Architectural Book

1.
Introduction
Brickwork Design
Walls
Loadbearing
Non­Loadbearing
Lintels & Openings
Reinforced Brickwork
Brick Rod
Mortar & Joints
Control Joints
Weather Resistance
Thermal Performance
Acoustic & Fire
Case Studies
Bibliography
Appendices
Loadbearing Walls
Loadbearing walls in small buildings
In the case of a small building, brick walls will often have the ability
to also support other parts of the building (that is, to be loadbearing)
without any particular modification. Masonry has traditionally been
used as the principal loadbearing system for buildings, ranging from
small single­storey housing to fairly tall commercial and industrial
buildings. In most cases, some thought will have to be given to the
form and detailing of the walls to make sure they are suitable to carry
these loads.
In order to carry vertical loads, the wall has to be continuous from top
to bottom.
Ideally, openings
should be rather
narrow and in­
line vertically,
rather than wide
or haphazardly
located on the
elevation.
Since walls rely on intersecting with each other to provide some of
their stability, continuous vertical openings would turn the wall into a
series of isolated piers. This layout would only be efficient if the
floors each served to tie the separate piers together at each level.
Openings in loadbearing walls
The Building Code of Australia requires lintels over openings in
loadbearing walls to have the same Fire Resistance Level (FRL) as the
wall itself, unless it falls within the scope of certain exemptions. The
exemptions allow non­fire­rated lintels in single storey buildings, and
in other buildings where the span does not exceed 1.8m and the wall
or leaf is not more than 150mm thick. In practice, this is another
reason for limiting the width of openings in loadbearing walls.
Layout of walls to support floor loads
In order to use the walls to support floor loads, we first have to
consider a suitable span for the floor structure. Conventional timber
joist floors seldom span more than 4 or 5 metres. Domestic concrete
slabs only improve on these spans a little, while commercial flat
concrete slabs commonly cover 6 to 8 metres between supports, and
floors using steel or concrete beams can extend these limits a little.
Slab systems can be continuously supported on walls, but beam
systems usually need thickened piers under the beams. Therefore
there are several different systems that might be considered:

2. If the building is narrow enough, the external walls alone can support
the entire floor structure. The floor
slabs (or slab and beam systems)
span right across. (See Support of
Slabs on Brick Walls)
If there are sufficient internal walls
(as, for example, in a hotel with a
series of small rooms) then the internal and external walls together
might support the entire floor load. In this case, it often happens that
the internal walls have only small doorways, while the external walls
have large windows. Therefore, most of the load will be taken directly
by the internal walls.
External walls and internal columns
If the building
requires large
internal spaces
without walls, the
floor loads might be
carried by the
external walls and a
series of internal
columns. This was a
common system for
many warehouses and woolstores at the end of the nineteenth century,
when either heavy timber or cast iron construction was used for the
floors and internal columns.
In this case the floors could be a concrete "flat slab" supported on the
internal columns, with or without thickened drop panels around the
columns. Alternatively, they could be either timber or concrete floors
with timber, steel or concrete main beams between the columns.
Stability of loadbearing walls
Early in the design of a building, decisions will be made about the
overall structural system and the character of the facades. These
decisions will take into account the characteristics of masonry walling
systems, and in turn they will influence the development of masonry
detailing.
In order to resist the horizontal loads, walls rely on either their own
thickness, or the support provided when two walls meet at right

3. angles. In modern buildings there is no need to use the very thick
walls of the Victorian era, and adequate stability can usually be
achieved either by having a lot of intersecting walls (as in the hotel­
type plan above), or by articulating the wall itself to provide both
strong modelling and stability.
The principal vertical
loads acting on any
wall will be its own
weight, and if it is
loadbearing, also the
loads from parts of the
building's floors and
roofs. It must be able
to support these loads.
An external wall will
be subjected to horizontal wind loads. It must be able to resist the
effect of the wind, which will be either to overturn the wall as a unit,
or to bend a panel of walling inward or outward between its supports.
In this respect, a loadbearing wall is stabilised to some extent by the
effect of the vertical load on top of it. Because of being attached to a
floor or roof structure at the top of the wall, it also is stabilised more
than a freestanding wall would be.
In seismic areas, walls will also be subject to earthquake loads, which
will generally have the effect of overturning either individual walls, or
the building as a whole. When severe seismic action is expected,
masonry can be reinforced to increase its ductility.
Two or three­storey loadbearing buildings
It is now common practice to use loadbearing walls for apartment
buildings up to three storeys. If all the floor plans are the same, there
are plenty of internal walls to carry the loads, and the maximum span
of the floors is only as large as the biggest room. The loads are carried
on the internal walls and the inside leaf of the external cavity walls.
This allows the outside leaf to continue for the full height without
interruption, avoiding any problems of how to treat exposed floor
slabs, and avoiding the need for horizontal expansion joints or
flashing at floor levels.
The outside leaf has little stability of its own, and relies on the cavity
ties to tie it back to the stiff box­like arrangement of internal walls.
Therefore the ties must be designed to be adequate for the purpose,
and to be corrosion­resistant so that they keep doing their job for the
life of the building. (See Weather Resistance of Metal Ties &
Inclusions.)
The structural requirements are discussed in more detail in Lawrence
(2000). The main problems are likely to be parts of the walls, usually
the exterior walls, where there are large openings and only small
lengths of wall between them.
The load carrying capacity of the walls is also affected by its
slenderness, and if the storey height is much greater than the usual
2.5m to 3m the reduction can be severe. This can also occur if split­

4. 2.5m to 3m the reduction can be severe. This can also occur if split­
level layouts, atriums, or
voids joining two levels are
included in the planning. In
these cases, it is possible to
thicken the inside leaf, or
include piers or offsets in the
walls, or reinforce the
brickwork. By expressing
deep piers on the inside or
outside of the building, or
using deep reveals to
openings, the character of the
building can be changed.
It is also possible, and fairly
simple, to construct a
diaphragm wall, in which the two leaves are some distance apart but
connected by cross walls. This defeats the waterproofing advantage of
having a continuous cavity, so it would generally be applicable to
freestanding walls either fully within the building enclosure, or fully
external to it.
Multi­storey loadbearing buildings
Buildings up to 10 or 12 storeys have been constructed from
loadbearing brickwork, both in Australia and overseas. In these cases
the structural requirements become more severe, both because of the
additional load of the building, and also because of the increased
effect of wind loads. Usually the strength of the bricks and of the
mortar have to be increased, and it is common for the lower storeys to
require full­brick (230mm) thick walls, at least in parts.
Many brickworks can and do produce high­strength bricks, but if they
are required to test and certify them at a particular strength, the cost
will increase, and the range of colours and finishes might be reduced.
Testing and certification of the mortar strength and the techniques of
laying (such as ensuring full bed joints) might also add something to
the cost. On the other hand, in a multistorey building with an
appropriate plan layout, the use of loadbearing brick walls can save
the cost of a separate structural frame, and of the details where the
walls abut columns and beams.
Examples of a number of apartment buildings, from five to 11 storeys
in height built during the 1960s, are presented in Krantz (c1967).

5.
One of the tallest buildings of loadbearing brickwork was the
Monadnock building in Chicago (Burnham and Root, architects,
1890), which has walls 1800 thick at the base. These stylised floor
plans give an indication of the relative thickness of the walls at the
ground level (upper plan), and partway up.
Monadnock building, Chicago
Support of slabs on brick walls
Brickwork tends to expand, whereas concrete shrinks. Also, the
concrete slab will deflect and rotate slightly at the edges when it
carries its own load. For these reasons, a bond­breaking layer is used
under the slab when it is supported on a brick wall. Commonly, two
layers of aluminium­cored dampcourse material, or of zincalume steel
in low­corrosion areas, are used for this purpose. This layer prevents
the slab bonding to the wall, which would otherwise cause a crack just
below the slab.
If there is a full­width flashing in the outside leaf, that will isolate the
brickwork from the slab it sits on. The inside leaf does not need a
flashing or dampcourse, but if the bricks are expected to be highly
expansive, a dampcourse would allow it to move independently of the
concrete.

6. It is preferable not to support the slabs on the outside leaf of the
external walls. This avoids showing the slab on the elevation, and
therefore avoids the flashing details required when the cavity is
crossed. It also avoids any problems caused by differential brick
growth between the two leaves (if they use different bricks), and
different thermal movement because the outside leaf is subject to the
weather.
If the slab does extend across both leaves, either a drip bar or a drip
groove is required in the underside of the slab in the cavity region, to
prevent moisture travelling across on the soffit of the slab and
damaging the internal wall.
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