341 Introduction

Fatigue and fracture are two important limit states that need to be checked in the design and evaluation of structures. Fatigue is the formation of a crack due to cyclic loading. The fatigue limit state is defined as the development of a through-thickness crack. This is a serviceability limit state and does not necessarily mean that the structure is in danger of fracture or collapse. Fracture is the rupture in tension or rapid extension of a crack leading to gross deformation, loss of function or serviceability, or complete separation of the component.

This section of the handbook presents an overview of information useful to structural engineers in evaluating the fatigue and fracture limit states of steel, aluminum, and concrete structural components. Topics include materials selection, design, and detailing for new structures, as well as assessment of existing structures. The emphasis of this chapter is on structural steel components, since aluminum and other metal components are not common in the primary load-carrying systems of most civil structures. Fatigue of concrete components is covered only briefly since it is rarely a significant problem. As a practical matter, fracture of concrete is checked by usual strength design calculations and therefore is not covered here. The fracture mechanics of concrete is covered elsewhere [1].

Although most of the examples involve buildings or bridges, the information is equally applicable to similar details in cranes, ships, offshore structures, heavy vehicle frames, etc. The primary difference between various structure types is in the applied loading, whereas the type of structure does not affect the resistance of the details to fatigue or fracture.

Since the scope of this section is limited to practical information, there are many interesting aspects of fatigue and fracture that are not discussed. There are several good texts that can serve as a starting point for more in-depth studies [2-4].

0 0

Post a comment