V Semester Civil CE2306 DRC by M.Alaguraj AP / Civil Page 1

MAHALAKSHMI

ENGINEERING COLLEGE

TIRUCHIRAPALLI - 621213.

QUESTION BANK

DEPARTMENT: CIVIL SEMESTER: V

SUBJECTCODE/NAME: CE2306/ DESIGN OF RC ELEMENTS

UNIT IV– LIMIT STATE DESIGN FOR BOND, ANCHORAGE SHEAR & TORSION

PART - A (2 marks)

1. Write about anchorage bars in tension.

Deformed bars may be used without end anchorages provided the development length required is satisfied. Hook should normally be provided for plain bars in tension.

The anchorage value of a band shall be taken as 4times the diameter of the bar for each 450 bend subjected to a maximum of 16 times the diameter of the bar.

The anchorage value of a standard U-type hook shall be equal to 16 times the diameter of the bar.

2. What are the various types of shear reinforcement?

Vertical stirrups

Bent up bars with stirrups

Inclined stirrups

3. What are the types of shear failure in reinforced concrete beam?

Shear tension

Flexure shear

Shear compression

Shear bond

4. Define bond stress.

The tangential or shear stress developed along the contact surface of the reinforcing bar and the surrounding concrete if generally termed as bond stress and is expressed in terms of the tangential force per unit nominal surface of the reinforcing bar.

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5. Define development length.

It is the additional length of rebar where anchorage is necessary. It is usually at the end of the reinforcement. Development also depends on the angle of anchorage.

6. Give the property of good a bond between concrete and reinforcement.

Sufficient cover for reinforcement

Richness of concrete

Using twisted bars, welding the stirrups bars with the main bars.

Roughness of steel.

7. Write about anchorage bars in compression

The anchorage length of a straight bar in compression shall be equal to the development length bars in compression

The projected length of hooks, bends and straight lengths beyond bends if provided for a compression, shall be considered for development length.

8. What are the types of shear reinforcement?

Vertical stirrups

Bent up bars with stirrups

Inclined stirrups

9. What are the types of shear failure in reinforced concrete beams?

Shear-tension (or) diagonal tension

Flexure- shear

Shear compression

Shear-bond

10. How do you prevent minimum shear reinforcements?

Brittle shear failure cracks which can occur without shear reinforcements.

Sudden failure due to bursting of concrete of concrete cover and bond to the tension reinforcements.

The shear reinforcements help to hold the main reinforcement while concreting forming an effective cage.

Formation of cracks due to the thermal and shrinkage stresses are minimized.

Shear reinforcement act as effective for the compression steel and make them effective.

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11. How do you develop bond mechanisms between concrete?

Chemical adhesion is the grip developed due to the gum like property of the gum like property of the hydration products of cement in concrete.

Frictional resistance developed due to the relative movements between concrete and steel bars depending up on the surface characteristics on the bars and the grip developed due to shrinkage of concrete.

Shearing resistance or dilatancy due to mechanical interlock developed as a consequence of surface protrusion as ribs in deformed bars.

12. List out the various types of reinforcement

Lapping of bars

Stirrups at splice locations

Staggered splicing

Mechanical connections

Butt welding of bars

Lap welding of bars

13. What are the criteria recommended by is 456-2000 for anchorage value of bond?

The radius of the bend be not less than twice the diameter of the round bar.

The length of the straight part of the bar beyond the end of the curve be at least four times the diameter of the round bar.

Whatever be the angle through which the bar is bend,the assumed anchorage value should not be taken as more than equivalent to the length of bar equal to sixteen times the diameter of the round bar.

14. What is the necessity of bending reinforcement?

Bars are bend under different circumstances

They may be bent from hooks so as develop proper anchorage.

Bars have to be bent so as to form loops as in the case of stirrups as shear reinforcement.

Bars may be also be bent to resist diagonal tension. They may also bent up to form necessary reinforcement for hogging bending moments.

15. What are the points to be considered in anchoring shear reinforcement?

Inclined bars: the development length shall be as for bars in tension. This length shall be measured as under.

In tension zone, from the end of the sloping or inclined position of bar

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In compression zone, from the mid depth of the beam

Stirrups,for stirrups and ties the complete development lengths and anchorage shall be deemed to have provided when the bar is bent through the angle of at least 90°

16. What are the criteria recommended by is 450-2000 for cover to reinforcement?

At each end of a reinforcing bar –not less not 25mm nor less than twice the diameter of

Such bar

For longitudinal reinforcement in a column –not less than 40mm nor less the diameter of such bar

For longitudinal reinforcement in a beams –not less than 25mm nor less the diameter of such bar

For tensile, compressive, shear and other reinforcement in a slab –not less than 15mmnor less the diameter of reinforcement

17. Give the property of a good a bond between concrete reinforcement

Sufficient cover for reinforcement

Richness of concrete

Using twisted bars ,

welding the stirrup bars with the main bars

Roughness of steel.

18. What is mean by end anchorage?

Mild steel bars embedded in concrete sometimes hooked so as to have proy per anchorage with concrete. If bars are provided with hooks, the necessary grip or bond length can be reduced. The anchorage value of the hook alone is considered as 16d where d is the diameter of the bar.

19. Write short note on splices in tensile reinforcement.

Splices at point of maximum tensile stress shall be avoided wherever possible, splices where used shall be welded, lapped or otherwise fully developed. In any case the splice shall transfer the entire computed stress from bar to bar.

Lapped splice in tension shall not be used for bars of the size larger than 36mm diameter and such splice shall preferably be welded.

20. Define modes of cracking under shear?

1. Diagonal tension failure

In this mode, an inclined crack propagates rapidly due to adequate shear reinforcement.

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2. Shear compression failure

There is crushing of the concrete near the compression flange above the tip of the inclined crack.

3. Shear tension failure

There is crushing of the concrete near the compression flange above the tip of the inclined crack.

4. Web crushing failure

There is crushing of the concrete near the compression flange above the tip of the inclined crack.

5. Arch rib failure

There is crushing of the concrete near the compression flange above the tip of the inclined crack.

21. Define development length

It is the additional length of the rebar where anchorage is necessary.

It is the usually at the end of the reinforcement. Development length also depends on the angle of anchorage. LD=12D.

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Part B (16 marks)

Problem no: 01

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Problem no: 02

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Problem no: 03

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Problem no: 04

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Problem no: 05

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Problem no: 06

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7. Describe the procedure for design of shear reinforcement. (APRL MAY 11) The nominal shear stress value is determined using the formula =shear force / (bxd) in KN/mm². The design shear strength of concrete is determined by using the tables in IS456-2000, page no 73, table no 19. Compare the nominal shear strength and design shear strength, the nominal shear stress value is less then design shear strength the minimum shear reinforcement is provided in the form of vertical stirrups, in the case IS456-2000-26.5.1.6 is referred. The nominal shear stress value is exceeds the design shear strength, shear reinforcement shall be provided in any of the following forms. a) Vertical stirrups b) Bent up bars along with stirrups, c) Inclined stirrups. Where bent up bars are provided their contribution towards shear resistance shall not be more than half that of the total shear reinforcement. Shear reinforcement shall be provided to carry a shear equal to the strength of shear reinforcement.

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