Fixing Points for Grabrails

Is there a way around stringent standards regarding fixing points for grabrails?

Interesting question! The 1100 Newtons of force
specified in Australian Standard AS1428 is in fact
a guestimate based on force calculations
(hopefully including a larger than average user).

Let me try and elaborate. The purpose of a
grabrail is to prevent a fall, in order to do this they
must remain stable when grabbed by a human
who has lost balance and is falling. Falling forces
are determined by force of gravity (acceleration
and terminal velocity) on something times its
weight. Weight (N) = mass (kg) x gravitational field strength (N/kg).

Let me give an example taken from some new
research into forces generated during mountain
climbing falls (Messner, Meraner, Schliernzauer,
Knuenz, & Nachbauer, 1999). In their example a
person with a (weight = 70 kg) performing
standardised falls generating a fall factor of z =
0.375. They calculated that the forces on anchor
points (in this case a belaying pin ranged from
4006 - 2083 N depending on direction of fall and
acceleration generated at initiation.

Now whilst this may seen shocking in light of the
moderate weight [i.e. not bariatic or obese person] and the seemingly small margin of error
incorporated in the 1100 N specified in the
standards, it shouldn't be too surprising as basic
physics tells us that terminal velocity occurs when the weight of an object is balanced by the drag of the object. Drag depends on the speed and the shape of an object. Streamlined objects like a fish or a Grand Prix car have a high terminal velocity, compared to most human beings falling. In other words, the greater the drag the higher the forces generated in falling on the grabrail fixing points.

Having said all of that, the Centre for Accessible
Environments (1999) produced notes to assist
OT's to understand Housing Adapation. These
notes had the following to say about principles
underlying 'best practice' of fixings pp 97-98.

Fixings for supports [rails & grabrails]

Fixings are designed to penetrate a structural
support material [brick, fibro, wood etc], and are
intended to expand within it or bond chemically
with it.

Screw fixings are made directly into timber or
metal and by means of plugs into masonry
(brick or blockwork). In the latter case, coach
screws are advisable for heavier supports.

Bolts or Loxins inserted into masonry are heavy
duty expanding fixings. Lighter duty expanding
fixings are designed to spread the load within
or behind lightweight material or linings (such
as plasterboard). They are thus not likely to
be suitable for grabrails or rails designed to
prevent humans falling.

Problems are presented by timber-framed
walls if the intervals between the vertical studs
do not provide sufficient flexibility in
positioning. Lightweight walls, typically of
blockwork, may also present problems.
Possible solutions include
• fixing 50mm-thick marine plywood across
existing studs, or between the studs in new
walls, and making fixings where required
• expanding or chemical anchor bolts into
weaker blockwork
• bolts right through wall where possible
• specialist products that spread the fixing load
across the wall or transfer it to the floor.
Fixings must always go through any linings and
into the timber or masonry.

If insulation is added to the internal face of a
wall, it should always be faced with plywood
before wall tiling or other finishes are applied.
Stainless steel fixings are usually advisable,
especially in damp areas such as showers.

Hope this helps!!

Cheers Katy

c.bridge@fhs.usyd.edu.au