INTEGRAL BRIDGES
INTEGRAL BRIDGES
Integral bridges in simple words can be defined as bridges without joints. Integral bridges are characterized by monolithic connection between the deck and the substructure (piers and abutments). They span from one abutment, over intermediate support to the other abutment, without any joint in the deck. Integral bridges have been constructed all over the world including India.
WHAT IS AN INTEGRAL BRIDGE?
Bridges constructed without any expansion joint (between spans or between spans and abutments) and without any bearings are called integral bridges.
CHARACTERISTICS OF INTEGRAL BRIDGES
The integral abutment bridge concept is based on the theory that due to the flexibility of the piling, thermal stresses are transferred to the substructure by way of a rigid connection between the superstructure and substructure
MOTIVATION BEHIND INTEGRAL BRIDGES
Ø To eliminate expansion joints in the deck
Ø When earthquake forces are predominant or when consideration like increased resistance to blasts the integral bridge concept is an excellent option.
Ø Less expensive
Ø Improved durability
Ø Easy to design
WHY GO FOR INTEGRAL BRIDGES?
The expansion joints and bearings, by virtue of their functions are sources of weakness in the bridge and there are many examples of distress in bridges, primarily due to poor performance of these two elements
PROBLEMS OF EXPANSION JOINTS AND BEARINGS
Ø Leaking of expansion joints and seals permit the surface run-off water from roadway
Ø Continual wear and heavy impact from repeated live loads as well as continual stages of movement from expansion and contraction
Ø Impact loadings from heavy commercial vehicles
Ø Elastomeric bearings can split and rupture due to unanticipated movements, or ratchet out of position.
Ø Malfunctioning of bearings can lead to unanticipated structural damage
Ø Joints and bearings are expensive
INTEGRAL ABUTMENT
The integral abutment is defined as abutment, which is connected to the bridge deck without any movement joint for expansion or contraction of the deck
WHY GO FOR INTEGRAL ABUTMENTS
- Simple Design
- Joint less construction
- Resistance to pressure
- Rapid construction
- Ease in constructing embankments
- No cofferdams
- Vertical piles (no battered piles)
- Simple forms
- Few construction joints
- Reduced removal of existing elements
- Simple beam seats
- Simplified widening and replacement
- Lower construction costs and future maintenance costs
- Improved ride quality
- It Design efficiency
- Added redundancy and capacity for catastrophic events
- Improve Load distribution
- Enhance protection for weathering steel girders
PLANNING CONSIDERATIONS
- Length of the Structure
- Climatic Condition
- Seismic Zone
- Type of Superstructure
- Type of Abutments
- Type of Foundations And Sub-Soil Conditions
- Geometry of the Structure
- Complexity in Analysis and Design
RECOMMENDED QUALITY IMPROVEMENT PRACTICE FOR INTEGRAL BRIDGES
Ø Develop design criteria or office practices for designing integral abutment and join less bridges
Ø In extending the remaining service lives of existing bridges
Ø exchange information in the areas of design, construction and maintenance of joints and joint less bridges
Ø The decision to install an approach slab should be made by the Bridges and Structures Office, with consultation from the Geotechnical group
Ø Standardize practice of using sleeper slabs at the end of all approach slabs
ADVANTAGES OF INTEGRAL BRIDGES OVER CONVENTIONAL BRIDGES
1. Simplified details for construction
2. Reduced life cycle cost and long term maintenance
3. Improved design efficiency Improved riding quality
4. Added redundancy with improved seismic performance Ease in constructing embankments
5. Elimination of water leakage on critical structural elements
6. Lesser tolerance restriction due to elimination of bearings and expansion joints
7. Faster construction
8. Simplified widening and replacement detail Useful for strengthening of existing bridges
EXAMPLES
1. Dankuni-Palsit Flyover
It is situated at the durgapur Expressway. The span arrangement for the overpass is15m + 2×22.0 m + 15m,continuous over the support. The deck is RC solid slab type integral with the twin piers. The bridge is a joint less bridge without any expansion joint over intermediate piers without any bearings
2. Kalkaji Flyover
A 150m integral flyover has been provided at the vital T-junction on Ring Road near Kalkaji Temple. The typical five span continuous deck (25m + 30m + 40m + 30m + 25m), has a voided slab reinforced concrete deck with a depth of 1.70m, which was hunched and increased to 2.20m at the piers supporting the 40.0m obligatory main span.
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