REINFORCED CONCRETEREINFORCED CONCRETE

• Reinforced concrete is a composite material which utilizes the concrete in resisting compression forces, and steel bars and/or wires to resist the tension forces.

• Concrete has great compressive strength (this is the ability to support great loads placed directly upon it).

• However it has very little strength to resist stresses or forces that tend to bend or pull it apart.

• The compressive strength of concrete is about 10 times its tensile strength.

• Steel reinforcement therefore becomes necessary to increase its tensile strength.

• Concrete is cast around reinforcement steel.

• As it hardens, it grips the steel to form a bond with it.

• This bond becomes stronger as the concrete hardens.

TYPES OF REINFORCEMENT

• Reinforcement steel is manufactured mainly in three forms:

        Smooth steel bars (Düz insaat demiri)

        Deformed steel bars (Nervürlü insaat demiri)

        Wine mesh steel bars (Hasır)

• Both smooth and deformed bars are produced in standard sizes.

• They are normally designated by a number of thickness, incating their diameter in mm.

• like: 8, 10, 12, 14, 16, 18, 20, 22, 24 with a difference that deformed bars is not produced normally in 8 mm. in diameter.

• Their standart length is 12 mt.

• Main difference between smooth and deformed bars is that the load carrying capacity.

• Deformed bar is greater than that of smooth bars.

• Wire mash is normally used to reinforce concrete slabs and walls.

• It comes in the form of right-angled steel bars welded to one another at the intersection points.

• Wire mesh reinforcement is manufactured in various sizes or wire diameters and in various sizes of spacing.

• The spacing and wire sizes may be equal in both directions or they may vary in size and spacing to form what is called one-way mesh.

FORM CONSTRUCTION

• Concrete and reinforced concrete structures require forms to provide the desired shape and surface texture.

• Forms may be made of wood, steel, fiberglass, hardboard and other materials.

• The forms must be strong enough to resist the forces developed by the plastic (liquid) concrete.

Forms generally have five elements:

1. Sheathing/ board

2. Studs/joists

3. Wales

4. Braces or supports

5. Ties and/or spreaders (see bottom the figure)

• Forms are applied to different building components in different ways. Therefore there are at least six different applications of concrete form, such as follows:

1. Footing

2. Walls

3. Slabs

4. Steps

5. Beams or columns

6. Masonry support

• Form maintenance is important because it reduces the cost by extending the life of a form.

• Many forms are damaged during stripping (removing them from cured concrete).

• They should be inspected, cleaned, repaired and lightly oiled after they are removed.

• A wire brush may be used to raise the grain and roughen the surface.

• A liberal amounth of oil should be applied a few days before the plywood is used.

PLACING STEEL REINFORCEMENT INTO FORMS

• The steel bars are at first stockpiled on site, and than shaped according to the measurements, thicknesses and shapes specified for each unit of reinforced- concrete, building component, by the structural execution design of the building under construction.

• Giving steel bars desired shapes can be carried out on the site through the help of simple scaffolding and steel bending and hooking devices and levers

• The location of the steel within the concrete mass may differ as to the type and position of the building component.

• It may be important to mention here the theory about this issue very briefly.

• When a vertical load is placed on a beam or slab that rests on upright supports, the beam or slab tends to sag in the center between the supports (see the above figure).

• During this bending action, a squeezing force created on the top of the beam.

• At the same time, a stretching force is exerted on the lower side.

• Where the beam passes over the supported column a sheer (cutting) force is present.

• Where the beam rest on the column, the forces are reversed.

• Tension force is on the top and compression force is underneath.

• In order to equalize these forces, the main steel bars are placed in the beam as shown in the below drawing.

• Steel reinforcement is mainlyplaced wherever the tension occurs.

• The steel bars are then bent accordingly. Others are added to these bars for equalizing other pressures that the building may be subjected like eartquake and wind pressure.

• The steel rods are generally spaced high enough from the bottom of the form to allow concrete to completely surround the rod.

• Saddles are used to hold reinforcement bars above the bottom of the form.

• Reinforcement steel must be placed and secured before any concrete is poured.

• This is important because flowing concrete will cause unsecured, loose reinforcement to drift or relocate.

• Each intersection is fastened by either a soft wire tie or weld