Mobile QR Code QR CODE
Export citation EndNote

  1. ๊ณต์ฃผ๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ & ๋„์‹œ์œตํ•ฉ์‹œ์Šคํ…œ๊ณตํ•™๊ณผ ๋Œ€ํ•™์›์ƒ (Graduate Student, Department of Architectural Engineering & Urban Systems Engineering, Kongju National University, Cheonan 31080, Rep. of Korea)
  2. LH๊ณต์‚ฌ ํ† ์ง€์ฃผํƒ์—ฐ๊ตฌ์› ์ฑ…์ž„์—ฐ๊ตฌ์› (Assistant Research Fellow, Land & Housing Institute, Korea Land & Housing Corporation, Daejeon 34047, Rep. of Korea 3)Assistant Manager, Iโ€™ST Structural Engineering Group, Seoul 05836, Rep. of Korea )
  3. (์ฃผ)์•„์ด์ŠคํŠธ ๋Œ€๋ฆฌ (Assistant Manager, Iโ€™ST Structural Engineering Group, Seoul 05836, Rep. of Korea)
  4. ๊ณต์ฃผ๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ ์—ฐ๊ตฌ๊ต์ˆ˜ (Research Assistant Professor, Department of Architectural Engineering, Kongju National University, Cheonan 31080, Rep. of Korea)
  5. ๊ณต์ฃผ๋Œ€ํ•™๊ต ๊ฑด์ถ•๊ณตํ•™๊ณผ & ๋„์‹œ์œตํ•ฉ์‹œ์Šคํ…œ๊ณตํ•™๊ณผ ๊ต์ˆ˜ (Professor, Department of Architectural Engineering & Urban Systems Engineering, Kongju National University, Cheonan 31080, Rep. of Korea )



์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ, ์ˆœ์ˆ˜๋น„ํ‹€๋ฆผ, ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ, GFRP ์‹œํŠธ, ์„ฌ์œ  ๋ณด๊ฐ• ๋ฐฉํ–ฅ
reinforced concrete, pure torsion, torsional strength, GFRP sheet, fiber reinforcing direction

1. ์„œ ๋ก 

์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๊ตฌ์กฐ๋ฌผ์—์„œ ์ฝ˜ํฌ๋ฆฌํŠธ ์ค‘์„ฑํ™”, ์˜ˆ์ƒ์น˜ ๋ชปํ•œ ์™ธ๋ถ€ํ•˜์ค‘, ์šฉ๋„๋ณ€๊ฒฝ์— ์˜ํ•ด ์ฆ๊ฐ€๋œ ํ•˜์ค‘์€ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๊ท ์—ดํญ ์ฆ๊ฐ€ ๋ฐ ๋‚ด๋ ฅ์ €ํ•˜๋ฅผ ์œ ๋ฐœํ•œ๋‹ค. ๋‚ด์™ธ๋ถ€ ์ž๊ทน์— ์˜ํ•ด ์†์ƒ์„ ์ž…์€ ๊ตฌ์กฐ๋ฌผ์€ ๋‚ด๊ตฌ์—ฐํ•œ ํ™•๋ณด์™€ ์œ ์ง€๊ด€๋ฆฌ ์ธก๋ฉด์—์„œ ๋ณด๊ฐ•๋˜์–ด์•ผ ํ•œ๋‹ค. ๊ตฌ์กฐ๋ฌผ์˜ ๋ณด๊ฐ•์„ ์œ„ํ•˜์—ฌ ๊ธฐ์กด์—๋Š” ๋ถ€์žฌ์˜ ๋‹จ๋ฉด์ฆ์„ค ๋ฐ ๊ฐ•ํŒ์˜ ์—ํญ์‹œ ์ ‘์ฐฉ์— ์˜ํ•œ ๋ณด๊ฐ•๊ณต๋ฒ•์ด ์ฃผ๋ฅผ ์ด๋ฃจ์—ˆ์œผ๋‚˜, ์ตœ๊ทผ์—๋Š” ์ค‘๋Ÿ‰ ๋Œ€๋น„ ๋†’์€ ๊ฐ•๋„๋ฅผ ๊ฐ€์ง€๋ฉฐ ๊ฒฝ๋Ÿ‰์„ฑ, ๋น„์ „๋„์„ฑ, ๋‚ด๋ถ€์‹์„ฑ ๋“ฑ์˜ ํŠน์„ฑ์„ ๊ฐ€์ง€๋Š” Fiber Reinforced Polymer(์ดํ•˜, FRP)๋ฅผ ์ด์šฉํ•œ ๋ณด๊ฐ•๊ณต๋ฒ•์˜ ์ ์šฉ์ด ์ฆ๊ฐ€ํ•˜๋Š” ์ถ”์„ธ์ด๋‹ค.

FRP๋ฅผ ์ด์šฉํ•œ ๋ณด๊ฐ•๊ณต๋ฒ•์ด ๋‹ค์–‘ํ™”๋˜๋ฉด์„œ ์ด๋“ค์˜ ์„ฑ๋Šฅ๊ฒ€์ฆ์— ๋Œ€ํ•œ ์‹คํ—˜ ๋ฐ ํ•ด์„์  ์—ฐ๊ตฌ๊ฐ€ ์ง„ํ–‰๋˜์–ด ์™”๋‹ค. ์ผ๋ฐ˜์ ์ธ FRP๋Š” Glass Fiber Reinforced Polymer(GFRP)์™€ Carbon Fiber Reinforced Polymer(CFRP)๋กœ ๊ตฌ๋ถ„ํ•  ์ˆ˜ ์žˆ์œผ๋ฉฐ RC ๊ตฌ์กฐ๋ฌผ์˜ ์„ฑ๋Šฅ ํ–ฅ์ƒ์„ ์œ„ํ•ด ๋ณด์ˆ˜๋ณด๊ฐ• ์žฌ๋ฃŒ๋กœ ์‚ฌ์šฉํ•˜๊ณ  ์žˆ๋‹ค. ๊ตญ๋‚ด์™ธ์ ์œผ๋กœ FRP๋กœ ๋ณด๊ฐ•๋œ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๊ตฌ์กฐ๋ฌผ์˜ ํœจ, ์ „๋‹จ ๊ฑฐ๋™ ๋ฐ ๋ณด๊ฐ• ๋ฐฉ๋ฒ•์— ๋Œ€ํ•œ ์—ฐ๊ตฌ( Lee et al. 1997; Triantafillou 1998; Kang et al. 2008 )๊ฐ€ ํ™œ๋ฐœํžˆ ์ง„ํ–‰๋˜์–ด ์™”๋‹ค. ๋˜ํ•œ ๊ตญ์™ธ์—์„œ๋Š” 2000๋…„๋Œ€ ์ดํ›„๋กœ FRP ๋ณด๊ฐ• ์‹œ์˜ ๋น„ํ‹€๋ฆผ ๊ฑฐ๋™์— ๋Œ€ํ•œ ์—ฐ๊ตฌ( Panchacharam and Belarbi 2002; Chalioris 2008; Jariwala et al. 2013; Alabdulhady and Sneed 2019 )๊ฐ€ ๊พธ์ค€ํžˆ ์ฆ๊ฐ€ํ•ด์™”๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ๊ตญ๋‚ด์—์„œ๋Š” ํœจ, ์ „๋‹จ์— ๋น„ํ•˜์—ฌ ๋ถ€์กฑํ•œ ๊ด€์‹ฌ๋„์™€ ์ •๋ฐ€ํ•œ ์‹คํ—˜ ๊ตฌํ˜„์˜ ์–ด๋ ค์›€์œผ๋กœ ์ธํ•˜์—ฌ FRP๋ฅผ ์ด์šฉํ•œ ๋น„ํ‹€๋ฆผ ๋ณด๊ฐ•์— ๊ด€ํ•œ ์—ฐ๊ตฌ๊ฐ€ ์ „๋ฌดํ•œ ์‹ค์ •์ด๋‹ค. RC ๋ถ€์žฌ์— ๋Œ€ํ•œ FRP์˜ ๋น„ํ‹€๋ฆผ ๋ณด๊ฐ•ํšจ๊ณผ๋ฅผ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” ๋ถ€์žฌ ๋ ˆ๋ฒจ์—์„œ์˜ ๋น„ํ‹€๋ฆผ ์‹คํ—˜๊ณผ์™€ ๋ถ„์„์ด ์„ ํ–‰๋˜์–ด์•ผ ํ•˜๋ฉฐ, FRP์˜ ๋ณด๊ฐ•๋Ÿ‰ ๋ฐ ๋ฐฉ๋ฒ• ๋“ฑ์˜ ์„ค๊ณ„๋ณ€์ˆ˜๊ฐ€ ๋ณด๊ฐ• RC ๋ถ€์žฌ์˜ ๋น„ํ‹€๋ฆผ ๊ฑฐ๋™์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ์„ ๊ณ ๋ คํ•œ ์„ค๊ณ„๋ฐฉ๋ฒ•์˜ ์ œ์‹œ๊ฐ€ ํ•„์š”ํ•˜๋‹ค.

์™ธ๋ถ€ ํŽธ์‹ฌํ•˜์ค‘, ์ˆ˜์ง ๋ถ€์žฌ ๊ฐ„ ๊ฐ•์„ฑ ์ฐจ, ์ž‘์šฉ ์ˆ˜์ง ํ•˜์ค‘์˜ ๋ถˆ๊ท ํ˜• ๋“ฑ์€ ๊ตฌ์กฐ๋ฌผ์— ๋น„ํ‹€๋ฆผ ํ•˜์ค‘์„ ๋ฐœ์ƒ์‹œํ‚ค๋ฉฐ( Kim et al. 2020 ), ๊ณผ๋„ํ•œ ๋น„ํ‹€๋ฆผ ํ•˜์ค‘์€ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ถ€์žฌ์— ๋‚˜์„ ํ˜•์˜ ์‚ฌ์ธ์žฅ ๊ท ์—ด์„ ์œ ๋ฐœํ•œ๋‹ค. ์ด์— ๋Œ€ํ•œ ๋ณด๊ฐ•์ด ์‹คํ–‰๋˜์ง€ ์•Š์„ ๊ฒฝ์šฐ, ๊ท ์—ด์ด ์ง„์ „๋˜๋ฉด์„œ ๋ถ€์žฌ๋Š” ์ทจ์„ฑ์ ์ธ ๊ฑฐ๋™์„ ๋‚˜ํƒ€๋‚ด๋ฉฐ ๊ธ‰์ž‘์Šค๋Ÿฝ๊ฒŒ ํŒŒ๊ดด๋  ์ˆ˜ ์žˆ๋‹ค. ์•ž์„œ ์–ธ๊ธ‰ํ•œ FRP ์‹œํŠธ ๋ณด๊ฐ•์€ ๋น„ํ‹€๋ฆผ ๋ถ€์žฌ์— ๋Œ€ํ•œ ๋ณด๊ฐ• ๋ฐฉ๋ฒ•์˜ ํ•˜๋‚˜๋กœ ๊ทธ ์ ์šฉ ๋ฐ ํšจ๊ณผ์— ๊ด€ํ•œ ์—ฐ๊ตฌ๊ฐ€ ์ฆ๊ฐ€ํ•˜๋Š” ์ถ”์„ธ์ด๋‹ค. RC ๋ถ€์žฌ์— ๋Œ€ํ•œ FRP์˜ ๋ณด๊ฐ• ํšจ๊ณผ๋Š” FRP์˜ ์ข…๋ฅ˜, ์ง์กฐ ํ˜•์ƒ, ๋ณด๊ฐ• ๊ฐ๋„์— ํฌ๊ฒŒ ์˜์กดํ•˜๋Š” ๊ฒƒ์œผ๋กœ ์•Œ๋ ค์ ธ ์žˆ์œผ๋ฉฐ, ๋ถ€์žฌ๊ฐ€ ์š”๊ตฌ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์„ ๊ฐ€์ง€๊ธฐ ์œ„ํ•ด์„œ๋Š” ์ด๋Ÿฌํ•œ ์ฃผ์š” ์„ค๊ณ„๋ณ€์ˆ˜๋ฅผ ๊ณ ๋ คํ•ด ์ ์ ˆํžˆ ๋ณด๊ฐ•๋˜์–ด์•ผ ํ•œ๋‹ค.

FRP๋ฅผ ์ ์šฉํ•œ ๊ตฌ์กฐ๋ฌผ์— ๋Œ€ํ•œ ๋น„ํ‹€๋ฆผ ๋ณด๊ฐ•๊ธฐ์ค€ ์ค‘ Fรฉdรฉration Internationale du Bรฉton(์ดํ•˜ fib)์€ ๋ณด๊ฐ•๋ฐฉ๋ฒ•๊ณผ FRP์˜ ์ข…๋ฅ˜๋ฅผ ๊ณ ๋ คํ•œ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ํ‰๊ฐ€์‹์„ ์ œ์‹œํ•˜๋Š” ๋ฐ˜๋ฉด, ACI 440.2R-17 (2017) ์€ FRP์— ์˜ํ•ด ๋ณด๊ฐ•๋œ ๋ถ€์žฌ์˜ ํœจ ๋ฐ ์ „๋‹จ๋‚ด๋ ฅ ํ‰๊ฐ€์‹๋งŒ์„ ์ œ์‹œํ•œ๋‹ค. ์ด์™€ ๋งˆ์ฐฌ๊ฐ€์ง€๋กœ KDS 14 20(MOLIT 2021) ๋„ ์ˆœ์ˆ˜ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ถ€์žฌ์— ๋Œ€ํ•œ ํœจ, ์ „๋‹จ, ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ํ‰๊ฐ€์‹๋งŒ์„ ์ œ์‹œํ•˜๊ณ  ์žˆ์–ด FRP์˜ ์ ์šฉ์— ๋”ฐ๋ฅธ ๋‚ด๋ ฅ ์ƒ์Šน์„ ๊ณ ๋ คํ•œ ์„ค๊ณ„๊ธฐ์ค€์˜ ๋ณด์™„์ด ํ•„์š”ํ•œ๋‹ค.

์ด ์—ฐ๊ตฌ์—์„œ๋Š” FRP๋กœ ๋ณด๊ฐ•ํ•œ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ถ€์žฌ์— ๋Œ€ํ•œ ๊ตญ๋‚ด ๊ตฌ์กฐ๊ธฐ์ค€์˜ ๋งˆ๋ จ์— ๊ทผ๊ฑฐ ์ž๋ฃŒ๋กœ ํ™œ์šฉํ•  ์ˆ˜ ์žˆ๋Š” ๋ฐ์ดํ„ฐ๋ฅผ ์ œ๊ณตํ•˜๊ธฐ ์œ„ํ•˜์—ฌ GFRP๋กœ ๋ณด๊ฐ•ํ•œ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ถ€์žฌ์— ๋Œ€ํ•œ ์ˆœ์ˆ˜๋น„ํ‹€๋ฆผ ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ๋น„ํ‹€๋ฆผ ๊ท ์—ด์ด ๋ฐœ์ƒํ•œ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ถ€์žฌ์— ๋Œ€ํ•œ ๋ณด๊ฐ• ์œ ๋ฌด ๋ฐ GFRP ์„ฌ์œ  ๋ฐฉํ–ฅ๊ณผ ๋ถ€์žฌ์ถ•์ด ์ด๋ฃจ๋Š” ๊ฐ์„ ๋ณ€์ˆ˜๋กœ ํ•˜์—ฌ ์ด๋“ค ๋ณ€์ˆ˜๊ฐ€ ๋ถ€์žฌ์˜ ๋น„ํ‹€๋ฆผ ๊ฑฐ๋™์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ์„ ํ™•์ธํ•˜์˜€๋‹ค. ๋˜ํ•œ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ KDS 14 20(MOLIT 2021), fib Bulletin 14(2001) ๋ฐ Tรคljsten(2002)์˜ ์ œ์•ˆ์‹๊ณผ ๋น„๊ตํ•˜์—ฌ FRP๋กœ ๋ณด๊ฐ•๋œ ๋ถ€์žฌ์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ํ‰๊ฐ€์‹์— ๊ด€ํ•œ ๊ตญ๋‚ด ๊ตฌ์กฐ๊ธฐ์ค€ ๋งˆ๋ จ์˜ ํ•„์š”์„ฑ์„ ์ œ์‹œํ•˜๊ณ , ๊ธฐ์กด ์ œ์•ˆ์‹๋“ค์ด ๊ฐ€์ง€๋Š” ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ์˜ˆ์ธก์˜ ์ •ํ™•์„ฑ์„ ํ™•์ธํ•˜๊ณ ์ž ํ•˜์˜€๋‹ค.

2. ํ˜„ํ–‰ ๊ธฐ์ค€ ๋ฐ ๊ธฐ์กด ์ด๋ก 

2.1 KDS 14 20

KDS 14 20(MOLIT 2021)์€ ๊ณต๊ฐ„ํŠธ๋Ÿฌ์Šค ๋ชจ๋ธ์— ๊ธฐ์ดˆํ•˜๊ณ  ์žˆ์œผ๋ฉฐ, ์Šคํ„ฐ๋Ÿฝ์˜ ํ•ญ๋ณต์„ ๊ฐ€์ •์œผ๋กœ ์‹(1)๊ณผ ๊ฐ™์ด ์Šคํ„ฐ๋Ÿฝ์˜ ์ธ์žฅ๋ ฅ๊ณผ ์ฝ˜ํฌ๋ฆฌํŠธ ์ŠคํŠธ๋Ÿฟ์˜ ์••์ถ•๋ ฅ์ด ์ด๋ฃจ๋Š” ํž˜์˜ ํ‰ํ˜•์— ์˜ํ•˜์—ฌ ๋ถ€์žฌ์˜ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์„ ์‚ฐ์ •ํ•˜๊ณ  ์žˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ์•ž์„œ ์–ธ๊ธ‰ํ•œ ๋ฐ”์™€ ๊ฐ™์ด ๊ตญ๋‚ด ๊ธฐ์ค€์€ ๋ณด๊ฐ•๋œ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ถ€์žฌ์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์—์„œ FRP์— ์˜ํ•œ ๋น„ํ‹€๋ฆผ ๊ธฐ์—ฌ๋ถ„์„ ๋ฐ˜์˜ํ•˜์ง€ ์•Š๋Š”๋‹ค.

(1)
$T_{n}=\dfrac{2A_{o}A_{t}f_{yt}}{s}\cot\theta$

์—ฌ๊ธฐ์„œ, $A_{o}$๋Š” ์ „๋‹จํ๋ฆ„ ์•ˆ์ชฝ์˜ ๋‹จ๋ฉด์ (mm2)์ด๋ฉฐ, $s$๋Š” ํ์‡„ํ˜• ํšก๋ณด๊ฐ•๊ทผ์˜ ๊ฐ„๊ฒฉ(mm), $A_{t}$๋Š” ํ์‡„ํ˜• ํšก๋ณด๊ฐ•๊ทผ์˜ ๋‹จ๋ฉด์ (mm2), $f_{yt}$๋Š” ํ์‡„ํ˜• ํšก๋ณด๊ฐ•๊ทผ์˜ ํ•ญ๋ณต๊ฐ•๋„(MPa), $\theta$๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ ์••์ถ•๋Œ€์˜ ๊ฒฝ์‚ฌ๊ฐ(degrees)์ด๋ฉฐ 45ยฐ๋กœ ๊ฐ€์ •ํ•œ๋‹ค.

2.2 fib Bulletin 14

fib Bulletin 14(2001)์—์„œ๋Š” ์„ฌ์œ  ๋ฐฉํ–ฅ๊ณผ ๋ถ€์žฌ ์ถ•์ด ์ด๋ฃจ๋Š” ๊ฐ์ด 90ยฐ์ด๋ฉฐ, 4๋ฉด์ด ๋ณด๊ฐ•๋œ ๊ฒฝ์šฐ์— ๋Œ€ํ•˜์—ฌ FRP์˜ ๋น„ํ‹€๋ฆผ ๊ธฐ์—ฌ๋ถ„์„ ๊ณ ๋ คํ•œ ๋น„ํ‹€๋ฆผ ์ €ํ•ญ๋Šฅ๋ ฅ ํ‰๊ฐ€์‹์„ ์ œ์‹œํ•˜๊ณ  ์žˆ๋‹ค. ํ‰๊ฐ€์‹์—์„œ ๋น„ํ‹€๋ฆผ์— ์ €ํ•ญํ•˜๋Š” ์ „๋‹จ๋ ฅ์€ ์‹ (2)์™€ (3)๊ณผ ๊ฐ™์ด ์ฝ˜ํฌ๋ฆฌํŠธ ๋ฐ ๋น„ํ‹€๋ฆผ ๋ณด๊ฐ•๊ทผ์ด ์•„๋‹Œ ๋ถ€์žฌ ์ „๋ฉด์— ๋ณด๊ฐ•๋œ FRP์— ์˜ํ•ด ์ง€๋ฐฐ๋œ๋‹ค.

(2)
$F_{fd,\:v}=\varepsilon_{fd,\:e}E_{fu}\dfrac{t_{f}b_{f}}{s_{f}}h\cot\theta$

(3)
$F_{fd,\:h}=\varepsilon_{fd,\:e}E_{fu}\dfrac{t_{f}b_{f}}{s_{f}}b\cot\theta$

์—ฌ๊ธฐ์„œ, $F_{fd,\:v}$, $F_{fd,\:h}$๋Š” ๊ฐ๊ฐ FRP์— ์ž‘์šฉํ•˜๋Š” ๋ถ€์žฌ ๋‹จ๋ฉด์˜ ์ˆ˜์ง๋ฐฉํ–ฅ ๋ฐ ์ˆ˜ํ‰๋ฐฉํ–ฅ ์ „๋‹จ๋ ฅ(N), $\varepsilon_{fd,\:e}$๋Š” FRP์˜ ์„ค๊ณ„ ์œ ํšจ ๋ณ€ํ˜•๋ฅ , $E_{fu}$(=$f_{fk}/\varepsilon_{fuk}$)๋Š” ๊ทนํ•œ ์‹œ์˜ FRP ํƒ„์„ฑ๊ณ„์ˆ˜(MPa), $f_{fk}$๋Š” FRP ์ธ์žฅ ๊ฐ•๋„์˜ 5 %, $\varepsilon_{fuk}$๋Š” FRP ๊ทนํ•œ ๋ณ€ํ˜•๋ฅ ์˜ 5 %, $t_{f}$๋Š” FRP์˜ ๋‘๊ป˜(mm), $b_{f}$๋Š” ๋ถ€์žฌ ๊ธธ์ด๋ฐฉํ–ฅ FRP ํญ(mm), $s_{f}$๋Š” FRP์™€ ์ฝ˜ํฌ๋ฆฌํŠธ ์‚ฌ์ด์˜ ์ƒ๋Œ€ ๋ณ€์œ„(์Šฌ๋ฆฝ๋Ÿ‰)(mm) ๋˜๋Š” FRP ์Šคํ„ฐ๋Ÿฝ์˜ ์ค‘์‹ฌ๊ฐ„ ๊ฐ„๊ฒฉ(mm), $b$๋Š” ๋ถ€์žฌ์˜ ํญ(mm), $h$๋Š” ๋ถ€์žฌ์˜ ๋†’์ด(mm)์ด๋‹ค.

FRP๋กœ ๋ณด๊ฐ•๋œ ๋ถ€์žฌ์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ($T_{fd}$)์€ ์ž‘์šฉํ•˜๋Š” ์ „๋‹จ๋ ฅ์— ๋ถ€์žฌ์˜ ํญ๊ณผ ๋†’์ด๋ฅผ ๊ณฑํ•˜์—ฌ ๋‹ค์Œ๊ณผ ๊ฐ™์ด ์‚ฐ์ •ํ•  ์ˆ˜ ์žˆ๋‹ค.

์‹(4)์—์„œ FRP์˜ ์„ค๊ณ„ ์œ ํšจ ๋ณ€ํ˜•๋ฅ ($\varepsilon_{fd,\:e}$)์€ ์‹ (5),(6) ๊ณผ ๊ฐ™์ด ์‚ฐ์ •ํ•œ๋‹ค.

(4)
$T_{fd}=F_{fd,\:v}b+F_{fd,\:h}h=2\varepsilon_{fd,\:e}E_{fu}\dfrac{t_{f}b_{f}}{s_{f}}bh\cot\theta$

(5)
$\varepsilon_{fd,\:e}=\varepsilon_{fk,\:e}/\gamma_{f}$

(6)
$\varepsilon_{fk,\:e}=k\varepsilon_{f,\:e}$

์—ฌ๊ธฐ์„œ, $\varepsilon_{fk,\:e}$๋Š” FRP์˜ ํŠน์„ฑ ์œ ํšจ ๋ณ€ํ˜•๋ฅ , $\varepsilon_{f,\:e}$๋Š” FRP์˜ ์œ ํšจ ๋ณ€ํ˜•๋ฅ ์ด๋‹ค. $k$๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ ์ธ์žฅ๊ฐ•๋„์— ๋Œ€ํ•œ ๊ฐ์†Œ๊ณ„์ˆ˜๋กœ 0.8์„ ์‚ฌ์šฉํ•˜๋ฉฐ, $\gamma_{f}$๋Š” ์žฌ๋ฃŒ ์•ˆ์ „๊ณ„์ˆ˜๋กœ 1.3์„ ์‚ฌ์šฉํ•œ๋‹ค.

FRP์˜ ์œ ํšจ ๋ณ€ํ˜•๋ฅ ($\varepsilon_{f,\:e}$)์€ ์„ฌ์œ ์˜ ์ข…๋ฅ˜์— ๋”ฐ๋ผ ๋‹ค์Œ๊ณผ ๊ฐ™์ด ์ œ์‹œ๋œ๋‹ค.

(7)
CFRP : $\varepsilon_{f,\:e}=0.17\left(\dfrac{f_{ck}^{2/3}}{E_{fu}\rho_{f}}\right)^{0.30}\varepsilon_{fu}$

(8)
GFRP : $\varepsilon_{f,\:e}=0.048\left(\dfrac{f_{ck}^{2/3}}{E_{fu}\rho_{f}}\right)^{0.47}\varepsilon_{fu}$

์—ฌ๊ธฐ์„œ, $f_{ck}$๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ ์••์ถ•๊ฐ•๋„(MPa)์ด๋ฉฐ, $\rho_{f}$๋Š” FRP ๋ณด๊ฐ• ๋น„, $\varepsilon_{fu}$๋Š” FRP์˜ ๊ทนํ•œ ๋ณ€ํ˜•๋ฅ ์„ ๋‚˜ํƒ€๋‚ธ๋‹ค.

2.3 Tรคljsten ์ œ์•ˆ์‹

Tรคljsten(2002)์€ FRP์˜ ๋น„ํ‹€๋ฆผ ์ €ํ•ญ ๊ธฐ์—ฌ๋ถ„์„ ํŠธ๋Ÿฌ์Šค ๋ชจ๋ธ์— ์ ์šฉํ•˜์—ฌ Fig. 1๊ณผ ๊ฐ™์ด ์„ฌ์œ  ๋ฐฉํ–ฅ๊ณผ ๋ถ€์žฌ ์ถ•์ด ์ด๋ฃจ๋Š” ๊ฐ $\beta$์™€ ์„ฌ์œ  ๋ณด๊ฐ• ๋ฐฉ๋ฒ•(์—ฐ์† ๋˜๋Š” ์Šคํ„ฐ๋Ÿฝ ๋ณด๊ฐ•)์— ๋”ฐ๋ฅธ ๋ณด์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ํ‰๊ฐ€์‹์„ ์•„๋ž˜์™€ ๊ฐ™์ด ์ œ์•ˆํ•˜์˜€๋‹ค. ์ œ์•ˆ์‹์€ fib Bulletin 14 ์˜ ํ‰๊ฐ€์‹๊ณผ ๋งˆ์ฐฌ๊ฐ€์ง€๋กœ ๋น„ํ‹€๋ฆผ ๋ณด๊ฐ•๊ทผ์˜ ์˜ํ–ฅ์€ ๊ณ ๋ คํ•˜๊ณ  ์žˆ์ง€ ์•Š๋‹ค.

Fig. 1 Fiber reinforcement method

../../Resources/kci/JKCI.2022.34.1.033/fig1.png

Case 1 : 4๋ฉด ์—ฐ์† ๋ณด๊ฐ• $\beta$=45ยฐ

(9)
$2.4t_{f}\varepsilon_{f}E_{f}=\dfrac{T}{bh}$

Case 2 : 4๋ฉด ์—ฐ์† ๋ณด๊ฐ• $\beta$=90ยฐ

(10)
$1.2t_{f}\varepsilon_{f}E_{f}=\dfrac{T}{bh}$

Case 3 : 4๋ฉด ์Šคํ„ฐ๋Ÿฝ ๋ณด๊ฐ• $\beta$=45ยฐ

(11)
$\dfrac{2.4t_{f}b_{f}\varepsilon_{f}E_{f}}{b_{f}+r}=\dfrac{T}{bh}$

Case 4 : 4๋ฉด ์Šคํ„ฐ๋Ÿฝ ๋ณด๊ฐ• $\beta$=90ยฐ

(12)
$\dfrac{1.2t_{f}b_{f}\varepsilon_{f}E_{f}}{b_{f}+r}=\dfrac{T}{bh}$

์—ฌ๊ธฐ์„œ, $r$์€ FRP ์Šคํ„ฐ๋Ÿฝ ์‚ฌ์ด์˜ ์ˆœ๊ฐ„๊ฒฉ(mm), $\varepsilon_{f}$๋Š” FRP์˜ ์œ ํšจ ๋ณ€ํ˜•๋ฅ ์ด๋‹ค. CFRP์˜ ๊ฒฝ์šฐ $\varepsilon_{f}$=0.6$\varepsilon_{fu}$๋ฅผ ์‚ฌ์šฉํ•˜๋ฉฐ, ์ด ์—ฐ๊ตฌ์—์„œ๋Š” GFRP์— ์ ์šฉํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ACI440.2R-17(2017)์—์„œ ์ œ์•ˆํ•˜๊ณ  ์žˆ๋Š” $\varepsilon_{f}=0.004$๋ฅผ ์‚ฌ์šฉํ•˜์˜€๋‹ค. $E_{f}$๋Š” FRP์˜ ํƒ„์„ฑ๊ณ„์ˆ˜(MPa)์ด๋‹ค.

3. ์‹คํ—˜๊ณ„ํš

3.1 ์‚ฌ์šฉ์žฌ๋ฃŒ

์‹คํ—˜์ฒด ์ œ์ž‘์—๋Š” ๋ฐฐํ•ฉ๊ฐ•๋„ 40 MPa์˜ ์ฝ˜ํฌ๋ฆฌํŠธ๋ฅผ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ์ง€๋ฆ„ 100 mm, ๋†’์ด 200 mm์˜ ๊ณต์‹œ์ฒด๋ฅผ ์ œ์ž‘ํ•˜์˜€์œผ๋ฉฐ, ์‹คํ—˜์ฒด์™€ ๋™์ผํ•œ ์กฐ๊ฑด์—์„œ ์–‘์ƒํ•˜์—ฌ ์ฝ˜ํฌ๋ฆฌํŠธ ์••์ถ•๊ฐ•๋„ ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์‹œํ—˜๊ฒฐ๊ณผ ํ‰๊ท  ์••์ถ•๊ฐ•๋„๋Š” 32 MPa์ž„์„ ํ™•์ธํ•˜์˜€๋‹ค. ์‹คํ—˜์ฒด ์ œ์ž‘์— ์‚ฌ์šฉ๋œ ์ฃผ์ฒ ๊ทผ๊ณผ ํšก๋ณด๊ฐ•๊ทผ์˜ ๊ฐ•๋„๋Š” SD300 ๋ฐ SD400 ๋“ฑ๊ธ‰์ด๋ฉฐ, ์ฃผ์ฒ ๊ทผ์—๋Š” D10 ๋ฐ D13, ํšก๋ณด๊ฐ•๊ทผ์—๋Š” D10 ์ฒ ๊ทผ์„ ์‚ฌ์šฉํ•˜์˜€๋‹ค. Fig. 2๋Š” ์ฃผ์ฒ ๊ทผ ๋ฐ ํšก๋ณด๊ฐ•๊ทผ์˜ ์‘๋ ฅ-๋ณ€ํ˜•๋ฅ  ๊ด€๊ณ„๋ฅผ ๋‚˜ํƒ€๋‚ด๋ฉฐ, ์ด๋“ค ์ฒ ๊ทผ์˜ ๊ธฐ๊ณ„์  ํŠน์„ฑ์„ Table 1์— ์ •๋ฆฌํ•˜์˜€๋‹ค.

Fig. 2 Stress-strain relationship of reinforcing bars

../../Resources/kci/JKCI.2022.34.1.033/fig2.png

Table 1. Mechanical properties of reinforcing bars

Grade

Type

$f_{y}$ (MPa)

$\varepsilon_{y}$

$E_{s}$ (MPa)

SD300

D10

352.0

0.0018

195,556

D13

366.2

0.0021

174,381

SD400

D10

434.6

0.0025

173,840

D13

402.7

0.0022

183,045

์‹คํ—˜์ฒด์˜ ๋น„ํ‹€๋ฆผ ๋ณด๊ฐ•์— ์‚ฌ์šฉ๋œ E-Glass ์„ฌ์œ ๋Š” Fig. 3๊ณผ ๊ฐ™์ด ํญ 5 mm, ๋‘๊ป˜ 0.365 mm์˜ ๋‹จ์„ฌ์œ (filament)๋“ค์ด ์ง๊ตํ•˜์—ฌ ๋ฐฉ์ง๋œ ์‹œํŠธ ํ˜•ํƒœ๋กœ ๊ตฌ์„ฑ๋˜๋ฉฐ, ์—ํญ์‹œ ์ˆ˜์ง€๋กœ ํ•จ์นจํ•˜์˜€๋‹ค. ๊ฒฝํ™”๋œ GFRP๋Š” ASTM D3039/D3039M-17(2017)์— ๋”ฐ๋ผ ์ธ์žฅ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์ธ์žฅ์‹œํ—˜ ๊ฒฐ๊ณผ, GFRP์˜ ์ธ์žฅ๊ฐ•๋„์™€ ํƒ„์„ฑ๊ณ„์ˆ˜๋Š” ๊ฐ๊ฐ 1,443 MPa์™€ 86,771 MPa์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. GFRP์˜ ์‘๋ ฅ-๋ณ€ํ˜•๋ฅ  ๊ด€๊ณ„๋Š” Fig. 4์— ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ, ์ด๋“ค์˜ ๊ธฐ๊ณ„์  ํŠน์„ฑ์„ Table 2์— ์ •๋ฆฌํ•˜์˜€๋‹ค.

Fig. 3 GFRP sheet

../../Resources/kci/JKCI.2022.34.1.033/fig3.png

Fig. 4 Stress-strain relationship of GFRP sheet

../../Resources/kci/JKCI.2022.34.1.033/fig4.png

Table 2. Mechanical properties of GFRP sheet

Type

Weight

(g/m2)

Area

(mm2)

Tensile strength

(MPa)

Tensile modulus

(MPa)

E-Glass

960

18.25

1,443

86,771

3.2 ์‹คํ—˜์ฒด ๊ณ„ํš

GFRP ์‹œํŠธ ๋ณด๊ฐ• ๋ฐ ์ฒ ๊ทผ ํ•ญ๋ณต๊ฐ•๋„์— ๋”ฐ๋ฅธ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ณด์˜ ๋น„ํ‹€๋ฆผ ๊ฑฐ๋™์„ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•˜์—ฌ GFRP ์‹œํŠธ ๋ณด๊ฐ• ์œ ๋ฌด, ์„ฌ์œ  ๋ฐฉํ–ฅ, ์ฒ ๊ทผ์˜ ํ•ญ๋ณต๊ฐ•๋„๋ฅผ ๋ณ€์ˆ˜๋กœ ์ด 5๊ฐœ์˜ ์‹คํ—˜์ฒด๋ฅผ ์ œ์ž‘ํ•˜์˜€๋‹ค. Table 3์€ ์‹คํ—˜์ฒด ์ผ๋žŒ์„ ๋‚˜ํƒ€๋‚ธ๋‹ค. ์‹คํ—˜์ฒด๋ช…์—์„œ GF๋Š” GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด์ด๋ฉฐ, N์€ ๋ณด๊ฐ•๋˜์ง€ ์•Š์€ ์‹คํ—˜์ฒด๋ฅผ ๋‚˜ํƒ€๋‚ธ๋‹ค. 45์™€ 90์€ ์„ฌ์œ  ๋ฐฉํ–ฅ๊ณผ ๋ถ€์žฌ์˜ ์ถ•์ด ์ด๋ฃจ๋Š” ๊ฐ์„ ๋‚˜ํƒ€๋‚ด๋ฉฐ, 3๊ณผ 4๋Š” ์ฒ ๊ทผ์˜ ๋“ฑ๊ธ‰์„ ๋‚˜ํƒ€๋‚ธ๋‹ค. ์‹คํ—˜์ฒด๋Š” Fig. 5์™€ ๊ฐ™์ด ์Šคํ„ฐ๋ธŒ์™€ ๋ณด๋กœ ๊ตฌ์„ฑ๋œ ์ผ„ํ‹ธ๋ ˆ๋ฒ„ ํ˜•ํƒœ๋กœ ๊ณ„ํšํ•˜์˜€๋‹ค. ์‹คํ—˜์ฒด์˜ ๊ธธ์ด๋Š” 2,000 mm, ๋‹จ๋ฉด์€ 400ร—600 mm๋กœ ๊ณ„ํšํ•˜์˜€๋‹ค. ์‹คํ—˜๊ตฌ๊ฐ„์—๋Š” ํ์‡„ํ˜• ํšก๋ณด๊ฐ•๊ทผ์„ 90 mm ๊ฐ„๊ฒฉ์œผ๋กœ ๋ฐฐ๊ทผํ•˜์˜€์œผ๋ฉฐ, ์‹คํ—˜๊ตฌ๊ฐ„ ์ด์™ธ์˜ ๊ตฌ๊ฐ„์—๋Š” 50 mm ๊ฐ„๊ฒฉ์œผ๋กœ ์‹คํ—˜๊ตฌ๊ฐ„๋ณด๋‹ค ์กฐ๋ฐ€ํ•˜๊ฒŒ ๋ฐฐ๊ทผํ•˜์—ฌ ์‹คํ—˜๊ตฌ๊ฐ„ ์ด์™ธ์—์„œ ๋น„ํ‹€๋ฆผ ํŒŒ๊ดด๊ฐ€ ๋ฐœ์ƒํ•˜์ง€ ์•Š๋„๋ก ๊ณ„ํšํ•˜์˜€๋‹ค.

Table 3. Properties of specimens

Specimens

$f_{ck}$(MPa)

(MPa)

$f_{yl}$ (MPa)

$f_{yt}$ (MPa)

Size (mm)

Longitudinal reinforcement

Transverse reinforcement

Angle of FRP

FRP sheet

$b$

$h$

$L$

N-3

35.4

322.4

334.2

400

600

2,000

6-D13+8-D10

D10

-

None

N-4

477.4

485.7

GF45-4

32.0

416.4

434.6

400

600

2,000

6-D13+8-D10

D10

45ยฐ

GFRP sheet

1 layer

GF90-3

360.1

352.0

90ยฐ

GF90-4

416.4

434.6

Note: $b$: beam width; $h$: beam height; $L$: beam length; $f_{yl}$: yield strength of longitudinal reinforcement; $f_{yt}$: yield strength of transverse reinforcement

Fig. 5 Details of specimens (unit: mm)

../../Resources/kci/JKCI.2022.34.1.033/fig5.png

GFRP ์‹œํŠธ์— ์˜ํ•œ ๋ณด๊ฐ• ์„ฑ๋Šฅ์„ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๋ณด๊ฐ• ๋Œ€์ƒ ์‹คํ—˜์ฒด๋“ค(GF45-4, GF90-3, GF90-4)์„ ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์‹œ๊นŒ์ง€ ๊ฐ€๋ ฅํ•œ ์ดํ›„, ์‹คํ—˜๊ตฌ๊ฐ„ ์ „๋ฉด์— ๊ฑธ์ณ ๋ณด๊ฐ•์„ ์‹ค์‹œํ•˜์˜€๋‹ค. GFRP ๋ณด๊ฐ•์€ ์ฝ˜ํฌ๋ฆฌํŠธ์™€ ์‹œํŠธ์˜ ์›ํ™œํ•œ ๋ถ€์ฐฉ์„ ์œ„ํ•˜์—ฌ ์ฝ˜ํฌ๋ฆฌํŠธ ํ‘œ๋ฉด์„ ๊ทธ๋ผ์ธ๋”ฉ ์ฒ˜๋ฆฌ ํ›„, ํ”„๋ผ์ด๋จธ์™€ ์—ํญ์‹œ ์ˆ˜์ง€๋ฅผ ๋„ํฌํ•˜์—ฌ ์‹œํŠธ๋ฅผ ๋ถ€์ฐฉํ•˜์˜€๋‹ค. ์‹œํŠธ๋Š” ์‹คํ—˜์ฒด์˜ ๊ธธ์ด ๋ฐฉํ–ฅ์œผ๋กœ ์–‘ ๋๋‹จ์—์„œ 150 mm ๋งŒํผ ๊ฒน์นจ ์ด์Œํ•˜์—ฌ ์‹คํ—˜ ์ค‘ ๋ถ€์žฌ ๋น„ํ‹€๋ฆผ์— ์˜ํ•œ ์‹œํŠธ์˜ ํƒˆ๋ฝ์„ ๋ฐฉ์ง€ํ•˜์˜€๋‹ค.

3.3 ๊ฐ€๋ ฅ ๋ฐ ๊ณ„์ธก๊ณ„ํš

์ด ์—ฐ๊ตฌ์—์„œ๋Š” ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ณด์— ์ˆœ์ˆ˜๋น„ํ‹€๋ฆผ์„ ๊ฐ€๋ ฅํ•˜๊ธฐ ์œ„ํ•˜์—ฌ Fig. 6๊ณผ ๊ฐ™์€ ๊ฐ€๋ ฅ์žฅ์น˜๋ฅผ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ๊ฐ€๋ ฅ์žฅ์น˜๋Š” 1,000 kN ์šฉ๋Ÿ‰์˜ ์•ก์ถ”์—์ดํ„ฐ์™€ ํšŒ์ „ ํ”„๋ ˆ์ž„(rotation frame), ๊ณก๋ฅ  ํ”„๋ ˆ์ž„(curvature frame)์œผ๋กœ ๊ตฌ์„ฑ๋œ๋‹ค. ์‹คํ—˜์ฒด๋Š” ํšŒ์ „ ํ”„๋ ˆ์ž„์— ๊ตฌ์†๋˜์–ด ์ผ์ •ํ•œ ๊ณก๋ฅ ๋กœ ๊ณก๋ฅ  ํ”„๋ ˆ์ž„ ์ƒ๋ถ€์˜ ๊ตฌ์ขŒ(ball bearing)๋ฅผ ๋”ฐ๋ผ ํšŒ์ „ํ•˜๋„๋ก ์„ค๊ณ„๋˜์–ด ์‹คํ—˜ ์ค‘ ํšŒ์ „์ถ•์˜ ์ด๋™์ด ๋ฐœ์ƒํ•˜์ง€ ์•Š๋Š”๋‹ค.

Fig. 6. Test setup of specimen

../../Resources/kci/JKCI.2022.34.1.033/fig6.png

๋น„ํ‹€๋ฆผ ํ•˜์ค‘์€ ๋ณ€์œ„์ œ์–ด ๋ฐฉ์‹์œผ๋กœ ๊ฐ€๋ ฅ์„ ์‹ค์‹œํ•˜์˜€๋‹ค. GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋˜์ง€ ์•Š์€ ์‹คํ—˜์ฒด๋Š” ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ์ดํ›„ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์˜ 80 %์— ๋„๋‹ฌํ•  ๋•Œ๊นŒ์ง€ ๊ฐ€๋ ฅ์„ ์‹ค์‹œํ•˜์˜€๋‹ค. ๋ณด๊ฐ• ์‹คํ—˜์ฒด๋Š” GFRP ์‹œํŠธ์— ์˜ํ•œ ๋ณด๊ฐ• ์„ฑ๋Šฅ์„ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์‹œ์ ๊นŒ์ง€ ๊ฐ€๋ ฅ ํ›„, GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•ํ•˜์—ฌ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ์ดํ›„ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์˜ 80 %์— ๋„๋‹ฌํ•  ๋•Œ๊นŒ์ง€ ์žฌ๊ฐ€๋ ฅ์„ ์‹ค์‹œํ•˜์˜€๋‹ค.

์ฃผ์ฒ ๊ทผ๊ณผ ํšก๋ณด๊ฐ•๊ทผ์˜ ๋ณ€ํ˜•๋ฅ ์„ ์ธก์ •ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๋ชจ๋“  ์‹คํ—˜์ฒด์—๋Š” Fig. 5(a)์™€ ๊ฐ™์ด ์Šคํ„ฐ๋ธŒ๋กœ๋ถ€ํ„ฐ ์ผ์ •ํ•œ ๊ฐ„๊ฒฉ์œผ๋กœ ์ŠคํŠธ๋ ˆ์ธ ๊ฒŒ์ด์ง€๋ฅผ ๋ถ€์ฐฉํ•˜์˜€์œผ๋ฉฐ, GFRP ์‹œํŠธ์˜ ๋ณ€ํ˜•๋ฅ ์„ ์ธก์ •ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์‹œํŠธ ์™ธ๋ถ€์— ์ŠคํŠธ๋ ˆ์ธ ๊ฒŒ์ด์ง€๋ฅผ ๋ถ€์ฐฉ(Fig. 5์ฐธ์กฐ)ํ•˜์˜€๋‹ค. ์‹คํ—˜์ฒด์˜ ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ์€ Fig. 7๊ณผ ๊ฐ™์ด ์‹คํ—˜๊ตฌ๊ฐ„ ์–‘๋‹จ๋ถ€์— ์„ค์น˜๋œ 100 mm ์šฉ๋Ÿ‰์˜ LVDT๋กœ๋ถ€ํ„ฐ ๊ณ„์ธก๋œ ๋ณ€์œ„๋ฅผ ์ด์šฉํ•˜์—ฌ ์‚ฐ์ถœํ•˜์˜€๋‹ค.

Fig. 7 Measurement plan

../../Resources/kci/JKCI.2022.34.1.033/fig7.png

4. ์‹คํ—˜๊ฒฐ๊ณผ ๋ฐ ๋ถ„์„

4.1 ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ-ํšŒ์ „๊ฐ ๊ด€๊ณ„

GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด์™€ ๋ณด๊ฐ•๋˜์ง€ ์•Š์€ ์‹คํ—˜์ฒด์˜ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ-ํšŒ์ „๊ฐ ๊ด€๊ณ„๋ฅผ Fig. 8์— ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ, ์‹คํ—˜๊ฒฐ๊ณผ์™€ ํ˜„ํ–‰ ๊ธฐ์ค€ ๋ฐ ๊ธฐ์กด ๋ชจ๋ธ์— ์˜ํ•ด ๊ณ„์ธกํ•œ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์„ Table 4์— ์ •๋ฆฌํ•˜์˜€๋‹ค. ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด๋Š” ๋ณด๊ฐ• ์ด์ „๊ณผ ์ดํ›„์˜ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ๊ฐ๊ฐ ์ ์„ ๊ณผ ์‹ค์„ ์œผ๋กœ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค.

Fig. 8 Torque-Twist relationships of specimens

../../Resources/kci/JKCI.2022.34.1.033/fig8.png

Table 4. Comparison of experimental and predicted results

Specimens

Experimental results

Predicted results

Ratio of experimental result to predicted result

Torque, Tn.exp

(kN๏ฝฅm)

Twist

(rad/m)

Tn.KDS

(kN๏ฝฅm)

Tn.Fib

(kN๏ฝฅm)

Tn.Tรคljsten

(kN๏ฝฅm)

Tn.exp / Tn.KDS

Tn.exp / Tn.Fib

Tn.exp / Tn.Tรคljsten

N-3

101.1

0.026

71.2

-

-

-

-

-

N-4

124.0

0.034

103.4

-

-

-

-

-

GF45-4

190.8

0.031

92.5

162.9

197.0

2.06

1.17

0.97

GF90-3

161.4

0.029

74.9

162.9

137.6

2.15

0.99

1.17

GF90-4

169.5

0.048

92.5

162.9

160.5

1.83

1.04

1.06

Fig. 8(a) ๋ฐ Fig. 8(b)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ๋ณด๊ฐ•๋˜์ง€ ์•Š์€ N-3์™€ N-4 ์‹คํ—˜์ฒด ๋ชจ๋‘ ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ 0.002 rad/m์—์„œ ๋น„ํ‹€๋ฆผ ๊ท ์—ด์˜ ๋ฐœ์ƒ๊ณผ ํ•จ๊ป˜ ์ดˆ๊ธฐ ๋น„ํ‹€๋ฆผ ๊ฐ•์„ฑ์ด ๊ธ‰๊ฒฉํžˆ ์ €ํ•˜๋˜์—ˆ๋‹ค. SD300 ๋“ฑ๊ธ‰์˜ ์ฒ ๊ทผ์„ ์‚ฌ์šฉํ•œ N-3 ์‹คํ—˜์ฒด๋Š” ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์ดํ›„ ์ฃผ์ฒ ๊ทผ๊ณผ ํšก๋ณด๊ฐ•๊ทผ์ด ์ˆœ์ฐจ์ ์œผ๋กœ ํ•ญ๋ณตํ•˜์˜€์œผ๋ฉฐ, ํšก๋ณด๊ฐ•๊ทผ ํ•ญ๋ณต ์งํ›„ ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ 0.026 rad/m์—์„œ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ 101.1 kN๏ฝฅm์— ๋„๋‹ฌํ•˜์˜€๋‹ค. ์ดํ›„ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ๊ฐ€ ์ ์ฐจ ๊ฐ์†Œํ•˜๋ฉด์„œ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ์˜ 80 %์— ๋„๋‹ฌํ•˜์—ฌ ์‹คํ—˜์„ ์ข…๋ฃŒํ•˜์˜€๋‹ค. SD400 ๋“ฑ๊ธ‰์˜ ์ฒ ๊ทผ์„ ์‚ฌ์šฉํ•œ N-4 ์‹คํ—˜์ฒด๋Š” ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์ดํ›„ ์ฃผ์ฒ ๊ทผ์ด ํ•ญ๋ณต, ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ 0.034 rad/m์—์„œ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ 124.0 kN๏ฝฅm์— ๋„๋‹ฌํ•˜์˜€๋‹ค. ์ดํ›„ ํšก๋ณด๊ฐ•๊ทผ์ด ํ•ญ๋ณตํ•˜์˜€์œผ๋ฉฐ, ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ๊ฐ€ ์ ์ฐจ ๊ฐ์†Œํ•˜๋ฉด์„œ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ์˜ 80 %์— ๋„๋‹ฌํ•˜์—ฌ ์‹คํ—˜์„ ์ข…๋ฃŒํ•˜์˜€๋‹ค.

๋ชจ๋“  ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด์˜ ์ดˆ๊ธฐ ๋น„ํ‹€๋ฆผ ๊ฐ•์„ฑ์€ ๋ณด๊ฐ• ์ด์ „ ์‹คํ—˜๊ฒฐ๊ณผ์™€ ์œ ์‚ฌํ•œ ๋ฐ˜๋ฉด, ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์‹œ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ์™€ ํšŒ์ „๊ฐ ๋ชจ๋‘ ์ฆ๊ฐ€ํ•˜์˜€๋‹ค. 45ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ GF45-4 ์‹คํ—˜์ฒด๋Š” Fig. 8(c)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์ดํ›„ ์ฃผ์ฒ ๊ทผ๊ณผ ํšก๋ณด๊ฐ•๊ทผ์ด ์ฐจ๋ก€๋กœ ํ•ญ๋ณตํ•˜์˜€์œผ๋ฉฐ, ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ 0.023 rad/m์—์„œ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ 190.8 kN๏ฝฅm์— ๋„๋‹ฌํ•˜์˜€๋‹ค. ์ดํ›„ ์Šคํ„ฐ๋ธŒ ๋ถ€๊ทผ์˜ ์‹คํ—˜๊ตฌ๊ฐ„ ๋๋‹จ์—์„œ GFRP ์‹œํŠธ์˜ ๋ฐ•๋ฆฌ ๋ฐ ํŒŒ๋‹จ์ด ๋ฐœ์ƒํ•˜๋ฉด์„œ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ๊ฐ€ ๊ฐ์†Œํ•˜์˜€์œผ๋ฉฐ, ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ์˜ 80 %์— ๋„๋‹ฌํ•˜์—ฌ ์‹คํ—˜์„ ์ข…๋ฃŒํ•˜์˜€๋‹ค.

90ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ GF90-3์™€ GF90-4 ์‹คํ—˜์ฒด๋Š” Fig. 8(d)์™€ (e)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ๋‘ ์‹คํ—˜์ฒด ๋ชจ๋‘ ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์ดํ›„ ์ฃผ์ฒ ๊ทผ๊ณผ ํšก๋ณด๊ฐ•๊ทผ์ด ๋ชจ๋‘ ํ•ญ๋ณตํ•˜์˜€์œผ๋ฉฐ, ๊ฐ๊ฐ ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ 0.029 rad/m์™€ 0.048 rad/m์—์„œ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ 161.4 kN๏ฝฅm์™€ 169.5 kN๏ฝฅm์— ๋„๋‹ฌํ•˜์˜€๋‹ค. ์ดํ›„ ๋‘ ์‹คํ—˜์ฒด ๋ชจ๋‘ ์Šคํ„ฐ๋ธŒ ๋ถ€๊ทผ์˜ ์‹คํ—˜๊ตฌ๊ฐ„ ๋๋‹จ์—์„œ GFRP ์‹œํŠธ์˜ ๋ฐ•๋ฆฌ์™€ ํŒŒ๋‹จ์ด ๊ด€์ธก๋˜์—ˆ์œผ๋ฉฐ, ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ์˜ 80 %์— ๋„๋‹ฌํ•˜์—ฌ ์‹คํ—˜์„ ์ข…๋ฃŒํ•˜์˜€๋‹ค.

4.2 ๊ท ์—ด ๋ฐ ํŒŒ๊ดด์–‘์ƒ

๋ฌด๋ณด๊ฐ• ์‹คํ—˜์ฒด์˜ ๊ท ์—ด ์–‘์ƒ ๋ฐ ๋ณด๊ฐ• ์‹คํ—˜์ฒด์˜ GFRP ์‹œํŠธ ํŒŒ๊ดด์–‘์ƒ์„ Fig. 9์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ๋ฌด๋ณด๊ฐ• ์‹คํ—˜์ฒด N-3๊ณผ N-4๋Š” Fig. 9(a)์™€ (b)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ์ดˆ๊ธฐ ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์ดํ›„ ๋น„ํ‹€๋ฆผ ๋ชจ๋ฉ˜ํŠธ๊ฐ€ ์ฆ๊ฐ€ํ•จ์— ๋”ฐ๋ผ ๊ท ์—ด์ด ์ง„์ „๋˜์—ˆ์œผ๋ฉฐ, ์‹คํ—˜๊ตฌ๊ฐ„์˜ ๋ณต๋ถ€์—์„œ ๊ท ์—ด ํญ์˜ ์ฆ๊ฐ€๊ฐ€ ๋šœ๋ ทํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ์ตœ์ข…์ ์œผ๋กœ๋Š” ๋น„ํ‹€๋ฆผ ๊ท ์—ด์˜ ์ง„์ „์— ๋”ฐ๋ฅธ ์ฝ˜ํฌ๋ฆฌํŠธ ์••๊ดด๋กœ ์ธํ•˜์—ฌ ๋น„ํ‹€๋ฆผ ํŒŒ๊ดดํ•˜์˜€๋‹ค.

Fig. 9 Crack and failure patterns of specimens

../../Resources/kci/JKCI.2022.34.1.033/fig9.png

GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ GF45-4, GF90-3 ๋ฐ GF90-4 ์‹คํ—˜์ฒด๋Š” Fig. 9(c), (d) ๋ฐ (e)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ์„ฌ์œ  ๋ฐฉํ–ฅ๊ณผ ๊ด€๊ณ„์—†์ด ๋ชจ๋‘ ์Šคํ„ฐ๋ธŒ ๋ถ€๊ทผ์˜ ์‹คํ—˜๊ตฌ๊ฐ„ ๋‹จ๋ถ€์—์„œ ์‹œํŠธ์˜ ๋ฐ•๋ฆฌ ๋ฐ ํŒŒ๋‹จ์ด ๋ฐœ์ƒํ•˜์˜€๋‹ค. ์ด๋Š” ๋‹จ๋ฉด์—์„œ ๋น„ํ‹€๋ฆผ ์‘๋ ฅ์ด ์ง‘์ค‘๋˜๋Š” ๋ชจ์„œ๋ฆฌ ๋ถ€๊ทผ์— ๊ตญ๋ถ€์ ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ์œผ๋ฉฐ, ๋ฐ•๋ฆฌ ๋ฐ ํŒŒ๋‹จ์ด ์ „์ด๋จ์— ๋”ฐ๋ผ GFRP ์‹œํŠธ์— ์˜ํ•œ ๋น„ํ‹€๋ฆผ ์ €ํ•ญ ๋Šฅ๋ ฅ์ด ๊ฐ์†Œํ•˜๋ฉด์„œ ์ฝ˜ํฌ๋ฆฌํŠธ ์••๊ดด์— ์˜ํ•˜์—ฌ ๋น„ํ‹€๋ฆผ ํŒŒ๊ดดํ•˜์˜€๋‹ค.

4.3 ๋ณ€ํ˜•๋ฅ  ๋ถ„ํฌ

GFRP ์‹œํŠธ์˜ ํšก๋ฐฉํ–ฅ ๋ณ€ํ˜•๋ฅ ๊ณผ ๋™์ผ ์„ ์ƒ์— ์œ„์น˜ํ•œ ํšก๋ณด๊ฐ•๊ทผ์˜ ๋ณ€ํ˜•๋ฅ ์„ ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ ๋‹จ๊ณ„์— ๋”ฐ๋ผ ๊ฐ๊ฐ Fig. 10๊ณผ Fig. 11์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. 45ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ GF45-4 ์‹คํ—˜์ฒด๋Š” Fig. 10(a)์™€ Fig. 11(a)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ 0.02 rad/m ์ดํ›„์— ํšก๋ณด๊ฐ•๊ทผ์ด ํ•ญ๋ณตํ•˜๋ฉด์„œ ์‹œํŠธ์˜ ํšก๋ฐฉํ–ฅ ๋ณ€ํ˜•๋ฅ ์ด ๊ธ‰๊ฒฉํ•˜๊ฒŒ ์ฆ๊ฐ€ํ•˜์˜€์œผ๋ฉฐ, ์ด๋Š” ์ฒ ๊ทผ ํ•ญ๋ณต ์ดํ›„ GFRP ์‹œํŠธ์— ์˜ํ•œ ๋น„ํ‹€๋ฆผ ์ €ํ•ญ์ด ์ฆ๊ฐ€ํ•˜์˜€์Œ์„ ๋ณด์—ฌ์ค€๋‹ค. ์‹œํŠธ์˜ ํšก๋ฐฉํ–ฅ ๋ณ€ํ˜•๋ฅ ์€ ๋ฐ•๋ฆฌ ๋ฐ ํŒŒ๋‹จ์ด ๋ฐœ์ƒํ•œ ์Šคํ„ฐ๋ธŒ์— ๊ฐ€๊นŒ์šธ์ˆ˜๋ก ์ฆ๊ฐ€ํ•˜๋Š” ๊ฒฝํ–ฅ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค.

Fig. 10 Strain distribution of GFRP sheet

../../Resources/kci/JKCI.2022.34.1.033/fig10.png

Fig. 11 Strain distribution of transverse reinforcement

../../Resources/kci/JKCI.2022.34.1.033/fig11.png

90ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ SD300 ๋“ฑ๊ธ‰์˜ ์ฒ ๊ทผ์„ ์‚ฌ์šฉํ•œ GF90-3 ์‹คํ—˜์ฒด๋Š” Fig. 10(b)์™€ Fig. 11(b)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ 0.01 rad/m ์ดํ›„์— ํšก๋ณด๊ฐ•๊ทผ์ด ํ•ญ๋ณตํ•˜๋ฉด์„œ ์‹œํŠธ์˜ ํšก๋ฐฉํ–ฅ ๋ณ€ํ˜•๋ฅ ์ด ๊ธ‰๊ฒฉํ•˜๊ฒŒ ์ฆ๊ฐ€ํ•˜์˜€๋‹ค. GF90-3 ์‹คํ—˜์ฒด๋Š” GF45-4 ์‹คํ—˜์ฒด์— ๋น„ํ•˜์—ฌ ์‹œํŠธ์˜ ๋ณ€ํ˜•๋ฅ ์ด ๋งค์šฐ ํฐ ํญ์œผ๋กœ ์ฆ๊ฐ€ํ•˜์˜€์œผ๋ฉฐ, ํšก๋ณด๊ฐ•๊ทผ์ด ์ผ์ฐ ํ•ญ๋ณตํ•˜๋ฉด์„œ ๋น„ํ‹€๋ฆผ์— ๋Œ€ํ•œ ์‹œํŠธ์˜ ๊ธฐ์—ฌ๋ถ„์ด ์ฆ๊ฐ€ํ•œ ๊ฒƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ๋‹ค.

90ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ SD400 ๋“ฑ๊ธ‰์˜ ์ฒ ๊ทผ์„ ์‚ฌ์šฉํ•œ GF90-4 ์‹คํ—˜์ฒด๋Š” Fig. 10(c)์™€ Fig. 11(c)์— ๋‚˜ํƒ€๋‚ธ ๋ฐ”์™€ ๊ฐ™์ด ๋น„ํ‹€๋ฆผ ํšŒ์ „๊ฐ 0.04 rad/m ์ดํ›„์— ํšก๋ณด๊ฐ•๊ทผ์ด ํ•ญ๋ณตํ•˜๋ฉด์„œ ์‹œํŠธ์˜ ํšก๋ฐฉํ–ฅ ๋ณ€ํ˜•๋ฅ ์ด ๊ธ‰๊ฒฉํ•˜๊ฒŒ ์ฆ๊ฐ€ํ•˜์˜€๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ GF45-4 ๋ฐ GF90-3 ์‹คํ—˜์ฒด์™€๋Š” ๋‹ค๋ฅด๊ฒŒ ํšก๋ณด๊ฐ•๊ทผ ํ•ญ๋ณต ์ด์ „๋ถ€ํ„ฐ ์‹œํŠธ์˜ ๋ณ€ํ˜•๋ฅ ์ด ์„œ์„œํžˆ ์ฆ๊ฐ€ํ•˜์—ฌ ๋น„ํ‹€๋ฆผ ์ €ํ•ญ์— ๊ธฐ์—ฌํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์œผ๋ฉฐ, ์ด์— ๋”ฐ๋ผ ์ฒ ๊ทผ์˜ ํ•ญ๋ณต์ด ์ง€์—ฐ๋œ ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

4.4 ์„ค๊ณ„ ๋ณ€์ˆ˜์— ์˜ํ•œ ์˜ํ–ฅ

์„ค๊ณ„ ๋ณ€์ˆ˜์ธ GFRP ์‹œํŠธ ๋ณด๊ฐ• ์œ ๋ฌด, ์„ฌ์œ  ๋ฐฉํ–ฅ, ์ฒ ๊ทผ ํ•ญ๋ณต๊ฐ•๋„๊ฐ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ์„ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์‹คํ—˜๊ฒฐ๊ณผ(Fig. 8๋ฐ Table 4 ์ฐธ์กฐ)๋ฅผ ์„ค๊ณ„ ๋ณ€์ˆ˜์— ๋”ฐ๋ผ ๋น„๊ตํ•˜์˜€๋‹ค. GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ GF45-4, GF90-4 ์‹คํ—˜์ฒด๋Š” ๋ฌด๋ณด๊ฐ• ์‹คํ—˜์ฒด N-4์™€ ๋น„๊ตํ•˜์—ฌ ๊ฐ๊ฐ 53 %, 37 % ๋†’์€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์„ ๋‚˜ํƒ€๋ƒˆ์œผ๋ฉฐ, GF90-3 ์‹คํ—˜์ฒด๋Š” N-3 ์‹คํ—˜์ฒด์™€ ๋น„๊ตํ•˜์—ฌ 60 % ๋†’์€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ด๋Š” GFRP ์‹œํŠธ๊ฐ€ ๋น„ํ‹€๋ฆผ์— ์ €ํ•ญํ•˜๋ฉด์„œ ์ฝ˜ํฌ๋ฆฌํŠธ ์••๊ดด๋ฅผ ์ง€์—ฐ์‹œ์ผฐ๊ธฐ ๋•Œ๋ฌธ์ด๋ฉฐ, GFRP ์‹œํŠธ ๋ณด๊ฐ•์ด ๋ถ€์žฌ์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ์ƒ์Šน์— ํšจ๊ณผ์ ์œผ๋กœ ์ž‘์šฉํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•˜์˜€๋‹ค.

45ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด GF45-4๋Š” 90ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด GF90-4์™€ ๋น„๊ตํ•˜์—ฌ 13 % ๋†’์€ ๋‚ด๋ ฅ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ด๋Š” 45ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์‹œํŠธ๊ฐ€ ๋น„ํ‹€๋ฆผ ๊ท ์—ด์— ์ˆ˜์ง์œผ๋กœ ๋ฐฐ์น˜๋˜๋ฉด์„œ ๋น„ํ‹€๋ฆผ ๊ท ์—ด์˜ ์ง„์ „์„ ์ง€์—ฐ์‹œ์ผœ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ์ƒ์Šน์— ๊ธฐ์—ฌํ•˜์˜€๊ธฐ ๋•Œ๋ฌธ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

SD400 ๋“ฑ๊ธ‰์˜ ์ฒ ๊ทผ์„ ์‚ฌ์šฉํ•œ ์‹คํ—˜์ฒด N-4๋Š” N-3 ์‹คํ—˜์ฒด์™€ ๋น„๊ตํ•˜์—ฌ 23 % ๋†’์€ ๋‚ด๋ ฅ์„ ๋‚˜ํƒ€๋‚ด์—ˆ์œผ๋ฉฐ, GF90-4 ์‹คํ—˜์ฒด๋Š” GF90-3 ์‹คํ—˜์ฒด์™€ ๋น„๊ตํ•˜์—ฌ 5 % ๋†’์€ ๋‚ด๋ ฅ์„ ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. ์ด๋Š” ๋ฌด๋ณด๊ฐ• ์‹คํ—˜์ฒด์˜ ๊ฒฝ์šฐ ์ฒ ๊ทผ์˜ ํ•ญ๋ณต ์ดํ›„ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์— ๋„๋‹ฌํ•˜๋ฉด์„œ ์ฒ ๊ทผ์˜ ํ•ญ๋ณต๊ฐ•๋„๊ฐ€ ์ค‘์š”ํ•œ ์š”์†Œ๋กœ ์ž‘์šฉํ•˜๋Š” ๋ฐ˜๋ฉด, GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด์˜ ๊ฒฝ์šฐ ์ฒ ๊ทผ์˜ ํ•ญ๋ณต ์ดํ›„ GFRP ์‹œํŠธ๊ฐ€ ๋น„ํ‹€๋ฆผ์— ์ €ํ•ญํ•˜๋ฉด์„œ ์‹œํŠธ์— ์˜ํ•ด ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์ด ๊ฒฐ์ •๋˜์—ˆ๊ธฐ ๋•Œ๋ฌธ์ด๋‹ค.

4.5 ์‹คํ—˜ ๋ฐ ์˜ˆ์ธก๊ฒฐ๊ณผ ๋น„๊ต

GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด์˜ ์‹คํ—˜๊ฒฐ๊ณผ์™€ ์˜ˆ์ธก๊ฒฐ๊ณผ(Fig. 8๋ฐ Table 4 ์ฐธ์กฐ)๋ฅผ ๋น„๊ตํ•˜์˜€๋‹ค. KDS 14 20(MOLIT 2021)์—์„œ ์ œ์•ˆํ•˜๋Š” FRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋˜์ง€ ์•Š์€ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ถ€์žฌ์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ํ‰๊ฐ€์‹์— ์˜ํ•œ GF45-4, GF90-3 ๋ฐ GF90-4์˜ ์˜ˆ์ธก๊ฒฐ๊ณผ(Tn.KDS)์— ๋Œ€ํ•œ ์‹คํ—˜๊ฒฐ๊ณผ(Tn.exp)์˜ ๋น„๋Š” 2.06, 2.15, 1.83์œผ๋กœ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ๊ณผ์†Œํ‰๊ฐ€ ํ•˜์˜€๋‹ค. ์ด๋Š” FRP์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์— ๋Œ€ํ•œ ๊ธฐ์—ฌ๋ถ„์ด ์‹์— ๋ฐ˜์˜๋˜์ง€ ์•Š์•˜๊ธฐ ๋•Œ๋ฌธ์ด๋‹ค.

fib Bulletin 14(2001)์—์„œ ์ œ์•ˆํ•˜๋Š” FRP๋กœ ๋ณด๊ฐ•๋œ ๋ถ€์žฌ์˜ ์„ฌ์œ  ์ข…๋ฅ˜์— ๋”ฐ๋ฅธ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ํ‰๊ฐ€์‹์— ์˜ํ•œ ์˜ˆ์ธก๊ฒฐ๊ณผ(Tn.Fib)์— ๋Œ€ํ•œ ์‹คํ—˜๊ฒฐ๊ณผ์˜ ๋น„๋Š” 1.17, 0.99, 1.04๋กœ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ์œ ์‚ฌํ•˜๊ฒŒ ์˜ˆ์ธกํ•˜์—ฌ, GFRP ์‹œํŠธ์˜ ์˜ํ–ฅ์„ ํ•ฉ๋ฆฌ์ ์œผ๋กœ ๋ฐ˜์˜ํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•˜์˜€๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ํ•ด๋‹น ์‹์—๋Š” ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์˜ํ–ฅ์ด ์‹์— ๋ฐ˜์˜๋˜์ง€ ์•Š์•„ 45ยฐ์˜ ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ GF45-4์˜ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ๊ณผ์†Œํ‰๊ฐ€ํ•˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค.

Tรคljsten(2002)์€ FRP์˜ ์œ ํšจ ๋ณ€ํ˜•๋ฅ  ๊ฐ’์„ $\varepsilon_{f}$=0.6$\varepsilon_{fu}$๋ฅผ ์‚ฌ์šฉํ•˜์˜€์œผ๋‚˜, ์ด๋Š” CFRP์˜ ์œ ํšจ ๋ณ€ํ˜•๋ฅ ์— ์ ํ•ฉํ•œ ๊ฐ’์ด๋ฉฐ, GFRP์˜ ์œ ํšจ ๋ณ€ํ˜•๋ฅ ์— ๋Œ€ํ•˜์—ฌ๋Š” ์–ธ๊ธ‰ํ•˜๊ณ  ์žˆ์ง€ ์•Š๋‹ค. ๋”ฐ๋ผ์„œ ์ด ์—ฐ๊ตฌ์—์„œ๋Š” ACI440.2R-17(2017)์—์„œ FRP๋กœ 4๋ฉด ๋ณด๊ฐ•๋œ ๋ถ€์žฌ์˜ FRP ์œ ํšจ ๋ณ€ํ˜•๋ฅ ๋กœ ์ œํ•œํ•˜๊ณ  ์žˆ๋Š” $\varepsilon_{f}$=0.004๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์„ ์‚ฐ์ •ํ•˜์˜€๋‹ค. Tรคljsten(2002)์ด ์ œ์•ˆํ•˜๋Š” ์„ฌ์œ  ๋ฐฉํ–ฅ๊ณผ ๋ณด๊ฐ• ๋ฐฉ๋ฒ•์— ๋”ฐ๋ฅธ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ํ‰๊ฐ€์‹์— ์˜ํ•œ ์˜ˆ์ธก๊ฒฐ๊ณผ(Tn.Tรคljsten)์— ๋Œ€ํ•œ ์‹คํ—˜๊ฒฐ๊ณผ์˜ ๋น„๋Š” 0.97, 1.17, 1.06์œผ๋กœ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ์œ ์‚ฌํ•˜๊ฒŒ ์˜ˆ์ธกํ•˜์˜€์œผ๋ฉฐ, ์„ฌ์œ  ๋ฐฉํ–ฅ์˜ ์˜ํ–ฅ์ด ํ•ฉ๋ฆฌ์ ์œผ๋กœ ๋ฐ˜์˜ํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•˜์˜€๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ Tรคljsten(2002)์˜ ์ œ์•ˆ์‹์€ ์ฒ ๊ทผ ๊ฐ•๋„์˜ ์˜ํ–ฅ์ด ๋ฐ˜์˜๋˜์ง€ ์•Š์•„ SD300 ๋“ฑ๊ธ‰์˜ ์ฒ ๊ทผ์„ ์‚ฌ์šฉํ•œ GF90-3์˜ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ๊ณผ์†Œํ‰๊ฐ€ํ•˜๋Š” ๊ฒƒ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค.

5. ๊ฒฐ ๋ก 

์ด ์—ฐ๊ตฌ์—์„œ๋Š” FRP ๋ณด๊ฐ•๊ณผ ๊ด€๋ จํ•œ ๊ตญ๋‚ด ๊ตฌ์กฐ๊ธฐ์ค€ ๋งˆ๋ จ์— ์•ž์„œ ์ฐธ๊ณ  ๊ฐ€๋Šฅํ•œ ๋ฐ์ดํ„ฐ๋ฒ ์ด์Šค ์ œ๊ณต์„ ์œ„ํ•ด GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋ณด์˜ ๋น„ํ‹€๋ฆผ ๊ฑฐ๋™์— ๊ด€ํ•œ ์‹คํ—˜์  ์—ฐ๊ตฌ๋ฅผ ์ˆ˜ํ–‰ํ•˜์˜€์œผ๋ฉฐ, ๋‹ค์Œ๊ณผ ๊ฐ™์€ ๊ฒฐ๋ก ์„ ์–ป์—ˆ๋‹ค.

1) ๋ชจ๋“  ์‹คํ—˜์ฒด๋Š” ๋น„ํ‹€๋ฆผ ๊ท ์—ด ๋ฐœ์ƒ ์ดํ›„ ์ดˆ๊ธฐ ๋น„ํ‹€๋ฆผ ๊ฐ•์„ฑ์ด ๊ธ‰๊ฒฉํžˆ ์ €ํ•˜๋˜์—ˆ์œผ๋ฉฐ, GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด๋Š” ๋ณด๊ฐ•๋˜์ง€ ์•Š์€ ์‹คํ—˜์ฒด์™€ ๋น„๊ตํ•˜์—ฌ ์ตœ๋Œ€ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์ด ํ‰๊ท  50 % ์ƒ์Šนํ•˜์˜€๋‹ค. ์ด๋ฅผ ํ†ตํ•ด GFRP ์‹œํŠธ ๋ณด๊ฐ•์ด ๋ถ€์žฌ์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ์ƒ์Šน์— ํšจ๊ณผ์ ์œผ๋กœ ์ž‘์šฉํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•˜์˜€๋‹ค.

2) GFRP ์‹œํŠธ๋Š” ์„ฌ์œ  ๋ฐฉํ–ฅ๊ณผ ๊ด€๊ณ„์—†์ด ์Šคํ„ฐ๋ธŒ ๋ถ€๊ทผ์˜ ์‹คํ—˜๊ตฌ๊ฐ„ ๋‹จ๋ถ€์—์„œ ์‹œํŠธ์˜ ๋ฐ•๋ฆฌ ๋ฐ ํŒŒ๋‹จ์ด ๋ฐœ์ƒํ•˜์˜€์œผ๋ฉฐ, ๋น„ํ‹€๋ฆผ ์‘๋ ฅ์ด ์ง‘์ค‘๋˜๋Š” ๋‹จ๋ฉด์˜ ๋ชจ์„œ๋ฆฌ ๋ถ€๊ทผ์—์„œ ๊ตญ๋ถ€์ ์œผ๋กœ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ์ด๋Ÿฌํ•œ ์‹œํŠธ์˜ ๋ฐ•๋ฆฌ ๋ฐ ํŒŒ๋‹จ์„ ๋ฐฉ์ง€ํ•˜๊ธฐ ์œ„ํ•ด์„œ๋Š” ์•ต์ปค ๋˜๋Š” ์•ต๊ธ€์„ ์„ค์น˜ํ•˜์—ฌ ์‹œํŠธ ๋ชจ์„œ๋ฆฌ ๋ถ€๊ทผ์˜ ๊ตฌ์† ์กฐ๊ฑด์— ๋Œ€ํ•œ ๊ฐœ์„ ์ด ํ•„์š”ํ•  ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค.

3) GFRP ์‹œํŠธ์˜ ๋ณ€ํ˜•๋ฅ ์€ ํšก๋ณด๊ฐ•๊ทผ ํ•ญ๋ณต ์ดํ›„์— ๊ธ‰๊ฒฉํžˆ ์ฆ๊ฐ€ํ•˜์—ฌ ๋น„ํ‹€๋ฆผ์— ์ €ํ•ญํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•˜์˜€๋‹ค. ์‹œํŠธ์˜ ๋ฐ•๋ฆฌ ๋ฐ ํŒŒ๋‹จ์ด ๋ฐœ์ƒํ•œ ์Šคํ„ฐ๋ธŒ์— ๊ฐ€๊นŒ์šธ์ˆ˜๋ก ๋†’์€ ๋ณ€ํ˜•๋ฅ ์„ ๋‚˜ํƒ€๋‚ด์–ด ์‹œํŠธ์˜ ์†์ƒ์ด ๋ณ€ํ˜•๋ฅ ์— ์˜ํ–ฅ์„ ๋ฏธ์ณค์Œ์„ ํ™•์ธํ•˜์˜€๋‹ค.

4) FRP์˜ ๋น„ํ‹€๋ฆผ์— ๋Œ€ํ•œ ๊ธฐ์—ฌ๋ถ„์ด ๋ฐ˜์˜๋˜์ง€ ์•Š์€ KDS 14 20์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ ํ‰๊ฐ€์‹์€ GFRP ์‹œํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹คํ—˜์ฒด์˜ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ๊ณผ์†Œํ‰๊ฐ€ํ•˜์˜€๋‹ค. fib Bulletin 14์™€ Tรคljsten์˜ ํ‰๊ฐ€์‹์€ ์‹คํ—˜๊ฒฐ๊ณผ๋ฅผ ํ•ฉ๋ฆฌ์ ์œผ๋กœ ์˜ˆ์ธกํ•˜๋Š” ๋ฐ˜๋ฉด, ์ด๋“ค ์‹์€ ๊ฐ๊ฐ ์„ฌ์œ  ๋ฐฉํ–ฅ๊ณผ ์ฒ ๊ทผ ๊ฐ•๋„์˜ ์˜ํ–ฅ์„ ๋ฐ˜์˜ํ•˜์ง€ ์•Š์•„ ์ด์™€ ๊ด€๋ จ๋œ ๋ณ€์ˆ˜๋ฅผ ๊ฐ–๋Š” ์‹คํ—˜์ฒด์˜ ๋น„ํ‹€๋ฆผ ๋‚ด๋ ฅ์„ ๊ณผ์†Œํ‰๊ฐ€ํ•˜๋Š” ๊ฒฝํ–ฅ์„ ๋‚˜ํƒ€๋ƒˆ๋‹ค.

๊ฐ์‚ฌ์˜ ๊ธ€

์ด ๋…ผ๋ฌธ์€ 2021๋…„๋„ ๊ต์œก๋ถ€์˜ ์žฌ์›์œผ๋กœ ์ค‘์ ์—ฐ๊ตฌ์†Œ์ง€์›์‚ฌ์—…(2019R1A6A1A03032988) ๋ฐ ์ •๋ถ€(๊ณผํ•™๊ธฐ์ˆ ์ •๋ณดํ†ต์‹ ๋ถ€)์˜ ์žฌ์›์œผ๋กœ ํ•œ๊ตญ์—ฐ๊ตฌ์žฌ๋‹จ(2018R1A2B3001656) ๋ฐ ์ •๋ถ€(๊ต์œก๋ถ€)์˜ ์žฌ์›์œผ๋กœ ํ•œ๊ตญ์—ฐ๊ตฌ์žฌ๋‹จ(2019R1I1A3A01058156) ๋ฐ ๊ตญํ† ๊ตํ†ต๋ถ€ ๊ตญํ† ๊ตํ†ต๊ธฐ์ˆ ์ด‰์ง„์—ฐ๊ตฌ์‚ฌ์—…(20CTAP-C152175-02)์˜ ์ง€์›์„ ๋ฐ›์•„ ์ˆ˜ํ–‰๋œ ์—ฐ๊ตฌ์ž„.

References

1 
ACI Committee 440 , 2017, Guide for the Design and Construction of Externally Bonded FRP Systems for Strengthening Concrete Structures (440.2R-17), Farmington Hills, Michigan, US: American Concrete Institute (ACI)Google Search
2 
Alabdulhady M. Y., Sneed L. H., 2019, Torsional Strengthening of Reinforced Concrete Beams with Externally Bonded Composites: A State of the Art Review, Construction and Building Materials 205, 148-163DOI
3 
ASTM D3039/D3039M-17 , 2017, Standard Test Method for Tensile Properties of Polymer Matrix Composite Materials. West Conshohocken, PA; ASTM International.Google Search
4 
Chalioris C. E., 2008, Torsional Strengthening of Rectangular and Flanged Beams Using Carbon Fibre-Reinforced-Polymers-Experimental Study, Construction and Building Materials, Vol. 22, No. 1, pp. 21-29DOI
5 
fib , 2001, Externally Bonded FRP Reinforcement of RC Structures (fib Bulletin 14), Lausanne, Switzerland; International Federation for Structural Concrete (fib), pp. 59-68Google Search
6 
Jariwala V. H., Patel P. V., Purohit S. P., 2013, Strengthening of RC Beams Subjected to Combined Torsion and Bending with GFRP Composites, Procedia Engineering 51, pp. 282-289DOI
7 
Kang D. E., Woo H. S., Choi K. S., You Y. C., Yi W. H., 2008, Evaluation of Shear Capacity of RC Beams Strengthened with Fiber Reinforced Polymers, Journal of the Architectural Institute of Korea Structure & Construction, Vol. 24, No. 10, pp. 3-10Google Search
8 
Kim M. J., Kim H. G., Lee Y. J., Kim D. H., Lee J. Y., Kim K. H., 2020, Pure Torsional Behavior of RC Beams in Relation to the Amount of Torsional Reinforcement and Cross-Sectional Properties, Construction and Building Materials 260, 119801DOI
9 
Lee L. H., Lee Y. T., Kim S. H., Lim D. K., 1997, Shear Performance of Repaired R/C Beams with Carbon Fiber Sheet, Journal of the Architectural Institute of Korea Structure & Construction, Vol. 17, No. 1, pp. 519-523Google Search
10 
MOLIT , 2021, Design Standard of Concrete Sturctural (KDS 14 20), Sejong, Korea: Ministry of Land, Infrastructure and Transport (MOLIT). (In Korean)Google Search
11 
Panchacharam S., Belarbi A., 2002, Torsional Behavior of Reinforced Concrete Beams Strengthened with FRP Composites., Osaka, Japan; In First FIB Congress, Vol. 1, No. 1, pp. 1-110Google Search
12 
Tรคljsten B., 2002, FRP Strengthening of Existing Concrete Structures: Design Guidelines, Division of Structural Engineering, Luleรฅ University of Technology, pp. 73-84Google Search
13 
Triantafillou T. C., 1998, Shear Strengthening of Reinforced Concrete Beams Using Epoxy-Bonded FRP Composites, ACI Structural Journal 95, pp. 107-115Google Search