Indian Road Congress (IRC) and Bridge Loading Standards: IRC Class AA, 70R, A and B Loading

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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.

IRC Class AA Loading

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.

IRC Class 70R Loading

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
IRC Class A and B Loading

Comments

  1. UnknownMay 4, 2021 at 12:10 PM

    Thanks. I was a bit confused when I went through the code. Keep posting.

    ReplyDelete

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