03 concrete & steel
Post on 18-Jul-2016
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Building Construction3. Concrete and Steel Construction
CE 2330Civil Engineering Materials and Construction
Structural Elements
• Foundation – isolated and combined footings, rafts, piles etc.
• Columns• Beams• Slabs
Construction with concrete
• Concrete – weak in tension, good in compression
• Steel used for reinforcing – provides load carrying capacity to tensile zones
• Why steel?• Other modern reinforcement options –
fibre reinforced plastic (FRP)
Concrete construction in India
• Reinforced cement concrete (RCC) most popular construction material (Why??)
• Concrete can be site-mixed or supplied from central mixing plants by ready mix concrete trucks
• In India, most concrete is still site mixed• Labour intensive construction…• Volume batching still prevalent…
For large projects…
Batching plants are set up and concrete is conveyed using conveyor belts / hoppers / trucks…
Critical aspects of concrete construction
• Reinforcement detailing• Formwork design• Concrete mixture design• Conveyance of concrete, placement,
compaction, finishing and curing
Reinforcement detailing
- Most critical aspect from design and performance perspective- Detailed structural analysis - followed by design- Rebar diameter and spacing- Provision of cover (use of cover blocks)
Formwork design
- Formwork should be able to support the pressure from concrete before it hardens
- Should be easy to assemble and dissemble- Popular materials – steel, wood, aluminium, plastic etc. (some combined
systems also available)
Concrete mixture design
• Concrete is designed to get a required (compressive) strength and workability
• Strength – specified by structural designer• Workability – specified by construction
(site) engineer• Volume batching vs. weigh batching…• Durability of concrete
Building with steel
• Excellent tensile strength and ductility make steel a top building material
• Can carry enormous compressive loads too…
• Steel elements are factory made – so quality is good
• Expensive!• Requires skilled manpower
Steel construction
• In India, steel construction is only favoured for industrial buildings (factories / workshops etc.) – Why is it so?
• Preformed segments are assembled at the construction site
• Most critical factor – connections!• Welds, rivets, bolts etc.
Steel concrete composites
• Can combine the response of steel and concrete in compression – hollow steel tubes filled with concrete
• Presence of concrete increases resistance against buckling
• Steel confinement around concrete ‘increases’ load carrying capacity
• ‘Cheating’ concrete to believe that it is not experiencing any tension!
• Pre-compression applied to concrete overcomes tensile stresses due to loading
Prestressed concrete
Types of prestressing
• Transfer of compressive stress to concrete is by steel (high strength strands)
• If strands are stressed before pouring concrete – pre-tensioning
• If strands are stressed after concrete has gained sufficient strength – post-tensioning (in this case, concrete is cast with a duct)
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