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TESTING -AND ANALYSIS OP THE ASBISMATIC BEIlAVIOUR OF VOLCANIC SLAG

CONCRETE BLOCK MASONRY INFILLED R/C FRAMES

DaiXin ~ang, Liu Sheng Wang Harbin Architectural and Civil Engineering Institute, Harbin, C~1na

ABSTRACT

The results of an experiment and analysis were presented here. It included investigation of single-story one-bay 1/3 scale infilled R/C frame models under cyclic quasistatic hor­igontal loading. It gave a discussion of restoring characters of the infilled frames, set up a restoring force modle of no­nlinear seismic response and established formulation of rest­oring .. force characeters with some parameters under investiga­tion. The longth of displacement of plostic hinges in the co­lumns of the infilled frames was formulated.

NOTATION LIST

EW.Ep---- modulus of elasticty of infill and frame respective1y.

H ---- inf111 height. HO---- longth of two plastlc hinges in a co1umn.

h---- longth of desplacement of plastic hinge. AWACIACR----cross-sectional ares of infill, left column and

right cOlumn, respective1y. -tW.tp---- thickness of infi1] and frame, respective1y.

bw. bF--·-- cross-sectional length of infi11 and frama, respective1y.

j ----the angular distortion of the infi11ad frame. ~ ----horizontal displacement.

ÂC---- horizontal cracking-displacement.

J ----ratio of hight to length of inf111.

fV ----shear strength of infil1.

NCL.NCR---- axial compressive load of left and right of column, respectively. . .

FWlJ.FFU---- horizontal 10ad beaving at fai1ure. Kw.Kp -----initia1 stiffness of infill and frame, respectively.

1'. -----ratio of initia1 stiffness of infil] to frame.

KC ----- initial (cracking) stiffness of infi1]ed frame.

o<. ----- "D" prarameter.

1.INTRODUCTION

A good seismic behaviour of the structura1 system of brick infilled frames is a fact stated by the investigatian af the

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Tangshan earthquake in China, and m~ny authors expound the fact that' the dynanic characteristics of the bare basis structural system by the inc.orporation of infills have significant change. But, now, it is a little for us to know the dynanic chracteris­tics of the volcanic slay concrete block infilled frames. It is rich in volcanic slay on the north-east of China. The volcanic slay concrete block 1s struetural material with the character1s­tics of the lighter in weight, the little thermal coefficient of conductiqn and load-bearing capacity. The dynanic behaviours of the reinforced and unreinforced the block masonry wall were studied completely in our institute. It is a good material for the volcanic slay concrete block in masonry and will be found a new use in the infilled frames.

2. MATERIALS AND f1ETHODS

The experimental models consisted of a series of six orthogonal-designing single-story one bay 1/3-scale infilled R/C cluctile frames, the infi11 being an nureinforced maso­nry wall conne.c-ted to the bounding columns of the frames with reinforced steel. Two bare frames were used as reference models. The thinkness of R/C frames and infills remained constant for alI the models (frame thinkness 20mm, infill thinkness 19mm), the hight of infills alI were 1000mm. Rein­forcement ratio for the columns and beams was 1%.The influence of the fOllowing parameter was investigation.

i) The leveI ofaxial compressive ratio of the columns. Two leveIs were chosen, one of 25% of the failure strength of the columns and another of 50%.

ii) The leveI of t he stiffness ratio of infi11 to frame. Three leveIs were chosen, 0.94, 1.42 and 2.90 of the stiffness ratio of infil1 to fram, respectively.

iii) The leveI of aspect ratio of height to longth. Two leveIs of the aspect ratio of height to 10nGth, 0.56 and 0.74, were chosen.

Lateral loading was applied by two single acting jating and inclucled full reversals of gradually increasing displa­cements. At every lateral loading or displacement leveI, two reversals were applied. The final result of the experimental investigation was one force-displacement curve for every frame lanolysising section of the curve between O to 4.0% of the angular distortion was used). The assessment of the dynan­ic behaviour of the infi11ed frames was performed on the basis of strength, initial stiffness, ductility and energ.}' dissipa­tion.

3. RESULTS OP i\tiAUSIS

3.1 Mode of Failure The failure modes of tho infilled frames are almost the

same as those of the correspondin~ bare frames, with the exception of the place ·of plastic hi!1ges at columns moving at SOme case, where slip failure of the infill across a horizon­tal mortar joint occur.

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Fig.1 lateral load-displac­ement curve-Bare frame

Fig.2 la teral load-displa­cement curve­infilled frame

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3.2 Curve of hysteresis loops and Envelopes i) The hysteresis loops of the bare frames are rich,

typical to the inelastic roration of the plastic hinges (Fig.') On the contrary, these of the infilled frame get pinching,ty­picaI to brittle behavlour due to lnfill cracklng (Fig.2)

ii) Lateral load-displacement envolpes of the infilled frames odescencl. brach follows and come near gradually to vertex of lateral load-dlsplacement envolpes of the correspond­ing bare frams, after reaching the , criticaI distortion (Fig.3)

3.3 Strength i) The cracking point of the envolpes of the infilled fram

is defined, When the infills crackiOng, and the lateral load of the infilled frames is defined cracking-load (the cracking stiffness is defined). The cracking-load of the infilled frames is greater than that of the corresponding bare frames, because, one is that infills are bound by frames infilled, then loteral shear force of the infills get greater, another is that frames are suported along bour side with its infills, then lateral load-bearing capacity of the frames is greater thun correspond­ing bare frames. The lateral crackingload of the infilled frames can be calculated from

Pc= ~~~; ~1 + ~ (1+ ':1:J:~2) ............. (11

~= ---~º~~~~~--- ... o •••••••••••••••••••• ( , a) n(ACL+ACR)+Aw

n = EC/gw ............................. (, b)

Where Õo is the quusi-stress of infi11s

ii) the lateral fuilurc load bearing of the infilled frames is more greater th~n that of the corr~sponding bare frames, because of the mutual effect of the infills and the frames. lt is said that one of the infills has a suporting effect on the frames, then the calculated height of the colu­mns of the frames is reduced and bearing-capacity of the frames gets greater, and another of the frams has a bindin~ effect on the infills (Fig.4), th~n the stress state of the infills come to two dimension compressive stress state and lateral bearing­capaci ty of the infl11s gets ~reater. The dymmic effect of the infilled frames vàry with the differcnt stiffness ratio of the infi11 to the frame. The stiffer the frame gets the stronr:er the hindin~ effect of t! ;e frame gets relatively and the weaker the suportin e effect of the infill gets relatively (Fig.5). lateral load of failure of the infilled frames is combined of lateral-load of the infil15 ~nd the frames, and it (Fu) is calculated from

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F = Ppu + FWU u • . • • • • • • • • • • • • • •• (2 )

2M 1 +2M FpU

u ur ----------HO

· . • . • . • . . . . • • . • . .. (2a)

HO H = ----------

1 + 0.07 ?\... · .................. ( 2b )

F

14()

infilled frame,

/2fJ

--~ ---- --bare fram~ ~

I~ig. 3 Lateral load-displacement envelopes

~ ~" r'----------.:- .,

Fig 4 the stress of bounding frame

Where MuL and MuR are the moment of bending of the left

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calumn and the ri,,::h t calumn af the frame. In the aseismatic design af the infilled frames, the

bearingshear capacity af the infilled frame calumns must be strengthened by formultian (2a), Sa that keeping the columns af the infilled frames fram shear failure.

The displacement langth af the plastic hinges in the frame columns is calculated fram

1 h = (1 - -------) H •••••••••••••••••• (3 ) 1-0.07 '"

The results of experiment shaw in table 1.

table 1

Pc' P , Pu u Pu' /Pu group element (KN ) (KN) (KN)

A2-Fs-S 70.000 155.000 160.74 t 0.964

1 A4-F -1 130.000 215.000 221 .014 0.973 s

A4-B-S 40.000 90.000

B4-F -s s 60.000 115.000 111 .634 1.030

2 B2-Fs -1 100.000 145.000 142.741 1 .016

Jl 4-B-S 40.000 60.000

C4-F -s 90.000 250.000 241 .268 1.036 3

~

C2-F -1 : s 130.000 280.000 281 . ~ j 1 0.994

D1-F-rl! 90.000 160.000

4 D1 -B-ll! 40.000 55.000

3.4 Intital stiffness and Ductility

i) The initital stiffness (cracking stiffness) af infilled frames is much greater than thut af t he bare frames, because af the mutual effect af t he infills and frames, The formulation af the intital stiffnQss is fallawing :

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KC=K ( 1 + 1..:.~~) •..•...•..... (4 ) 'ti J\..

EWtW KW = 0.63 -3--- ............. (4a)

y +31 3

EC b t F 0.9 ------« ............. (4b)

KW À =--

KF

H3

.......•••.••.•••. (4c)

Fig. '5 suporting .. effect of infilled frames

F

/4

Fig. 6 model of restoring force curve

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ii) The energy dissipution of the infilled frames is much ~reater th:m that of the bare frames and is significant especially at low distortion, becau~e the system dissipates energy thraugh friction across the infill cracks. The cluctil­ity af the infilled frames i9 satisfactory.

3.5 Moldes of Restoring-Force Three phuse degenerading model of the infiJ Jed frames is

simplified from the loud-displacement of the infilled frames (Pjf 6). the every phase stiffness (K) as calculated from

•.•••.••••••••••••.•• (5 )

K2 KC ( 0.045 + 0.0749 ) •••••••. (6 ) ---------------

À

K3 -0.02Kc ••.•....•.•••••......• (7)

-0.043 Á -0.17 KC(

D. ) Ac whill A ~ 10

f Âc A(

K'= ~ ••• (8)

~ Ã -0.005

:Ã~ -0.55 A

KC ( -Ãc ) whilJ -Kc > 10

4. CONCLUSTION It proof ttat the composite structure system of thA frames

infiJJed t '1 ~ r.:2.S0nl'y ~1Í1J hus better dynamic effect, then to he fauna a use of aseismat.ic structure. It must be found a Good n8W use of the volcanic slnc; concrete block .masonry to infilled frames for aseismutic desi{;n in seismatlc eare.