U.S Department of Transportation Federal Highway Administration
Improving Inspection Access at Segmental Bridge Abutments
Notice: Personal protection equipment (PPE) should be worn during inspection and construction operations.
A series of videos has been produced to encourage the design and detailing of post-tensioned bridges
to accommodate non-destructive evaluation
This video addresses improving inspection access at abutments of segmental bridges
Consider a segmental bridge built using the span-by-span method of construction.
The span lengths of this bridge are 150 feet and the depth of the box girder is 9 feet.
The end of the last span is supported by an abutment where inspection access is often difficult.
The abutment of this bridge is elevated and pile supported.
The abutment is comprised of an abutment seat, back wall, wing walls, and curtain walls.
An expansion joint is placed between the end of the bridge and the roadway approach slab.
The end of the approach slab is supported on the abutment back wall.
Elastomeric bearings are used to support the bridge on the abutment seat.
The back wall is seen immediately at the end of the bridge superstructure.
Post-tensioning tendons of a span-by-span bridge are typically inside the box girder,
external to the concrete.
Access to inspect the external tendons is through the inside of the bridge.
At interior supports the post tensioning tendons overlap to provide longitudinal continuity.
The tendons are located near the top of the girder to offset negative bending over the piers.
Leaving the pier segment, the tendons move to the bottom of the box girder,
passing through tendon deviators.
In this position the tendons offset positive bending in the center of the spans.
At the ends of the bridge, the tendons again deviate up,
creating a more uniform distribution of stress in the bridge.
The longitudinal post-tensioning tendons anchor in heavily reinforced diaphragms of the abutment segments.
The diaphragms are also post-tensioned vertically to help distribute the post-tensioning forces into the bridge.
Access to inspect the tendon anchorages is required
to evaluate the condition of the tendons.
Unfortunately, the proximity of the abutment back wall to the end of the bridge severely
limits access for inspection.
It is this limitation that we wish to improve upon.
Now let’s consider an alternate abutment layout.
The new layout replaces the typical abutment with one that has an inspection vault.
The vaulted abutment provides access for the inspection of the post-tensioning tendons.
The inspection vault is created by moving the back wall away from the end of the bridge.
An extension of the abutment seat serves as the floor of the vault.
A top slab designed to carry traffic from the bridge to the approach slab is required.
The expansion joint is now placed between the bridge and the top slab of the vaulted abutment.
Front walls are added to the abutment in order to enclose the vault and limit access from outside.
The inspection vault is reached from inside the bridge passing through the opening in
the abutment segment diaphragm.
Now, from inside the vault, the ends of the post-tensioning tendons are readily accessible.
Inspectors can more easily view the condition of the anchorages and perform non-destructive testing.