Bridge Technology Series: Improving Inspection Access at Segmental Bridge Abutments

Bridge Technology Series: Improving Inspection Access at Segmental Bridge Abutments


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.

Danny Hutson

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