Transcript Lateral Supporting Systems

(1) Materials
Reinforced Concrete
VS Steel
Reinforced Concrete
Materials
Advantage
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good resistance to weather & chemical, and good sound and thermal insulation
the structure system is more rigid, thus, less severe problem associated with
sway deflection, floor vibration, and local column buckling
higher fire resistance
minimal maintenance is required
materials required to make concrete are readily available in the local market,
thus no pre-ordering is necessary
local contractors are firmly familiar with RC construction
can be cast into any versatile shape, thus, allow more flexible design
fairly tolerable on last minute changes from Client and Architect
waterproofing can be easily applied with different degree of waterproofing
can produce a good finished surface, thus, no painting is necessary
Reinforced Concrete
Materials
Disadvantage
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general heavier and hence more expensive foundation resulted
special care must be taken to ensure esthetic appearance against cracks
induced by creeping and shrinkage effects
intensive amount of falsework and shuttering are required
easily affected by weather condition, this will prolong construction time
Steel
Materials
Advantage
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fast construction, weather independent
flooring can be cast at the same time where formwork are provided by unpropped corrugated steel decking
lightweighted, thus, less expansive foundation can be designed (i.e. shallow
foundation.)
assembly is simple, since all members can be pre-fabricated prior to delivery
to site
structure tends to be shallower in structural depth, thus, more space will be
provided for service routing
with high strength to weigh ratio, suitable for long span construction.
Steel
Materials
Disadvantage
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Long pre-ordering and delivery time would be required since majority
members are to be import from overseas
Early decision on member size & connection details are required so as to allow
for ordering and shop drawing preparation.
Steel members require special treatment and protection on fire & corrosion.
Special surface treatments are needed:
Low cost – Sprayed System (Mineral fibre sprayed systems,
Vermiculite/gypsum/cement system)
External System (Mineral fibre boards/batts, Vermiculite/gypsum boards,
Plasterboard)
Preformed System
Intumescent Coatings
Water or Concrete filled structural hollow sections
Concrete casings
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Steel
Materials
Disadvantage
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frequent maintenance is required
skilful labors are required for fabrication, erection, and welding
large area on site is required for storage of structural member prior to erection
sensitive to temperature change and vibration
steel members will deflect appreciably under total load, needs pre-cambering
fabrication needs heavy plant and crane
(2) Structural Systems
Vertical Load Supporting System
• Lateral Load Supporting System (x & y directions)
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Structural Systems
Cantilever without
back span
Columns do not
vertically align
Too long cantilevers
Cantilever from
column without
back span
Heavy loading on long
span transfer beam
Long Slender Columns
(3) Structural Forms
Floor Supporting Systems
Structural Forms
(Floor Supporting System)
w
L
• Shear
α L
• Moment
α L2
• Deflection α
Deflection depends on:
•Span
•Structural Depth
•Loading
•Restraints
L4
Different forms of Bracing
Structural Forms
(Bracing)
Athletic Centre, Sydney, Australia
State Hockey Centre
Irregular Form
Federation Square
(4) Preliminary Member Sizing
Typical service zone requirements
Reinforced Concrete
RC beams
Typical s /d
Typical span
Continuous
15 – 20
10 – 15
Up to 10m
10 – 20m
Simply supported
12 – 15
8 – 12
Up to 10m
10 – 20m
Cantilever
5–7
7m
Steel
Element
Typical s /d
Typical span
Floor beams (UB’s)
(include floor slab
15 – 18
Up to 12m
Plate girder
10 – 12
Up to 12m
Castellated UB’s *
14 – 17
12 – 20m
Lattice girders (RSA’s) +
12 – 15
Up to 35m
Lattice girders (Tubular)
15 – 18
Up to 100m
Roof trusses (pitch >20o)
14 – 15
Up to 17m
Space Frames
20 – 24
Up to 60m
* Avoid if high point loads; increase Ireq by 1.3
+ Precamber by L/250
Typical column size
Appendix: Preliminary design charts
Appendix: Preliminary design charts (cont’d)
Appendix: Preliminary design charts (cont’d)
Appendix: Preliminary design charts (cont’d)
Appendix: Preliminary design charts (cont’d)
Appendix: Preliminary design charts (cont’d)
Appendix: Preliminary design charts (cont’d)
(4) References
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Fuller Moore, Understanding Structures, Boston,
WCB/McGraw-Hill, 1999.
Institution of Structured Engineers, Manual for the design
of reinforced concrete building structures, London, the
Institution, 1985.
Institution of Structured Engineers, Manual for the design
of steelwork building structures, London, the Institution,
1989.
Ove Arup & Partners, Structural scheme design guide,
London, Arup Research & Development, 1998.