Text

theses

Stiffened and unstiffened fillet-welded tube-to-transverse plate connection details are widely used for mast-arm and base-plate connection in highway support structures in New Jersey and many other states. However, repetitive wind loads which induce cyclic fatigue stresses are the primary source of failure at fatigue critical locations such as tube-to-stiffener and tube-to-base plate welded connection. The resistance of fatigue critical connections details has been an on-going research topic due to limited experimental work and the variability in existing fatigue testing results.
The main objective of this dissertation is to evaluate fatigue resistance of both unstiffened and stiffened fillet-welded tube connection details. Synthetic data analysis, Finite Element (FE), strain-life corrosion fatigue resistance model, fatigue reliability analysis were performed to determine the fatigue performance of fillet-welded connections.
Existing fatigue test data was collected to perform a synthetic data analysis and then analysis results were used to as fatigue input data in ANSYS Workbench platform and for the proposed SWT corrosion model. The fatigue resistance obtained from the FE analysis is expressed in terms of fatigue life, fatigue damage, and fatigue safety factor. The local stress level at fatigue critical locations was evaluated using a static FE model for different number of stiffeners and boundary conditions.
The effect of corrosion on the fatigue resistance on stiffened fillet-welded tube connection was studied using a modified Strain-Life Smith-Watson-Toper (SWT) corrosion model. Chemical components and material properties of ASTM steels were also investigated for corrosion-resistant weathering steel and low-carbon steel. Corrosion Index, I, was obtained to estimate the corrosion resistance by following the equations from ASTM G101 Standards (ASTM G101, 2004). Under various corrosion categories, the proposed Constant Amplitude Fatigue Thresholds (CAFT) were obtained for weathering steel, low-carbon steel, hot-dip galvanized steel, and fillet-welded connection details.
This dissertation also includes a reliability-based fatigue assessment for the potential crack initiation at the tip of stiffeners at the tube-base plate connection. A synthetic analysis of 1-hour averaged wind data from two New Jersey weather stations was performed. The wind data was transformed to the transient domain to represent the turbulent natural wind phenomena and effective stress ranges and number of cycles were obtained using the Rainflow counting technique. A statistical analysis for existing test data was conducted to obtain stress-life (S-N) fatigue coefficients. Results from the reliability-based assessment and the probabilities of crack initiation can provide needed information to state officials for establishing inspection frequencies of tube-to-transverse plate connections of sign structures.

ETD_9148

doi:10.7282/T3T72N3X

Ph.D.

Includes bibliographical references

by Hyungjoo Choi

ETD doctoral

The author owns the copyright to this work.