Transcript Slide 1

Working at Height
Design of Suspended Access
Raymond Gold – Managing Director RDG Engineering Ltd
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The design of an access/protection
system has the overarching
commitment to provide protection for
both the operatives above and
employees, public and infrastructure
alike below.
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What is the design for?
The construction of a platform or
barrier that provides protection and
segregation for a workforce carrying
out the construction work above an
active railway and public area alike.
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What does the barrier comprise of?
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What does the barrier comprise of?
• A single level barrier
A single level provides both the combined
working and protection level.
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Single level barrier
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What does the barrier comprise of?
• Multilevel barrier
Two or more levels are provided; usually the
lowest one provides the ultimate protection,
levels above provide access and load carrying
capabilities.
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Multilevel barrier
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Temporary Works Responsibilities
CRE
Checker
PM
DPE
Designer
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Design Specification and Brief
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Design Specification and Brief
Network Rail Standards
No specific standards for suspended
access protection barriers, scaffolds or
temporary access/protection structures
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Design Specification and Brief
Network Rail Standards
BSI Standards - Scaffold / Access
BS 12811 Parts 1 & 2 Temporary works
equipment.
BS 5974 Code of Practice for the planning,
design, setting up and use of temporary
suspended access equipment.
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Design Specification and Brief
Network Rail Standards
BSI Standards - Scaffold / Access
Industry Standards
NASC TG20:08 Guide to Good Practice for
Scaffolding with Tubes and Fittings –
Volumes 1 & 2
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Design Specification and Brief
Network Rail Standards
BSI Standards - Scaffold / Access
Industry Standards
BSI Standards – Structural Standards
Structural steelwork, Aluminium and Timber
Standards
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Design Specification and Brief
Network Rail Standards
BSI Standards - Scaffold / Access
Industry Standards
BSI Standards – Structural Standards
‘End user’ Specification
Work scope, performance specification and
activity schedules
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Design Specification and Brief
Network Rail Standards
BSI Standards - Scaffold / Access
Industry Standards
BSI Standards – Structural Standards
‘End user’ Specification
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Typical Customer Criteria
Protection barrier against activities
being undertaken
Safety in and ease of construction
Provides weather/noise/fumes protection
No impact on activities beneath barrier
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Key Elements
•Where ever possible structural redundancy
should be incorporated in any design.
•Protection against incremental collapse should
be achieved by providing compartmentalised
structures.
•Normal design factors of safety employed for
the above items.
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Key Elements
In many instances it is not possible to buildin an elements of redundancy as part of the
standard solution.
For these items either increased factors of
safety are used or additional ‘fail-safe’
measures are incorporated.
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Design Loads
Erection loads  Part completion
 Storage of construction
materials
 Loads encountered
during relocation
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Design Loads
Dead loads
 Self weight of
component parts of
primary structure
 Secondary access
 Additional protection
 Canopies
 Access routes
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Design Loads
Imposed loads - Platform working loads
 Blanket UDL
 Localised load bays and
materials storage
 Materials transit routes
 Access routes
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Design Loads
Imposed loads - Platform imposed loads
 Snow
 Wind
 Services
 Dynamic
 Materials impact
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Dynamic Loads
 Vibration
 Horizontal
 Vertical
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Dynamic Loads
Vibration:
In general, plant vibration is unlikely to cause
any significant increase in loading. However, the
loosening effects on bolts, wedges and other
friction connections should be considered,
particularly when external vibrators are used.
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Dynamic Loads
Horizontal:
Forces from moving plant, or from materials
being deposited on or off the protection layer
or being carried across the deck by plant or on
moving equipment. Allow for horizontal forces
in any of the possible directions of movement
equivalent to 10% of the static load of the
moving items where the rate of travel < 2 m/s.
For speeds > 2 m/s the horizontal force should
equate to 33% of the moving load.
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Dynamic Loads
Vertical:
To allow for dynamic loading from loads moving
vertically. The static loading of the moving item
should be increased by 25% when using
mechanically operated lifting gear, and by 10%
when using manually operated lifting gear
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Dynamic Loads
Movement:
To allow for dynamic effects resulting from
distortion and flexing when relocating a
suspended access/protection
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Impact Loads
ALL falling materials shall be contained
A very tall order - Is this possible?
- It MUST be possible!
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Impact Loads
What constitutes failure?
What are the limits of acceptability for the
structural performance of a decking material.
• No structural damage to the barrier.
• Penetration of the barrier but object
contained, barrier to be repaired.
• Object penetrates barrier, slowed by impact
but continues falling.
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Impact Loads
What are the causes?
Temporary Work Materials of construction
Piece sizes and weight
Tools and equipment
Movement of materials
Personnel falls
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Impact Loads
What are the causes?
Demolition Work Removal of steelwork
Cladding & rails
Suspended services
Air handling units
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Impact Loads
What are the causes?
Permanent Work Removal of rivets & bolts
New steel sections & plate
Suspended services
Permanent access systems
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Impact Loads
Typical 5 kg Weight Items
crow bar; lump hammer; steel
bracket; piece of glazing;
scaffold tube; hand held tools
shape, mass, distance
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Impact Loads
A metal object weighing 5 kg
falling through a vertical
distance of 5.0m and coming
to an almost instantaneous
rest has a potential force on
impact of 250 kN (25 tonne)
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0.0200
0.0500
0.1000
0.1250
0.1500
0.2000
0.2500
0.5000
1.0000
0.0100
100
0.0020
0.0018
0.0015
0.0010
Impact Load Values (kN)
250
Impact Loads
200
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Impact force of a 5kg
mass falling from 5 m
50
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Deflection on Impact (m)
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Impact Loads
Incidents due to:
• Personnel falling/tripping whilst working
• Losing grip on an item
• Poor work practices
• Failure of a component part
• External force applied
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Impact Loads
Possible Scenario
Hand held chiselling machine e.g. Rivet chisel
falls onto the protection/crash deck. The
machine falls chisel point down and
penetrates the deck but the body of the
machine stops it falling through the deck. The
chisel stops abruptly causing the chisel bit to
be shaken free which then falls to the public
area below
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Impact Loads
Theoretical Design/Practical Tests
• Is it possible to accurately determine impact
loads and their effect?
• On site testing of possible scenarios.
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Construction
Risks during construction of a protection
platform can be mitigated by assembling
as much of the platform at ‘ground’ level
and elevate into position, or construct in
elevated designated areas.
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Construction
The means of mitigating the risks associated
when using a protection barrier are many and
varied and range between:
•selection of materials
•reduction in vertical distance between the
protection systems and the work zone
•risk assessment and modifications to work
practices commercial considerations that
might be brought to bear.
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Construction – Deck Materials
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Profiled metal decking
Plain metal plate
Composite materials
Plywood
Scaffold boards
Netting
Rubber
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Construction – Localised Materials
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Polystyrene blocks
Air bags
‘Bean’ bags
Netting
Metal plate
Fibreglass panels
Collapsible frames
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Construction – Detailing
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Connection details
Sealing of all gaps
Edge protection
Handrails
Encapsulation
Sealing around protuberances
Stepped access
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Inspection
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Standard 7 day inspection
Gaps, changes in use etc.
Bespoke inspections
Changes in edge protection
Sealing around protuberances
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If All Else Fails
Carry out work during
possession and
isolation periods?
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