Masonry Beam Calculator: CMU Lintel Design (TMS 402)

1 · Beam

CMU width ASTM C90

Depth courses

Clear span opening

Bearing length §5.2.1

in.

Unit weight TEK 14-13

Beam supports unreinforced masonry (deflection ≤ L/600 and 0.3 in.) Compression face braced continuously (e.g. by a floor or roof)

2 · Reinforcement & materials

Bottom bars number

Bar size

Depth to bar d (blank = h − 2.25 in.) in.

in.

Stirrups

Stirrup spacing in.

in.

f'_m §9.1.9

psi

f_y Grade 60

ksi

Mortar (for modulus of rupture) Tbl 9.1.9.2

3 · Loads (service, unfactored)

Uniform dead plf

plf

Uniform live plf

plf

Uniform roof live plf

plf

Point dead lb

Point live lb

Point load from left support ft

Enter the masonry above the opening as dead load. Arching action may reduce it (NCMA TEK 17-1D); the calculator applies the loads you enter. Self-weight is added automatically.

How the masonry beam calculator works

This free masonry beam calculator checks a reinforced concrete masonry (CMU) lintel or bond beam over an opening using TMS 402-16 strength design, the edition referenced by the Florida Building Code, 8th Edition (2023). Choose the block width and number of courses, the bottom bars, optional stirrups, f'm, the span and bearing length, and the loads, and the checks update as you type.

What it checks

Flexural strength φM_n = 0.9A_sf_y(d − a/2) with the 0.80f'_m stress block, and the minimum steel requirement M_n ≥ 1.3M_cr
Shear strength: V_nm = 2.25A_n√f'_m plus stirrups V_ns = 0.5(A_v/s)f_yd, limited to 4A_n√f'_m
Service deflection with the effective moment of inertia, against L/600 and 0.3 in. when the beam supports unreinforced masonry
Lateral support of the compression face (32b and 120b²/d), minimum bearing length and maximum bar size
Maximum reinforcement ratio for information, and shear and moment diagrams

Method

The beam is fully grouted, as TMS 402 requires for reinforced masonry beams. The effective span is the clear span plus the depth, but not more than the distance between the centers of the bearings. Self-weight is added to the dead load, and strength checks use the ASCE 7-22 combinations 1.4D, 1.2D + 1.6L + 0.5Lr and 1.2D + 1.6Lr + L.

Deflection uses the service loads D + L + Lr with the effective moment of inertia I_e = (M_cr/M_a)³I_n + [1 − (M_cr/M_a)³]I_cr, where I_cr comes from the cracked transformed section.

Assumptions and limitations

Simply supported single span with uniform loads and one point load. Continuous and fixed-end beams are not covered.
One layer of bottom bars. Top bars, compression steel and torsion are not included.
Loads are applied as entered. Arching action of the masonry above the opening, which can reduce the load on a lintel, is not calculated.
Deep beams with a span-to-depth ratio below about 3 need the deep-beam provisions of TMS 402, which are not checked.

Frequently asked questions

How deep should a CMU lintel be?

Start with the span: one course (8 in.) often works for short openings with light loads, and two or more courses are common for wider openings or heavier loads. Deflection and shear usually decide the depth for short, heavily loaded lintels, and flexure for longer ones.

Does a masonry lintel need stirrups?

Many lintels do not, because the masonry shear strength 2.25An√f'm is enough. When the factored shear exceeds that, add stirrups or use a deeper lintel. The calculator shows when stirrups are needed.

What load should a lintel carry?

The weight of the masonry above the opening plus any floor or roof loads that bear on it. When the masonry above can arch, the lintel may only need to carry a triangle of masonry, as described in NCMA TEK 17-1D. Enter the load you decide to use.

Why is the deflection limit L/600?

TMS 402 limits the deflection of beams that support unreinforced masonry to L/600 and 0.3 in. so the masonry above does not crack. For other cases the calculator reports the deflection for information.

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For educational and preliminary design purposes only. Always verify results with a licensed PE.