Integral Bridge Structures
Bridges constructed without any expansion joint (between spans or between spans and abutments) and without any bearings are called integral bridges. In its simplest form, an integral bridge may be viewed as a box culvert or a portal frame structure, where the road surfaces are continuous from one approach embankment to the other.
There are several advantages of adopting an integral concept. Some of them are as follows:
- The Simple Detail – The design & detail are much simplified with rapid construction and with fewer construction joints can be achieved with integral bridges. With the use of integral bridge construction, the requirement of close tolerances near the expansion joints is altogether eliminated. Bridge seating no longer require wedges to ensure horizontal seating of bearings. Minor mislocation of the piers and abutments do not create any fit-up problems.
- Lower Construction Cost – Integral bridges have low initial cost as compared to conventional expansion joint bridges.
- Design Efficiency – Tangible efficiencies are achieved in substructure design due to an increase in the number of supports over which the longitudinal and transverse forces may be distributed.
- Improved Riding Quality – Smooth jointless construction improves vehicular riding quality and diminishes vehicular impact stress levels.
- Added Redundancy – Integral bridges provide added redundancy and capacity for all types of catastrophic events. While designing a bridge for seismic forces, considerable economy can be achieved by providing integral supports as the horizontal forces are shared by more number of piers and abutments. Further, the use of integral pier and abutment supports eliminates loss of girder support; the most common cause of damage to bridges in case of seismic event.
- Simplified Widening & Replacement – Integral bridges are convenient to widen and easy to replace. There are no expansion joints to match and no difficult temperature settings to make.
It is recommended that integral structures be used in following situations:
- For culverts (single or multicell box)
- For bridge with bridge lengths less than 60m and skew angle less than 30o.
- For bridges where piers and abutments are tall.
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