II. D IA GR AM TEG A NGA N -RE G ANG AN BAJA TULANGAN
1 1 . 1. U M U M
Dia.gr am t e g ang an - r eg ang an b a j a t u l a n g a n p a d a u m u m n y a d a p at dibedakati atas d u a b a g i an :
!. D i a g r a m t e g a n g a n - r e g a n g a n u n t u k b a j a l u n a k (mild steel). D i a g r a m dari. b a j a ini m e m p u n y a i " Y iel d P l a t e a u " y a n g panjang, s e h i n g g a b a j a t e r s e b u t m e m p u n y a i d u k t i l i t a s y a n g bes a r .
2. D i a g r a m t e g a n g a n - r e g a n g a n u n t u k b a j a k e r a s (mutu tinggi). D i a g r a m d a r i b a j a ini m e m p u n y a i "Yi eld P l a t e a u " ya n g pondok, s e h i n g g a b a j a t e r s e b u t m e m i l i k i d u k t i l i t a s y a n g keeiJ.. T y p e b a j a s e m a c a m ini s a n g a t t i n g g i t i t i k lelehnya, t e t a p i s e g e r a s e t e l a h m e n c a p a i t i t i k l e l e h n y a b a j a t e r s e b u t a k a n c e p a t p ut us d e n g a n m e m b e r i k a n s e d i k i t u l u r a n .
1 1. 2. DI AG RA M TEG A NGA N -RE G ANG AN MO NOTON
D i a g r a m t e g a n g a n - r e g a n g a n b a j a t u l a n g a n y a n g d i g u n a k a n dal am k o n s t r u k s i b e t o n b e r t u l a n g d i p e r o l e h d a r i h a s i l t e s t tarikan m o n o t o n ( s e l a n j u t n y a d i a g r a m n y a d i s e b u t d i a g r a m
9
t e g a n g a n - r e g a n g a n monoton). S e p e r t i y a n g d i t u n j u k k a n p a d a gaiobar 2. J.. , c u r v a awal sarnpai t i t i k leleh A menunjukkatj d a e r a b e l a s t i s linear. s e t e l a h m e n c a p a i t i t i k l e l e h A m a k a ak an t e r j a d i p e r t a m b a h a n r e g a n g a n d e n g a n s e d i k i t a t a u t a n p a a d a n y a p e r t a m b a h a n t e g a n g a n , s a m p a i p a d a t i t i k B. K e m u d i a n ba.ja t u l a n g a n m e m a s u k i d a e r a h s t r a i n - h a r d e n i n g , d i m a n a p e r t a m b a h a n r e g a n g a n d i i k u t i o l e h p e r t a m b a h a n t e g a n g a n y a n g c u k u p b e s a r . h a l ini t e r u s b e r l a n g s u n g s a m p a i m e n c a p a i t e g a n g a n m a x i m u m p a d a t i t i k C. M e l e w a t i t i t i k C, p e r t a m b a h a n r e g a n g a n a k a n m e n y e b a b k a n t e g a n g a n n y a t u r u n s e c a r a d r a s t i s s a m p a i p u t u s di t i t i k D. K e m i r i n g a n k u r v a p a d a d a e r a h e l a s t i s l i n e a r m a n y a t a k a n M o d u l u s e l a s t i s i t a s , E s . U n t u k d a e r a h s t r a i n - h a r d e n i n g , S t r a i n - H a r d e n i n g modulus, Esh, d i n y a t a k a n d e n g a n g a r i s s i n g g u n g d a r i awal g a r i s l e n g k u n g t ersebut. B i a s a n y a p e n e n t u a n n i l a i E s h c u k u p s u l i t k a r e n a p e n e n t u a n g a r i s s i n g g u n g n y a t i d a k d a p a t d i l a k u k a n s e c a r a tepat. T e g a n g a n p a d a t i t i k A rnenunjukkan t e g a n g a n l e l e h n y a d a n m e r u p a k a n s u a t u p a r a m e t e r y a n g s a n g a t p e n t i n g d a r i b a j a tulangan. K a d a n g - k a d a n g c u r v a t e g a n g a n - r e g a n g a n m e n u n j u k k a n d e n g a n jelas t e g a n g a n le leh atas ( u p pe r y i e l d str e n g t h ) d a n t e g a n g a n leleh b a w a h (l ow e r y i e l d s t r e n g t h ) s e p e r t i y a n g d i t u n j u k k a n p a d a g a m b a r 2.2. B e s a r r e l a t i f t i t i k leleh atas b e r g o n t u n g p a d a k e c e p a t a n p e n g e tesa n, b e n t u k p e n am pa ng , d a n k e a d a a n d a r i c o n t o h b a j a tulangan. T i t i k leleh b a w a h b i a s a n y a d i n g g a p s e b a g a i p a r a m e t e r k a r a k t e r i s t i k y a n g b e n a r d a n d i p a k a i u n t u k m e n e n t u k a n t e g a n g a n leleh b a j a tulangan.
Pan,]ang y i e l d p l a t e a u (A-B p a d a g a m b a r 2.1) s e c a r a u m u m irierupakxin s u a t u f u n g s i d a r i t e g a n g a n baja. B a j a H i g h - s t r e n g t h H i g h - C a r b o n b i a s a n y a m e m p u n y a i y i e l d p l a t e a u y a n g jaub lobih p e n d e k d a n total, r e g a n g a n y a n g l ebih k e c i l s e b e l u m p u t us j ik a d i b a n d i n g k a n d e n g a n b a j a L o w e r - S t r e n g t h Low--Carbon. U n t u k b a j a C o l d - Worked , d a e r a h s t r a i n - h a r d e n i n g d a p a t m u l a i d e n g a n s e g e r a s e t e l a h t e r j a d i l eleh y a n g p e r t a m a d a n s e r i n g t i t i k l e l e h n y a t i d a k b e g i t u jelas. D a l a m hal ini m a k a t e g a n g a n l e l e h n y a d i t e n t u k a n s e p e r t i y a n g d i t e t a p k a n d a I a m s t, and a r t . B a j a h a r u s c u k u p d u c t i l e u n t u k m e n g i m b a n g i r e g a n g a n p l a s t i s y a n g b e s a r s e b e l u m putus. Ha l ini s a n g a t d i p e r l u k a n u n t u k m a n j a w i n kearnanan d a r i struktur. S p e s i f i k a s i d a r i b a j a p a d a u m u m n y a h a n y a m e n e t a p k a n p e r p a n j a n g a n y a n g d i p e r l u k a n p a d a s a a t putus. D i a g r a m - d i a g r a m t e g a n g a n - r e g a n g a n y a n g d i p e r o l e h da r i h a s i l t e s t t a r i k a n d a p a t d i a s u m s i k a n c u k u p b a i k u n t u k rnev/akili d i a g r a m - d i a g r a m t e g a n g a n - r e g a n g a n u n t u k b a j a t u l a n g a n a k i b a t t e k a n a n . D a r i h a s i l - h a s i l p e r c o b a a n y a n g tel ah d i l a k u k a n ol e h b e b e r a p a p e n e l i t i m e n u n j u k k a n bahv/a asumsi t e r s e b u t d i a t a s c u k u p l a ya k d a n d a p a t diterima. G a m b a r 2.1
11
t u l a n g a n y a n g d i g u n a k a n d a l a m k o n s t r u k s i b e t o n bertulang.
Gainbar 2.2. D i a g r a m t e g a n g a n - r e g a n g a n b a j a t u l a n g a n y a n g m e n u n j u k k a n a d a n y a t i t i k le leh atas d a n b a w a h
1!.3. ANALISA DI AG RAM TEG A NGAN -RE GANGA N MONOTON
Da .lam p e r e n c a n a a n t e r h a d a p gempa, k i t a p e r l u m e n g e v a l u a s i t e g a n g a n b a j a p a d a r e g a n g a n - r e g a n g a n y a n g jauh m e l e b i h i t i t i k lelehnya, agar lebih a k u r a t d a l a m m e n e n t u k a n t e g a n g a n l e nt u r s u a t u ba.gi.an k o n s t r u k s i p a d a k e m u n g k i n a n d e f o r m a s i y a n g b e s a r s e l a m a t e r j a d i g e m p a kuat. P a r a p e n e l i t i s e b e l u m n y a t e l a h m e n e n t u k a n b e b e r a p a i d e a l i s a s i d a r i d i a g r a m t e g a n g a n - r e g a n g a n monoton. S e t e l a h m e n g e v a l u a s i i d e a l i s a s i - i d e a l i s a s i t e r s e b u t d e n g a n inembandi n g k a n h a s i l - h a s i l p e r c o b a a n t a r i k a n d a n tekanan, o l e h " M a n d e r , d k k " d i a n j u r k a n s u a t u p e r u m u s a n a l t e r n a t i f ?/ang a ka n d i p a k a i d a l a m s t u d y ini. D i a g r a m t e g a n g a n - r e g a n g a n y a n g d i a n j u r k a n oleh Mander, d k k menffandung e n a m p a r a m e t e r d a s a r yaitu: fy , fsu , Esh , Jilfi , & s h , B s u .
K e e n a m p a r a m e t e r t e r s e b u t d i p a k a i u n t u k m e m b e n t u k c u r v a t e g a n g a n - r e g a n g a n m o n o t o n s ep e r t i y a n g d i t u n j u k k a n p a d a g a m b a r 2.3.
Curva diagram tegangan-regangan tersebut dapat d i. j e .1 o i jkan s b b : n) O n e r a h E last is ( 0 < < £,y ) fy ~ Et Et ~ Es (2.1) (2.2) Diinana: B y = f s / E Et a d a 1ah t a n g e n t m o d u l u s Es a d a l a h m o d u l u s e l a s t i s i t a s
b) Daerah Yield Plateau ( £,y < £ s < £>sh )
fs • = fy (2.3)
0. 0 (2.4)
e) D a e r a h s t r a i n - h a r d e n i n g ( B s h < < S s u )
D a e r a h s t r a i n - h a r d e n i n g m ulai p a d a s a a t t e g a n g a n n y a m e l e v m t i te g a n g a n l e leh (pada r e g a n g a n Esh) s am p a i p a d a
r eg an g an u 11 i m a t e (£,su).
R e g a n g a n u l t i m a t e a d a l a h r e g a n g a n p a d a s a a t t e r j a d i t e g a n g a n u l t i m a t e (f s u ) , b u k a n r e g a n g a n p a d a s aa t p u t u s y a n g
terjadi p a d a t e g a n g a n y a n g lebih keeil.
M a n d e r . d k k b e r p e n d a p a t b a h w a m o d u l u s s t r a i n h a r d e n i n g a d a l a h s u a t u p a r a m e t e r y a n g h a n y a d i p e r l u k a n u n t u k m e n e t a p k a n c u r v a s t r a i n - h a r d e n i n g d i s a m p i n g k o o r d i n a t awal
(Gsh, fy) d a n k o o r d i n a t aklrir (£,su,fsu).
A d a d u a c a r a p e n d e k a t a n y a n g d i p a k a i u n t u k m e n e t a p k a n c u r v a s t r a i n - h a r d e n i n g yaitu:
j.. C a r a y a n g d i p a k a i o l e h " P o p o v ”.
C u r v a t e g a n g a n - r e g a n g a n d a p a t d i c a r i d e n g a n m e n g g u n a k a n fungs i. i n t e r p o l a s i p o l y n o m i a l m e l a l u i s e j u m l a h t i t i k k o n t r o l
y a n g d i t e n t u k a n .
P e n d e k a t a n ini m e m e r l u k a n s e j u m l a h k o o r d i n a t d a r i c u r v a d i a g r a m t e g a n g a n - r e g a n g a n t a r i k a n d a n t e k a n a n p a d a c u r v a strain-hardening', d a n h a r u s d i p e r o l e h d a r i pe rpobaan.
X. C a r a y a n g d i a n j u r k a n o l e h "Burns a n d Seiss", y a n g k e m u d i o n d i p e r b a h a r u i o l e h "Kent d a n Park", d a n juga d i p a k a i o l e h "Lislei", yaitu: M e n g g u n a k a n s u a t u p e r s a m a a n g a r i s a n t a r a r e g a n g a n s t r a i n - h a r d e n i n g , sh d a n r e g a n g a n ultimate, Esu . O l e h M a n d e r , d k k d i p a k a i c a r a y a n g ke 2. d a n c a r a ini p u l a y a n g d i p a k a i d a l a m s t u d y ini. D e n g a n k o o r d i n a t awal (fcsh.fy) d a n k o o r d i n a t a k h i r (Gsu.fsu) d a r i c u r v a s t r a i n - h a r d e n i n g , k i t a d a p a t m e n e n t u k a n m o d u l u s s t r a i n - h a r d e n i n g , Bsh. P e r s a m a a n d a r i k e d u a t i t i k k o o r d i n a t t e r s e b u t b e r b e n t u k s u a t u "power c u rv e " d e n g a n kooi'dinat t e g a n g a n - r e g a n g a n u l t i m a t e s e b a g a i k o o r d i n a t awalnya. d a n d a p a t d i t u l i s sbb: P (2.5) " fsu -- fs ■ £,sU - £s fsu -- fy &su - 6sh T e g a n g a n y a n g t e r j a d i a d a l a h :
fa = fsu + (fy - fsu)
& s u - £s £ s u - £ s h (2.6) Dirnana: p a d a l a h s t r a i n - h a r d e n i n g p o w e r d a n d a p a t d i t e n t u k a n d e n g a n m e n d i f e r e n s i a l p e r s . ( 2 . 6 ) u n t u k m e m b e r i k a n t a n g e n t m o d u l u s :
15 d f s El; d = P fsu fy £su - £s &su - £ s h P-l (2.7) &su - &sh k a r e n a m o d u l u s s t r a i n - h a r d e n i n g (&sh) t e r j a d i p a d a s a at £s - c-sh maka: Et psh = p fsu - fy Bsu - £ s h (2.8) ata u P Esh g s u - $ s h (2.8) fsu - fy Persainaan (2.9) m e n y a t a k a n b a h w a p a d a l a h p e r b a n d i n g a n a n t a r a s t r a i n - h a r d e n i n g m o d u l u s (Esh) d e n g a n s e c a n t m o d u l u s d i a n t a r a k e d u a t i t i k k o o r d i n a t tersebut. R e g a n g a n y a n g t e r j a d i d a p a t d i n y a t a k a n sbb: 1/P 6 s £ s u + (&sh - gsu) fsu fs (2.9) fsu ■- fy Dari p e r s a m a a n (2. 5 ),(2.8) d a n (2.9) d i d a p a t s u a t u n il ai t a n g e n t m o d u l u s e l a s t i s i t a s d a r i d a e r a h s t r a i n - h a r d e n i n g , y a i t u : 1-1/p Et Esh fsu -- f £ (2.1 0) fsu - fy B e n t u k d i a g r a m t e g a n g a n - r e g a n g a n s e p e r t i ini y a n g d i g u n a k a n d a l a m a n a l i s a m o m e n t - c u r v a t u r e p e n a m p a n g - p e n a m p a n g b e t o n b e r t u l a n g u n t u k rnendapatkan n i l a i f a k t o r o v e r s t r e n g t h lent ur d i d a l a m s t u d y ini.
Ji 4. D IAG R AM TE GA NG A N-R E GAN G AN PEMBEB ANA N BE RUL ANG Yang dirnaksud d e n g a n p e m b e b a n a n b e r u l a n g d i s i n i a d a l a h b e ban t a r i k atau t e k a n s a j a y a n g d i k e r j a k a n p a d a c o n t o h b a j a t ul an ga n , kernudian b e b a n t e r s e b u t d i l e p a s k a n d a n d i b e b a n i lagi, d e m i k i a n s e te r usnya. D a l a m p r a k t e k b i a s a n y a s u a t u k o n s t r u k s i b e t o n b e r t u l a n g aka n d i b e b a n i s e c a r a b e r u l a n g - u l a n g s e l a m a u m u r b a n g u n a n tersebut. J i k a b eban p a d a s u a t u c o n t o h b a j a d i l e p a s k a n s e b e l u m p u t u s m a k a c u r v a a ka n t u r u n p a d a p a n j a n g b a g i a n r e g a n g a n d an s e j a j a r d e n g a n g a r i s elastis. J i k a d i b e b a n i lagi m a k a c u r v a akan n a i k k e m b a l i k e c u r v a asalnya. L i h a t ga.mbar 2 . 4 : J i k a b e b a n k e c i l m a k a c u r v a m a s i h d a l a m d a e r a h e l a s t i s d a n d i t u n j u k k a n o l e h g a r i s e l a s t i s OA. J i k a b e b a n t e r u s d i p e r b e s a r m a k a p a d a s u a t u s a a t ak an t erjadi p e l e l e b a n p a d a b a j a tulangan, d a n p a d a s a a t m e n c a p a i leleh m a k a t i t i k t e r s e b u t a d a l a h t i t i k leleh (titik A ) . Hal ini a k a n m e n y e b a b k a n b a j a t u l a n g a n m e n g a l a m i p e r t a m b a h a n p a n j a n g t a n p a a d a n y a p e r t a m b a h a n t e g a n g a n (beban) s am p a i b e r a k h i r pada. t i t i k D (da e ra h Y i e l d Plateau). S e t e l a h itu p e r t a m b a h a n beban akan m e n y e b a b k a n c u r v a t e g a n g a n - r e g a n g a n rnemasuki d a e r a h s t r a i n - h a r d e n i n g ( g a r i s D - E ). J i k a s e b e l u m m e n c a p a i t i t i k D,rnisal p a d a t i t i k C, b e b a n d i l e p a s k a n m a k a c u r v a a k a n t u r u n di t i t i k B d e n g a n m e m b e n t u k g a r i s y a n g s e j a j a r d e n g a n g a r i s e l a s t i s O A ( B C // O A ) d a n j i k a d i b e b a n i lagi d e n g a n b e b a n y a n g s a m a m a k a c u r v a akan n a i k k e m b a l i ke c u r v a asa.1 di t i t i k C m e n g i k u t i g a r i s B C
17 d e n g a n k e m u n g k i n a n ad a n y a sedik.it p e n y i m p a n g a n s e b a g a i a k i b a t d a r i " S t r a i n - h a r d e n i n g E f f e c t ”. Ha l y a n g s a m a b e r l a k u p u l a untuk. p e l e p a s a n b e b a n d a n p e m b e b a n a n k e m b a l i d e n g a n b o ban y a n g s a m a p a d a d a e r a h s t r a i n - h a r d e n i n g s e p e r t i y a n g ditun.juk.kan. o l e h g a r i s FG ( FG // O A ). Sesua i d e n g a n k e a d a a n d i a g r a m t e g a n g a n - r e g a n g a n b a j a t u l a n g a n p a d a g a m b a r 2.4 m a k a d i a g r a m t e g a n g a n - r e g a n g a n m o n o t o n m e m b e r i k a n s u a t u i d e a l i s a s i y a n g baik. s e b a g a i c u r v a s e l u b u n g d a r i d i a g r a m t e g a n g a n - r e g a n g a n p e m b e b a n a n berulang. Gainbar 2.4. D i a g r a m t e g a n g a n - r e g a n g a n p e m b e b a n a n berulang.
11.5. D1AGKAM T E G A N GA N -RE G ANG AN P E M B E B A N A N BOL A K - B A L I K
J i k a s u a t u s t r u k t u r m e n e r i m a b e b a n g e m p a k u a t m a k a s t r u k t u r t e r s e b u t mengalarni p e m b e b a n a n b o l a k - b a l i k y a n g d a p a t m e n y e b a b k a n t e g a n g a n n y a b e r a d a d a l a m d a e r a h p o s t - e l a s t i s .
( a ) Wi t h Un s y n v n e t r i c a l S t r a i n C y c l e s
( b ) Wi t h S y m m e t r i c a l S t r a i n C y c l e s
G a m b a r 2,5. D i a g r a m t e g a n g a n - r e g a n g a n b a j a t u l a n g a n a k i b a t p e m b e b a n a n bo l a k - b a l i k .
19 A k i b a t p e m b e b a n a n b o l a k -balik, d i a g r a m t e g a n g a n - r e g a n g a n b a j a t u l a n g a n n y a a m a t b e r b e d a d e n g a n a k i b a t p e m b e b a n a n t a r i k atau t e k a n saja, s e p e r t i y a n g d i t u n j u k k a n p a d a g a m b a r 2.5. J i k a b a j a t u l a n g a n m a s i h b e r a d a d a l a m k e a d a a n e l a s t i s a k i b a t b e b a n tarik, m a k a p e r t a m b a h a n p a n j a n g y a n g d i a l a m i baja t u l a n g a n a k a n s e b a n d i n g d e n g a n p e r t a m b a h a n b e b a n n y a . J i k a b e b a n t a r i k d i l e p a s k a n m a k a c u r v a a k a n t u r u n d a n s e j a j a r d e n g a n g a r i s elastisnya, d a n k e m u d i a n d i b e r i k a n b e ba n y a n g b e r l a w a n a n (tekan) m a k a c u r v a t e g a n g a n - r e g a n g a n n y a y a n g t e r j a d i t i d a k lagi l i n e a r , t e ta pi b e r u p a g a r i s l e n g k u n g p a d a t e g a n g a n y a n g jauh lebih k e c i l dari t e g a n g a n leleh. T e r j a d i n y a c u r v a y a n g d e m i k i a n ini d i s e b u t d e n g a n " B a u s c h i n g e r effect". p r i l a k u c u r v a y a n g d e m i k i a n d i p e n g a r u h i o l eh " s t r ai n history", w a k t u p e m b e b a n a n d a n t e m p e r a t u r . U n t u k m e n y e d e r h a n a k a n d i a g r a m t e g a n g a n - r e g a n g a n b a j a t u la n g a n a k i b a t p e m b e b a n a n b o l a k - b a l i k y a n g c u k u p rumit, oleh p a r a ahli s e r i n g d i g u n a k a n s u a t u p e n d e k a t a n yaitu: " E l a s t i c - p e r f e c t l y p l a s t i c i d e a l i z a t i o n " s e p e r t i y a n g d i t u j u k k a n p a d a g a m b a r 2.6 (a) d a n 2.6 (b). A d a d u a jenis d i a g r a m t e g a n g a n - r e g a n g a n b a j a t u l a n g a n a k i b a t p e m b e b a n a n b o l a k - b a l i k y a n g d i t i n j a u d a r i m a y o r i t a s jenis p e m b e b a n a n n y a . Y a n g p e r t a m a j i k a s a l a h s a t u jenis p e m b e b a n a n n y a lebih b e s a r da ri p a d a jenis p e m b e b a n a n y a n g lain, s e p e r t i y a n g d i t u n j u k k a n p a d a g a m b a r 2.5 (a), d i m a n a p e m b e b a n a n t a r i k lebih b e s a r dari p e m b e b a n a n t e k a n ,s e h i n g g a s e b a g i a n b e s a r c u r v a d i a g r a m t e g a n g a n - r e g a n g a n b a j a t u l a n g a n b e r a d a p a d a sisi r e g a n g a n tarik. Y a n g k e d u a a d a l a h
p e m b e b a n a n t a r i k d a n t e k a n s a m a b e s a r n y a s e h i n g g a c u r v a d i a g r a m t e g a n g a n - r e g a n g a n b a j a t u l a n g a n t e r l e t a k s i m e t r i t e r h a d a p k e d u a sisi regangannya, s e p e r t i y a n g d i t u n j u k k a n p a d a g a m b a r 2.5 (b). B e r d a s a r k a n p a d a h a s i l - h a s i l e x p e r i m e n d i a g r a m t e g a n g a n - r e g a n g a n , o l eh "Kato,dk.k" d i t u n j u k k a n b a h w a d i a g r a m t e g a n g a n - r e g a n g a n m o n o t o n a k i b a t t a r i k a n d a n t e k a n a n m e m b e r i k a n s u a tu i d e a l i s a s i y a n g b a i k u n t u k d i a g r a m t e g a n g a n - r e g a n g a n a k i b a t p e m b e b a n a n bolak- ba li k. U n t u k le bih j e l a s n y a d a p a t d i l i h a t p a d a g a m b a r 2.7 (a),(b) d a n (c). (tnnr.icm) G a m b a r 2.6 (a) " B a u s c h i n g e r e f f ec t" d a r i b a j a t u l a n g a n a k i b a t b e b a n b o l a k - ba li k.
21
(te n sio n )
G a m b a r 2.6 (b) " E l a s t i c - p e r f e c t l y p l a s t i c i d e a l i s a t i o n " u n t u k b a j a t u l a n g a n a k i b a t b e b a n b o l a k - balik.
C o m o r Sues*, f\ S lr . n ii <\ (,>) (first locuhn;)) U n ln .u h m j |>e ,m<;h |lm i:;jr } S o l l c n c d t»r;m th " (Bouschinger c U e c i) S x • a < n ( b ) i>lr«ss. f\ Sttom i . G a m b a r 2.7 D i a g r a m t e g a n g a n - r e g a n g a n b a j a a k i b a t b e b a n b e r u l a n g ( R e v e r s e d loading)
23
II. 6. P EN GARUH K EC EP A T A N P E M B E B A N A N PADA PA HAME T E B - P A R A M E T E R DIA G RAM TEGANG AN- REGAN GAN
D i d a l a m a n a l i s a m o m e n t - c u r v a t u r e u n t u k m e n d a p a t k a n f a k t o r o v e r s t r e n g t h , p e r l u d i p e r t i m b a n g k a n p e n g a r u h k e c e p a t a n p e m b e b a n a n karena, s e p e r t i y a n g d i t u n j u k k a n s ebe l umnya, p n e m b e b a n a n y a n g c e p a t a k a n m e n y e b a b k a n b e r t a m b a h b e s a r n y a t e g a n g a n leleh b a j a tulangan. K e c e p a t a n p e m b e b a n a n akan ineiripengaruhi k e c e p a t a n r e g a n g a n y a n g t e r j a d i p a d a b a j a t u l a n g a n d a n beton. k e c e p a t a n p e m b e b a n a n u n t u k k e a d a a n Q u a s i - s t a t i c p a d a u m u m n y a d i a m b i l s e b e s a r 0. 00 00 1/ se c. P e n g g u n a a n b e s a r n y a t e g a n g a n l el e h y a n g d i u k u r p a d a k e c e p a t a n r e g a n g a n y a n g t i n g g i ak a n m e n y e b a b k a n o v e r e s t i m a t e p a d a t e g a n g a n l e n t u r d a r i s t r u k t u r - s t r u k t u r p e n a h a n gempa.. t e t a p i k a r e n a b e b a n g e m p a b e r s i f a t d y n a m i s m a k a hal ini d i a n g g a p c o c o k u n t u k m e n d a p a t k a n k e m u n g k i n a n f a k to r o v e r s t r e n g t h y a n g m u n g k i n t e r j a d i s e l a m a g e m p a kuat. O l e h M a m n d e r , d k k d i t u n j u k k a n b a h w a p e n g a r u h k e c e p a t a n r e g a n g a n y a n g t i n g g i p a d a t e g a n g a n l e leh d a p a t d i p e r h i t u n g k a n d e n g a n m e m o d i f i k a s i h a r g a d a r i k e a d a a n q u a s i - s t a t i c d e n g a n m e n g g u n a k a n f a k t o r p e m b e s a r d y n a m i s sbb: ( fs )dyn = Ds fs (2.11) Dimana: ( f s ) d y n a d a l a h t e g a n g a n leleh y a n g d i u k u r p a d a k e c e p a t a n r e g a n g a n y a n g tinggi. fs a d a l a h t e g a n g a n l e l e h y a n g d i u k u r p a d a k e a d a a n q u a s i - s ta ti c. Ds a d a l a h f a k t o r p e m b e s a r dynamis, y a n g u n t u k b a j a r i n g a n d i t e n t u k a n sbb :
* U n t u k b a j a y a n g m e n g a l a m i t a r i k a n : 1 / 6 Ds = 0 . 9 5 3 [ 1 + ( 8 / 7 0 0 ) ] (2.12) * U n t u k b a j a y a n g m e n g a l a m i t e k a n a n : 1/6 Ds = 0 . 9 66 [ 1 + ( 8 / 5 0 0 ) ] (2.13) Dirnana: 6 a d a l a h k e c e p a t a n r e g a n g a n u n t u k k e a d a a n q u a s i - s t a t i c y a n g diasurnsikan s e b e s a r = 0 . 00001/sec. D e m i k i a n p u l a u n t u k t e g a n g a n ultimate, fsu , m o d u l u s e l a s t i si t a s, Es , M o d u l u s s t r a i n - h a r d e n i n g , Esh, d i p e r h i t u n g k a n p e n g a r u h k e c e p a t a n r e g a n g a n y a n g t i n g g i d e n g a n m e m o d i f i k a s i h a r g a d a r i k e a d a a n q u a s i - s t a t i c d e n g a n m e n g g u n a k a n f a k t o r p e m b e s a r d y n a m i s s e p e r t i u n t u k t e g a n g a n leleh, fy . S e d a n g k a n u n t u k r e g a n g a n p a d a s a a t t e r j a d i n y a s t r a i n - h a r d e n i n g , B s h d a n r e g a n g a n ulti m ate , 8 s u , o l e h H a n d or, dick d i a n g g a p t i d a k d i p e n g a r u h i ol eh k e c e p a t a n pe m b eb a n an .
Unl.uk te g a n g a n leleh t u l a n g a n s e n g k a n g , fyh , juga d i p e r h i t u n g k a n p e n g a r u h k e c e p a t a n p e m b e b a n a n s e p e r t i u n t u k t e g a n g a n leleh, fy.
