MIDTERM

Question 1

Can be found in the same way as that of a reinforced concrete

Answer 1

Ultimate Moment of Resistance

Question 2

The steel is strained in order to produced the prestressed force

Answer 2

Ultimate Moment of Resistance

Question 3

The steel strain should be taken as that due to bending plus that due to prestress force after loss

Answer 3

Ultimate Moment of Resistance

Question 4

Formula for Ultimate Moment of Resistance

Answer 4

Mu = fpb · Aps · (d-dn)

Question 5

For a rectangular beam, or a flanged beam in which the flange thickness is not less than

Answer 5

0.9x

Question 6

If d>0.9x

dn is?

Answer 6

0.45x

Question 7

What are the several causes of contraction of steel wires effecting the reduction (loss) in the prestressed concrete beam

Answer 7

1. Pre-tensioning
2. Post-tensioning
3. Loss due to elastic deformation

Question 8

It undergoes a gradual reduction with time from the stages of transfer due to various causes

Answer 8

Initial prestressing

Question 9

The force which is used to stretch the wire to the required length must be available all the time as prestressing force is the steel is to be prevented from?

Answer 9

Contracting

Question 10

Can be seen during the process of anchoring (loss in prestress)

Answer 10

Pretensioning

Question 11

The stressed tendon tends to slip before the full grip is established, thus losing some of its imposed strain (induced stress)

Answer 11

Loss due to anchorage draw-in

Question 12

From the time the tendons are anchored until transfer of prestressing force to the concrete, the tendons are held between the two abutments at a constant length

Answer 12

Pretensioning

Question 13

The stretch tendons during this time interval will lose some of its induced stress due to phenomenon known as

Answer 13

Relaxation of Steel

Question 14

As soon as the tendons are cut, the stretched tendons tends to go back to their original state, but are prevented from doing so by the interfacial bond developed between

Answer 14

The concrete and the tendons

Question 15

The tendons are located inside ducts, and the hydraulic jacks held directly against the member

Answer 15

Post-tensioning

Question 16

Can be seen during the stressing operation of tendons (loss in prestress)

Answer 16

Post-tensioning

Question 17

During stressing operation, the tendons tend to get straightened and slide against duct, thus resulting in the development of

Answer 17

Frictional Resistance

Question 18

The stress in the tendon at a distance away from the jacking end will be smaller than that indicated by the pressure gauge mounted on the jack known as

Answer 18

loss due to friction

Question 19

The loss of prestress due to deformation of concrete depends on the modular ratio and the average stress in concrete at the level of steel

Answer 19

Loss due to elastic deformation

Question 20

Prestress in concrete at the level of steel symbol

Answer 20

fc

Question 21

Modulus of elasticity of steel symbol

Answer 21

Es

Question 22

Modulus of elasticity of conrete symbol

Answer 22

Ec

Question 23

Modular Ratio

Answer 23

Le

Question 24

Formula of
Strain in concrete at the level of steel

Answer 24

fc / Ec

Question 25

Formula of Stress in steel corresponding to this strain

Answer 25

(fc / Ec) · Es

Question 26

Formula of Elastic Deformation of Concrete

Answer 26

Le · fc

Question 27

Formula pf Loss of stress in steel

Answer 27

Le · fc

Question 28

Results in shortening of tensioned wires and hence contributes to the loss of stress

Answer 28

Loss due to shrinkage

Question 29

Is influenced by the type of cement, aggregate and the method of curing used

Answer 29

Shrinkage of concrete

Question 30

Use of high strength concrete with low water cement ratio results in ______ and consequent loss of prestress

Answer 30

Reduction in shrinkage

Question 31

Progressive loss of water from concrete is its primary cause

Answer 31

Drying shrinkage

Question 32

Is higher at the surface of the member

Answer 32

The rate of shrinkage

Question 33

____ between the interior surface of large member may result in strain gradients leading to surface cracking

Answer 33

The differential shrinkage

Question 34

Is essential to prevent cracks due to shrinkage in prestress members

Answer 34

Propoer curing

Question 35

Moist curing is restored in order to prevent shrinkage until the time of transfer

Answer 35

Pretensioned members

Question 36

The total residual shrinkage strain will be larger in pretensioned members after transfer of stress is a recommendation made by code

Answer 36

IS:1343

Question 37

Total residual shrinkage symbol

Answer 37

εcs

Question 38

The loss of stress in steel due to creep of concrete can be estimated if the magnitude of ultimate creep strain or creep-coefficient is known

Answer 38

Loss due to creep