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Title On the Damage to the Hakodate College by the Tokachioki Earthquake, 1968

Author(s) Ohno, Kazuo; Shibata, Takuji

Citation Memoirs of the Faculty of Engineering, Hokkaido University, 13(Suppl2), 123-140

Issue Date 1973-03

Doc URL http://hdl.handle.net/2115/37920

Type bulletin (article)

File Information 13Suppl.2_123-140.pdf

Hokkaido University Collection of Scholarly and Academic Papers : HUSCAP

IZ3

ON THE DA)orLGE TO THE }IAKODATE CObLEGE BY THE TOKACHrOK: EARTHQUAKE, 1968

Kazuo OHNON Makuji SH:BAMAww

1. GeneraZ view of the damages to reinforced concrete bu±ldings inHakodate City

OnZy one foun-stoni.ed schooZ-buiZding of =einforced concrete

construct±on at the Hakodate CoXZege was heaviZy destroyed by theTokachiokrk earthquake, 1968, aZthough the other reinforced coneretebui:dings in the same area suffered a Zittle or no damage. Mhe campus of the CoZlege is situated on a hUZ in the eastern suburbsof Hakodate City as is shown in Fig. 1. 0riginally, there were four

bufi.Zdings in the campus as is sho"m in F±g. 2: one steel-framed gymasiumand three reinforeed conerete buiZd±ngs (the main four-storied school-bui:ding, a thxee--storied sohooZ-bui:ding and a three-storied dormitory). The Hakodate Technieal CoZlege which has a number of reinforeed

coltcrete buUdtugs ±s Xocated near this campus: a three-pstor±ed school-building, three three--storied dormitor±es and ten two-storied dweZling-houses. After the earthquake, some craeks were observed in these buildings,but aZmost no damage was deteeted in their structural strength, exceptingthe four-#storied building the present papene is now concerned. Speaking of the damaged bu±ldings in Hakodate City, details of damagesin aZ: the reinforced concrete buildings in four specific regions shown inMg. 1 were investigated. The number of buiXdings of reinforeed concrete±n･these reg±ons was 270 at the t±me of the earthquake, but the number ofdamaged buildings was rather smaZZ. Fig. 1. shows the pereentages ofthese damaged buiZdings, where symboX N means no damage and MA, Ms, SA, Ssmean the foZlowing e2assifications of damages: D{A: partialZy damaged in the reinforced concrete frames and the earthquakeh-resisting walZs, in whieh some repair is required. MB: somewhat damaged in the expansion joints, outdoor emergancy staircases, penthouses of the roofs, chiinneys and attached' eorridors, in which some repair is required. SA: cracks were observed in the reinforced concrete frames and the

earthquake-resisting walZs, in wh±ch no repair is required. SB: slightZy damaged in non--structuraX members like partition walls,

curtain walls and f±xtures. The-above-mentioned observations include 24 school-buildings of pr±maryschools, middle schooXs and high sehools. A haZf of them are three-storied

and the remaining each quarter ±s four-storied and two--storied. Distri-bu'tion of the degree of damages is cXassified according to the items ofdamages a,s foZlows: MA-1, Ms-O, SA-7, S6-8, N--8. The data show that thenumber of bvtildings with no damage is about one-third of the observedschooi-buUdings. It ±s notabZe that th±s resuXt is cons±derably different from thepercentage of buUdings with no damage in whole number of observed buildings. ' ' '2. Strueture of the destroyed school-building of the Hakodate College

- Professor. ",K Assistant Professor. Hokka±do University

124

This four-storied sehool-building had a long and narrow plan of anopen L-shape as is shovfn in Fig. 5, The east wing (9.Z mx27.3 ia) was

£inished in 1964 and the north-west wing (9.1 m x72.8 m) was constructed in1966. There was an expansion joint near the bent corner of the buildingwhich was included in the second work of eonstruction. The structure ofthis expansion joint was somewhat incomplete, because the floor slab of

each story was constructed ¢ontinuously over the joint, although theexternal girders and walls were separated from the columns at the joint(see Fig. S)･ In the structural design, the columns were 50 cmx 80 cm which is thecommon dimension in each floor, The axial reinforeement of the eoZumn in

the first story cons±sted of 26 plain bars of 22 mrn diameter and thereinforcing ratio corresponded to 2.47 9S. Hoops weTe 9 mm in diameter andthe spacing was specified to be 200 mm throughout the whole length of theco1umn, The wall girders in the long direction of the buUding were 20 em inthictmess and 150 em in depth, to which the floor slabs were connected at

the m±ddle of the g±rder depth. These girders were connected to thecolumns so that the insides of girder and column were flush as is shown in

Fig, 4, The eeeentric±ty between the axes of girder and eoZum was 30 cm,The footing gixders in the same direction had a eross--section of 20 cm ×:80 cm and the eccentricity between girder and co:umn was the same as thosein the upper Moors･

Besides the above-ment±oned structur&1 eo:umns, there were non-structuTal pilasters which had a eross--section of 45 emx57 cm in themiddle of each spacing between structural columns. The pUasters werereinforced w±th only four plain bars of 16 mm diameter and they had nofoundation, About a haXf of pilasters were used as the chirBneys with eZay

pipes ±nside, The dimension of girders ±n the short direction was 40 em×75rviOO em,The beams in the short direction of 50 cm×70 em were a:so arranged in themiddle of each spacing between girders, rig±dly eonneeted to the piXasters, There were considerably small amounts of bearing walls in this school-building, as is shown in Table 1,

3. Detailsofthedamage

Newspapers reported immediately after the earthquake that the four-storied building col!apsed into three--storied one in a moment (F±g. 6).Almost all of the colums and waUs in the first .story were exhaustivelydestroyed. These damages were eonsiderabZy intensified by the aftershockwhich attaeked the building in the evening on the same day. There was some difference of damages between the north-west wing blockand the east wing block of the building. In the former, the skeleton upperthan the second story fell down so that the bottom of wall-girders of thesecond floor touehed the top of t.he first Noor wall-girders, because allof the columns in the first story were destroyed into pieees (Fig. 7).

Regarding theupperstories,thecoZumnsandwall-girdersinthemiddleone-third of the north-west wing were severely damaged (Fig. 9).Especially, the girder-column joints were destroyed and the pilasters felldown separated fTom the egall-girder (Fig.10). In the east pging, thedamages of columns of the first story were some what less and the columnsat the east end of the building kept almost their original forms, thoughmany severe cracks were observed on them (Mg. 8). These crack patterns

125

suggested that the column would be subjected to a large shearing force inthe Zong direction of the building (Fig. Il). AZmost a21 of the columns in the upper stories of the whole buildingalso had many shear cracks of the same kind (Fig. 12, 15). Some spiralcracks which spread on the surfaces of coZumns were also observed. Thisfeature of cracks suggested that the columns would be subjected to l4).considerabXy :arge torsiona: moments (Fig, Of course, all of the waZls in the first story were damaged. ThewaXks with a thickness of IO cm around the main entrance, which was

s±tuated in the center of the east wing, were obliquely shorn into two partsand feZX down overXapping each other (Fig. Z5).

The waZls with the thickness of l2 cm, wh±ch were located at the bothsides of the staircase ±n the middZe of the north-west wing, were badlydamaged in the first story, so that the staircase from the first floor to 9).the second fZoor was destroyed (Fig. The external wall with 'thickness of 20 cm which was located ･at thebent eornor of the building was broken as will be seen in Fig. 16. Moreover, the emergency staircase of steel construction whieh wasanchored to the outside of the north-west end walZ was shaken off andovertu=ned,

4. Mnfoirmations obtained from the sufferers of the earthquake

When the earthquake attacked this building, about two hLmdred studentswere seudying in the north-west wing block in four classes: one class inthe second-story, two classes in the third-story and one class in thefourth-story. Whe informations obtained fTom these students and professorscould be summerized as fo:Zows:(Z) The vibration of the buiZd±ng in the short direction became severe inthe first Z5 seconds, then it continued more than two minutes, About ahaZf of students (aZZ students in the second-story and a large part ofstudents in the third--story) took their refuge to the outdoor passlngtlirough down the staj.rease in the north-west wing. However,. 'the otherstudents, especialZy aZmos't all students in the fourth-story stayed in

the±r lecicure-room by the gu±dance of the professor.(2) Some students who intended to take refuge a littie later found thedestruction of the staircase in the first-story, and ran toward the outdooremergency staircase, UnfoTtunately this staircase was overturned and astudent who was deseending along 'the staircase was shaken off and heavUy??jUrllSier about -three minutes from the beginning of the earthquake, (it

was impossibZe to prove this period), -irhe students who stiil stayed in the

upper stories felt a shock and then they felt as if they were on thedescending eZevator, because the fZoors fell down s:owly about two meters,PeopZe who had aZready taken refuge on the ground reported that thebuilding bZock B severely knocked on the block A, and then the block Aknocked on the block B, and that immediateiy after these knockings thewhole building fell down as sZow as a slow--motion picture.(4) Aftev the earthquake ceased, the students in the upper stories triedto take refuge aZong the firehoses which were hanged from the window to theground and four students including a female student succeeded. In the 'meanwhile it was informed that the staircase in the east end of 'the

bu±Zding as well as the corridors of upper stor±es were stUl available topass through, and alX peassons eouid safely go outside.

126

5. Cheekup of the structuraX design of the bui].ding

The structune of the buLj-1.asng was caXcu:ated by iche "Standard Methodfor the CaXcuXation of Reinforced Concx'ete Structu:ees" recomrnended byArchi'tectvLral :nstitute of Japan. The strength of concrete was specifiedto be l80 kg/cma and the eoeffic: )nt of horizontaZ force was assumed to be

O.Z8. The procedure of nunericaZ caZeuZation was generaIZy aeceptabXe, but

the foZZowing questions were remained on the stvuctura: des±gn:(x)

(2)

adjacentnormalwhichthea prettymoment(3)

stiffnesshad vex'ypiZastersprettytheir ,maln(4)

of twoconsti7ucteddifficultthe case of a severe earthquake,

6. Some investigations after the earthquake

(1) The foundation of the buiZdrkng In spite of the heavy damage$ of the buiZding, it seemed that thefoundation of every column was not damaged, because the cracks which wereobserved in the footing-tie walZ-girders were very sXight. Whe resuZt ofthe survey on the leveZ of whole footing-tie walX-･girders which wasundertaken by ]YIr. S. Takamiya showed a maximum unevenness of about 5 cm.However, it is difficul't to judge whether this unevenness was directly

eaused by the earthquake or it was inherent £rom the t±me of construction The authors made a Zoad tes't on the ground neasc the buUd±ng toobtain the Xoact--depress±on cu:rves shown in ]Yri.g. ].7. As the estirnated

The connecting joint of coZuJnn and waZZ-gj.rder. a) The eecentricity between the axes of wall-girdex and coZumn wouZd cause a torsionaZ momen't in the colLum (]?ig. X4). However,

the effect of th±s eccentricity had been negXected. b) There was no consideration 'to seeure the anehorage of the

reinforcement qf walZ-girder to the colunm. Moreover, some of the reinforcement of waZ:-girder was arranged outside the reinforcement of the eoZumn (ffig. 4)e c) The effect of rigid zone of joine panel was neglected in the stress

anaZysis. Xt wouZd derive unsafe envoy for the estimation of bending moments of the membex}s.

The axiaZ reinforcement o±' coZumn The axial reinforcement oti] coZumn was saved about 20 % by taking the

reinforeement into considera'tion as is shown in Fig. 5. Xn the cai"eiZation, the reinforcement shouZd be 54--22(I} instead of 26--22cP

was specified in the bZue-print. Zt had been already cZarified by

authors that khose k±nds of saving of axrka: rel,nfovcement wouZd denive amount of decrease in coZumn strength in case of bi-axiaZ bending

e ?ilas'ters and internaZ wa2Zs Sinee the piZasters and the internaX walls which had ac'tuaZZy a Zarge

in the orig±nal s'tate were negZec'ted ti.n the stcees$ anaZysis, they poor reinforcement. Therefore, it can be supposed that the and those waXZs wouXd easrkZy be destroyed, because ichey would have Zarge share of shearthng force at firse. It can a:so be supposed thaic destruction wou].d eause a sudden increase of sheaning force in the columms. Zncomp:ete expansion joint The structures were caleuZated by as'suming that 'the buiZding eonsisted isolated blocks. However, the fZoor sZab of each story was continuously over the expansion join't. :t wouZd be very to estimate the effee't ol' 'the intexeaction between two bZocks in

e

127

weight of the buiZd±ng on eaeh footing of eo:umm was about 20 t/mZ, itcould be supposed that the design o£ footing had been reasonab:y aceeptabZeand probabZy uneven sett±ng of the £oundation would not oceur even in thecase of the earthqUake so far as the above-mentioned.Ioad test is referred.(2) [Dhe geoMogical survey of the underground Mr. S. Takamiya made a number of core-boring tests of the undergroundnear the damaged buiZding as is shown in Fig. Z8. The basic stratum of tuff is distributed at 8AJ9 meters under theground $urface. There are two layers of sandy loam of about 5 metersthickness above the stratum of tuff. The penetration test shows acomparatively small N-value for the lower Zayer- Besides, a very soft humusof 50 rv40 em thickness is sandwitehed between these two layers.(3) Period of mi.cro-tremor of the ground An investigation on the micro-tremor of the grounds was carried outby Mr. M. Kawaji. The resul.ts shown in Table 2 suggest that th'e groundnear the destroyed building might have a singular property fox theearthquake compared with the other ground.(4) Quality of concrete used for the building According to the observation on the crushed pieces of the concrete,the mixture consited of too mueh fine sands and very little quantity ofgraveZs. The compressive strength presumed'from the Schmidt hammer test

were considerably less than the des±gned strength as are shown i.n MabZe 3,Further, iche eompress±ve strength o£ eonerete sampZed from the skeXeton ofbuilding aZso showed poor values as axe shown in TabZe 4. These factsimmediately mean that the shearing strength of concrete as well as bond

strength between eoncrete and Teinforcement weve aXso infer±or to thespecified values i.n design. Of course, the influenee of the low strengthof concrete is to be most serious for the column.(5) Details of actuaX eoluLrnns

The cross-sections of 43 columns in the first story were carefuXlymeasured and it was found that 12 columns had obviously smaZler dimensionsthan the designed cross-section.

As regards the hoops of coZmms, they were distributed with a spac±ngof about 250 mrn though the spae±ng was specified to be 200 mm. Moreover,there was no hoop in the column a't some of the joint panels of columms and?i6' 5dePghod of proper vibration of bunding

An approximate calculation on the period of proper vibration of thenorth-west wing of the destroyed building was performed by the foZZowingassumptions: (a) The expansion joint was su£ficiently effective. (b) Lateral shear distributi.on coeffieient for the column was esti.mated by ''Dr. Muto's methed", As regards the waZX, the shea-ring deformation was taken into considerati.on, (c) The verti.ca]. Zoad was 'taken as the sum of the dead Zoad and the

decreased live-load accoyding to the officia]. specifieation of Japanese Building Code. (d) In the calculation for the short direction, bending and sheax'ing

deformations of slabs were taken into account, The two- dimensional modeZ of 4 mass points in vertical direction and 8 mass points in long direetion was adopted to represent the building structure. (e) The period of proper vibration was calculated by "?ower Method".

128

The results are summerized in Table 5, where A: aZl of the columns and pilasters had the stiffness, walls were also taken into consideration.

A': waZls in the first story on the both s±des of the staircase lost their resistance. B: only the pilasters in the first story lost their stiffness. C: all of the piZasters and waZZs in every story lost their stiffness.The resuXts of the same kind of the calculation on the non-damagedschool-buiZding are shown in Table 6. :t must be noticed that the plan ofthe three-storied school-buiZding was Zocated perpendicular to that of thedestroyed building.(7) Experimental study on the models of the coZumns. An experimental investigation was carried out to study the behavior ofthe faUure of reinforced concrete member under the combined stress of

axiai foree, bending moment and shearing force. The deta±Zs of the investi-gation are described in another paper.

7, Presumption on the causes of the destruction

It is said that people felt the vibration in the short direction atfirst. If the informations obtained from them were reUable, the defor-mation of the building in the short direction would have inf:uence on the

first damage, though the vibration in the long d±rection would also takepart in the faUure. The authors presumed that the first damage of the

bu±lding would be the failure of the walXs around the stairease in thenorth--west wing block. Because, the waZls were not designed to resist theshearing force, however the existence of walZs would eause pretty largeshearing force in them. It was a special feature of this earthquake that nearly constant

vibration cont±nued more than two minutes after the main shock of abouta haZf minute.

After the destruction of the above-mentioned walls, the per±od of theproper vibration of buUding would increase, as is suggested in Table 5(A'),and it would be possible that the deformation of buUdj.ng was intensified.The :arge$t deformation of the structuraZ frame wouXd oceur at the frameNo.7 or No,8, because the buUding was connected with the east wing blockat the frame No.Z6, and the frame No.1 was stiffened by the load-bearingwali. Moreover, the Zarge deformation in the short direction of the frame

would g±ve rise to the additionaZ deformation in the long direction due eothe open L-shaped plan of the building. It couZd be supposed that the repetition of such large deformationsof the frame was continued for a few hundred cycles and that the bondstrength between cOncrete and the axial reinforcement of column wasgradually weakened. Ii'inally the columns of the frame No.7 or No.8 were destroyed becauseof the resultant shearing forces･(in short direction and long direction)aeted on the cracked columns. And then the failure of aXl the columns inthe first story would be caused one after another. Therefore, the buildinglooked like to have fallen down very s:owly. Thus, the collapse of thebuilding would have started at the middle one-third of the north--west wing

block before the whole bu±lding was pulled down suecessively. It can be supposed that the out-door emergency staircase would be

shorn o±'f from the wall when the building was collapsed.

129

Table 1, WaZl rate in±n the f±rst

eachstory

directio" ?E.PthSII

CoMlapsedbuiXdinEastwing North-west.wzng

Survivedthree-'storciedbuikding.

ShortdireetionLongdirection

l2e24.3

2p6Oe9

The waZl rate means the ratio of the total Zength ofdirection of plan to the floor area. The vaZues inrepresented by converting into the nominaZ Zength ofthiekness of l5 cm so as to hold the cross-sectionaZthe same with that of the actual waZl.

walls in eachthe table adee

waZl with a area of wa:Z

TabZe 2. Period of micro-tremor (by ]vrr. M. Kawaji)

n

Orientation N-S E--W U-DPredom, Mean Predom. Mean P=edQm. MRalt

Position period period period per±od period per±od

Aroundthe a O.36 (O.IO O.26 Oe26 O.29destroyed Oe44 O.34building b o,lo O.2Z O.08 O.20 O.Z4 O.I5

i Oe1.8 Oe22 O.I8 o,2o Oe].6 O,:L6

c O.S2 Oe48 O.56o.so O,44

k o.so Oe44d Oe1-6 Oe28 O.44 O.46 Oei2 O.Z7e Oe44 Oe42 Oe24 Oe22f Oe14 O.z6 Oel4 O.i5 O.Z8 O,X6s Og52 O.54 Oe51 Oe]-6 Oe24j Oe44p Oe29 O.06 Oe25 Oel8 Oe27

Oe34r O.44

oOe45 O.35 O.Z4 O.2Z

The3-storied g O.iO o.zo O.08 Oe12 O.08 O.IOsehool- 2 O.06 O.].O O.l.O o.zo O.06 O.IO

bu.ilding

Thedormitory 5 O.10 Oe14 O.08 Oel2 O.IO o.zl

TheHakodate 4 o.Io Oel2 o.zo Oe].2 O,ILO O.Z2Techn.ColleeAhighschoo:

5 O.08 O.09 o.o2 O.07 O.08 O.09

TheHakodate 6 O.10 O.13 Oel2 Oel5 O.10 Oe:L5

,WeatherBureau

inthec±ty

l30

Table 5. Concrete strength preswned by Schmidt hammer

Colum Measuredhardness PresumedstrengthR Fckg/cm2

TCSt6-A 5Ze1 17Z

hD1CSIT 28e5 Z45

q,H tc$z 29el 1513 tCNf6 51.I l71-co tCNtT 50e3 Z60ajm tCNt8 31e3 Z75

tCNmo 28e7 147

?neran 159

1Csa 28o9 1491CSs 50.1 261tCs6 26o2 122tCS8 29o4 15･4

y tCS9 25.3 ll3,H.H..

tCSIO 31.9 l79

P1CSt2 55.0 190

gg tCSt3 37gl 230? tC$t6 34.8 208

stp tCNI 23.0 90ts tCN2 26.5 l25ta iCNfo 28o4 144

fCNtl 35.2 2J21CNI3 25e7tCNts 22eO 80sCN16 29o9 159

Mean 151

Hardness is theThe formuZa for

avexsagepresumpt

value oflon zs

measuredFc = IO R

values - 140

at 20o

points.

131

Table 4. Concrete (

strengthby Mro T.

by core--sampZingHattori)

Theposition Sizeof Specific Compr. Young'smod,testpiece

cm

gravity strengthkg/em2

a:ogc/k3g/c.2

column tCsq 15tpx30 2.21 I08 le52tCS7 l5epx15 2.18 1511CN9 l5rpxl5 2.18 76tCN7 lo.2".2o 2e24 102 l.44tCNT lo.2a.2o 2e25 105 l.27tCN8 15ipx30 2.22 (87) 1e38tCNS Z5epx30 2o23 96

p±lastertPNg

1PN915tpx3015epx30

2.172.17

170142

1.72,

1e54girder ?Gsm 15ipxl5 2.50 !30 l.52

Table 5. Theof

estimated period ofthe building

proper vibration( sec.)

A At B c

Longdirection Tl

T2T3

O.225O.076O.049

ua

mny

-

O,250O.081O.050

O.275O.095o.o62

Shortdirection Tt

T2T3

Oe229O.157O.110

O.283O.168Oell4

O.401O.222O.122

Oe552O.275O.I92

Table 6. Theof

estimatedthe three

periodstoried ofproperv±bration ･school-building (sec.)

Longdirection Tt oo 150

T2 O.058T3 o

o 039

Shortdirection Tl o e 222T2 o o

106T3 o

o 096

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