multi-storey framed structures

8/10/2019 Multi-storey Framed Structures

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What is Multi storey Building?

A multi-storey building is a building that hasmultiple floors above ground in the building.

Multi-storey buildings aim to increase thearea of the building without increasing thearea of the land the building is built on,

hence saving land and, in most cases, money(depending on material used and land pricesin the area).


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Abu Dhabi InvestmentAuthority Tower

International Commerce Centre,

Hong Kong


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NO. OF STOREYS

Multi-storey building consists of buildingsof more than 1-storey.

MATERIAL

Construction materials may differdepending on the number of storey of the

building. Timber can be used for building not more

than 3-storeys high.


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Steel Reinforced Concrete

Timber


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Availability of material / labour Cost

Speed of erection

Method of construction Transportation

Possibility of standardizing the sizes of thestructural members

Size and nature of site Modification

Fire resistance required


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For buildings of more than 5-storeys high, steelis the most suitable material to be used.

Steel is: Light in weight - easy to transport; less load on

foundation

Inorganic - will not decay, bend, crack or peel off High strength & durabilitysafety structure; Quality control - prefabricatedin the factory under

effective quality control less manpower, fasterconstruction

Less maintenance;

Cost effective;

Not at risk to delays


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Heavier; dead load; Non-recyclable;

High risk in crack & mould growth;

Higher total cost;

Duration of work long, risk to delay

Flexible design


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Element Steel Concrete

Site

consideration

Made under factory conditionBS/MSFabricated off site

Strict supervision on site

Work carried on site

Cost andspeed oferection

Erection by skilled- labour,quickly and accuratelyEarly completion but may belimited due to the large

number of complicatedconnections

Combination of skilled andunskilledSite space required forstorage and mixing

Cheaper in cost but longer inconstruction

Designconsideration

Extension need to expose bythe removal of any fireresisting casing

Flexibility in design monolithic in nature and notconfine to standard sectionsbut limit to the cost offormwork

Fireresistance

Requires protective covervarying in nature andthickness / sprayed asbestos

Provide a substantial degreeof fire resistance varied bythe cover thickness

Type ofconstruction

Dry constructionClean site

Wet constructionMessy site


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FLOOR SYSTEM

The principal structural elements of a typicalmulti-storey building comprise floors, beams

and columns. A wide variety of alternativeforms and arrangements can be used in multi-storey steel framed structures.

Floor slabs:Severaldifferenttypes of slabcan be used,in either

composite ornoncompositeform.


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COMPOSITE FLOOR SYSTEM The system consist of simply supported universal

Beam acting compositely with a thin concrete slab(concrete topping) supported on metal deck

Metal decking, which spans between secondarysteel beams usually spaced at between 2.5 and 3mcentres.

Steel stud are welded through the decking onto the

flange of the beam below to form a connectionbetween steel beam and concrete slab

Concrete is then poured onto the decking, usuallyby pumping, to make up the composite system.

Metal decking acts both as permanent formwork for

the concrete, eliminating the need to provide props,and as tensile reinforcement for the slab.

Steel bars are included in the slab to preventcracking and to provide reinforcement in the eventof degradation of the decking in a fire.


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Slimdek is a proprietary shallow floor system. It is acomposite system comprising of an asymmetric slim

floor beam contained within the depth of the slab.


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There are many types of steel deckingavailable. Some of the advantages of thecomposite metal deck system are: act as permanent shuttering which can eliminate

the need for slab reinforcement and propping ofthe construction. The floor deck serves as a working platform

during construction and as formwork for asitecast concrete slab

reduce the overall depth of structure. Provides upto 2 hours fire resistance (500C collapse)without additional fire resistance and 4 hourswith added thickness or extra surface protection.


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light, adaptable system that can be cut awkwardshapes and can easily be drilled or cut out foradditional service requirements. Reduce frameloading and foundation cost.

Simple, rapid construction


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NON - COMPOSITE FLOORSYSTEM

For shorter spans, precastconcrete floor slabs can beused with steel beams. Theprecast units may besupported on the top flangeof universal beams or onthe bottom flange


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Universal beams supporting pre-cast floorunits have advantages over other forms ofconstruction.

This system offers:

Fewer floor beams since pre-cast floorunits can span up to 6 to 8 m. without thedifficulty. No propping is required.

Shallow floor construction can be obtainedby supporting pre-cast floor units on shelf

angle. Fast construction because no time is

needed for curing and development ofconcrete strength.


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Disadvantages: Composite action not readily achieved

without a structural floor screed.

Heavy floor unit are difficult to erect inmany location and require use of specialmachines.

Small opening can be cut in the field,narrow openings parallel to slab span arepreferred, engineering analysis is requiredfor wide opening


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Apart from the method of construction, theappropriate choice of building materials isamongst the important factors in theconstruction of multi-storey buildings. The

material for structural frame can be madefrom steel, in-situ reinforced concrete andpre-cast concrete.

Compare the choice between steel structuresto pre-cast concrete frame based on theprincipal factors considered in their selection.

multi-storey framed structures

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