دانلود رایگان مقاله رفتار باند آلیاژ حافظه دار (SMA) شن و ماسه پوشش داده شده در میلگرد در بتن

Abstract

The distinct superelastic properties and flag shape hysteresis of shape memory alloys (SMAs) make them an ideal candidate for the design and development of various structural components in civil infrastructure. Due to the fact that SMA reinforcement has significantly different properties than conventional steel, structures reinforced with SMA will behave differently. The design equations used for steel reinforced concrete structures are not applicable while using SMA as reinforcement in concrete. This study investigated the bond behavior of SMA rebars (with and without sand coating) in concrete using 56 pushout specimens. The test results are explored to evaluate the influence of concrete strength, bar diameter, embedment length, and surface condition. Surface modification using sand coating notably improved the bond strength of SMA rebar. Finally, empirical equation based on statistical analyses is presented to predict the maximum average bond strength. The proposed equation reasonably calculates the average bond strength of SMA reinforcing bars in concrete.

7. Summary and conclusions

This study investigated the bond behavior of smooth and sand coated shape memory alloy bars in concrete. Experimental investigations were carried out using pushout tests to investigate the influence of concrete strength, bar diameter, concrete cover, embedment length, and surface condition on the bond strength of SMA rebar. The results from 56 pushout tests lead to the following conclusions: 1. The stress–slip curve of SMA rebar can be divided/idealized into four stages: elastic stage, ascending stage, linearly descending stage and residual stage. 2. The surface roughness of SMA rebar significantly affects the failure pattern as well as the bond strength. Concrete with smooth SMA rebars resulted in simple pushout failure whereas sand coated rebars resulted in splitting failure. 3. The bond strength of both smooth and sand coated SMA rebar is significantly influenced by the concrete strength, bar diameter and embedment length but is independent of concrete cover. 4. The application of sand coating increased the bond strength between concrete and SMA rebar by developing friction and interlocking forces in addition to the adhesion mechanism. The coarser the sand size, the more is the improvement in bond strength. 5. A new equation for calculating the bond strength of SMA rebar in concrete is proposed based on the experimental study. For different strengths of concrete, bar diameters, surface condition and embedment length, the proposed equation is in good agreement with the experimental results. The present study only considered pushout tests for investigating the bond behavior of SMA rebar in concrete. Further study need to be conducted considering SMA reinforced beams with and without lateral reinforcement. Further study needs to be carried out considering different types of SMA rebar to develop a more comprehensive bond–slip relationship for SMA rebar in concrete.