Description and Analysis of Floating Bridges

162 Pages·2017·8.66 MB·English

by  Kristina Husevåg Lund

Description and Analysis of Floating
Bridges
Kristina Husevåg Lund
Marine Technology
Submission date: June 2017
Supervisor: Bernt Johan Leira, IMT
Norwegian University of Science and Technology
Department of Marine Technology

Description and Analysis of
Floating Bridges
Kristina Husev˚ag Lund
June 9, 2017
Supervisor: Professor Bernt Johan Leira
Department of Marine Technology

Preface
This master’s thesis is the product of the work performed by student Kristina
Husev˚ag Lund during the spring semester 2017 at the Norwegian University of
Science and Technology. The master’s thesis is based on the work performed in
the project thesis during the fall of 2016. The assignment has been to demon-
strate how static and dynamic analyses can be performed on a simplified model of
a floating bridge. The chosen bridge is a proposed crossing of Bjørnafjorden. In
addition, threeotherbridgeswereanalysedtostudyhowvariationsofcross-section
geometry and number of supports affect the responses.
The scope was purposed by my supervisor Professor Bernt Johan Leira, and I
would like to thank him for guidance throughout the work with my thesis. Fi-
nally, I would like to thank my classmates for help when performing the analyses
and for proofreading.
Trondheim, June 9, 2017
Kristina H. Lund
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Abstract
During the project Ferry-free coastal route E39, directed by National Public Road
Administration,NPRA,sevenferry-crossingsareintendedtobereplacedbystraight
crossing. One of these is Bjørnafjorden, where a proposed crossing is a multi-span
suspension bridge, supported by two tension leg platforms, TLPs. A simplified
model of this proposed crossing was created in Abaqus/CAE. Further, three ad-
ditional models were created to study how the number of supports and alteration
of cross-section affect the responses.
The first two horizontal eigenfrequencies were compared to available eigenfrequen-
cies from NPRA. All models had higher eigenfrequencies, which indicates that the
models are stiffer, or that the mass and added mass are smaller, or a combination.
For the static analysis, three loads were applied. These were current at the floater
and traffic and wind along the bridge. The environmental loads were determined
for 1-year, 50-year and 100-year return periods. The longitudinal and vertical dis-
placement along the bridge, in addition to bending moment, were determined for
every model. When the number of supports were increased, the vertical displace-
ment was significantly reduced, while the largest vertical displacement occurred
for the model with reduced thickness of the horizontal beams in the cross-section.
This was also true for the longitudinal displacement when only the environmental
loads were applied.
For the dynamic analysis, an incoming harmonic wave was applied in horizontal
and vertical direction at the floater. Two wave periods were utilized; the first is a
feasible period and the second is the first obtained eigenperiod. Resonance caused
significantly larger motions for the floaters. Generally, a reduction of the cross-
section’s thickness on horizontal beams resulted in an increased sway response,
while the largest response in heave occurred for a reduced cross-section height.
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