Repair of steel bridge girders damaged by distortion-induced fatigue
Tez Türü: Doktora
Tezin Yürütüldüğü Kurum: University of Kansas, yüksek lisans fakültesi, Amerika Birleşik Devletleri
Tez Danışmanı: Adolfo B. Matamoros
Tezin Onay Tarihi: 2011
Tezin Dili: İngilizce
Özet:
This study investigates the repair of steel bridge girders
damaged by distortion-induced fatigue. The study is presented in three parts.
The first part describes finite element modeling techniques used to evaluate
the potential for fatigue cracks in steel girders subjected to
distortion-induced fatigue. The modeling techniques employed in this study were
intended to identify areas near welded connections in bridge girders with the
highest potential for developing fatigue cracks, and to evaluate the
effectiveness of retrofit measures in reducing the potential for crack
propagation near welded connections with existing fatigue cracks. Computer
simulations correlated well with experimentally observed crack patterns and
were useful in providing an indication of the effectiveness of various retrofit
measures. The second part of the study investigates the use of composite
materials to repair fatigue damage in steel girders. A total of 17 specimens
with pre-existing fatigue cracks were tested under cyclic loading to evaluate
the performance of composite overlays when used to repair fatigue damage in
steel structures. Two control specimens were tested without overlays and the
remaining 15 were repaired with Carbon Fiber Reinforced Polymer (CFRP) overlays
of various thicknesses. Results indicate that this method was very effective,
and that proper implementation of this type of repair can reduce the crack
propagation rate to negligible values. The third part of the study consisted of
physical and computer simulations of 914-mm (36-in.) deep girder-cross frame
subassemblies subjected to cyclic loading. The simulations were carried out to
investigate the stress demands caused by distortion-induced fatigue and to
evaluate the effectiveness of various retrofit measures. Previously used repair
methods for distortion-induced fatigue damage have attempted to reduce the
stress demand in the web gap iv region by increasing the flexibility of
cross-frame to girder connection or by restraining the lateral motion of the
cross-frame by attaching the connection plate to the slab. A new retrofit
approach was investigated in this study designed to reduce the stress demand in
the web gap region by distributing the force at the girder-cross frame
connection over a larger area. A new retrofit detail is proposed based on this
approach, which consists of adding steel angles connecting the girder web and
the connection plate, and a steel bar on the back side of the girder web to
distribute the lateral force over a wider region of the web. Experimental and
computer simulation results are presented showing that this repair method is
very effective in preventing the growth of horseshoe-shaped cracks around the
web-cross frame connection and of straight cracks near the junction between the
flange and web.