Civil Engineering Reference
In-Depth Information
sheet steel. In these cases the
masonry would be separately
founded with the steel frame used
primarily for carrying floor and roof
(Figure 3.7).
Dimensional stability, deflections
etc
A characteristic defect of this type of
construction is shrinkage of concrete
frames which squeezes brick
cladding which has not been provided
with horizontal soft joints at storey
height intervals. This is exacerbated
by the expansion of fired clay
brickwork. It is unlikely to occur if
concrete or calcium silicate units are
used, as these also shrink in sympathy
with the frame. The effects of these
movements are exaggerated if the
brickwork is set proud of the frame to
allow the use of brick slips to mask
the concrete support nibs. This
happens because the eccentric loads
cause bowing and the stresses have to
be born by only two thirds of the
bearing area of the bricks (Figure
3.8).
Both the concrete shrinkage and
the brick expansion are more rapid at
the outset and take several years to
complete, but some can take decades
before they start becoming apparent.
Since this detail (with the brick slips)
has now fallen out of use, the number
of further failures will probably start
dwindling.
Remedial work
(133)
entails the
following procedure:
●
14 or 16 gauge cold rolled steel strip
Inner lining of
woodwool or
prefabricated
plasterboard
Reinforced concrete frames
Masonry on reinforced concrete
frames frequently left the frame
exposed, being carried on the
horizontal beam with only a slight
projection from the frame face. This
practice almost inevitably leads to
weatherproofing difficulties at the
frame-to-masonry joint.
Alternatively steel shelf angles are
sometimes to be found fixed to beams
or slabs, in which case the detailing
can be similar to that for steel
framing.
Sill struts
below
window
openings
2
3
/
4
in baseplate set
into concrete plinth
Sawn natural stone
Natural stone, sawn into sheets
sometimes as thin as 50 mm, is
increasingly being used for
claddings. Research at BRE and
elsewhere has shown that some types
of stone undergo a significant loss of
strength when subjected to
environmental loads, in particular
thermal cycles. More information is
available in BRE Information Paper
IP 6/97
(131)
and in BS 8298
(132)
.
Trench fill
Figure 3.7
Detail of the construction of a Trusteel Mk II
house
checking the lateral stability of the
masonry if the vertical spanning is
interrupted by a soft joint
●
checking that adequate tying exists
between the outer panel and the
columns, and between the outer
panel and any inner infill masonry
●
checking the condition of nibs,
which may be damaged or sheared
off, and repairing or replacing
them with shelf angles or corbel
studs
Main performance
requirements and defects
Strength and stability
Brick cladding on steel frames, as
already noted, is for high-rise
construction mostly carried on shelf
angles at suitable points in the
structure, usually at floor levels
where adequate bearings and soft
joints are needed. For low-rise work,
the masonry may well be separately
founded on conventional footings.
One of the most important criteria
for strength and stability is the
integrity of fixings for the cladding,
particularly in multi-storey buildings.
A variety of tie patterns may be used
to connect the walling to the frame.
Some may be factory fixed to the
frame, in which case it is essential
that they permit vertical adjustment
or are flexible.
Reinforced
concrete frame
shrinks
No movement joint
cutting new movement joints and
making sure that they are fully
compressible
●
installing additional ties if required
for stability
●
Movement joint
closed
Movement joint not taken to face of brick slips
For coefficients of linear thermal
and moisture expansion etc, see
Chapter 1.2.
Figure 3.8
Shrinkage of a reinforced concrete frame
leading to brick slips detaching
