134 Designing and making shelving arrangements
and the shelves should be nailed or screwed to them –
especially if using relatively weak shelving material, such
as chipboard, Contiboard, OSB (oriented strand board)
or MDF (medium- density fibreboard).Splayed bearings to shelf- ends and
sides
Figures 7.2(g)(h): The traditional method for joining
solid- or slatted- shelves at right- angles to each other –
as in a small storage cupboard or (in the case of slatted
shelves) in an airing cupboard – is to splay the ends to
an angle of about 60° to 70° and form splayed hous-
ings in the shelf- sides to accommodate them. These
splayed joints (or bearings) are usually dry- fixed and
panel- pinned, but could be glued as well.Figure 7.2 (g) Three- sided shelf arrangement in a
cupboard, with a splay- ended shelf between the outer
shelves; note that the back- edge bearer (only partly
shown) should be taken right across the wall, under the
three shelves. (h) Slatted shelves.(g)(h)LOADS ON SHELVES LIKENED
TO LOADS ON FLOOR JOISTS
The so- called live- loads on floor joists in residential
properties refer to the aggregate weight of furniture,
fittings, etc, and the number of people who are likely
to use the dwelling – and the formulae to determine
the sectional size of the joists required over certain
spans incorporate tested margins of safety and do
not have to take into account the actual weight of the
furniture or fittings, the actual number of occupants
and visitors likely to load the floors, or their actual
en masse bodyweight related to anorexia or obesity.
Neither, therefore, does the formula given below
for residential (non- commercial or industrial) shelf-
thicknesses related to span have to take into account
the actual size and weight of the books, magazines and
other items to be placed upon them.Spacing of indented end- cleats and
brackets
Regardless of whether the ends of these shelves butt
up against walls or not, the end- cleats and brackets are
normally set in (indented) from the shelves’ ends by
a certain amount, thereby creating cantilevered ends.
And if the amount of indent is calculated, rather than
guessed at, the strength of the remaining shelf- lengths
between the brackets will be significantly improved –
as will the degree of deflection. The simple formula for
a uniformly distributed load is:
Indent = 0.207 × Overall Length of shelf.
For example, a shelf with an overall length of
1500mm would be 0.207 × 1500 = 310.5 (say 310mm)
indented bracket each end. Note, though, that the
formula is for a theoretical uniformly distributed load –
and yet in practical terms, the shelves are more likely
to be unevenly loaded. I would recommend, therefore,
that the formula for unevenly distributed loads should
produce an indent reduced by about 25%. This would
produce a formula of:
Indent = 0.155 × Overall Length of shelf.
Therefore, the same length shelf of 1500mm would
be 0.155 × 1500 = 232.5 (say 232mm) indented
bracket each end – instead of 310mm for shelves with
a uniformly distributed load. Note again though that
the remaining 1036mm between the brackets should
be checked out against the shelf- span formula below,
as certain lengths of shelves will obviously require
intermediate brackets.
Back- edge bearers
Figure 7.2(f ): Note that shelves being supported by
vertical cleats and brackets can be additionally strength-
ened by pre- fixing horizontal shelf- length bearers to the
wall, directly below the shelves and seated on the cleat-
tops, as illustrated below. The back- edge bearers would
be of the same section and chamfered detail as the cleats
**Figure 7.2 (f) Front elevation of a mid- area shelf fixed
to a back- edge bearer seated on vertical cleats. The
three brackets are omitted. (*) The asterisks highlight the
calculated indents for the brackets at each end. Note that
- because of the chamfer – the cleats should be scribed
or housed- in to the underside of the bearer.