دانلود رایگان مقاله انگلیسی مدل های کلافی برای نیمه اتصالات بتن مسلح شده افت یافته - الزویر 2018

ABSTRACT

A reinforced concrete half-joint bridge consists of suspended span dapped-end beams or a full-width deck supported on the nibs of abutments or adjacent beams. The design of their disturbed regions is traditionally performed by means of strut-and-tie modelling. The design provisions found in standards and codes can be used for the assessment of existing structures with minor adjustments. However, current documents provide limited guidance on the incorporation of deterioration aspects such as corrosion, insufficient anchorage lengths, and crack formation. Experiments performed on 12 half-joint beams demonstrated the effects of single defects, but synergistic effects were also found to exist and might lead to much higher reductions than expected from the sum of individual defects. These results were compared to different strut-and-tie models (STMs) and the application of STMs to achieve the highest lower bound estimate of the load carrying capacity is discussed. For the beams studied in the current work, the predictions based on codes and standards, combined with appropriate methods to incorporate deterioration effects, led to safe load bearing capacity estimates. However, the developed STMs seem to be, in some instances, unable to pick up alternative load paths that develop as soon as the capacity of a certain tie is reached. Hence the actual capacities might be higher than what is obtained from the STM calculations.

Conclusions

The design of disturbed regions in reinforced concrete half-joints is traditionally performed by means of strut-and-tie modelling. A truss consisting of struts and ties is assumed as a system to transfer the forces through the D-region into the B-region. The design provisions found in standards and codes can be used for the assessment of existing structures with minor adjustments. However, current documents provide limited guidance on the incorporation of deterioration aspects such as corrosion, insufficient anchorage lengths, and crack formation. To reflect corrosion, a reduction in the cross-sectional area of the reinforcing bar, and thereby the capacity of the tension tie, can be incorporated. Insufficient anchorage lengths can be taken into account using a proportional reduction in the tie capacity or by penalising the residual bond capacity. In this paper, suggestions have been made to allow assessors to incorporate longitudinal crack formation into the capacity checks. It is suggested to reduce the bond strength of the concrete by a factor ranging from 0.85 to 0.3 depending on the confinement conditions and the crack state. In some cases, the reduction factor can even be as low as 0.0. Experiments performed on 12 half-joint beams demonstrated the effects of single defects. Synergistic effects also exist and might lead to much higher reductions than expected from the sum of individual defects.