chapter 3 - reinforced concrete

8/10/2019 Chapter 3 - Reinforced Concrete

1/15

IN THIS TOPIC, THE STUDENTS WILL LEARN:

1) THE CHARACTERISTICS OF REINFORCED CONCRETE.

2) THE BASIC KNOWLEDGE OF STEEL

REINFORCEMENT.

3) THE DIFFERENCES BETWEEN CONCRETE AND STEEL.


2/15

3.1 BASIC CONCEPT OF REINFORCED

CONCRETE

3.1.1 DEFINE THE REINFORCED CONCRETE

1) Concretein which steelis embedded in such a manner that the two materials

act together in resisting forces.

2) The reinforcing steelrods, bars, or meshabsorbs the tensile, shear, and

sometimes the compressive stresses in a concrete structure.

3) Plain concrete does not easily withstand tensile and shear stresses caused by

wind, earthquakes, vibrations, and other forces and is therefore unsuitable in

most structural applications.

4) Concrete is strong in compression, but weak in tension, thus adding

reinforcement increases the strength in tension.

5) In reinforced concrete, the tensile strength of steel and the compressive

strength of concretework together to allow the member to sustain these

stresses over considerable spans.

6) In addition, the failure strain of concrete in tension is so low that the

reinforcement has to hold the cracked sections together.


3/15

3.1.2 REINFORCED CONCRETE USED IN CONSTRUCTION

1) Concrete is reinforced to give it extra tensile strength; without reinforcement,

many concrete buildings would not have been possible.

2) Reinforced concrete can encompass many types of structures and components,

includingslabs, walls, beams, columns, foundations, frames and more

.

3) Reinforced concrete can be classified asprecast

orcast in-situ concrete

.

4) Much of the focus on reinforcing concrete is placed on floor systems.5) Designing and implementing the most efficient floor system is key to creating

optimal building structures.

6) Small changes in the design of a floor system can have significant impact on

material costs, construction schedule, ultimate strength, operating costs,

occupancy levels and end use of a building.


4/15

3.1.3 PROPERTIES OF REINFORCED CONCRETE

1) Reinforced concrete structures are typified by their strength, beauty, bulk and

longevity.

2) It is the material of choice for many structures where these characteristics are

required.

3) For a strong, ductile and durable construction the reinforcement shall have the

following properties:

High strength.

High tensile strain.

Good bond to the concrete.

Thermal compatibility.

Durability in the concrete environment.

In most cases reinforced concrete uses steel rebars that have been inserted

to add strength.


5/15

4) However, reinforced concrete structures have several shortcomings which may

preclude it as a building material, including:

a) It needs mixing, casting and curing, all of which affect the final strength of

concrete.

b) The cost of the forms used to cast concrete is relatively high.

c) It has low compressive strength as compared to steel (the ratio is about 1:10

depending on material) which leads to large sections in columns/beams ofmultistory buildings cracks develop in concrete due to shrinkage and the

application of live loads.


6/15


7/15

3.2.2 CHARACTERISTIC OF STEEL REINFORCEMENT

1. Rebar steelhave a series of ridges that bind it automatically to the concrete with

friction, but it can still be pulled out of the concrete with enough force, an

occurrence that often comes before a collapse of the building.

2. To prevent such a failure, rebar is either deeply inserted into surrounding structural

areas, or bent and hooked at the ends which locks it around the rebars and concrete.

3. Rebar steelthat are made of unfinished steel make it easy to rust.

4. Rust causes very harsh internal pressure on the surrounding concrete, leading to

cracking, splintering and finally structural failure.

5. This is a noticeable problem where the concrete is exposed to salt water, or in bridges

built in areas where roadways are salted in winter, or in marine applications.6. Stainless steel rebar may be used in these occurrences at greater initial cost, but

drastically lowers the cost for the servicing life of the project.


8/15

3.2.3 TYPES OF STEEL REINFORCEMENT

1. Reinforcing bars are produced in three (3)grades:

a) Hot Rolled Mild Steel which have a yield strength by 250 N/mm2.

b) Hot Rolled High Yield Steel have a yield strength by 460 N/mm2.

c) Cold Worked High Yield Steel have a yield strength by 460 N/mm2.

2. Hot-rolled mild steel usually has a smooth surface. Therefore, this type of steel is bent

easily and requires a small radius. For example, wire bonding steel poles or small logs.

3. Hot rolled high yield steel is steel with a carbon content of more than mild steel. It is

manufactured with a rough surface that overlap.

4. Cold Worked High Yield Steel have overlapping surface-shaped spindles, also known as

"deformed bar..

5. Bar for reinforcement are available with diameters of 6, 8, 10, 12, 16, 20, 25, 35 and 40

mm.

6. Type of steel reinforcement are indicated by the code R for mild steel and Y for the high

yield steel.


9/15


10/15

b) Pairs BarHorizontal distances not less than Hagg+ 5 mm. Vertical

distances not less than 2/3 Hagg. If the bar is paired side by side, the vertical

distance must be not less than Hagg+ 5 mm.

c) A Group of BarHorizontal and vertical distances not less than Hagg+ 15

mm.

3.2.4 ADVANTAGES OF STEEL REINFORCEMENT

a) Steel reinforcement is easy to place.

b) It minimizes random cracking.

c) Curling and displacement can be minimized with steel reinforced concrete.

d) Steel reinforcement reduces and controls crack width.

e) It can increases reserve strength of concrete slab up to 16 %.

f) Steel reinforcement saves costs over lifespan of the concrete slab.


11/15


12/15

3.3.2 THE REINFORCEMENT USED DUE TO TENSION COMPRESSION FORCE

1) If the load is applied in the center

of plane, bendingwill occurs.

2) When bending occurs, the surface

of the plane is compress due to

the COMPRESSION FORCE

and the bottom is a state of

stretcher caused by TENSIONFORCES.

3) Max. force is occurred in the arch

bottom of bending surface.

4) If plane is made without the

rebar, it will crack andeventually collapse.

5) Adding the rebar at bottom plane

can prevent the plane from

collapse.


13/15

3.3.3 THE REINFORCEMENT USED DUE TO SHEAR FORCES

A shear load is a force that tends to produce a

sliding failure on a material along a plane that isparallel to the direction of the force.

Shear strength of a plane is held in a plane that is

connected between the compression force of

concrete & steel tension force.

One way to overcome this shear is inclined to the

steel rebar to the right angle 90) of the crack .

Rebar in the longitudinal plane is to withstand

bending and to resist shear especially if it is

combined with metal fasteners (see Figure A)The most effective method to overcome this

problem is to have a 45 bend bar across the

plane which crack is expected to g row.


14/15


15/15

3.3.3.3 CONTINUOUS BEAM (BALAK SELANJAR)

i. A continuous beam is a structural component that provides resistance to bending

when a load or force is applied.

ii. These beams are commonly used in bridges.

iii. A continuous beam has more than two points of support along its length.

iv. These are usually in the same horizontal plane, and the spans between the

supports are in one straight line.

chapter 3 - reinforced concrete

Documents