دانلود رایگان مقاله انگلیسی پلیمر تقویت شده فیبر به عنوان تقویت خارجی برای لنگر درجا سیگنال در لولای پلاستیکی - الزویر 2018

ABSTRACT:

This paper presents a test of cast-in anchors in the plastic hinge zone of a reinforced concrete column. Design codes, such as ACI 318-11, do not allow concrete anchors in concrete that could be substantially damaged during an earthquake unless special reinforcement is provided. Steel reinforcement has been proven effective in protecting core concrete; however, it does not protect cover concrete, which is critical to the shear behavior of anchors. Fiber reinforced polymer (FRP) composite material was used in this study to protect cover concrete around the test anchors. The column specimens were subjected to quasi-static cyclic loading while the single anchors were loaded in cyclic shear. Compared with the anchors in unprotected concrete, the FRP reinforced anchors developed a higher shear capacity at a much smaller displacement. This indicates that FRP fabrics can be effective as external reinforcement for concrete anchors. Meanwhile, a systematic study is needed before practical applications.

5. Conclusion

Steel braces may be used to strength reinforced concrete (RC) frames, in which anchor connections must be installed in the plastic hinge zones of RC members. The current design codes, such as ACI 318-11, require special reinforcement for anchors in potentially damaged concrete. Anchor reinforcement has been developed for anchors in shear or tension, and verified using tests of single cast-in anchors embedded in undamaged concrete and significantly damaged concrete. The test results indicate that the special anchor reinforcement can be effective in protecting core concrete; however, the steel reinforcement cannot protect cover concrete, which is critical for the anchor shear behavior.

Fiber reinforced polymer (FRP) wrapping was attempted in this study to protect cover concrete near the anchors installed in the plastic hinge zone of a reinforced concrete column. The FRP fabrics were proportioned to carry the full design shear capacity of the anchors. The column was subjected to reversed cyclic deformation while the test anchors were simultaneously subjected to reversed cyclic loading. Compared with the anchors in unprotected concrete (Specimen S1), the anchors embedded in the concrete protected by two 51-mm [2-in.] wide FRP fabrics (Specimen S3) developed much higher shear capacity, and allowed much smaller deformation. This was largely attributed to the fact that the cover concrete spalled in Specimen S1 while the spalling was restrained by the FRP wrapping.

It is envisioned that a stiff connection is critical for the desired seismic performance of the steel braces. FRP wrapping seems a viable solution in this case. Meanwhile, further study is needed to better understand the effectiveness of FRP wrapping and to determine the anchorage requirements of the FRP fabrics as external reinforcement for concrete anchors.