Transcript Considerations for safe erection of falsework

Falsework
• Definition
• Any temporary structure used to support a
permanent structure during its erection
until it becomes self supporting
• Code of Practice
• BS5975:1982 Code of Practice for
Falsework BSI
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Falsework 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
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Falsework Solutions
• Designed Solutions
• All situations where standard solutions
deemed as inappropriate require design
specific to the circumstance
• Competent person to design & supervise
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Falsework Solutions
• BS5975 provides all necessary details
and information for the design in
respect of recommended practices,
workmanship, checking and the
setting out of individual party
responsibilities
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Common Types of Falsework
• Birdcage Scaffold Falsework
(to support soffit form)
• Mobile Scaffold Tower
(an elevated working platform)
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Common 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
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Considerations for safe
erection of falsework
• Design considerations
• 1. Design
of
falsework
recommended to follow BS 5975.
is
• 2. Make sure that the falsework has
been designed with due regard to:
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Considerations for safe
erection of falsework
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the type of and extent of loading
having adequate foundations
correct choice and use of materials
having provision for lateral stability
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Considerations for safe
erection of falsework
• Construction considerations
1. Construction of falsework is recommended
to follow BS 5975
• 2. 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.
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Considerations 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.
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Considerations 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.
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Considerations 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
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by falsework.
Considerations for safe
erection of falsework
• 12.
BS 5975 recommends a
temporary works coordinator to be
appointed:
a) to coordinate all falsework activities
b)to implement inspection and advise
actions, and
c) to issue formal permission to strike
falsework when the permanent
works had attained adequate
strength to be self-supporting.
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Falsework Design
Procedures
• Design Standard:
• British Standard 5975 (1982). Code of
Practice for Falsework
• Code of Practice on Wind Effects Hong
Kong - 1983
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Falsework Design
Procedures
• Loading
• Self-weight - scaffolding, formwork
(Check when final arrangement is
known)
• Imposed Loads - concrete,
construction operations
• Environmental Loads - wind loading
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Falsework Design
Procedures
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Falsework Design
Procedures
• Layout of Falsework
• Vertical members
• Design should meet the overhead
formwork requirements
• Check capacity of standard tubes
(BS1139) or proprietary metal frame
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Falsework Design Procedures
• Horizontal members (lacing)
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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.
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Falsework Design Procedures

Check the effective length for
used/new standard tubes allowed by
BS.
 Check the self-weight of scaffold
vs the assumed value.
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Falsework Design Procedures
• Wind Loading
• Consider 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 +
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scaffolding) by:
Falsework Design Procedures
• Determine the maximum wind force acting
on the whole falsework (formwork +
scaffolding) by:
a)Establish the wind force diagram.
b)Determine the maximum wind force Wm.
c)Determine the moment of maximum wind
force MWm.
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Falsework Design Procedures
• Calculate the distribution of applied
vertical loads
• Determine 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
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Falsework 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 MHt
• III. wind forces MWm
• Use the greater of (I) or (II) or [(II)
+ (III)]/1.25
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Falsework Design Procedures
• Combine applied and induced vertical
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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.
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Falsework Design Procedures
• Diagonal bracing
• Determine the maximum of HV, Ht, &
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[Ht+Wm]/1.25
Use 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.
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Falsework 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.
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Falsework Design Procedures
•Foundations
•Carefully 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
kPa
Non-cohesive Soil
Cohesive Soil
600 - 10 000
100 - 600 kPa
75 – 600 kPa
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Checklist for Mobile Scaffold
Tower
..\Teaching_Notes\TEMP_WK\multimedia\Scaffold-MobileTower.jpg
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Checklist for Mobile Scaffold
Tower
• Dimensions
• Height between lifts not to exceed
standard spacing
• Loading
• No overloading working platform nor
the scaffold structure
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Checklist for Mobile Scaffold
Tower
• Vertical Standards and Joints
made with Couplers
• Standards must be vertical and stable
• Joints to be staggered
• Correct fittings used
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Checklist for
Mobile Scaffold Tower
• Bracing Members
• tower 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
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Checklist for
Mobile Scaffold Tower
• Ladders
• to 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
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Checklist for
Mobile Scaffold Tower
• Working platforms
• close boarded
• timber decking in good conditions and evenly
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supported with correct overhang
gap for access to the platform closed with
swivelling bar.
Security of any stacked materials
Least base to height ratio external 3:1, internal
3.5:1
Size within base dimension
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Checklist for
Mobile Scaffold Tower
• Guardrails and toeboards
• To avoid objects and persons falling from
elevation.
• Castor Wheels with Safety Locks
• ensure they cannot fall off if out of contact with
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the ground
check brakes are fitted and in working conditions
castors are greased regularly and rotate freely
Foot ties as close to wheels as practicable
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Checklist for
Birdcage Scaffold
• Sole board and foundation condition
• Line of standards and ledgers
• Line & spacing of transoms
• Diagonals in both directions
• Ties
• Security of boards, toeboards, and
guardrails. Maximum gap at wall.
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Checklist for
Birdcage Scaffold
• Security and correct use of couplers and
fittings
• Condition of tubes & fittings
• Even spread of load on platform
• Means of access
• Overloading
• Security of stacked materials
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Falsework on Sloping Ground
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