structural design ii pu

8/11/2019 Structural Design II pu

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STRUCTURAL DESIGN II301008


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STRUCTURAL DESIGN II

Teaching scheme Examination scheme

Lectures: 4 hours/week Theory: 100 Marks

Practical: 4 hours/week Term work: 25 Marks

Oral: 50 Marks

Design should be based on IS: 456- 2000


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INTRODUCTION TO DESIGN METHODS

Working stress

It is a method of design in RCC structures,

which stresses of materials is calculated by usin

working load and compared with allowable stres

considering a linear stress strain relation ship.


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INTRODUCTION TO DESIGN METHODS

Ultimate Load

In ultimate load method, the working loads are increased

suitable factors to obtain ultimate loads. These factors are calle

factors. The structure is then designed to resist the desired ultim

loads. This method takes into account the non-linear stress-stra

behavior of concrete.


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LIMIT STATE METHOD

The acceptable limit for the safety and serviceability requirem

before failure occurs is called a "limit state".

The object of design based on the limit state concept is to ach

acceptable probability that a structure will not become unserv

in its life time for the use for which it is intended, that is ,it will reach a limit state. A structure with appropriate degrees of reli

should be able to withstand safely all loads that are liable to a

throughout its life and it should also satisfy the serviceability

requirements.


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LIMIT STATE METHOD

Limit State of Collapse

1. Flexure

2. Torsion

3. Shear

Limit state of serviceability

1. Deflection

2. Cracking

3. Fire


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INTRODUCTION TO REINFORCED CEMCONCRETE(RCC OR RC)

Concrete is strong in compression and weak in tension.

Hence the member which are subjected to both tensile and

compressive stresses are made up of Reinforced Cement Co

Reinforced concreteis a composite materialin

which concrete'srelatively low tensile strengthand ductilityar

counteracted by the inclusion of reinforcement having higher t

strength and/or ductility.
http://en.wikipedia.org/wiki/Composite_materialhttp://en.wikipedia.org/wiki/Concretehttp://en.wikipedia.org/wiki/Ultimate_tensile_strengthhttp://en.wikipedia.org/wiki/Ductilityhttp://en.wikipedia.org/wiki/Ductilityhttp://en.wikipedia.org/wiki/Ultimate_tensile_strengthhttp://en.wikipedia.org/wiki/Concretehttp://en.wikipedia.org/wiki/Composite_material


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VARIOUS LOADS, EFFECTS AND FORCESCOMING ON THE STRUCTURE

Dead Load (IS 875 Part 1)

Live load or Impose load(IS 875 Part2)

Wind Load (IS 875 Part 3)

Snow Load (IS 875 Part 4)

Earthquake Forces(IS 1893)

Shrinkage, Creep and Temp.(IS 875 Part 5)(for ordinary buildings w

lateral dimension do not exceed 45m, these effects are neglected)


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UNIT WEIGHTS OF PCC AND RCC

Unit Weight of PCC24 kN/cu.m

Unit Weight of PCC25 kN/cu.m

as per IS 456 -2000 Cl19.2.1 p.no32


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CHARACTERISTICS STRENGTH OFCONCRETE(FCK) (CL-36.1,P.NO67)

The characteristic strength of the concrete is the compressive stren

the(fck) concrete cubes of size 150 mm tested at 28 days. And com

strength of cubes should not fall not more than 5% of this strength.

For logical understanding-

If 100 Cubes are casted by same the concrete and after 28 days the

have 20 N/mm2 compressive strength or little bit more and 4 cubes h

compressive strength less than 20 N/mm2, then the characteristic str

concrete is 20N/mm2.


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CHARACTERISTIC LOAD (CL 36.2)

Theterm characteristic load means that value of load which

percent probability of not being exceeded during the life of the

structure. Since data are not available to express loads in stat

terms, for the purpose of this standard, dead loads given in IS

(Part l), impose loads given in IS 875 (Part 2), wind loads give875 (Part 3), snow load as given in IS 875 (Part 4) and seism

given in IS 1893 shall be assumed as the characteristic loads


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DESIGN VALUES

Materials

The Design strength of the materials, fd is given by

fd=f/m

Where

f =characteristic strength of the material (see 36.1), and

m =partial safety factor appropriate to the material and the

state being considered.


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PARTIAL FACTORS FOR LOAD(CL.36.3.

The design load, Fd is given by

Fd=F*f

where

F = characteristic load(see cl-36.2), andf=partial safety factor appropriate to the nature of loading and

state being considered.(given on Table 18 pg -68)


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ASSUMPTIONS MADE IN LIMIT STATE OCOLLAPSE: FLEXURE (IS 456-2000, CL-PG 69)

Plane sections normal to the axis remain plane after bending.

assumption ensures that the cross-section of the member doe

warp due to the loads applied. It further means that the strain

point on the cross-section is directly proportional to its distanc

the neutral axis.

The maximum strain in concrete at the outer most compressio

is taken as 0.0035 in bending

The acceptable stress-strain curve of concrete is assumed to

parabolic


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ASSUMPTIONS MADE IN LIMIT STATE OCOLLAPSE: FLEXURE (IS 456-2000, CL-PG 69)

The tensile strength of concrete is ignored.

The maximum strain in the tension reinforcement in the sectio

failure shall not be less than fy/(1.15 Es) + 0.002, where fy is

characteristic strength of steel and Es = modulus of elasticity


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SINGLY REINFORCED BEAM

A singly reinforcedbeam is one in which the concrete elem

only reinforced near the tensile face and the reinforcement, c

tension steel, is designed to resist the tension.


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SINGLY REINFORCED BEAM


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DOUBLY REINFORCED BEAM

A doubly reinforcedbeam is one in which besides thereinforcement the concrete element is also reinforced n

compressive face to help the concrete resist compressi

latter reinforcement is called compression steel. When

compression zone of a concrete is inadequate to resist

compressive moment (positive moment), extra reinforcehas to be provided if the architect limits the dimensions

section.


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DOUBLY REINFORCED BEAM

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