دانلود رایگان مقاله انگلیسی عملکرد خستگی اسلب های بتنی مسلح شده متعامد: تحقیقات تجربی - الزویر 2018

ABSTRACT

The fatigue performance of reinforced concrete slabs was investigated under clearly defined bending conditions with large scale tests. Two series of four tests exhibiting orthogonal reinforcement layouts at different orientations were subjected to constant force-amplitude cyclic loading. The reinforcement direction in the reference series of tests coincided with the direction of principal moment. In the second series of tests, a deviation of 45° between the principal moment and reinforcement direction was introduced. The effect of inclined reinforcing bars with respect to the principal moment direction on the fatigue strength of structural concrete slabs is described. Direct measurement of reinforcing steel strains enabled a characterisation of the redistribution of internal forces within the cross-section after failure of individual bars until global failure of the slab.

7. Conclusions

The present experimental campaign was carried out to investigate the fatigue performance of orthogonally reinforced concrete slabs wherein the principal moment and reinforcement direction do not coincide. On the basis of the experimental results, a number of conclusions could be drawn with regards to the load-carrying behaviour of slabs under high levels of cyclic loading. The main conclusions can be summarised as follows:

7.1. General

Fatigue represents a realistic hazard scenario for reinforced concrete slabs with a typical reinforcement content. For predominant bending action, a relatively gradual but continuous deterioration of the loaddeformation behaviour is observed. Measurable changes in structural response occur upon failure of individual bars; especially pronounced were the increases in reinforcing steel strains. A detailed inspection of the exposed bar fractures in all four tests indicate that the local milling of the instrumented bars along the longitudinal rib, as indicated in Fig. 5, was not significantly detrimental for the fatigue properties. Out of a total of 50 bar fractures, only two occurred within the milled regions. Changes in the concrete deformations on the slab top surface and soffit were also observed upon reinforcement rupture. The occurrence of bar failures was characterised by localisations of concrete strains and curvatures in the critical cross-sections. Furthermore, local increases in crack widths were observed in the proximity of bar fractures as well as the formation of secondary cracks in some cases. Global failure in bending occurs when the residual flexural strength, following rupture of individual reinforcing bars, falls below the bending demand. Such a mode of failure was observed in all four tests.