Reinforced Concrete Structure

• What is RC Concrete?

– Concrete that needs to be strengthened in tension

– Concrete good in compression poor in tension

• How?

– Steel bars embedded into the concrete

– Cut to a variety of shapes

– Cut & bent on site or delivered cut & bent

– Shape Codes

Formwork

• Before a concrete structure can be cast a mould has to be made

– This called formwork

• Formwork can be made from timber, metal, GRP and Polystyrene

• Formwork can be made with patterns in it and/or motifs

– Often called ribbed formwork

– Labour intensive, therefore expensive

• Formwork can be proprietary

• Fixing and supporting formwork is crucial.

• Accurate calculations are required if the formwork is not to burst open.

• Formwork can be massive and supported/reinforced by steel strongbacks and walings.

• Formwork design is serious business.

• Accurate setting out is vital

• Re-use?

Falsework

• Falsework is the part of formwork that supports the forms.

– Bridge decks, bridge abutments, multi-storey (table forms)

• It is important to keep the reinforcement in the formwork in position

– Reinft. must not move when concrete is poured.

Concrete

• Designed mixture of cement, sand, aggregate and water

– Water/cement ratio crucial

– Cement is most expensive

• Manufactured to a BS 810

– Aggregates must be clean and chemically inert

– Course aggregates can be pit gravels, beach gravels, crushed angular stone and/or crushed blastfurnace slag

– Air entraining

• Testing

– Specification will describe tests

Reinforcement

• Hot rolled mild steel bars, BS 4449

– Most common, 6mm to 40mm, max length generally 12m

• Hot rolled & processed high tensile alloy bars, BS 4486

– Less common

• Steel wire, BS 4482

• Steel fabric, BS 4483

– 200mm x 200mm, 1.54kg to 6.16kg per square metre

• Reinforcement cutting, bending and placing is a skilled job

• Accuracy is crucial

• Reinforcement must not move during pouring

• Can be constructed in or out of mould

• Needs careful handling/lifting to install to ensure no deformation

Placing Concrete

• By hand

• By ready-mix lorry

• By skip

• By cableway

• By pumping

• By conveyor

– Which ever way discharge needs careful control to prevent segregation

– Not less than 5C

– Within 30min of discharge

– Needs compacting – vibrating

– Needs curing

Joints

• Contraction joints

• Expansion joints

• Joggle joints

• Sliding joints

• Temporary joints

Waterbars

• Used if shrinkage of concrete would cause leaks in water retaining structures