Applications for the CI LUD®
CI LUDs are suitable for use in any
structure that will benefit from the transmission of dynamic shock
forces. Some examples are given below.
Multispan Bridge Decks under Seismic Loading
The longitudinal forces
generated in a bridge deck subjected to earthquake are functions of
the deck mass and are usually greatly in excess of those caused by
traffic acceleration and braking. They require constraint from the
substructure at bearing level. For the viaduct shown in
figure 1 the restraint was
originally provided by the central fixed pier alone. Any increases
in seismic loading requirements, which appear regularly in new codes
as earthquake experience and knowledge accumulates, overload the
Ideally the force should be shared equally between all the bridge
supports. But, unlike the central fixed pier, the others must allow
the deck to move.
Introduced on the 'free' piers, the CI LUD offers little resistance
to normal deck movement. Its employment transforms a free support
pier during an earthquake into a temporarily fixed support pier,
allowing this pier to be included in the seismic load-resisting
elements of the structure.
Figure 1 shows a typical
arrangement of the CI LUDs at the 'free' piers.
Strengthening of Existing Structures
Many simply supported multispan
bridges now require strengthening because traffic has become heavier
and faster, the traction and braking loads have exceeded the
original design specification.
Moreover, damage by road salt, carbonation or alkali/silica reaction
(ASR) has weakened many supporting structures. CI LUDs placed across
the joints to introduce load-sharing between piers can reduce the
individual pier loadings to a level that eliminate the need for
expensive structural repairs.
The traction and braking force capacity of existing viaducts can be
increased using CI LUDs. Many viaducts, particularly river crossing
approaches, have a long series of simply supported deck spans, often
carried on high substructure piers.
Each span is usually simply supported, with each pier carrying one
span on fixed bearings and the other on free bearings as shown in
Consequently the traction and braking forces must be applied
individually to each deck in the viaduct. On any given deck the main
resistance is offered by the pier carrying the fixed bearing.
A substructure of this type having say, 10 piers of equal stiffness
theoretically has a total resistance capacity of ten times the deck
design traction and braking longitudinal loads. In practice that
capacity is unattainable because of the simply supported
Figure 2 shows how all this
capacity can be mobilised by the attachment of CI LUDs at the
CI LUDs assist structural
integrity and stability in many kinds of structures subject to
sudden ground settlements and other severe loadings. For example,
they are used in safety design against catastrophic collapse in the
event of mining subsidence. Other applications include safety design
against accidental impact in nuclear power stations and resistance
to surge forces in hydraulic pipelines. They can also provide
substructure attachments for typhoon or hurricane gust loading, used
in the same way as in earthquake protection, mounted longitudinally
CI LUDs can also be used to transmit impact loads across the
movement joints in bridge parapets. BS6779.