masonry strength f_k (compression parallel to the bed joints): [SANS 10164-2 6.2.2.1, 6.2.3] PASS Bar size and spacing: [SANS 10164-2 7.6.2, 7.6.4] 110.0 ≤ 230.0 mm OK Lap length (tension): [SANS 10164-2 7.6.7] INFO End anchorage left: [SANS 10164-2 7.6.9.2] 120.0 ≤ 135.0 mm OK End anchorage right: [SANS 10164-2 7.6.9.2] 120.0 ≤ 135.0 mm OK Infill concrete grade >= 25: [SANS 10164-2 5.4.2.1, Table 1] 25.0 ≤ 25.0 MPa OK Cover to the steel: [SANS 10164-2 9.2.5, Table 18, 7.6.6 b] 40.0 ≥ 20.0 mm OK Corrosion protection of the steel: [SANS 10164-2 9.2.1, Tables 15-16] PASS

RC and precast lintels use the same load triangle; their bending, shear and deflection follow the concrete code. The calc sheet shows every formula.

Run this example yourselfOpen the free STATIX lintel calculator and press Load the example (1,8 m opening in a 230 brick wall) under "How it is calculated". Change any value and every step updates, with a calc sheet.
Open the lintel calculator

A worked example for learning, not a design. Check every value against the current code and your own project, and have the design checked and signed by a registered professional engineer.

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