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Comparative study of IRC 21 vs IRC 112

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See discussions, stats, and author profiles for this publication at: http://www.researchgate.net/publication/281714298
Comparative Study of Slab Culvert Design usingIRC 112:2011 and IRC 21:2000
Article
· May 2015
CITATIONS
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Shreedhar RGogte Institute of Technology
33
PUBLICATIONS
9
CITATIONS
SEE PROFILE
Available from: Shreedhar RRetrieved on: 20 October 2016
IJSRD - International Journal for Scientific Research & Development| Vol. 3, Issue 05, 2015 | ISSN (online): 2321-0613
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www.ijsrd.com
107
Comparative Study of Slab Culvert Design using IRC 112:2011 and IRC 21:2000
Shivanand Tenagi
1
R. Shreedhar
2
1
P. G. Student (Structural Engineering)
2
Associate Professor
1,2
Department of
Civil Engineering
1,2
KLS Gogte Institute of Technology, Belagavi, Karnataka, India
Abstract
—
Reinforced concrete slab type decks are often referred to as culverts and are commonly used for small spans. Slab culverts are important hydraulic structures used in the construction of highway roads. In India, till now culverts are designed and constructed according to Indian road congress guidelines as per IRC: 21-2000 code in which working stress method is used. Recently Indian road congress has introduced another code IRC: 112-2011 for design of prestress and RCC bridges using limit state method. In regards to this, present study has been performed to know how design of IRC-112 differs from IRC-21 and an attempt is made to study undefined parameters of IRC: 112-2011 such as span to depth (L/d) ratio. Present study is performed on design of RC s
lab culvert using “working stress method” using “IRC: 21
-2000 and limit state method using IRC: 112-
2011” code specifications. It is observed
that in working stress method, the allowable L/d ratio is 13 and in limit state method, the L/d ratio of 20 is most preferable. Quantity of materials required in limit state method is compared with quantity of material required in working stress method and it is found that concrete can be saved up to 30 to 35% using limit state method.
Key words:
IRC 112:2011, IRC 21:2000 I.
I
NTRODUCTION
Fig. 1: Typical 3D view of slab culvert A structure which provides a way for the flow under the road way is called culvert. It helps in crossings of water course like nallas, streams and drainage channel under the road way. Slab and box are the two main types in culverts. In box culvert top slab, bottom slab and vertical walls are monolithically connected to each other where as in slab culvert top slab is resting over the vertical walls (abutments /piers) but has no monolithic connection between them. This paper mainly deals with design of slab culvert with IRC: 112-2011 and IRC: 21-2000. Usually culverts are constructed if span is less than 10m, for span greater than 10m bridge structures are used. For up to 6m span normal concrete is used, for greater than 6m span prestressed concrete is used for the construction. A culvert helps to flow water from one side to another side without obstruction and it also helps in balancing the flood water on both the sides of the structure.
II.
M
ETHODOLOGY
A.
Working Stress Method 1)
Calculation of Depth of slab
Assume L/d ratio
From above L/d ratio calculate effective depth and overall depth
2)
Calculation of Effective span
Effective span is least of
Clear span + effective depth
Centre to centre of bearings Fig. 2: Cross section of Deck slab
3)
Calculation of dead load B.M per meter width of slab
Dead weight of slab Dead weight of W.C Dead load B.M
4)
Calculation of Live load B.M:
Consider the three classes of loadings i.e. Tracked loading, wheeled loading and train loading as per I.R.C:21:2000 Fig. 3: Position of load for maximum bending moment
Calculation of effective length of dispersion Effective length of dispersion L
d
= f+ 2(h + D)
Calculation of effective width of dispersion b
eff
= k
X
(1 -
) + b
w
(IRC: 21-2000) b
w
= g + 2h Where, f = track or wheel contact length h= wearing coat thickness D= slab overall depth b
eff
= dispersion of effective width K = constant of dispersion width X= C.G of the concentrated load from the nearer support distance g= width of wheel or track
Comparative Study of Slab Culvert Design using IRC 112:2011 and IRC 21:2000 (IJSRD/Vol. 3/Issue 05/2015/026)
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108
Finally calculation of area of steel is done by using working stress method formulas.
5)
Calculation of shear stresses
Maximum shear force occurs at the support when the live load is nearer to a support. Here the design shear is conservatively taken as that at the support.
Calculation of effective length of dispersion
Calculation of effective width of dispersion Fig. 4 Position of load for maximum shear
Nominal shear stress = Ʈ = V
u
/ bd k
1
= 1.14 -0.7d k
2
= 0.5+ 0.25
ρ where ρ =
Ʈ
c
= permissible shear stress = k
1
k
2
Ʈ
co
B.
Limit State Method
Calculation of Bending Moments and Shear forces remains same as per working stress method except 1.5 is multiplied for final design moments and design shear forces. In this design moment is checked with limiting moment of resistance and finally area of steel is calculated using design bending moment.
1)
Design shear reinforcement is calculated as per I.R.C:112-2011 (clause 10.3.2)
V
Rdc
= [0.12
K
(80
ρ
1
f
ck
)
0.33
+ 0.15
ϭ
cp
] b
w
d K = 1 +
≤ 2.0
ϭ
cp
is limited to 0.2f
cd
ρ
1
= A
s1
/b
w
d ≤ 0.02
2)
Checks for limit state of serviceability:
Check for Limit State of Deflection:
∆
=
] W = average intensity L = Effective length of span a = Load Effective length
E = Young’s Modulus of concrete = 5000
√
I = Moment of Inertia =
Check for limit state of crack width: Fig. 5: Cross section and strain diagram
Calculation of B.M at service load, M
s
E
c
= 5000
√
= 5000
√
= 25000 N/mm
2
E
ce
= 0.5E
c
M = E
s
/ E
ce
Determination of N.A at working loads
m A
st
(d-x) I
c
=
+ m A
st
(d-x)
2
Є
1
=
Є
m
= Є
1
–
() () ()
Crack width = 3
C
min
Є
m
III.
R
ESULTS AND DISCUSSIONS
The slab culvert of span 4m to 10m is analysed for various IRC loadings as per IRC 21-2000 by working stress method for L/d ratios 12, 13 and 14 and same spans are analysed as per IRC 112-2011 by limit state method for L/d ratios 18, 19, 20, 21 and 22. The critical case for loading is tracked vehicle as compared to wheeled and trained vehicle and hence taken for all the calculations in arriving effective depth and bending moment.
A.
Working Stress Method
Fig. 6: Assumed effective depth in mm Fig. 7: Required effective depth in mm With comparison of assumed effective depth and required effective depth as shown in Fig. 6 and Fig. 7, it can be concluded that the depths obtained for L/d ratio of 14 as shown in figure 6 is not sufficient as it less than the required depth as shown in figure 7 to satisfy the necessary design checks. Though L/d ratios of 12 and 13 satisfy the required depth, the L/d ratio of 13 is economical in comparison to L/d ratio of 12. Hence L/d ratio of 13 is preferable for the design of slab culvert by working stress method and corresponding effective depth and volume of concrete can be adopted.
Comparative Study of Slab Culvert Design using IRC 112:2011 and IRC 21:2000 (IJSRD/Vol. 3/Issue 05/2015/026)
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109
Fig. 8: Volume of concrete in m
3
B.
Limit state method
Fig. 9: Assumed effective depth in mm Fig. 10: Required effective depth in mm With comparison of assumed effective depth and required effective depth as shown in Fig. 9 and Fig.10, it can be concluded that the depths obtained for L/d ratios of 21 and 22 as shown in Figure 9 is not sufficient as it less than the required depth as shown in figure 10 to satisfy the necessary design checks. Though L/d ratios of 18, 19 and 20 satisfy the required depth, the L/d ratio of 20 is economical in comparison to L/d ratios of 18 and 19. Hence L/d ratio of 20 can be considered for the design of slab culvert by limit state method and corresponding effective depth and volume of concrete can be adopted. Fig. 11: Volume of concrete in m
3
Fig. 12: Deflection in mm Spans varying from 4m to 7m for L/d ratios of 21 and 22 do not satisfy the deflection criteria as the deflection is greater than the permissible value i.e. (span/1000). For spans 8m, 9m and 10m for L/d ratios of 21 and 22, the deflection criteria is satisfied because as span increases the total load acting on the span gets dispersed. It is also observed that for all the spans of 4m to 10m, the L/d ratios of 18, 19 and 20 satisfies the deflection criteria. Fig. 13: Crack width in mm Crack width criteria are also satisfied for all spans with different L/d ratios as shown in Fig. 13. As per IRC-112:2011, the crack width up to 0.2mm is permissible.

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