Canadian use of precast concrete units

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright

Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.

Questions? Contact the NRC Publications Archive team at

PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.

NRC Publications Archive

Archives des publications du CNRC

This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Canadian use of precast concrete units

Holbek, K.

https://publications-cnrc.canada.ca/fra/droits

L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site

LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.

NRC Publications Record / Notice d'Archives des publications de CNRC:

https://nrc-publications.canada.ca/eng/view/object/?id=e89a3fcf-dbc0-41a5-93a8-9537e3f43da7

https://publications-cnrc.canada.ca/fra/voir/objet/?id=e89a3fcf-dbc0-41a5-93a8-9537e3f43da7

Ser

'

rHt_

N21t2

no. 216

e . 2

BTDG

NATIONAL RESEARCH COUNCIL

CANADA

CONSEIL NATIONAL DE RECHERCHES

30665

Canadian

Use

of Precast

Concrete

Units

A N A L Y Z E D

by

K. HOLBEK

(President, Schokbeton

Quebec

Inc., St. Eustache,

Quebec)

q:i611

Reprinted from

"Towards Industrialised Building" The Third CIB Congress, Copenhagen, 1965

Technical Paper No. 216 of the

Division of Building Research

OTTAWA

April, 1966

NRC 8957

-2 - 7 / Y X ' / '

This publication is being distributed by the Division of Building Re-search of the National ReRe-search Council. It should not be reproduced in whole or in part, without permission of the original publisher. The Division would be glad to be of assistance in obtaining such permission.

Publications of the Division of Building Research may be obtained by mailing the appropriate remittance, (a Bank, Express, or Post Office Money Order or a cheque made payable atpar in Ottawa, to the Receiver General of Canada, credit National Research Council) to the National Research Council, Ottawa. Stamps are not acceptable.

A coupon system has been introduced to make payments for publi-cations relatively simple. Coupons are available in denominations of 5, 25 and 50 cents, and may be obtained by making a remittance as indicated above. These coupons may be used for the purchase of all National Research Council publications.

A list of all publications of the Division of Building Research is available and may be obtained from the Publications Section, Division of Building Research, National Research Council, Ottawa, Canada.

Canadian use of precast concrete units

In the continuous efforts by Canadian builders to keep actual building costs down, by the Canadian architects to look for better buildings materials, and in the day-to-day fight for pro-fitable markets in the highly competitive construction field in Canada, the precast concrete industry was born and has come of age to a degree where it now occupies a substantial part of the over-all building material market, all within a little more than a decade.

The demand to reduce manpower requirements at the site, to decrease the overall construction time and to make construction efficient throughout the year, notwithstanding the comparatively long and severe Canadian winters, led to a national market for precast concrete in the early fifties, served mainly by a few pioneers who startod specialised firms in this field. Some of these pioneers have built their firms into substantial plants to-day, others have fallen by the wayside but their place has been taken by new firms, in many cases offsprings of firms already established in the building industry and having the necessary funds to start and maintain a proper precast concrete set-up.

The development ofprecast concrete units, however, has been hampered by several factors which undoubtedly are common in varying degrees in many other countries. Peculiar to Canada are the widely scattered isolated market areas covering not more than half a score spread from the Atlantic to the Pacific. A11 these ditrerent areas are governed by different Provincial and/or Municipal building codes, most of these with no provisions for precast and/or prestressed concrete and only recently has a national building code comprising this item been developed, but the speed by which this has been accepted across the country is most encouraging.

Another factor holding back the development of precast is the complete lack of standardisation of even the simplest building components, and modular construction is practically unknown in Canada. Some manufacturers have standardised sections on a local basis only, as described later.

Furthermore the Canadian construction practice of bidding jobs based upon architects' drawings and specifications still leaves plenty of opportunities for substitution of material and conse-quently does not encourage extensive special pre-bid research, testing, mock-up or investigation for specific jobs. Also by limiting the engineering and production time between orders and deliveries the advantages of prefabrication are diminished to some degree.

Most of the specifying authorities cannot specify special pro-cesses or systems, either from an engineering or production basis, but must keep the bidding open for all the different manufacturers with the result that all the details, joints, connections, handling and erection, which are often the key to an economic solution, do not fit any particular manufacturer, and changes and substitutions at this stage normally do not improve the picture.

Although the National Research Council has done a tremen-dous amount of research and work towards making the construc-tion industry an all-year round operaconstruc-tion, it is only recently that this research has included prefabrication. The same can be said about the cement companies but fortunately there are recent developments towards more applied research in the field of pre-cast concrete. Sporadic research in this field is also carried out at the Universities. As this research becomes more generally availa-ble the results will appoar at the educational level thus making the designers of to-morrow more familiar, not only with the advan-tages of prefabrication but also with the discipline it enforces on designers.

Last, but not least, the strongest deterrents against prefabri-cation to day are the so-called "hidden taxes" on the materials at the manufacturing stage. In Canada provincial taxes vary from Province to Province, up to a maximum of 6)1 and recently an additional lllFederal Sales Tax was imposed. The initial efect of this was to penalize prefabrication compared to on-the-job manufacturing by the general contractors thus emphasizing the climatic cycle operations of the construction industry. Some

F t .

improvements have been negotiated but this problem is not easy. It helps, however, to explain the complete non-existence of some precast products in Canada which have been precast in Europe for decades.

The precast concrete industry in Canada has developed a pro-duct range which can be divided into two main categories:

1) Standard products made from standard permanent forms with some adjustments for variations in height, width, etc. the use of which is promoted by extensive sales literature covering all physical and design criteria in easy-to-read table form.

2) Custom designed products to suit the individualjobs. Among the precast standard products the main items are: - Flat Hollow Core Slabs varying from 16 in. to 48 in. in width, and depths from4" to 8" with spans up to 30 ft;

- Double Tees also called Twin Tees, Wing Slabs, etc. varying from 4 ft. to 8 ft. in width and from 12 in. to 24 in. in depth, giving spans up to 75 ft;

- Single Tee Slabs or Lin Tees varying in width from 4 ft. up to the Giant Tees of 10 ft. width in depths from 8 in. to 54 in. providing spans well above 100 ft.

In the second group the main products are precast beams and columns, special structural shapes like arches, folded slabs and particularly all architectural concrete panel work.

Most plants are producing products within both groups and mostjobs involve products from each. In the field ofstandard pro-ducts the technological changes in the production, combined with a broader acceptance of these standard products, have resulted in a "big volume" approach to these items, with a consequent competitive price range and fairly standard quality controls.

The second group ofproducts has been helped over the last few years by the increasing average size of the jobs which, to a casual observer, appear somewhat bigger than individualjobs in Europe, outside of Government developments. Consequently custom features, like special desigrrs and forms, can be kept to a manage-able portion of the overall cost.

The most significant development in the precast concrete in-dustry during the last few years has been the ability of the indus-try to make their products fulfil several pwposes simultaneously, that is in combining architectural and structural qualities and incorporating as many of the services as feasible.

The highly competitive marketing of the precast concrete has developed many ingenious solutions to specific jobs by using standard structural units for architectural purposes and vice versa (the use ofpanel walls for structural purposes). This development was partly caused by a selling philosophy rather than a design approach. (See figures I and 2\.

Fig. 1. Load carrying, insulated, one storey office wall panels

F t .

Fig. 2. Window-wall panels used as outer bearing wall for pre-cast floor units at McGill University Arts Building.

This development has been highly successful on outstanding individual jobs and as designs improve with respect to weather resistance, insulation, moisture control etc. the technology devel-oped may eventually lead to some standardised and modular design throughout the country.

This development is especially apparent in the institutional, industrial and commercial field where Canada is now catching up with the European practice especially in the architectural treat-ment of panels and the increasing sizes of these panels.

The main reason for the trend towards larger panels is to cut handling and erection time but although great strides have been made we arc a long way from the mechanised erection of most European countries.

In areas other than institutional, industrial and commercial. such as the housing field in all its aspects, from single dwelling to multiple dwellings, prefabrication is practically unknown in Canada. This is partly due to the factors mentioned earlier in this paper as affecting prefabrication in general but also due to the availability oftraditional wood and a consumer resistance against buying prefabrication which the layman still considers synonym-ous with uniformity in appearance.

Since the war the percentage of multiple family dwellings of the overall dwelling construction has remained constant at about 25\ and both types of dwellings have mostly been built by in-dividual small to medium-size contractors, thus making all eforts by the precast industry towards standardisation, planning and development of reasonable size projects rather frustrating.

There are, however, signs that the 25 \ is going to increase and as bigger developers also appear to be interested in this market we may be entering a construction phase similar to the European practice over the next decade or two.

As an indication of the growth irf the precast industry, it is interesting to note that more than twenty companies from coast to coast, representing 901 of the precast concrete industry have been able to form the Canadian Prestressed Concrete Institute and in less than two years have produced a 500-page handbook of precast prestressed concrete covering the Canadian codes,

ex-273

planations and comments on same, particular design applications and graphs, typical specifications and plant requirements, and last but not least a considerable amount of connection details based upon a design philosophy which should help the future designers towards a better understanding of the proper applica-tion and detailing of these all-important connecapplica-tions.

It is exceedingly difficult to cover any particular development of the precast concrete industry or to draw any conclusion of any advanced design or technology not previously experienced or solved by the precast industry in other countries, mainly because the precasting technique is still so much on a custom-designed and custom-made basis as described above.

Although the industry has produced jobs across the country of outstanding design, production or erection qualities which have created considerable interest also outside its border, we still con-sider ourselves on the receiving end of any research developments and find an easier task in listing the technical and economic problems yet to be solved. Undoubtedly some of these problems are common to other countries and it is possible that in many cases solutions have been found but communication between the national research organizations, or between the individual companies and their national research bodies is not yet function-ing smoothly enough.

Here again the highly competitive nature of the construction industry and the young age of the precast industry combine to make most firms ignore any long-term or complicated research, and the research and testing departments of these firms have been tied down to day-to-day production problems urgently demanding solutions because valuable time and production costs were in-volved.

Therefore the industry has yet to face the need for a broader and more forward looking research, and it is the writer's opinion that this must be done by the industry as a whole either as direct participant in such research or at least as a guiding participant or coordinating factor among the existing research facilities such as the National Research Council, the Cement Industry and all the many new University facilities.

Among the more important technical problems facing our in-dustry to-day are:

1) Insulation of wall panels suitable for present-day humidified and air-conditioned high-rise buildings;

2) Actual stress deformations due to temperature changes with the wide and rapidly changing range experienced in the Canadian climate;

3) Earthquake criteria for design of precast structures; 4) Improved low-cost joint details with a minimum of mainte-nance and site work;

5) Additional testing of connections to determine ultimate strength and to develop desigp criteria.

Some ofthe above problems have undoubtedly been solved in other countries but many ofthese solutions are not suitable for the severe construction problems in Canada caused by the great distances, remote construction sites and the severe winter condi-tions.

As a typical example it is worth noting that connections be-tween precast elements in Canada must be bolted and /or welded. Any casting on site without protection and heating is impractical for nearly half the year and consequently cannot be considered at the design stages when timing of the job is uncertain.

The Canadian Prestressed Concrete Institute is now seriously considering this connection problem and will probably €nlist the help of several university facilities and research programs to complete their program, which entails extensive testing of re-commended standard connection types.

If the Canadian precast industry should make strides in solving any of the above listed problems it may be able to convey these results into research papers useful for other countries or research bodies and we are looking forward to the day when the exchange ofresearch and development techniques in our particular field is a two-way street, both for collection of results by others and publication of our own research achievements on a broader basis than is presently the case.