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Fatigue and Fracture

Fatigue and Fracture 53.1 53.2 53.3 Introduction Redundancy, Ductility, and Structural Collapse Fatigue Resistance Classification of Details in Metal Structural Components • Detailing to Avoid DistortionInduced Fatigue • Classification of Details in Concrete Structural Components • Classification of Stay Cables • Characterization of Truck Loading for Fatigue Robert J. Dexter University of Minnesota John W. Fisher Lehigh University 53.4 53.5 Fracture Resistance Summary 53.1 Introduction Bridges do not usually fail due to inadequate load capacity, except when an overweight truck is illegally driven onto an old bridge with very low load rating. When bridge superstructures “fail,” it is usually because of excessive deterioration by corrosion and/or fatigue cracking rather than. | Dexter R.J. and Fisher W.F. Fatigue and Fracture Bridge Engineering Handbook. Ed. Wai-Fah Chen and Lian Duan Boca Raton CRC Press 2000 53 Fatigue and Fracture 53.1 Introduction 53.2 53.3 Robert J. Dexter University of Minnesota John W. Fisher Lehigh University 53.4 53.5 Redundancy Ductility and Structural Collapse Fatigue Resistance Classification of Details in Metal Structural Components Detailing to Avoid Distortion-Induced Fatigue Classification of Details in Concrete Structural Components Classification of Stay Cables Characterization of Truck Loading for Fatigue Fracture Resistance Summary 53.1 Introduction Bridges do not usually fail due to inadequate load capacity except when an overweight truck is illegally driven onto an old bridge with very low load rating. When bridge superstructures fail it is usually because of excessive deterioration by corrosion and or fatigue cracking rather than inadequate load capacity. Although most deterioration can be attributed to lack of proper maintenance there are choices made in design that also can have an impact on service life. Yet the design process for bridges is focused primarily on load capacity rather than durability. This chapter of the handbook will inform the reader about a particular aspect of durability i.e. the fatigue and fracture failure mode and about detailing for improved resistance to fatigue and fracture. Only aspects of fatigue and fracture that are relevant to design or assessment of bridge deck and superstructure components are discussed. Concrete and aluminum structural components are discussed briefly but the emphasis of this section is on steel structural components. The fatigue and fracture design and assessment procedures outlined in this chapter are included in the American Association of State Highway and Transportation Officials AASHTO specifications for bridges 1 . Some of the bridges built before the mid-1970s when the present fatigue-design specifications were adopted may be susceptible .