Indian Road Congress (IRC) and Bridge Loading Standards: IRC Class AA, 70R, A and B Loading
Indian Road Congress
Indian Road Congress
(IRC) is the governing body which decides the rules and regulation along with
technical details regarding roads, highways, and bridges. The first loading
standard in India was published by IRC in 1958 and subsequently reprinted in
1962 and 1963. The metric version was
introduced in the second revision published in 1964.
IRC Bridge Loading Standards
The standard IRC loads
specified in IRC: 6-2000 are not changed since 1958 and grouped under four
categories as detailed below:
1. IRC Class AA Loading
In this category, two
types of vehicles are specified and they are grouped as tracked vehicle and
wheeled vehicles. The tracked vehicle simulating an army tank of 700 KN and
wheeled vehicle of 400 KN (a heavy army truck) are standardized for the
designing of all the bridges located on National Highways and State Highways.
2. IRC Class 70R Loading
The following vehicles
are considered for the design under this category:
(a)
The tracked vehicle of the total load of 700 KN with
tracks each weighing 350 KN each
(b)
Wheeled vehicle of the total load of 400 KN with each
wheels weighing 100 KN each
(c)
Wheeled vehicle with a train of vehicles on
seven axles with a total weight of 1000 KN
The option (a) might
seem to be the same as the tracked vehicle of IRC Class AA. But, it is slightly
different from the tracked vehicle of IRC Class AA. In this category of IRC
Class 70R, the contact length of the vehicle is 4.87m, the total length of the
vehicle from nose to tail is 7.92m and the specified minimum distance between
successive vehicles is 30m.
Similarly, in option
(b) it is specified that the total load of 400 KN is distributed equally on
each wheel with 100 KN each which is different from the wheeled vehicle of IRC
Class AA.
Option (c) is one more consideration of a vehicle that is taken into account while designing under this category. It is the wheeled vehicle with a train of vehicles on seven axles with loads as shown in the figure which adds up to a total of 1000 KN.
3. IRC Class A Loading
The IRC Class A loading
is consists of a wheel load train of a total load of 554 KN. It comprises a heavy-duty truck with two trailers that transmit loads from 8 axles varying from a
minimum of 27 KN to a maximum of 114 KN as shown in the figure. This type of loading
is recommended for all roads on which permanent bridges and culverts are
constructed.
4. IRC Class B Loading
The loading of this
class is similar to the Class A loading except that the axle loads are of
lesser magnitude. The total axle loads of this Class are 332 KN with a train of
wheeled vehicles on eight axles as shown in the figure.
This type of loading is adopted for temporary structures and timber bridges.
IRC Class A and B Loading |
Thanks. I was a bit confused when I went through the code. Keep posting.
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