Bridge loading

Bridge loading

1. “Refer IRC 6-2014

While designing the bridges the following loads and forces should be
considered where applicable.

Dead load

Live load

Dynamic load

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
Wind load

Centrifugal forces of vehicle due to curvature of bridge
Horizontal forces due to water currents

Buoyancy

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

RWONS

Lou

2. ms u

Class 70R load A

Wheeled load
Tracked load

Single, Two and Seven
Axel wheeled load

Tracked load

3. 20 11321243 3 3 3 20 C/Cdistance of axle (m)
>< <- >< >< > Total length of a train = 18.8m
| pl | | | | | CLASS A LOADING (KN)
2727 114 114 68 68 68 68 Total load = 554 KN
1616 68 68 41 41 41 41

CLASS B LOADING (KN)

f
18m 8
—
B .

: E Lim Cross section

3.2m

Carriageway

BE Width © F

sem Uniformly increasi

niformly increasing
EE EST re en 150 mm
w
Above 6.1m 1.2m 150 mm

Plan

4. Class 70R tracked vehicle

5. Class 70R Loading Cross-section of Class 70R two

axel wheeled load 400KN
70R seven axel wheeled load 1000 KN Î
| Cc
80 120 120 170 170 170 170 KN |
| 1.22m
| 2.79m
—— 2.79m | Plan
= Value of Cis same as of 70R
tracked loading
= Min. distance between wheeled
e 356 152,213 137 305 137 loads of Class70R is 30 m

Plan

6. Minimum Wheel Spacing and Tyre Size of Heaviest Axle

2.79m
0.86 m
<=
0.61 m | al
041m <>
‘LU Type
Contact area of tyre may be obtained from
2.79m the corresponding tyre load, tyre pressure
0.38m and tyre tread width. Tyre tread width may
be taken as overall tyre width minus 25 mm
germ | up to tyre 225mm and 50 mm for tyres over
0.41m <> 225 mm width.
‘M’ Type
Maximum tyre pressure = 5.273 Kg/cm?
2.79m
023m, 0.25 m
se [D OÙ w
051m <>

‘N’ Type

7. Class AA tracked vehicle

Total Weight 700 KN

3.6m

See

7.2m

<< >

Cross-section of Class AA tracked
vehicle

Multi lane bridge
25.3m

Class AA wheeled vehicle

Cross-section of Class AA
wheeled load 400KN

nea |

37.5 62.5 62.5 37.5 KN

1 EB HE) 015m
1.2m
y Be Be

Plan

1200

8. IRC Live Loads

+ 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. Combination of Live Loads

Carriage || No'of =
E Live loads
Way (m) || lane
<5.3 1 Class A loading for 2.3m width and for remaining width 500 Kg/m?
De 2 One lane of Class70R/AA loading or two lanes of Class A loading
29.6 3 One lane of Class 70R/AA for every two lanes with Class A loading
<13.1 for remaining lanes or three lanes of Class A loading
213.1
<16.6 a}
216.6 One lane of Class 70R/AA for every two lanes with Class A loading
<20.1 5 for remaining lanes or one lane of class A for each lane
220.1
<23.6 6

10. Class A

For Single Lane Bridge

For Two Lanes Bridge

For Two Lanes Bridge

For Three Lanes Bridge

11. Class A Class A Class A

For Three Lanes Bridge

05m 0.5m 05m

Class A Class A Class 70R (W/T)

05m 05m For Four Lanes Bridge

Class A Class A Class A Class A

05m 0.5m 05m 0.5m

For Four Lanes Bridge

7OR (W/T)

For Four Lanes Bridge

12. Length of bridge <7.5 m; Intensity of load = 4 or 5 KN/m?
>7.5m; Intensity of load < 4 KN/m?

P=P’-(40L-300)/9 for up to 30 m span
P=(P’- 260 + 4800/L) x (16.5- W)/15 for greater than 30 m span

P’= 4 or 5 KN/m?
P — Intensity of load
W - Width of foot way

owe | —

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

13. 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 x Impact factor

For class Aand 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
12m RCC Bridge

+ 25% for spans up to 23 m and in accordance with the curve in the code for spans greater the
23m Steel Bridge

14. IF in %
55

50>

A and B (Steel bridge )

A and B (Concrete bridge )

s-AA/70R tracked (Concrete bridge )

Class AA/7OR tracked (steel bridge )

Class AA/70R wheeled ( concrete bridge)

+ + t t t t + t t t t Rd
20 25 45 Span of bridge, m

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.

16. Forces due to frictional resistance offered by bearing

A 5 ——————————<<-—
Span without bearing => <=
F,/2 or uW F,/2 or uW
Span with fixed
se >
and free bearing > =
LW F,- pW
Span with A >
E =
q 4 = =>
elastomeric bearings E, /2+ só

17. 7 F À

= = =>

uw CLS, +F,xS,/5S CLS, + Fx S,/25
2. Self induced longitudinal forces

Forces induced by Creep, Shrinkage or Effect of Temperature
Variation

18. Wind load = Wind load on the structure
+ Wind load on the live load

F,=P,xAxGxCp

F, =0.25F, for beam type bridge
=0.5 F, for truss type bridge

Fr - Wind load in transverse direction

F, - 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
Cp - Drag coefficient Cp 2 1.3 depending upon b/d ratio and type of superstructure

Wind load on live load = Length of live load x 3m x F,

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

19. Horizontal forces due to water current =
Pressure of water current X Area of structure exposed to water

Pressure of water current P = 52 KV2 [kg/m]

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

20° deviation of river course shall be considered in the calculation of the
pressure due to water current

20. P,=1/2K,yH?

P,=1/2K,yH2

Kr =

cos*(@— a) EN

x
CL CEE sin(@ + 8)sin(G—1)

[a+ cos(a— 1) cos(a + Sy!

cos*(@+ a) El

cos? acos(a— 65)

[1 sin(@ + §)sin(O+0),,

cos(a — 1) cos(a — 8)

21. 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.

Fog = Ap x (Dead load + Partial Live load)

where,
A, =2/2xI/RxS/g

22. a)
b)

Culverts and minor bridges up to 10 m span in all seismic zones

Bridges in seismic zones II and Ill satisfying both limits of total length not
exceeding 60 m and spans not exceeding 15 m

Bridges more than 150 m span

©, =

oS

Bridges with piers taller than 30 m in Zones IV and V

Cable supported bridges, such as extradosed, cable stayed and suspension
bridges

Arch bridges having more than 50 m span

Bridges having any of the special seismic resistant features such as seismic
isolators, dampers etc.

Bridges using innovative structural arrangements and materials.

23. Mononobe Okabe Theory
(Modified Coulomb’s Theory)

P,=1/2K,yH?
Pp=1/2KpyH?

Ka = (140 y) x cos"0-y-0) x 1
= (14%, A
TEEN
cos(a — 1) cos(a +6 + y)
cos"(9+ a— y) 1
Kp = (140 y) x x
cost cos? acos(a—6 +) o sin(O +5)sin(0+1—y)
[ costa 0 cota 54 y),
ÿ = tan tt a

lta

24. _ W- Weight of water bound in enveloping cylinder
F=C An w W=nR?H x Unit wt. of water
R — Radius of enveloping cylinder
H - Submerged height of pier

A,- Horizontal acceleration coefficient
C— Hydrodynamic coefficient

Pier

Ground
Shaking

Enveloping
Enveloping cylinder

round cylinder

Shaking

25. 0-50%

26. 21s se Vas [se eje Ve Is Im [=
a

¡EE
7

(ol peor our
ja
peor pea,

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.

Y

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

28. AASHTO Standard of Live Loads

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.
H loading

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. Truck Loading

8000 lbs 32000155 H 20-44 8000 lbs 32000 Ibs 32000 lbs HS 20-44
6000 lbs 24000lbs H 15-44 6000 Ibs 24000 Ibs 24000 lbs HS 15-44
= a 1 6 a a a 1 ai
2 = a. a
a 10 14-30
—

Lane Loading

18000 Ibs for bending moment H 20-44
| 26000 Ibs for shear force HS 20-44
640 Ibs/ft

13500 Ibs for bending moment

HS 15-44

19500 Ibs for shear force
480 Ibs/ft H 15-44

30. Maximum bending moment (kN-m)

IRC loading — AASHTO ES
Span 9 (HS20-44) HA HB

mp One Two

¡One lane] Two lane| One lane Two lane | One lane | Two lane | lane 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

31. Maximum Live Load Shear Force
for Two Lane Simply Supported Bridge (kn-m)

1800

1694
1600 +
509
1400 +

1200

1000 1020 u2=2== == + AASHTO

--

800 - . ——BS

. TR 750
600

400
200

10m 20m 25m 30

32. Maximum Live Load Bending Moment
for Two Lane Simply Supported Bridge (kn-m)

14000

12000
11468

10000

8000

F--IRC
m AASHTO
—BS

6000

4000

2000

10m 20m 25m 30