RILEM Reinforced Concrete Conference in Stockholm

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Technical Note (National Research Council of Canada. Division of Building Research), 1957-07-01

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RILEM Reinforced Concrete Conference in Stockholm

Legget, R. F.

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NATIONAL RESEARCH COUNCIL OF CANADA

7r

ｾｉｾ［［ｾ

ｾＺｾｇ

ｒｅＺａｾｾ

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No.

230

NOT FOR PUBLICATION

PREPARED BY RoF_o Legget CHECKED BY

FOR INTERNAL USE

APPROVED BY

PREPARED FQR

SUBJECT

DATE July, 1957

nRILEM" REINFORCED CONCRETE CONFERENCE

IN STOCKHOLM

Bond and crack formation in reinforoed concrete was th

subject of an ｬｮｾ･ｲｮ｡ｴｩｯｮ｡ｬ symposiumg held in Stookholm, Sweden,

from June 27th to 29th, whioh was attended by two hundred engineers

and-scientists from twenty-five countries. That a technical

sUbjeot apparently so detailed should have attracted such

world-wide attention might be urprising did it not ref1ect the keen

interes 1n Europe in the use of very high work1ng stresses in

both steel and onerete, and the steadily increasing reoognition

and use of ftul imat 10 d d ignn with reinforced concrete.

N"rth Amari an Interes was shown by the presence of

Raymond Co Reese, new Chairman of the AoCoIo Design Code Commi tee.

or

the two hundred participants, however» only eight were from he

WG tern Hemisphere (one each from Argentinsg the Dominica Republic

and Canad # with five from the U.SoAo}o One American paper only

wa subm1 ted, by Do atsteln and RoG. Mathey of the Division of

Building Technology of the National Bureau of Standards, Wa hington.

For y-four pap rs in all were accepted from fif een of the

oountries repre ented at the Sympos um o Al w re preprinted§ B

-ere also the ummaries by the gener 1 report rs for the eight

seotions into which the main subj et was bro n down. A th

conteren its lfp even these umma ies w re presented in abstrac

only leaving most of the e ing time for ge ral discussion 1

the two official anguagasg Eng 1sh a d Frencho This was add by"

m· skilful combined BWmmary and translation by 10 Cyong an

･ｬ･ｾｴｲｩ･｡ｬ englneerl

Discussion ranged from a thr a-dimensional mathematioal

analyst of crack formation, through a oona1d ration of wha e ctly

is meant by a "hair-o aek" to a critical analysis of he aotual

er ck found and mea sUI"ed in lS1"g gr ups of t1"ucture 1n Holland

and F'rano@0 Consensu of the mee ing ws s that!) a1tho-q,gh many

aspects of tra crac' ng n r Inforced eon rete are not y t 11y

und rstood,9 enough is own 0 sugg at ba ch crack ar - not

2

-generally caused by the use of porous concrete, nor those due to

shrinkage0 Once again, therefore, stress was placed upon the

basic necessity of obtaining concrete of the best possible quality, and upon placing it effioiently, if injurious effects upon

reinforoed concrete units are to be avoided.

Professor Waclaw Olszak of Warsaw, Poland, ｰｲ･ｾ･ｮｴ･､ to

the meeting the first version 1n English of a mathematical treatment

which he has developed which explains the formation

ot

_{cracks in}

reinforced concrete numbers under load, and does so in three

dimensions and for non-homogeneous ｭ｡ｴ･ｲｩ｡ｾｳＬＧｳｴ｡ｲｴｩｮｧ with an

investigation of principal stresses. Other more simple

two-dimensional theories of crack formation were presented and discussed. Some of these relate to the width of crack whioh may be anticipated and some to the probable spacing of cracks along a beam, the two being inter-related.

The application of the leading theories to the actual

results of 150 beam tests was analysed by Professor H. Rusch (of

the Technische Hochschule, Munich). By plotting values for the

difference between observed and theoretical values for crack spacing, divided by observed values, Dr. Rusch was able to show that all the main theories give results usually with an accuracy

of

70%,

the formula developed in his own laboratory having a mean

accuraoy of about ＹＵｾｯ

There was useful discussion about the actual widths of

cracks and the slippage of bars and their measurements, an ingeneous radiographic technique being described by Professor RoH. Evans and

Ao Williams of the University of Leeds, England. The one American

paper (by Watstein and Mathey) described the determination of the decrease in crack width between the concrete surface and the

surface of the reinforcing steel, a finding that was appreciatively mentioned by several discussorso

There was, however, a general feeling that since the width of cracks varies so much, and since cracks rarely form in straight lines, little was to be gained by attempting great accuracy in the

measurement of crack widthso This directed attention to a very

simple measuring device, described by JoF. Borges and J.A. e Lima

of the Laboratoria Nacional de Engenharia Civil, Lisbon, Portugal. It consists of a rigid plastic scale upon which are drawn a series

of black lines with thicknesses varying from 0.05 mm o to

5

Mmo

Used for direct visual comparison with cracks in beamsl it was

reported to be easy to use and to give reasonably accurate results.

ｾ

3

-Behind all the detailed oonslderation of crack widths 1s the supposition that there is probably some critical dimension

above which ･ｲＸｾｫｳ will csuse serious trouble through c0prosion

of thereinforeing steelo

After

a review

of all

the evidence

ｰｲ･｡･ｮｴ･､ｾ Profeasor Lobry

de

Bruynj) of' the Teehnisohe aogeschool.

Delft9 Holland,ry reported that there was still no ｡ｧｲ･･ｾ･ｮｴ as to

what this dimension was and that other instigators of corrosion. particularly the use of porous concrete,ry were probably of much more serious moment.

This view was reflected by a report presented by

L" Carpent1erj) Chief' Engineer SoN oCoFo9 ParisD upon the study

of the results of a questionnaire ciroulated in conneotion with the very large number of reinforoed concrete structures now in

us on e ｾ nch N tiona R 1lw YSo Although the replies received

were vari ble in v 1 eo ina they were SUbjective to a considerable

d gz-eel> hey did show tha l'ansverse c:racking has not been harmful

in gen 1"81 Ｈｾ tho ,gh 10 g1 dinal cl"'acking

at

_{beams has been), the}

general cono uslon ｢･Ｑｮｾ the the survey had revealed nothing to

ugg st any dep rtur f,rom the at ndard ｾｴｨｯ､ｳ of reinforced

oonorete design used by'SoNoCoFo

A similar oonolusion could be drawn from reports presented

by Prof'esao1" AoM8 Raaa (of the,Teohnische Hogeschoolg Delft) upon

field surveys of oracking In

165

exposed structures in the Netherlands,

and upon

140

proteoted ｳｴｲｵｯｴｵｲ･ｾｯｕｳｩｮｧ the Dutoh ruatgrade IV

as a ｯｾＱｴ･ｲＱｯｮｄ the results showed that only for cracks wider than

ｏｾＷｭｭｯ was rusting or the steel always worse tha,n the c;riterion

adoptedg and this 0 ly for he xposed structurese It was stressed

that this ra ult was p 11 n y 0 ly and all those attending the

conter ｮｾ re ged 0 do al they could to assembJa more field

､｡ｴｾ of ｡ｾ 81 r oki g9 and B e ｦ･ｾｴｳＹ as one of the soundest

as _{ｾ pon which farth ｾ advan in ｲ･ｩｮｦｯｾｾｾ､ oonorete design can}

be fom-ideao

Amongst gaps in the present ｾｴ｡ｴ･ of ｾｯｷｬ･､ｧ･ which were

stressed were the problsM3 of eraoking due to shear stressg and the

ｯｲ｡ｾｫｩｮｧ of ｾ･ｩｮｦｯｲ｣･､ ooncrete ｷ｡ｬｬｾ UIlder load o Gaps of another

oort were highlighted by reportaJ of the chaotic state

ot

_nomenclature

for reinforoed concrete ､Ｖｾｩｧｮ ｴｴｾｴ was revealed when individual

national design speeificat10ns were axamineao

An

unusually interesting

presentation by Professor ｍｵｲｂｾｾｨ･ｮ of ｍｏｓｾｏｗＹ UoSoSoR09 introduced

not only a new basis for r6inforced concrete design but still further

varlet, ｯｮｾ in t rmino ogre ｰｾｯ Issor ｍｵｲＢｾｳ･ｨ･ｮ presented a eopy of

the bo in whioh his new,' ry 1s published» to

the

Chairman of

the Symposiume A ｾｯｵｧｨ t· ns atlan of the title Ｑｾ "Crack aesistance,

Stiff as and Strength of R 1 or ad Concrete"o (Copies of the book

and of the enta iv d sign c d based upon the theory are available

... 4

-The meetings featured a good deal of discussion of the

pros and cons of the standard pull-out test for bond. Professor

Ao Paduart, of the Free University of Brussels, Belgium, proposed

a new set of standard dimensions for pull-out test specimens, .

based upon the. diameter of the bar being tested. This proposal,

and a strongsugge s tion tha t some ac tion be taken to promote uniformity in nomenclature, was passed by the Conference for consideration to the Permanent Commission of RlLEM (under the auspice s of which the Symposium was' organized), with appropriate reference to the work of the recently activated Technical Committee

71

ot _I.S.O.

-The Symposium was organized and conducted under the

distinguished leadership of Dr. Georg ｗ･ｳｴｬｵｮ､ｾ the Director of

the Swedish Cement and Concrete Research Institute. The papers

and discussions w11l eventually be published in three ｶｯｬｾＸＺ

inquir1es should be addressed to the Secretary of the Conferenc•• Dr. Sven edman, care of the above noted Institute, Drottn, Kristinas

Vlg. 26,

Stockholm

70,

Sweden.

RlLEM is the short name ot the Interna tiona 1 Union of Testing and Rese"arch Laboratories tor Materials and structure,

first formed in

1947.

It now has over

400

individual members,

representing

250

research organizations in

37

nations. The

SecDetary General is MoRo LIHermite, whose office is at 12 Rue Brancion, Paris, Franceo

\.

,