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Journal of the Korea Concrete Institute

J Korea Inst. Struct. Maint. Insp.
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  • Korea Citation Index (KCI)




ํƒ„์†Œ์„ฌ์œ ์‰ฌํŠธ, ๊ตฌ์†, ์ฝ˜ํฌ๋ฆฌํŠธ, ์ตœ๋Œ€์••์ถ•๊ฐ•๋„, ๊ฐ•๋„์ถ”์ •์‹, ๋ณด๊ฐ•ํšจ๊ณผ, ์‘๋ ฅ๏ผ๋ณ€ํ˜•๋ฅ  ๊ณก์„ 
CFRP sheet, Confinement, Concrete, Maximum compressive strength, Strength model, Strengthening effect, Stress-strain curve

1. ์„œ ๋ก 

1.1 ์—ฐ๊ตฌ ๋ฐฐ๊ฒฝ ๋ฐ ๋ชฉ์ 

์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ(Reinforced Concrete, RC)๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๋‹จ ์ ์ธ ์ธ์žฅ๊ฐ•๋„๋ฅผ ์ฒ ๊ทผ์œผ๋กœ ๋ณด๊ฐ•ํ•˜์—ฌ ์ˆ˜๋งŽ์€ ๊ฑด์ถ•๋ฌผ๊ณผ ํ† ๋ชฉ๊ตฌ ์กฐ๋ฌผ์— ๊ด‘๋ฒ”์œ„ํ•˜๊ฒŒ ์ ์šฉ๋˜์–ด์ง€๊ณ  ์žˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌํŠธ ๋Š” ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ค‘์„ฑํ™”์™€ ์ฒ ๊ทผ์˜ ๋ถ€์‹, ํ•˜์ค‘ ์กฐ๊ฑด์˜ ๋ณ€ํ™”, ์œ ์ง€ ๊ด€๋ฆฌ์˜ ์†Œํ™€๋กœ ์ธํ•˜์—ฌ ๊ตฌ์กฐ๋ฌผ์˜ ๋‚ด๋ ฅ์„ฑ๋Šฅ์ด ๊ฐ์†Œํ•˜๊ฒŒ ๋˜์–ด ๋ณด๊ฐ• ๋Œ€์ฑ…์ด ์ ˆ์‹คํžˆ ์š”๊ตฌ๋œ๋‹ค(Kim, 2006).

๋‚ด๋ ฅ ์„ฑ๋Šฅ์ด ๊ฐ์†Œํ•œ ๊ตฌ์กฐ๋ฌผ์˜ ๋ณด๊ฐ•๋ฐฉ๋ฒ•์œผ๋กœ๋Š” ์ฒ ๊ทผ์ฝ˜ํฌ๋ฆฌ ํŠธ ๋ถ€์žฌ์™€ ๊ฐ•ํŒ์„ ์—ํญ์‹œ๋กœ ๋ถ€์ฐฉํ•˜๋Š” ๊ฐ•ํŒ์••์ฐฉ๊ณต๋ฒ•, ๋ณด๋‚˜ ๊ธฐ ๋‘ฅ์„ ์ฆ์„คํ•˜๊ฑฐ๋‚˜ ์†์ƒ๋œ ๋‹จ๋ฉด์„ ๋ณต๊ตฌํ•˜๊ฑฐ๋‚˜ ํ™•๋Œ€ํ•˜๋Š” ๋ฐฉ๋ฒ•์ด ์ฃผ๋กœ ์‚ฌ์šฉ๋˜์—ˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ์ด๋Ÿฌํ•œ ๋ณด๊ฐ•๋ฐฉ๋ฒ•์€ ๊ตฌ์กฐ๋ฌผ์˜ ์ค‘๋Ÿ‰ ์ฆ๊ฐ€, ๋„“์€ ์ž‘์—… ๊ณต๊ฐ„ ์š”๊ตฌ์™€ ์ด์šฉ ๊ณต๊ฐ„ ์ œํ•œ, ๋ณด๊ฐ•์žฌ์˜ ๋ถ€์‹ ๋“ฑ ๋งŽ์€ ๋‹จ์ ์„ ๊ฐ€์ง€๊ณ  ์žˆ๋‹ค. ์ด๋Ÿฌํ•œ ๋ฌธ์ œ์ ์„ ํ•ด๊ฒฐํ•˜๊ธฐ ์œ„ํ•ด 1980๋…„๋Œ€์— ๋“ค์–ด์™€์„œ๋Š” ๋ฏธ๊ตญ, ์ผ๋ณธ์„ ์‹œ์ž‘์œผ๋กœ ๋ณตํ•ฉ์„ฌ์œ ์™€ ์ˆ˜์ง€๋ฅผ ์ด์šฉํ•œ ๋ณด๊ฐ•๋ฐฉ๋ฒ•์ด ์ œ์‹œ๋˜์—ˆ๊ณ  1990๋…„๋Œ€๋ถ€ํ„ฐ ๋ณตํ•ฉ์„ฌ ์œ ๋ฅผ ์ด์šฉํ•œ ๋ณด๊ฐ• ํšจ๊ณผ์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๊ฐ€ ํ™œ๋ฐœํžˆ ์ง„ํ–‰๋˜์–ด ์™”์œผ ๋‚˜ ๋Œ€๋ถ€๋ถ„ ํœจ๋ถ€์žฌ์— ํŽธ์ค‘๋˜์–ด ์žˆ๋‹ค. ๊ตญ๋‚ด์—์„œ ์••์ถ•๋ถ€์žฌ์— ๋Œ€ ํ•œ ์—ฐ๊ตฌ๋Š” ๋ถ€์žฌ์˜ ๋‹จ๋ฉดํ˜•์ƒ(Hwang, 2000), ๋ณด๊ฐ•๋Ÿ‰(Chung et al., 1998; Hwang, 2000; Hwang, 2001), ๋ณด๊ฐ•์žฌ์˜ ๊ฒน์นจ๊ธธ์ด (Shin et al., 1995; Chung et al., 1998), ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๊ฐ•๋„ (Hwang, 2001) ๋“ฑ์˜ ์˜ํ–ฅ์— ๋Œ€ํ•œ ์‹œํ—˜์—ฐ๊ตฌ๊ฐ€ ์žˆ๋‹ค. ๊ทธ๋Ÿฌ๋‚˜ ์ œ ํ•œ๋œ ๋ณ€์ˆ˜์˜์—ญ์œผ๋กœ ์ธํ•˜์—ฌ ๊ณ ๋ คํ•˜์ง€ ๋ชปํ•œ ๋ถ€๋ถ„์ด ์กด์žฌํ•˜๊ณ  ์žˆ์–ด ๊ธฐ์กด ์—ฐ๊ตฌ๊ฒฐ๊ณผ๋ฅผ ๋ณด์™„ํ•˜๊ธฐ ์œ„ํ•œ ์ถ”๊ฐ€์ ์ธ ์‹คํ—˜์ด ํ•„์š” ํ•œ ์‹ค์ •์ด๋‹ค. ๋”ฐ๋ผ์„œ ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๋ณด๊ฐ•์žฌ์˜ ๊ฒน์ˆ˜, ๊ธฐ๋‘ฅ์˜ ํฌ ๊ธฐํšจ๊ณผ, ํ˜•์ƒ๋น„ ๋ฐ ๊ฒน์ด์Œ ๊ธธ์ด์˜ ์˜ํ–ฅ์— ๋Œ€ํ•ด ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜ ์—ฌ ๊ทธ ๊ฒฐ๊ณผ๋ฅผ ๋น„๊ต, ๋ถ„์„ํ•˜์˜€๋‹ค. ๊ทธ๋ฆฌ๊ณ  FRP๋กœ ๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌ ํŠธ์˜ ๊ฐ•๋„๋ชจ๋ธ ์˜ˆ์ธก์‹์ด ๋งŽ์€ ์—ฐ๊ตฌ์ž๋“ค(Samaan et al., 1998; Miyauchi et al., 1999; Lam and Teng, 2002; Youm et al., 2004) ์— ์˜ํ•ด ์ œ์•ˆ๋˜์–ด ์žˆ๋Š”๋ฐ, ๋ณธ ์—ฐ๊ตฌ์—์„œ์˜ ์‹œํ—˜๊ฒฐ๊ณผ์™€ ๊ธฐ์กด ์—ฐ ๊ตฌ๊ฒฐ๊ณผ๋ฅผ ์ •๋ฆฌํ•˜๊ณ  ์ด๋ฅผ ๋ฐ”ํƒ•์œผ๋กœ ๊ธฐ์กด์— ์ œ์•ˆ๋œ ๊ฐ•๋„์˜ˆ์ธก๋ชจ ๋ธ๋“ค์˜ ์ •ํ™•์„ฑ์„ ๊ฒ€์ฆํ•˜์˜€๋‹ค.

1.2 ๊ธฐ์กด ์—ฐ๊ตฌ๊ฒฐ๊ณผ

FRP ์‰ฌํŠธ(sheet)๋ฅผ ์ด์šฉํ•˜์—ฌ ์ฝ˜ํฌ๋ฆฌํŠธ ์••์ถ•๋ถ€์žฌ์˜ ๋ณด๊ฐ•ํšจ ๊ณผ์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋Š” 1990๋…„๋Œ€๋ถ€ํ„ฐ 2000๋…„๋Œ€๊นŒ์ง€ ํ™œ๋ฐœํžˆ ์—ฐ๊ตฌ ๊ฐ€ ์ง„ํ–‰๋˜์—ˆ์œผ๋ฉฐ, ํŠนํžˆ ์••์ถ•๊ฐ•๋„์— ์˜ํ–ฅ์„ ๋ฏธ์น  ์ˆ˜ ์žˆ๋Š” ์˜ํ–ฅ ์ธ์ž์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๊ฐ€ ์ฃผ๋ฅผ ์ด๋ฃจ์—ˆ๋‹ค. ์••์ถ•๊ฐ•๋„์— ์˜ํ–ฅ์„ ๋ฏธ์น  ์ˆ˜ ์žˆ๋Š” ์ฃผ์š” ์ธ์ž๋กœ๋Š” ๋ถ€์žฌ์˜ ๋‹จ๋ฉดํ˜•์ƒ, FRP ์‰ฌํŠธ์˜ ๋ณด๊ฐ•๋Ÿ‰, ์‰ฌํŠธ ๋ฐ ์—ํญ์‹œ์˜ ์ข…๋ฅ˜, ๋ณด๊ฐ•์žฌ์˜ ๊ฒน์ด์Œ ๊ธธ์ด, ์ฝ˜ํฌ๋ฆฌํŠธ ๊ฐ•๋„ ๋“ฑ์ด ์žˆ์œผ๋ฉฐ, ์ด๋Ÿฐ ์˜ํ–ฅ์ธ์ž๊ฐ€ ์••์ถ•๊ฐ•๋„์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ์„ ์ • ๋Ÿ‰์ ์œผ๋กœ ํ‰๊ฐ€ํ•˜๊ธฐ ์œ„ํ•ด ๋งŽ์€ ์—ฐ๊ตฌ๊ฐ€ ์ง„ํ–‰๋˜์—ˆ๊ณ  ๊ทธ ๊ฒฐ๊ณผ๋ฅผ ํ† ๋Œ€๋กœ ๊ฐ•๋„์˜ˆ์ธก๋ชจ๋ธ๋„ ๋‹ค์–‘ํ•˜๊ฒŒ ์ œ์•ˆ๋˜์—ˆ๋‹ค.

๊ธฐ์กด ์—ฐ๊ตฌ์—์„œ ์‰ฌํŠธ๋ฅผ ์ด์šฉํ•œ ๋ณด๊ฐ•๋ฐฉ๋ฒ•์€ ๋ถ€์žฌ์˜ ์ธก๋ฉด ์ „ ์ฒด๋ฅผ ๊ฐ์‹ธ๋Š” ๋ฐฉ๋ฒ•๊ณผ ๋ ์ฒ˜๋Ÿผ ๊ฐ์•„์„œ ๋ณด๊ฐ•ํ•˜๋Š” ๋ฐฉ๋ฒ•์ด ์žˆ์œผ๋ฉฐ, ๋Œ€๋ถ€๋ถ„ ์ธก๋ฉด ์ „์ฒด๋ฅผ ๊ฐ์‹ธ๋Š” ๋ฐฉ๋ฒ•์„ ์‚ฌ์šฉํ•˜์˜€๋‹ค. FRP ์‰ฌํŠธ์˜ ๋ณด๊ฐ•ํšจ๊ณผ๋Š” ๋ฌด๋ณด๊ฐ•๊ณต์‹œ์ฒด์˜ ์••์ถ•๊ฐ•๋„์— ๋Œ€ํ•œ ๋ณด๊ฐ•๊ณต์‹œ์ฒด ์•• ์ถ•๊ฐ•๋„์˜ ๋น„(์ดํ•˜, ๊ฐ•๋„๋น„)๋กœ ํ‘œํ˜„ํ•˜์˜€์œผ๋ฉฐ ๋ณด๊ฐ•๋Ÿ‰(์‰ฌํŠธ ๋‘ ๊ป˜)์— ๋Œ€ํ•ด ๊ฐ•๋„๋น„๋Š” ๋น„๋ก€์ ์œผ๋กœ ์ฆ๊ฐ€ํ•˜๋Š” ๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ด์—ˆ ๋‹ค(Chung et al., 1998; Miyauci et al., 1997; Miyauci et al., 1999; Hwang, 2000; Hwang, 2001). ์‰ฌํŠธ์˜ ๊ฒน์ด์Œ ๊ธธ์ด๊ฐ€ ์ฆ ๊ฐ€ํ•จ์— ๋”ฐ๋ผ ์••์ถ•๊ฐ•๋„๋„ ์ฆ๊ฐ€ํ•œ๋‹ค(Shin et al., 1995)๋Š” ์—ฐ๊ตฌ๊ฒฐ ๊ณผ๊ฐ€ ์žˆ์œผ๋‚˜ ์ด ์—ฐ๊ตฌ๋Š” ๊ฒน์ด์Œ ๊ธธ์ด๋งŒ์˜ ์˜ํ–ฅ์ด ์•„๋‹ˆ๋ผ ๋ณด๊ฐ• ๋Ÿ‰์—๋„ ์˜ํ–ฅ์„ ๋ฏธ์น˜๋„๋ก ๋ณ€์ˆ˜๋ฅผ ์ •ํ•˜์—ฌ์„œ ์—ฐ๊ตฌ๊ฒฐ๊ณผ์— ๋Œ€ํ•ด ์žฌ๊ณ ํ•  ํ•„์š”๊ฐ€ ์žˆ๋‹ค. ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๊ฐ•๋„์˜ ์ฆ๊ฐ€์— ๋”ฐ๋ผ ๊ฐ•๋„๋น„ ๋Š” ๊ฐ์†Œํ•˜๋Š” ๊ฒฝํ–ฅ(Kim, 2003; Park, 2001; Youm et al., 2004) ์ด ๋‚˜ํƒ€๋‚˜๊ณ  ์žˆ๋‹ค.

2. ์‹œํ—˜๊ณ„ํš

2.1 ์‹œํ—˜์ฒด

์‹œํ—˜์ฒด๋Š” Fig. 1์— ๋‚˜ํƒ€๋‚ธ ๊ฒƒ๊ณผ ๊ฐ™์ด ์ง๊ฒฝ์ด 100 mm์ด๊ณ , ๋†’์ด๊ฐ€ 200 mm์ธ ์›์ฃผํ˜• ์‹œํ—˜์ฒด๋ฅผ ๊ธฐ์ค€์œผ๋กœ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ํฌ ๊ธฐ ํšจ๊ณผ๋ฅผ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์ง๊ฒฝ์ด 75, 125 mm์ด๊ณ , ํ˜•์ƒ๋น„ (H/D)๊ฐ€ 2.0์ธ ์‹œํ—˜์ฒด๋ฅผ ์ œ์ž‘ํ•˜์˜€์œผ๋ฉฐ, ํ˜•์ƒ๋น„์˜ ์˜ํ–ฅ์€ ์••์ถ• ์‹œํ—˜๊ธฐ์˜ ๋†’์ด๊ฐ€ 350 mm๋กœ ์ œํ•œ๋˜๋ฏ€๋กœ ์ง๊ฒฝ์ด 75 mm์ธ ์‹œ ํ—˜์ฒด๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ํ˜•์ƒ๋น„์˜ ์˜ํ–ฅ์„ ํ™•์ธํ•˜์˜€๋‹ค. 1์ฐจ ์‹œํ—˜์—์„œ ๊ฐ ๋ณ€์ˆ˜๋ณ„๋กœ ์‹œํ—˜์ฒด๋ฅผ 3๊ฐœ์”ฉ ์ œ์ž‘ํ•˜์˜€์œผ๋ฉฐ, ๋ฐ์ดํ„ฐ์˜ ์œ ์‹ค๊ณผ ์‹œํ—˜ ๊ฒฐ๊ณผ์˜ ํฐ ํŽธ์ฐจ๋กœ ์ธํ•ด ์ถ”๊ฐ€ ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€์œผ๋ฉฐ, ์ถ”๊ฐ€ ์‹œํ—˜์‹œ ๋ณ€์ˆ˜๋ณ„๋กœ 2๊ฐœ์”ฉ ์ œ์ž‘ํ•˜์—ฌ ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ๊ฐ ์‹œํ—˜ ์ฒด๋ณ„ ์ƒ์„ธ๋Š” Table 1์— ์ •๋ฆฌํ•˜์˜€๋‹ค.

Fig. 1

Test Specimen

JKSMI-19-10_F1.jpg
Table 1

Summary of test parameters

Parameter Specimen Layers Dimension (mm) H/D & Overlap length (mm)
- T0 - D=100 H=200 H/D=2.0
No. of layers T1 1 D=100 H=200 H/D=2.0 (OL=30)
T2 2
T3 3
Specimen size T4 1 D=75 H=150 H/D=2.0 (OL=30)
T1 D=100 H=200
T5 D=125 H=250
Aspect ratio (H/D) T4 1 D=75H=150 H/D=2.0 (OL=30)
T6 D=75 H=225 H/D=3.0 (OL=30)
T7 D=75 H=300 H/D=4.0 (OL=30)
Overlap length T8 1 D=100 H=200 H/D=2.0 (OL=0)
T9 H/D=2.0 (OL=15)
T1 H/D=2.0 (OL=30)
T10 H/D=2.0 (OL=45)

2.2 ์‚ฌ์šฉ ์žฌ๋ฃŒ

2.2.1 ์ฝ˜ํฌ๋ฆฌํŠธ

์‹œํ—˜์ฒด ์ œ์ž‘์—๋Š” ์ผ๋ฐ˜ ๋ ˆ๋ฏธ์ฝ˜ ์ œํ’ˆ์„ ์‚ฌ์šฉํ•˜์˜€์œผ๋ฉฐ, ์‚ฌ์šฉ ๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์žฌ๋ฃŒ์‹œํ—˜๊ฒฐ๊ณผ๋ฅผ Table 2์— ์ •๋ฆฌํ•˜์˜€๋‹ค.

Table 2

Characteristics of concrete

Uniaxial compressive strength(MPa) 33.3
Slump(cm) 9.8
Maximum size of aggregate(mm) 25
Type of cement Portland Type 1
Air content(%) 3.2

2.2.2 ํƒ„์†Œ์„ฌ์œ ์‰ฌํŠธ(CFRP sheet)

๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ์ผ๋ณธ T์‚ฌ์—์„œ ์ œ์กฐ๋œ FTS-C1-30์„ ์‚ฌ์šฉํ•˜ ์˜€์œผ๋ฉฐ ์ด ์‰ฌํŠธ๋Š” ํด๋ฆฌ์•„ํฌ๋ฆด๋‹ˆํŠธ๋ž„(Polyacrylonitrile, PAN) ๊ณ„์ธ ํƒ„์†Œ์„ฌ์œ ์‰ฌํŠธ๋กœ ์ฝ˜ํฌ๋ฆฌํŠธ ๊ตฌ์กฐ๋ฌผ์˜ ์œ ์ง€๋ณด์ˆ˜์— ๋งŽ์ด ์‚ฌ ์šฉ๋˜๊ณ  ์žˆ๋Š” ์ œํ’ˆ์ด๋‹ค. Table 3์— ์ œ์กฐ์‚ฌ์—์„œ ์ œ๊ณตํ•œ ์žฌ๋ฃŒ์˜ ๋ฌผ์„ฑ์น˜๋ฅผ ์ •๋ฆฌํ•˜์˜€๋‹ค.

Table 3

Mechanical properties of CFRP sheet

Model FTS-C1-30
Tensile strength (MPa) 3,480
Modulus of elasticity (MPa) 2.30 105
Thickness (mm) 0.17
Density (g/cm3) 1.82
Ultimate elongation at break (%) 1.5

2.2.3 ์—ํญ์‹œ(Epoxy)

ํƒ„์†Œ์„ฌ์œ ์‰ฌํŠธ๋ฅผ ์ ‘์ฐฉํ•˜๋Š”๋ฐ ์‚ฌ์šฉ๋œ ์—ํญ์‹œ๋Š” S์‚ฌ์˜ Sikadur- 31์ œํ’ˆ์„ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ์ด ์—ํญ์‹œ๋Š” ๋ชจ์ฒด์˜ ์Šต์œค์—ฌ๋ถ€์— ์ƒ๊ด€ ์—†์ด ์‹œ๊ณต์ด ๊ฐ€๋Šฅํ•˜๊ณ  ๋‹ค์–‘ํ•œ ๊ฑด์„ค์žฌ๋ฃŒ์— ๋Œ€ํ•œ ์ ‘์ฐฉ๋ ฅ์ด ๋งค ์šฐ ์šฐ์ˆ˜ํ•˜๋ฉฐ, ๊ณ ๊ฐ•๋„, ๊ณ ํƒ„์„ฑ, ๋‚ด๋งˆ๋ชจ์„ฑ, ๋‚ด์ถฉ๊ฒฉ์„ฑ์ด ์šฐ์ˆ˜ํ•œ ๊ฒƒ์œผ๋กœ ์•Œ๋ ค์ ธ ์žˆ๋‹ค. Table 4์— ์—ํญ์‹œ์˜ ๋ฌผ์„ฑ์„ ์ •๋ฆฌํ•˜์˜€๋‹ค.

Table 4

Mechanical properties of epoxy

Model Sikadur-31
Tensile strength (MPa, 14-day) 25
Bond strength (MPa, 14-day) 16.8
Modulus of elasticity (MPa, 7-day) 2,689.7

2.3 ์‹œํ—˜ ์žฅ์น˜ ๋ฐ ์ธก์ • ๋ฐ์ดํƒ€

์‹œํ—˜์€ M์‚ฌ์—์„œ ์ œ์ž‘ํ•œ ์••์ถ•๊ฐ•๋„์‹œํ—˜๊ธฐ, MT-150AC(1,470 kN)๋ฅผ ์‚ฌ์šฉํ•˜์˜€์œผ๋ฉฐ, Photo 1์— ๋‚˜ํƒ€๋‚ธ ๊ฒƒ๊ณผ ๊ฐ™์ด ์‹œํ—˜์ฒด๋ฅผ ์„ค์น˜ํ•˜์—ฌ ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์‹œํ—˜์‹œ ์ธก์ •ํ•œ ๋ฐ์ดํ„ฐ๋Š” ์ถ•๋ฐฉ ํ–ฅ ํ•˜์ค‘๊ณผ ๋ณ€์œ„, ์‹œํ—˜์ฒด ์ค‘์•™์—์„œ์˜ ์ข…,ํšก ๋ณ€ํ˜•๋ฅ , ์‹œํ—˜์ฒด ์ƒ ๋‹จ์—์„œ์˜ ํšก๋ฐฉํ–ฅ๋ณ€ํ˜•๋ฅ ์„ ์ธก์ •ํ•˜์˜€์œผ๋ฉฐ, ๋ฐ์ดํ„ฐ ์ˆ˜์ง‘์€ M์‚ฌ ์˜ ๋™์ ๋ณ€ํ˜•๋ฅ ์ธก์ •๊ธฐ(MDS16)๋ฅผ ์‚ฌ์šฉํ•˜์˜€๋‹ค.

Photo 1

Test setup

JKSMI-19-10_P1.jpg

3. ์‹œํ—˜ ๊ฒฐ๊ณผ ๋ฐ ๋ถ„์„

์›ํ˜•๊ณต์‹œ์ฒด์— CFRP ์‰ฌํŠธ๋กœ ๋ณด๊ฐ•ํ•œ ์‹œํ—˜์ฒด์— ๋Œ€ํ•˜์—ฌ ์ผ์ถ• ์••์ถ•์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•œ ๊ฒฐ๊ณผ Table 5์™€ ๊ฐ™์€ ๊ฒฐ๊ณผ๋ฅผ ์–ป์—ˆ์œผ๋ฉฐ, 1์ฐจ ์‹œํ—˜๊ฒฐ๊ณผ๋Š” 1~3, ์ถ”๊ฐ€์‹œํ—˜๊ฒฐ๊ณผ๋Š” 4~5๋กœ ํ‘œ์‹œํ•˜์˜€๋‹ค. Table 5 ์—๋Š” ๊ฐ ์‹œํ—˜์ฒด ๋ฐ ๋ณ€์ˆ˜๋ณ„ ์ตœ๋Œ€ํ•˜์ค‘, ์••์ถ•๊ฐ•๋„, ๊ฐ•๋„๋น„์™€ ํŒŒ๊ดด ๋ชจ๋“œ๋ฅผ ์ •๋ฆฌํ•˜์˜€์œผ๋ฉฐ, ์‹œํ—˜๊ฒฐ๊ณผ ์ค‘ ํŽธ์ฐจ๊ฐ€ ํฐ ๋ฐ์ดํ„ฐ๋Š” ์ œ์™ธ ํ•˜์—ฌ ๋ถ„์„ํ•˜์˜€๋‹ค. T6-1 ์‹œํ—˜์ฒด๋Š” Loadcell๊ณผ ๋™์ ๋ณ€ํ˜•๋ฅ ๊ธฐ ๊ฐ„ ์˜ ์—ฐ๊ฒฐ ๋ถˆ๋Ÿ‰์œผ๋กœ ์ธํ•ด ํ•˜์ค‘๊ฐ’์„ ์–ป์„ ์ˆ˜ ์—†์—ˆ๋‹ค.

Table 5

Summary of test results

JKSMI-19-10_T5.jpg

3.1 ๋ณด๊ฐ• ๊ฒน์ˆ˜์— ๋”ฐ๋ฅธ ์˜ํ–ฅ

CFRP ์‰ฌํŠธ์˜ ๊ฒน์ˆ˜์— ๋”ฐ๋ฅธ ๋ณด๊ฐ•ํšจ๊ณผ๋ฅผ ๊ฒ€ํ† ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์‰ฌ ํŠธ๋ฅผ 1๊ฒน(T1), 2๊ฒน(T2), 3๊ฒน(T3)์œผ๋กœ ๋ณด๊ฐ•ํ•˜์—ฌ ์••์ถ•๊ฐ•๋„์‹œํ—˜ ์„ ์ˆ˜ํ–‰ํ•˜๊ณ , ๋ฌด๋ณด๊ฐ• ์‹œํ—˜์ฒด(T0)์™€ ๋น„๊ตํ•˜์˜€๋‹ค. Fig. 2๋Š” ๋ณ€์ˆ˜ ๋ณ„ ์‘๋ ฅ๏ผ๋ณ€ํ˜•๋ฅ  ์„ ๋„๋ฅผ ๋ณด์—ฌ์ฃผ๊ณ  ์žˆ์œผ๋ฉฐ, ๋ณด๊ฐ• ๊ฒน์ˆ˜๊ฐ€ ์ฆ๊ฐ€ ํ• ์ˆ˜๋ก ์ตœ๋Œ€์‘๋ ฅ๊ณผ ๋ณ€ํ˜•๋ฅ  ๋ชจ๋‘ ์ฆ๊ฐ€ํ•˜๋Š” ๊ฒฝํ–ฅ์„ ๋‚˜ํƒ€๋‚ด๊ณ  ์žˆ๋‹ค. CFRP ์‰ฌํŠธ์˜ ๋ณด๊ฐ• ๊ฒน์ˆ˜์— ๋Œ€ํ•œ ๋ณด๊ฐ•ํšจ๊ณผ๋ฅผ ํ™•์ธํ•˜๊ธฐ ์œ„ ํ•˜์—ฌ ๋ณด๊ฐ• ๊ฒน์ˆ˜์— ๋Œ€ํ•œ ๊ฐ•๋„๋น„(Strengthening ratio, fโ€ฒcc/ fโ€ฒco)๋ฅผ Fig. 3์— ๋‚˜ํƒ€๋‚ด์—ˆ๋‹ค. CFRP ์‰ฌํŠธ์˜ ๋ณด๊ฐ• ๊ฒน์ˆ˜๊ฐ€ ์ฆ๊ฐ€ํ•จ์— ๋”ฐ ๋ผ ๊ฐ•๋„๋น„๊ฐ€ ์„ ํ˜•์ ์œผ๋กœ ์ฆ๊ฐ€ํ•˜๋Š” ๊ฒฝํ–ฅ์„ ๋‚˜ํƒ€๋‚ด๊ณ  ์žˆ๋Š”๋ฐ, ์ด๋Š” CFRP ์‰ฌํŠธ์˜ ๊ณ ํƒ„์„ฑ์  ํŠน์„ฑ์œผ๋กœ ์ธํ•ด ๋ณด๊ฐ• ๊ฒน์ˆ˜๊ฐ€ ์ฆ๊ฐ€ ํ•จ์— ๋”ฐ๋ผ ํšก๊ตฌ์†์••์ด ์„ ํ˜•์ ์œผ๋กœ ์ฆ๊ฐ€ํ•˜๋ฉฐ, ์ด๋กœ ์ธํ•ด ์••์ถ• ๊ฐ•๋„๊ฐ€ ์ฆ๊ฐ€ํ•˜๊ธฐ ๋•Œ๋ฌธ์ด๋‹ค. ๋ณด๊ฐ• ๊ฒน์ˆ˜์— ๋Œ€ํ•œ ๊ฐ•๋„๋น„๋ฅผ ํšŒ๊ท€ ๋ถ„์„ํ•œ ๊ฒฐ๊ณผ ์‹ (1)๊ณผ ๊ฐ™์€ ๊ฒฝํ–ฅ์„ ๋ณด์ด๊ณ  ์žˆ์œผ๋ฉฐ, ๊ฒฐ์ •๊ณ„์ˆ˜ (R2)๊ฐ€ 0.99๋กœ ๋งค์šฐ ๋†’์€ ์ƒ๊ด€์„ฑ์„ ๋ณด์ด๊ณ  ์žˆ๋‹ค.

Fig. 2

Stress-strain curves (layers)

JKSMI-19-10_F2.jpg
Fig. 3

Effect of layers on strengthening ratio

JKSMI-19-10_F3.jpg
(1)
f cc โ€ฒ f co โ€ฒ = 0.96 n + 1 R 2 = 0.99

์—ฌ๊ธฐ์„œ, n์€ ๋ณด๊ฐ•์žฌ์˜ ๊ฒน์ˆ˜์ด๋‹ค.

3.2 ์‹œํ—˜์ฒด์˜ ํฌ๊ธฐ์˜ ์˜ํ–ฅ

์‹œํ—˜์ฒด์˜ ํฌ๊ธฐ์— ๋”ฐ๋ฅธ ๋ณด๊ฐ•ํšจ๊ณผ๋ฅผ ๊ฒ€ํ† ํ•˜๊ธฐ ์œ„ํ•ด ์‹œํ—˜์ฒด์˜ ์ง๊ฒฝ์„ 75, 100, 125 mm๋กœ ๋ณ€ํ™”ํ•˜์—ฌ ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ํ˜•์ƒ ๋น„(H/D)๋Š” 2.0์œผ๋กœ ๊ณ ์ •ํ•˜์˜€์œผ๋ฉฐ, CFRP ์‰ฌํŠธ๋Š” ๋ชจ๋‘ 1๊ฒน์œผ ๋กœ ๋ณด๊ฐ•ํ•˜์—ฌ ๊ฒฐ๊ณผ๋ฅผ ๋น„๊ตํ•˜์˜€๋‹ค. Fig. 4๋Š” ๋ณ€์ˆ˜๋ณ„ ์‘๋ ฅ๏ผ๋ณ€ํ˜• ๋ฅ  ์„ ๋„๋ฅผ ๋ณด์—ฌ์ฃผ๊ณ  ์žˆ์œผ๋ฉฐ ์ง๊ฒฝ์ด ์ปค์งˆ์ˆ˜๋ก ์ตœ๋Œ€์‘๋ ฅ์ด ์ž‘ ์•„์กŒ๊ณ , ๋ณ€ํ˜•๋ฅ  ๋˜ํ•œ ๊ฐ์†Œํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. Fig. 5๋Š” ์ง๊ฒฝ ์— ๋Œ€ํ•œ ๊ฐ•๋„๋น„๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์œผ๋กœ ์‹œํ—˜์ฒด์˜ ์ง๊ฒฝ์ด ์ฆ๊ฐ€ํ•จ์— ๋”ฐ๋ผ ๋ณด๊ฐ•ํšจ๊ณผ๋Š” ๊ฐ์†Œํ•จ์„ ์•Œ ์ˆ˜ ์žˆ์œผ๋ฉฐ, ์ด๋ฅผ ํ†ตํ•ด ํšก๊ตฌ์†์•• (fl, ์‹ (4))์ด ์ง๊ฒฝ์— ๋ฐ˜๋น„๋ก€ํ•œ๋‹ค๋Š” ์ด๋ก ์„ ์‹œํ—˜์„ ํ†ตํ•ด ์ฆ๋ช… ํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค. ์‹ (2)๋Š” ์ง๊ฒฝ์— ๋Œ€ํ•œ ๊ฐ•๋„๋น„๋ฅผ ํšŒ๊ท€๋ถ„์„ํ•œ ๊ฒฐ๊ณผ ์ด๋ฉฐ, ๊ฒฐ์ •๊ณ„์ˆ˜ R2์€ 0.83์ด๋‹ค.

Fig. 4

Stress-strain curves (diameter effect)

JKSMI-19-10_F4.jpg
(2)
f cc โ€ฒ f co โ€ฒ = 1 , 162.7 D - 1.39 R 2 = 0.88

์—ฌ๊ธฐ์„œ, D๋Š” ์‹œํ—˜์ฒด์˜ ์ง๊ฒฝ์ด๋‹ค.

3.3 ํ˜•์ƒ๋น„ ์˜ํ–ฅ

์‹œํ—˜์ฒด์˜ ํ˜•์ƒ๋น„(H/D)์— ๋”ฐ๋ฅธ ๋ณด๊ฐ•ํšจ๊ณผ๋ฅผ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•˜ ์—ฌ ๋™์ผํ•œ ์ง๊ฒฝ(75 mm)์—์„œ ํ˜•์ƒ๋น„๋ฅผ 2~4๋กœ ๋ณ€ํ™”์‹œ์ผœ ๋ณด๊ฐ• ํšจ๊ณผ๋ฅผ ๋น„๊ตํ•˜์˜€๋‹ค. Fig. 6์€ T4, T6, T7 ์‹œํ—˜์ฒด์˜ ์‘๋ ฅ๏ผ๋ณ€ํ˜• ๋ฅ  ๊ณก์„ ์„ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์œผ๋กœ, ํ˜•์ƒ๋น„๊ฐ€ ์ปค์งˆ์ˆ˜๋ก ์ตœ๋Œ€ ์‘๋ ฅ๊ณผ ์ตœ ๋Œ€ ๋ณ€ํ˜•๋ฅ ์ด ๊ฐ์†Œํ•˜์˜€์œผ๋ฉฐ, ์ด๋Š” ์„ธ์žฅ๋น„์˜ ์˜ํ–ฅ์œผ๋กœ ์‘๋ ฅ์ด ๊ฐ์†Œํ•˜๋Š” ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค. ๊ฐ™์€ ์‘๋ ฅ ๊ฐ’์—์„œ ํ˜•์ƒ๋น„๊ฐ€ ์ปค์ง ์— ๋”ฐ๋ผ ๋ณ€ํ˜•๋ฅ ์ด ์ฆ๊ฐ€ํ•˜์˜€๊ณ , ๊ฐ™์€ ๋ณ€ํ˜•๋ฅ  ๊ฐ’์—์„œ๋Š” ํ˜•์ƒ๋น„ ๊ฐ€ ์ปค์ง์— ๋”ฐ๋ผ ์‘๋ ฅ์ด ๊ฐ์†Œํ•˜๋Š” ๊ฒฝํ–ฅ์„ ๋ณด์ด๊ณ  ์žˆ๋Š”๋ฐ ์ด๋Š” ์„ธ์žฅ๋น„์™€ ์ž„๊ณ„์‘๋ ฅ๊ฐ„์˜ ๊ด€๊ณ„๋ฅผ ๊ทธ๋Œ€๋กœ ๋‚˜ํƒ€๋‚ด๊ณ  ์žˆ๋‹ค. Fig. 7 ์€ ํ˜•์ƒ๋น„์— ๋”ฐ๋ฅธ ๊ฐ•๋„๋น„๋ฅผ ๋‚˜ํƒ€๋‚ธ ๊ฒƒ์œผ๋กœ ํ˜•์ƒ๋น„๊ฐ€ ์ฆ๊ฐ€ํ•จ ์— ๋”ฐ๋ผ ๊ฐ•๋„๋น„๊ฐ€ ์˜ค๋ชฉ๊ณก์„ ์ ์œผ๋กœ ๊ฐ์†Œํ•˜๊ณ  ์žˆ์œผ๋ฉฐ ๊ด€๊ณ„์‹์€ ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค.

Fig. 5

Effect of diameter on strengthening ratio

JKSMI-19-10_F5.jpg
Fig. 6

Stress-strain curves (aspect ratio)

JKSMI-19-10_F6.jpg
Fig. 7

Effect of aspect ratio on strengthening ratio

JKSMI-19-10_F7.jpg
(3)
f cc โ€ฒ f co โ€ฒ = 3.87 H D - 0.46 R 2 = 0.73

์—ฌ๊ธฐ์„œ, D๋Š” ์‹œํ—˜์ฒด์˜ ์ง๊ฒฝ, H๋Š” ์‹œํ—˜์ฒด์˜ ๋†’์ด์ด๋‹ค.

3.4 ๊ฒน์ด์Œ๊ธธ์ด์˜ ์˜ํ–ฅ

๊ฒน์ด์Œ๊ธธ์ด์˜ ์˜ํ–ฅ์— ๋Œ€ํ•ด์„œ๋Š” Shin et al.(1995)์™€ Chung et al.(1998)์— ์˜ํ•ด ์—ฐ๊ตฌ๋œ ๋ฐ”๊ฐ€ ์žˆ์œผ๋‚˜ ๊ฒน์ด์Œ ๊ธธ์ด์˜ ๋ฒ”์œ„๋ฅผ Shin et al.(1995)๋Š” ๋‘˜๋ ˆ์˜ 20~120%๋กœ, Chung et al.(1998)์€ ๋‘˜๋ ˆ์˜ 50~150%๋กœ ๊ฒฐ์ •ํ•˜์—ฌ ์‹คํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์ด๋“ค์˜ ์—ฐ ๊ตฌ๊ฒฐ๊ณผ ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ ๋‘˜๋ ˆ์˜ 20%์ธ ๊ฒฝ์šฐ ๊ฒน์ณ ์ด์€ ๋ถ€๋ถ„์—์„œ ํŒŒ๊ดด๊ฐ€ ๋ฐœ์ƒํ•˜๋‚˜ ๊ตฌ์†ํšจ๊ณผ์—๋Š” ํฐ ์ฐจ์ด๊ฐ€ ์—†์—ˆ์œผ๋ฉฐ, 30%์ด ์ƒ์ธ ๊ฒฝ์šฐ ๋ณด๊ฐ•ํšจ๊ณผ์— ์˜ํ–ฅ์„ ์ฃผ์ง€ ์•Š๋Š”๋‹ค๊ณ  ๋ฐœํ‘œํ•˜์˜€๋‹ค. ๋”ฐ ๋ผ์„œ ๋ณธ ๋…ผ๋ฌธ์—์„œ๋Š” ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ ๋‘˜๋ ˆ์˜ 20% ๋ฏธ๋งŒ์ธ ๊ฒฝ์šฐ ๋ณด๊ฐ•ํšจ๊ณผ์— ์–ด๋–ค ์˜ํ–ฅ์„ ๋ฏธ์น˜๋Š”์ง€ ํ™•์ธํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ๊ฒน์ด์Œ๊ธธ์ด์˜ ๋ฒ”์œ„๋ฅผ ๋‘˜๋ ˆ์˜ 0~15%๋กœ ์ •ํ•˜์˜€์œผ ๋ฉฐ, 5%๊ฐ„๊ฒฉ์œผ๋กœ ๋ณ€ํ™”ํ•˜์—ฌ ์‹œํ—˜์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. Fig. 8์€ ๋ณ€์ˆ˜๋ณ„ ์‘๋ ฅ๏ผ๋ณ€ํ˜•๋ฅ ์„ ๋‚˜ํƒ€๋‚ด๊ณ  ์žˆ์œผ๋ฉฐ, ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ ์—†๋Š” T8 ์‹œ ํ—˜์ฒด๋งŒ ์‘๋ ฅ๊ณผ ๋ณ€ํ˜•๋ฅ ์ด ์ž‘๊ฒŒ ๋‚˜ํƒ€๋‚˜๊ณ  ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ 5~15% ์ธ T9, T1, T10 ์‹œํ—˜์ฒด๋Š” ์ถ•๋ฐฉํ–ฅ ์‘๋ ฅ๏ผ๋ณ€ํ˜•๋ฅ  ๊ฑฐ๋™์ด ์œ ์‚ฌํ•จ ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ๋‹ค. Fig. 9๋Š” ๊ฒน์ด์Œ๊ธธ์ด์— ๋Œ€ํ•œ ๊ฐ•๋„๋น„์˜ ์˜ํ–ฅ ์„ ๋ณด์—ฌ์ฃผ๊ณ  ์žˆ์œผ๋ฉฐ, ๋ณด๊ฐ•๋น„(Confinement ratio, fl/ fcoโ€ฒ)๊ฐ€ ๋™ ์ผํ•œ ๊ธฐ์กด์—ฐ๊ตฌ๊ฒฐ๊ณผ(Hwang, 2000; Shin et al., 1995)์™€ ํ•จ๊ป˜ ๋ถ„ ์„ํ•˜์˜€๋‹ค. ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ ์—†๋Š” ๊ฒฝ์šฐ(T8)๋Š” ๊ฒน์ด์Œ๋ถ€๊ฐ€ ์ „์ฒด์  ์œผ๋กœ ๋ฒŒ์–ด์ง€๋ฉด์„œ ํ• ๋ ฌํŒŒ๊ดด ํ˜•ํƒœ๋ฅผ ๋ณด์˜€์œผ๋ฉฐ, ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ 5%์ด์ƒ์ธ ๊ฒฝ์šฐ์—๋Š” ๋Œ€๋ถ€๋ถ„ ๊ฒน์ด์Œ๋ถ€๋ถ„์ด ๋–จ์–ด์ ธ ๋‚˜๊ฐ€๋ฉฐ ํŒŒ ๊ดด๋˜์—ˆ๋‹ค. ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ ์—†๋Š” ๊ฒฝ์šฐ์—๋Š” ์•ฝ 30%์ •๋„์˜ ๋ณด๊ฐ• ํšจ๊ณผ๊ฐ€ ๋‚˜ํƒ€๋‚ฌ์œผ๋ฉฐ, ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ 5%์ด์ƒ์ธ ๊ฒฝ์šฐ์—๋Š” ์•ฝ 100%์˜ ๋ณด๊ฐ•ํšจ๊ณผ๊ฐ€ ์ผ์ •ํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ๋”ฐ๋ผ์„œ CFRP ์‰ฌํŠธ ๋กœ ๋ณด๊ฐ•ํ•˜๋Š” ๊ฒฝ์šฐ ๊ฒน์ด์Œ๊ธธ์ด๋ฅผ ๋‘˜๋ ˆ์˜ 5% ์ด์ƒ์œผ๋กœ ์‹œ๊ณตํ•ด ๋„ ๋ณด๊ฐ•ํšจ๊ณผ์— ํฐ ์˜ํ–ฅ์ด ์—†๋‹ค.

Fig. 8

Stress-strain curves (overlap length)

JKSMI-19-10_F8.jpg
Fig. 9

Effect of overlap length on strengthening ratio

JKSMI-19-10_F9.jpg

Fig. 9์—์„œ ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ 10%์ธ ์‹œํ—˜์ฒด(T1)์˜ ๊ฒฝ์šฐ ๋ณด๊ฐ•ํšจ ๊ณผ๊ฐ€ 120%์ •๋„๋กœ ๋‹ค๋ฅธ ์‹œํ—˜์ฒด์— ๋น„ํ•ด ํฌ๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋Š”๋ฐ, ์ด๋Š” ๋‹ค๋ฅธ ์‹œํ—˜์ฒด๋“ค๊ณผ ๋‹ฌ๋ฆฌ ๊ฒน์ด์Œ๋ถ€์—์„œ ํŒŒ๊ดด๋˜์ง€ ์•Š๊ณ  CFRP ์‰ฌ ํŠธ์˜ ์ธ์žฅํŒŒ๋‹จ์— ์˜ํ•ด ํŒŒ๊ดด๋˜๋ฏ€๋กœ ๊ตฌ์†ํšจ๊ณผ๊ฐ€ ๋” ํฌ๊ฒŒ ๋‚˜ํƒ€๋‚œ ๊ฒƒ์ด๋‹ค. ๊ฒน์ด์Œ๋ถ€์—์„œ์˜ ํŒŒ๊ดด๋Š” ๊ฒน์ด์Œ๊ธธ์ด ๋ฟ๋งŒ ์•„๋‹ˆ๋ผ ์—ํญ ์‹œ์˜ ๋ถ€์ฐฉ๊ฐ•๋„๋„ ์˜ํ–ฅ์„ ๋ฏธ์น˜๋Š” ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋˜๋ฉฐ ์—ํญ์‹œ์˜ ๋ถ€ ์ฐฉ๊ฐ•๋„์— ๋Œ€ํ•œ ์ถ”๊ฐ€์ ์ธ ์—ฐ๊ตฌ๊ฐ€ ํ•„์š”ํ•  ๊ฒƒ์œผ๋กœ ์‚ฌ๋ฃŒ๋œ๋‹ค.

4. CFRP ์‰ฌํŠธ๋กœ ๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๊ฐ•๋„์ถ”์ •

4.1 FRP๋กœ ๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๊ฐ•๋„์ถ”์ •์— ๋Œ€ํ•œ ๊ธฐ์กด์—ฐ๊ตฌ

ํšก๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์— ๋Œ€ํ•œ ์••์ถ•๊ฐ•๋„ ์ถ”์ •์‹์€ ๋Œ€๋ถ€๋ถ„ ๋‹ค์Œ ๊ณผ ๊ฐ™์€ ํ˜•ํƒœ๋กœ ์ •๋ฆฌ๋œ๋‹ค.

(4)
f cc โ€ฒ f co โ€ฒ = 1 + k 1 f 1 f co โ€ฒ

์—ฌ๊ธฐ์„œ, fcc โ€ฒ๋Š” FRP๋กœ ๋ณด๊ฐ•๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ตœ๋Œ€์••์ถ•๊ฐ•๋„, fco โ€ฒ๋Š” ๋ฌด๋ณด๊ฐ• ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ตœ๋Œ€์••์ถ•๊ฐ•๋„, fl์€ ํšก๊ตฌ์†์••, k1์€ ํšก๊ตฌ์†์œ ํšจ๊ณ„์ˆ˜์ด๋‹ค. ์ด ๋ชจ๋ธ์€ Richart et al.(1928)์ด ์œ ์••์œผ ๋กœ ๊ตฌ์†ํ•œ ์ฝ˜ํฌ๋ฆฌํŠธ ์‹œํ—˜์ฒด์— ๋Œ€ํ•ด ์‹คํ—˜ํ•œ ๊ฒฐ๊ณผ๋ฅผ ์ •๋ฆฌํ•˜์—ฌ ์ตœ์ดˆ๋กœ ์ œ์•ˆํ•œ ์‹์ด๋ฉฐ, ์ œ์•ˆ์‹œ k1์€ 4.1์ด์—ˆ๋‹ค. ์ด ํ›„ ๋‹ค๋ฅธ ์—ฐ ๊ตฌ์ž๋“ค์— ์˜ํ•ด ๋ ์ฒ ๊ทผ์ด๋‚˜ ๋‚˜์„ ์ฒ ๊ทผ์œผ๋กœ ํšก๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ ์˜ ๊ฐ•๋„์ถ”์ •์‹์ด ๋ฐœํ‘œ๋˜์—ˆ๋‹ค. ์‹ (4)๊ฐ€ FRP๋กœ ๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌ ํŠธ์— ๋Œ€ํ•ด์„œ๋„ ์ง์ ‘ ์ ์šฉ์ด ๊ฐ€๋Šฅํ•˜๋‹ค๋Š” ๊ฒƒ์€ Fardis and Khalili(1982)์— ์˜ํ•ด ์ œ์•ˆ๋˜์—ˆ์œผ๋ฉฐ, Fig. 10์— ๋‚˜ํƒ€๋‚ธ ๊ฒƒ๊ณผ ๊ฐ™ ์ด FRP ์ธ์žฅ๊ฐ•๋„์— ์˜ํ•œ ํšก๊ตฌ์†์••(fl)์€ ๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ํฌ์•„์†ก ํšจ๊ณผ์— ์˜ํ•œ ํŒฝ์ฐฝ์‘๋ ฅ๊ณผ ๊ฐ™๋‹ค๊ณ  ๊ฐ€์ •ํ•˜์˜€๋‹ค. ๋”ฐ๋ผ์„œ ํšก๊ตฌ์†์••์€ ์‹ (5)์™€ ๊ฐ™์ด ์ •๋ฆฌ๋œ๋‹ค.

Fig. 10

Confining action of FRP composite

JKSMI-19-10_F10.jpg
(5)
f l = 2 f frp t D

์—ฌ๊ธฐ์„œ, ffrp๋Š” FRP์˜ ์ธ์žฅ๊ฐ•๋„, t๋Š” FRP์˜ ๋‘๊ป˜, D๋Š” FRP ๋กœ ๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์ง๊ฒฝ์ด๋‹ค.

FRP๋กœ ๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์— ๋Œ€ํ•œ ๊ฐ•๋„์ถ”์ •์‹์€ ์‹ (4)์˜ k1 ์„ ์ˆ˜์ •ํ•˜๋Š” ํ˜•ํƒœ๋กœ ์ œ์•ˆ๋˜์—ˆ์œผ๋ฉฐ, Table 6์— ์ด๋ฅผ ์ •๋ฆฌํ•˜์˜€ ๋‹ค. ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ์‹œํ—˜๊ฒฐ๊ณผ์™€ ํ•จ๊ป˜ ๊ธฐ์กด์— ์ˆ˜ํ–‰๋œ ์—ฐ๊ตฌ ๊ฒฐ๊ณผ ๋ฅผ ์ •๋ฆฌํ•˜์—ฌ ๊ฐ•๋„์ถ”์ •์‹์„ ์ œ์•ˆํ•˜์˜€์œผ๋ฉฐ, ๊ธฐ์กด ๊ฐ•๋„์ถ”์ •์‹์˜ ์ •ํ™•์„ฑ์„ ๊ฒ€์ฆํ•˜์˜€๋‹ค.

Table 6

Strength models for FRP confined concrete

Model K 1

Karbhari and Gao (1997) 2.1 f t f co โ€ฒ - 0.13
Samaan et al. (1998 Miyauchi et al. (1999)) 6.0 f l - 0.3
Saafi et al. (1999) 2.2 f l f co โ€ฒ - 0.16
Toutanji (1999) 3.5 f l f co โ€ฒ - 0.15
Lam and Teng (2002) 2.0

4.2 ์‹œํ—˜๊ฒฐ๊ณผ ๋ฐ ๊ธฐ์กด์—ฐ๊ตฌ๊ฒฐ๊ณผ ์ •๋ฆฌ

๊ฐ•๋„์ถ”์ •์‹์„ ์ œ์•ˆํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๋ณธ ์—ฐ๊ตฌ์—์„œ ์ˆ˜ํ–‰ํ•œ ์‹œํ—˜๊ฒฐ ๊ณผ์™€ ๊ธฐ์กด์˜ ์—ฐ๊ตฌ๊ฒฐ๊ณผ(Bae et al., 2000; Chung et al., 1998; Demers and Neale, 1994; Harmon and Slattery, 1992; Howie and Karbhari, 1994; Hwang, 2000; Karbhari and Gao, 1997; Kim, 2003; Lee and Jeong, 2003; Matthys et al., 1999; Miyauchi et al., 1997; Miyauchi et al., 1999; Modarelli et al., 2005; Park, 2001; Picher et al., 1996; Shin et al., 1995; Soudki and Green, 1996; Watanable et al., 1997; Xiao and Wu, 2000; Youm et al., 2004; Zhang et al., 2000)๋ฅผ ์ •๋ฆฌํ•˜์˜€๋‹ค. CFRP ์‰ฌ ํŠธ๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ๋ณด๊ฐ•ํ•œ ์‹œํ—˜ ๊ฒฐ๊ณผ๋งŒ ์‚ฌ์šฉํ•˜์˜€์œผ๋ฉฐ, ํ˜•์ƒ๋น„๋‚˜ ๊ฒน์ด์Œ๊ธธ์ด์™€ ๊ฐ™์ด ๋ณด๊ฐ•ํšจ๊ณผ์— ์˜ํ–ฅ์„ ๋ฏธ์นœ ์‹œํ—˜๊ฒฐ๊ณผ๋Š” ์ œ์™ธ ํ•˜์˜€๋‹ค. ์ •๋ฆฌํ•œ ๊ฒฐ๊ณผ๋Š” Table 7๊ณผ ๊ฐ™์œผ๋ฉฐ, ์ด ๋ฐ์ดํ„ฐ ์ˆ˜๋Š” 204 ๊ฐœ์ด๋‹ค.

Table 7

Data set of test results of CFRP-confined concrete specimen

JKSMI-19-10_T7.jpg

4.3 ๋ฐ์ดํ„ฐ ๋ถ„์„ ๋ฐ ๊ธฐ์กด๋ชจ๋ธ ๋น„๊ต

Fig. 11์€ Table 7์— ์ •๋ฆฌํ•œ ๋ฐ์ดํ„ฐ๋ฅผ ๋„์‹ํ™”ํ•˜์—ฌ ๊ธฐ์กด์˜ ๊ฐ•๋„์ถ”์ •์‹๊ณผ ๋น„๊ตํ•œ ๊ทธ๋ž˜ํ”„์ด๋‹ค. ๊ทธ๋ž˜ํ”„์— ๋‚˜ํƒ€๋‚ธ ๊ฒƒ๊ณผ ๊ฐ™ ์ด Toutanji(1999)์™€ Miyauci et al.(1999), Samaan et al. (1998)์€ ๊ฐ•๋„๋ฅผ ๊ณผ๋Œ€์ถ”์ •ํ•˜๊ณ  ์žˆ์œผ๋ฉฐ, ๊ทธ ์™ธ์˜ ์‹๋“ค์€ ๋ณธ ๋ฐ ์ดํ„ฐ ๋ฒ”์œ„์—์„œ ๋น„์Šทํ•˜๊ฒŒ ์ถ”์ •ํ•˜๊ณ  ์žˆ๋‹ค. ์‹œํ—˜๋ฐ์ดํ„ฐ์— ๋Œ€ํ•ด ํšŒ๊ท€๋ถ„์„ํ•œ ๊ฒฐ๊ณผ ๋ฐ์ดํ„ฐ์˜ ๊ฒฝํ–ฅ์„ ๊ฐ€์žฅ ์ž˜ ๋‚˜ํƒ€๋‚ด๋Š” ์„ ํ˜•์‹ ์€ ์‹ (6)๊ณผ ๊ฐ™์œผ๋ฉฐ, ๊ฒฐ์ •๊ณ„์ˆ˜(R2)๊ฐ€ 0.85๋กœ ์ƒ๊ด€์„ฑ์ด ๋†’๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค.

Fig. 11

Comparison of strength models

JKSMI-19-10_F11.jpg
(6)
f cc โ€ฒ f co โ€ฒ = 1.00 + 2.28 f l f co โ€ฒ R 2 = 0.85

Table 8์€ ๊ฐ ์ถ”์ •์‹๋ณ„ ์‹œํ—˜๊ฐ’(fcc โ€ฒ )์— ๋Œ€ํ•œ ๊ฐ•๋„์ถ”์ •๊ฐ’์˜ ๋น„์— ๋Œ€ํ•ด ํ†ต๊ณ„๋ถ„์„ํ•œ ๊ฒฐ๊ณผ๋ฅผ ๋‚˜ํƒ€๋‚ด๊ณ  ์žˆ๋‹ค. ๋ฐ์ดํ„ฐ ๊ณ„์—ด ๋ณ„๋กœ ํ‰๊ท ๊ฐ’์ด ๋‹ค๋ฅด๋ฏ€๋กœ ํ‘œ์ค€ ํŽธ์ฐจ๊ฐ€ ์•„๋‹Œ ๋ณ€๋™๊ณ„์ˆ˜(=ํ‘œ์ค€ ํŽธ์ฐจ/ํ‰๊ท ๊ฐ’)๋ฅผ ์‚ฌ์šฉํ•˜์—ฌ ๋ฐ์ดํ„ฐ์˜ ๋ถ„ํฌ๋ฅผ ๋น„๊ตํ•˜์˜€๋‹ค. ์•ž ์„œ ๊ทธ๋ž˜ํ”„์—์„œ ํ™•์ธ๋œ ๊ฒƒ๊ณผ ๊ฐ™์ด ํ†ต๊ณ„๊ฒฐ๊ณผ์—์„œ๋„ Miyauchi et al.(1999), Toutanji(1999)์™€ Samaan et al.(1998)์ด ๊ฐ•๋„๊ฐ’ ์„ ๊ณผ๋Œ€ํ•˜๊ฒŒ ์ถ”์ •ํ•˜๊ณ  ์žˆ๋‹ค. Karbhari and Gao(1997), Saafi et al.(1999), Lam and Teng(2002)์€ ๋น„๊ต์  ์ •ํ™•ํ•˜๊ฒŒ ๊ฐ•๋„ ๋ฅผ ์ถ”์ •ํ•˜๊ณ  ์žˆ์œผ๋‚˜, ๋ณธ ๋…ผ๋ฌธ์—์„œ ์ œ์•ˆํ•œ ์ถ”์ •์‹์„ ์‚ฌ์šฉํ•˜ ๋Š” ๊ฒƒ์ด ์‹คํ—˜๊ฐ’๊ณผ์˜ ๋ณ€๋™ ํญ๋„ ๊ฐ€์žฅ ์ž‘๊ณ  ์ •ํ™•ํ•˜๊ฒŒ ์ถ”์ •ํ•˜ ๊ณ  ์žˆ๋‹ค.

Table 8

Statistical performance of strength models for FRP-confined concrete as assessed by data set

Model Predicted fccโ€™ to test ratio

Average Standard deviation Coefficient of Variation (%)

Karbhari and Gao (1997) 1.02 0.141 13.8
Samaan et al. (1998) 1.11 0.173 15.6
Miyauchi et al. (1999) 1.12 0.162 14.4
Saafi et al. (1999) 1.05 0.145 13.8
Toutanji (1999) 1.30 0.191 14.7
Lam and Teng (2002) 0.96 0.133 13.9
Best fit trend line 1.00 0.135 13.4

[i] Number of datapoints = 204

5. ๊ฒฐ ๋ก 

๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” CFRP ์‰ฌํŠธ๋กœ ํšก๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ ๊ณต์‹œ์ฒด์— ๋Œ€ํ•˜์—ฌ ๋ณด๊ฐ• ๊ฒน์ˆ˜, ์‹œํ—˜์ฒด์˜ ํฌ๊ธฐ, ํ˜•์ƒ๋น„, ๊ฒน์ด์Œ๊ธธ์ด๋ฅผ ๋ณ€ํ™” ์‹œ์ผœ ์‹œํ—˜ํ•œ ๊ฒฐ๊ณผ๋ฅผ ๋ถ„์„ํ•˜์˜€๊ณ , ์‹œํ—˜๊ฒฐ๊ณผ์™€ ๋”๋ถˆ์–ด ๊ธฐ์กด์— ๋ฐœํ‘œ๋œ ์‹œํ—˜๋ฐ์ดํ„ฐ๋ฅผ ํ†ตํ•˜์—ฌ CFRP ์‰ฌํŠธ๋กœ ๋ณด๊ฐ•๋œ ์ฝ˜ํฌ๋ฆฌํŠธ ์˜ ๊ฐ•๋„์ถ”์ •์‹์„ ๋น„๊ต ๋ถ„์„ํ•˜์—ฌ ์–ป์€ ๊ฒฐ๋ก ์€ ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค.

  1. CFRP ์‰ฌํŠธ๋กœ ํšก๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ์••์ถ•์„ฑ๋Šฅ์€ ์‰ฌํŠธ์˜ ๊ตฌ ์†ํšจ๊ณผ์— ์˜ํ•ด ํฌ๊ฒŒ ๊ฐœ์„ ๋˜์—ˆ์œผ๋ฉฐ, ๋ณด๊ฐ•๊ฒน์ˆ˜์— ๋”ฐ๋ผ ์••์ถ• ๋‚ด๋ ฅ ํ–ฅ์ƒํšจ๊ณผ๊ฐ€ ํฌ๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค.

  2. CFRP ์‰ฌํŠธ๋กœ ๋ณด๊ฐ•๋œ ์ฝ˜ํฌ๋ฆฌํŠธ ์‹œํ—˜์ฒด์˜ ๋ชจ๋“  ์กฐ๊ฑด์„ ๋™ ์ผํ•˜๊ฒŒ ์œ ์ง€ํ•˜๊ณ  ํฌ๊ธฐ๋ฅผ ๋ณ€ํ™”์‹œํ‚ฌ ๊ฒฝ์šฐ, ํฌ๊ธฐ๊ฐ€ ์ปค์งˆ์ˆ˜๋ก ๋ณด๊ฐ•ํšจ๊ณผ๋Š” ๊ฐ์†Œํ•˜์˜€๋‹ค. ์ด๋Š” ํšก๊ตฌ์†์••(fl)์ด ์ง๊ฒฝ(D)์— ๋ฐ˜๋น„๋ก€ํ•˜๊ธฐ ๋•Œ๋ฌธ์ด๋ฉฐ, ๋ณธ ์‹œํ—˜์„ ํ†ตํ•˜์—ฌ CFRP์— ์˜ํ•œ ํšก ๊ตฌ์†์••์˜ ์ด๋ก ์ ์ธ ๋ถ€๋ถ„์„ ์ฆ๋ช…ํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

  3. ์‹œํ—˜์ฒด์˜ ํ˜•์ƒ๋น„(H/D)๊ฐ€ ์ฆ๊ฐ€ํ•จ์— ๋”ฐ๋ผ ๋ณด๊ฐ•ํšจ๊ณผ๋Š” ๊ฐ์†Œํ•˜ ์˜€์œผ๋ฉฐ, ์ด๋Š” ์„ธ์žฅ๋น„์™€ ์ž„๊ณ„์‘๋ ฅ๊ฐ„์˜ ๊ด€๊ณ„๊ฐ€ CFRP ์‰ฌํŠธ๋กœ ๋ณด๊ฐ•๋œ ์‹œํ—˜์ฒด์—์„œ๋„ ๋™์ผํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚จ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

  4. CFRP ์‰ฌํŠธ๋กœ ๊ฐ์‹ผ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๊ฒน์ด์Œ๊ธธ์ด๊ฐ€ ์—†๋Š” ๊ฒฝ์šฐ์— ๋Š” ๋ณด๊ฐ•ํšจ๊ณผ๊ฐ€ 30%๋ฐ–์— ๋‚˜ํƒ€๋‚˜์ง€ ์•Š์•˜์œผ๋‚˜ ๋‘˜๋ ˆ์˜ 5% ์ด ์ƒ์œผ๋กœ ๊ฒน์ด์Œํ•œ ๊ฒฝ์šฐ์—์„œ๋Š” ๋ณด๊ฐ•ํšจ๊ณผ๊ฐ€ 100%๋‚˜ํƒ€๋‚ฌ์œผ ๋ฉฐ, 5%์ด์ƒ์˜ ๋ฒ”์œ„์—์„œ๋Š” ๊ฒน์ด์Œ๊ธธ์ด๋ฅผ ๋ณ€ํ™”์‹œ์ผœ๋„ ๋ณด๊ฐ• ํšจ๊ณผ์— ํฐ ์˜ํ–ฅ์ด ์—†์—ˆ๋‹ค.

  5. ๋ณธ ๋…ผ๋ฌธ์—์„œ์˜ ์‹œํ—˜๊ฒฐ๊ณผ์™€ ๊ธฐ์กด์— ์ˆ˜ํ–‰๋œ ์—ฐ๊ตฌ๊ฒฐ๊ณผ๋ฅผ ๊ธฐ ์ค€์œผ๋กœ CFRP ์‰ฌํŠธ๋กœ ๊ตฌ์†๋œ ์ฝ˜ํฌ๋ฆฌํŠธ์˜ ๊ฐ•๋„์ถ”์ •์‹์„ ๋‹ค ์Œ๊ณผ ๊ฐ™์ด ์ œ์•ˆํ•˜์˜€๋‹ค.

    f cc โ€ฒ f co โ€ฒ = 1.00 + 2.28 f l f co โ€ฒ

  6. ๊ธฐ์กด ๊ฐ•๋„์ถ”์ •์‹์„ ๋น„๊ตํ•œ ๊ฒฐ๊ณผ, Miyauchi et al.(1999), Samaan et al.(1998), Toutanji(1999)์€ ๊ฐ•๋„๋ฅผ ๊ณผ๋Œ€์ถ”์ •ํ•˜ ๊ณ  ์žˆ์œผ๋ฉฐ, Karbhari and Gao(1997), Lam and Teng(2002), Saafi et al.(1999)์€ ๋น„๊ต์  ์ •ํ™•ํ•˜๊ฒŒ ๊ฐ•๋„๋ฅผ ์ถ”์ •ํ•˜๊ณ  ์žˆ ์Œ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

๊ฐ์‚ฌ์˜ ๊ธ€

์ด ๋…ผ๋ฌธ์€ 2015ํ•™๋…„๋„ ์ œ์ฃผ๋Œ€ํ•™๊ต ํ•™์ˆ ์ง„ํฅ์—ฐ๊ตฌ๋น„ ์ง€์›์‚ฌ ์—…์— ์˜ํ•˜์—ฌ ์—ฐ๊ตฌ๋˜์—ˆ์Œ

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