Building Construction Handbook, Eighth Edition

Typical situations ~

notched joist over wallplate notched joist to steel beam

RSJ or UB

h = height

above notch

wallplate

d = depth

of joist

h = height

clear of

notches

It is necessary to ensure enough timber above and/or below a

notch to resist horizontal shear or shear parallel to the grain.

To check whether a joist or beam has adequate horizontal shear

strength:

v¼ðV3dÞ...ð2bh^2 Þ

Using the data provided in the previous two pages as applied to

the design of a timber joist of 225¾50 mm cross section, in this

instance with a 50 mm notch to leave 175 mm (h) clear:

v¼ð (^2250) ¾ (^3) ¾ 225 Þ...ð (^2) ¾ (^50) ¾ (^175) ¾ 175 Þ¼ 0 :496 N=mm^2
Shear strength parallel to the grain is given as 0.710 N/mm^2 so
sufficient strength is still provided.
BS 5262-2: Structural use of timber. Code of practice for
permissible stress design, materials and workmanship.
Bressummer (or breastsummer) beam ~
notched joists housed
into large timber beam
bressummer
beam
A long, large section timber beam carrying joists directly or
notched and housed (as shown). A dated form of construction for
supporting a masonry wall and floor/ceiling joists in large
openings. Often found during refurbishment work over shop
windows. Steel or reinforced concrete now preferred.
Notched Timber Joists and Beams