On Structural Reliability
James T. P. Yao and Hiroshi Kawamura
In this paper, we summarize our viewpoints on structural reliability including the effects of structural control and symptom-based reliability. Structural reliability depends very much on temporal factors. Traditionally, structural reliability has been defined as the probability of the useful life of a given structure exceeding a certain time-period, t. At one time, Professor C. Cempel, a mechanical engineer in Poland, tested 3,000 diesel engines, all were 10-year old. Some of these engines were used almost continuously while others were used sparingly during these ten years. The symptom measured was the noise level after an engine was started. The noisier the engine, the shorter remaining life it had. The same principle may be applied to civil engineering structures. For example, consider highway bridges. Some of these bridges had high volume of heavy traffics and subject to corrosion while others with light traffic and no chance for corrosion. As another example, some buildings are subjected to heavy internal and external loads while others to light loads. However, it is not clear as to what symptoms are indicative of structural damage in these structures. Recently, many active control systems (both passive and active) have been developed and used in bridges and buildings, especially in Japan. Active control devices may be considered as additional redundancies in the structure, and thus improving the structural reliability. Fuzzy control has also been studied. In the seventies, efforts were made to apply structural reliability in design codes resulting in LRFD (Load and Resistance Factor Design) specifications. Nevertheless, almost every expert is an analyst. We believe that no further progress can be made unless more experiments will be conducted. Structural reliability will be applied to performance-based design, and structural performance should be assessed for structural sustainability and adaptability to the temporal changes of natural and social environments. Our viewpoints along these lines have been expressed herein.
existing structures, structural control, stractural reliability, symptoms, fuzzy theory