Upload
brittany-skinner
View
215
Download
0
Tags:
Embed Size (px)
Citation preview
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