scaffolding association queensland...additional horizontal scaffold tubes that are fixed to at least...
TRANSCRIPT
Scaffolding Association Queensland
Presented by Richard Morrison
Technical Manager, Layher Australia
Bracing
THEME
The evolution of bracing
Bracing for buildings, bridges and scaffolding
Current bracing applications
I want to show you how to:
1. Build safer scaffolding
2. Build faster
3. Win more jobs
ANCIENT STRUCTURES
Parthenon, Athens Greece
Thick, Heavy Stone blocks– All forces in compression!
BRIDGE BRACING
Bracing in bridge building- Compression forces
Ponte San MartinoA span of bridges
BRACING MATERIAL
17th century Robert Hooke
Vapours of iron?
Different colours when heated,Different springiness,Different hardness.
In fact early studies of carbon steel.
IRON BRIDGES
Ironbridge England, 100 foot span crossing the River Severn built 1781.
Cast Iron. Wooden bridges design. Compression structure.
COMPRESSION BRACING
• Compression generally means using heavy materials
• Robust structural forms
BRACING – WIND RESTRAINT
John Hancock Centre building Chicago100 storeys or 344 metres.Second tallest building in the world 1965 Architect Fazlan Khan Columns movedWind X- bracing
Space saving – efficiency.
Wind restraint on external face.
BRACED STRUCTURES AND BRIDGES
The Leaden Hall Building 225 m 4th Tallest
The Gerkin2003
The Cheese grater
BRACING EFFICIENCY
The centre Pompidou, Paris- Lightweight tension bracing
NO BRACING
What if bracing is not present………Oopphs!!.
SAVING WEIGHT
What bracing is the most efficient? Bi-plane wing bracing consisted of small diameter tensioned steel wires.Wire wheels invented by aeronautical engineer George Cayley in 1808.
HOW PRACTICAL IS TENSION BRACING
Wire wheel spokes suspend the axle from the top of the wheel rim.Wheel spokes – slender tensioned steel rods?
Modular Technical scaffolding bracing:Slender, light weight bracing best used in tension applications. - quick to erect and dismantle. - design scaffold bracing as tension members rather than compression members.
WHY NOT BAMBOO
It isn’t heavy!
Pros:• High strength to weight ratio• Readily available where it growsCons:• Safety• Random connections• Labour intensive• Weather affected
MODULAR TECHNICAL SCAFFOLDING BRACING?
Made from High strength, tubular carbon steel:- quick to erect and dismantle- light weight,- labour efficient, - strength efficiency.
But why is it needed?
BRACING TYPES
Three types of bracing:1. Braced Frame- Tension, Compression or Tension and Compression
2. Shear Wall- Typical of Timber framed house construction- Lift shafts, stair wells
3. Moment Resistant Frame- Bolted or welded connections
Most expensive !!!
No access!!
Scaffold bracing! Which is the most efficient?
AUSTRALIAN STANDARDS AND CODE OF PRACTICE
Australian Standards:• AS/NZS 1576.1 2010 Under revision• AS/NZS 4576 1995 Under revision
Workplace Health and Safety Queensland- Scaffolding Code of Practice 2009
AS/NZS 1576.1 2010 Clause 2.8.3.2 Bracing of compression members
The supplier’s documentation shall provide guidelines for the bracing
requirements of compression members of prefabricated systems and bracing patterns for a complete assembly.
provide guidelines for the bracing requirements
of compression members…
AUSTRALIAN STANDARDS AND CODE OF PRACTICE
AS/NZS 4576 1995 Clause 8.6 RIGIDITYRigidity is achieved through the use of fabricated frame units, fixed mesh panels or diagonal bracing systems.
Page 57: Bracing and tie members may be fixed by right-angle couplers to additional horizontal scaffold tubes that are fixed to at least two standards with right-angle couplers.
RigidityDiagonal bracing systems
may be fixed by right-angle couplers
Workplace Health and Safety Queensland- Scaffolding Code of Practice 2009
Appendix 1: DictionaryBrace – a member fixed diagonally to two or more members of the scaffold to provide rigidity of the scaffold.
Appendix 2: Inspection checklist❑ Is the bracing adequate?
STANDARDS FIGURES
AS/NZS 4576 1995 Under revision
16 No Couplers32 No Bolts and Nuts!
THE MAGIC COMPONENT
Layher Technical Brochure 2017
Tension
Compression
WIND FORCES ON STRUCTURES
Location - exposure to open water, open grassland or built up areas.Shielding – ground slopes and buildingsHill shape factors.
WIND FORCES
Suction or negative air pressure
Scaffolded Building Plan ViewAircraft wing
Suction or negative air pressure
FACADE BRACING
Negative wind pressure Reduce Effective length
Longitudinal wind
BRACING ARRANGEMENT
Unrestrained rectangle.
Restrained rectangle
Unrestrained scaffold
Diagonals provide structure stability!
Why do we need correct bracing?1. Forces are present ??2. Self weight of structure3. Axial and eccentric imposed loads4. Wind5. Pin jointed structure6. Slender members7. Displacement8. Buckling9. Brace to resist forces….
Model display
BRACING CONTINUOUS LOAD PATH
Bracing using node to node Arrangement Deflected shape
Node
DISCONTINUOUS LOAD PATH
Induced Standard Bending Deflected shape
?
?
?
RANDOM LOAD PATH
Eccentric loading => Induces Bending
e
ACCUMULATION OF FORCES
DIAGONAL ARRANGEMENT – PARALLEL COMPROMISE
Upper parallel diagonals Deflected shape
PARALLEL BRACING WITH ISSUES!
Parallel diagonals Deflected shape
DIAGONAL ARRANGEMENT – LOAD PATHS
Continuous Broken Bending Higher Parallel Lower Parallel
FACADE BRACING
Structurally goodInduces unwanted standard bending.
ACCESS BIRDCAGE SCAFFOLDING – BRACING
Each line of standards must be BRACED. Horizontal stiffening is achieved from decking at
working platform level. Horizontal bracing 4m vertical centres,or
alternatively tie the scaffold off adjacent permanent structures.
Elevation
Plan
Diagonals effective Two bays and Three bays
Plan
Vertical Diagonal Bracing
MOBILE ROLLING TOWER BRACING
FREE STANDING SCAFFOLDING TOWERS
Note • Opposing Diagonals• Ballast for stability
CANTILEVERS USING DIAGONAL BRACES
Layher Technical Brochure 2017
Tension
Compression
HUNG SCAFFOLDING USING TENSION BRACING
CANTILEVERS USING DIAGONAL BRACES
Model display
BRACING IN SCAFFOLD LIFTING OPERATIONS
Crane eyelet with 3 half couplers
Spindle attachment with wedge head
Standard Lock
Brace all bays.Plan brace to resist lateral lifting forces.
BRACING IN SCAFFOLD LIFTING OPERATIONS
ALUMINIUM LATTICE BEAM BRACING
BRACING IN SCAFFOLD FOOT BRIDGE LIFTING OPERATIONS
Safe erection on the ground
Quick, efficient installation on supports.
SCAFFOLDING FOOT BRIDGE
Model display
TEN REMINDERS
1. Design where possible with tension members
2. Tension bracing is usually the most efficient.
3. Bracing forces increase in size from top to the bottom of a scaffold
4. The importance of the load path – continuity of forces.
5. Diagonal bracing should meet other members at node points.
6. Tension members are not limited by length
7. Compression members are restricted by buckling
8. Beware of buckling in compression members
9. Brace for large lateral forces when lifting large scaffolds.
10. Adopt spreader beams when craning large scaffolds.