Akademik Veri Yönetim Sistemi
Tezin Türü: Doktora
Tezin Yürütüldüğü Kurum: Yıldız Teknik Üniversitesi, Fen Bilimleri Enstitüsü, Türkiye
Tezin Onay Tarihi: 2020
Tezin Dili: İngilizce
Öğrenci: SAIF ALDIEN SAMI SHAKIR SHAKIR
Danışman: Fatih Alemdar
Özet:
Orthotropic steel decks (OSDs) are one of the most choosen solutions when the
dead-weight is the primary concern. Especially for bridges which are movable or
have long-spans weight of the structure becomes important. Due to their light
construction style and low rigidity under heavy wheel loads, significant structural
safety issues regarding to the fatigue have been observed on these type of bridges.
Fatigue problems manifest themselves as cracks running through especially in the
connections and over time these can be even greater concern as the traffic loads
almost always tend to increase. It was found that most of the fatigue cracks occurred
at the welded connection details, such as the rib-to-deck plate, rib-to-diaphragm,
and rib-to-diaphragm-to-deck plate (RDDP). These connections are sensitive to
fatigue cracking due to highly concentrated stress and residual stress at welded
connections. In particular, rib-to-rib (RR) butt-welded connections are also among
the most prone locations to fatigue type failure in OSDs and in considerable number
of bridges these fatigue cracks which are related with sensitive details have been
reported. Due to dynamic factors in their service life bridges with an orthotropic steel deck (OSD) are prone to fatigue cracking and failure. Studies concerning the
cases which use (RR) butt-welded connections are limited in the literature. In this
study, a set of cyclic loading experiments is carried out for the investigation of the
fatigue life and crack propagation characteristics of full-scale rib-to-rib (RR) buttwelded connections with trapezoidal cross-sections. Then two repairment methods
based on bonded carbon fiber reinforced polymer layers (CFRP) and bolted steel
plates (BSP) for the failed specimens are utilized and fatigue life improvements are
tested on the repaired specimens. In the bonded CFRP method, five layers of CFRP
were bonded to the existing damaged longitudinal ribs with an epoxy resin layer. In
the bolted steel plates method, the steel plates were bolted to the existing damaged
longitudinal ribs by bolts. Both repairments are considered lightweight
propositions (between 2 and 13 kg/m2), which is especially important in movable
bridge applications. The aim of applying the repair is to reduce the stresses at the
(RR) butt-welded connections and extend the fatigue life of orthotropic bridge
decks. The cyclic test rig is first verified under static loading with strain gage
readings which are compared to finite element simulations. Then failure modes and
stiffness curves are obtained with cyclic experiments. Crack growth characteristics
are observed as provided by dye-penetrant and dynamic stiffness crack detection
methods. Crack lengths against the number of cycles were recorded for construction
of the fatigue strength (S-N) Curves as given in AASHTO (2007). Test revealed that
as long as the bond quality of the CFRP layers the steel plates was maintained, the
decrease in stress demand was enough to extend the fatigue life from AASHTO
fatigue-design Category E’ for the unrepaired configuration to the infinite fatigue life
range. Test results also showed that the dynamic stiffness curve was drastically
improved for the repaired specimens. To better understand the experimental
results a numerical study based on finite element simulations is undertaken as well.
The stress field for specimens with cracks is obtained. The improvement of the
crack-tip stress field and J-values are shown for the repaired specimens in the
simulations. The results indicate remarkable decrease in stress levels in fatigue
sensitive details after the application of proposed repair methods. Overall, the
performance of these two lightweight methods for repairing movable OSD proved
to be efficient and durable. A step forward in the design approach of evaluating the
repairment of (RR) butt-welded connections in OSD has been established