Issue 9

Z.H. Qian et alii, Frattura ed Integrità Strutturale, 9 (2009) 105 - 112; DOI: 10.3221/IGF-ESIS.09.11 106 From the British Standard BS5400 is one of the most important specifications in the last century [2] , and recently, some new specifications or standards were accomplished, such as Eurocode3 (2004) [3] and AASHTO (2005) [4]. These specifications provide a mass of information to design steel bridges. Among of these, Eurocode 3 and AASHTO already have some specific guidelines to orthotropic deck bridges. S-N curves in Eurocode 3, for fatigue design, are shown in Fig. 1. Figure 1 : Fatigue strength curves for direct stress ranges (Eurocode3, 2004). The orthotropic deck is consisted by a deck plate supported in two mutually perpendicular directions by transverse diaphragms (or crossbeam) and longitudinal stiffeners (or ribs). It is effectively an ORTHOgonal anisoTROPIC (orthotropic) deck. Orthotropic deck is widely utilized for long span bridges in recent decades with the development of computing methodologies and fabricating technologies. It was first used in Germany after the Second World War in order to reduce the construction material, since steel being in short. Nowadays, orthotropic deck bridges are very popular in Europe, particular in Germany. Meanwhile, more and more orthotropic bridges are being built in China, Japan, U.S.A., and other countries. Orthotropic deck has many advantages, main of one is the light weight, high strength, few deck joints, durability, rapid construction and life-cycle economy. However, fatigue problem is unavoidable at orthotropic deck bridges due to the complex structure and the large number of welded connections. Fig. 2 shows a summary of welded connection details at orthotropic deck bridges [5] . It is obvious that most of these are potentially liable to cause fatigue cracking taking account into concentrated stress and residual stress in welded connections. In the past years various technologies were studied to improve the fatigue performance of welded joints. The fatigue life can be increased through surface treatment, reducing residual stress as well as optimizing design of structure. Among of these, peening, as a cold treatment technology, is one of the most widely utilized in engineering, bringing better surface properties and producing beneficial compressive stress [6]. Both of them can improve the fatigue strength of welded connections. This last technology is still highly improving. Figure 2 : Main welded connections in a typical orthotropic bridge deck (Gurney, 2006)