working at height design of suspended access raymond gold – managing director rdg engineering ltd...

Working at HeightDesign 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 barrierA 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 barrierTwo 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

Designer

Checker

CRE

DPE

PM

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Design Specification and Brief

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Design Specification and BriefNetwork Rail Standards

No specific standards for suspended access protection barriers, scaffolds or temporary access/protection structures

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Design Specification and BriefNetwork Rail Standards

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.

BSI Standards - Scaffold / Access

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Design Specification and BriefNetwork Rail Standards

NASC TG20:08 Guide to Good Practice forScaffolding with Tubes and Fittings – Volumes 1 & 2

BSI Standards - Scaffold / Access

Industry Standards

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Design Specification and BriefNetwork Rail Standards

Structural steelwork, Aluminium and Timber Standards

BSI Standards - Scaffold / Access

Industry Standards

BSI Standards – Structural Standards

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Design Specification and BriefNetwork Rail Standards

Work scope, performance specification and activity schedules

BSI Standards - Scaffold / Access

Industry Standards

BSI Standards – Structural Standards‘End user’ Specification

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Design Specification and BriefNetwork Rail Standards

BSI Standards - Scaffold / Access

Industry Standards

BSI Standards – Structural Standards

‘End user’ Specification

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Typical Customer CriteriaProtection barrier against activitiesbeing 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 build-in 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 constructionmaterials

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 LoadsVibration: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 LoadsHorizontal: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 LoadsVertical: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 LoadsMovement:To allow for dynamic effects resulting from distortion and flexing when relocating a suspended access/protection

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Impact LoadsALL falling materials shall be contained

A very tall order - Is this possible?- It MUST be possible!

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Impact LoadsWhat 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 LoadsWhat are the causes?

Temporary Work Materials of constructionPiece sizes and weightTools and equipmentMovement of materialsPersonnel falls

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Impact LoadsWhat are the causes?

Demolition Work Removal of steelworkCladding & railsSuspended servicesAir handling units

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Impact LoadsWhat are the causes?

Permanent Work Removal of rivets & boltsNew steel sections & plateSuspended servicesPermanent access systems

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Impact LoadsTypical 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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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)

Impact Loads

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Deflection on Impact (m)

Impact force of a 5kg mass falling from 5 m

Impact Loads

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Incidents due to:• Personnel falling/tripping whilst working• Losing grip on an item• Poor work practices• Failure of a component part• External force applied

Impact Loads

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Impact LoadsPossible 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 LoadsTheoretical Design/Practical Tests

• Is it possible to accurately determine impact loads and their effect?• On site testing of possible scenarios.

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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.

Construction

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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.

Construction

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• Profiled metal decking• Plain metal plate• Composite materials• Plywood• Scaffold boards• Netting• Rubber

Construction – Deck Materials

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• Polystyrene blocks• Air bags• ‘Bean’ bags• Netting• Metal plate• Fibreglass panels• Collapsible frames

Construction – Localised Materials

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• Connection details• Sealing of all gaps• Edge protection• Handrails• Encapsulation• Sealing around protuberances• Stepped access

Construction – Detailing

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• Standard 7 day inspection• Gaps, changes in use etc.• Bespoke inspections• Changes in edge protection• Sealing around protuberances

Inspection

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Carry out work during possession and

isolation periods?

If All Else Fails