Mitchell Welding & Iron Works, Inc.

Flush Beam Substitution

Find a shallower steel beam that fits inside the floor and still carries the load. Answer the questions; the answer updates as you go.

1The beam on the drawings

The engineer's beam is the yardstick. The calculator checks it under the same loads so you can see how hard it is actually working.

Any W shape, like W12x40
Span between supports
ftin
Center of bearing to center of bearing

2Room for the beam

A flush beam has to fit within the floor framing. The beam can be no deeper than the joists, minus anything that sits on top of the steel.

in
Subtract a nailer or shim that sits on the beam, e.g. 1 1/2" for a 2x
Beam depths to consider

3Is the top of the beam braced?

An unbraced beam can roll sideways and buckle long before it bends. Joists or blocking fastened to the beam hold the top flange in place.

4What the beam carries

Use the floor loads when you know the joist spans. If you don't, size the new beam to carry everything the specified beam could carry.

Joists frame into the beam from
ft
ft
Dead / live
/psf
Wall or other load along the beam
deadlive, lb/ft
A wall above is about 10 psf of wall area: an 8 ft wall adds 80 lb/ft dead
Point loadsPosts or beams from above that land on this beam

5Stiffness, ends and steel

Deflection limits keep the floor from feeling bouncy and protect finishes. Building codes require at least L/360 for live load on floors.

How the beam ends are supported
in
Used for point loads

Calculations follow AISC 360-16 (LRFD) for simply supported W shapes, with AISC v15.0 section properties. This is a preliminary sizing tool. A beam substitution must be approved by the engineer of record before it is ordered or installed.