1. T.Chhay NPIC
VII. RbEvgEdkbgáb; b¤RbEvgEdkRCYs
1> esckþIepþIm
lkçN³bnSúIKñarvagEdk nigebtug enAkñúgeRKOgbgÁúMebtugGarem:QrelIeKalkarN_ PaBs¥itrvagsMPar³
TaMgBIreRkayebtugkkrwg. RbsinebIsésrEdkEdlmanmuxkat;mUlRtg;RtUv)anbgáb;enAkñúgebtug caM)ac;eKRtUv
mankMlaMgmYyRKb;RKan;edIm,ITajsésrEdkenaHecjBIebtug. RbsinebIRbEvgbgáb;énsésrEdkenAkñúgebtug
manRbEvgEvgRKb;RKan; enaHsésrEdkGaceFVIkardl;cMnucyar edayTukRbEvgxøHrbs;sésrEdkenAkñúgebtug.
kMlaMgs¥itGaRs½yeTAnwgPaBkkitEdk nigebtug. kMlaMgkkitmanT§iBlCacMbgBI PaBKeRKIménépÞxagrbs;s
ésrEdk karlayebtug karRskmaD nigkMras;ebtugeRsamEdk. EdkfñaMgGMeBA deformed bar pþl;nUvPaBs¥it
l¥CagEdkmUl. ersIusþg;ebtugkan;EtFM kan;EtmanPaBs¥itCag. kMras;ebtugeRsabEdkkan;EtRkas; kugRtaMg
PaBs¥itrbs;Edkkan;EtFM.
CaTUeTA ersIusþg;PaBs¥itTTYlT§iBlBIktþaxageRkam³
- ersIusþg;rbs;Edk f / RbEvgbgáb;kan;EtEvg sMrab; f kan;EtFM
y y
- KuNPaB nigersIusþg;sgát;ebs;ebtug f ' / kalNa f ' kan;EtFM enaHRbEvgbgáb;kan;Etfy
c c
- muxkat;Edk KMlat nigTItaMgrbs;EdkenAkñúgmuxkat;ebtug. EdkbeNþayEdldak;kñúgKMlatbBaÄr
FMCag 30cm énebtugenAEpñkxageRkaménEdkEdlRtUvbgáb; b¤t manersIusþg;TabCagGaRs½y
edaykarrYmmaD nigkarRsk rbs;ebtugGMLúgeBldMeNIrkarkkrwgrbs;ebtug. dUcKña
KMlatEdkkan;EtFM pþl;nUversIusþg;s¥it kan;EtFM eRBaHvapþl;nUvépÞebtugRKb;RKan;CMuvijEdk.
- kMras;ebtugeRsabEdk. kMras;kan;EttUc bgáeGaymankareRbH.
- karTak;rbs;Edkxag. karTak;EdkxagRKb;RKan; karBarnUvkareRbHebtugCuMvijEdk
2> kugRtaMgénPaBs¥itedaykarkac;begáag
eKmanFñwmmYyRbEvg dx rgnUvbnÞúkBRgayesμI. edayeGaym:Um:g;EdlekIteLIgenAEpñkmçagCa M 1
nigmçageTotCa M ehIy M mantMélFMCag M . m:Um:g;nwgbegáItnUvkMlaMgsgát; nigkMlaMgTajxagkñúg.
2 1 2
eday M > M enaH T > T dUcKña C > C .
1 2 1 2 1 2
enAmuxkat;NamYyenaH T = M
jd
Edl jd CaédXñas;
dM
T1 − T2 = dT =
jd
RbEvgEdkbgáb; b¤RbEvgEdkRCYs 117

2. Department of Civil Engineering viTüasßanCatiBhubec©keTskm<úCa
b:uEnþ T = T + u ∑ Odx
1 2
Edl u CakugRtaMgs¥itmFüm
∑ O CaplbUkbrimaRténmuxkat;r)arenAEpñkrgkarTaj
dUcenH T − T = u ∑ Odx = dM
1 2
jd
dM 1
⇒u= ×
dx jd ∑ O
Eteday dM
dx
=V
V
⇒u =
jd ∑ O
mü:ageTotedIm,IsMrYlkñúgkarKNna j RtUv)ansnμt;esμInwg 0.87
dUcenH u = 0.87V ∑ O
d
edayersIusþg;énPaBs¥it RtUv)ankat;bnßyedayemKuN φ = 0.85 enaH
V
Un =
φ 0.87d ∑ O
3> RbEvgbgáb;sMrab;tMbn;Taj l d
RbsinebIsésrEdkbgáb;kñúgebtug rgnUvkMlaMgTaj T enaHkMlaMgTajenaHRtUvTb;edaykugRtaMgs¥it
rvagsésrEdk nigebtug. kMlaMgTajGtibrmaRtUvmantMélesμInwg A f Edl A muxkat;sésrEdk. kMlaMg
s y s
enHRtUv)anTb;edaykMlaMgkñúg U Ol Edl U kugRtaMgs¥itcugeRkaymFüm l RbEvgbgáb;Edk nig O bri-
n d n d
maRtsésrEdk (πD) . kMlaMgTaMgBIrenHRtUvEtesμIKñaedIm,ImanlMnwg.
As f y = U nOld
As f y
⇒ ld =
U nO
Development Length of Reinforcing Bars 118

3. T.Chhay NPIC
eday A = πd nig O = πd
2
b
s b
4
db f y
⇒ ld =
4U n
mann½yfa RbEvgbgáb;GaRs½ynwg muxkat;Edk ersIusþg;rbs;Edk nigkugRtaMgs¥itEdlCaGnuKmn_eTA
nwg f ' . c
c 1
U n = 0.5 f 'c ( − )
db 2
0 .5 f y db
⇒ ld =
c 1
f 'c ( − )
db 2
edayeGay c = 1.5d b
0.5 f y
ld = db
f 'c
smIkarRbEvgbgáb;sMrab;tMbn;Taj Edl)anBIkareFVIBiesaFn_ ehIyRtUv)ansMrYledayKN³kmμkarKW
αβγλ
d ehIy l > 300mm
9 f
l = y
10 f ' c + K
d b d
tr
c ( )
db
Edl c +d K ≤ 2.5 tr
b
α emKuNTItaMgr)ar
α = 1.3 sMrab;EdkEdldak;manKMlatx<s;Cag 30cm BIEdkbgáb;
α = 1 sMrab;krNIepSgeTot
β emKuNRTnab;Edk
β = 1.5 sMrab;Edklab epoxy-coating ehIymanRTnab;karBarebtugtUcCag 3d nigmanKMlatEdk
b
tUcCag 6d b
β = 1.2 sMrab;Edklab epoxy-coating krNIepSgeTot
β = 1 sMrab;EdkminmanlabfñaMkarBar
γ emKuNTMhMEdk
γ = 0.8 sMrab;EdkEdlmanGgát;p©ittUcCag b¤esμI 19mm
γ = 1 sMrab;EdkEdlmanGgát;p©itFMCag b¤esμI 22mm
λ emKuNTMgn;ebtug
λ = 1.3 sMrab;ebtugRsal
λ = 1 sMrab;ebtugFmμta
RbEvgEdkbgáb; b¤RbEvgEdkRCYs 119

4. Department of Civil Engineering viTüasßanCatiBhubec©keTskm<úCa
cKMlatEdk b¤RTnab;ebtugkarBarEdk
c RtUvmantMéltUckñúgcMeNamkrNITaMgBIrxageRkam³
- cMgaytUcCageK Edlvas;BIépÞebtugmkGkS½Edk
- mYydgknøHénKMlatEdk EdlKitBIGkS½mkGkS½
K snÞsS½EdkTTwg
tr
Atr f yt
K tr =
10 sn
Atrmuxkat;EdkTTwg
f ersIusþg;EdkTTwg
yt
s KMlatEdkGtibrmarbs;EdkTTwgKItBIGkS½mkGkS½
n cMnYnEdkTTwg
Et K RtUv)aneKsnμt;mantMélesμIsUnüedIm,IsMrYldl;karKNna
tr
4> RbEvgbgáb;sMrab;tMbn;sgát; l dc
RbEvgbgáb;sMrab;tMbn;sgát;RtUv)aneKKitfamanRbEvgxøICagRbEvgbgáb;sMrab;tMbn;Taj eRBaHkMlaMgxøH
RtUv)anbBa¢ÚneTAebtugedaysésrEdk nigmü:ageTotvaminmansñameRbHenAtMbn;TMBk;. RbEvgbgáb;sMrab;tMbn;
sgát;RtUv)ankMNt;eday
l =
dc
0.24d f
f'
b:uEnþvaRtUvmantMélFMCag 0.044d f ehIyvaminRtUvmantMéltUcCag 20cm .
b y
b y
c
5> TMBk;;
TMBk;RtUv)aneRbIenAxagcugr)ar enAeBlEdlRbEvgbgáb;Rtg;EdlvaRtUvkarmantMéltUcCagRbEvgbgáb;
caM)ac;. )ann½yfa r)arEdlmanTMBk;xagcug RtUvkarRbEvgbgáb;xøICagr)arRtg;. Ggát;p©itGb,brmarbs;BMnt;
Edlvas;BIépÞxagkñúgrbs;TMBk; D ERbRbYleTAtamGgát;p©itrbs;r)ar³
b
Development Length of Reinforcing Bars 120

5. T.Chhay NPIC
- sMrab; DB10 − DB25 / D = 6d b b
- sMrab; DB28 − DB36 / D = 8d b b
- sMrab; DB43 − DB58 / D = 10d b b
RbEvgbgáb;sMrab;r)arEdlmanTMBk;RtUv)ankMNt;edayrUbmnþxageRkam³
0.24 βλ f y
ldb = db
f 'c
Edl
β emKuNRTnab;Edk
β = 1.2 sMrab;Edklab epoxy-coating
β = 1 sMrab;EdkminmanlabfñaMkarBar
λ emKuNTMgn;ebtug
λ = 1.3 sMrab;ebtugRsal
λ = 1 sMrab;ebtugFmμta
RbEvgbgáb;rbs;r)arEdlmanTMBk;RtUv)anKuNCamYyemKuNsMrab;krNIxageRkam³
- r)arEdlmanGgát;p©ittUcCag 36mm EdlmanTMBk;Bt;mMu 90 Bak;edayEdkkg bBaÄr b¤edkEdl
o
manKMlatminFMCag 3d RbEvgbgáb;RtUvKuNCamYy 0.8 .
b
RbEvgEdkbgáb; b¤RbEvgEdkRCYs 121

6. Department of Civil Engineering viTüasßanCatiBhubec©keTskm<úCa
- r)arEdlmanGgát;p©ittUcCag 36mm EdlmanRTnab;karBarEdkxagFMCag 6cm RbEvgbgáb;RtUv
KuNCamYy 0.7 .
- r)arEdlmanGgát;p©ittUcCag 36mm EdlmanTMBk;Bt;mMu 180 Bak;edayEdkkgbBaÄrehIyman
o
KMlatminFMCag 3d RbEvgbgáb;RtUvKuNCamYy 0.8 .
b
6> kartEdk
enAeBlEdlEdkmanRbEvgxøI eKcaM)ac;RtUvtvaedaydak;bRBa¢ÜsKñanUvRbEvgmYysmRsbedIm,IbBa¢Únkug
RtaMgénPaBs¥itBIr)armYyeTAr)armYy. kartEdkGaceFVIeLIgedaykartbRBa¢Üsmux nigkarpSa. karrEdkeday
Development Length of Reinforcing Bars 122

7. T.Chhay NPIC
karbRBa¢ÜsminGaceFVIeTA)aneT sMrab;r)arEdlmanGgát;p©itFMCag 36mm . sMrab;tMNrpSa RtUveFVIeLIgeday
eGayTwkbnSamanersIusþg;esIμ 125% énersIusþg;rbs;Edk.
kartEdkminRtUv)anGnuBaØtieGayeFVIenARtg;muxkat;Edlmanm:Um:g;GtibrmaeT. elIsBIenH eKk¾RtUv
eCosvagkartEdkRtg;TItaMgEtmYykEnøg edIm,IeCosvagkarFøak;exSayrbs;muxkat;ebtug kareTIsETgEdk
nigkarBi)akcak;ebtug.
k> kartEdkenAtMbn;rgkarTaj l st
RbEvgtEdk l = l RtUv)aneRbIenAeBlEdlmuxkat;Edk ticCagBak;kNþalRtUv)ant nigmuxkat;Edk
st d
eRbIR)as;esμI2dgmuxkat;RtUvkar RtUv)antTaMgGs;. RbEvgtEdk l = 1.3l RtUv)aneRbIenAeBlNaEdlkart
st d
EdkeFVIeLIgenATItaMgEtmYy EtCasMNUmBr eKminRtUvtEdkenAkEnøgdUcKñaeLIy. sMrab;RKb;krNI RbEvgtEdk
minRtUvmantMéltUcCag 30cm .
x> kartEdkenAtMbn;rgkarsgát; l sc
RbEvgtEdkenAtMbn;sgát; l RtUvmantMélFMCagb¤esμIRbEvgbgáb;enAtMbn;rgkarsgát;.
sc
l = 0.0724 f d
sc ysMrab; f ≤ 400MPa
b y
l = (0.13 f − 24)d sMrab; f > 400MPa
sc y b y
sMrab;RKb;krNI RbEvgtEdkminRtUvmantMéltUcCag 30cm . RbsinebIebtugEdlykmkeRbImanersIu-
sþg;tUcCag 20MPa enaHRbEvgtEdkRtUvKuNnwg 1.3 . sMrab;ssrEdlmanEdkkgragCarWus½r enaHRbEvgt
EdkRtUvKuNnwg 0.75 EtsMrab;EdkkgFmμtaRtUvKuNnwg 0.83 b:uEnþminRtUvtUcCag 30cm .
7> karbBaÄb;Edk
ersIusþg;m:Um:g;enAkñúgFñwmCaGnuKmn_eTAnwgkMBs;RbsiT§iPaB d / TTwgFñwm b / nigmuxkat;Edk A sMrab;
s
karEdleKsÁal;ersIusþg;Edk f nigersIusþg;ebtug f ' . sMrab;FñwmEdlmanTTwg nigkMBs;efr enaHmuxkat;Edk
y c
ERbRbYleTAtamm:Um:g;Bt;EdlmanGMeBItambeNþayFñwm. dUcenHeKcaM)ac;RtUvbBaÄb;Edk enAkEnøgNaEdleK
minRtUvkarvaedIm,ITb;Tl;nwgkugRtaMgBt;. sMrab;krNIxH dUcCaFñwmCab; EdksMrab;m:Um:g;viC¢man RtUv)aneKBt;
ø
eLIgelIedaymMu 45 edIm,Ipþl;CaEdkrgkMlaMgTajsMrab;m:Um:g;GviC¢manenAelITMr.
o
ersIusþg;m:Um:g;rbs;FñwmrgkarTajenARKb;muxkat;TaMgGs;RtUv)ankMNt;eday
a
M u = φAs f y (d − )
2
édXñas; ERbRbYlBImuxkat;mYyeTAmuxkat;mYytambeNþayFñwm dUckarERbRbYlbrimaNsésr
(d − )
a
2
EdkEdr eTaHCay:agenHk¾eday eyIgeXIjfabMErbMrYlédXñas;mantUcbMput ehIyminmantMélxusKñaeRcInBImux
RbEvgEdkbgáb; b¤RbEvgEdkRCYs 123

8. Department of Civil Engineering viTüasßanCatiBhubec©keTskm<úCa
kat;m:Um:g;GtibrmaeT. dUcenH eKGacsnμt;faersIusþg;m:Um:g;sMrab;muxkat;smamaRtnwgkMlaMgTaj b¤muxkat;
sésrEdk edayKitTaMgRbEvgTMBk;.
edIm,IkMNt;TItaMgénkarbBaÄb;Edk düaRkamm:Um:g;EdlekItBIkMlaMgxageRkARtUvKUrmuneK. düaRkamersIu
sþg;m:Um:g;RtUv)anKUrenAelIRkaPicEtmYy edIm,IbgðajTItaMgsésrEdkxøHEdlminRtUvkarRbEvgEvgCagtMrUvkar.
ersIusþg;m:Um:g;cugeRkaysMrab;sésrEdkmYysésrKW³
a
M ub = φAsb f y (d − )
2
Edl a=
As f y
0.85 f 'c b
Asb - muxkat;EdkmYysésr
cMnucRbsBVrvagbnÞat;ersIusþg;m:Um:g; CamYydüaRkamm:Um:g;xageRkA bgðajBITItaMgEdleyIgGacbBaÄb;
Edk)an. b:uEnþeKcaM)ac;RtUvbEnßmRbEvgEdkedIm,IPaBs¥itCamYyebtug. ACI Code )ankMNt;faRKb;Edk
EdlbBaÄb;RtUvbEnßmRbEvgesμInwgkMBs;RbsiT§PaBrbs;Fñwm b¤ 12φ ¬edayyktMélmYyNaEdlFMCageK¦
elIsBIenH ACI Code )ankMNt;fay:agticNas; 1 énsésrEdksMrab;m:Um:g;viC¢manRtUvbgðÚseTAkñúgTMr
3
sMrab;FñwmTMrsamBaØ.
Development Length of Reinforcing Bars 124