In this file covered Cantilever construction method.

1. Balanced Cantilever
Bridge
Submitted by: Jeelkumar Patel
(18bcl039)

2. Introduction
• The balanced cantilever method of bridge construction used for bridge with
few spans ranging from 50 to 250m. The bridge can be either cast-in-place or
precast.
• The deck is erected segmentally on each side of the pier in a balanced
sequence to minimize load unbalance and longitudinal bending in piers and
foundations.
• This construction method is particularly advantageous on long spans, in
marine operations, and where access beneath the deck is difficult.

3. • It is highly suitable for structure cable-stayed bridges. Because once
segments are placed, they will be supported by new cable –stays in each
construction stage.
• Therefore, no auxiliary supports are required, and hence it is both
economical and practical method for long cable-stayed bridge.
Balanced Cantilever bridge

4. PROPORTIONING OF MEMBERS
• To get the most economical design, the proportioning of the members
should be such that the sections at mid-span and at support satisfy
both the structural and architectural requirements and at same time
require minimum quantity of materials.
• The cantilever lengths are usually made from 0.20 to 0.30 of the main
span. This ratio depends on the length of the main span and the type
of suspended span the cantilever has to support as well as the number
of cantilevers (single or double) available for balancing the mid-span
positive moment etc.

5. • Type of Superstructure:
The superstructures may be of solid slab, T-beam and slab, hollow box girder
etc.
One hollow-box balanced cantilever bridge

6. CANTILEVER CONSTRUCTION METHOD
• Very ancient technique
• Structure is built component above ground level
• Most recent : construction of cable stayed bridges, extra-dosed bridge etc.
• Prestressed concrete bridges:
Cast in-situ segments or pre-cast segments
Integral with pier or on bending

7. Longitudinal Span Configuration
• Typical 3 Span system
• Typical 4 or more span system

8. • No such luxury in today’s congested urban area

9. Procedure for balanced cantilever method of cast-in-situ bridge
construction
• After the construction of lower infrastructure of the bridge is completed, Fig. bridge
construction begins at each pier.
Construction of lower infrastructure of bridge

10. • Special formwork is positioned and cast-in-situ pier segment is begun, Fig. the complete
pier segment is then used as an erection platform to support a form traveler for cast-in-
place segments.
Position of special formwork

11. • Therefore, soffit shuttering, shuttering for web & deck shuttering is fixed on both sides of
pier as shown in fig.
Soffit, web and Deck shuttering Shuttering soffit, web and decks

12. • Then concreting is done on both sides of the pier as shown in fig. The segment production
rate for form travelers is usually one segment every 5 days per traveler.
Concrete placement

13. • Cast-in-situ segments range between 3m to 5m in length with formwork moving in tandem
with each segment.
• Segment construction is continued until a joining midpoint is reached where a balanced pair
is closed as demonstrated in fig. The construction of closer section of a bridge is shown in
fig.
Bridge construction progression Construction of closer section of the bridge

14. ADVANTAGES:
• Single-sided support
• Uniform bridge construction
• Less time required
DISADVANTAGES:
• Very expensive
• Complications during construction
• Lack of multiple supports

15. APPLICATION:
This type of construction has been used in a large number of bridges around
the world. Spans of up to 70 m have been built with a constant cross section,
but a variable depth cross section is required for longer spans.