Abstract




 
   

IJE TRANSACTIONS C: Aspects Vol. 28, No. 3 (March 2015) 350-359   

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  ULTIMATE UNBONDED TENDON STRESS IN CFRP STRENGTHENED POST-TENSIONED INDETERMINATE I-BEAMS CAST WITH HSCS
 
A. A. Maghsudi and Y. Askari D.
 
( Received: August 31, 2014 – Accepted: January 30, 2015 )
 
 

Abstract    Based on the bending experiment for two-span continuous post-tension beams with unbounded tendons and externally applied CFRP sheets, the analysis of the stress increment of unbonded tendons is monitored in the loading process. Since self-compacting concrete (SCC) is a suitable innovation,, understanding the implementation of this type of concrete on the ultimate unbonded tendon stress is critical. For these aims, results of four continuous un-bonded post-tensioned I-beams in two groups were cast and monitored by electrical strain gauges andare presented here. In the first group, the beams (UPN1-12, SUPN1-12) consisted of high strength normal concrete (HSNC), while in the second group (UPS1-12, SUPS1-12) high strength self-compacting concrete (HSSCC) were tested. The beams are made which are compared with the theory proposed by different codes, and a preliminary modification is given for each code equation. The results of standard error of estimate Sy/x , indicates that for two types of HSCs (strengthened and non-strengthened beams), the ACI 318-2011 provides better estimates than AASHTO-2010 model, whereas this model provides better estimates as compared toBS 8110-97.Comparison of increase in experimental ultimate tendon stress of beams indicates that the increase in tendon stress at ultimate state in strengthened beams is lower than that in non-strengthened beams cast with HSCs.

 

Keywords    Strengthened, CFRP Sheet, Unbonded Tendons, Stress Increases, High Strength Normal and Self-Compacting Concrete, Continuous Beams

 

چکیده   

اساس آزمایش خمشی صورت گرفته برای تیرهای پس­کشیده سراسری دو دهانه، با کابل بدون پیوستگی و مقاومسازی شده و نشده با الیاف کربن، افزایش تنش در کابل­ها در مراحل مختلف بارگذاری پایش گردیده است. از آنجاکه بتن خودمتراکم، اختراعی مطلوب در صنعت بتن به شمار می­آید، لذا آشنائی با تاثیر این نوع بتن بر افزایش تنش در چنین کابل­هائی امری ضروری است. در مقاله حاضر، آزمایشبارگذاری چهار تیر یپیوسته پس کشیده با مقطع I شکل که در دو گروه مجزا ساختهو با نصب انواع کرنش سنج­های الکتریکیدر حین بارگذاری پایش، و نتایج مربوطهارائهشدهاست. گروه اول، شاملتیرهای (UPN1-12, SUPN1-12) ساخته شده با بتن معمولی مقاومت بالا و گروه دوم شامل تیرهای (UPS1-12, SUPS1-12) ساخته شده با بتن خودمتراکم مقاومت بالا می باشد. همچنین، مقایسه نتایج آزمایشگاهی تیرها با آیین­نامه­های مختلف ارزیابی شده و اصلاح مقدماتی در روابط هر یک از آئین نامه­ها پیشنهاد شده است. نتایج حاصل از تخمین خطای استاندارد (sy/x) نشان داد که آیین­نامهACI318-2011نسبت به آیین­نامه AASHTO-2010 و آیین­نامه AASHTO-2010 نسبت به آیین نامه BS 8110-97 تخمین بهتری از تنش در کابل­های فاقد پیوستگی در حالت نهایی دارد. به علاوه، میزان افزایش تنش در حالت نهایی در تیرهای مقاومسازی شده کمتر از تیرهای مقاومسازی نشده (ساخته شده با بتن مقاومت بالا) می­باشد

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