Proposed Field Test of Prestressed Reinforced Concrete Beam at Cobourg, Ont.

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Technical Note (National Research Council of Canada. Division of Building Research), 1952-10-23

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Marcon, L. J.

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DIVISION OF BUILDING RESEARCH

NATIONAL RESEARCH COUNCIL OF CANADA

TEClHIN][CAL

NOT FOR PUBLICATION

NOT]E

No.

131

FOR INTERNAL USE

.PREPARED BY

PREPARED FOR

L. J. Ma.rcon C.J1.&H.C.

CHECKED BY J. I. Lawson _{APPROVED BY}

R.F. Legget 23 October 1952 SUBJECT _{Proposed Field Test of Prestressed}

Reinforced Concrete Beam at Cobourg,Ont.

Defence Construction Limited are at present constructing for the Department of National Defence (Army) four large ordnance storage warehouses at Cobourg, Ontario. The buildings are located adjacent to main ｃｾｎＮｒＮ lines. Each warehouse will be 500 .,feet long by 250 feet wide, of single storey construction, thus covering an area of 0029 acres. It has been designed as a reinforced concrete

pile supported structure by C.C. Parker, consulting engineer of

Hamilton$ Ontario. Following the calling of public tenders, contract for the construction of the buildings was awarded to the Richard ,and B. A. Ryan Corr.pany of Toronto at a price of about $900,000 each. Large roof beams are

a

ｰｲｯｭｩｮ･ｾｴ ｰ｡ｾｴ of the design. For these bewns the contractor ｳｵ｢ｾｬｬｩｴｴ･､ an alternative design which had been prepa.red by the Precompression Comps.ny Ltc.r, of Montreal. After discussion, this design was accepted by the consulting engineer and by D.C.L., and the job is procsed:trg on this basis. Central Hortgage and Housing Corpor-ation, thj....ough the11' region.al office at Toronto are supervising and inspecting construction for ｄｾｃｾｌｯ In view of the innovations

presented by the new beron design, ｃＮｍｾｈｇｃｯ have requested the Division of Building Research, N.R.C., as their ":'esearch wing", to investigate the field testing of one beam to destruction.

(2) Details of Beams:

Each roof beam will consist of two precast prestressed fifty foot units, to the dimensions and shape shown on the accompanying

sketch. The beam will be made continuous over the centre support by the erection of two fifty foot units into place and the coupling of

these by means of the prestressing rods. Concrete with a

7

day strength of 5,000 p.s.i. is specified for the bewns. The prestressing wire

ｳｴｲ･ｾｴｨ requirements prescribed were as follows: Minimum yield strength (0.2%, offset) 160,000 p.s.i. and minimum ultimate strength 215,000 p.s.i. The Magnel system of prestressing is being used, load being applied to

the ｾ｡ｲｳ by means of a hydraulio jack. The gap between the fifty toot units will be filled with a dry pack· concrete mix. The beam receives

its ｾ｡ｴ･ｲ｡ｬ stability at the central support, since only at the centre support are the purlinsrigidly fixed to the beam.

.. ('I

., e.\.

..

2

-(3) ｾＮｧｲＮ and Test ｌｯ｡ｾＺ

The beams have been designed to carry a roof load of

40

pounds per square foot applied through purlins at the points shown in the sketch through brackets caet integrally with the beams. This amounts to a point load of

17,730

pounds for each point of

application. If, therefore, a test load of two and a half times the nOl"'IllaJ. live load is used" a total load of

151

tons would have to be handled. The i,might of each hundred foot beam is about 26 tons.

(4) f-ossi 'ble Te s t Meｴｨｯ､ｾＺ

Two methods of applying test loads have been considered:-(a) Dead loading supported at panel points; and

(b) Hydraulic jaoks or some similar mechanical system of loading, operated either in tension or compression. The idea of using dead ｷ･ｩｾｾｴｳ has been rejected because of the total loads which would have to be handled and of the fact that all expenditures for this part of the test procedure would be cQmpletely wasted. Further, there is no con.venient supply near the job of such concentrated loads of steel ingots in sufficient ｱｵ｡ｮｾｩｴｹ for the testo The ilecessary rigging would also be costly and complicated.

It has been suggested that a prestressed beam could be tested by using a reaction beam built into the ground which would be used to anchor the loading apparatus. The disadvantage of using such a beam is 'that it would have to be very large (about

3'

by

5'

by lOOt) and so be ve'!:'] expensive with no possible future use.

(5) §?sge5ted Test ｍ･ｴｾｾ､Ｚ

After most carof'al consideration, the staff of the Division have come to the conclusion that trill best method of test to follow will be to use two prestressed beams and to test one against the

other in a horizontal positiono This will involve the cost of a

second beam but it is thought that this ｷｾｬｬ be much less than the cost of building a special ｡ｮｃｾｬｏｲ beam. Expenditure on mechanical loading devices will not be 1-:asted since ｪ｡ｾｫｳ etc., and all

instrumentation will be salvaged and so be available for other usee. The exact method of applying the load will depend upon equipment which is found to be available or obtainable but rough sketches of possible set-ups are shown in the accompanying sheet.

(6) Bracket Tests:

In order to represent actual loading conditions, the beams should be loaded in the test by applying loads to the purlin seats. It is estimated that if this were done, the brackets might ｾ｡ｩｬ

shoul4 be applied through suitable saddles to the tops of the beams. In ｯｲ､･ｾ to complete the test, separate loading tests upon specimen

｢ｬＧ｡ｾＩＺＺＺＺ･ＭｬｾＸ Hill be undertakon upon broken beam samples obtained after theY' nave b6en loaded to ､ｾｳｴｲｵ｣ｴｩｯｮＮ These tests can be done in a laboratory with a standard testing machine.

(7) Pro"Eosed Loading Sclledllle:

It is proposed to apply loads in the test in accordance with tho procedur'8 in the National Building Code (p. 111). This specifies

ＡﾷｉｾｬｦＮｬ t: :

"When a load test is required by the authority having

jurlsd.iction,9 the member' or ｰｯｲｾ［ｬｯｮ of the structure under consideration shall be subjected to a superimposed load equal to one and one-half

times the live load. This load shall be left in position for a period of Ｒｬｾ hours before removal", Ii', during the test, or upon removal of the load, the member or por-t:ion of the member shows signs oi' weakness or faulty construction, it shall be reconstructed or strengthened in accordance with the requirements of the National Building Code.

"Ii' within 24 hours after the removal of the load, the slabs

or beaTTls do not Sl10W a 1'80overy of at least

75

per cent of the maximum

defleotion shovln dl1ring the 24 hours under load, the test loading shall be repeatedo The stru0ture·shall be considered to have failed to pass

the test if, within

24

hours, tte recover,rafter the seoond test is not at least

75

per cent of the maximum deflection shown during the 3econd testcli

To check on possible creep, it is suggested that the beams be then loaded to t.-lO and one-half times the design load and left in this condition for a period of two weeks. The beams would then be loaded to destructione The designer has stated that they will probably fail at a load of four times the design load which is equivalent to a load of 42.9700 lbs. at each panel point.

(8)

_{---_-.}

Instrumentation:_ｾＭ

Deflections would be measured at midspan and at all quarter points by means of dial indicators which can be supported independent-ly of the beams. Load measuring instruments will depend upon the method used for applying the loads but the possibility of using electric strain gauges is being seriously considered. Since the test will have to be carried out at the construction site, after the start of winter weather, instrumentation will have to be kept to the minimum possible, consis-tent with obtaining all essential information from the test.

(9) Conclusion:

The call to undertake this test has oome to the Division rather suddenly and it is required that the test be carried out with

4

-a M.:lnimu.."l1 of dej,.uy. It is believed that it will be the first test

of 'chis kind to be carri8d out in Canada; it will certainly be the first such test to be supervised ｾｹ the Division. This brief note has therefore been prepared to circulate to friends of the Division to advise them of the test in the first instance, and to solicit cl'i tical corrnnent and suggestions from all those who see the note and who have had experience in this type of test work. The Division would welcomes in particular, corrnnent on the following points:

(1)

Is the general test method proposed sound, in view of all tha circumstances?

(2) Subject to the availability of equipment, is there

any ｰｲ･ｦｯｾ･ｮ｣･ as between tension and compression

load:i.r..g«(

(3)

Has experience with similar tests shown the necessity for any special precautions either in loading or in instrumentation?

Search is naturally being made in the literature for reference to any relevant test procedures. A brief list of references so far discovered is appended; advice of other useful papers will be appreciatedo

Since the project is a public one, it will be possible for tho Division to publish the results obtained in the tests. It will

｢ｾ a special pleasure to see that COpio8 of all reports are sent to all to whom copies of this preliminary note are being sent.·

MAGJiliL, Gus tave

Prestressed Goncrete - (London-Concrete Publications Limi ted - 194.8)

ABELES:} P.. W.

The Principles and Practice of Prestressed Concrete-(Loncon-Grosby Lockwood

&

80n1 Ltd. - 1949)

KOMENDANT, AQEo

Preatressed Concrete Structures (New York-McGraw-Hi11 Book ｇｯｾｰ｡ｮｹ Inca - 1952)

FORNEROD, M.

Load & ｄ･ｳｴｬＢｵＰＧｾｩｯｮ Test of 160 Fte Girder Designed for

First ｲｾ｡ｳｴｲ･ｳＸ･､ Concrete Bridge in UoS.Ao (flliladelphia) Memoires Abhllndlungen Publications vol. 10 ... 1950 .. pages 11 to

35.

MACKEY, So

ａｾ Investigation of the Stress Distribution in a Welded Plate Girder for the Uargam Plant - {London - In the ｓｴｲｾｯｴｵｲ｡ｬ Engineer vol. XXVIII noo 1 Jun$ 1950 -pages 28 to

42;

MASTERMAN,. O"Jo

Prec..;t1"8ssed Conc!'ete Developments at the Field Test Unit Thatched Earn ｾＬ (London - In SJcructural Engineer vol. ｘｘｖｉｾｉ - noo 10 .. Oc'i:cber 1950 - pages 2l.j.6 to 264) ABELES, P"Wo

Breaking Tests on Three Full Size Prestressed Concrete Bridg8 Beams - (London - In the Structural Engineer vol. XXIX no. 5 - May 1951 - pages 149 - 160)

CEMENT and CONCRETE ASSOCIATION

Testing of Prestressed Concrete Footbridge at the South Bank, 29th, 30th April and 1st May, 19520

THE ARCHITECTS JOURNAL

Test on Prestressed Concrete Prototype Frame

(Westminster vol. 116 .. no. 3001 - September 4, 1952 page 295)

AUSTIN COMPANY

Austin Tests Prestressed Beams to Destruction - Cleveland (In Concrete .. vol. 59 .. no. 10 - October 1951

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