Civil Engineering Reference
In-Depth Information
columns. A shop unit (SU) or more commonly 'unit shop' is
typical of a single trading unit akin to a traditional high street
shop with a single shop window frontage. Units of a smaller
size only accessible from a small frontage and up to 10 m² in
area will often be referred to as kiosks or 'lock-up' units.
Depending upon the type and size of the unit the storey
height requirements will vary. Large stores needing to give the
impression of volume as well as requiring a greater depth of
ceiling for services (such as air ducts) will generally need to be
provided with a storey height of 5.1-5.5 m and possibly more
if large spans are required for the structure. MSUs and SUs
typically require a storey height of 4.5 m or minimum of 4.0 m
clear to structure. These are the heights which retailers require
to merchandise the space and to maximise sales.
The spacing of the column grid therefore needs to take
account of the variety of factors described above. By virtue of
their large volume space LSUs will invariably require a large
column grid. A common department store grid will be 12 m ×
10.2 m, although some LSU retailers may require up to 14 m.
Others may be happier to work with a 9 m × 9 m grid but rarely
will it be less than this in an LSU. There may also be differ-
ent uses above or below (for example, car parking) which may
drive an optimum grid spacing.
The starting point for the ideal width of an SU is based upon a
notional 7.0 m (23 feet) width, which will typically allow for an
economical structure as well. The columns in a single SU will
then occur in the division wall between units (some retailers
may also require these to be flush in the wall without projecting
into their unit). An MSU typically being a combination of mul-
tiple shop units will be based on a similar grid with columns
occurring within the trading floor. In these units, the optimum
frontage:depth ratio may also dictate the column grid.
In mall or shopping centre design, developers or owners
require the shop units to have maximum flexibility of size so
that shops of many widths and sizes can be created without too
much hindrance from the structure. This is generally because
at the time of design, tenants are unlikely to have been signed
up to take space and even if they have, they may not define any
specific requirements to be incorporated into the structure (for
example, lift pits, staircases or escalators) until the structure
itself has already been built.
It is therefore important that such requirements are kept in
mind and probable or notional positions for openings allowed
for at certain locations in the design. Ongoing flexibility of
layout in future years is also important since turnover of retail-
ers is common. As they grow or shrink or change sales practices
(for example, through online (internet) trading and the need
for goods to be picked up rather than displayed - known as
'click-n-collect') retailers often require different sized spaces.
Floor loading requirements in retail are commonly accom-
modated by an overall allowance of 5 kN/m² which will meet
the majority of high street retailers' requirements for both
sales and back-of-house (storage). Some may require a fur-
ther allowance of 1 kN/m². LSUs may typically have higher
requirements for storage or warehouse areas often at 7.5 kN/
m². Plant requirements for regular shop units or even MSUs
are not great since such units are not highly serviced typically
being based on requirements simply comfort cooling provi-
sion (e.g., external condenser units). Plant loads of 4 kN/m²
will often suffice in these instances. For LSU use, plant will
be more extensive and may include heavier equipment such as
chillers, air handling units and water tanks; therefore a typical
plant loading of 7.5 kN/m² is the normal allowance.
In SUs (a typical unit shop) or MSUs there is often a require-
ment for the introduction of a mezzanine floor, either from the
outset of construction or for later addition. This is a floor to be
introduced between the ground floor and first floor soffit to cre-
ate two floors of trading although the envelope is still regarded
as being one storey. Historically the introduction of a mezzanine
(typically by a tenant) neither attracted rent to the landlord nor
affected business rates on the additional floor area. However,
changes in legislation have affected this beneficial position in
terms of rates, and landlords often now have rental leases based
either on turnover or actual sales area. Nevertheless, structurally
the load of such a floor, whether added from the first or later,
needs to be allowed for along with some consideration of how
such a structure might be physically (and safely) introduced
later together with any effect it may have on the original struc-
ture (for example, foundations or loading or physical placement
of load on supporting columns).
A further aspect of shopping centres is often their need to be
developed for mixed use, the most common being car parking
on roofs or in basements beneath. Leisure facilities, typically
restaurants or cinemas, and residential uses are also commonly
combined with a retail centre to bring about added value. The
differing requirements for combined use become more difficult
to accommodate when vertically stacked and inevitably differ-
ing column grids are required. Differing column grids invariably
require transfer structure (typically beams) which will prove to
be expensive. Consideration should therefore be given to how
an arrangement might work whereby columns could be aligned
throughout the height of the structure in part or throughout thus
avoiding the need for transfer members or a transfer deck.
Provision of car parking beneath a retail centre is extremely
common. These two uses can often prove to be the most com-
patible in terms of commonality of column spacing. A column
grid of 7.5 m defined to be the ideal minimum in the width of
a shop unit should simply require adjustment to 7.8 m or 8 m
in order to align with a suitable car park column placement
every third car park bay. Similarly in the opposing direction a
column grid of 8 m (or 16 m) will suit both the retail and car
park levels thus allowing continuation of columns through the
heights of both spaces, avoiding the need for more expensive
and deeper transfer structure.
Developments for food retail use, particularly supermarkets,
require slightly different consideration to those for 'leisure'
shopping. Supermarkets, defined as those having typical sales
floor of greater than 2500 m² and anything up to 17 000 m² for
