Civil Engineering Reference
In-Depth Information
Joints
It is most important that satisfactory
designs are prepared in advance for
crossover and tee-joints, and
especially where vertical and
horizontal joints are not in the same
plane, to check for continuity. It is
also advisable to have standby
designs available for the extremes
of variability which might be found in
assembly.
Graphical aids for tolerances and
fits
(153)
gives comprehensive
guidance on the relationship between
the sizes of joints and components in
external walls.
strong, gusty winds, and due to
slipperiness when there is ice or snow
on ladders and scaffold boards.
Assuming work stops under these
conditions, an idea of likely lost
time is given in Table 3.2. The data
shown in this Table are based on wind
speed at the standard height of 10 m.
For higher buildings, even more
interference may be expected.
Table 3.2
Work time lost on low and medium-
rise buildings owing to bad weather
∗
Hours lost per day
January
July
Heathrow
worst in 5 years
4.5
1.5
average
3.4
0.9
best in 5 years
2.1
0.2
Glasgow
worst in 5 years
Work on high-rise buildings
For work on high-rise buildings, or
where prefabricated overcladding
panels larger than one storey in height
are used, it will normally be more
practicable to lift the overcladding
into position by crane at the time of
fixing. For this, a more onerous wind-
speed limitation will apply,
considering the difficulties of safely
handling and positioning
large, lightweight panels. Restricted
visibility due to fog will also prevent
safe operation of cranes, and
slipperiness criteria will also apply.
In these conditions, a rule of thumb
for lost time is to double the hours
lost for low and medium-rise.
There is also the possibility that
certain types of operation, such as
joint sealing, may not be practicable
when the weather is wet or cold,
presenting a further possible cause
of delay.
The likely time of year when
installations will take place, and
hence the moisture and temperature
conditions of both original structure
and overcladding, should be taken
into account in the specification. To
illustrate the point, the sizes of
overcladding panels will generally be
at a maximum in high summer, and
clearances will need to be set
accordingly so that tolerances on
joints, for example, are not exceeded
when the panels are at their smallest
in winter.
The original building will have
been constructed with very high
dimensional variation; deviations are
often considerably greater than
expected. Before any overcladding is
specified the building should be
measured, as special provisions may
be required.
6.2
1.8
average
5.0
1.2
best in 5 years
3.6
0.6
* Predicted average lost time in hours per day between 07.00
and 17.00 h GMT, assuming work stops when mean hourly wind
speed exceeds 12 m/s, and there is snow, sleet or hail falling.
Storage and handling of materials
All materials must be stored flat on
pallets under cover and protected
from the weather and the activities
of other trades. Any moisture
penetrating between stored boards
will cause permanent surface
staining. Protective paper or plastics
sheet stuck to decorative faces should
not be removed until after fixing.
Troughed sheeting in light gauge
steel relies upon a combination of
PVC based and galvanized coatings
to give corrosion protection. It is
therefore essential that the material is
carefully handled and stored. One of
the main dangers results from
dragging one sheet over another
which can mean the protective
coating on the lower sheet being
scratched by sharp edges.
Restrictions due to weather
conditions
The extent to which cladding work is
likely to be delayed or interfered with
by bad weather will depend on the
method of access and type of
construction, but the risks of hold-ups
should be given some consideration.
Work on low and medium-rise
buildings
For work on low and medium-rise
buildings using prefabricated
cladding panels of no more than one
storey in height, it will normally be
most efficient to work from access
scaffolding, with the materials lifted
onto the scaffolding platforms in
advance. There will be safety risks
associated with handling the panels in
