basic structural design consideration

7/31/2019 Basic Structural Design Consideration

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By . Professor,

Department of

Civil

EngineeringBUET

Consultant



BUILDING DESIGN

ARCHITECTURAL DESIGN STRUCTURAL DESIGN

AESTHETICS

STRENGTH

FUNCTIONALITY

SERVICEABILITY

STABILITY DEFLECTION

DURABILITY VIBRATION

ECONOMIC



DEAD LOAD

WIND LOAD

LIVE LOAD EARTHQUAKE LOAD

OTHER LOAD

SOIL PRESSURE

RAIN LOAD

SNOW LOAD

TEMPERATURE LOAD



LOAD COMBINATION

ACCORDING TO BNBC THERE ARE 26 LOAD COMBINATION

1.4 DL

1.4DL+1.7LL

1.05DL+1.275WLY

1.0 DL‐1.27 WLY 1.3305DL‐1.4025EQLY+1.275LL

1.3305DL+1.4025EQLY+1.275LL

1.05DL+1.275LL+1.275WLX

‐

0.9DL+1.3WLX 1.3305DL+1.4025EQLX

1.3305DL‐1.4025EQLX . . .

1.05DL+1.275LL+1.275WLY

0.9 ‐1.3

0.9DL+1.3WLY

1.3305DL+1.4025EQLY

1.3305DL‐1.4025EQLY

1.05DL+1.275LL‐1.275WLY 0.9DL‐1.3WLY

1.3305DL+1.4025EQLX+1.275LL1.05DL+1.275WLX

0. 14 +1.430.614DL‐1.43EQLX

1.05DL‐1.275WLX 1.3305DL‐1.4025EQLX+1.275LL

. .

0.614DL‐1.43EQLY



LOAD TRANSFER MECHANISM

XIALLY

FLEXURAL

SHEAR + FLEXURE

PURE SHEAR

AXIAL + FLEXURE

TORSION

TORSION + SHEAR



MATERIALS PROPERTIES

STRESS‐STRAIN PROPERTIES

RUPTURE/ FAILURE PROPERTIES

FATIGUE

BEARING CAPACITY

CONSOLIDATION



STRESS‐STRAIN PROPERTIES

Concrete Stress

‐Strain

Curve



Stress‐Strain Curve For Steel



Creep and Stress Rupture Properties

reep ropert es

Creep is a time‐dependent deformation of a material

while under an a liedload that is below its yield

strength. It is most often

occurs at elevated ,

materials creep at room

temperature. Creep

terminates in rupture if

steps are not taken tobring to a halt.



of cyclic loading in the elastic regime. Failure is the end result of a process involving the initiation and growth of a crack, usually at the site of a stress

concentration on the surface.



AXIALLY LOADED MEMBER

Short Reinforced Concrete Compression y Short ‐ slenderness does not need to be considered –

column will not buckle

y Only axial loadCross‐sectional Areas:

s

=

A c = Area of concrete A g = Total area

F = stress in steel

Fc = stress in concrete

From Equilibrium:P = A cf c + A sf s



Short Concrete Columns

For ductile failure – must assure that steel

crushes.Strain in steel at yield ~0.002ε = 0.002 corresponds to max. stress in concrete.Concrete crushes at a strain ~ 0.003

= ’ s y c c



Reinforcement Ratio

y = A A

y ACI 318 limits on ρ for columns: 0.01≤ρ≤0.08 (practical ρmax = 0.06)

y Substitute ρ=A s/A g and A g=A s+A c into equilibrium

equation:P = A g[ρf y +f’c(1‐ ρ)]



Short Concrete Columns

P = A g[ρf y +f’c(1‐ ρ)]Safet Factors

y Resistance factor, Ф = 0.65 (tied), Ф = 0.70 (spiral)

y ’ c . , ,

y Stray moment factor for columns, K1

y = 1

y K1=0.85 for spiral reinforcement

ФPn = Ф K1 A g[ρf y +0.85f’c(1‐ ρ)]



Short Column Design Equation= ’ ‐ 1

, u n

⎤⎡ −uP '1

⎥⎦⎢⎣−c

gc y K f f .

)'85.0( 1φ

[ ])1('85.01

ρ ρ φ −+≥c y

ug

f f K A



Transverse Reinforcement

Used to resist bulge of concrete and buckling of steel



LATERAL TIES



FLEXURAL MEMBER



Data:y

Rectangular Beam Design

y Material properties – f’c, fyy All section dimensions – b and h

Required:-

1. Calculate the dead load and find Mu

2. d = h – cover – stirrup – db /2 (one layer)

and find As

4. Use As to find a

5. Use a to find As (repeat…)

6. Choose bars for As and check ρ max & min

7. Check Mu<φ Mn (final condition)

8. Desi n shear reinforcement stirru s

9. Check deflection, crack control, steel

development length.



PURE SHEAR



TORSION

TORSIONAL SPECIMEN

TORSIONAL STRESS DISTRIBUTION

basic structural design consideration

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