LEARNING OUTCOME STUDENT SHOULD BE ABLE TO : Describe the different between plain and
reinforced concrete (CO1) Identify the elements of reinforced structures and their respective functions (CO1; CO3)
INTRODUCTION What is plain concrete? Plain concrete = cement + fine aggregate + coarse aggregate +
water Has greater crushing or compressive strength than tensile strength Generally plain concrete considered to be 10 times stronger in compression than tension Plain concrete member will failed in tension when the load acting on it
What is reinforced concrete? Reinforced concrete is where a
reinforcement in the form of steel bars is placed in areas where tensile stress will develop under load Concrete and steel have different properties ○ When combined, steel is able to provide the tensile strength and probably some of shear strength ○ While concrete, strong in compression, protects the steel to give durability and fire resistance
PROPERTIES OF STEEL AND CONCRETE
concrete
Properties
steel
Tensile strength
poor
good
Compressive strength
good
good (depending on slenderness)
Shear strength
fair
good
Durability
good
corrodes
Fire resistance
good
poor (suffers rapid loss of strength at high temperatures)
Requirements of reinforcement
Capability to achieve tensile strength Must be material that can be easily bent to any required shapes Must be capable to develop adequate bond with concrete Similar coefficient if thermal expansion is required Available at reasonable cost which is acceptable to the overall design concept
READY-MIXED CONCRETE : TYPE OF MIX Transit-mixed • mix is done completely in truck
Central-mixed • mix is complete in a stationary mixer and is delivered in a truck operating at agitating speed Shrink-mixed
• mix is partially done in a stationary mixer and is completed in a truck mixer
Stationary mixer
Stationary mixer
Truck mixer
Advantages of ready-mixed concrete : • Ensure accuracy in mix proportion • More efficient job site operation • eliminates time spent in quantities estimating of cement and aggregates required and labour to handle and mix material • Eliminated storage of raw materials • Specialized equipment / personnel for job mixing is not required • Concrete can be delivered at time required, eliminating time lost waiting to start or finish a job • Efficient large volume production • Can be delivered in exact quantity required, minimizing waste and costly reordering of raw materials • Cost is made known to purchaser through quotations
REINFORCED CONCRETE COMPONENTS BEAMS
COLUMNS
STAIRS
SLABS
FOUNDATION
BEAMS Horizontal structure member used to carry vertical load, shear load and sometime horizontal load. Beam can be vary in their complexity of design and reinforcement The correct design of RC beam :
sufficient strength to resist both compression and tensile forces Can resist shear failure ( if design shear exceed, shear reinforcement
should be provided ) Reinforcement should be provided at support if diagonal shear (approximately 45°) failure occur
BEAMS Shear occurs at or near the support as a diagonal failure line at an angle of approximately 45° to the horizontal and sloping downwards towards the support Stirrups are provided in beams, even where not required for shear resistance, this is to minimize shrinkage cracking and to form a cage for easy handling
COLUMNS
Vertical member that carrying the beam and floor loading to the foundation Compression member Since concrete strong in compression, it may concluded that if compressive strength of concrete is not exceed, no reinforcement will be required All bar in compression should be tied by link passing around the bar Min number bars of column should not be less : 4 for rectangular columns 6 for circular columns
RC slab will behave in same manner as a RC beam
The designer will analyse the loadings, bending moments, shear forces and reinforcement requirements on slab strip 1.0 metre wide
SLAB In practice, reinforcement will be fabricated to form a continuous mat
Three basis form RC slab: • Flat slab floors or roofs • Beam and slab floors or roofs • Ribbed floors or roofs
TYPE OF RC SLAB
1) FLAT SLABS
Contain between two plain surfaces and can
either simple or complex Design of complex form: ○ based upon the slab acting as a plate in which
the slab is divided into middle and column strips Simple flat slabs: ○ Can be thick or heavy ○ Giving clear ceiling height ○ Economic up to span of 9m ○ Can be designed to one way or two way ○ Generally designed as simply supported beam ○ Common practice provide top reinforcement at support
2) BEAM AND SLAB Consists of beams framing into
columns and supporting slabs spanning between beams. This is traditional system Large spans are possible and the reinforcement is generally not complicated The negative moments will occur over the internal supports required top reinforcement
3) RIBBED FLOORS Consists equally spaced ribs
usually supported directly by columns Either one-way spanning known as ribbed slab or twoway spanning known as waffle slab This type is not very common because formwork costs and low fire rating
Ribbed slab
Waffle slab
Function s
STAIRS
- Escape from emergency (fire) - Access from one level to another
Characterist ic
Regulation s
- Non-combustible - Strong - Hard wearing
-Refer to the Building Regulations:-- materials of stairs must be non-combustible materials -Specifications:-- 1:2:4 -- Aggregate 20mm -- Cover 15mm, 1-hr fire resistance -- Mild steel or high yield steels bar
Source: Building Regulations 2014 (Part K 1.1.4)
Elements
Functions
Going
Horizontal distance between the nosing of a tread
Rise
Vertical distance between the top of a tread and the top of the tread, landing or ramp
Tread
The upper surface of a step
Flight
The part of a stairway
Tapered step
A step
FOUNDATION Function • To transmit loads from superstructure to the ground. • To transfer the nonuniform load of the superstructure to the sub soil, so it minimize the nonuniform settlement • To provides the stability against the undermining , souring flood water and the burrowing animals. • To provides the safety against sliding. • To provides a level surface for the construction of the superstructure.
Characteristic • Cheaper and easy to construct • Strong
TYPICAL SUBSOIL BEARING CAPACITY:Type • Rocks, granite and chalks • Non cohesive soils, compact sands, loose uniform sands • Cohesive soils, hard clays and silts • Peat and made ground
Bearing capacity (kN/m) • 600-10000 • 100-600
• <600 • To be determined by investigation
FACTOR AFFECTING THE SELECTION OF FOUNDATION 1.Loads from building • Depends on types of structure • The dead and life load • External load (wind load)
1.Types of soil • Bearing capacity of soil • Behavior of soil • Presence of water table
Types of structure in neighbourhood • See the types of foundation neighbourhood used
TYPES OF FOUNDATIONS Shallow foundation • Transfer the loads to ground at a point near to the ground floor of the building • Examples: isolated, strips, raft
Deep foundation • Transfer the loads to ground some distance below the ground floor of the building • Examples: pile
1.
Isolated / Pad foundation
Function: • to support and transmit the loads from piers and column to the ground
Used: • If the column close to the site boundary, so suitable used rectangular shape. • Load on footing are less • The bearing capacity of soil is high
Advantange: • Most economic plane shape (square) • Simple
2.
Strip foundations
Function: • is a continuous strip of concrete to spread the weight of a load-bearing wall across an area of soil
Used: • Single storey building
3.
Raft / Matt foundation
Function: • To spread load over the entire area of the site
Types of raft foundations: • Solid slab raft • Beam and slab raft • Cellular raft
Solid slab raft
â&#x20AC;˘- column at equal distance and equal distributed load on the foundation â&#x20AC;˘- having uniform slab thickness - Foundation slab are reinforced, with two steel meshes - One at the lower face and another at upper face
Beam and slab raft
â&#x20AC;˘- column load unequal distributed or foundation is very heavy â&#x20AC;˘- stiffness is principal requirement to avoid excessive distortion of the structure as a result of variation in the load distribution on the raft, in such case slab and beam type raft foundation is provided
- beams are provided with the flat slabs - beams add stiffness to the raft foundation
Cellular raft
•- constructed for very heavy loads •- for loose soil or where the soils tends to settlement •- thickness slab must exceed 1 meter
- consists two slabs where a beam is constructed of two slabs in both directions forming hollow cellular raft foundation - highly rigid and more economical than other foundations in such type of poor soil condition. - The internal walls are used to spread load over the raft and divide the voids into cells