Rating is evaluation of safe load carrying capacity of existing bridges. There are different systems for rating in the world. In India mainly analytical, load testing and correlation methods are followed. Rating has reduced economic burden on authorities for some time. Rating has provided people with direction for follow up actions such as repairs, strengthening rehabilitation. It is becoming preferable, both environmentally and economically to upgrade bridges rather than to demolish and rebuild them. Deterioration of bridges wear from environmental influences and from traffic loads require rehabilitation and renewal programs to maintain even current service levels on the bridge infrastructure network. Demands for high durability, longer service life, reduced maintenance cost and cost/performance optimized. This paper deals with the rating of bridges and different methods of strengthening with its world wide applications.

1. JNTU COLLEGE OF ENGINEERING, ANANTAPUR.
PRESENTATION BY….
R.RAGHAVENDRA K.MADHAVULU
III/IV B.Tech, Civil III/IV B.Tech, Civil

2. CONTENTS
:
1. SCOPE
2. RATING METHODOLOGY
3. PROCEDURE FOR RATING
4. STRENGTHENING
5. POSTING
6. CONCLUSION
7. REFERENCES

3. SCOPE :
 INTRODUCTION…
 RATING…
 NECESSITY OF RATING…
 LOADS FOR RATING…
 Poor quality
* DEAD LOAD
* LIVE LOAD
* IMPACT

4. RATING METHODOLOGY:
GLOBAL PRACTICES
 LOADS
 STRESSES
 FATIGUE
 DESIGN PHILOSOPHY
RATIING SYSTEM
 ANALYTICAL METHOD
 CORRELATION METHOD
 LOAD TEST METHOD

5. ANALYTICAL METHOD
 It is applicable when as built or contract drawings and
specifications followed are available or when such drawings can be
prepared by site measurements to an acceptable level of accuracy.
CORRELATION
 METHOD
This method is adopted when the safe carrying capacity of
structure can be ascertained by correlating the sectional details of the
DIFFERENT GRAPHS USED IN METHOD
structure.

6. LOAD TEST METHOD
 It is applicable when no construction drawings and specification
originally followed are available or when such details are not possible to
be obtained an site.
 PROOF TEST
 FAILURE TEST
VEHICLES FOR TESTING
 Test vehicles are chosen such that
they are the next heaviest vehicle than
the predominant heavy load presently
passing over the bridge.

7. Study all available data, Detailed field or Where
drawing, etc. lab investigation
• Mcap : Moment resisting
Compute section capacity in moment and
shear at selected location
Assess capacity of selected section.
reduction factor
(η) • Vcap : Shear resisting
Compute Mcap and Vcap
capacity at selected section.
Compute effect of all loads • MDL and VDL : Moment and
other than live loads at
selected
shear of all loads other than
Compute MLL = ηMcap – MDL
VLL = ηVcap – VDL At live loads at selected section.
selected locations
• MLL and VLL : Net resisting
Compute maximum LL capacity minus effect due to
moment and shear at
selected locations all loads other than live loads.
• MLL and VLL : maximum
Compare Bridge rated For
MLL ~ MLL corresponding IRC possible effect (moment and
standard Live
VLL ~ VLL Loading hear) including impact effect.

8. SPACING AND NUMBER OF VEHILES
 Closer spacing of vehicles in urban areas is a frequent possibility.
Urban traffic is mixed and slow as against the heavy and fast traffic
for which the rating is proposed and high impact percentage.
 SINGLE LANE BRIDGE
SPACING
Standard and heavy trucks 30 Mt
Articulated vehicles 18.5Mt
 DOUBLE LANE BRIDGE
Double lane bridges are
those with carriageway
width above 5.5m and
up to 7.5 m for all spans. Vehicle arrangement

9. PROCEDURE FOR
RATING
 CALCULATION OF SAFE AXEL LOAD
 RATING OF BRIDGES (IRC S.P.67)
CLASS FOUR SIX CLASS FOR MORE
WHEELERS WHEELERS THAN 6
MAX. SINGLE MAX. WHEELERS
AXLE LOAD SINGLE AXLE MAX. SINGLE
LOAD AXLE LOAD
3R 1.1 t 1.0 t 30 R 14.0 t
5R 3.4 t 2.2 t 16.0 t
40 R
9R 5.8 t 3.5 t 17.5 t
50 R
12 R 7.5 t 4.8 t 19.0 t
60 R
18 R 10.0 t 7.6 t 20.0 t
70 R
24 R 12.0 t 8.5 t

10. STRENGTHENING :
 ADDITION OF UNSTRESSED OR PRE-SRTESSED STEEL
 INSTALLATION OF EXTERNAL PRE-STRESSED
REINFORCEMENT
 BONDED REINFORCEMENT
 INCREASE OF THE CONCRETE CROSS-SECTION
CARBODUR CFRP PLATE SYSTEMS
 IT CONSIST OF CARBON FIBER
Material properties of carbodur CFRP plates
E – Modulus Tensile Strength Elongation @ Break
N/mm2 N/mm2
Carbodur S 165’000 2’800 > 1.7
Carbodur M 210’000 2’800 > 1.35
Carbodur H 300’000 1’350 > 0.45

11. BONDING OF CFRP
PLATES :
Test results
Test Specimen Fbr [KN] Ybr [mm] Εbr
Specimen 1 Curing 161 70 6.61
without oscillation
Specimen 4 176 75 6.55
Curing with oscillation

12. POSTING
 Posting is a method to restrict the loading on the existing
bridge.
CONDITION POSTING
RATING > LOAD NOT REQUIRED
RATING < LOAD REQUIRED
 TRAFFIC RESTRICTIONS
8 SPEED RESTRICTION 8 FOOT PATH LOADING
8 GEOMETRIC RESTRICTIION
 ALTERNATIVES TO POSTING
8 FRAME BARRIERS 8 FREQUENT INSPECTION
8 LANE LIMITS 8 REPAIR

13.  POSTING SIGN
Regulatory signs
are installed on either
Side of bridge
 ENFORCEMENT
Restrictions in
respect of Max.
load, Geometrical
limits, Speed for
safety of brides.

14. CONCLUSIO
• N :
Rating helps to determine the safe carrying capacity of
bridges, thus the structure can be made safe for use.
• Accidents can be avoided due to collapse of the old
bridges which have undergone deterioration by posting.
• Follow-up actions can be taken according the rating
of bridge such as and this current or future loading on
the bridge repairs strengthening or demolition of old
bridge and construction of new bridge.

15. REFERENCES
:
* Bridge Engineering –
D.R.Phatak
* WWW.GOOGLE.COM
* WWW.ALTAVISTA.COM
* Public works department, Nasik
* Indian Road congress, Special
Publication 37

16. ?
R.RAGHAVENDRA