TOP 7 : STEEL STRUCTURE

1: With percentage increase of carbon in steel , decreases its
A: Strength
B: Hardness
C: Brittleness
D: Ductility  

2:Poisson's ratio for steel within elastic limit , ranges from
A: 0.15 TO 0.20
B: 0.25 TO 0.24
C: 0.25 TO 0.33
D: 0.33 TO 0.35

3: The slenderness ratio of a column is zero when its length 
A: IS ZERO
B: IS EQUAL TO ITS RADIUS OF GYRATION
C: IS SUPPORTED ON ALL SIDES THROUGHOUT ITS LENGTH
D: IS BETWEEN THE POINTS OF ZERO MOMENTS

4:Maximum permissible slenderness ratio of compression members which carry dead and superimposed load, is
A:350
B:250
C:180
D:80

5:The effective length of a weld, is taken as the actual length
A: Minus the size of weld
B: Minus twice the size of weld
C: Plus the size of weld
D: Plus twice the size of weld

6:A beam is defined as a structural member subjected to
A: Axial loading
B:Transverse loading
C: Axial and transverse loading

7:The best compression member section for column is:
A: Single angle section
B: Double angle section
C: Channel section
D: I-section

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Los Angeles Abrasion Test , Why and How To Perform

LOS ANGELES ABRASION TEST:

This is hardness test for aggregates, used in Laboratory  to determine the hardness value or abrasion value 

APPARATUS :

 Los Angeles Abrasion Testing Machine ,

Abrasive Charge – Cast iron or steel balls ,
Test sieve – 1.70 mm IS sieve ,

 Balance of capacity 10 kg , Oven , Tray

The aggregate used in surface course of the highway pavements are subjected to wearing due to movement of traffic. 

When vehicles move on the road, the soil particles present between the pneumatic tyres and road surface cause abrasion of road aggregates. 

The steel reamed wheels of animal driven vehicles also cause considerable abrasion of the road surface. 

Therefore, the road aggregates should be hard enough to resist abrasion. 

The principle of Los Angeles abrasion test is to produce abrasive action by use of standard steel balls which when mixed with aggregates and rotated in a drum for specific number of revolutions also causes impact on aggregates. 

The percentage wear of the aggregates due to rubbing with steel balls is determined and is known as Los Angeles Abrasion Value.

Key point of los angles test:

Rotate the machine at a speed of 30 – 33 revolutions per minute. The number of revolutions is 500 for grading A, B, C & D and 1000 for grading E, F & G. The machine should be

5 kg of sample for grading A, B, C & D and 10 kg for grading E, F & G

THE CALCULATION PART:

Original weight of aggregate sample = W1 g

Weight of aggregate sample retained = W2 g

Weight passing 1.7mm IS sieve = W1 - W2 g

Los Angeles Abrasion Value = (W1 - W2) / W1 X 100

Los angeles abrasion value should lies in below given range for different types of roads

Types of pavement layers                                         Max. Permissible Abrasion Value in %

1:WBM , SUB BASE COURSE                                                      60%

2:WBM BASE COURSE WITH BITUMEN SURFACE               50%

3: BITUMEN BOUND MACADAM                                             50%

4:WBM SURFACING COURSE                                                    40%

5: BITUMINOUS PENETRATION MACADAM                              40%

6:BITUMINOUS SURFACING DRESSING CEMENT
 CONCRETE SURFACING COURSE                                              35%

7:BITUMINOUS CONCRETE SURFACING COURSE                   30%

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BAR BENDING SCHEDULE IMP

You may also like this topic of Estimation: 

How to calculate Quantity of Cement :Sand: Aggregate

If you are searching some important interview questions about cement than this article will boost your  knowledge today. 

                       Cement : The backbone of construction

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What is actually poisson's ratio.. Read it u will learn something most important

Poisson's ratio is defined as the negative of the ratio of the lateral strain to the axial strain for a uniaxial stress state. If a tensile load is applied to a material, the material will elongate on the axis of the load ﴾perpendicular to the tensile stress plane﴿,

Tensile deformation is considered positive and compressive deformation is considered negative. The definition of Poisson's ratio contains a minus sign so that normal materials have a positive ratio. Poisson's ratio, also called Poisson ratio or the Poisson coefficient, or coefficient de Poisson, is usually represented as a lower case Greek nu, n. 









Note: Poisson's Ratio has no units

Poisson's ratio is sometimes also reffered to as the ratio of the absolute values of lateral and axial strain. This ratio, like strain, is unit less since both strains are unit less.

For stresses within the elastic range, this ratio is approximately constant. For a perfectly isotropic elastic material, Poisson's Ratio is 0.25, but for most materials the value lies in the range of 0.28 to 0.33.

Generally for steels, Poisson's ratio will have a value of approximately 0.3. This means that if there is one inch per inch of deformation in the direction that stress is applied, there will be 0.3 inches per inch of deformation perpendicular to the direction that force is applied.


In other words poission ratio indicates the fraction by which a material is deformed by the action of compressive  or tensile(elongating) force in one of its perpendicular direction...

the best example to understand its physical effect is when u stretch a rubber band,it increases its length and at the same time,its diameter decreases , amount of decrement is given by poisson's ratio wrt its elongation

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Characteristic strength of concrete

Characteristic strength of concrete is one of the important properties of concrete which indeed unanimously by design engineeror any other person involved in the construction sector.

The compressive strength of concrete is given in terms of the characteristic compressive strength of 150 mm size cubes tested at 28 days (fck)- as per Indian Standards (ACI standards use cylinder of diameter 150 mm and height 300 mm). The characteristic strength is defined as the strength of the concrete below which not more than 5% of the test results are expected to fall.

This concept assumes a normal distribution of the strengths of the samples of concrete.

                               

Normal Distribution curve on test specimens for      determining compressive strength

The above sketch shows an idealized distribution of the values of compressive strength for a certain number of test specimens. The horizontal axis represents the values of compressive strength in MPa. The vertical axis represents the number of test samples for a

particular compressive strength. This is also termed as frequency.

The average of the values of compressive strength (mean strength) from the graph is 40 MPa. The characteristic strength (fck) is the value in the x-axis below which 5% of the total area under the curve falls. From the graph we can clearly say that 30 MPa is the characteristic strength of the given concrete mix. The value of fck is lower than fcm (40 MPa- mean strength) by 1.64σ, where σ is the standard deviation of the normal distribution.

So we can say the given concrete mix has a characteristic strength of 30 MPa or it is a M30 grade mix.

   M- Mix

* Note: For a 95% confidence level k=1.64 , hence k value varies on the confidence level of the experiment

Definition:

Characteristic strength of concrete is the strength of concrete specimens casted and tested as per given code of practice and cured for a period of 28 days; 95% of tested cubes should not have a value less than this value.

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BURJ KHALIFA : THE NAME TELLS EVERYTHING== >>

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==>FAILURE OF BOLTED JOINTS

FAILURE OF BOLTED JOINTSè

1=>SHEAR FAILURE OF BOLTS

ð  DUE TO SLIP OF PLATES

ð  TWO TYPES OF SHEAR => SINGLE SHEAR AND DOUBLE SHEAR

2=>BEARING FAILURE OF BOLTS

ð  CRUSED AROUND HALF CIRCUMFERENCE

3=>BEARING FAILURE OF PLATES

ð  PLATE CRUSHED

ð  PALTE MATERIAL WEAKER THAN BOLT MATERIAL

4=>TEARING OR TENSION FAILURE OF PLATES

ð  BOLT STRONG THAN PLATE

5=>BLOCK SHEAR FAILURE

ð  THIS TYPE OF FAILURE OCCURS WITH SHEAR ON ONE PLANE AND TENSION ON PERPENDICULER PLANE LEADING TO FALL ON HATCHING PORTION OF THE PLATE

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