Design classes for falsework Class A Class B1 Class B2 Slab area < 0.3 m² Simplified design (ie 300mm) in BS EN 12812 and/or in Beams < 0.5 m² accordance with Design in relevant accordance Clear span < 6.0 m EuroCodes with relevant EuroCodes Height < 3.5 m Most falsework (measured to underside in this class of permanent works) But there is a γ m x 1.15 3 of 4
BS 5975 : 2008 Code of practice for temporary w orks procedures and the permissible stress design of falsew ork First published 1982 Permissible Stress £270 Chairman: Frank Marples 4 of 4
BS 5975:2008 BS 5975:2008 New Loadings New Loadings on Falsew ork on Falsew ork
Construction Operations - Working Area Load Allow for a Service Class 1 load of only 0.75 kN/m² over the entire area, including access and working areas. i.e. only 30mm extra concrete ! BS 5975 - The British Standard Heap - Cl 17.4.3.1 1 of 3
load 0.75 kN/m² Service Class 1 Working area 2 of 3 Working Area Load BS 5975 Clause 17.4.3.1
Additional Transient In-situ Concrete Load In-situ concrete loading Total load equal 3m 3m 0.75 kN/m² to 1.75 kN/m² to 10% concrete load Working area Service Class 1 load 0.75 kN/m² 2 of 3 BS 5975 Clause 17.4.3.1
In-situ Concrete Construction Operations Loads Summary Thickness calcs Total Up to 300mm 0.75 + 0.75 1.50 kN/m 2 10% of weight 300 to 700mm 0.75 + 10% t 0.75 + of concrete Over 700mm 0.75 + 1.75 2.50 kN/m 2 Slab thickness t 3 of 3
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Permanent formwork minimum construction load of 1.50 kN/m 2
Working Areas - Access for striking Wherever falsework requires removal of individual pieces, for example striking primary or secondary bearers, consideration should be given to a working platform about two metres below the underside of the permanent works. Where the formwork and falsework is handled in large areas, provision for access to make-up areas should be considered. ( Use Service Class 1 load - 0.75 kN/m 2 ) 1 of 2 BS 5975 Clause 19.1.1
2 of 2 Consider access underneath for striking Tall frame structure
BS 5975:2008 BS 5975:2008 The Four Design The Four Design Checks for Falsew ork Checks for Falsew ork
Falsew ork Analysis It is recommended that for each falsew ork structure FOUR design checks be carried out: Check ONE - on the STRUCTURAL STRENGTH of the individual members and their connections to transmit the applied loads / forces ; Check TWO - on the LATERAL STABILITY of both individual members and the structure as a w hole; Check THREE - on the OVERALL STABILITY of the falsew ork structure; Check FOUR - on POSITIONAL STABILITY to ensure the falsew ork does not slide. Source: BS 5975 Clause 19.4.1.1
THINK VERTICAL THINK HORIZONTAL and then, THINK HORIZONTAL AGAIN and again, and again, and again.
BS 5975:2008 BS 5975:2008 Check One Check One Structural Strength Structural Strength
Adjustable telescopic Published November 1999 1 of 6 BS EN 1065 steel props Committee: CEN £150.00
Class Max. Extension Characteristic strength A 25 2.50 m 20.40 kN A 30 3.00 m 17.00 kN BS EN 1065 A 35 3.50 m 14.60 kN A 40 4.00 m 12.80 kN B 25 2.50 m 27.20 kN B 30 3.00 m 22.70 kN B 35 3.50 m 19.40 kN B 40 4.00 m 17.00 kN B 45 4.50 m 15.10 kN B 50 5.00 m 13.60 kN B 55 5.50 m 12.40 kN C 25 2.50 m 40.80 kN Props to have C 30 3.00 m 34.00 kN minimum of C 35 3.50 m 29.10 kN 1.0m adjustment, C 40 4.00 m 25.50 kN and not to be C 45 4.50 m 22.70 kN intentionally C 50 5.00 m 20.40 kN dis-engaged C 55 5.50 m 18.60 kN D 25 to D55 2.50m to 5.50m 34.00 kN 2 of 6 E 25 to E55 2.50m to 5.50m 51.00 kN
Characteristic strength Characteristic strength is the value at w hich is the value at w hich 95% of those tested 95% of those tested w ill fail above value w ill fail above value ( ie 5% w ill fail below value ) ( ie 5% w ill fail below value ) 3 of 6
Stellenbosch - South Africa - 2009 Removed TWO internal walls 200mm thick x 14m slab 4 of 6
Supplier claim 29.80kN characteristic load Thin walled props 3.2m (too short) 5 of 6
BS5975:2008 Safe Working Load - BS EN 1065 props erected 1 o out-of-plumb with 10mm eccentricity of load 6 of 6
BS 5975:2008 BS 5975:2008 Check Tw o Check Tw o Lateral Stability Lateral Stability
BS 5975 : Horizontal Disturbing Force Clause 19.2.9.1 At each phase of construction falsework should resist the applied vertical loads PLUS a horizontal disturbing force the greater of EITHER 2½ % W OR the summation of wind force, erection tolerance ( 1% W) , concrete pressure force, water and wave forces, dynamic and impact forces, forces from the permanent works (e.g. stressing etc.) etc.. 1 Of 2
Falsework’s horizontal disturbing force F H Design for Load W minimum lateral stability load of 2½ % W or know n lateral loads PLUS 1%W 2 of 2 (BS 5975 : Clause 19.2.9.1 )
Load Case 1 - Erected but not concreted Lateral Forces :- Maximum wind load plus 1% known vertical loads (BS 5975 and Class B1) Increases to at least 2% of known vertical loads if Class B2
Load Case 2 - While placing the permanent w ork / concrete Lateral Forces :- Working wind load plus 1% known vertical loads including full concrete load (BS 5975 and Class B1) Increases to 2% known vertical loads if Class B2 NOTE: I f the structure is not connected to a permanent structure then the full wind load might need to be considered consult with the Temporary Works Designer (TWD ) -
UK BS 5975 load Case - Minimum stability Horizontal disturbing force F H will be a minimum of 2½ % total vertical load including self weight, concrete, and full construction operations load
Top Restrained Load Case - connected to Permanent Works Restraining force R H will be a minimum of:- 2½ % (vertical loads) (BS 5975 and Class A) or 2 % (self weight) plus maximum wind (Class B2) or NOTE: Although bracing is not shown, the 2 % (vertical loads) structural strength still needs checking plus working wind (Cat. 2) and bracing may be required (Class B1 and B2) to create effective nodes.
Conditions of use stated by supplier require top restraint
1 of 3
2 of 3
North Staffs PFI SGB GASS braced for 2½ % W 3 of 3
Or is it ? Top restrained falsework
Lateral Stability of steel beams - Web stiffeners For structural steelwork at points of reaction or concentrated load, web stiffeners should be provided at ALL loading transfer points including supports, UNLESS calculations are provided to show that such stiffeners are not required. Web stiffeners No Calculations (BS 5975 : Annex J Clause J.1)
BS 5975:2008 BS 5975:2008 Back propping Back propping flat slabs flat slabs
European Concrete Building Project (ECBP) - 4th floor Backpropping Falsew ork Formw ork 1 of 1
Method One - One level of backpropping Distribution of Applied Loads This is 70% of Distribution of Applied Load using Elastic Props the applied load using Rigid Props and is in addition SLAB PROP SLAB PROP to the existing 100% load on the slab 100% NEW Slab to be cast 100% 100% Falsework load (w p ) - P p 70% Supporting slab (1) 50% Backprops (w b1 ) 50% 30% + P p Lower slab (2) 50% 30% + P p With preloaded props to value P p BS 5975 Cl 19.3.4 Table 20
Method One - Tw o levels of backpropping Distribution of Applied Loads This is 65% of Distribution of Applied Loads using Elastic Props using Rigid Props the applied load and is in addition SLAB PROP SLAB PROP to the existing 100% NEW Slab to be cast 100% load on the slab 100% 100% Falsework load (w p ) Supporting slab (1) - P p 65% 33% Upper Backprops (w b1 ) 67% + P p 35% Lower slab (2) 33% 23% Lower Backprops (w b2 ) 12% 33% + P p Lower slab (3) 33% 12% + P p BS 5975 Cl 19.3.4 With preloaded props to value P p Table 20
Part Tw o - Changes since 2009 Part Tw o - Changes since 2009 (c) Scaffolding (c) Scaffolding Temporary construction, w hich is required to provide a safe place of w ork for the erection, maintenance, repair or demolition of buildings and other structures and for the necessary access
Harsco Infrastructure
BS EN 12811-1 : 2003 Part 1: Scaffolds - Performance requirements and general design Published June 2004 £182.00 Chairman: CEN TC 53 “States BS 5973 withdrawn”
BS EN 12811-1 Introduces:- TWO Load Combinations : In Service Condition One platform with full imposed service load and the next above or below with 50% of service load Plus in absence of wind a lateral force of 0.3 kN / bay / working area Out of Service Condition Full wind load (BS EN 1991-1-4) and imposed Service Load limited to only 25% or 50%
NASC Guide for TG20:08 Volume 1 Scaffolding w ith tubes and fittings November 2008 120 pages Authors: Dr M.H.R. Godley Eur Ing P.F. Pallett Based on BS 5973 and updated to BS EN 12811-1 with simplified BS 6399 wind information Information for erection and use of standard scaffolds and includes FOUR summary tables of safe heights for scaffolds £135 + p&p Vol 1 & 2 Source : NASC 1 of 4
TG20:08 Volume 2 November 2008 128 pages TECHNICAL DATA Information on weights and properties, additional wind info., worked examples, and method for height of unclad scaffolds. Safe Height tables for :- 3 tables fully loaded inside boards 3 tables part ledger braced scaffolds Fuller calculation method heights: 24 tables fully ledger braced 12 tables part ledger braced (alt. ties) £135 + p&p Vol 1 & 2 2 of 4
TG20:08 Supplement 1 February 2011 16 pages Takes account of the Wind Code BS EN 1991-1- 4:2005 + A1:2010 using a simplified method to update the SAFE HEIGHT tables for Basic Scaffolds Incorporates Apprendix H for use of ties on UNCLAD scaffolds erected to open structures. Source : NASC 3 of 4
TG20:08 Overview TOOLBOX TALK Published by National Access and Scaffolding Confederation in July 2009 Plus a FREE Powerpoint toolbox presentation from www.nasc.org.uk £2.50 Handy Pocket Sized booklet Available from NASC 4 of 4
SG4 : 10 Preventing Falls in Scaffolding Published by National Access and Scaffolding Confederation with Foreword by HSE in December 2010 £25 60 pages Available from NASC 1 of 5
SG4 : 10 No longer permitted to traverse along a platform (known as tunnelling method) Create “scaffolders safe zones” For scaffolds with 2m lifts use of Step-ups Figure 39 2 of 5
Erection hop-up for next guardrail Quick release connection 3 of 5
SG4 : 10 Introduces use of ‘Scaffolders Safe Zone’ Reaching below guardrail “clip-on” Figure 9 Figure 12 4 of 5
SG4:You User Guide Preventing Falls in Scaffolding Published by National Access and Scaffolding Confederation with Foreword by HSE ( 84pp January 2011) Handy Pocket Sized booklet £5 Available from NASC 5 of 5
Designation of Scaffolds to TG20:08 EXAMPLE 3 – 5 - 1 S F Load Class 3 (General Purpose) Inside boards Number of boards Special case Inside boards assumed lightly between standards with 1.8m fully loaded loaded bay length I.e. Load Class Number of inside boards ( 0, 1 or 2) TG20 Cl 4.2 page 19
BASIC Scaffolds to TG20 Guide to T&F Scaffolds Part Boarded Fully Boarded 2 m lifts with possible 2.7m pavement lifts Tied to the building façade: either at alternate lifts 4m or at every lift Ledger bracing at alternate bays Façade bracing fitted every SIX bays but note: Plan bracing needed every FOUR lifts, and every twelve bays if façade braced across single bay
The controlling Table 1 Load Desig tion Activity Load M ax Max Class kN/m² Bay Boards 1 0.75 2.7m 3 1 - 3 - 0 Inspection, v. light duty 2 1.50 2.4m 4 2 - 4 - 0 Light duty 3 General purpose 2.00 2.1m 5 3 - 5 - 0 4 + 1 3 - 4 - 1 4 + 2 3 - 4 - 2 ( inside boards are 0.75 ) 5 + 1 3 - 5 - 1 5 + 2 3 - 5 - 2 4 Heavy Duty 3.00 1.8m 5 4 - 5 - 0 4 + 1 4 - 4 - 1 4 + 2 4 - 4 - 2 ( inside boards are 0.75 ) 5 + 1 4 - 5 - 1 5 + 2 4 - 5 - 2 Source TG20:08 Vol. 1 Table 1 page 21
Typical independent tied scaffold TG20 Figure 1 page 18
Ledger bracing alternate bays Façade bracing every Ties shown at alternate lifts SIX bays - to top platform Plan bracing Plan bracing NOT required NOT required Tie assembly 1 of 2
Plan bracing REQUIRED between Façade bracing every ties as façade brace is NOT SIX bays - to top platform between ledger braced frames H > 8m every FOUR lifts and every twelve bays Tie assembly 2 of 2
ALL sheeted & debris netted - unclad over 15m One transom at every lift within 300mm of ledger braced standards fitted with right angle or swivel fittings Ledger bracing Tie assembly 1 of 1 TG20 Cl. 10.2 (page 51)
Part Three : Changes in 2011 Part Three : Changes in 2011 (a) Wind (a) Wind (b) Formw ork (b) Formw ork
Part Three : Changes in 2011 Part Three : Changes in 2011 (a) Temporary Works Wind (a) Temporary Works Wind
Status of Wind Codes in the UK BS 6399-2: 1997 Loading for buildings, Part 2: Code of practice for wind loads, was published in July 1997 TG20 (scaffolding) first published in 2005 a simplified method based on BS 6399-2 Supplement No. 1 uses BS EN 1991-1-4+A1 The European Code BS EN 1991-1-4:2005+A1:2010 was amended in March 2011 (£246) The UK National Application Document (£170) was also amended in March 2011 The Background Information PD 6688 (£182) to the Annex was published in December 2009 ALL British Standards superseded by European Standards were withdrawn on 31 st March 2010
Wind in Temporary Works Aim: same procedure in all temporary works Falsework - BS 5975:2008 +A1:2011 to introduce revised simplified method based on the UK NA to BS EN 1991-1-4 +A1 Scaffolding - TG20 Supplement No. 1 now issued Formwork - Revision will include the same method extended to suit climbing formwork. Duration of work ( assume less than two years) Simplified method will use similar factors and town descriptions as existing for structures less than 50m with “orography” and less than 100m without “orography”.
Information needed by designer Location of the site How far from the nearest sea? less than 0.1km, 2 km, 10 km or 100 km Is it in a town that extends more than 2 km from the site in all directions? Is the topography fairly flat around the site, or is it near the top of the hill, or part-way up ? What is the altitude of site? ( in metres above sea level) Duration of work ( normally less than two years ) Is the falsework or the scaffold to be unclad, debris netted or sheeted?
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