e-mosty June 2017: Osman Gazi B. US Suspension. Hålogaland B. e-mosty June 2017: Suspension Bridges | Page 48

along the cable. The estimated strength of the cables
therefore requires statistical extrapolation from the
relatively small amount of data collected. Cable wires
gradually deteriorate through corrosion, crack
initiation, and crack growth, culminating in a sudden
break. This releases energy which can be detected
through a network of acoustic sensors. Dehumidification was programmed for installation
following internal cable investigations, which revealed
the existing cable protection strategies were less than
effective. The design of the system was initiated in
2010 and the Westbound Bridge dehumidification
system was commissioned in 2014, while the
Eastbound Bridge was commissioned in 2015.
Some bridge owners have installed acoustic
monitoring systems that listen 24/7 to the whole
length of the cables for breaking wires. This provides
valuable and in some cases crucial important long-
term information on the structural health of main
cables. Following the Bay Bridge, AECOM designed the cable
dehumidification on the twin suspension bridges
making up the Delaware Memorial Bridges between
Delaware and New Jersey. Construction began in early
2016 and the cable dehumidification systems are
anticipated to be completed by late 2017 to early
2018.
Two key pieces of data are generated by the acoustic
monitoring – hotspots indicating significant wire-
break activity and the long-term trend of cumulative
wire breaks. This data enables the bridge owner to
have an increased knowledge and confidence in the
actual health of the cables.
Since 2010, eight bridges are now in various stages of
project development or delivery (Table 1), equating to
nearly 25% of the US major cable suspension bridge
inventory.
Cable strength and durability are influenced by many
complex interrelated factors including construction
quality, long-term performance of constituent
materials, and human responses to these. As main
cables are the primary load carrying elements of the
structure, it is important that their condition is known
and closely monitored. Diminishing tensile strength
factor of safe