ASSESSMENT OF RESIDUAL LIFE OF GIRDERS OF BRIDGE No

11x 48.5 m spans in bridge No. 75 were constructed and open to traffic in
the year 1993 and since than the bridges of steel plate girders have been
abandoned.
4.0 METHODOLOGY:
For assessment of residual life of the girders of the bridges, the procedure
as given in BS – 5400 part – 10 , code of practice for fatigue has been
followed. The procedure given in clause 9.0 of the above code for railway
bridges has been used. Two methods for fatigue assessment of railway
bridges are given in clause 9.2 & 9.3 of the code. In method –1,
assessment is done without damage calculation and in method –2,
damage is calculated by using Miner’s summation rule. Both these
methods have been used for the assessment of residual life.
4.1 Method – 1: Fatigue life assessment without damage calculations:
4.1.1 General:
BS-5400 part 10 is a comprehensive code which is based on the concept
of cumulative fatigue damage. The fatigue assessment is based on
Palmgren-Miner’s damage summation model. For fatigue assessment of
railway bridges, the methodology for determination of stress range has
been described for different type of connections and a simplified
procedure has been given for determining the limiting value of the
maximum range of stress for the specified design life for two different
types of standard loadings. Details of RU loading ( Ref; Table- 1) has
been used for calculating the remaining fatigue life, as it is more severe
than IRS MBG loading. As per code, RU loading allows for all
combinations of vehicles currently running or projected to run on railways
in the Continent of Europe, including the United Kingdom and is to be
adopted for the design of bridges carrying main line railways of 1.4 m
gauge and above. The nominal type RU loading consists of four 250 KN
concentrated loads preceded and followed by a uniformly distributed load
of 80 KN/m The code specifies different factor k1, k2, k3, k4 & k5 for design
parameters such as design life, multiple cycle of stress loading, type of
standard loading, annual GMT and multiple lane loading respectively.
The code gives specific methodology and tables to calculate the factors
for different design parameters.
4.1.2 Limiting Stress Range, σT
The constant amplitude non-propagating stress range, σ0 for the
constructional detail is chosen appropriately on the basis of Table – 17 &
Table 8 of the code. The limiting stress range σT is calculated for RU
loading as under:
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