Slab Bridge Final

7/29/2019 Slab Bridge Final

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Recommended for spans less than 9 m

ROHAN PERSAUD

1.0 INPUTS BRIDGE ENGINEERING

Concrete density: 25 kN/m3

Width of bridge : 8.7 m

Wearing course density: 22 kN/m3

Clear span : 6 m

Carriageway width 7.5 m Clause 112.1 of IRC:6 -minimum carrage way width

Foothway with(each side): 0.6 m

Slab thickness : 500 mm

Wearing course thickness: 75 mm

Width of bearing: 400 mm

Main bar dia.: 20 mm

Clear cover : 25 mm ERROR: IRC:21-Cla.304.3 : Min Clear Cover 40 mm

Distribution bar dia. 12 mm

Effective depth (d): 465 mm

Effective Span (l): 6.4 m

2.0 Dead loads

Self wt. of slab: 12.5 kN/m2

Self wt. of Wearing course: 1.65 kN/m2

Total: 14.15 kN/m2

2.1 Max. Bending Moment: 72.448 KNm. per m width of slab.

2.2 Maximum Shear force : 45.28 KN. per m width of slab.

ANALYSIS OF SIMPLY SUPPORTED SLAB BRIDGES -IRC :6-2010, IRC:21-2000




3.0 Live loads

3.1 Class AA Tracked VehicleTable 2 of IRC:6 -for two lanes design purpose consider one lane of class AA vehicle.

Impact factor : 19.75 %

Note: The track vehicle is places symmetrical of the span.

Effective length of load: 4.75 m 45o

dispersion

Effective Width of one track (be): 5.43 m

Net effective width: 6.99 m

3.1.1 Intensity of loading : 25.25 KN/m

2

3.1.2 Max. Bending Moment : 120.69 KNm. Per m width of slab.

Shear Force :

New Effective Width of one track (be) 5.13 m

New Net effective width: 6.84 m

New Intensity of loading : 25.79 KN/m2

3.1.3 Max. Shear Force : 77.05 KN Per m width of slab.

Effective width of dispersion of both tracks, providing minimum clearance of 1.2 m and allowing for

overlap of dispersion.




3.2 Class AA wheeled Vehicle

Table 2 of IRC:6 -for two lanes design purpose consider one lane of class AA vehicle.

Impact factor : 25 %

Width of dispersion parallel to span: 1.23 m

Effective length of load along the

span : 2.43 m

Effective width of load perpendicular

to span (be): 4.72 m


3.2.1 Intensity of loading : 31.60 KN/m2


Shear Force :

New Effective Width of one track

(be): 3.17 m




Dispersion areas overlap(45 degrees), and loads are placed

symmetrical to the centre of span

Effective width of dispersion all wheels, providing minimum clearance of 1.2 m and allowing for





3.3 Class A wheeled Vehicle

Table 2 of IRC:6 -for two lanes design purpose consider two lane of class A vehicle.

Impact factor : 36.29 %

Width of dispersion parallel to span: 1.33 m

Effective length of load along the

span : 2.530 m

Effective width of load perpendicular

to span (be): 4.922 m


Limited effective width: 8.7 m

3.3.1 Intensity of loading : 14.12 KN/m2


Shear Force :

New Effective Width of one track

(be): 6.423 m


Limited effective width: 8.7 m



Design Bending Moment : 120.69 KNm Live load

72.448 KNm Dead load193.14 KNm Per m width of slab.

Design shear force : 77.05 KN live load

45.28 KN Dead load

122.33 KN Per m width of slab.

Effective width of dispersion all wheels, providing minimum clearance of 1.2 m and allowing for


Dispersion areas overlap(45 degrees), and loads are placed

symmetrical to the centre of span



Design Bending Moment : 193.14 KNm Per m width of slab.

Design shear force : 122.33 KN Per m width of slab.

1.0 INPUTS Interpulate using table :

1.5 0.46

Concrete Grade : M 25 100As/bd: 0.52 x : 0.34 N/mm2

Bar Grade : Fe 415 1.75 0.49

2.0 ALLOWABLE STRESS DESIGN :

Premissable compressive stress of concrete (Qcb): 8.33 Mpa

Premissable tensile stress of rebars (Qst) : 200 Mpa

Modular ratio (m) : 10 IRC-21: cl 304

Neutral axis depth factor (n): 0.29

Lever arm factor (j): 0.90

Coefficient of Resistance (R): 1.10

2.1 Depth :

Ultimate Moment (Mu) =Rbd2

Effective depth requited (dreq) = sqr.(Mu/b.R) where b=1000 mm for slab

Effective Depth required (dreq) : 418 mm

Effective Depth provided (d prov) : 465 mm

The Provided Depth of Slab is Sufficient

2.2 Main Tension Reinforcement :

Area of tension rebars required (Asreq )= M/(Qst.j.d prov )

Asreq = 2302 mm2 per meter width of slab

Area of Tension Rerbars provided (As prov) : 2418 mm2 per meter width of slab

Minimum Reinforcement (Asmin) : 600 mm2 per meter width of slab

Maximum Reinforcement (Asmax) : 20000 mm2 per meter width of slab

As prov = 8 # bars at 150 mm c/c parallel to span

The Provided Area of Reinforcement is Sufficient

DESIGN OF SIMPLY SUPPORTED SLAB BRIDGES -IRC :6-2010,IRC:21-2000,IS:456-2010



2.3 Distribution Tension Reinforcement:

Bending Moment Caused by Lateral Distribution of load (M lat) = 0.3 Mlive + 0.2 Mdead IRC-21: cl 305-18

Mlat : 50.7 KNm Per m width

Effective depth to distribution dar (d1) : 449 mm

Area of tension rebars required (Asreq )= Mlat/(Qst.j.d1

)

Asreq = 626 mm2 per meter width of slab

Area of Tension Rerbars provided (As prov) : 904 mm2 per meter width of slab

Minimum Reinforcement (Asmin) : 600 mm2 per meter width of slab

Maximum Reinforcement (Asmax) : 20000 mm2 per meter width of slab

As prov = 8 # bars at 150 mm c/c perpendicular to main bars

IRC:21-Cla.303.4: Spacing -150mm for crack control

The Provided Area of Reinforcement is Sufficient

2.4 Strinkage and Temperature Reinforcement at top of slab :

Maximum spacing of bars : 300 mm IRC:21-Cla. 305.10

Minimum steel area : 250 mm2 per meter width of slab

As prov = 5 # bars at 250 mm c/c Both ways

The Provided Area of Reinforcement and Spacings are Sufficient

2.5 Shear Check

Maximum Shear Force : 122.33 KN

Design Shear Stress : 0.26 N/mm2

Max. Permissable Shear Stress : 1.9 N/mm2

Permissible Shear Stress:

(100.As prov)/(b.d) : 0.52

By Interpulation using above table

Permissable Shear stress in concrete (Tc) : 0.34 N/mm2

The Section is Adequte for Shear Resistance

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Slab Bridge Final