REINFORCED 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: Sheathing/ board Studs/joists Wales Braces or supports Ties and/or spreaders (see bottom the figure)

Forms are applied to different building components in different ways Forms are applied to different building components in different ways. Therefore there are at least six different applications of concrete form, such as follows: Footing Walls Slabs Steps Beams or columns 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