曲げとせん断を受ける鉄筋コンクリート梁の塑性変形性能における寸法効果

(1)

愛知工業大学研究報告

第25号B 平成2年 173

S

i

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e

E

f

e

c

t

on P

l

a

s

t

i

c

Deformatio:

n

Capacity o

f

Reindorced Concrete Beams under Shear and Frexu:

r

e

Sachio

KOIKE

and Shigemitu

HATANAKA

*

曲げとせん断を受ける鉄筋コンクリート梁の

塑性変形性能における寸法効果

小池狭千朗

e

畑中重光本

A series of bending tests of reinforced concrete (RC) beams of various sizes and uniaxial compression tests of confin巴dconcretes used in the compressive zones of theRC

beams were carried out to巴xaminetheir plastic d巴formationalbehavior.Based on the

t巴stresults， the effect of th巴sizeof sp巳cimenson the deformation behavior ofRC baems

and confined concretes were discussed. It was found that both the stress-strain behavior of confined concrete and the moment-curvature behavior of RC beams become more brittle with increasing size of specimen r巴gardlessof the spacing of stirrups

1.INTRODUCTION

For the applica七ion of p工在日七ic d巴sign m七hod七o reinforced concrete(RC) fram巴s

，

i t i s七he first requisi七e 七hat consti七u七iv巴RC memb巴rs are ductil巴日nough forもhe redistribu七ion of momen七 and for the forma七工on of plas七ic collapse mechanism. To discuss analytically the deformational capac工七Y of RC members

，

七he effects of various parame七ers should be fu工ly examined wi七h respec七七o 七he charac七eristics of a p

ユ

astic h工nge of RC

members.

The authors have already examined七he curva七ur巴distribu七ion charac七日ris七ics of RC beams and found七ha七七he in巴rease in duc七ility in the failure zone of an RC member also acc巴lera七日日七he ex七巴nsion of

七he fai工ure zone

，

and as a result

，

the plas七ic deforma七ional capa巴工七y of 七h巴

建築学科

who

ユ

e RC memb巴r incr巴ases [1

，

2]. The siz巴

of sp巴cimens七es七ed was

，

however

，

mu口h

smaller (section of RC beam: 9.7x19.4 cm)

七han七he sユze of ac七ualRC beams.

Th巴 purpose of 七he pres巴nt s七udy工日

七0 巴xamine，七he巴ffect of七he specimen siz巴

on七he plas七ic deforma七ional capacity of RC beams under fle主ure and shear

，

and on

七he duc七ili七y of confined concre七日s und巴r compress工on.

2.EXPERIMENTAL PROCEDURES 2.1 Outlinr of experim巴nt

The follow工ng 七wo series of

experlmen七日 were carried ou七.

(1 )RC beams

Ou七lin巴of七h巴experimen七ofRC beams is shown工n Table 1. Testing variables

(2)

174 小池狭千朗。畑中重光

lSi b:wid七h of specirnen

，

h: dep七h of specirnen

，

ls: 1ength of shear span of sp巴巴お日n). spacing of 百七工rrups(S)

，

and

七日nsi1e re工ぱorcernent ra七io(P七).Diarne七日rs of s七irrups were se1ected for the 1atera1 reinforcernent ratio 七o b巴 approxirnate1y

0.3 % for 七h巴 specirnen wi七h s七工rrups of S=b. The nurnber of bearn specirnens was 18 for P七=1.4%

，

39 for P七=2.1%

，

乱

nd 18 for Pt=2.8%i 七h旦七 is

，

七he tota1 nurnb巴r was 75.

Figure 1 shows exarnp1es of もhe

d巴七a工1ing of reinforcernen七 of RC be旦rns. Addi七工ona1 10ngi七udina1 and web re工ぱorci時 bars (web reinforcernent ra七io was 1arger七han 1.2%) were arrang巴d in one

side of the bearns

，

as shown in七he figure. Hereinaf七巴r

，

七he righ七 hand side of 七he bearn日ユn Fig.1 工日 referred to as 11七es七ed

span" and 七he 0七h巴r side "non一七es七ed span".

Tab1e 1 Ou七1ine of experirnen七of RC bearn Size of be祖 (h=2b) ※1 ※2 S Pt Section Rε.bar Stir(r闘tIP) is bXh (c風) (百) 7. 3x14. 6 DlO φ3圃2 b/4 4h 1.4 9. 7x19. 4 D13 φ3圃9 12. 5X25. 0 D16 φ4.9 6h b/2 2.1 15. OX30. 0 D19 φ5.7 段l b 2.8 20. OX40. 0 D25 φ8.0 [NoteJ※1 : Dia!l詑terof longitudinal reinforcingbar ※2: Dia畠eterof stirrup，

i

s : Le昭thof shear sp削 ( 日 )Concre七e prisrns

Ou七1ine of the experirnen七of concret巴

prisrns is shown工n Tab1e 2. The wid七h(b) of七he secもion of prisrns and七he arrangernen七 of 1atera工 reinforcernen七 was designed 七o be 巴onsi日七日n七 wi th the cornpress工ve zones of RC bearns. The

heigh七(H) of prisrns was chosen七o b日七hr巴e t工I四日七he wid七h(b) of七he section. The nurnber of specirnens prepared for each factor was 12

，

and the七o七a1 nurnber was 240.

2.2 Fabrica七ion and口uring of specirn日ns

Ordinary Port1and cern巴n七， river sand

(<5 rnrn)

，

and ri ver grave1 (5 ru 25 rnrn) were used for七he fabr工ca七ion of concre七e. Water-cernen七ra七io of 55% was chosen

，

and slump was 15 cm. The m巴巴hanica1 proper七工es

臨冊期間相柵藤村令官許可萌日ユz b~ 7.3cm Series ~τt

E

両市噌町市田口

F

b~ 9.7cm Series L-

ττ-VH

t

L

言

r

1 lTTTTTfTTT日司

自子

医三三割111 b ~ 1 5.0c m S e r i e s ! l ! u 6 h 11 b φ1/4 inch boltー"'-- J，..." ... 九

o

8 r2一世2.3

町一一司自}

S : Spacing of Stirrup. Pt: Percent品geof longi- b~20.0cm Series 一_j l_J 1 1 b t日dinalreinforcingbar

b胃idthof be翻， h : Height of beam Fig. 1 Detailing of reinforcem巴nt (ls=6h)

Tab1e 2 Out1ine of巴xperiment of

concr巴七e prism Size of pris圏 Hoop Section _E_E₌_E₃_b_i_g_b₍_t_E_E₎ Di趨eter SNS ciEZ bXb (c圃) φ (瞳) 7.3X 7.3 21. 9 3.2 9.7X 9.7 29.1 3.9 b/4 12.5X12.5 37.5 4.ヲ b/2 15.0X15.

。

45.0 5.7

_。

b

_。

20. OX20. 0

品

。

&

Tab1e 3 Mechanica1 properties of 10ngユ七udina1 bar Dia畠邑t阜r Yield strengせl 地xi瞳幽stre時世l Elongation {圏)

t

国

f

!

clln (旬f/ca2) (耳) D10 3912 5589 26固5 D13 3644 5325 27.3 D16 36

品

2 5387 24.1 D19 3822 5793 24.1 D25 3640 5714 24.8

(3)

曲げとせん断を受ける鉄筋コγクリト梁の塑性変形性能における寸法効果

of longitudinal and la七eral r巴inforcing

bars us巴d are shown in Table 3 and Table

4

，

respect工vely. Concr巴te was cast

horizon七ally for all 七he specimens

，

and cured in a room un七ュ工 the tests. Tests

W巴re carried ou七a七七he age of 6 we巴ks・ 2.3 Me七hods of loading and measuremen七

(1) RC beams

T h e m e七hods of loading and rneasuremen七日 of curvature and d巴flec七ion

175 of specimens are illustra七ed in Fig.2. Concen七T旦七ed load was appl工ed a七七he

mid-span of七he beams whos巴 shear span

lengths

，

i.e. dis七an巴e frorn七he sユde face

of a colurnn七o a suppor七ed poin七， are 4h"v 8h (where

，

h :dep七h of bearns).

Th日 curva七ures and d巴flec七ions in

1 ラ.h region from七he cri tical sec七ion of the 七es七巴d span wer巴m巴asured by six

巴ouples of deformation transducers(D.T.)

which were se七七o七he screw bol七s embedded in a bearn at the pit巴h of 0園5h and at th巴

Tab

ユ

e 4 Mechanical proper七ies of lateral bar Dia配ter _Y_i_e_l_d₍_匂_s_t_f_/_r_E_c_{略 )}_d_油 _同紙1_{園臨}₍_U_s_t_f_/_r_E_E_隠)_d_せ₁ _E_l_o_略_a_t₍_耳_i_O₎_B (翻) 3.2 2415 3426 29.2 3.9 2280 3347 40.9 4.9 1931 30ω 41.6 5.7 2983 3890 31.5 8.0 2654 3531 32.5 Load Shear D.T.

Fig.2 Me七hods of loadユng and measuremen七日

400 。『一一-0Sニb/4 &----.8 S=b/2 巴ー--fJS= b

@一-_

S=o

。

AA 相/

一

y

r

ィ

-p d

+

議

L

4 q

y

n u ハU ハu n U 5 0 5 0 司 J ﹃ J 勺〆山内 4 N E U ¥ 阿国ぷ)同ト。 Z 同区ト∞ Prism W/C=55% 150 7.3 9.7 12.5 1 5.0 20.0 WIDTH(cm)

，

b

Fig.J Me七hod of s七rain measurernen七

3.ち日 ω Prism W/C=55% 0---0 S=b/4 ゐー--8S= b /2 日一---DS=b 舎一一場S=

∞

;-- 3.0

c

M X 2.5 Z 4

ミ

'

a

.

-

a

'

t

"

冶 E入貝 ¥ 、也

、子ー玄'

ー

¥

百

点γ ‘ 可珍一一一一 @ トーベ

-<

2.0 0:: ト ∞1.5 嘩「 1.0 7.3 9.7 12.5 1 5.0 20.0 WIDTH(cm)

，

b

(4)

176 小池狭千朗・畑中重光

sarne 1巴vel as 七he七op and 七he bo七七orn surfaces of the bearn. Hereユnafter

，

the curva七ur巴rneasur巴d regions ar巴referred七o as七he "firs七， second， and七hird regions" frorn 七he cri七ユca工 sec七ion. R巴la七ive defl巴ction be七ween 七he critical section

and 七he supported poin七of 七he七es七巴d span was also rneasured.

(2) Concre七日 prisrns

The rne七hod of s七rain rn巴asurernen七 of

巴on巴rete prisrns is illustra ted in Fig. 3.

Specirnens were loaded under七he constan七

n υ n u n u n u n u n u n u n u A A Y 司 3 q 4 咽 i b .

一

N E υ ¥ 刷切さ凹回国民ト凶

。

2 4 6 8 10 12 STRAIN IX10-"I. ec (a)S=b n u n u n u n U A M -﹃ 3 b . f E υ ¥ 斗4 回よ4200 7.3cm (/) ~ 100 出ト (/) 2 4 6 8 10 12

。

STRAIN IX10-31.εc (b)S=b/2 n u n u n u n u A 日 1 2 J h U R 一付臣 U ¥ (/) 的 100r/S=b/ll 国 6

←

4 (/)

。

2 8 10 12 STRAIN IX10-"I. ec (c)S=b/4

F工g.6 Size effect on stress-strain

curv巴

S七rain ra七e of abou七2 x 10-3/rnin園 up to

七he specified strain (E; =5x1 0-3) in general. The longi七udinal s七rain was rneasur巴d by a coupl巴 of deforrna七ion transducers (rneasuremen七leng七h was 2b).

3.TEST RESULTS AND DISCUSSIONS 3.1 Concre七e prisrns

(1)Cornpressi刊 strength

F工gure 4 shows 七he巴ff巴巴七 of specim巴n siz巴 on the cornpressiv巴 E七reng七h of

n v n v n u n u n u n U 4 τ q J 内ふ勺-一 N E υ ¥ ヤ回ぷ一一一一一 S=b/ll - ー一一S=b/2 /一一ーー一一一一一 S=b

ι

一一ー、 ~で一一 S=回一~ ¥ ¥ n u n u

-一回目凶凶↑目 ¥ 一、、、一、、ー一ーー

一

、

-

_{一一一一一}

'-.._ 、、、、

。

2 4 6 8 10 12 STRAIN(xI0-"I. eC (a)b=7.3crn 一ーー一-S=b/4 ーー『ーーS=b/2 一一一一一 S=b 一一一S三回 n u n u ' i )凹凹凶出ト凹

六

ご

と

ー一-_→_ー、、 --~ー-ーーー_{一一一一一}

。

2 4 6 8 10 12 STRAIN (xI0-31.εc (b)b=12.5cm b i二400卜一一一一一 S=b/il 刊 l ー ¥ ー - - - -S=b/2 百十 ι、 ¥ : ; 1 ""¥".'-.~ ー一一一一 S=b

ミ

300

十 /

¥

"

，

~...._ 一一一 S=同 I ! ¥ ¥ ¥ ...._ 刷~ I ¥ 、、 -凶 I I ¥、 ¥ 、 . _ _ .'i2001寸 1

ω

、

υ ¥

;.: 100 Iイ ¥

~

~b~2~.0~m-，---~

(/)

o

2 4 6 8 10 12 STRAfN (X10-31.εc (c)b=20.0crn

F工g.7 Effec七of spacing of hoops on str巴ss-strain巴urve

(5)

曲げとせん断を受ける鉄筋コンクリート梁の塑性変形性能における寸法効果

₁

₇

巴onfined concret巴for var工ous spacing (8) in巴r巴as工ng size of specimen regardless of of hoops. 1七is shown， for plain concre七e 七he spacing of hoops.

(8=∞) and confined concr巴七ewi七h hoops of

larg巴spacing (8=b)，七ha七七he compressive Figures 7(a)七hrough 7(c) show七he s七rength increases wi七h in口reasing sユze of effect of spa巴ing of hoops on七h巴 σ-E

specimen which is similar七end巴ncy to七he curve of confined concre七e for var ious earlier tes七resul七of plain con巴rete [3]. s士zes of specimen. The compressive

8uch siz巴巴ffe巴七， however， is no七百七reng七h is higher and七he descending recogniz巴d for confin巴d concrete wi七h portion of σ -E curve is less s七eep.for

hoops of small spacing (8=b/4，b/2). 七he small巴r spacing of hoops. No七e 七ha七七his七endency is more remarkable for (2)8train a七peak s七ress smaller specimens.

Figure 5 shows七he effec七of specimen 3.2 RC beams slze on七h巴B七rain ( E m) a七七he peak

str巴ss of confin巴d 巴oncre七巴 for various (1)Momen七一巴旧va七ure curve spacing of hoops図 It is shown

，

for plain

巴oncr巴七e (8=∞) and coぱ in巴d巴oncr巴七ewi七h Figure 8 shows an example of measured hoops of large spacing (8=b)，七ha七七he moment index (M/bd 2) -curva七ur巴 index(中 .d) value of E m土s hardly affec七ed by the curve (hereinafter

，

referred to as M-中 spe巴im巴n siz巴 in bとヲ。7 巴m. For 巴onf工ned curve). No七e七ha七七he mornent of each con口rete with hoops of small spacing region is represen七日d by 七he maximum

(8=b/4，b/2)， howev?r，七he valu巴of E m momen七工n the r巴gion，and th巴M-中 curves decreases almos七 cons七antly wi七h of七he firs七 and second regions are increasing size of specimen. repres巴nted by巴nvelope curves. Following

dis巴ussions are based on七he envelope

(3)8七T巴ss-sもrain curv巴 curves. The failure pa七七ern of 七he specim巴n is illus七ra七巴d七og巴七her with the Fig凹 es 6(a)七hrough 6(c) show七he curves.

effect of specimen size on七he stress(σ)ー

日七rain( E) curve of confin巴d concr巴七e for 1七is observed in Fig.8 七ha七七he the hoops of various spacings. Here

，

measured M-中 curves of differ巴nt regions

damage of concre七e occurr巴d around七he are significan七ly differen七 from each mid-height of specimens， so七ha七 all七he other. The巴urva七ure in七he second region damaged zones were wi七hin七he s七rain does no七d巴crease bu七 in巴reases wi七h 七he me旦surem巴n七 r巴E工on of spec工mens. The decrease in七he momen七 in the firs七

figures show七ha七七he desc巴nding por七ions re gion. In七he七hird region， curvature o f σ -E curves become s七e巴per wi七h decreases wi th decreasing momen七 after a

N 100 甘

2

8

0

N

B

'

60 、 ¥

生

霊

20 0 E 一一一一0.5h ---1.0 h ---1.5 h

¥

叩 % 7 h 1 0 J r b b 2 一 - 一一一一一一 s t b t s p

。

5 10 15 20

。

5 10 15 20 CURVATURE (X10-2 )

，

d・4 CURVATURE (X10-2 )

，

d・4

(6)

小池狭千露目・畑中重光

d工fferen七 d巴P巴nding on 七he curva七ure measuremen七 1eng七h even in the same specimen. Figure

9

shows the M-中 curves averaged over七he 1eng七h of O. 5h

，

1. Oh

，

and 1.5h from 七he巴ri七工ca1 sec七ion. The M-中 curve shows more bri七七1e behavior as

七he curva七ur巴 measur巴四百n七 1eng七h becomes 工onger.

178

sma11 amoun七 of p1astエ巴 curvature deve1oped. Name1y

，

in七he first and second regions

，

p1as七ic deformation star七百七O

deve10p before七he maximum momen七 of七he region reaches the yie1ding moment in the firs七T巴gion。

七he damag巴 1oca1ization

，

巴urves become qui七日 Because of m巴asuredM-中一一一一S=b/4 一一一 S=b/2 一一一一-S=b n I C % ウパ h I Q u n b ヮ “ c d f ? u b d p N 100 甘 2 8 0

N

"

_、_、 6 0

戸

40 Z 凶 E O Eさ一一一一b= 7.3 cm --b= 9.7 cm 一一 b= 12.5 cm 一一一b= 1 5.0 c m S = b

.

e

s =6 h Pt=1.4% 20 N 100 甘』

主

80

<

;

60 、¥ ~ 40 同冨

。

冨 20 20 d.中 n

。

ρ b n

、

l -ユ n c o a-工 P 4 g b n M O V r p ゐ u h

r

o

r -- ユイ l + υ f {

、

見 M e p i v o r U 4uc c 向日中 n 工 -V 心 M U 1

-e ρ b - 工 p r 5 10 15 CURVATURE (X10-2 )

，

。

20 d・4 5 10 1ラ CURVATURE (X10-2₎

，

。

N 100 甘

2

8

0

「巨 U 、、

芦

40 2 ~ 20 0 冨 (a)P七=1.4% S = b

.

e

s =6 h p t=2.1%

。

20 d・中 5 10 1ラ CURVATURE (XIO-2 ) ， N 100 甘

2

8

0 <

_、

<

_、_、

;

60 E 4 0 同 E言

。

E三 20

。

(a)Effec七of specimen sユze(b)

S

80~~

心

60ij "¥-'，、ミ~

¥ 、

~ 40~

、

¥

量

2 O U S 3 1 c m ¥ ¥ ー

言

t

P t = 2.1% 一一一一一汁一一一一S=b/4 -S=b/2 一一ー一一S=b (b)P七=2.1% 一一一一b= 7.3 cm -b= 9.7cm - b= 12.5 cm - --- b = 1 5.0 c m

、

¥

: 、下

1111% 、吋守、 hHQU で b62 子、 QU4L 、一 q U 8 ι v p A

S

8 O

c

60

官

40

E

E吉 20 d <t 5 10 15 CURVATURE (X10-2₎， 20

。

20 d・4 5 10 15 CURVATURE (X1 0-2₎

，

。

(b)Effec七 of spacing(S) of hoops curv日 Fユg.12 Ca1cu1a七ed M-中 curve (c)Pt=2.8% Fig.10 S工ze effec七 on M-，中 (1.0h region)

(7)

尚げとせん断を受ける鉄筋コンクリト梁の塑性変形性能における寸法効果

1

7

9 ~

80 ト U Z M

星

20U 0 札冨

。

代 100 甘』 " 80 山富凶 N--;60問、 ¥ 仲

官

40刊 Z

星

20 0 5

。

ー一一一一b= 7.3 cm 一一一ード 9.7 c m 一一ー一一b=12.5 cm 一一一一一b=15.0 cm 0.0雪 0.10 0.15 0.20 DEFLECTION， o/h (a)P七=1.4% 0.05 0.1 0 0.1 5 0.20 DEFLECTION

，

o/h (b)P七=2.1% ーー二::-.~"'""_一_、ー_ー_去_、でτ、、一一一一一-b= 7.3cm -一一 -b= 9.7crn 一一一一b=12.5 cm 一一一←ーb=15.0 cm S = b i s =6 h ¥ '<'，， '¥、

"

¥

¥ P t =2.8% 0.05 0.10 0.1ち DEFLECTION

，

o/h (c)p七=2.8%

Fig.13 Size eff巴C七 onM-中

curve (1.5h region) 0.20

The damage genera11y conc巴n七ra七ed工n

the 1.0h reg工on frorn七h巴巴ri七工ca1 sect工on. Therefore

，

bas巴d on 七he averaged M-中

curves of 七he f工rs七 and s巴cond regions

，

七he effec七日 of various fac七ors on the f1exura1 deforma七iona1口apaci七y of RC

beams are discussed in七he fo

ユ

10wing. Figures 10(a) through 10(口)show the size eff巴口七 in 七he M-中 curves of the specirnens

of 18=6h

，

S=b for various va1ues of P七.

The M-中 curves of small巴r size specim巴n

is in g巴nera1 more duc七工1e

，

which is consis七en七with the七endency of七h巴 0-E curves of concrete spec工mens. Figure 11

shows 七h巴 eff日ct of s七irrup spa巴ing on M-中 curves. The srnaller七he spac工ng of

stirrups，七he rnore duc七ile becorn巴E七h巴

M-中巴urv巴@

Figures 12(a) and 12(b) show the M-中 curv日s obtain巴d by the calcu1a七ion wi七h

七he 0 -E curves of concr色te prisrns and s七eel bars. The ana1yti巴a1巴urves represent qua1ユもa七ively sirni1ar 七endency concerning 七he effec七日 of 七he specirnen size and s七lrrup spaclng 七o the experimenta1 curves in Figs.10(b) and 11. However

，

a1l the 日.na1yti巴a1 curves show more britt1巴 behavior 七han the experirnen七a工 ones七o be cornpared.

(2)Deflec七ion of 1.5h region

As工Sm巴n七ioned in Sec七ion3.2(1)

，

七he damag巴 genera11y concentra ted in the 1.0h regユon from 七he cri七ica1日日巴七ion. Therefore

，

i t 工s considered possユb1e 七o

predic七七he deforma七ional capaci七y of a whole beam by eva1uating 七he re1ative deflec七ion of 1. 5h region from the critica1 s巴C七ion inc1uding 七h巴e1as七工c zone free from outs七anding darnage. Not巴

七ha七， a1七hough七he shear d巴f1ec七ionrnay be negl工gib1e as far as the u1tirnate

def1ec七工on of the who1巴 beam is concerned

，

七he con七r工bu七工on of 日hear def1ect工on to

七he七口七a1 def1巴c七ion is no七 so sma11 compared wi七h fl巴xural def1ect工on in such

a short 1ength of 1.5h [4].

Figures 13(a) and 13(b) show the siz巴 effect in the deflec七ion( 6) of the 1. 5h region of七he specirnens of S=b

，

ls=6h. Here，七he deflection ( 6) is norrna1iz巴d by

七he heエgh七(h) of a beam in七he x-axis to dis巴uss the size eff巴巴七.It is seen 工n七he figure七ha七M/bd2-6/h curves (M-6 curve) of srna11er size specirn巴ns ar巴工n genera1 more ducti1巴， wh工ch工E口onsis七巴n七with the

七巴ndency of 七h巴 M-中 curves of 1. Oh reg工on. Further

，

the sarne七巴ndency is observed in七he b巴ams of ls=4h and 8h。

(8)

180 小池狭千朗・畑中重光

1 .

5 h~

P

Q

4h

ム

6h

口

8 h

: / 〆ノ

0.5 h

P

t

=2.1%

，

b=9.7cm

s

b b // 2 b/4 (a)3pacing of stirrups (3) 7.3

cm

9.7

cm

12.5 cm

15.0

cm

S=b

，

i

s=8h

Pt

2.8% 1.

4%

2 .

1 %

(c)Tensile r巴infor巴巳men七ra七io(P七)

hhh 468

0 ム

口

p

94 ム 4 F 4 戸門止ノ。一一〈トー-0ーーや

Pt=2.1%

，

_S=b/2b

7.3 9.7 1 2.5 1 5 20 (b)3ize of specimen (b) 1 5 J P

o

s=b

ム

S=b/2

口

S=b/4 ムロ一一一四一一ー一ーの告白戸ペプ~ -. ----;/

-

-口----ノ/ ~

一

_一

σ

ム

Pt=2.1%

，

b=9.7cm

ts

4h

6h 8 h (d)3hear span 1e珂th(ls)

Fig.14 Effect of ea巴h factor on 1p

(3)Leng七h of fai1ure zon巴

To eva1ua七e quan七i七a七iv巴1y 七he effe巴t of various factors on the M-中

re1a七工ons of RC beams，七he tes七ed spans of RC b巴ams wer巴工dea1ized in七O 七MOzones，

i.e. fai1ure and non-fai

ユ

ur巴 zones

，

accord工ng to the degree of d旦mag日 [1

，

2) .

Figures 14(a)七hrough 14(d) show七he effec七of each fa巴七or on the 1ength of idea1ized fa工1ure zone(lp). Here

，

reg工ons

where七he com-pressive fiber strain exc日eded 0.004 wer巴 regarded as th巴

fai1ure zone [1).

According七o the f工gur巴s

，

i)七he va1ue

of 1p七ends七o increase wi七h七he decrease in七he spacing(3) of stirrups (Fig.14(a))

，

ii)i七 is hard1y aff巴巴七ed by 七h巴 specim巴n size(b) and tensi1e reinforcemen七

ra七io(P七) (Figs.14(b) and 14(c))

，

and ii工)the va1ue of 1p incr巴ases wi七h七he

increasing 1eng七h(ls) of shear span (Fig・14( d) ). In addi七ion七o七h巴s七a七巴即n of工i工)， no七e tha七七he b巴hav工or of a sec七ion wi七hin七he fai1ure zone(lp) ュs a1so grea七工y affected by 七he shear span 1eng七h

，

i.e.

，

七he behavior becom巴日 more

duc七ile wiもh decreasing shear span 1ength

due to七he effec七of moment gradient [2).

4.CONCLU3ION3

The fo11owing conc1usions can be drawn fro四七he present study.

1)Both七h巴日tress-strain curve of confined

concrete pr工sms and mom巴nt-curva七ure curve

of RC b巴ams be巴ome more brit七工e with

increasing size of specimen regard1ess of

(9)

曲げとせん断を受ける鉄筋コンクリト梁の塑性変形性能における寸法効果 181

2)The siz巴effect on七he leng七h of fa工lure 2) Kosaka，Y.， Tanigawa，Y.， Ha七anaka，S. and zone(lp) was hardly obs巴rved. Therefor巴， Miwa， .R.， "Plastic Hinge of R巴工 n-th巴 size eff巴巴t on 七he Momen七-curvature forced Concr巴七e Bearns，" Trans. of Cern. curve is considered grea七ly due七口七h巴 Assoc. of Japan， Vol.40， 1986， pp.580-size effec七on七he s七ress-s七ra工n behavior 583 (in Japan巴se)。

of concrete in七he cornpressive zone of a

bearn. The effec七 of七he other factors on 3) Koike，S.， Okufuji，K. and Okuya，Y，・"Size lp was found alrnos七七he sarne as in the Effec七on Express工on for S七ress-S七rain prev工ous repor七[2]. Curves of Concrete Und巴r Cornpression and

i ts Applica tion for Mornent-Curva七ure R巴lationships of Reinforced Concre七巴

REFERENCES

1) Ha七anaka，S.，Kosaka，Y.， Tanigawa，Y. and Miwa

，

R.

，

"Curvaもure Localiza七ion 工n

Plas七ic Deforrna七ion Range of RC Bearns Under Flexure

，

"

J our図 of S七ruc七。 and

Const. Eng. (Trans. of AIJ)

，

No. 371

，

Jan.1987

，

pp.27-38.

Beams，" Tran日。 of JCI， Vol.9， 1987，

pp.249-256.

4) Hatanaka，S.， Kosaka，Y. and Tan工gawa，Y・9

"Modeling of Pla日七ic Zone for RC Beam日

of Flexur丘1 D巴forma七ion Predo皿ina七ing

Type

，

"

Proc. of Ninth World Conf. on Ear七hquake Eng・， Tokyo-Kyo七0， Japan，

Vol.4

，

1988

，

pp.457-462.