Cobourg Beam Test: Fourth and Final Progress Report

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Technical Note (National Research Council of Canada. Division of Building Research), 1953-08-20

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Cobourg Beam Test: Fourth and Final Progress Report

Marcon, L. J.; Legget, R. F.

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DIVISION OF BUILDING RESEARCH

NATIONAL RESEARCH COUNCIL OF CANADA

.,'

'Jr

E

C

1HIN II CAlL

NOTlE

No.

153

NOT FOR PUBLICATION _{FOR INTERNAL USE}

CHECKED BY

ｾ Aug.20, 1953.

PREPARED BY L.J.Marcon

R.F.Legget

PREPARED FOR

Central Mortgage and Housing Corporation.

SUBJECT

Cobourg Beam Test

Fourth and Final Progress Report

APPROVED BY _R.F.L.

SPECIAL NOTE: THIS REPORT IS A SUMMARY OF THE RESULTS OBTAINED IN THE TEST. IT IS ISSUED FOR PRIVATE INFORMATION ONLY WITH THE APPROVAL OF CMHC. NO INFORMATION IN THIS NOTE IS TO BE REPRODUCED OR USED IN ANY FORM WHATSOEVER. A FINAL AND COMPLETE

REPORT IS BEING PREPARED AND SHOULD BE AVAILABLE BEFORE THE END OF 1953. IT IS HOPFD THAT A SUMMARY OF THE COMPLETE TEST MAY EVENTUALLY BE PREPARED AND RELEASED FOR PUBLICATION.

This note is to record the results of the tests on the prestressed reinforced concrete beam at Cobourg, preparations for which have been outlined in three previous progress reports (Technical Notes No.131,

No.150 and No.152). The loading of the test beam was carried out succeas-fUlly in accordance with the outline given in Technical Note No.152.

After being under load for approximately one month, the beam was finally subjected to extreme loading on August 6th. A number of those to whom copies of these notes have been sent, and other representatives, were present on this occasion. The beam was finally subjected to a load consist-ing of dead load plus five and a half times the live load without failure. At this point one of the jacks became displaced, it is believed through a broken shackle bolt in one of the transom fittings, and this displaced the entire test setup. The beam sprang back and regained its original position, again without complete failure, although with some serious cracking.

After careful consideration of all factors, it was decided not to go to the trouble and expense of rearranging the entire test setup merely for the purpose of breaking the damaged beam. Tests were conducted on the. strength of the purlin seats before the beam was finally broken up and

removed. The test setup and instrumentation all worked most satisfactorily so that the, test has yielded all the anticipated information except the actual ultimate breaking load.

4It

The following is a brief factual summary of the significant features of the test:- Dead load of roof structure is equivalent to 37.4 psf of roof area. Dead load at each purlin point is therefore

7.78

kips. Total dead load carried by 100 ft. beam is

85.6

kips. Live load is 40 psf of roof area. Live load at each purlin point is therefore

8.)2

kips and total live load carried by complete beam is 91.5 kips.

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NOe Date May 25 1 June 30 2 J1.+ne 30

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Jqly 1 July 1 .July 2 2

-LOADS APPLIED TO' BEAM Load

-Beam prestressed

Dead load (D.L.) of roof structure (37.4 pst)

Dead load plus 100% Live load (77.4 pst)

D.L. plus 100% L.L. (77.4 pst)

D.L. plus 150% L.L. (97.4 psf)(National Building Code Test) Load held tor 24 hours

Asymmetric loadings . Span A Span B

ｾ

7 8 .July 2 July 3 Jllly 3 Aug.

5

Aug.

5

D.L. plus 100% L.L. (77.4psf) D.L. (37.4 psf) D.L. (37.4 psf) D.L. plus 100% L.L.(77.4 pst)

D.L. plus 150% L.L. (Both spans 97.4 psf). This load was held for

28

days. Load removed on July 31st.

ｄＮｌｾ plus 2 L.L. (117.4 psf) Asymmetric loadings. Span A Span B 9 10 Aug.

5

11 Aug.

5.

12 Aug.

6

ｬｾ Aug.

6

-. T

6

.1.4 Aug .. C.L. plus ｬｾ L.L. (97.4 psf) D.L. (37.4 psf) D.L. (37.4 ｾｳｦＩ D.L. plus 2 L.L. (117.4 pst)

D.L. plus 22 L.L. (Both spans 137.4 psf) Load

D.L. plus 3 L.L. (157 psf) D.L. plus 3t ｌＮｾＮ (177 psf) D.L. plus 52 L.L. (257 psf)

This load was just rea.ched when the jacks were displaced.

•

•

3

-DEFLECTIONS

Prestressing the beam raised the mid span points 0.14". The deflections recorded below are' maximum values obtained: Symmetrical Loads

Dead load

Dead load plus 100% live load D.L. plus It L.L. D.L. plus 2 L.L. D.L. plus

J

L.L. D.L. plus

4

L.L. D.L. plus

5

L.L. D.L. plus

5i

ｌＮｌｾ Asymmetric Lpadings D.L. plus 1 L.L. D L• • p us1 Ｑ ＭＲｾ L L• • D.L. plus 2 L.L. 0.11" 0.22" 0.29" 0.34" 0.55" 1.21"

2.6"

3.3"

O.Jl"

0.42"

0.50" National Building.Code Test

On applying D.L. plus It L.L. the beam deflected 0.295". After a 24 hour period the deflection increased to 0.341", or an increase of 115%.6n removing ｬｯ｡､ＮＭＯｾ･ deflection

recovery was 95%. The National Building Code minimum is 75%. Sustained Load Test

On July 3 the beam was loaded up to D.L. plus l t L.L. Beam sustained this load for 28 days. On July 31, the load was removed and beam was allowed a 5 day recovery period.

Immediate deflection after applying D.L. plus It L.L. was 0.287". After 28 days this deflection increased to 0.431, or an increase of 150%. After the

5

day recovery period the deflection was reduced to 0.114".

CRACKS IN BEAM

The first cracks were noticed two days after the sustained load of D.L. plus l t L.L. was applied to the beam. This crack appeared at the top of the center haunch. When the load was incr&ased to dead load plus 2t L.L. the first cracks at the center of Span A appeared. Unsymmetric loading of D.L. plus 2 L.L. produced further cracks at the same location.

Under increased loads, cracking increased at the locations mentioned and in other places. A detailed record of the

cracks was obtained and will be reproduced in a final report. Under extreme loading some of the cracks extended up to the neutral axis of the beam but all of these closed up when the load was released.

4

-After the almost instantaneous release of the maximum load, the beam whipped back into its horizontal position, displacing itself slightly in a horizontal direction. In its rebound, it must have reversed its curvature since five cracks were found later in the tension flanges of

the beam and these had not healed up as did all the previous cracks under normal loading •

. Those in the Division of Building Research responsible for this test would like to record here their appreciation to those who attended the test on August 6th for their

interest. As has been made clear in these notes, the entire test project has been a co-operative venture between D.B.R.

and the Research Division of the Hydro-Electric Power Commission of Ontario, to the staff of which thanks are

here recorded for their invaluable ｡ｳｳｩｳｾ｡ｮ｣･ and co-operation. The staff at Cobourg of C.M.H.C. and the various contractors involved have been most helpful as have also local

representatives of the Canadian Army. Without the remarkable co-operation which featured all aspects of the project, it could not have been brought to such a satisfactory conclusion.