Recommended for spans less than 9 m
ROHAN PERSAUD
1.0 INPUTS BRIDGE ENGINEERING
Concrete density: 25kN/m3 Width of bridge : 8.7 m
Wearing course density: 22kN/m3
Clear span : 6m
Carriageway width 7.5m Clause 112.1 of IRC:6 -minimum carrage way width Foothway with(each side): 0.6m
Slab thickness : 500mm
Wearing course thickness: 75mm
Width of bearing: 400mm
Main bar dia.: 20mm
Clear cover : 25mm ERROR: IRC:21-Cla.304.3 : Min Clear Cover 40 mm
Distribution bar dia. 12mm
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: 14.15kN/m2
2.1 Max. Bending Moment: 72.448KNm. per m width of slab. 2.2 Maximum Shear force : 45.28KN. 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 Vehicle
Table 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 : 25.25KN/m2
3.1.2 Max. Bending Moment : 120.69KNm. 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 : 25.79KN/m2
3.1.3 Max. Shear Force : 77.05KN 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
Net effective width: 6.51 m
3.2.1 Intensity of loading : 31.60KN/m2
3.2.2 Max. Bending Moment : 99.54KNm. Per m width of slab. Shear Force :
New Effective Width of one track
(be): 3.17 m
New Net effective width: 5.37 m New Intensity of loading : 38.29KN/m2
3.2.3 Max. Shear Force : 75.38KN Per m width of slab.
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 overlap of dispersion.
ANALYSIS OF SIMPLY SUPPORTED SLAB BRIDGES -IRC :6-2010, IRC:21-2000
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
Net effective width: 8.76 m
Limited effective width: 8.7 m
3.3.1 Intensity of loading : 14.12KN/m2
3.3.2 Max. Bending Moment : 45.85KNm. Per m width of slab. Shear Force :
New Effective Width of one track
(be): 6.423 m
New Net effective width: 9.51 m
Limited effective width: 8.7 m
New Intensity of loading : 5.56KN/m2
3.2.3 Max. Shear Force : 11.29KN Per m width of slab.
Design Bending Moment : 120.69 KNm Live load 72.448 KNm Dead load
193.14KNm Per m width of slab.
Design shear force : 77.05 KN live load
45.28 KN Dead load
122.33KN Per m width of slab.
Effective width of dispersion all wheels, providing minimum clearance of 1.2 m and allowing for overlap of dispersion.
Dispersion areas overlap(45 degrees), and loads are placed symmetrical to the centre of span
Design Bending Moment : 193.14KNm Per m width of slab. Design shear force : 122.33KN 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) : 418mm
Effective Depth provided (dprov) : 465mm
The Provided Depth of Slab is Sufficient 2.2 Main Tension Reinforcement :
Area of tension rebars required (Asreq )= M/(Qst.j.dprov ) Asreq = 2302mm2 per meter width of slab
Area of Tension Rerbars provided (Asprov): 2418mm 2
per meter width of slab Minimum Reinforcement (Asmin) : 600mm2 per meter width of slab Maximum Reinforcement (Asmax) : 20000mm2 per meter width of slab Asprov = 8 # bars at 150 mm c/c parallel to span
2.3 Distribution Tension Reinforcement:
Bending Moment Caused by Lateral Distribution of load (Mlat) = 0.3 Mlive + 0.2 Mdead IRC-21: cl 305-18
Mlat : 50.7KNm Per m width
Effective depth to distribution dar (d1) : 449mm Area of tension rebars required (Asreq )= Mlat/(Qst.j.d1 )
Asreq = 626mm2 per meter width of slab
Area of Tension Rerbars provided (Asprov) : 904mm2 per meter width of slab Minimum Reinforcement (Asmin) : 600mm2 per meter width of slab Maximum Reinforcement (Asmax) : 20000mm
2
per meter width of slab Asprov = 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 Asprov = 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 : 0.26N/mm2
Max. Permissable Shear Stress : 1.9N/mm2 Permissible Shear Stress:
(100.Asprov)/(b.d) : 0.52 By Interpulation using above table
Permissable Shear stress in concrete (Tc) : 0.34N/mm2
