Một số vấn đề về an toàn của
kết cấu dàn l5ới không gian

!"#$ %&"'() *+,-& ./
0#$# %&+12- *+,-& .+1
!345-& 67' .89 :;1 <=-&

Abstract: !"#$%&'"#()*+#$,)-',-)"#*$#.*+/0#-$*1(#*1#2*",#3&45#6-,#$74"#*,$#%)76/"4$#
&)"#17,#$7/8"+9#:1#,!*$#%&%")5#,!)""#%)76/"4$#7;#$%&'"#()*+#$,)-',-)"$#&)"#'71$*+")"+9#
!"#;*)$,#%)76/"4#*$#,!"#$,)"1(,!#7;#$%&'"#()*+#$,)-',-)"9#
!"#$"'71+#*$#,!"#&1&/0$*$#7;#,!"#$,)"$$#<#$,&,"#7;#,!"#=0/*1+)*'&/#&1+#$%!")*'&/#
6-,,71$9#
!"#,!*)+#%)76/"4#*$#,!"#&$$"$$4"1,#7;#,!"#)"/*&6*/*,0#7;#$,)-',-)"9#
7#*//-$,)&,"5#$74"#">&4%/"$#&)"#'71$*+")"+9#
#
1. Mở đầu
0>? 9@+ A/- B4C' D"E-& &',- FG F4H9 IJ AK-& 3L-& 3G' ?3(- ?"> &'C' ?3M-& -"'N+ ?"OP DQ
&R- F;1S FT U;1 A=-& 9V9 9E-& ?3W-" 9X D"Y+ FL BC-S FZ' "[' D\ ?"+O? 9,M#
%"5 -"]-& 4+ F'T) ^4H? ?3L' 9_, D>? 9@+ A/- B4C'S )/ -X F,-& AR- AR- ?",1 ?"> 9V9
A7-& D>? 9@+ ?3+1N- ?"`-& -"4a A/- ^W DbM ?"cPS A/- d( ?E-& 9`? ?"cPS de- f ^[ )V' d(
?E-& 9`? ?"cPS "g )V' A;1 ^#^##
ở h'g? %,)S ?3(- F45-& 9E-& -&"'gP "MV F@? -4C9S -"'N+ 9E-& ?3W-" ^4H? D"Y+ FLS 9X
"W-" AV-& Fi9 d'g?S 1(+ 9R+ ?"' 9E-& -",-" -"4a 9+-& ?"T ?",MS -"/ &, I;- d,1S -"/
9E-& -&"'gP ^#^# F4H9 U;1 A=-& j -"'N+ -k'S ?3M-& FX 9V9 -"/ ?"'>? D> FG 9"8- D>? 9@+
A/- B4C' D"E-& &',- B/) )V' 9"l# m"n-& "7-S -"/ ?"' F@+ *+R- %&=, o./ %L'pS -"/ ?"'
F@+ ?"T ?",M %,) 6q-"S I;- d,1 *+`9 ?> %L' r/' ^#^# %"'N+ FN ?/' 9@P rLS 9s-& -"4
9V9 9E-& ?3W-" -&"'(- 9t+ uvS wS xS y###z FG F4H9 ?'>- "/-" FT P";- ?{9" B| ?"+1>? ^/ ?"=9
-&"'g) D>? 9@+ A/- B4C'S -"}) 3~? 3, D>? B+O- 9R- ?"'>? 9"M ^'g9 IJ AK-& A/- B4C'
D"E-& &',- ^/M U;1 A=-& 9E-& ?3W-"#
h'g9 9"> ?7M -~? ^/ ?",-" 9s-& FG F4H9 ?'>- "/-" ?7' )L? I` -k' omk D"{ 6E-& -"S

-"O- F4H9S ^W ->+ P"V? I'-" )E )l- ?"W )E)l- -"[S ?"=9 -&"'g) FG 9" ỉ 3, F'N+ FX#
!"lM B| ?"+1>? D>? 9@+S ?7' 9V9 F'T) -~? &'], 9V9 ?",-" ^`- 9X )E)l-S D"' Ik Fồ "MV
9M' B/ D"CP o)E)l- d}-& D"E-&p ?"W "g Ik Fồ "MV 9"q+ B=9 Dc) "k- "g ?"=9# !3M-& D"'
?, deM Fe) ,- ?M/- 9"M "g D"CPS -&"ĩ, B/ "g Dc) "k- )/ FG ,- ?M/-S ?"W "g ?"=9 B7'
9/-& ,- ?M/-#
2.2 An toàn của nút
h'g9 9M' -~? B/ ,- ?M/- D"E-& D'T) ?3, ^/ ?'- ?4j-& -"4 ^O1 -"5 ?"=9 -&"'g) 9" ỉ 9X ?"T
9"@P -"O- F4H9 ^C' D>? 9@+ A/- )V' Fk- &'e-S -"4-& ^C' 9V9 ?345-& "HP P"t9 ?7P ?'>-
"/-" ?"=9 -&"'g) &iP -"'N+ D"X D"ă-# Mi? D"V9S ^N B| ?"+1>?S D"' 9"> ?7M 9V9 -~?
D"E-& 9"ỉ -"5 ?"=9 -&"'g) )/ P"e' 9R- 9X ?{-" ?MV- D'T) ?3,#
%>+ D"E-& ?{-" ?MV- D"X )/ d'>? F4H9 -~? ,- ?M/- F>- )t9 -/MS 9"8- ^O? B'g+ B/) -~?
3, I,M ?
!"lM ?'(+ 9"+Y- -4C9 -&M/' u6zS ->+ D>? 9@+ ,- ?M/- ^C' 9"ỉ I` FL ?'- 9O1 b =xS5 ?4k-&
F4k-& ^C' UV9 I+@? ?'- 9O1 P
$
=0S999767y 0S9999S ?"W 9V9 F'T) -`' P"e' 9X )t9 ,-
?M/- 9,M "k- -"'N+S 9K ?"T B/ b =5S0S ?4k-& F4k-& ^C' UV9 I+@? ?'- 9O1 P
$
=0S9999967y
0S9999999#
!"lM ?'(+ 9"+Y- ?"'>? D> -"/ )V1 F'g- -&+1(- ?J 9_, M\ ?"W P
$
=0S9999999 v#
Rõ 3/-& -&45' ?, q+1 Fq-" ,- ?M/- 9_, -~? 3@? 9,M# %>+ ^O1 ^O? B'g+ -~? P"e' F4H9 9"8-
-"4 ?"> -/M B/ "HP B| ? 6T 9"8- ^O? B'g+ -~? "HP B|S deM Fe) ,- ?M/- 9,MS D{9" ?"4C9
P"ù "HP 9"ỉ 9X w 9M- F45-& dổ ?3H 9"M -",+ B/ -&"'(- 9t+ ?37-& ?"V' t-& I+@? 9_, -~?
^/ D>? "HP ^C' ?"=9 -&"'g) FT D'T) ?3,#

2.3 Sai số do lắp dựng
ML? Fi9 F'T) q+,- ?38-& 9_, D>? 9@+ A/- B4C' B/ 1(+ 9R+ ^N BắP A=-& 9X FL 9"{-" UV9

0{9" ?"4C9 "W-" "89S Fi9 ?34-& ^O? B'g+ ^/ 9V9" ?"t9 &', 9E-& 9"> ?7M -~? ?+ ỳ ?"+L9 ^/M
?ừ-& BM7' 9E-& ?3W-" ^/ ?3W-" FL 9E-& -&"g 9_, ?ừ-& q+`9 &',#
?9@9A9 B!CD1(#%!E%#,F1!#,7E1##
r/' ?MV- Fi? 3, B/ D'T) ?3, dN- 9"M )L? -~? d@? Dỳ ?3(- )L? A/- )V' D"E-& &',-# mV9"
?"t9 ?'>- "/-" -"4 I,+a I,+ D"' 9X D>? q+e -L' B=9 ?3M-& 9V9 ?",-" A/-S 9"~-& ?E' ?{-"
?MV- D'T) ?3, dN- 9"M 3'(-& -~? F45-& D{-" 69)S 9"q+ ?V9 AK-& 9_, -&M7' B=9 9X &'V ?3q
d}-& v6 !/?",-"# mK ?"T B/ ^C' 9@+ ?7M -~? ?3KS ^'g9 ?{-" ?MV- -~? F4H9 F4, ^N ?{-" 9"M
)L? FM7- 0S5 9) ?"lM 9"'N+ A/' 9_, ?3K# 6T Fk- &'e- "MVS 9X ?"T D",' dVM BV? ?3K 0S5 9)

-/1 9@+ ?7M ?õ 9V9 P"R- ?J I"lBBI oj ?37-& ?"V' t-& I+@? P"n-&p# !õ D>? q+e t-& I+@?
d'>- A7-& ?7' 9V9 -~? FØ-" 9_, I"lBBIS 9X ?"T D>? B+O- -~? B/ dN- ",1 D"E-&#
hC' 9V9" )E "W-" "MV -~? ?3K -"4 ?3(- 9X ?"T D"n-& Fq-" ^C' )L? 9V9" 9"', P"R- ?J
"HP B| ^/ F_ )q-S D>? q+e ?{-" ?MV- F4, 3, ?õ )V1 ?{-" B/ 9X I,' I` 9X ?"T 9"@P -"O-
F4H9#
?9@9@9 GH,#I-J#,F1!#,7E1#
• <4C' F;1 B/ )L? ^/' D>? q+e ?{-" ?MV- -L' B=9 9_, )L? ^/' I"lBB ?"+L9 -~? ?3K F45-&
D{-" 69) ?3(-S ?"cP m!x -"4 )E ?e j ?3(-S Fk- ^q DGfS9)#
c¾t ngang nót
c¾t däc nót
BuL«ng c/êng ®é cao
Long ®en
Ecu
TÊm bÞt
Th©n trô
TÊm bÞt
hµn gãc
Thanh chèng L=150
.W-" v# 0>? 9@+ )V' 9M+PEB ",' BCP ^/ 9@+ ?7M -~? ?3K
90#5
5x7#v
xv#v
5x9#w
88#y
500#9
0#0
0#0
0#0
37
LO•<v
x
6v#9
x9w#v
v9#w
x9x#w
60#8
x66#6
0#0
0#0
0#0
37
LO•<v
vy5
y6#w
x85#9
xw#y
x89#0
yx#v
x69#x

vx6#9
x57#7
wx#w
x60#v
vxy#5
xv5#w
0#0
0#0
0#0
153
LO•<v
x
v5x#y
ywx#6
wx#9
yw5#7
v5v#x
x7x#7
0#0
0#0
0#0
153
LO•<v
vy5
v59#x
yw5#y
wx#5
yw7#y
v57#w
x7y#5

v8y#5
x69#6
y0#w
x77#9
v76#v
xw7#6
0#0
0#0
0#0
232
LO•<v
vy6
v79#5
xxy#y
5w#0
x50#x
v6x#6
x0x#6
0#0
0#0
0#0
232
LO•<v
xyx
v7y#6
xxy#v
yw#y
xyy#7
v6y#v
w98#6

wv0#9
xww#x
67#x
x5y#0
v79#w
x06#6
0#0
0#0
0#0
318
LO•<v
5w0
v98#8
xv8#5
69#w
x50#v
v67#w
x0x#x
0#0
0#0
0#0
450
LO•<v
xy5
wyy#0
xx0#6
76#v
x7y#8
v99#7
xwy#8

wvw#v
x0y#v
95#9
x6y#5
v5v#8
xv7#v
0#0
0#0
0#0
550
LO•<v
xyy
w55#7
xv6#x
v08#w
x98#y
v7x#6
xy5#9
0#0
0#0
0#0
550
LO•<v
5w9
wwv#6
x06#0
v09#x
x8v#0
vy6#7
xxw#8

w60#y
x09#x
vy0#v
yw7#w
vyw#6
x76#7
0#0
0#0
0#0
669
LO•<v
7w5
wvx#7
w95#w
vyv#5
y0v#8
v07#w
x60#x
0#0
0#0
0#0
669
LO•<v
5x0
w6x#x
xv7#8
v5y#7
yy7#6
vxx#y
x98#0


h'g9 ?{-" ?MV- D'T) ?3, -~? 9R+ ?"=9 9"@? F4H9 F4, ^N IM IV-" t-& I+@? d'>- A7-& ?7'
?õ-& F'T) ?3M-& -~? ^C' t-& I+@? d'>- A7-& 9"M P"cP 9_, ^O? B'g+ 9"> ?7M -~?# m"~-&
?E' FG ?'>- "/-" U;1 A=-& P"R- )N) 9"', -~? ?"/-" 9V9 P"R- ?J D"`' 9X D{9" ?"4C9 ?+ ú
|# 0>? "HP ^C' P"R- )N) ?{-" ?MV- D>? 9@+ I½- 9XS 9K ?"T B/ $•Pw000S ^C' D"e -¨-&
9_, )V1 ?{-" -"4 "'g- -,1S 9X ?"T -X' 3}-& D>? q+e )/ )V1 ?{-" 9+-& 9@P B/ ?'- 9O1
F4H9 D"' ?, 9"', -~? 9R+ F_ )q- ^/ "HP B|#
?9?9@9 #GH,#I-J#,F1!#,7E1#1K,#'L-##
%"4 ^O1S ^C' 9V9" 9"', -~? ?"/-" 9V9 P"R- ?J IMB'AI "HP B|S -L' B=9 ?7' 9V9 F'T) ?3M-&
-~? F4H9 ?{-" ?MV- ^/ D'T) ?3,# mX ?"T D>? B+O- -~? B/ dN- ",1 D"E-&S -&45' D\ I4 9X
?"T 9"8- 9V9 ?"E-& I` -~? "HP B|S &'~P 9"_ FR+ ?4 "M/- ?M/- 1(- ?;) ^C' 9E-& ?3W-" 9_,
)W-"#
<4C' F;1 B/ )L? ^/' D>? q+e ?{-" ?MV- -L' B=9 9_, -~? 9R+ F45-& D{-" v69)S ?"cP m!x
-"4 )E ?e j ?3(-a
.W-" w# ME "W-" "MV -~? 9R+ F45-& D{-" v69)


BiÓu ®å S-MIN
v
w
5
6
7
8y
x
fy000 fw000 0
Nót
kG/cm2
Sè thø
tù nót
SOLIDLOADJOINTS11S22S33S12S13S23S-MAXS-MIDS-MINSVM
1
xwy
LO•<v
•w89
fxx08#07
f9x8#8vv
fvw87#wx
f85w#v9
f5w7#9
f77#0x96
f6y9#67
fvv86#7
fx697#7
w8v8#v5
2

<w89
f9#0yy97
fv9y#y6y
v0w#5x8
f588#5
fv8#07
f5v#v89w
y9y#978
v0y#756
f700#706
v056#v
5
w05w
LO•<v
Ew89
x0#7y5
fvx7#95w
80#5665
fy0w#56
fv#w9
fxw#609y
x59#075
80#yx86
fy66#v5y
7w7#vv9
6
w6w8
LO•<v
Fw89
0#9y05y

fv65#76
59#096
v9#880v
fvvx#y7
fyx5#6v
f70v#vyx
509#7w5
BiÓu ®å S-MAX
v
w
x
y
5
6
7
8
fv000 0 v000
Nót
kG/cm2
Sè thø
tù nót
SOLIDLOADJOINTS11S22S33S12S13S23S-MAXS-MIDS-MINSVM
1
xww
LO•<v
•xww
fvvy8#x
f795#6
f5x6#w
wvv#y

0#0
fy66#v
f599#y
5y5#v
4
vy7y
LO•<v
<xww
fv97#y
fxy6#9
xy#6
f89#6
fw0#9
v0#v
x7#y
fv58#x
fx88#8
x69#5
5
w050
LO•<v
Exww
f97#7
fwyy#w
x8#8
f87#5
f7#w
x#y
x9#5
f57#5

8
x778
LO•<v
.xww
fy#0
f9#7
f76#8
fx#y
6#v
fx#5
fv#8
fvv#w
f77#y
7v#y
BiÓu ®å S-MIN
v
w
5
6
7
8
y
x
fv500 fv000 f500 0
Nót
kG/cm2
BiÓu ®å S-MAX
v
w
x

?38-& B4H-& 9V9 ?",-" A/- ^/ -~?# P"R- )N) ?{-" ?MV- D>? 9@+ $P w000 9X 9"t9 -ă-&
&V- ?e' ?38-& AM ?38-& B4H-& de- ?";- 9V9 9@+ D'g- &;1 3, -(- 9"ỉ ?'>- "/-" ?{-" ?MV-
9V9 ?"/-" P"R- ?ĩ-" ?e' 9Z- B7'# 6T Fk- &'e- ?, 9X ?"T B@1 ?ổ-& ?38-& B4H-& ?E- + U/ &ồ
+ 9"`-& -X-&+-~? ?"lM D'-" -&"'g) ox0f>y0DG/)
w
p# m"8- P=x5DG/)
w
# <M D"E-&
D",' dVM D>? 9@+ 9J, ?35' ^/M 9"4k-& ?3W-" -(- 9R- q+1 ?e' ?38-& 9_, -X ^N x6 -~? ?3(-
^/-" ?3(- 9_, A/-# Mỗ' -~? 9"q+ )L? B=9 P
m!
a

#DGy56
v8
x5
*R*P9?
w
A
==

hO1 ?ĩ-" ?e' )V' 9X "4C-& ?ừ ?3(- U+`-& A4C'S 9X F''T) Fi? ?7' 9V9 -~? ?"+L9 BCP ?3(-S
9X &'V ?3q d}-& &'V ?3q ?e' ?3+-& dW-" ox5DG/)
w
p -";- ^C' A'g- ?{9" 9"q+ ?e' 9_, -~? FX
o3'(-&v8 -~? ?"+L9 ^/-" ?3(- 9ù-& 9Z- 9X ?"() ?"/-" P"R- AM ?e' ?38-& 9J, ?35' &;1 3,p#
G'V ?3q ?ĩ-" ?e' F4H9 ?"T "'g- ?3M-& de-& ?e' ?38-& A4C' F;1#
.
W-" x# Mi? 9ắ? A89 )V'


w
p
<M )V' "W-" 9"[)
9R+ -(- &'V ?3q "g I`
D"{ FL-& m ?7' )L?
F'T) ?",1 Fổ' ?"lM
&X9 -&"'(-& 9_, ?',
-`' F'T) FX ^C' ?;)
9R+ ^/ )i? P"n-& -})
-&,-&# !"lM de-& 9"ỉ
Aẫ- UV9 Fq-" "g I` D"{
FL-& ?"W ?M/- dL P"R-
)V' ?"'>? D> FN+ 9"q+
&'X "~?# 6T Fk- &'e-
9"M ?{-" ?MV- ^/ ?"'(-
^N ,- ?M/- ?, B@1 m
=m
90
=fvSw5# 0>? q+e
?{-" B=9 &'X Fi? ?7' 9V9
^/-" ?"lM P"4k-&
P";- DỳS ?;) P";- Dỳ
B/ ?;) 9"[) 9R+# !'>- "/-" -"OP &'V ?3q ?e' ?38-& &'X ^/M )V' ?3M-& $Pw000 d}-&
9V9" D",' dVM B=9 &'X ?OP ?3+-& 9X F'T) Fi? ?7' FR+ ?3(- 9_, 9V9 ?",-" 9"`-& "4C-&
?;)S 9X "4C-& ?3K9 v o?3K9 'fjp 9_, 9V9 ?",-" -/1S 9X &'V ?3q ?",1 Fổ' P"K ?"+L9 A'g- ?{9"
9"q+ ?e' 9_, -~?S F4H9 ?{-" ?MV- 9"M ?3M-& de-& d(-a
stt
vành
độ dàI
cạnh đáy

vw0#9
fyyv#75
5
v560
w#87
79#98x
vvv#9x
fy08#975
6
vyx0
w#67
75#80x
v0y#vx
fx80#y75
7
vw90
w#yy
70#996
95#v6
fxy7#7
8
vvyw
w#v8
65#56w
85#0w
fxv0#65
9
w0v5
x#y8
9w#7xw

#

4.4. Kiểm tra bền và ổn định thanh dàn:
mă- 9t ^/M de-& D>? q+e ?ổ "HP ?e' ?38-&S ^'g9 D'T) ?3, dN- ^/ ổ- Fq-" 9"M ?ừ-& 9@+
D'g- ?",-" A/- F4H9 ?'>- "/-" -"4 9V9 9V9" ?"E-& ?"45-&# 0>? q+e 9"M ?"@1 ?3M-& 9e w
?345-& "HP B'(- D>?S -L' B=9 ?"+ F4H9 ?3M-& ?",-" -"[ ?"+, 3@? -"'N+ IM ^C' D"e -ă-&
9"q+ B=9 9_, ?",-"# h'g9 9"8- ?'>? A'g- ?",-" ),-& "R+ -"4 ?"Me )G- 1(+ 9R+ D'>-
?3~9#
4.5. Tính toán độ tin cậy của dàn theo tiêu chuẩn bền:
r/' ?MV- Fi? 3, B/ UV9 Fq-" 9"ỉ I` FL ?'- 9O1 b 9_, A/- )V' 9M+PMB ^C' &'e ?"'>? -~? B/
dN-#
N9]9A9^E'#V_1!#,!&4#$`S#
Tham số hình học:
m"'N+ A/' ?",-" A/- ?3(- 9V9 BCP o9V9 ?",-" 9"'N+ A/' w009) p 9X à
L
= w009)S
L
=
v09) oAM BắP A=-&p#
645-& D{-" 9V9 ?",-" A/- < 9X à
<
= =5S79)S
<
= 0#0579)#
m"'N+ A/1 `-& ?",-" A 9Xa à
A
= =0#x59)S
A
= 0#0x59)
Tham số vật liệu:

),U

P"K ?"+L9 ^/M 0y d'>- -&ẫ+ -"'(- B/ oLS <S AS Ep# mR- ?{-" UV9 I+@? ,- ?M/-
zpuoPP
MA),U3Md$

<

=
S B4H-& A= ?3] M=


zu
MA ),U

#
6T ?{-" P
$
?, ?{-"
M
M

à
=
a
ở F;1S
p)/DGo0vS709
88S5
yv69


# 6i?
max

= FoLS <S AS Ep
f 6L -"71 o?`9 FL d'>- ?"'(-p 9_,
max

?"lM L# 9)
DG
vxxS0
v0
0vS709xyS7v0
v0L
F
),UI,+
=






−
=




58S66v
057S0
0vS709xS67v
057S0<
F
),UI,+
−=






−
=






σ−σ
=
∂
∂

⇒ 6L Bg9" 9"+Y- 9_,
max
σ
AM < I'-" 3, B/a


−
=






σ−σ
=
∂
∂

⇒ 6L Bg9" 9"+Y- 9_,
max
σ
AM A I'-" 3, B/a

pDGo559S6w0x5S0#UySv787#
A
F
'
AA
=−=σ
∂
∂
=σ

f 6L -"71 o?`9 FL d'>- ?"'(-p 9_,

∂

⇒ 6L Bg9" 9"+Y- 9_,
max
σ
AM E I'-" 3, B/a

p9)/DGow65S0w0x89Uv0UxSv#
E
F
'
w5
EE
−=−=σ
∂
∂
=σ
−

!, 9X FL Bg9" 9"+Y- 9_,
max
σ
B/a

w
E
w
A
w
<

M
≈=
σ
µ
=β
$+1 3, P
f
≈v0
f5

mX ?"T D>? B+O- A/- )V' 9X FL ?'- 9O1 9,M

Kết luận
1. h@- FN ,- ?M/- 9_, D>? 9@+ A/- B4C' D"E-& &',- B/ ^@- FN 3@? P"t9 ?7PS ?3(- F;1 9"ỉ
Uc? )L? I` D"{, 97-" 9_, ^@- FN# r/' ?MV- ổ- Fq-" ^/ A,M FL-& 9_, A/- 9"4, F4H9 Uc?
F>-# LM7' D>? 9@+ A/- B4C' B/ D>? 9@+ -"ẹS 9X D"Y+ FL BC-S 3@? -"71 9e) ^C' &'X dGMS ^@-
FN ổ- Fq-" D"{ FL-& 9s-& B/ ^@- FN 9R- q+,- ?;)#
2. Mt9 FL ,- ?M/- 9_, -~? FZ' "[' 9,M ^4H? dO9 IM ^C' ?",-"S 6!m P"e' F4H9 9M' d}-&
v# <M FX FG D"E-& F4, ^/M ?{-" ?3M-& Ik Fồ 6!m# h@- FN -/1 9X )L? | -&"ĩ, ?"=9 ?> B/
D"' 9"8- ^O? B'g+ ^/ D{9" ?"4C9 9_, 9V9 -~? P"e' deM Fe) ,- ?M/- 3@? 9,M IM ^C' ?",-"#
m"{-" ^W B| AM FX )/ -&45' ?, D"E-& F4, -~? ^/M Ik Fồ ?{-" -L' B=9#
3. !'>P ?"+ 9V9 ?"/-" ?=+ 9_, -4C9 -&M/'S AR- AR- B/) 9"_ 9V9 ?"/-" ?=+ FX B/ 1(+ 9R+
F`' ^C' 9V9 -"/ U;1 A=-&# hC' ?'-" ?"R- FXS 9X Bẽ ?3M-& ?4k-& B,' &R- h'g? %,) -(- 9X
)L? ?'(+ 9"+Y- ?"'>? D> D>? 9@+ A/- B4C' D"E-& &',- P"ù "HP F'N+ D'g- h'g? %,)#
Lời cảm ơn:
Chúng tôi xin chân thành cám ơn GS-TS Nguyễn Văn Phó đã cho nhiều gợi ý quý
báu trong khi hoàn thành nghiên cứu này.
mE-& ?3W-" "M/- ?"/-" ^X' I= "ỗ ?3H 9_, 9"4k-& ?3W-" -&"'(- 9t+ 9k de- o-&/-" 9k
"89p#