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Tuesday, February 28, 2012
Mekanika Teknik I (KL 1402)Mekanika Teknik I (KL 1402)
Minggu V
GAYA DALAM (MOMEN, GAYA
GESER dan GAYA NORMAL)
Muhammad Zikra
Jurusan Teknik KelautanInstitut Teknologi Sepuluh Nopember Surabaya
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Apa itu Gaya Internal ?
Straight two-force member AB is in
equilibrium under application of F and
-F .
Internal forces equivalent to F and -F are
required for equilibrium of free-bodies AC
and CB.
Gaya Internal : gaya yang mengikat bersama berbagai
bagian struktur sehingga struktur tersebut menjadi kokoh
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Reaksi pada Balok
Beams are classified according to way in which they are supported.
Reactions at beam supports are determinate if they involve only three
unknowns. Otherwise, they are statically indeterminate.
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GAYA DALAM
Tanda MOMEN (M)
Sebuah balok diatas 2 perletakan mendapat
beban P diatasnya
Melendut sisi atas tertekan
sisi bawah tertarik Momen yang timbul positif
Momen adalah positif jika:Sisi atas tertekan (-)Sisi bawah tertarik (+)
P
-
+
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Tanda MOMEN (M)
Sebuah cantilever dengan beban P diujung
sisi atas tertarik (memanjang)
sisi bawah tertekan (memendek)Momen yang timbul negatif
Momen adalah negatif jika:Sisi atas tertarik (+)Sisi bawah tertekan (-)
P
-
+
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Tuesday, February 28, 2012
Tanda Gaya Normal (N)
Gaya normal= gaya yang searah sumbu batang
N1
N2N2
N1
aksireaksi
N = (-)
N = (+)
Bila gaya menarik titik ² tanda positif (N= + )Bila gaya menekan titik
²tanda negatif (N= - )
CD B A N1N2
Nc & ND ?
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Tanda Gaya Lintang (D)
Gaya lintang (D)= gaya yang tegak lurus sumbu batang
D = (+)
D = (-)
Titik A jumlah gaya kiri titik keatasatau
jumlah gaya kanan titik kebawahTitik B jumlah gaya kiri titik kebawah
atau
jumlah gaya kanan titik keatas
tanda positif (D=+)
tanda negatif (D=-)
P
RA=1/2P RB=1/2P
BA
½ L ½L
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Tuesday, February 28, 2012
RINGKASAN
Gaya Momen(M)
tanda
Gaya Normal
(N)
tanda
Gaya Lintang
(D)tanda
(+)
(+)
(+)
(-)
(-)
(-)
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Prosedur Menyelesaikan Soal
Gambar FBD (Free Body Diagram) dari soal
Jangan lupa kasih perjanjian tandanya
Gambar gaya reaksi yang ada
Kalau ada beban terdistribusi merata, cari dulu besar gayaresultan, dan posisinya
Hitung besar gaya reaksi di tumpuan, menggunakan
§ V = 0
§ H = 0
§ M = 0
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2... 1
1111
x xq x P Mx
BkeC dari
M omen P ersamaan
!
p
)(..
2
1.
2
1111 parabola
pers
xq x P Mx !
)(.)(
2
1)..().( 2222211 parabola pers x P a xa xq xa P Mx
Ake Bdari
!
p
Sebuah konsol (kantilever) dengan beban seperti pada gambar:
P2
A B
RVA
RHA
x1
MA
P1
P3
q kg/m¶
x2
a
C
2... 1
1111
x xq x P Mx
BkeC dari M omen P ersamaan
!
p
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Tuesday, February 28, 2012
2111
111
).(
.
tan
int
P xaq P Dx Ake B
xq P Dx BkeC
g ba sumbulurustegak yang gaya
ang LGaya
!p
!p
Gaya Normal
Gaya yang searah sumbu batang
)tan(3 g ba se panjang P N !
2111
111
).(
.
tan
int
P xaq P Dx Ake B
xq P Dx BkeC
g ba sumbulurustegak yang gaya
ang LGaya
!p
!p
P2
A B
RVA
RHA
x1
MA
P1
P3
q kg/m¶
x2
a
C
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Tuesday, February 28, 2012
Sebuah balok diatas 2 perletakan dengan beban seperti pada
gambar:
Diminta: Gambar Bidang Momen, Gaya Lintang dan Bidang
Normal (Bid M, N dan D)??
A B
RA RB
10 m 2 m2m
q2= 1 t/m¶
q1= 2 t/m¶
6 m
D EC
P1= P2=6 ton
P3=2 tP4=3 ton
22 P1V=2 ton
P1H=2 ton
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JAWAB: Mencari Reaksi Vertical
)(1310
1.1.24.67.6.212.2
01.2.24.7.6.112.10.
0
21
o!
!
!
!§p
ton R
q P q P R
M R
AV
V AV
B AV
)(910
2.2.3.6.26.611.1.2
02.3.6.16.11.2.210.
0
12
o!
!
!
!§p
ton R
P q P q R
M R
AV
V BV
A BV
Control 0!§V
0)913()2.166.22(
0)()2.26.1( 21
!
! BV AV V R Rq P q P
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Tuesday, February 28, 2012
Reaksi Horizontal
)(7322
0
431
n!!
!!§
ton R
P P P R H
B
H B
Menggambar Gaya Lintang
ton R P D
Atitik dikanan D D
Atitik dikiri Dton P D
kiridarilihat AC
AV V Akanan
Akanan
V Akiri
11132
)(
)(2
1
1
!!!
!!
p
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Tuesday, February 28, 2012
ton D
ton D x
linier pers xq D
D A
Dkanan
Dkiri
x
7612132
1121326
)(.1132
!!
!!p!
!
p
Dari titik D s/d B tidak ada beban jadi BI D ANG Dn
sama senilai Dd kanan
q1= 2 t/m¶
A B
RA RB
2 m
q2= 1 t/m¶
6 m
D EC
P1= P2=6 ton
P3=2 t P4=3 ton
22 P1V=2 ton
P1H=2 ton
x
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Lebih mudah kalau dihitung dari kanan
ton D Btitik kiri D
ton Dm x D
x xq Dx
D
Bkiri Bkiri
Bkanan Bkanan
E
792)(
2)2(
.2
0
2
222
!!p
!p!
!!
!
q1= 2 t/m¶
A B
RA
RBV= 9 ton
2 m
q2= 1 t/m¶
6 mD EC
P1= P2=6 ton
P3=2 t
P4=3 ton
22 P1V=2 ton
P1H=2 ton
x2
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Tuesday, February 28, 2012
BID ANG NORM AL (N)
ton N kiridari
ton N
kanandaridihitung E B
ton N N
tonton N
kiridaridihitung B D
Atitik dikiri Dton P N
kiridaridihitung DC
kanan B
kanan B
kanan Dkiri B
kanan D
H kiri D
3)74(
3
4
4)22(
)(21
!!p
!
p
!!
!!
p
!!
p
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Tuesday, February 28, 2012
q1= 2 t/m¶
A B
RB2 m
q2= 1 t/m¶
6 m
D EC
P2=6 ton
P3=2 t P4=3 ton
P1V=2 ton
P1H=2 ton
x
q1= 2 t/m¶
A B
RB
q2= 1 t/m¶
D EC
P2=6 ton
P3=2 tP4=3 ton
P1V=2 ton
P1H=2 ton
x1
d Mxd x
d Mx
M a ximum M omen
x xq Mx
parabola xq x x Mx
Dke Adari
M omen P ersamaan
0
4.11.12
1
)(.12
1.13)2(2
1
1
1
1
2
11
2
1111
!
!
!
p
tm M xutk
M xutk linier x x P Mx
AkeC dari
M omen P ersamaan
kiri A
C
V
42.22
00)(2
.1
!!p!
!p!
!!
p
111 !
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m x xqd x
d Mx
d x
d Mx
M a ximum M omen
5.5011.1
0
..2
11
1
1
1
1
111
!p!!
!
!
Letak dimana harga M ma x = Letak dimana harga ( D=0)
tmq M
m x 2
5.26
4)5.5.
(11
)5.5.
(1
2
1max5.5
2
1 !!p!
M encari titik dimana M =0
)(62.10
3756.0
04.11
04.11).2(2
1
04.11.12
1
'
1
1
1
2
11
1
2
11
1
2
11
mungkintidak m x
m x
x x Mx
x x Mx
x xq Mx
!
!
!!
!!
!!
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tm M xutk
M xutk
kanandaridihitung
parabola xq Mx
B E
tm M m x
B
E
D
24.1.2
12
00
)(.221
26466366
2
2
2
22
1
!!p!
!p!
!
p
!!p!
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Contoh Soal
Given: The loading on the beam as
shown.Find: Support reactions at A and B.
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Contoh Soal 4 (jawaban)
SOLUTION:
Taking entire beam as a free-body,
determine reactions at supports.
§ ! :0 A M
0m.48kN45
m.24kN45m.81kN90m.27
!
D
kN117! D
:0§ ! y F
0kN54kN117kN54kN90 ! y A
kN81! y A
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TUTORIAL QUESTION: DRAW THE SHEAR FORCE AND BENDING MOMENT DIAGRAMS
FOR THE FOLLWING BEAM. ALSO STATE THE MAXIMUM BENDING MOMENT AND
HOW FAR AWAY IS IT FROM THE LEFT HAND END OF THE BEAM.
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TUTORIAL QUESTION: DRAW THE SHEAR FORCE AND BENDING MOMENT DIAGRAMS
FOR THE FOLLWING BEAM.
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TUTORIAL QUESTION: DRAW THE SHEAR FORCE AND BENDING MOMENT DIAGRAMS
FOR THE FOLLWING BEAM.
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Contoh Soal 5
Tentukan Reaksi di A dan B
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Soal Tantangan
Given: The loading on the beam as shown.
Find: Reaction at B and A
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Tentukan Reaksi di A dan C
Soal Tantangan (2)
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