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Harbor
Upgrade Reinforcement
Introduction
Important parameters for external reinforcing are stiffness, strength,
flexibility, durability, and reliability. Carbon fiber reinforced
plastic (CFRP) was chosen to externally reinforce the Bravo 25 deck
because of its high strength-to-weight ratio and other beneficial
characteristics. Due to its high strength and low weight, additional
reinforcing could be added to the existing steel reinforced concrete
without adding excessive mass. CFRP high strength and stiffness
translated to smaller amounts of reinforcing which yielded an easier
installation that is more efficient. CFRP is corrosion resistant
and possesses outstanding fatigue properties. It strengthens and
stiffens existing reinforced concrete sections while it mitigates
crack width and growth. CFRP also restricts crack growth into the
compression zone of the section, thereby increasing the punching
shear strength of the concrete deck slab.
Of all fibers, NFESC has determined high strength carbon possessed
the best resistance to the extremes of the maritime industrial environment.
It required the least amount of intrusion into the top of the deck
for embedded reinforcement and the least quantity and effort to
add to the bottom surface to achieve required strength and stiffness.
The upgrade design process necessitated an analysis to determine
the structural response to required loading and calculation of the
existing structural resistance. External CFRP reinforcing was then
added to those elements where the required response exceeded the
structural resistance. The resistance of the upgraded elements is
greater than the required load response plus a factor of safety
greater than 2.
Problematic Traits. CFRP has no plastic deformation prior to rupture,
so plastic hinges for load redistribution do not form in the traditional
sense of steel reinforcing. Epoxy thermal expansion coefficients
are 7 times larger than concrete. Different thermal properties will
increase stress between the concrete and adhesive interface. Cutting
slots to embed CFRP rods on the top side will increase chances of
initiating concrete cracks at the slot root that runs parallel to
the reinforcement.
Risks Affecting Safety. CFRP lacks a lengthy track record in civil
structures, which presents several risks. CFRP lacks reliable quality
control for strength and geometric properties. It is subject to
impact damage and precautions must be taken to protect it from exposure
in industrial areas. The long-term effects of the waterfront environment
such as saltwater, high humidity, etc., on the concrete CFRP bond
line are not well established. The fatigue strength and creep rates
of the CFRP-concrete interface are not known. Most cold setting
epoxies experience a decline in shear modulus and a reduction in
shear strength at high temperatures from solar radiation.
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