TG20:13 The Changes
TG20:13 TG20:13 • Introduction and background to TG20:13
• The NASC Suite of Documents • Legal Framework and Endorsements • TG20 Compliant Scaffolds Types • Wind • Ties and Anchors • Summary
TG20:13 TG20:13 • Introduction and background to TG20:13
• The NASC Suite of Documents • Legal Framework and Endorsements • TG20 Compliant Scaffolds Types • Wind • Ties and Anchors • Summary
What is TG20? • TG20 represents the general rules of the scaffolding industry. It is mainly a technical document, and therefore therefore not very readable. • It is aimed at tube and fittings, but a number of aspects ( eg foundations, board supports, scaffold boards, access) equally apply to systems. • Calculations would be required for every tube and fittings scaffold without TG20. It provides ‘ standard configurations’
• It can be considered the industry Code of Practice.
Purpose of New Guidance Previous versions of TG20 have permitted only a narrow scope of Basic or Standard Scaffolds without design. One of the main objectives of TG20:13 is to reduce the number of designs required, and enable the rules to be understood and applied without recourse to specialists. It is in many ways a new set of rules. The CISRS Basic Scaffold Inspection Course will now run to 3 days. The eGuide software gives better results than the Operational Guide.
Introducing TG20:13 ‘ A comprehensive guide to good practice for tube and fitting scaffolding’
TG20: 13 Changes 1.
Now includes NASC SG and TG document content
2.
Wind code now more specific from BSEN 1991-1-4
3.
New windmap ( Operations Guide explains types)
4.
TG20 Compliant Scaffolds explained
5.
TG20 Operations Guide
6.
Choice of Limit State or Permissable Stress in design approach.
7.
Façade Bracing can be in single bay
8.
Scaffold designations unchanged but only part of the story
9.
Doubled standards now specifically mentioned
10.
Transom tubes now have 25mm tolerance through the coupler.
11.
Telescopic Transoms encouraged
12.
Detailed info on use of Hop-Up Brackets
13.
Band and Plates now mentioned
14.
2.4m Bays only permitted in Operational Guide, not 2.7m.
15.
More emphasis on 900mm board spacings on 3Kn Class 4
16.
Laminated and plastic boards included, plastic can overhang 180mm, not 150mm.
17.
Max span of boards does not mention 50 or 63mm boards, just scaffold boards
18.
Readylok / Prefabricated Transom Units now included
19.
Lift Shaft Towers added
20.
Structural Transoms included
21.
Transom couplers : no longer refers to sheeted scaffolds needing right angle or swivels, but ‘TG20 compliant’
TG20: 13 Changes 24 Plan Bracing wording expanded to explain 25 Guardrails should use right angle couplers, not swivels or putlog couplers
26 Single Guardrails ok on unboarded lifts. 27 Guardrail height defined as 950 to 1260 if scaffold boards as toeboards (?) 28 Extending platform by 6 ft still ok, design if longer 29 New Cantilever Platform wording
30 Extensive New Tie text, inc sheeting options and their effect. 31 More tie classes: now 4 ( class B) 32 Tie details no longer in Design Guide, but Operations Guide 33 ( minimal re-use of some anchor types in OG)
34 Abnormal facades: inspect with teleboom 35 Rakers: more stringent requirements for external Rakers, inc wing bracing, resistance to uplift. 36 Access is mainly in the Operations Guide
37 Access hierarchy: integral ladder bay may be substituted 38 Ladder Towers projecting beyond the scaffold are a special case 39 Pavement Lifts major new guidance
eg modified ties not mandatory
40 Openings and bridges have much more guidance 41 Bridging includes 750mm beams 42 Internal and external façade bracing required around openings
TG20: 13 Changes 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67
Loading Bays: now can be 4.0m, not 3.0m Loading Bay Gates now included Loading Bays which project beyond the façade are special cases “ “ Guardrail wording now ensures protection at all times Ladder beams now stated as 3.05m, not 3.35m Birdcages : definition no longer ‘ multiplicity’ of standards, but a grid New load classes Dimensions now relate to load classes of birdcages “ can be wider than 2.1m with ladder beams used More birdcage illustrations ( Operations Guide has far more bracing details) Indoor birdcages now refer to BSEN 12811 for wind Overturning factors of safety now 1.5 not 1.2 Single lift birdcages :brace one in 4 bays. The maximum number of unbraced internal bays is governed by the number of lifts Access Towers new 0.75kN load class Outriggers mentioned for towers Tied Towers have new text: ? tied every lift? Mobile Towers have no TG20 compliant designs ( some info in Design Guide) Design assumptions for internal and external towers stated Limited wind conditions for compliant towers ( Wind Management system in Op Guide) At least 2 lifts of external towers should be boarded to resist overturning Public Access Staircases now more fully detailed, inc references More details from BSEN12811 on Tube and Fittings Stairs.
TG20: 13 Changes 68 69 70 71 72 73
74 75 76 77 78 79 80 81 82 83 84 85 86 87
Foundation Loadings provided to aid clients Tolerances are emphasised Special Scaffolds not in Operational Guide Node point restraint mentioned Protection Fans: statement of general limitations “ “ New Fan Standard is coming Stair Towers : greater revised text, same loadings Dimensions from BSEN 12811 now included. Staircases No toeboard requirement unless… Cantilever scaffolds : similar text, but more specific about the way load is applied to the structure. Safety during erection now included. Lifting Gantries: unchanged, but CAD mentioned Temporary Buildings : Out, now in TG9 Definition of Class A in Op Guide is fittings, not paint drips Class A Fan illustration no longer wire shown Class C Fan : vertical drop 6m, not 10m Decking: Safety netting now included Projecting of Fan included ( limited in OG?) Pavement Frames : much more detail Identification of EN74 Couplers
Legal Framework and Endorsements
Work at Height Regulations 2005 Schedule 3 – part 2 additional requirements for scaffolding 7) Strength & stability calculations for scaffolding shall be carried out unless… a) A note of calculations, covering the structural arrangements contemplated is available; or, b) It is assembled in conformity with a generally recognised standard configuration.
HSE Support ‘The Work at Height Regulations 2005 require that strength and stability calculations are carried out for scaffolds unless they conform to a recognised standard… …HSE is pleased to acknowledge that TG20 has been written by NASC to provide such a standard…’ Heather Bryant, Chief Inspector of Construction Health and Safety Executive
UKCG Support ‘We applaud and support the work of the NASC which will no doubt result in safer scaffolding… The UKCG recommend the adoption and standardised use of TG20:13… both within and outside the construction sector.’ Stephen Ratcliffe, Director UK Contractors Group
TG20 Compliant Scaffolding
TG20 compliant scaffolds have been designed by structural calculation in accordance with BS EN 12811.
Design advice should be sought for any scaffold outside of the scope of TG20 Compliant Scaffolding.
TG20 compliant scaffolds were previously referred to as ‘Basic’ or ‘Standard’ Scaffolds.
TG20 Compliance Sheets
Demonstrates compliance and that bespoke design is not required. Typical Scaffolds included in TG20:13 Operational Guide (Chapter 03). Wider variations included in the TG20 eGuide. Design advice must be sought for any scaffold outside the scope of a TG20 Compliance Sheet.
What is a ‘Basic’ Scaffold? Main requirements: • Double row of Standards, • Ledger Bracing • Façade Bracing every 6 bays • Conforms to Table 1: Load Classes, Bay lengths, Widths. • Only two working lifts: one 100% loaded, other 50% loaded • Max lift height 2.0m • No loading of materials by mechanical means • Wind Loading factor ‘S’ no greater than 40. • Alternate pairs of Standards ledger braced • Vertical ties spacing not to exceed 4m ( 2 lifts) • Façade bracing is across two bays. Otherwise Plan Bracing has to be fitted
Designed Scaffolds Per HSE •
Dead / Flying/ Raking Shores
•
Cantilevered scaffolds
•
Truss-out Scaffolds
•
Access Birdcages
•
Façade retention
•
Buttressed free-standing scaffolds
•
Temporary roofs and temporary buildings
•
Loading Bays founded on the ground
•
Mobile and static towers outside base/height limitations
•
Free standing scaffolds outside base/height Limitations
•
Temporary ramps and elevated roadways
•
Staircases and fire escapes
•
Spectator Terraces and Seating Stands
•
Bridge scaffolds
•
Towers requiring guys or ground anchors
•
Pedestrian footbridges or walkways
•
Slung and Suspended scaffolds
•
Protection fans, Nets and Pavement Frames
•
Power line crossings
•
Lifting gantries and towers
•
Sign board supports
•
Temporary Storage on Site
The New TG20 Guides The Operations Guide incorporates aspects of the old Technical Guidance and the SG and TG NASC series.
The Operational Guide • Conversational, readable style • Lots of good illustrations • Incorporates elements of Design, Safety and Technical Guidance documents plus eGuide references.
TG20 Compliant Structures
TG20:13 Compliant Scaffold Types • • • • • • • • • • • • •
Tied Independent Scaffolds Free-Standing Independent Scaffolds Towers Interior Birdcages Tied Putlog Scaffolds Loading Bays Ladder Access Towers Chimney Scaffolds Bridging with Beams Reinforced Transom Units ( Readylok) Light Duty Protection Fans Pavement Lifts Cantilevered Access Platforms
Compliant Scaffolding Types
Tied Independent Scaffolding
Independent Scaffolds • •
• • • • •
Includes sheeted, debris netted and non-sheeted. Operational Guide covers scaffolds up to 16m height, but the eGuide extends this up to 50m. Façade Bracing: Single bay bracing is sufficient to avoid Plan Bracing. Maximum bays size restricted to 2.4m Guardrails should employ right angle couplers, not Putlog Couplers Wider choice of decking materials Emphasis on Structural Transoms Doubled Standards have new section
Lift Heights and Headroom
• •
TG20 Compliance Sheets allow lifts up to 2m Compliant Scaffolds, however, can be determined in the TG20 eGuide up to 3m
Tube
TG20 Compliant Scaffolds only permits the following types of tube to be used:
BS EN 39 type 4 (4mm) galvanised steel tubes or equivalent
High-tensile galvanised steel tubes with a diameter of 48.3mm, thickness of 3.2mm, in accordance with BS EN 10210-1
The following types may not be used without design:
BS EN 39 type 3 steel tubes
Aluminium
tubes
Other dimension, material or grade
Scaffold Boards
Platforms constructed from timber boards or decks of other materials
BS2482 Timber board (softwood)
BS2482 Board (with nail plate option)
Double Standards New Text On Double Standards • May be required where additional ties or reduced bay lengths are not suitable. • Will have its own Base Plate. • May not need to go to full height • Secondary standard is connected to the ledger.
Foundations • • • •
Loads newly available in Operational Guide to assist clients More foundation detail in Design Guide than before. Typical foundation design( leg) load is stated to be 19.7kN. Need for regular inspection of foundations.
Number of lifts
2
3
4
5
6
8
Foundation Load (kN)
10.5
11.8
13.1
14.4
15.7
16.4
( Load Class 4)
Structural Transoms •
Structural Transoms are required for all TG20 Compliant Sheeted independent scaffolds, whether full or partly cladded and including some debris netted scaffolds.
Compliant Scaffolding Types
Towers
Towers • • • •
Now three duty classes of tower: 0.75/1.5/2.0kN/m2 The eGuide provides a restricted range of external tower designs which are dependent on a wind management system. Base dimensions now up to 2.7 x 2.7m No TG20 compliant designs are published for mobile towers
Stationary Free Standing Towers Load Class
Maximum Load
Typical Uses
Minimum Maximum Bay Bay Dimensions Dimensions
1
0.75kN/m2
Very Light Duty
1.2 x 1.2m
2.7 x 2.7m
2
1.5kN/m2
Light Duty
1.2 x 1.2m
2.1 x 2.1m
3
2.0kN/m2
Heavy Duty Towers
1.2 x 1.2m
1.8 x 1.8m
Compliant Scaffolding Types
Interior Access Birdcage Scaffolding
Interior Access Birdcage Scaffolding
• Now 3 classes, not just 0.75Kn/m2
0.75 1.5 2.0
Compliant Scaffolding Types
Tied Putlog Scaffolding
Compliant Scaffolding Types
Free-standing Independent Scaffolding
Compliant Scaffolding Types
Loading Bay
Loading Bays Loading Bays • Revised dimensions, including 4.0m bay length. • There are standard versions of 10kN and 15kN loading • Loading Bay Gates now included.
Compliant Scaffolding Types
Ladder Access Tower
Stairways Compliance to BSEN12811-1 Illustrated in Operations Manual
Compliant Scaffolding Types
Chimney-stack Scaffolding
Compliant Scaffolding Features
Bridging with Beams
Bridging with Beams • • • • •
Now allows for use of Aluminium Beams, as long as the same properties as the eGuide programme. Includes 750mm deep beams TG20 Compliant bridges span 2 or 3 bays, dependent on which depth of beam supporting ( nominally 305 or 610mm) Minimum structural properties of beams are in the Operational Guide, Supports 10 boarded lifts with 1 inside board Supporting more lifts by repeating the bridge.
Prefabricated Beams Beam Properties Steel or aluminium beams used within TG20 compliant scaffolds must comply with the minimum structural properties shown below: Structural property
Minimum value
Safe working moment resistance with Compression chord restraints at 1.2m spacing Safe working shear resistance Minimum ladder beam properties Structural property
12.5 kNm
8.3kN
Minimum value
Safe working moment resistance With compression chord restraints at 1.2m spacing
27kNm
Compliant Scaffolding Features
Prefabricated Transom Units ( Readylok / ‘Bones’ )
Compliant Scaffolding Features
Light duty protection fans
Compliant Scaffolding Features
Pavement Lifts
• Changed tie arrangements • Max 2.7m pavement lift height • Max 2.44m headroom
Lift Shaft Tower
Lift Shaft Tower • Maximum height 34m • Loading 0.75kN/m2 on 2 lifts • Maximum length 2.7m • Securely butted in all 4 directions- no ties required.
Compliant Scaffolding Features
Cantilevered Access Platforms
• Should be at the same level as the main working platform
Temporary Roofs • Temporary Roofs are no longer covered by TG20, but by TG9
Hoardings More appropriately covered by TWF Hoarding Guide
Simplified Wind Classifications Wind exposure affects the maximum height and tie duty, especially when sheeted or netted. A simple wind exposure classification illustrated here is used with the TG20 Compliance Sheets (chapter 3) A more accurate wind analysis is used in the TG20 eGuide, which can result in increased safe heights and reduced tie duties. Further advice is provided for designers in TG20 Design Guide. Wind exposure is classified as ‘ moderate’, ‘high’ or ‘extreme’ Other factors to be considered are ‘site topography’ ‘seasonal variations’ and ‘wind
Ties & Anchors The Operational Guide now provides very extensive ( 30 pages ) guidance on this subject, not within the Technical Design Guide. The information seems to go further than the TG4 NASC guide.
Ties & Anchors
Hilt-Type
Plastic Plug
Self-Tapping
eg Excalibur
Ties & Anchors • Tie details no longer in Technical Guide, but extensively in the Operations Guide • Importance of impermeable facades= TG20 Compliance • Permeable sheeted/ debris netted = designed • Additional Tie Load Class • Double proof-testing of nylon anchor positions if re-used. • Compliance sheets mainly based on 16m2 frequency.
Enforcement • TG20:08 to be officially withdrawn on 30th June 2014
• There should be a ‘ bedding in period
