Civil Engineering Reference
In-Depth Information
(a)
(b)
(c)
Figure 20.1
Masonry bonding (a) English bond; (b) Flemish bond; (c) Stretcher bond
compressive strength, the tying allows load sharing under lateral
(wind) loads and decreases slenderness under vertical loads.
Cavity construction can be recognised by stretcher bonding
of the external leaf.
UK, calculated in accordance with the clause 6.5 (equation 4).
The previous British Standard gave more specifi c guidance for
collar-jointed construction, suggesting these can be designed
as cavity walls or solid walls providing the following criteria
are met:
20.2.6.2 Solid walling
Thin solid walls, one brick or block thick, are used for both
non-load-bearing and load-bearing partitions. Brickwork par-
titions are less common in modern construction, although they
can be used for aesthetic reasons.
Solid brickwork for external walls of buildings is normally
associated with older buildings (i.e. pre-1930s); however, it is
widely used in external works such as retaining structures and
free-standing walls, where damp penetration would not affect
the performance. Where solid brickwork is used, it can be rec-
ognised by the brick bonding, i.e. Flemish, English or stretcher
(half bonding) (see
Figure 20.1
).
Solid dense or lightweight blockwork walls are prevalent in
modern construction. They are used for internal partitions or
around core areas and can give greater fl exibility as they are
manufactured in a range of thicknesses, for example, 70 mm,
100 mm, 140 mm.
Where walls exceed 140 mm wide, these are often con-
structed using units laid fl at, low density units or with specially
made units to avoid health and safety concerns over lifting
units greater than 20 kg.
Each leaf is min 90 mm thick.
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■
Walls are designed based on the strength of the weakest unit and
differential movement is considered; i.e. in mixed construction,
blockwork will dictate the spacing of joints.
The eccentricity of the load should be less than 20% of wall
■
thickness.
1.5 kN shear ties spaced at 900 mm vertical and 450 mm horizon-
■
tal centres should be used, embedded a minimum of 50 mm into
each leaf. Alternatively bed-joint reinforcement may be used.
k values in the design of compressive strength are modifi ed.
■
20.2.6.4 Rubble fi ll construction
Rubble fi lled walls are not often employed in modern con-
struction and are not covered by BS EN1996-1. Historically
random rubble fi lled wall construction was used for large ma-
sonry walls or piers, where hollow, bonded masonry walls and
piers were fi lled with a mixture of mortar and random rubble
(IStructE, 1996).
20.2.6.5 Grouted walls
Grouted walls are sometimes employed for external retaining
walls or to improve the strength of cavity walls. These consist
of two leaves of masonry separated by a cavity, fi lled with a
grout or concrete. The leaves are tied together with either wall
ties or bed-joint reinforcement.
20.2.6.3 Collar-jointed construction (clauses 8.5.2.3)
Collar-jointed walls are similar in construction to cavity walls
yet have smaller mortar fi lled cavities, around 20 mm thick.
This construction typically uses 100 mm wide units tied
together to form 215-220 mm wide construction. This allows
solid wall construction using differing masonry units (i.e.
brick/block) and mitigates the need for special units or blocks
laid fl at for larger partitions.
BS EN1996 specifi es collar jointed construction should have
a minimum of 2 evenly distributed ties per square metre in the
20.2.7 Mortar joints (clause 8.1.5)
Mortar joints are required vertically (perpend-joints) and hori-
zontally (bed-joints) to adequately bond masonry units together.
Typically, these are 10 mm thick, allowing dimensional
