A　novel　method　for　fatigue　reliability　assessment　of　welded　joints　in　steel　bridges　is　proposed　by　considering　multiple　effects　in　terms　of　the　stress　concentration　phenomenon　at　the　welded　joint　as　well　as　the　reduction　of　the　effective　cross-sectional　area　and　the　degradation　of　the　fatigue　behavior　due　to　steel　corrosion.　The　proposed　method　is　applied　to　assess　the　fatigue　reliability　of　a　typical　welded　joint　in　the　instrumented　Tsing　Ma　Bridge　using　the　long-term　strain　monitoring　data.　By　exploring　the　stochastic　characteristics　of　the　hot　spot　stress　range,　the　reduction　model　of　the　cross-sectional　area,　and　the　fatigue　behavior　degradation　function　of　the　welded　joint,　a　fatigue　reliability　model　considering　multiple　effects　is　developed　in　the　framework　of　a　continuous　probabilistic　formulation　of　Miner＇s　damage　cumulative　rule.　A　standard　daily　stress　spectrum　accounting　for　highway　traffic,　railway　traffic,　and　typhoon　effects　is　derived　by　statistically　analyzing　the　long-term　strain　monitoring　data.　A　multi-modal　Probability　Density　Function　(PDF)　of　the　standard　daily　stress　spectrum　is　obtained　by　use　of　the　method　of　finite　mixture　distributions　in　conjunction　with　a　Genetic　Algorithm-based　(GA-based)　mixture　parameter　estimation　approach.　A　comparative　study　is　conducted　to　investigate　the　effects　of　stress　concentration　and　steel　corrosion　(i.e.,　reduction　of　the　effective　cross-sectional　area　and　degradation　of　the　fatigue　behavior)　on　the　failure　probability　and　reliability　index　versus　the　predicted　fatigue　life　of　the　welded　joint.　The　results　show　that　the　fatigue　reliability　of　the　welded　joint　is　significantly　influenced　by　the　effects　of　stress　concentration　and　steel　corrosion.