Dinh gii khi ndng xult hidn khdp ddo va phdn phdi t^i md men tinh todn trong gvA tian cho phdp eda tidu chuIn [1] eho ti^g td hop t i i trpng. Khi siJrdung d p khdng kdt dinh (unbo[r]
Trang 1A N H HUdNG CUA M O M E N T H Q CAP DEN KHA NANG
CHIU UON CUA DAM LIEN TUC BE TONG iJNG LUCTRUdC
Ngd l i m Thao
ABSTRAQ
The interaction of secondary moment
and moment redistribution in
multi-span prestressed conaete beams is
discussed Recommendations are
made for changes to TCXDVN 356:2005
^ a t the effects of secondary moment
due to prestressing should not be
neglected when calculating tiie design
moment
TS Ngd Lim Thao
C&ng ty CP tuvIn 6i\i tuva xay dung
HUD-CIC
Diddng: 0903412644
Email: ngolamthao@gmail.com
I.Ditvinde
Anh hudng eda md men thd d p (secondary moment), ddn khd ndng chju udn eda kdt clu sidu tinh bd tdng dng lyc trUdc (ULT) hidn nay vln dupe nhin nh^n theo edc thidt kd kdt clu be tdng cdt thdp hidn hdnh eda Vidt Nam TCXDVN 356:2005 vd eda Nga CHttn 52-01-2003 ddu bd qua dnh hUdng eda
md men thd d p thi cde tidu ehuIn nhu ACl 318-2011 (My), BS 8110-1997 xem md men
d c tdi trpng tinh todn khdc Bdi bdo dd edp ddn dnh hudng eda md men thd d p den khd ndng chju ufin eda dim lidn tyc bd tdng ULT trong tUong tdc vdi sU phdn phdi lai md men
2.M6menthi}cip
- Xdt dim iidn tge bd tdng ULT vd^ bd trf quy d^o edp nhu trdn hlnh la Gid sir khdng tdn tai d e gdi tUa trung gian, khi ehju tde dgng eda ULT dim se bj vdng Idn (hlnh 1 b).E]d ddm bdo didu kidn tdm vidcthye tdcda dim Id
ehuyen Vi bing 0 tai vi trf gdi tya, tai dd phli
xult hidn phin lye (h1nh 1 e) Phin lyc ndy sd
gpi Id md men thd cSp, phin bidt v(A md msn
so d p (primary moment) do ULT gdy ra khi trpng tlm d p d^t Ideh vdi trpng tdm tidt didn
Md men M, do ULT tde dgng tdn dim Id tdng eua md men sd d p M, vd md men ttid
d p M , :
M, = M,+M, (I) trong do:
M, = P, (2)
P - lye dng trude hidu qud
e - dd Ideh tlm eda d p so vdi trpng tlm tidt didn (hlnh la)
Md men M, cd thd dupe xde djnh dupc bing d e phUcmg phdp cOa co hpc kdt clu phdn tich ddm lidn tge chiu tdc dgng eda t^l trpng d n bing [2, 6], md men thd d p M, dupe xde djnh ti^ cdng thde (1)
-Tuydn d p thieh dgng:
Ung suit eda bd tdng trdn tidt didn ed thd
(a) Dim lidn tuc be tdng ting luc trudc
(b) D ^ lien tiJc b\ u6n do ung luc tnidc ne^u khdng c6 g6i tua giOa
^ ^
-1 -1
(c) Fhan luc tai g^i dd
(d) Bi^u 66 md men thi} c3p
Hmh 1 M6 men thi} cjp trong dim IKn tMC bitAng UU
7 0 miKlH* 03J012
Trang 2c
f ^
-
IbAr-HinhlMAmenkhdpdlo
dupe thay t h d b i n g gid tri eda h p p lye C Quy
tich vj trf didm d i t hpp lye C dpc theo d u kidn
dupc gpi Id C-line [2,6] Trong d i m lidn tue, m o t
tuydn d p dupc g p i Id thich d g n g (concordant)
dudng trpng t d m d p (c.g.s}, m d m e n t h d d p
b i n g 0 ndn bidu d d m d men Mt cdng triing vdi
bidu d d m d men M,
Vide xdc d j n h tuydn edp thich dgng Id tim
mdt dudng c.g.s thich hpp n h l t trong vide
khdng l^i m d m e n do ngoai lyc gdy ra Vd ly
n i m ngodi klidl p h ^ m vi tidt didn d i m Khi d d
ta cd t h d didu chlnh b i n g d e h ddng phdp
chuydn djch d d n g d^ng d d cd dupe d u d n g c.g.s
bidu d d mdmen gdy bdi ngo^i lUc trdn d i m
tidn tge dupe t i n h t o l n vdi eo sd tai cdc gdi tya
khdng cd chuydn v[, ndn ndu d u d n g d p c.g.s
dupc b d tri theo bidu d d d d sd cho nhCmg bidu
dd mdmen cd hlnh d i n g t u o n g t y , do viy se
khdng g l y chuydn vi t^i ede gdi tua Vdy vdi m d t
mpi bidu d d mdmen vdi m d t ty Id ve tuy y gdy
ddu cho m ^ t tuydn edp thieh dgng eda d i m lidn
tge d d Mdl C-line cdng chfnh Id m d t tuyen edp
mdmen gdy bdri ngoai lye tdc d y n g trdn d i m
3 Sy p h i n p h d i l^i n $ i l y c t r o n g d i m lidn
t y c b d t d n g d n g l y c trUdc
Xdt tidt d l f n bd t d n g edt t h d p ehju udn d
tr^ng thdi dupe gpi Id Iia (hlnh 2) Khi dat ddn
ti^ng thdi ndy, dng s u i t trong cdt t h d p dat ddn
cudng d d tinh todn eda edt t h d p Rs (cdt t h d p
o b nhd hon cUdng d d chju ndn t i n h t o l n eda
bd t d n g Khi m d men do t l i trpng tdng ten, dng
suit tror>g edt t h d p khdng d d i , c h i edn dng s u i t
cOa bd t d n g vdng ndn t i n g tdn cdng vdi vide
m d rdng khe ndt t r o n g vOng kdo Td trang t h i i
ndn b d t d n g d9t ddn eUCmg d d tinh todn Id m d t
qud trinh m d rdng khe ndt, tidt didn d u d n g n h u
quay quanh trye t n j n g hda Tidt didn n h u v | y
gpi Id k h d p ddo, D | c didm khdp ddo eda tidt
d i ^ bd t d n g edt t h d p ed d | c didm Id ehju dupc
theo bidu t h d e M^=R,A,z (3)
t r o n g d d :
Aj - didn tieh tiet didn ngang eda cdt t h d p chiu keo
z - d n h tay d o n (hlnh 2)
Khdp d d o c d tdc dung phdn phdi lai ndi luc trong he kdt c l u sidu tinh NgUdi thiet ke eo the
chieu h u d n g ed Idi.Tuy vay vide dieu chlnh md men udn d d e tiet didn trong kdt d u sidu t i n h phdi cd didu kien Mde d o eho phep phan phdi lai ndi lye Rd (%) ed t h d dUpc t i n h theo:
Rd=1 .m (4) M^ - m d men d o t l i trong tinh todn gay ra tinh theo so do ddn hdi tai cdng tidt didn xdt (M,> M ^
Tidu c h u i n ACl 318-2011, BS8110-1997 eho phdp sy phdn phdi lai ndi lye, trong d d m d men
cdt t h d p ed kdt dinh vd khdng vupt qud 20%
gid trj eda m d men ddn hdi tuong dng Trong TCXDVN 356:2005 [2] vd CHwH 52-01-2003 khdng ehd t h d n g qua han chd chieu cao vdng ndn
TheoT.Y Un (6], khi d d n g phdp chuydn dich ddng dang (linear transformation) eda dUdng
eua d i m lidn tge bd t d n g dtig lye trUdc Didu
d d cd nghTa l i t d tuyen d p khdng thich dgng
dang sang edp thieh dung se khdng Idm thay
khdc, khi tfnh todn khd ndng chiu tyc eda e l u kidn khdng d n xdt den m d men t h d d p Dd dieu d d x i y ra, t i t c l d e khdp ddo phdi dUpc hlnh thdnh t r o n g qud trinh phdn phdi lat m d men d d d i m tidn tge chuydn vd thanh kdt c l u
d g n g eda t i n h tdi vd hoat tdi t i n h todn Quan didm ndy dupe thda nhdn trong nhieu thap k j
thiet kd (Nga, Viet Nam, My ) Sau nay, t d nam
kidn bdn Mde d u v i y trong ACl 318-02 (muc
Rl 8.10.3, ndm 2002) van dua ra n h ^ n dinh r i n g
m d men t h d d p se t i i n g 0 khi d e k h d p ddo da hlnh thdnh hdt Nhu vdy khi vide p h i n phdi lai
dinh thi vide xdt den m d men t h d d p trong d e
Viet nam va Nga hidn nay vSn chua d e c i p ddn
kdt e l u be tdng Ong lUe trudc sidu tinh Cdc ket qud nghidn cdu mdi g i n d l y [4, 5] cho t h i y tdc dgng eda m d men t t i d d p khdng
bj dnh hudng eda vide hlnh thdnh khdp ddo trong d i m lidn tue, nd x u l t hidn khdng ehl d trang thdi lam viee ddn hdi md cd trong tr^ng thdi sau dan hdi eda ede tidt didn d i m , nghia id
lai ndi l y c Tidu c h u I n ACl 318 tU ndm 2005 cho ddn tidu e h u I n ban hdnh ndm 2011 ACl 318-11 [4] da cd nhung su thay d d i phCi h p p vdi quan
d u d i m , sdn Ildn tge bd tdng dng lyc trudc chju tdi trong ddng phdn bd ddu, khi xdt ddn
ducmg d gida nhjp sd dupe tdng Idn, trong khi
dgng tuydn edp thfch dgng sd Idm d o n gidn vide phdn tich, tuy nhidn vide tao ra tuydn d p
dd loai b d m d men t h d d p trong d i m tidn tuc
edng D I u tidn Id do edp khdng the b d tri vdt
d d md men tai gdi tUa d e t r i n h sU t d n hao dng
s u i t do ma sat vd t i p t n j n g dng s u i t cgc b d
tfnh hidu q u i kinh te, khi ehpn quy d^o c i p d n chpn d d Idch t l m Idn n h l t cho phdp cua d p so vdi trpng t l m tiet didn d tiet didn trdn got tya v i tai gida nhjp ddm
Quy trinh t i n h t o i n md men thiet kd eda
d i m lidn tge bd tdng dng lyc trudc n h u sau: Xde dinh m d men do tdi trpng t i n h t i l vd hoat tdi tfnh todn vdi cac t r u d n g h p p c h i t hoat
t l i b i t Ipi
Trang 3® ®
^.^TTTTTTTlMmn^ ,
^^ip^
®
Hiflh 5 M5 men do t i i trpng can b3ng M,
^^^^mrMTMn]^
^^IP^
®
15rii/2 |_
(a)Bieu ^ mo men sa cap M,
^ — - - u x u j j j j j j j j j j j m ^
i-M.IAB)
lOm
®
(b) Bieu do mo men thu cap M2
Hint) 6 M6 men so cap v l dil} cap
Xdc d j n h m d m e n t h d d p
Cdng tde dgng md men td tinh tdi vd tK>at
t i l vd md men thd d p
Xde d)nh md men khdp ddo eda cic tidt
didn Dinh gii khi ndng xult hidn khdp ddo va
phdn phdi t^i md men tinh todn trong gvA tian
cho phdp eda tidu chuIn [1] eho ti^g td hop t i i
trpng Thdng thudng sy phdn phdi sd tam gidm
gida nhjp Do gid tri Idn nhlt eda d c mo men
dm vd duong Id d d c td h ^ tdi trong khdc nhau
md men sau khi phin phdi t^i Khi siJrdung d p
khdng kdt dinh (unbonded), vide phin phdi l^i
md men d n dga trdn nghidn cdu vd ly thuydt vd
thyc nghidm dd cd eo sdtinh todn
Qt^ tiinh ndy cd sy tt»y ddi ddng kd so
vdi quy trinh d i dupe trinh bdy trong [6L dd Id
kd ddn md men thd d p mH>g td hpp tdi trong
tnJdc khi xdt ddn sy phdn phdi lai eda md men
4 Thf du tfnh t o i n Xet d i i bdn lien tge ba nhjp dang dim (hinh 3) vdi chieu ddy bdn h = 30em
\miiiv:
Bd t d n g ed d p d p ehju nen BBS
CapTIS ed cudng d p 1860 MPa (ket dinh)
73/trpng:
Trpng luong t)dn t h i n : w = 750 k g / m ' Cac tinh t i l tdidc w_= 200 k g / m ' Hoat tdi tieu chuan: w, = 300 k g / m ' Quy dao d p (hinh 4):
Chpn e , = e = e = 4cm
_ h / 2 + ( h - e ; )
e, = 1 6 , Scm
h j = h - ( e j + ej) = 22cm
a , = a j = a, = 11an Tdi trpng d n b i n g :
Sd lupng d p dupe b d t r i t i 7 d p / 1 m vdi liic
d n g hidu q u i tinh todn P=99669 k g
Nhjp BC w ^ 8Ph, 7 7 9 k g / m
Xdc dtnh m d men t h d d p :
M d m e n d o tdi trpng d n b i n g M t (hinh 5):
M ^ = - 8 8 5 4 k g m / « , = 15166 kgm
M ^ = - 6 7 4 2 k g m
M d m e n so d p (hlnh 6a):
M , „ = M , ^ =-99669.0,11=-10963 kgm M,g = 94885.0,11 = 10963 kgm
M d men t h U d p (hlnh 6b):
M ^ = M ^ - M , „ = 2109 kgm
M „ = M , - M , g = 4202 k g m
M ^ = M ^ - M , ^ = 4 2 2 1 k g m
M d m e n tinh todn M^:
Xdt t r u d n g h p p t m h t i l vd hogt tdi tinh todn tde d u n g d d u trdn cd 3 nhjp d i m So sdnh md men t i n h todn M u theo 2 trudng h p p t d hpp t i l
d p (vdi hd sd t d hpp b i n g 1) Kdt q u i tfnh todn theo hai t r u d n g h p p t d h p p cho t h i y cd sy sai lech d i n g kd (bdng 1) TCr bidu d d m d men cd
t h d x e m xdt didu ehinh bidu d d m d men tinh
gid^ han cho phdp
B d n g i
M.(AB)(kqm) M.(B)(kgni) tWBOfkgni)
quaM])
6623 -27254 18J08
M.(irit d6iMi] S731 -23052
22530
Salsl
24K
I M 18,7H
5 K A I i i i n
Md men thy d p tdn t^i d khi dd hlnh thdnh kh<!^ ddo trong kdt d u sidu tinh bd tdng dhg tyc
phdi lai md men De ning cao tinh an todn vd hidu qu i eOa kdt d u dim (sdn) lidn tge bd tdng dng lyc trudc tidu chuin Vidt nam TCX13VN 356:2005 ndn nghidn cdu xdt ddn md men did
d p khi kidm tra khd ndng chiu udn eda d u kidn
TAILIEUTHAMKHAO
1 Phan Quang Mmh, Ngo The Phong, NgiQfn Oinh C6ng Ket d u be ^ cA t h ^ PhJn (iu kKn o r l i i n Nhi w i t Itlii IQtKT.HaN6i2011
1 Phan (hiang Mhh Sin phing b i lang Aig hK t n t t cing SIU Nha mat bdn ICHICT, Ha No, 2010
3 TCXDVN 356:2005: Itf! cJU b« tong va b» tong cA Ihtp-ntil (takthKtiK
4 AQ 318-11 Bddmg Code Reqwrement for Stntctml ConoecKlKI 318-11] and ConHnentar); 2011 S.Bondr,tB Moment RedbtribudoKPimopIn and Practice,
n n g « 31M2 Pit Journal, V 1 Na 1 Pofl-Tenswied tatme, Phoeno AZ, JvL 2003
6 t l Un, Ned H Bums Design of PresDessed CoooeK Scrocnms k)hn Wiejr i Sons New Vude, 1987
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