Construction of Cantilever Bridge - List of Various Technologies UsedTweet
For cast-in-place and precast segmental bridges a balanced bridge is usually constructed. Cast-in-place bridges are constructed for brief bridges with longer span, and for longer-bridges with shorter span precast segmental bridges are constructed.
There are two ways to construct the bridge – one, by self-launching suspension movable scaffolding system which works on free erection sequences, two, linear movement erection process.
To construct the balanced bridge using precast segments ground cranes, lifting frames and self-launching gantries are used. Self-launching gantries work on the principle of linear movement erection. Whereas, for free of charge erection sequence process ground cranes and lifting frames works.
Usually, box beam sections are used for the making of a balanced bridge . Precast segments are often used for a span of 50-70m if the depth of the span is constant. just in case the depth of span is varying then the demand for flexural capacity of the span would be more. during which case it's difficult to use the precast segment. Lifting and transportation of heavy segments also becomes difficult. Thus, for such scenarios cast-in-segments are used.
Listed below are the foremost common erection technologies used for precast and cast-in-place segments for balanced cantilever bridges:
- Ground Cranes
- Deck-supported Lifting Frames
- Self-launching Gantries
- Form Travelers
- Suspension Movable Scaffolding System
For the erection of a balanced bridge an honest access is required throughout the length. The quickest and easiest erection system with least investment is provided by cranes. Different segments are often erected using cranes directly . the rationale why a bridge is made using ground crane is to supply access to the location and height of the piers as a balanced bridge is usually constructed in inaccessible terrains.
For the development of balanced bridge which can be of long and curved span, tall piers and spans located over water deck-supported lifting frames are used. In cases like this exceptional lifters can affect heavier sections and narrow boat conveyance can help in minimizing geometry and weight limitations.
For cable-stayed bridges lifting frames are used. it's also considered a typical solution for erection when the location and time factors restrain the utilization of in-place casting. albeit there are interruptions while moving to subsequent pier, the lift frames can handle erection conditions which usually are inconsistent with ground cranes and self-launching gantries.
- Fixed Lifting Frame
The connection of the fixed lifting frames is secured to the tip of the cantilever and features a particularly restrictive load-carrying capacity. The turning arms can lift from behind or horizontally and are wont to balance cantilever bridges due to the twist that they will transfer to the deck. it's easier to put segments on the table and therefore the anchoring of segments to the deck becomes necessary during the operation.
It is wont to complete a fast erection process and also limit ground interruptions. Using the gantries direct erection of support from one abutment to a different is feasible and therefore the precast segments are often directly deployed over the finished surface of the bridge.
If two bridges are being constructed nearby then the gantry are often employed by moving it from one bridge to a different . A faster construction rate can therefore be achieved. to maneuver and lift the precast segment a few of derricks are used. just in case the precast segments are transported to the bridge then the derrick picks them up at the backside end of the gantry.
The old gantries had an equivalent length as of the span to be erected. alittle length of span and gantries results in closer supports. just in case of shorter gantries, the front of the cantilever has got to face more of the loading. Thus, the erection of the table becomes a posh process.
The new gantries are twice the length of the bridge span and support is provided by the center span. Therefore, there's little or no need for extra support. New age gantries are often wont to construct a extended span truss. the value of erection comes down because the continuous pre-stressing throughout the length leads towards decrease within the quantity of reinforcement.
Now, self-launching gantries are even more widely used as no ground cranes are required during the method , the need for labour also reduces and therefore the launching and placement of pier tables is straightforward also .
Form travelers are wont to erect bridges by in-place casting when the span of the bridge is long but the general length of the bridge is brief for segmental precasting. For the erection of a curved bridge in-place casting is required because it becomes difficult otherwise to supply consistent curved segments. The length of the casting cell for the shape traveler is 5m which may be designed for a carrying capacity of up to 500 tons.
To create more working space for the labour working platforms are built. The stressing platform is suspended from the front bulkhead in order that the fabrication and tension of the top-slab tendons are often made possible.
A pair of form travelers must be accommodated by the table with a length of 8-10m during the initial stage of balancing a cantilever.
It takes 2-4 months for the casting of the entire cells because the form travelers have the restriction of working space, complex geometry during operation and different phases for casting the whole segment.
It is wont to erect cast-in-place balanced bridge . it's supported on one side of the entire bridge and therefore the other side of the leading pier. Two casting cells are used at an equivalent time between the support and therefore the table at the mid-span.
After the casting is completed on the mid-span, the girder is launched on subsequent span. Accordingly, the position of the casting cells is shifted to subsequent span for the development of a replacement segment.
For rectilinear or somewhat curved spans of 100-120 m suspension movable scaffolding system is employed . the most girder of the bridge is 1.5 times longer than the bridge span.
The movable scaffolding system helps in improving access from the finished bridge and settles the support during erection, along side it less pre-stressing is required for the bridge so on reduce the development loads.
Using this technology, cast-in-place segments are often formed which is up to 20m wide and 12m long . Moving the casting cells to subsequent pier requires just hours instead of weeks. Movable scaffolding system helps in minimizing the utilization of ground cane and thus the development process becomes much faster and therefore the labor cost is additionally reduced substantially.