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concrete

51

REINFORCEMENT AND ACCESSORIES

apparent cost of the stairs. This is a false

view, however, since the overall cost of

connectors, when labour and finishing works

are included, can be in the region of £300 per

landing compared to using angles.

Once installed, steel angles must be

concealed and fire-protected. This operation

is frequently not included in anyone’s work

package, leading to potential disputes.

Similarly, operations such as checking bolt

torques, and indeed the design of both angle

and fixings, are often not included in costs.

Erectionoperations

When erecting landings, particularly in a

high-rise structure, it is beneficial that the

stairwell is free from obstructions that would

impede the lowering in of precast elements. If

angles are used then these cause obstructions,

requiring different lifting techniques.

The alternative is to fix angles piecemeal,

working off the landing below. For telescopic

connectors, the stairwell is completely free of

any obstructions (see Figure 3), thus allowing

a free route for the crane. This is achieved

by seating the connectors into recesses in

the wall. Forming these recesses used to be

a drawback in itself, but now, preformed

recess formers make the task easy, even with

slipformed walls (see Figure 4).

Design

Angles and their fixings are a safety-critical

element and should be designed by a

competent engineer. Too often, drawings

vaguely show an angle with the note ‘design

by others’. This design element and that

of the fixings should be clearly defined in

contract documents, spelling out who is

Figure 5: Impractical

tying detail.

Caption

Figure 2: Bedding between precast and angle.

Figure 3: Stairwell clear of obstructions.

Figure 4: Preformed recess.