![PART B (5*16 = 80 MARKS)
11. (a) What are the methods involved in the design ofreinforced concrete structures? Briefly explain the
design procedure ofthe methods
1. Working stress methods 2.Limit state method 3. Ultimate load method
Working stress method – only service load is considered, safety factor is not considered
Design procedure – 1. Stresses 2. C/s dimensions 3. Load cal4.moment and shear force
5. Check for moment 6.Main reinforcement 6.number of bars
7. Shear reinforcement
Limit state method – satisfies both safety and serviceability
Design procedure - 1. Characteristics strength and yield strength 2.c/s dimensions
3. Eff height 4. Ultimate Load calc 5. Limiting moment
OR
11. (b) A reinforced concrete beam ofspan 5m has a section 250mm*500mm. The beam is rein with 3 bars of
16mm dia on tension side at an eff depth of450mm and 2#16mmdia on comp side. Estimate the maximum
permissible live load on the beam USE M15 and Fe250
Ϭst = 140 N/mm2
: Ϭcbc = 5 N/mm2
: b = 250 mm: d = 450mm
Asc = 2 x П/4 x 162
= 401.92mm2
m = (280)/ (3 x Ϭcbc) = 18.67
Ast = 3 x П/4 x 162
= 602.88mm2+
To calculate Actual NA
(bna2
)/2 + [1.5m – 1] Asc [n – dc] = m Ast [d-n]
na = 141.08mm
nc = k x d
= 180.019mm
nc > na – The section is over reinforced
Ϭ'cbc = ((n-dc)/n ) x Ϭcbc
= ((141.08 – 50)/141.08) x 10.92
= 7.04 kN/m2
Mr = ((250*14.08*5)/2 )(450-141.08/8) + [1.5x18.67 – 1] x 7.04 x 401.92 [450-50]
= 66kNm
Selfweight = BD x unitweight
= 0.25 x 0.50 x 25
= 3.125kN/m
Ms = wl2
/8 = 9.76 kNm
Mr = Ms + ML
66 = 9.766 + (wx52
)/8
W =18kN](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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- 1. B.E./B.Tech. DEGREE EXAMINATION. APRIL/MAY 2015 Fifth Semester Civil Engineering CE 2306 – DESIGN OF REINFORCED ELEMENTS (Regulation 2008/2010) Time: Three hours maximum: 100 Marks (IS 456-2000 and SP 16 Design Charts tables are permitted) Use of Relevant BIS Standards and hand book is permitted Answer ALL questions PART – A (10*2 = 20 MARKS) 1. What are the assumptions made in the elastic theory of reinforced concrete structures? Ans: Assumptions ofElastic Theory: Both steel and concrete act together and are perfectly elastic at all stages The modular ratio can be used to determine the stresses in steel and concrete The design moments and shear in structures are calculated by elastic analysis with characteristics loads applied on the structures 2. List down the types of shear failures observed in the reinforced concrete member. Ans: Shear –Torsion – due to diagonal tension Shear – bending – due to diagonal bending Shear – bond - due to diagonal crack formed by bending 3. Why corner Reinforcements are provided in a two way slabs Ans: To resist the curl-up or twisting of edges of the slab 4. What is meant by Doubly reinforced beam Ans: section reinforced with both tension and compression zone 5. Define Torsional shear Ans: Equal and opposite moment applied at both ends of structural elements or its part about its longitudinal axis is termed as torsional shear 6. What is Development length Ans: Ld = (ɸϭb) / 4τbd 7. Differentiate long and short column Ans: leff/ lateral dim < 12 – short column Leff/lateral dim >12 – long column 8. What are the advantages of providing helical reinforcements instead of lateral ties in a circular column Ans: The axial load carrying capacity of column is increased by 5% The continuity in the spiral ties change the fixity point 9. Define Safe bearing capacity of soil Ans: Allowable bearing capacity is the maximum pressure which is considered as safe with respect to shear failure and settlement 10. Under what situations trapezoidal footings are preferred Ans: when load is unequal and restriction on sides then the shape of footing
- 2. PART B (5*16 = 80 MARKS) 11. (a) What are the methods involved in the design ofreinforced concrete structures? Briefly explain the design procedure ofthe methods 1. Working stress methods 2.Limit state method 3. Ultimate load method Working stress method – only service load is considered, safety factor is not considered Design procedure – 1. Stresses 2. C/s dimensions 3. Load cal4.moment and shear force 5. Check for moment 6.Main reinforcement 6.number of bars 7. Shear reinforcement Limit state method – satisfies both safety and serviceability Design procedure - 1. Characteristics strength and yield strength 2.c/s dimensions 3. Eff height 4. Ultimate Load calc 5. Limiting moment OR 11. (b) A reinforced concrete beam ofspan 5m has a section 250mm*500mm. The beam is rein with 3 bars of 16mm dia on tension side at an eff depth of450mm and 2#16mmdia on comp side. Estimate the maximum permissible live load on the beam USE M15 and Fe250 Ϭst = 140 N/mm2 : Ϭcbc = 5 N/mm2 : b = 250 mm: d = 450mm Asc = 2 x П/4 x 162 = 401.92mm2 m = (280)/ (3 x Ϭcbc) = 18.67 Ast = 3 x П/4 x 162 = 602.88mm2+ To calculate Actual NA (bna2 )/2 + [1.5m – 1] Asc [n – dc] = m Ast [d-n] na = 141.08mm nc = k x d = 180.019mm nc > na – The section is over reinforced Ϭ'cbc = ((n-dc)/n ) x Ϭcbc = ((141.08 – 50)/141.08) x 10.92 = 7.04 kN/m2 Mr = ((250*14.08*5)/2 )(450-141.08/8) + [1.5x18.67 – 1] x 7.04 x 401.92 [450-50] = 66kNm Selfweight = BD x unitweight = 0.25 x 0.50 x 25 = 3.125kN/m Ms = wl2 /8 = 9.76 kNm Mr = Ms + ML 66 = 9.766 + (wx52 )/8 W =18kN
- 3. 12. (a) Design a one way R.C slab – S.S at both edges for a public building with a clear span of 4m supported on 200mm masonry wall. Live load 5kN/m2 Use M20 and Fe415 1) Span / depth = 25 ; D = 190mm 2) Effective span = 4.16m ( 4+0.16m or 4+0.2 – whichever is lesser) 3) Load = total load 10kN/m ( Self weight + L.L + F.F) 4) BM = wl2 /8 = 21.63kNm : SF = wl/2 = 20.8kN 5) Main Rein = Ast = (M)/( Ϭst x j x d) = 645.92 mm2 : spacing = 121.59mm2 6) Distribution bar = 0.12% of c/s area = 228 mm2 ; spacing = 220mm 7) Check for shear = if permissible shear stress is maximum than nominal shear stress – Safe