e-mosty June 2017: Osman Gazi B. US Suspension. Hålogaland B. e-mosty June 2017: Suspension Bridges | Page 52

Figure 3: AECOM cable dehumidification projects in the UK – Forth Road ←, M48 Severn ↑, Humber →
The principle of dehumidification is applied to
suspension bridge cables by developing dry air within
mechanical plant rooms and then injecting the dried-
air into the cables. The cables are wrapped with an
elastomeric membrane and heat sealed to keep the
dry air in and water out. 3. BAY BRIDGE DEHUMIDIFICATION PROJECT
Once the dry air is in the cable, it travels through the
voids between the cable wires or strands, resulting in
a drying process with the residual moisture from
within the cable removed at the exhaust points as
moisture laden air (Figure 5). Since cable dehumidification was new to the United
States, the Maryland Transportation Authority
decided to use a Design-Bid-Build (DBB) project
delivery method, but combined it with a single-step
Competitive Sealed Proposal (CSP) procurement
method to incorporate both a technical and price
component in the selection process.
When the dry air is first injected into the cables, the
drying process begins. This is where any pre-existing
condensate is removed from the cable.
The design of the dehumidification systems was
initiated in 2009/2010 with procurement of the
construction contract in 2011.
The technical proposal required the prospective
bidders to submit both qualifications and technical
approach to perform the work.
In accordance with Maryland regulations, the
technical and price proposal were submitted
concurrently and each was equal-weighted in the
As this occurs, the relative humidity is reduced until it
is below the critical threshold where it is then
sustained such that corrosion becomes practically
negligible. The system operates on a continuous basis
thereafter.
3.1 Contract Overview
0
20
40
60
80
Relative Humidity %
100
Figure 4: Relationship between corrosion and RH
Figure 5: Cable voids used to inject dry air
2/2017