e-mosty June 2018 American Bridges American Bridges | Page 39

Risk Based Inspection of Complex
Bridges in the USA
Barry Colford, AECOM
Figure 1: Inspecting the Brooklyn Bridge
1. Introduction
Currently, in the USA, the Federal Highways
Administration (FHWA) requires all bridges with a
span length equal to or greater than 20 ft. to be
inspected every 24 months as per the National Bridge
Inspection Standards 1 . In addition, the inspection of
fracture critical bridges requires 100% hands-on
access for the full-length of all fracture critical
members. The Standard also states that increased
inspection frequency may be required after
consideration of factors such age, traffic
characteristics, and known deficiencies.
In addition, individual States can establish criteria to
determine the need and level of effort required for
increased inspection frequency. It is recognized that
2/2018
complex bridges, such as movable bridges and cable
supported bridges, may require special inspection
procedures but there are no set guidelines for such
structures.
This prescriptive inspection regime based on a
minimal set interval has been written to suit State and
other local authorities with a large number of
standard shorter span bridges and has obvious
strengths and weaknesses. It ensures uniform
coverage of all structures while allowing some
flexibility but does not differentiate between simple
and more complex structures. In addition, although
there is now more and more consideration of element
level inspection, such a regime of set inspections is
difficult to apply to large complex structures.