Presentation on theme: "Falsework Definition Any temporary structure used to support a permanent structure during its erection until it becomes self supporting Code of Practice."— Presentation transcript:
1FalseworkDefinitionAny temporary structure used to support a permanent structure during its erection until it becomes self supportingCode of PracticeBS5975:1982 Code of Practice for Falsework BSI
2Falsework Solutions Standard Solution Used for the support of floors and beams where the loading is of normal type in commercial and residential concrete construction and where the height of support is within the range of standard telescopic props
3Falsework Solutions Designed Solutions All situations where standard solutions deemed as inappropriate require design specific to the circumstanceCompetent person to design & supervise
4Falsework SolutionsBS5975 provides all necessary details and information for the design in respect of recommended practices, workmanship, checking and the setting out of individual party responsibilities
5Common Types of Falsework Birdcage Scaffold Falsework(to support soffit form)Mobile Scaffold Tower(an elevated working platform)
6Common Types of Falsework Table Form (originated in UK), now “Flying Form” (USA term)-soffit & its supporting structure to be struck, re-erected as one unit- combined soffit form and falsework, could be hydraulically operated;- wider leg spacing hence heavier leg load
7Considerations for safe erection of falsework Design considerations1. Design of falsework is recommended to follow BS 5975.2. Make sure that the falsework has been designed with due regard to:
8Considerations for safe erection of falsework · the type of and extent of loading· having adequate foundations· correct choice and use of materials· having provision for lateral stability
9Considerations for safe erection of falsework Construction considerations 1. Construction of falsework is recommended to follow BS 59752. Check carefully by competent personnel that the falsework construction follow exactly that shown on the drawings and in the specification produced by the designer prior to loading the falsework. Throughout the loading period a careful watch is kept to identify any distress and take any necessary remedial action.
10Considerations for safe erection of falsework 3. No alteration whatsoever should be made without consultation with and approval of the designer.4. Materials to be inspected before use.5. Only load-bearing couplers to be used for scaffolding components.
11Considerations for safe erection of falsework 6. he area under sole plates to be compacted well and preferably provided with a rigid concrete foundation. Vertical falsework members to be located centrally.7. Use high-tensile pin and never use a makeshift pin at the forkheads.
12Considerations for safe erection of falsework 8. Props not to be bent and erected plumb.9. Do not overextend the screw jacks at the top and base of the adjustable props.10. Provide adequate horizontal and diagonal bracing elements.11. Do not overload the deck (when stocking materials or plants) supported by falsework.
13Considerations for safe erection of falsework 12. BS 5975 recommends a temporary works coordinator to be appointed:to coordinate all falsework activitiesto implement inspection and advise actions, andto issue formal permission to strike falsework when the permanent works had attained adequate strength to be self-supporting.
14Falsework Design Procedures Design Standard:British Standard 5975 (1982). Code of Practice for FalseworkCode of Practice on Wind Effects Hong Kong
15Falsework Design Procedures LoadingSelf-weight - scaffolding, formwork(Check when final arrangement is known)Imposed Loads - concrete, construction operationsEnvironmental Loads - wind loading
17Falsework Design Procedures Layout of FalseworkVertical membersDesign should meet the overhead formwork requirementsCheck capacity of standard tubes(BS1139) or proprietary metal frame
18Falsework Design Procedures Horizontal members (lacing)· Increase applied vertical load by 10 % to allow for the effect of continuity of the primary beam on support reactions.· Increase applied vertical load by 2 % to allow for the vertical loads induced by horizontal loads.
19Falsework Design Procedures · Check the effective length for used/new standard tubes allowed by BS.· Check the self-weight of scaffold vs the assumed value.
20Falsework Design Procedures Wind LoadingConsider the falsework height, basic wind speed, site topography, and other relevant factors.Determine the design wind speed and the dynamic wind pressure.Determine the maximum wind force acting on the whole falsework (formwork + scaffolding) by:
21Falsework Design Procedures Determine the maximum wind force acting on the whole falsework (formwork + scaffolding) by:Establish the wind force diagram.Determine the maximum wind force Wm.Determine the moment of maximum wind force MWm.
22Falsework Design Procedures Calculate the distribution of applied vertical loadsDetermine the horizontal forces.I. horizontal force equivalent to 2.5 % of applied vertical loads, the smallest allowable horizontal force Hv (applied at soffit level). Moment MHv
23Falsework Design Procedures II. horizontal force resulting from the erection tolerances, impulsive forces, sloping soffits..etc. 1.0 % of applied vertical load Ht (applied at soffit level). Moment MHtIII. wind forces MWmUse the greater of (I) or (II) or [(II) + (III)]/1.25
24Falsework Design Procedures Combine applied and induced vertical loads and compare actual and estimated maximum loads on standards/proprietary scaffold frame.Induced vertical loads (VHv, VHt, VWm), applied vertical loads (V) and the combined vertical loads (max. of V=VHv, V+VHt, [V+VHt+VWm]/1.25 are calculated.Allow 10 % for continuity overload.Check the estimated max. load per standard/scaffold frame.
25Falsework Design Procedures Diagonal bracingDetermine the maximum of HV, Ht, & [Ht+Wm]/1.25Use the least of(I) coupler capacity(II) safe load of diagonal as a strut.(which depends on the number of fixing at various levels of the scaffolding)Design numbers of traverse diagonal bracing required.
26Falsework Design Procedures Design numbers of longitudinal diagonal bracing required.Check overall stability of the complete falsework under various combinations of vertical and horizontal loads. Factor of safety (FoS) should be at least 1.2.Provide kentledge or other form of holding down if the FoS is below the minimum requirement.
27Falsework Design Procedures FoundationsCarefully assess whether the ground is original soil or fill.Check the bearing capacity of the soil is not exceeded.Bearing Capacity for Soils & Rocks:Unweathered Rock kPaNon-cohesive Soil kPaCohesive Soil – 600 kPa
28Checklist for Mobile Scaffold Tower Checklist for Mobile Scaffold Tower..\Teaching_Notes\TEMP_WK\multimedia\Scaffold-MobileTower.jpg
29Checklist for Mobile Scaffold Tower DimensionsHeight between lifts not to exceed standard spacingLoadingNo overloading working platform nor the scaffold structure
30Checklist for Mobile Scaffold Tower Vertical Standards and Joints made with CouplersStandards must be vertical and stableJoints to be staggeredCorrect fittings used
31Checklist for Mobile Scaffold Tower Bracing Memberstower braced on all sides and in plan at each alternate lift starting at the base lift and also under deck level to keep the structure stable against lateral forces and toppling failure.Plan brace at base, every alternate lift and under working platform
32Checklist for Mobile Scaffold Tower Laddersto be lashed top and bottom on each stile, and fixed to the narrow side of the tower so as to provide vertical access by the operatives
33Checklist for Mobile Scaffold Tower Working platformsclose boardedtimber decking in good conditions and evenly supported with correct overhanggap for access to the platform closed with swivelling bar.Security of any stacked materialsLeast base to height ratio external 3:1, internal 3.5:1Size within base dimension
34Checklist for Mobile Scaffold Tower Guardrails and toeboardsTo avoid objects and persons falling from elevation.Castor Wheels with Safety Locksensure they cannot fall off if out of contact with the groundcheck brakes are fitted and in working conditionscastors are greased regularly and rotate freelyFoot ties as close to wheels as practicable
35Checklist for Birdcage Scaffold Sole board and foundation conditionLine of standards and ledgersLine & spacing of transomsDiagonals in both directionsTiesSecurity of boards, toeboards, and guardrails. Maximum gap at wall.
36Checklist for Birdcage Scaffold Security and correct use of couplers and fittingsCondition of tubes & fittingsEven spread of load on platformMeans of accessOverloadingSecurity of stacked materials
37Falsework on Sloping Ground ..\Teaching_Notes\TEMP_WK\multimedia\Soffit Form Sloping Details003.jpg