INCREMENTAL INCREMENTAL PUSH PUSH

LAUNCHING LAUNCHING METHODMETHOD

ConceptConcept

The basic concept of INCREIMENTAL PUSH The basic concept of INCREIMENTAL PUSH

LAUNCHING METHOD (ILM) is to prefabricate LAUNCHING METHOD (ILM) is to prefabricate approximately 10m to 30m long units of the bridge under approximately 10m to 30m long units of the bridge under factory conditions behind an abutment and launch the units by factory conditions behind an abutment and launch the units by sliding them on Teflon bearings into final position without the sliding them on Teflon bearings into final position without the

aid of scaffolding.aid of scaffolding.

The total deck slab of the bridge is subdivided The total deck slab of the bridge is subdivided longitudinally into section of 10m to 30m length, longitudinally into section of 10m to 30m length, depending upon the length of the span and time depending upon the length of the span and time available for construction.available for construction.

Each section is concreted immediately behind Each section is concreted immediately behind the abutment of the bridge in steel framed forms.the abutment of the bridge in steel framed forms.

These steel frames which remain in same place These steel frames which remain in same place for concreting all sections.for concreting all sections.

The forms are designed in such a way that it can be moved The forms are designed in such a way that it can be moved transversely or rotated on hinges to facilitate easy stripping transversely or rotated on hinges to facilitate easy stripping after sufficient hardening of the concrete.after sufficient hardening of the concrete.

The forms are hydraulically or mechanically activated to The forms are hydraulically or mechanically activated to ensure rapid stripping. ensure rapid stripping.

This is the launching This is the launching equipment, which consists equipment, which consists of a combination of of a combination of hydraulic jacks acting hydraulic jacks acting vertically and horizontally vertically and horizontally on sliding bearings.on sliding bearings.

The sliding bearing consists The sliding bearing consists of concrete blocks covered of concrete blocks covered with stainless steel and with stainless steel and Teflon-coated reinforced Teflon-coated reinforced elastometic pads.elastometic pads.

A section is manufactured in formwork in lengths corresponding A section is manufactured in formwork in lengths corresponding to one-third to one-half of the normal span length. After the to one-third to one-half of the normal span length. After the stripping of the forms, tendons are inserted and stressed.stripping of the forms, tendons are inserted and stressed.

The section is then jacked forward, sliding on the Teflon, which, The section is then jacked forward, sliding on the Teflon, which, in turn, is affixed to stainless steel plates on top of the piers. in turn, is affixed to stainless steel plates on top of the piers.

A new section is then constructed immediately adjoining the rear A new section is then constructed immediately adjoining the rear end of the first. Pre-stressing tendons are spliced so that the two end of the first. Pre-stressing tendons are spliced so that the two segments are joined as one longer pre-stressed unit and then segments are joined as one longer pre-stressed unit and then jacked forward another length.jacked forward another length.

At the head of the first section, a steel nose consisting of a light At the head of the first section, a steel nose consisting of a light truss is attached to facilitate reaching of the first and subsequent truss is attached to facilitate reaching of the first and subsequent piers without including a too large cantilever moment during piers without including a too large cantilever moment during construction.construction.

The second and following sections are concreted directly on the The second and following sections are concreted directly on the face of the hardened portion and the longitudinal reinforcement face of the hardened portion and the longitudinal reinforcement can continue across the construction jointcan continue across the construction joint..

The pushing is achieved by hydraulic jack which acts against the The pushing is achieved by hydraulic jack which acts against the abutment.abutment.

Launching ProcessLaunching Process

Low capacity hydraulic jack would be enough to move Low capacity hydraulic jack would be enough to move the bridge decks.the bridge decks.

Intermediate pier supports or towers may be used to Intermediate pier supports or towers may be used to give temporary support across longer spans since the give temporary support across longer spans since the practical limit of a span length for this type of practical limit of a span length for this type of construction is about 60 meters.construction is about 60 meters.

When launching from both ends of the bridge, different When launching from both ends of the bridge, different curvatures may be used, but this must be constant for each curvatures may be used, but this must be constant for each launching point. Similarly, the super-elevation must be launching point. Similarly, the super-elevation must be constant.constant.

After the launched bridge is in place, the bearing seats may be After the launched bridge is in place, the bearing seats may be jacked up to remove the Teflon, and the permanent bearings jacked up to remove the Teflon, and the permanent bearings are installed. Jacking points should have the required are installed. Jacking points should have the required supplemental reinforcing to permit this application of force at supplemental reinforcing to permit this application of force at a location offset from the permanent bearings.a location offset from the permanent bearings.

Features of the incremental launching method

Construction is carried out completely without falsework, so Construction is carried out completely without falsework, so that there is no problem in passing over obstacles below, such that there is no problem in passing over obstacles below, such as roads, railways, rivers, buildings areas.as roads, railways, rivers, buildings areas.

The superstructure is made up of units of 15 to 25 m length, The superstructure is made up of units of 15 to 25 m length, each completed in one week; there are no joints, since each each completed in one week; there are no joints, since each unit is concreted directly against the preceding one.unit is concreted directly against the preceding one.

It is a economic construction technique.It is a economic construction technique.

To achieve quality work with reduced amount of labour.To achieve quality work with reduced amount of labour.

It is a speedy construction technique.It is a speedy construction technique.

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