- 1. While designing the bridges the following loads and forces should be considered where applicable. 1. Dead load 2. Live load 3. Dynamic load 4. Longitudinal forces a. Longitudinal forces by the tractive effort of vehicles b. Longitudinal forces by braking of vehicles c. Longitudinal forces due to frictional resistance of expansion bearings 5. Wind load 6. Centrifugal forces of vehicle due to curvature of bridge 7. Horizontal forces due to water currents 8. Buoyancy 9. Force exerted by earth pressure 10. Load induced by temperature variation effect 11. Load induced by creep, shrinkage and other secondary effect 12. Erection load 13. Loads induced by earthquake Bridge Loading Refer IRC 6-2014
- 2. IRC Bridge Live Load Vehicular load Pedestrian load Class A load Class B load Class AA load Class 70R load • Wheeled load • Tracked load • Single, Two and Seven Axel wheeled load • Tracked load Normal load Represents normal vehicular traffic Abnormal load Represents industrial or military vehicular traffic
- 3. Class A/B Loading CLASS A LOADING (KN) Total load = 554 KN CLASS B LOADING (KN) 68 68 68 68 27 27 114 114 16 16 68 68 41 41 41 41 20 1.1 3.2 1.2 4.3 3 3 3 20 C/C distance of axle (m) Total length of a train = 18.8m g f Cross section 1.8 m B W 1.1m 3.2m 1.2m Plan Carriageway Width G F 5.3 to 6.1m Uniformly increasing from 0.4 to 1.2.m 150 mm Above 6.1m 1.2 m 150 mm
- 4. Class 70R Loading Class 70R tracked vehicle Total Weight 700 KN 4.57m 7.92m 90m 90m Cross-section of Class 70R tracked vehicle 0.84m C 1.22m 2.06m 0.84m 350KN 350KN Carriage way width (m) Minimum value of C (mm) ≥5.3m 1200
- 5. Cross-section of Class 70R two axel wheeled load 400KN C Class 70R Loading 80 120 120 170 170 170 170 KN 70R seven axel wheeled load 1000 KN 1.22m 2.79 m Plan Value of C is same as of 70R tracked loading Min. distance between wheeled loads of Class70R is 30 m 2.79 m 3.96 1.52 2.13 1.37 3.05 1.37 Plan
- 6. Wheel Arrangement of 70R Wheeled Load ‘L’ Type 2.79 m 0.86 m 0.41 m 0.61 m ‘M’ Type 2.79 m 0.41 m 0.61 m 0.38 m ‘N’ Type 2.79 m 0.51 m 0.51 m 0.25 m 0.23 m Contact area of tyre may be obtained from the corresponding tyre load, tyre pressure and tyre tread width. Tyre tread width may be taken as overall tyre width minus 25 mm up to tyre 225mm and 50 mm for tyres over 225 mm width. Maximum tyre pressure = 5.273 Kg/cm2 Minimum Wheel Spacing and Tyre Size of Heaviest Axle
- 7. Cross-section of Class AA wheeled load 400KN C 37.5 62.5 62.5 37.5 KN Class AA Loading [Refer Annex] Total Weight 700 KN 3.6 m 7.2m 90m Cross-section of Class AA tracked vehicle 1.2m 2.05m 0.85m 0.85m C 350KN 350KN 1.2m Plan 0.6m 1m 0.6m 0.3m 0.15m Carriage way width (m) Minimum value of C (mm) Multi lane bridge ≥5.3m 1200
- 8. • 70R loading is adopted on all roads on which permanent bridges are constructed. Bridges designed for 70R loading should be checked for Class A loading. • Class AA loading is adopted on specified location on which permanent bridges are constructed. Bridges designed for Class AA loading should be checked for Class A loading. • Class A loading is adopted on all roads on which permanent bridges are constructed. Bridges designed for Class A loading should be checked for Class AA/70R loading. • Class B loading is adopted on specified location on which temporary bridges are constructed.
- 9. Carriage Way (m) No of lane Live loads <5.3 1 Class A loading for 2.3m width and for remaining width 500 Kg/m2 ≥5.3 <9.6 2 One lane of Class70R/AA loading or two lanes of Class A loading ≥9.6 <13.1 3 One lane of Class 70R/AA for every two lanes with Class A loading for remaining lanes or three lanes of Class A loading ≥13.1 <16.6 4 One lane of Class 70R/AA for every two lanes with Class A loading for remaining lanes or one lane of class A for each lane ≥16.6 <20.1 5 ≥20.1 <23.6 6
- 10. 0.4 m 1.8 m 1.7 m 1.8 m Class A Class A 1.8 m 0.4m 5 KN / m2 2.3 m 0.15m 0.5m Class A 1.2m Class 70R (W/T) 1.2m 1.8 m 0.4 m 0.15m 0.5m Class A Class 70R (W/T) Combination of live loads For Single Lane Bridge For Two Lanes Bridge For Two Lanes Bridge For Three Lanes Bridge
- 11. 1.2m 1.8 m 0.4 m 0.15m 0.5m Class A 1.8 m 0.5m Class A 1.8 m 0.5m Class A 1.2m 1.2m Class 70R (W/T) 1.2m Class 70R (W/T) 1.2m 1.8 m 0.4 m 0.15m 0.5m Class A 1.8 m 0.5m Class A 1.8 m 0.5m Class A 1.2m 1.8 m 0.5m Class A 1.2m 1.2m 1.8 m 0.4 m 0.15m 0.5m Class A Class 70R (W/T) 1.8 m 0.5m Class A 1.2m Combination of live loads For Three Lanes Bridge For Four Lanes Bridge For Four Lanes Bridge For Four Lanes Bridge
- 12. Live load information required for analysis of bridge deck • Type of load • Number of axle of vehicle • Magnitude of load on each axle • Spacing of axle • Contact area of wheel /track • Spacing of vehicle in transverse and longitudinal direction • Maximum lane load • Reduction of live load in excess of two lanes • Arrangement of wheel in case of 70R wheeled and train loading • Combination of live loads Pedestrian Load Length of bridge ≤7.5 m ; Intensity of load = 4 or 5 KN/m2 >7.5m; Intensity of load ≤ 4 KN/m2 P = P’ – (40L – 300)/9 for up to 30 m span P = (P’ – 260 + 4800/L) × (16.5 – W)/15 for greater than 30 m span P’ = 4 or 5 KN/m2 P – Intensity of load W – Width of foot way L – Span of bridge
- 13. For class A and B loading • Impact factor fraction for RCC bridge = 4.5/(6+L) • Impact factor fraction for Steel bridge = 9/(13.5+L) For Class AA and Class 70R loading for span less than 9 m • For tracked vehicles: 25% for span up to 5m linearly reducing to 10% for spans of 9 m • For wheeled vehicles: 25% For tracked vehicles for spans of 9 m or above • 10% up to a span of 40 m and in accordance with the curve in the code for spans greater than 40 m of RCC Bridge • 10% for all span of Steel Bridge For wheeled vehicles for spans of 9 m or above • 25% for spans up to 12 m and in accordance with the curve in the code for spans greater the 12 m RCC Bridge • 25% for spans up to 23 m and in accordance with the curve in the code for spans greater the 23 m Steel Bridge Impact Load Moving live load with its dynamic effect. Dynamic effect of live load is calculated by the impact factor. Impact load = static value of live load × Impact factor
- 14. 5 10 20 25 45 0 0 10 25 50 55 A and B ( Steel bridge ) A and B ( Concrete bridge ) Class AA/70R tracked ( Concrete bridge ) Impact Factor Span of bridge, m IF in % Class AA/70R tracked ( steel bridge ) Class AA/70R wheeled ( Concrete bridge )
- 15. 1. Externally applied longitudinal forces • Tractive effort caused through acceleration of driving wheels • Braking effort due to application of brakes to the wheels • Frictional resistance offered by free bearings due to change of temperature, shrinkage and creep Force due to braking effort Braking effort is invariably greater than the tractive effort so taken as a design longitudinal force. It is computed as follows. • For single or two lane bridge, braking loads taken as 20%of the first train load and 10% of the loads of succeeding trains. • For multilane bridge, braking load is taken as in (a) for the first two lanes and 5% of the loads on the other lanes. • The force due to braking effort shall be assumed to act 1.2m above the roadway. LONGITUDINAL FORCES
- 16. Forces due to frictional resistance offered by bearing Fh/2 or µW Fh/2 or µW µW Fh - µW Fh /2+ sδ Fh /2+ sδ I. Simply supported deck on unyielding support Span without bearing Span with fixed and free bearing Span with elastomeric bearings
- 17. 2. Self induced longitudinal forces Forces induced by Creep, Shrinkage or Effect of Temperature Variation II. Simply Supported/ Continuous deck on flexible support 1 2 3 µW CL Sn + Fh X Sn /∑S CL Sn + Fh X Sn /∑S
- 18. Wind load = Wind load on the structure + Wind load on the live load FT = PZ × A × G × CD FL = 0.25 FT for beam type bridge = 0.5 FT for truss type bridge FT - Wind load in transverse direction FL - Wind load in longitudinal direction of bridge PZ - Design wind pressure A - Exposed area of structure / live load to wind G - Gust factor ; G = 2 for 150 m span CD - Drag coefficient CD ≥ 1.3 depending upon b/d ratio and type of superstructure Wind load on live load = Length of live load × 3m × FT In the case of live load G is taken equal to 1.2m and point of application of wind load is 1.5 m. Described method of wind load calculation is valid for bridges of span upto150m and height of pier upto 100m WIND LOAD
- 19. Pressure of water current P = 52 KV2 [kg/m2] Where K- shape factor of the pier ( k= 0.5 -1.5) V- velocity of the water current at the point, where pressure intensity is to be calculated. [m/sec] Intensity of pressure due to water current depends on • Direction of current • Velocity of water current • Shape factor of the pier • Maximum scouring depth 200 deviation of river course shall be considered in the calculation of the pressure due to water current HORIZONTAL FORCES DUE TO WATER CURRENT Horizontal forces due to water current = Pressure of water current X Area of structure exposed to water
- 20. FORCE EXERTED BY EARTH PRESSURE PA=1/2KAγH2 PP=1/2KPγH2 PP PA δ ì 0.42H H Coulomb’s Theory
- 21. Seismic Force Method of computation of Seismic Force • Elastic Seismic Acceleration Method In this method static analysis is made and seismic force is obtained for acceleration corresponding to the fundamental mode of vibration. • Elastic Response Spectrum Method In this method dynamic analysis is made to first and higher modes of vibration and forces are obtained for each mode by using of response spectrum. In elastic seismic acceleration method force due to earthquake is calculated as follows. Feq = Ah × (Dead load + Partial Live load) where, Ah = Z/2 × I/R × Sa/g
- 22. Bridges need not be checked for seismic effects Bridges need special investigation for seismic effects
- 23. FORCE EXERTED BY DYNAMIC EARTH PRESSURE PA=1/2KAγH2 PP=1/2KPγH2 PP PA δ ì 0.6H H Mononobe Okabe Theory (Modified Coulomb’s Theory)
- 24. FORCE EXERTED BY HYDRODYNAMIC PRESSURE R Ground Shaking Enveloping cylinder Pier R Ground Shaking Enveloping cylinder Pier F = C Ah W W- Weight of water bound in enveloping cylinder W = πR2H × Unit wt. of water R – Radius of enveloping cylinder H – Submerged height of pier Ah- Horizontal acceleration coefficient C – Hydrodynamic coefficient H/R C 1 0.39 2 0.58 3 0.68 4 0.73
- 25. Load Combinations in the Design of Bridge [WSDM] Combination of loads I II A II B III A III B IV V VI VII VIII IX Increase in permissible stress according to load combination 0 - 50 %
- 27. IRC 6 define four cases separately i.e. foundation, stability, limit state of strength and limit state of serviceability to be considered in Limit State Design Method. In each cases, there are further three combinations of loads to be considered. Three combinations of limit state of strength and stability are • Basic combination • Seismic combination • Accidental combination These combinations are given separately for serviceability check and foundation design. Partial safety factors for loads for different combinations and for different works are not similar. They are chosen as specified in code Refer IRC 6 – 2010, Table 3.1, 3.2, 3.3 and 3.4 for combination of loads Load Combinations in the Design of Bridge [LSDM]
- 28. • HS loading It consists of truck with semi-trailer or the corresponding lane loading. Lane load consists of a uniform load per unit length of traffic lane combined with a concentrated load (one concentrate load for simply supported span and two concentrated load in case of continuous span). HS loading may be HS 20-44 and HS 15-44. It consists of a two-axle truck or the corresponding lane load. Lane load consists of a uniform load per unit length of traffic lane combined with a single concentrated load (two concentrated load in case of continuous span). H loading may be H 20-44 and H 15-44.
- 29. Lane Loading H 20-44 HS 20-44 HS 15-44 H 15-44 18000 lbs for bending moment 26000 lbs for shear force 13500 lbs for bending moment 19500 lbs for shear force 640 lbs/ft 480 lbs/ft 8000 lbs 6000 lbs 32000 lbs 24000 lbs H 20-44 H 15-44 8000 lbs 6000 lbs 32000 lbs 24000 lbs 32000 lbs 24000 lbs HS 20-44 HS 15-44 Truck Loading 6' 14' 6' 14'-30’ 14' AASHTO Live Loading
- 30. Maximum bending moment (KN-m) Span (M) IRC loading AASHTO BS (HS20-44) HA HB One lane Two lane One lane Two lane One lane Two lane One lane Two lane 5 687 687 231 462 243 488 756 838 10 1548 1548 573 1146 694 1388 1863 2095 15 2725 2725 1073 2146 1336 2672 3331 3776 20 4198 4198 1552 3104 2175 4350 5654 6379 25 5680 5680 2022 4044 3156 6312 7862 8914 30 7058 7058 2481 4962 4151 8302 10085 11468 35 8412 8412 2935 5870 5184 10368 12315 14043 40 9739 9739 3379 6758 6340 12680 14550 16663 45 11059 11059 3863 7726 7501 15002 16788 19288 50 12496 12496 4597 9194 8656 17312 19029 21914 Responses of bridge in different codal standard
- 31. Maximum Live Load Shear Force for Two Lane Simply Supported Bridge (KN-M) 596 716 738 750 1020 1509 1619 1694 0 200 400 600 800 1000 1200 1400 1600 1800 10m 20m 25m 30 IRC AASHTO BS
- 32. Maximum Live Load Bending Moment for Two Lane Simply Supported Bridge (KN-M) 1146 3104 4044 4962 2095 6379 8914 11468 0 2000 4000 6000 8000 10000 12000 14000 10m 20m 25m 30 IRC AASHTO BS