8/6/2019 Ha and Hb Bridge Loading1

1/1

Projects Site Map Con tact Us David Childs B.Sc.,C.Eng.,MICE Go

Home

Design Notes

Abutments

Bearings

Deck

Drainage

Foundations

Joints

Parapets

Piers

Wing Walls

Design Calculations

DesignSpreadsheets

TutorialsAbutment Design

Grillage Analysis

HA & HB Loading

Influence Lines

PrestressedConcrete Beams

Steel Beams

Workshop

Welcome

Bridge Pictures

Codes and Books

Links

Home | Tutorials | HA & HB Loading | HA and HB Load Example

HA and HB Type Loading

History

The first standard vehicle load for highway bridges in the UK was introduced in 1922. British Standards

introduced a traffic live load requirement in BS 153 Part 3 in 1923, which was later revised in 1925 and

1937. The Type HA uniformly distibuted loading was introduced in 1945 and the concept of a Type HA and

HB load was included in the 1954 edition of BS 153: Part 3A. In 1961 the HB load was specified in terms

of units and varied depending on the class of road, with 45 units required for Motorways and Trunk Roads

and 37.5 units for class i and class ii roads. A requirement for all public roads to be designed for at least

30 units of HB was introduced in 1973.

HA Loading

BD 37/01 of the Design Manual for Roads and Bridges says that Type HA loading is the normal design

loading for Great Britain and adequately covers the effects of all permitted normal vehicles other than

those used for abnormal indivisible loads. Normal vehicles are governed by the Road Vehicles

(Authorised Weight) Regulations 1998, referred to as the AW Vehicles and cover vehicles up to 44 tonne

gross vehicle weight. Loads from these AW vehicles are represented by a uniformly distributed load and a

knife edge load. The loading has been enhanced to cover:i) impact load (caused when wheels 'bounce' i.e. when striking potholes or uneven expansion joints).

ii) overloading

iii) Lateral bunching (more than one vehicle occupying the width of a lane).

The magnitude of the uniformly distributed load is dependent on the loaded length as determined from

the influence line for the member under consideration. For simply supported decks this usually relates to

the span of the deck.

HB Loading

BD 37/01 of the Design Manual for Roads and Bridges says that Type HB loading requirements derive

from the nature of exceptional industrial loads (e.g. electrical transformers, generators, pressure vessels,

machine presses, etc.) likely to use the roads in the area.

The vehicle load is represented by a four axled vehicle with four wheels equally spaced on each axle. The

load on each axle is defined by a number of units which is dependant on the class of road. Motorways and

trunk roads require 45 units, Principal roads require 37.5 units and other public roads require 30 units.

One unit of HB is e ual to 10kN er axle. There are five HB vehicles to check althou h most vehicles can

DAVIDCHILDSB.SC., C.ENG., MICE

3/8/2011 HA and HB Bridge LOADING

demon.co.uk/tutorial/tuha.html 1