An integral bridge contains no

expansion joint An expansion joint, or movement joint, is an assembly designed to hold parts together while safely absorbing temperature-induced expansion and contraction of building materials, and vibration, or to allow movement due to ground settlement or seis ...

s to accommodate enlargement due to increased temperature. Horizontal (axial) movements due to thermal expansion and braking loads are instead transferred to the fill adjacent to the abutment. The omission of the expansion joint removes a pathway for the penetration of chloride-bearing road salts to the bridge's sub-structure. In the United Kingdom there is a presumption that most new short to medium length bridges will be of the integral type. An early example of an integral bridge is masonry arch bridge. Some of the earliest examples of integral bridges in reinforced concrete were constructed as part of the United Kingdom's

M1 motorway The M1 motorway connects London to Leeds, where it joins the A1(M) near Aberford, to connect to Newcastle. It was the first inter-urban motorway to be completed in the UK; the first motorway in the country was the Preston By-pass, which ...

in 1959.

Description

An integral bridge contains no

s, spanning

monolithic A monolith is a monument or natural feature consisting of a single massive stone or rock. Monolith or monolithic may also refer to: Architecture * Monolithic architecture, a style of construction in which a building is carved, cast or excavated ...

ally from

abutment An abutment is the substructure at the ends of a bridge span or dam supporting its superstructure. Single-span bridges have abutments at each end which provide vertical and lateral support for the span, as well as acting as retaining walls ...

to abutment. Movement due to thermal expansion and contraction or braking loads is accommodated by the end walls or abutments. Where intermediate supports are specified (e.g. bridge piers) these may also serve to resist thermal expansion movements. The omission of the expansion joint removes a significant maintenance and durability issue, as it serves as a point of ingress for

road salt Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/ ...

s which allows the abutment, piers and deck soffit concrete to come under chloride attack that can cause degradation and eventual span failure. A 1989 British study showed that the majority of expansion joints surveyed in existing bridges had failed and allowed water (and hence salt) ingress. The movement experienced at the abutment in an integral bridge is an order of magnitude greater than those designed with movement joints. The size of movement depends on the stiffness of the bridge structure and the fill adjacent to the abutment (which is subject to compaction). The movement is largest in the upper portion of the abutment, where thermal effects are greatest.

Highways England National Highways, formerly the Highways Agency and later Highways England, is a government-owned company charged with operating, maintaining and improving motorways and major A roads in England. It also sets highways standards used by all f ...

specify that integral bridges should be designed to limit movement to . Due to repeated expansion and contraction cycles the backfill adjacent to the abutment is subject to ratcheting, whereby the material's stiffness is increased. The maximum stiffness level is reached after around 100–200 thermal expansion cycles.

Types

Highways England recognises four types of integral bridge, defined by the construction of their abutments: *Frame abutments where the abutment acts as a retaining wall to the surrounding fill, connecting to the deck in a manner that allows for transfer of bending moments, shear forces and axial loads. *Embedded abutments, extending to a depth below the retained fill with restraint provided by the embedded length. *Bank pad abutments, designed to move horizontally to accommodate expansion and contraction of the deck. These must be of adequate weight (or a deck flexible enough) to avoid uplift forces due to differential settlement. *End screen abutments, which act only to retain the surrounding fill and transfer horizontal loads from the bridge deck to the fill. The vertical loads are transferred from the deck by means of a separate support system. The supports may be designed to take only vertical loading or accommodate the horizontal movement. Where

bridge bearing A bridge bearing is a component of a bridge which typically provides a resting surface between bridge piers and the bridge deck. The purpose of a bearing is to allow controlled movement and thereby reduce the stresses involved. Possible causes o ...

s are used on an integral bridge (as is often the case for end screen abutment types) the structure is sometimes referred to as semi-integral.

Use

It is widely accepted that short to medium length bridges should be designed as integral structures to minimise maintenance requirements. Highways England's

Design Manual for Roads and Bridges The Design Manual for Roads and Bridges (DMRB) is a series of 15 volumes that provide standards, advice notes and other documents relating to the design, assessment and operation of trunk roads, including motorways in the United Kingdom, and ...

(applicable to the whole of the UK and many parts of it, including the section on integral bridges, applying to the Republic of Ireland) states that all bridges with deck length less than and

skew Skew may refer to: In mathematics * Skew lines, neither parallel nor intersecting. * Skew normal distribution, a probability distribution * Skew field or division ring * Skew-Hermitian matrix * Skew lattice * Skew polygon, whose vertices do not ...

of less than 30 degrees should be designed as integral structures unless there is a compelling reason to do otherwise.

References

{{Reflist Bridges by structural type