عملکرد لرزه ای ستون های بتنی مسلح با استحکام بالا
Abstract
1- Introduction
2- Experimental program
3- Test results and discussion
4- Effect of section size on moment capacity
5- Conclusions
References
Abstract
It has been shown that as concrete strength increases, the size effect becomes more pronounced in both samples and members. However, the effect of section size on the seismic performance of high-strength reinforced concrete columns requires further confirmation. For this purpose, six high-strength reinforced concrete columns were subjected to monotonic and cyclic loading in this study. The experimental results indicate that the relative nominal flexural strength, average energy dissipation coefficient, factor of safety, and local factor of safety all exhibited a strong size effect by decreasing as the column size increased. Moreover, the size effect on the factor of safety was stronger for high-strength columns than for conventional columns. The observed changes in the factor of safety were in good agreement with the Type 2 size effect model proposed by Bažant; so, using the local factor of safety and Bažant’s Type 2 model, the code equation for moment capacity was modified to provide a constant factor of safety regardless of column size.
Introduction
As the scale of engineering structures increases, the safety of their larger components has become one of the primary topics of concern, especially when taking into account the use of high-strength concrete [1]. The size effect, defined as the change in structural behavior with changing size rather than material, though not yet captured by the conventional design process, is increasingly accepted in theory [2–10]. Indeed, a large number of experimental results have demonstrated that the size effect exists in plain concrete samples and structural concrete components, such as plain concrete columns [11,12], reinforced concrete (RC) beams [13–15], RC columns [16–18], and RC beam-column joints [19–20]. Moreover, the size effect has been found to be more significant in high-strength concrete than in conventional concrete [1,12,21,22], but the size effect on the seismic performance of highstrength RC columns remains to be determined. In this study, the classical model of the size effect law was first investigated so that the correct theoretical model could be applied to a structural design. The scaling problem of primary interest is the effect of a structure’s size on its nominal strength [2]. The structural ultimate load predicted by any deterministic strength theory (e.g. the elastic, plastic, or elastoplastic strength criteria) applied to ductile materials exhibits no size effect. In 1921, Griffith [3] proposed linear elastic fracture mechanics (LFEM) and introduced fracture mechanics into the study of size effect. For brittle, geometrically similar structures, linear elastic fracture mechanics shows that nominal strength decreases as structure size increases, following the trend of an inclined asymptote with a slope of −1/2. Then Weibull [4,5] derived an equation capturing the size effect on mean structural strength based on the Weibull distribution. This approach is certainly valid for various fine-grain ceramics and for metal structures embrittled by fatigue. Bažant identified the Type 1 size effect [2,8], the Type 2 size effect [6], and the universal size effect law [9]. These laws are suitable for quasi-brittle materials, such as plain concrete samples and components, whose properties are between those of ductile and brittle materials.