Anna University, B. ARCH. DEGREE EXAMINATION

### FIFTH SEMESTER, DESIGN OF STRUCTURES –II

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Yield stress for Fe 415 grade reinforcement is 415 N/mm^{2} and for working stress method permissible tensile stress in reinforcement is 0.55 times the yield stress and permissible compressive stress in bending is one- third of the characteristic compressive strength of concrete. For the limit state of strength a load factor of 1.5 shall be used.

**PART- A** (10 x 2 = 20 marks)

Answer all Questions

1. Define the characteristic strength of materials and characteristic loads.

2. What are the different grades of concrete and reinforcement bars recommended for

reinforced concrete structural members?

3. What are the assumptions made in the working stress method of analysis of reinforced

concrete members?

4. Determine the ratio between the depth of neutral axis and the effective depth of

reinforced concrete rectangular beams with Fe 415 grade tensile reinforcement for

balanced sections.

5. What are the partial safety factors for strength of concrete and reinforcement bars?

6. Determine the limiting value of the ratio between the neutral axis depth and the

effective depth of reinforced concrete beams with Fe 415 grade tensile bars for limit

state of collapse.

7. What are the maximum and minimum percentages of tensile reinforcement

recommended for reinforced concrete beams?

8. What are the factors governing the permissible shear stress in concrete and what is the

distance of critical section for the design of shear reinforcement in beams generally

carrying uniformly distributed load.

9. What are the span to effective depth ratios recommended for cantilever slabs, simply

supported and continuous slabs to satisfy their approximate stiffness?

10. What are the minimum percentage and maximum spacing recommended for non-

structural reinforcement for temperature and shrinkage and structural tensile

reinforcement in reinforced concrete slabs.

**PART – B** (5 x 16 = 80 marks)

11. For the limit state strength design of a single reinforced concrete section derive the

equation for x_{u}/d, and limiting moment M_{u,} limit in terms of p_{t}, f_{y}, f_{ck, }where x_{u}, is

the actual depth of neutral axis, f_{y, }and f_{ck, }are the characteristic strengths of tensile

reinforcement and concrete, respectively, and p_{t, }= A_{s / }b d, A_{s }is the area of tensile

reinforcement, b and d are the width and effective depth, respectively, of the beam.

12.a) A simply supported single reinforced concrete rectangular beam of 250 m, width

and 500 mm total depth with effective cover of 30 mm and effective span of 6 m

carries uniformly distributed service load of 8 kN/m in addition to self weight.

Determine the following using working stress method with M 20grade concrete and Fe 415 grade reinforcement: i) total design working load per metre, ii) Effective depth required for balanced section, iii) Area of tensile reinforcement for balanced section.

### OR

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12.b) A simply supported single reinforced rectangular beam of 300 mm, width x 600

mm depth with an effective span of 8 m carries two concentrated loads of 15 kN at

the one–third points in the span. Determine the following using working stress

method of design with M 20 grade concrete and Fe 415 grade reinforcement: i)

maximum design moment due to concentrated loads and the self weight of the

beam, ii) depth and area of tension reinforcement for the balanced section.

13.a) A cantilever R.C. beam of 4m span having 300 mm width and total depth of 600

mm contain four Fe 415 grade reinforcing bars of 20 mm diameter. Using working

stress method of design with M 20 grade concrete and an effective cover of 35 mm

calculate the maximum uniformly distributed service load carried by the beam if

reinforcement and concrete are fully stressed to their permissible values.

OR

13.b) A T beam floor slab of 125 mm flange thickness with 250 mm web width and 500

mm total depth contains four Fe 415 grade reinforcement bars of 16 mm diameter.

The centre to center distance of T beams is 4 m. Using working stress method of

design with M 20 grade concrete and an effective cover of 35 mm calculate the

following if the effective span of the T beam is 6m: i) effective width of

compression flange of the T beam; ii) actual depth of neutral axis; balanced depth

of neutral axis; iii) compressive force C above the neutral axis; iv) resisting moment

of the section.

14.a) A reinforced concrete rectangular cantilever beam of 3 m span carries an imposed

service load of 30 kN/m in addition to self weight. The width and total depth of the

beam are 250.0 mm and 500 mm, respectively. Draw the shear force diagram

indicating maximum shear force and its location from the support. Determine the

following using limit state method with an effective cover of 35 mm for tensile

reinforcement: i) the distance of the critical section for the design shear force from the edge of the support, ii) spacing of 8 mm diameter two legged stirrups of Fe 415 grade if the permissible shear stress in concrete is 0.4 Mpa., iii) maximum permissible spacing of vertical stirrups.

**OR **

14.b) A simply supported reinforced concrete beam of 6 m effective span carries 25

kN/m, in additional to its self weight. The width and overall depth of the beam are

250 mm and 450 mm, respectively. Draw the shear force diagram and determine

the following using limit state method with an effective cover of 35 mm: i) the

distance of the critical section for design shear force, ii) design shear force if the

permissible shear stress in concrete in 0.5 Mpa., and iii) spacing of 8 mm diameter

Fe 415 grade vertical stirrups, minimum area of vertical stirrups.

15.a) A cantilever roof slab of 2.5 m span and 3.5 m width carries a total load of 10.0 kPa

including its self weight. Using limits state method with M 20 grade concrete and

Fe 415 grade reinforcing bars determine the following: i) effective depth

recommended from span to effective depth ratio for cantilever slabs, ii) effective

depth required for ultimate limiting moment, and iii) spacing of 10 diameter Fe 415

grade reinforcement bars at support, maximum permissible spacing of tensile

reinforcement.

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15.b) A rectangular R.C. floor slab of effective spans 10 m x 4 m carries an imposed

working load of 7 kPa. Using limit state method of design with M 20 grade concrete

and Fe 415 grade reinforcement determine the following: i) effective depth required

using the recommended span depth ratio without modification factor for tensile

reinforcement, ii) ultimate load intensity on the slab assuming effective cover of 25

mm and load factor of 1.5, iii) spacing of 10 mm diameter rod of Fe 415 at the

center of the slab in both directions. Use moment coefficients of 0.122 and 0.02 for

short and long spans respectively.