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8/12/2019 BTNG NG LC TRC

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BTNG NG LC TRC

1-1 Khi Nim Chung1-2 u Khuyt im Ca Btng Ct Thp LT

1-3 So Snh BTCT LT V BTCT Thng

1-4 Phn Loi BTCT LT

1-5 Vt Liu Dng Cho Btng LT

a. Btng

b. Thp

c. Neo V Cc Vt Liu Khc


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BTCT ULT (Cng Sau) S Dng B SiThp Cng Cao


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BTCT ULT (Cng Sau) S Dng Thanh ThpCng Cao


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ng Gel:

-c t trc trong cu kin BTCT ULT phngphp cng sau

- Thp dng to ng sut trc c lun quang gel ny


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Va bm:

- Dng bm vo cc ng gel trong phngphp cng sau nhm l bo v ct thp

-m bo v mt cng , tnh d chy vkhng co ngt

- C nhiu loi va:


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Master Builder: SS Mortar

Masterflow 928 Set 45 Set 45 HW Construction Grout

Embeco636 Plus Grout Set Grout

ThoRoc: 747 Rapid-Setting Grout HF Precision Grout

Sonneborn: SonoGrout10K


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Chng 2- Cc Phng Php GyULT

2-1 Phng Php Cng Trc (Cng Trn B)(Pretensioning):

- Neo mt u ct thp vo mt b (A)

-u ct thp cn li t vo b kia (B) ko cng ct thp

- Khi ko cng mc cn thit th neo ct thp vo b Bv tin hnh t khun btng

- Khi btng kh cng cng cn thit th bung ctthp, sau ct ct thp ri cc cu kin


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2-2 Phng Php Cng Sau (Cng Trn Btng)(Post-Tensioning):

-t ct thp vo trong ng gel ri btng

- Khi btng kh cng cng cn thit th dngkch t vo btng ko cng ct thp

- C th neo ct thp mt u v ko u kia hoc kong thi hai u (i vi cu kin c ct thp dngcong v chiu di cu kin ln)


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- Khi ko cng ct thp mc cn thit th neo chtct thp li

- Qu trnh cng thp ng thi cng l qu trnh nn

btng

- Tu tng trng hp cn thit m bm va vo trongng gel bo v ct thp


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2-3 u nhc im ca cc phng php:

Phng Php Cng Trc:

- Phng php cng trc c u im l c thlm hai b vi khong cch kh xa (75-100 m) cng mt lc btng cho nhiu cu kinging nhau

- Phng php cng trc ch yu dng cho cc

cu kin t ct thp cng theo ng thng,dng ct thp c dnh tt vi btng

- Ch yu dng cho sn xut cc cu kin lpghp c kch thc va v nh


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2 C


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2-4 Cc tn tht ng sut trong btngctthp ULT v cch tnh ton:

* Cu kin cng trc:

Trong :

= Tn tht ng sut do co ngn n hica btng

= Tn tht ng sut do tnh chng ca thp

= Tn tht ng sut do t bin ca btng

pSHpCRpRpESpT fffff

pESf

pRf

pCRf


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= Tn tht ng sut do co ngt ca btng

* Cu kin cng sau:

Trong :

= Tn tht ng sut do bin dng ca neo (tut neo)

= Tn tht ng sut doma st ca ct thp vi thnh nggel

pSHf

pSHpCRpRpESpFpApT fffffff

pAf

pFf


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2.4-1 Tn tht ng sut do co ngn n hica btng:

Trong :

pESf

cspES nff

c

s

E

En

Modul n hi ca thp ULT

Modul n hi ca btng


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= ng sut trong btng ti v tr trung tm b thp do

lc cng trc gy ra

csf

c

ics

A

Pf

Lc cng trc

Din tch mt ct tit dinca cu kin


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Trong trng hp c k n trng lng bn thn cu kinv cp lch tm so vi trc ca cu kin:

c

D

c

icsI

eM

r

e

A

Pf

2

2

1

Moment qun tnh ca tit din

Moment do trng lng bnthn ca cu kin

lch tm (e) ca

Thp so vi trc cukin

c

c

A

I


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2.4-2 Tn tht ng sut do tnh chng ca thp

pRf

* Cp c t chng thp (low-relaxation tendons): fpy = 0.90fpu

55.045

loglog '

12'

py

pi

pipR f

ftt

ff

Mt cch gnng: 1212 loglogloglog ttttt

(1)

Cng thc (1) tr thnh:

55.045

log '

'

py

pi

pipR

f

ftff

(t = n v tnh theo gi)


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* Cp cng bnh thng (stress-relieved tendons): fpy = 0.85 fpu

Thay th tr s 45 thnh s 10 trong cc cng thc trn

* V D:Tnh hao tn ng sut do tnh chng ca thp


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2.4-3 Tn tht ng sut do t bin ca BT

pCRf

cs

c

PStpCR fE

ECf

ut Ct

tC

60.0

60.0

10

csf ng sut trong btng ti v tr trng vi trung tm cacp

Hng s = 2-3

Thi gian = ngy

Eps= Modul n hi ca cp

Ec = Modul n hi ca btng


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ACI-ASCE a ra mt cng thc thc hnh tnh hao tnngsut do t bin:

csdcsE

EKf ff

c

PS

CRpCR

Trong :KCR= 2.0 cho cu kin cng trc= 1.6 cho cu kin cng sau

csf ng sut trong btng ti v tr trng vi trung tm cp thi im ngay sau khi ct cp

csdfng sut trong btng, v tr trng vi trung tm cp,do ti trng tnh tc dng (sau khi cu kin chu ng

lc trc)


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V D:

Tnh hao tn ng sut do t bin ca

btng


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2.4-4 Tn tht ng sut do co ngt caBT

psSHpSH Ef (1)

Hoc:

RHS

VEKf psSHpSH

10006.01102.8 6 (2)


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Trong :KSH= 1.0 cho cu kin cng trcEps= Modul n hi ca cp

S

V= t s gia th tch v din tch b mt ca cu kin

RH = m ca mi trng

i vi cu kin cng sau, Ksh c xc nh theo bng


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p dng c cng thc (1), ta phi xc nh bin dngdo co ngt theo thi gian:

+ Btng dng h bng m sau 7 ngy:

uSHtSH

t

t

35

+ Btng dng h bng hi nc sau 3 ngy:

uSHtSH t

t

55

Trong :

uSH

= 780x10-6

in./in.


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V D: Tnh tn tht ng sut do co ngt ca

btng:


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CC CNG THC TNH TN THT NG SUTTHEO H N V SI

Mt ng sut do tnh chng ca thp:

* Cp c t chng thp (low-relaxation tendons): fpy = 0.90fpu

55.045

loglog '

12'

py

pi

pipRf

fttff

(t = n v tnh theo gi)* Cp cng bnh thng (stress-relieved tendons): fpy = 0.85 fpu

Thay th tr s 45 thnh s 10 trong cng thc trn


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Mt ng sut do co ngt ca btng:

RHS

VEKf

psSHpSH

10006.01102.8 6

Trong :KSH= 1.0 cho cu kin cng trc

= [0.92 , 0.45] tng ng vi 1 ngy n 60 ngy, chocu kin cng sauEps= Modul n hi ca cp

RH = m ca mi trng


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+ Btng dng h bng m sau 7 ngy:

uSHtSH

t

t

35

+ Btng dng h bng hi nc sau 3 ngy:

uSHtSH tt

55

Trong :

uSH

= 730x10-6

mm/mm.

Nu tnh theo phng php ph thuc thi gian:

psSHpSH Ef

Trong

uSH = 800x10-6mm/mm.


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Mt ng sut do ma st:

KLffpF 28.31

L = mt


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Mt ng sut do tut neo:

PS

A

pA ELf

Ghi ch:

'5.1 043.0 cc fE

'5.1 043.0 cici fE


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mNlbin

mN

ftlb

MPapsi

mmN

mNMPa

113.0

593,14

006895.0

10 226

31830 mkg

32403m

kg

Cho btng nh

Cho btng thng


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Chng 3: Tnh ton ng sut trong cukin btng ULT

3-1 S lm vic ca BTCT ng lc trc:

Khi chu ti trng, trong kt cu BTCT xut hinnhng vng chu ko. Ct thp ULT c tch yu trong nhng vng ny, gy ra ng sutnn trong btng nhm trit tiu hoc lm gimng sut ko do ti trong gy ra, lm cho btng

khng b nt hoc c b nt th b rng khe ntl b.


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3-2 ng sut trc trong ct thp:

-ng sut trc trong ct thp l ng sut cto ra khi ko cng.

-ng sut ny cng ln th cng hiu qu nhng

khng c ln qu s gy nguy him trongqu trnh thi cng hoc khi s dng.


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3-3 Cng ca btng khi chu ng lctrc (khi ct cp):

C th tin hnh ct cp nn trcbtng khi n t 70%-80% cng tiuchun (cng c xc nh thiim 28 ngy sau khi btng)


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3-4 Tnh ton ng sut trong cu kin BTCTULT:

Ch 4 T h T C Ki


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Chng 4-Tnh Ton Cu KinChu Un


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