Construction of Concrete building PDF

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lecture notes for cocb...

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Lecture 1Lecture 2- Concrete Main things that we will learn-

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Concrete Introduction

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Portland Cement –

history, manufacture

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chemical composition

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types of cement

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Aggregates and Water

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Admixtures

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Properties of concrete

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manufacture and workability

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strength and durability

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specifying and ordering

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tests

Curing

Concrete Introduction•

Mixture of Cement, Water, Coarse & Fine aggregate, Admixtures (if required)

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The aim is to mix these materials in amounts to make concrete that is easy to: transport, place, compact, & finish. And which will set, and harden, to give a strong and durable product. The amount of each material (i.e. cement, water and aggregates) affects the properties of fresh and hardened concrete.

History of cement•

Ancient Egyptians used calcined (thermal decomposition) impure gypsum (CaSO 4).

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The Greeks and Romans used calcined limestone† and later learned to add lime and water, sand and crushed stone or brick and broken tiles. This was the first concrete in history. Thermal decomposition of limestone: CaCO3 → CaO + CO2 at 848°C Basic is when limestone is heated at very high temp. which creates CaO + CO 2

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The Romans ground together lime and a volcanic ash to produce what became known as pozzolanic cement from the name of a village of Pozzuoli, near Vesuvius.

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Patent for ‘Portland cement’ was taken out by Joseph Aspdin, a Leeds builder, in 1824. Cement was prepared by heating a mixture of finely divided clay and hard limestone in a furnace until CO2 had been driven off. The name Portland cement, given originally due to the resemblance of the colour and quality of the set cement to Portland stone – a limestone quarried in Dorset – has remained throughout the world. (Hence ‘OPC’)

Manufacture of Portland cement •

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Dry Method – most common o Limestone (CaCO3) is crushed, usually in two progressively smaller crushers o Add iron ore or fly ash and ground, mixed and fed to a cement kiln. Heat to about 1500°C. o Elements unite to form a new substance called clinker, grey balls about the size of marbles. o The cooled clinker is inter-ground with gypsum in a ball mill consisting of several compartments with progressively smaller steel balls. Wet Method – raw materials are ground with water before being fed into the kiln o Limestone (CaCO3) is crushed, usually in two progressively smaller crushers, then fed into a ball mill with the clay dispersed in water. There the comminution of the limestone (to the fineness of flour) is completed, and the resultant cement slurry is pumped into storage tanks. The slurry is a liquid of creamy consistence, with a water content of between 35 to 50%. The lime content of the slurry is adjusted by blending with slurries from different storage tanks. o The slurry is passed into a rotary kiln where pulverised coal is blown in by an air blast to temperatures from 1300 to 1500°C. o At first water is driven off and CO 2 is liberated: further on the material becomes liquid and lime, silica and alumina recombine to become ‘clinker’ – hard balls of ceramic-like material. The cooled clinker is inter-ground with gypsum in a ball mill consisting of several compartments with progressively smaller steel balls.

Chemical composition of Portland cement: Raw materials consist mainly of lime, silica, alumina, and iron oxides

After processing, the four major constituents of cement are: Silica and alumina make gypsum

Hydration of cement •

In the presence of water, the silicates and aluminates form products of hydration, which in time produce a firm and hard mass – the hardened cement paste

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The C2S provides most of the ultimate long term strength and the C3S gives the high early strength

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Since hydration starts at the surface of the cement particles, it is the total surface area of cement that represents the material available for hydration

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The rate of hydration depends on the fineness of the cement particles, and for a rapid development of strength high fineness is necessary (320-380 m2/kg for GP to 450-650 m2/kg for HE)

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Question – Where did the water go?

Lecture 4- (from slide 18) Anchorage and Development Length of Deformed Bars in Tension, L sy.t –

The anchorage and lap length formula in AS3600 for a straight piece of deformed bar in tension is: k1 = 1.3 for a horizontal bar with >300mm conc below or 1.0 otherwise

The formula above gives the amount of embedment (in the concrete) required for the reinforcing bar to receive the full strength/force (P) This expression shows that: –

yield stress of the bar increases, the anchorage length increases;

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clear spacing between adjacent parallel bars increases, the anchorage length decreases;

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actual cover to the bar increases, the anchorage length decreases;

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higher grade of concrete is used, the anchorage length will decrease; and

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bar diameter increases, the anchorage length will also increase.

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Lapped splices for bars in tension have to have a length not less than the development length.

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Lapped splices in compression are subject to a series of requirements Lap length in compression as slightly shorter than the lap length in tension.

The complete table is on lecture 4 slide 19 and it talks about how much lapping required in a wall for a reinforcement bar. (the chat is only when we are considering straight t bars)

At least 2 wires must overlap Overlap at end of sheet with overhang, all fabric styles Overlap at side of sheet, rectangular meshes, RL1218 to RL718, and square mesh SL81 Overlap at side of sheet, square meshes edge side-lapping wires SL102 to SL52, SL63 and SL53 Additional lap-splice strip. The cross-wires are being spliced in this example, so the cross-sectional area (bar or wire sizes and spacing) must match. This example shows an INCORRECT method of lapping. Only one mesh is overlapped here instead of two as required. bar hooks and cogs •

Reducing tensile development length by standard hooks –

a hook or cog reduces the development length by 50%

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‘standard hook’ includes 135° and 180° hooks and 90° cogs.

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should not be used in sections thinner than about 12 bar diameters, or in top bars in slabs

hooks, cogs and splices •

ends of bars are often bent 90° or 180° to provide anchorage, or are bent to keep the bar within the confines of the concrete.

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The length of steel needed to physically make each hook is given.

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The length of steel in a bar with a hook is the overall length of the straight portion plus hook or cog length.

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AS3600-2001 requires a longer hook to provide end anchorage of a beam ligature than the standard hook – bars used as shear reinforcement shall be anchored to develop the yield strength of the bar at mid-depth of the member.

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The anchorage of shear reinforcement may be achieved by hooks, cogs, welding of the traverse bars or welded splices.

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Adequately anchored if: –

bends in bars shall enclose a longitudinal bar with a diameter larger than the diameter of the fitment bar.

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a fitment hook should be located preferably in the compression zone of the structural member, where anchorage conditions are most favourable. Such an anchorage is considered satisfactory, if the hook consists of a 135º or 180º bend with a nominal internal diameter of 4db plus a straight extension of 10db or 100 mm, whichever is the greater.

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where a fitment hook is located in the tension zone, stirrup spacing is multiplied by 0.8

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fitment cogs shall not be used when the anchorage of the fitment is solely in the cover concrete of the beam

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fitment cogs are not be used when the fitment cog is located within 50mm of any concrete surface (AS3600-2009)

welding reinforcing bars and welding rules •

Welding of reinforcement must comply with AS1554 Structural Steel Welding –

in general, preheat is not required

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heat input should be controlled to avoid changing the metallurgical properties of the steel and hydrogen controlled electrodes should be used

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tack welds require a minimum 4 mm throat and a minimum length equal to the diameter of the smaller bar being welded

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no welds within 3 db from any part of the reinforcement that has been bent and restraightened (AS3600-2009)

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no straightening or bending of a bar within 75 mm of a weld location

tolerances and bar spacing •

Construction requirements for reinforcing steel –

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fabrication tolerances for bars and mesh •

For lengths up to 600mm

-25, +0mm

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For lengths over 600mm

-40, +0mm

bars and mesh used as a fitment •

For deformed bars and mesh

-15, +0mm

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For plain round bars

-10, +0mm

overall offset dimension of •

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a cranked column bar

-0, +10mm

Positioning of reinforcement and tendons –

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For positions controlled by cover •

In beams, slabs, columns and walls

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In slabs-on-ground

-10, +20mm

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In footings cast in ground

-10, +40mm

-5, +10mm

For positions not controlled by cover •

The location of tendons on a profile

5mm

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The position of the ends of reinforcement

50mm

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Spacing of bars in walls and slabs, and

of fitments in beams and columns

10% of the specified spacing, or

15mm (greater)

cover to reinforcing bars •

Cover for concrete placement –

Size and configuration of reinforcement

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Cover for corrosion resistance

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exposure classification and concrete grade

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cast against ground – increase by 10mm (damp-proof membrane) or 20mm

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Climatic Zones - Australia

F’c= characteristic strength of concrete

Different exposure requires different strength.

design for fire resistance •

The fire resistance period depends on the thickness of the concrete cover to the steel reinforcements

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Insulating materials may be used to increase fire resistance period

60 60

Worked example: main bar dia. = 20, ligature dia. = 10, cover = 40, beam width = 200, FRP = 120

Look at slide 38 for other values crack control reinforcement •

Crack control for tension and flexure in reinforced beams (AS3600 Cl. 8.6.1) –

Provide minimum area of reinforcement in a tensile zone of a beam

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Distance from the side or soffit of beam to the centre of the nearest longitudinal bar shall not exceed 100mm

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Control maximum steel stress

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Crack control in the side face of beams (AS3600 Cl.8.6.3)

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Where overall depth exceeds 750mm, provide longitudinal reinforcement: 12mm bars at 200mm centres or 16mm bars at 300mm centres, in each side face.

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Crack control at openings and discontinuities

Provide additional reinforcements

Crack control for flexure in slabs (AS3600 Cl.9.4.1) –

Provide minimum area of reinforcement in a tensile zone of a slab

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Centre-to-centre spacing of bars in each direction shall not exceed the lesser of 2.0D s or 300mm.

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Control maximum steel stress

Crack control for shrinkage and temperature effects (Cl.9.4.3) –

primary direction – no additional reinforcement is required to control expansion or contraction cracking

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secondary direction (unrestrained slabs) – minimum area of reinforcement shall be (1.75-2.5scp) bD x 10-3

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secondary direction (restrained slabs – minor degree of control) – minimum area of reinforcement shall be (1.75-2.5scp) bD x 10-3

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secondary direction (restrained slabs – moderate degree of control) – minimum area of reinforcement shall be (3.5-2.5scp) bD x 10-3

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secondary direction (restrained slabs – strong degree of control) – minimum area of reinforcement shall be (6.0-2.5scp) bD x 10-3

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greater reinforcement ratios for more severe exposure environments

Crack control at openings and discontinuities –

Provide additional reinforcements

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in slabs

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minimum area of secondary reinforcement shall be (Ast )=(1.75-2.5scp) bD x 10-3

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effective prestress in concrete, (scp) = 0 for normal reinforced concrete slabs

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Ast = 0.00175 bD

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Worked example: –

if D = 200mm, Ast = 0.00175 x 1000 x 200 = 350 mm2/m

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spacing = lesser of (400, 300) = 300 mm

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use N12@300mm spacing (367 mm2/m)

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If D = 120mm, Ast = 0.00175 x 1000 x 120 = 210 mm2/m

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spacing = lesser of (240, 300) = 240mm

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use N12@250mm spacing (440 mm2/m)

reinforcing carpets 500PLUS BAMTEC reinforcing carpets Features •

Prefabricated reinforcing steel ‘carpets; to a wide range of shapes and sizes

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Individual rebars are welded to flexible steel straps, which can connect up to hundreds of bars together

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Carpets can contain different types and sizes of bars, have bars at different spacings

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On site, the carpet is simply lifted into place and unrolled onto continuous bar chairs

Benefits •

Fast, saves up to 80% of steel fixing costs

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Improved accuracy and quality

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Less material waste and scrap

Week 3- RC theory design aims safety –

safely resist the actions (loads) expected to be imposed on it

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review all possible failure modes to ensure that nothing important has been overlooked

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robust and possess structural integrity

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damage to a small area of a structure should not lead to collapse of a large part

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fire resistance

serviceability –

under normal operating and load conditions, a structure must behave satisfactorily

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should not deflect or deform excessively or vibrate, or cause discomfort or unease to the occupants

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cracking should not impair the structure’s functionality

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attractive and well proportioned, but usually architects are responsible for the appearance unless for bridges

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minimise initial cost, construction time and life-cycle costs

aesthetics

economy

Flexural capacity -beam...