Project Summary Sheet

Project Summary Sheet
Project Acronym:
Name of Group Leader:
User -Project Title:
Facility:
HyIII-GWK-17
Alberto Lamberti, University of Bologna
Large-scale measurements of extreme wave loadings on
exposed jetties
Large Wave Channel GWK
Summary:
The main objective of these experiments is to
calibrate loading models on jetty decks through
the evaluation of scale corrections to existing or
improved methods. Within the HRW-Bologna-Rome
“Exposed Jetties” project wave loads were measured
in a small-scale hydraulic model. Unfortunately
compressibility of air does not allow applying Froude
scaling law to slamming and impact pressures/
forces.
During the experiments wave loads were measured
on beam and deck elements of an idealized pier deck
at close-to-full scale, which may be used for scale
corrections to existing loading models based on
small-scale data.
“Wave-in-deck forces” cover all wave forces applied
to a platform or jetty deck. Wave-induced vertical
forces on horizontal decks or platforms may be
classified as impulsive forces large in magnitude
and short in duration occurring at the instant of
contact between the wave crest and the platform
of the deck, followed by a pulsating positive and/
or negative force. Different methods were used to
separate impulsive and pulsating loads, and thus to distinguish between loads that can certainly
be applied using quasi-static assumptions, and those that will require consideration of the dynamic
characteristics of the jetty.
Regarding the structure, the following configurations were tested: a flat deck and a deck with lower
beams forming three bays with and without venting. Wave pressures on the front face, on upper
deck surface and on lower deck surface were measured by 24 pressure transducers. Impulsive
loads are proportional to sound celerity in water, in its turn dependent on air entrainment;
therefore aeration is measured with three combined pressure and aeration transducers (developed
by University of Plymouth), installed on the deck front, on the deck central bay and on the
channel bed. Forces on the deck are obtained by integration of measured pressures. Some of the
transducers are mounted facing upward to measure inundation loadings. Data were acquired at 4
kHz sampling frequency.
Wave loading on a suspended deck was measured under several wave attacks. Regular and
irregular wave attacks were used in 4 and 5 m water depth, as well as focused wave groups to
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Project Summary Sheet
generate the highest waves in irregular attacks that could not be generated in their entirety.
Measurements included incident, reflected and transmitted waves, and velocity profiles along the
vertical in front of the structure. Videos are available for all tests.
Wave loading was measured under very well documented conditions and with a very high time
resolution. Data are compared with small scale tests results according to Froude scaling law
and differences were identified. A scaling law for loading accounting for scale effects due to air
compressibility and different air content was proposed and verified.
The focused wave group technique, which could allow much shorter tests enabling evaluation of
extreme loads, was verified by comparison with long duration irregular wave tests.
The existing guidelines (K. McConnell et al., 2004) will be updated if necessary accounting for the
new results, providing in any case more reliable estimates of full scale loading.
Publications:
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