Transcript Toolbox Talk

TG20:08 | Toolbox Talk
Published by the
August 2009
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To be read in conjunction with
TG20:08 Toolbox Talk Overview Pocket Guide.
Available to order from www.nasc.org.uk
An Attendance Register is also available to download
(free of charge) from www.nasc.org.uk
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Objective
The purpose of this presentation is to give current CISRS cardholders
an overview of NASC guidance TG20:08 and to provide a summary
of the main changes brought about by the introduction of
BS EN12811-1 and the subsequent withdrawal of BS 5973.
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TG20:08
The NASC has recently issued new guidance that will impact on all tube and
fit scaffold design in the UK.
TG20:08 has been issued as the industry technical guidance on the use of
the European Standard BS EN12811-1 and applies to all tube and fitting
scaffolds from the most basic to the most complex structure.
TG20:08 is based on the previous UK British Standard BS 5973:1993 . Access
and working scaffolds and special scaffold structures in steel, which was
withdrawn by British Standards because it was not compatible with the new
European Standard BS EN 12811-1.
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Overview
Fundamentally, the principles of BS 5973 remain unchanged and there are
very few changes in the day-today work of a scaffolder. Although the scope
of TG20:08 is generally wider than in previous guidance, it is the justification
of the design that has altered rather than the scaffold structure itself.
While dealing with many common applications, TG20:08 defines a range of
scaffolds, referred to as ‘Basic scaffolds’, for which no further design is
required to establish the capability of the scaffold.
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The Main Differences | Load Classes
TG20:08 covers 4 load classes only:
Example
Designation 3-4-2 indicates a Load class 3 scaffold, 4 boards wide with 2 inside boards
Designation 3-4-2S indicates a Load class 3 scaffold, 4 boards wide with 2 inside boards and a bay length of 1.8m
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The Main Differences | Load Classes conti…
When in use a scaffold can only have one working platform carrying the full
service load shown for its class and one working platform (above or below)
carrying 50% of the service load shown for the class.
Refer to Table 1 for more detailed information
Scaffolds can be erected with a maximum of 2 inside boards. The inside
boards of Basic scaffolds are assumed to be lightly loaded for access only
(0.75kN/m2).
Maximum spacing for board transoms is 1200mm for load classes 1-3 and
900mm for load class 4 (Heavy duty).
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The Main Differences | Load Classes conti…
All ‘Basic Scaffolds’ are fully ledger braced unless they are designed in
accordance with BS EN 12811-1.
Ledger braces should be fitted to alternate pairs of standards at all lifts.
Lift heights are normally 2m but there is a provision for a 2.7m pavement lift.
Where ledger bracing is omitted from the bottom lift, such as a pavement
scaffold, the scaffold must either be tied at the top of the bottom lift or
stabilised by other means such as Rakers.
Lines of ties are installed at every lift or at alternate lifts.
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The Main Differences | Boarded Lifts
Basic scaffolds can be defined as either part boarded or fully boarded.
Definition:
Part boarded scaffolds only have two lifts boarded while all the others
remain un-boarded.
Fully boarded scaffolds have all lifts boarded.
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The Main Differences | Boarded Lifts conti…
For compliance with SG4 single guardrails have been added to the TG20:08 illustration
for Part boarded scaffolds.
Whether fully boarded or part boarded a Basic Scaffold can only have one working
platform carrying the full service load shown for its class and one working platform
(above or below) carrying 50% of the service load shown for the class.
When the scaffold is sheeted or has debris netting fitted, the top lift must be tied. This
applies whether the lift is boarded or un-boarded.
Where ledger bracing is omitted from the bottom lift, such as a pavement scaffold,
the scaffold must either be tied at the top of the bottom lift or stabilised by other
means such as Rakers.
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The Main Differences | Façade Bracing
Facade/Sway bracing is fitted to the outside standards to the full height of the scaffold
every 6 bays. It should extend across two ledger braced bays (preferred), be in a
continuous line, or fitted over a single bay.
If the scaffold is fitted with facade bracing over a single bay and the scaffold is greater
than 8m in height, then plan bracing will be required.
All facade bracing should be connected to EVERY outside standard with swivel
couplers or to extended transoms with right angle couplers.
Braces should be fixed within 300mm of the intersection of ledger and standard.
Joints in continuous facade bracing should be made by either overlapping the two
lengths of tube by 300mm and joining them with two parallel couplers or by
using a Class .B. sleeve coupler.
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The Main Differences | Plan Bracing
Where scaffolds are greater
than 8m in height and the
facade bracing covers a
single bay only, plan bracing
must be fitted to make one
braced panel every 12 bays
and every 4 lifts.
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The Main Differences | Ties
It is recommended that Independent tied scaffolds have lines of ties
installed at every lift or at alternate lifts. A scaffold achieves its maximum
height when the lines of ties are at every lift.
It is also recommended that ties should be connected to both the inside and
outside standards. If ties are connected to the inside standard only, the
anchor point must be able to provide a horizontal restraint parallel to the
building facade, unless it can be provided by other means such as suitable
end returns or butting tubes in recesses or inside corners.
The ties should be evenly distributed over the scaffold and at least 50% of
the ties should be fixed to ledger-braced standards. This applies to unclad,
debris netted and sheeted scaffolds.
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Warning regarding use of Tie Patterns (c) and (f)
The tie patterns shown in (c) and (f) should be used with caution. Although the
number of ties has been reduced, the tie force shown in the safe height tables
for each tie position is doubled. Consideration needs to be given to the type of
anchor that is being used. Most anchors have a maximum load capability in
concrete of 6.1kN. In reality a significant number of anchors will be put into
softer material, including brick and lightweight blocks. In this instance the anchor
capability could be reduced to below 4kN.
For this reason, tie patterns (c) and (f) have been limited to the maximum
safe heights shown for Standard Duty ties only. Where the Standard tie duty
is doubled (i.e. 2 x 6.1kN) to 12.2 kN, then at least two anchor points will be
required at each tie position. If the base material is made from softer material,
this could increase the number of anchors required at each tie position to three
or four. If this happens, it may be preferable to increase the number of tie points,
and tie patterns (b) and (e) could be considered more suitable.
Please note that information in the tables for safe heights of scaffolds with
Heavy Duty ties cannot be used with tie patterns (c) and (f).
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Additional items for reference
It is recommended that sheeting and debris-netting, where needed, should
always be fitted to the outside of the scaffold members.
In unclad scaffolds greater than 15m
in height, in all sheeted scaffolds and
in all debris netted scaffolds, one
transom should be fitted with right
angle or swivel couplers within 300mm
of each ledger-braced frame at every
lift, unless a through tie is already
fitted within 300mm of the ledger
braced frame with right angle or
swivel couplers.
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Additional items for reference conti…
In unclad scaffolds less than 15m in height, all transoms may be fitted with putlog
couplers, including those fitted within 300mm of each ledger-braced frame.
In accordance with NASC guidance SG4, every
non-boarded lift should be fitted with a single
guardrail (at least 950mm to the top of the
guardrail from the working platform level) as a
minimum on each temporary working platform
This guardrail must remain in place as the
temporary working platform moves to another
lift. All working lifts must be complete with
double guardrails.
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Additional items for reference conti…
Both facade and return guardrails should be connected to the corner
upright at every lift with right angle couplers (best practice) or swivel
couplers.
Scaffolds must not be loaded with materials by mechanical means, such as a
rough terrain forklift truck.
All scaffolds that are not covered by the tables in TG20:08 require a
structural design.
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Building Façades
In TG20:08 it is assumed that the building facade is impermeable and only
has a small number of openings. If the building facade has a large number
of openings, then the scaffold will be subjected to a higher wind loading and
therefore should be specially designed.
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Responsibilities of Employers &
Management
Before commencement on site your employer has a duty to provide you with a
safe system of work, which may include but not be limited to providing you
with details of:
the pre-site survey report
a copy of the scaffold design drawing or the safe height calculations, in
accordance with TG20:08, and the designation of the scaffold
overall dimensions of the scaffold structure
details of the tie pattern and type of tie required
a copy of the risk assessment and the scaffold plan (method statement)
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The NASC Guide - TG20:08 represents good scaffolding practice
but compliance with it does not give immunity from relevant
legal requirements.
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Summary
Overview
Load Classes/Duty
Boarded Lifts
Façade/Sway Bracing
Plan Bracing
Ties
Additional items for reference
Building façades
Responsibilities of Employers & Management
Any Questions ?
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