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50

www.concrete.org.uk

M

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concrete

REINFORCEMENT AND ACCESSORIES

T

he vast majority of landings are

supported from the stairwell walls

using one of two methods: bolted-

on steel angles or proprietary

telescopic connectors. These two methods

are very different from each other in almost

every aspect and a comparison of these

differences reveals how time and money

can be wasted, while either introducing or

eliminating health and safety risks, according

to the chosen method.

Health, safety andperformance

Perhaps of the greatest concern is what

happens when drilling for the angle fixings

hits vertical reinforcement in the wall. To

reposition the hole requires redrilling the

angle, which is time consuming, costly and

may not satisfy loading requirements. The

temptation therefore is to simply drill at an

angle to miss the bars. The result of this is

fixings that do not sit squarely against the

steel angle (see Figure 1). The capacity of

such fixings is a matter of conjecture, but it

certainly would not be as intended and must

be a concern.

From a practical aspect, further problems

must be faced if the angle is not exactly

horizontal. Packing or bedding must be

installed (see Figure 2), which entails

working beneath the landing while it is still

on the crane hook. This goes against all

sensible health and safety advice and is only

one of the drawbacks of bolted-on angles

on-site. For the drilling, power is needed,

creating trip hazards with trailing cables, and

the drilling itself is a prime source of hand–

arm vibration, dust and noise.

When using telescopic connectors,

operations are carried out from the top of

the landing only, and it is recommended

that landings are supported by a temporary

staging while this is

done.No

power or tools

are necessary.

For both methods, edge protection should

be used where falls are possible.

Economics

It is only possible to make economic

comparisons when the whole operation is

taken into account. For steel angles,most of

the cost is for the angles and fixings, along

with a relatively high site labour element. For

telescopic connectors, the main item is the

cost of the connectors, but with fairly low

site costs. The actual cost of the connectors

is borne by the precaster, thus inflating the

Effective installation of precast

stairs in high-rise construction

Figure 1: Badly seated

fixings due to hitting steel.

Formany years, the preferred formof stairs in high-rise construction has been precast concrete.

Produced off-site, they can be delivered and installed as required by the site programme to create

instant access (and egress) as the structure goes up. Additionally, aswithmost precast concrete,

they can bemanufacturedwith high-quality finishes, not requiring further cosmeticwork.

Cliff Billington

of

Invisible Connections

reports.