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Testing the Efficiency of Wood Epoxy Reinforcement SystemsAuthor(s): Paul StumesSource: Bulletin of the Association for Preservation Technology, Vol. 7, No. 3 (1975), pp. 2-35Published by: Association for Preservation Technology International (APT)Stable URL: http://www.jstor.org/stable/1493504 .

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TESTING THE EFFICIENCY OF WOOD EPOXY REINFORCEMENT SYSTEMS

by Paul Stumes P. Eng.*

INTRODUCTION

Wood, as a structural material, is constantly exposed to several agents of deterioration, such as fungus, insects, vandalism, etc. The likelihood of deterioration increases with age, therefore the preservation and rehabilitation of wood in historic structures is a major concern for conservationists.

Modern wood preservatives are usually well suited to retard the deterioration. However, up till quite recently there were no methods at our disposal to rehabilitate those structural members which were at an advanced stage of deterioration and could no longer carry their load. Such members had to be replaced with new timber. In historic buildings this is an undesirable practice because it destroys historically or artistically important materials. Consequently there is a great need for a technique which can restore the original strength of deteriorated wooden structures, in situ.

An intensive search for a suitable technique has been carried out for a long time, without any real success. Finally during the past two decades the introduction of epoxy resins to the field of historic restoration, brought about some encouraging new results.

Independently, and often unaware of each others work, preservationists in many countries have developed certain new methods for the rehabilitation of decayed structural timber. These methods, which are basically the same, replace the missing wood with an epoxy resin and reinforce the decomposed sections with high tensile inserts. Such systems have been in use for sometime in Canada, the Netherlands, the United Kingdom, the USA, and other countries.

Just recently in the APT Bulletin (Vol. VII, No. 1, 1975) Mr. T.H.M. Prudon provided a very interesting account of the so called "BETA" system.

Our readers will find some illustrations in this article about a project, in Canada, where a similar method has been used. The building is a 17th century masonry structure in Quebec City (See Figure 1 and Figure 1.1).

* Mr. Stumes is a Restoration Engineer with the Restoration Services Division, Department of Indian and Northern Affairs, Ottawa.

ADr Vol. VII No. 3 1975 2



Fig. 1 Houses on Quebec City, P.Q. were used in the ( 40, the house in 1

ADr Vol. VII

the C6te du Palais, W.E.R. systems

conservation of No. the foreground.

No. 3 1975 3

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- ~ e x .. ... o * .. .. r / ...i . -4L^

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Fig. 1.1 W.E.R. reinforced floor joists in No. 40 C6te du Palais.

Key: 1. Masonry of external wall. 2. Decayed end of floor

joist. 3. Steel reinforcing plate. z. Floor joist. 5. Floor board.

The upper photograph shows a view from below, and the lower is a view from above.

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For the sake of simplicity, in this article the rehabilitation of decayed wood with epoxy resins and reinforcements will be called the W.E.R. system.

This name originates from the initials of the basic components:

W - ood E - poxy R - einforcement

THE ROLE OF THE COMPONENTS OF THE W.E.R. SYSTEM

Basically, the W.E.R. system is the replacement of the disintegrated parts of the wood with an epoxy resin, and reinforcement with high tensile inserts.

If the natural cavities inside the wood are not suitable to receive the reinforcement then concealed grooves are cut for this purpose (See Figure 2).

The role of the components could be summarized as follows:

Wood

In general, the remaining structural strength of the decayed wood is fully utilized. If the deterioration is too advanced, then the wood serves only as a mould and the load is carried by the epoxy and the inserts. This permits the preservation of important historic material even when it is too weak to carry its own weight.

Reinforcement

Reinforcement carries the tension, compression and shear components of the stresses. It has the same role here as the steel bars have in concrete.

Glass-fibre, aluminium, steel, or other materials may be employed as reinforcement. The most economical in our experience in the majority of cases, is the use of round steel bars.

Epoxy Resin

Epoxy resin has a double role in the W.E.R. system. First it replaces the decomposed or missing parts of the wood, in every respect. It will fill the voids and will also add considerable strength. The structural strength of epoxy is 2 to 3 times that of the sound wood. Epoxy adheres equally well to wood and to most reinforcing materials, such as steel, aluminum, glass-fibre, etc. This ensures that the dissimilar materials are permanently bonded together and under stresses they react in unison. It should be noted that epoxy does not adhere to polyester resin. Epoxy is

A r Vol. VII No. 3 1975 5



Wood reinforced with metal plate. Improved compression, tension and horizontal shear strength. Much improved Modulus of Elasticity. Slightly improved buckling.

Wood reinforced with strategically placed bars. Much improved tension and compression strength. Improved resistance to deflection. No improvement in buckling.

Wood reinforced with double tension and compression bars. Structural strength improved all around. Great resistance to buckling. Reinforcement completely concealed. Installation may be difficult.

Fig. 2 Typical sections of W.E.R. systems.

Vol. VII No. 3 1975 6

N

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ADr



injected into the wood in liquid form. It has the ability to completely fill all irregular shapes, and it hardens without appreciable shrinkage.

The manufacturing process, and certain chemicals which are added by the manufacturer, have a marked effect on the properties of the epoxy. Two types of epoxies are used most frequently for the W.E.R. system.

Type A: This is the epoxy which is generally available from most suppliers. It is sometimes called "casting epoxy resin" and is widely used for the fabrication of high strength, thin wall, F.R.P. structures (Fiberglass Reinforced Plastic). This type of epoxy is suitable where a high strength adhesive film is required or for penetration of porous materials. It may be brittle if used in bulk and it can be sensitive to great variations of temperature.

Type B: These are the epoxies which are either manufactured specially for the W.E.R. system or have been converted by the user with appropriate additives. Certain brands of epoxies which are made for structural repairs of masonry, also belong to this category.

WHY THE TESTING PROGRAM?

Unfortunately some of the developers of the W.E.R. systems have not taken all the properties of the components into consideration. Sometimes the design of reinforcement is based on rules of thumb and on loosely founded assumptions. The volume of resin, the size and positioning of reinforcing bars, etc., have been left to the judgement of the restorer. Our engineers, who are accustomed to the scientific mathematical design of structures, could not accept this risky situation. They would not face the possibility of a structural collapse, nor would they approve the waste of consistently over- sized components.

In order to place the design of wood rehabilitation on a technically acceptable foundation, we, at the Restoration Services Division of D.I.N.A., initiated an extensive testing program.

The purpose of the testing program has been twofold:

(1) To find the latent weak points of the W.E.R. system and its components.

(2) To establish valid design parameters.

A:) Vol. VII No. 3 1975 7



For our tests an epoxy resin was selected, which was commercially available from handy sources all over North America. I do not have to stress the importance of this point to those of my collegues whose efforts were hindered by the complications of ordering certain materials from overseas. Our epoxy belonged to the previously described Type B.

Following a pre-selective process, we added 25% (by weight) of Diatomaceous Earth to the epoxy. This material proved to be an inexpensive bulking agent. Also, it increased the heat resistance and resiliency of the resin.

In our tests ordinary mild steel bars and plates were normally used as reinforcement. These provided the most favourable weight to strength and rigidity ratios.

All tests, and most of the testing apparatus, were designed by the writer of this report. The tests were carried out during a two year period by the following institutions:

Conservation Laboratory, Restoration Services Division, D.I.N.A:

Glue line test, Effect of preservatives.

Building Research Division, National Research Council:

Fire rating test.

Eastern Forest Products Laboratory, Environment Canada:

Exploratory test, Effect of preservatives, Structural strength tests.

Laboratoire de Construction du Quebec, Inc.:

Glue line test, Heat expansion, Adhesion at high temperatures, Loaded composite beams at high temperature.

This article presents to the readers of the APT Bulletin the results of these tests, in a concise form.

THE TESTING PROGRAM

1. Exploratory Test

An exploratory test was conducted first to ascertain the feasibility of the concept prior to expending substantial sums on the test program.

A^r Vol. VII No. 3 1975 8



50 / ORF WOOD EA,Ws,3H H GrOU.-H

Drawing of test specimen

Sound wood

I

Split under pressure V04 W.E.R. Reinforc..... t Reinforced.

Photo of specimen after test F. 3 Et ... s

Fig. 3 Exploratory test of a W.E.R. system.

AF ' Vol. VII No. 3 1975 9

Lr\ ON

4,,

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II



The exploratory test was carried out on a simulated "partially deteriorated" beam. The deterioration of the beam was simulated by cutting through the material by 50% in one location and 95% in another. Such conditions frequently prevail in wooden beams which rest on masonry walls.

This beam has been reinforced with the W.E.R. system and tested. It was simply supported at both ends and a concentrated load applied at the centre of the span.

After the application of sufficient pressure, the sound wood split at the centre but the weakened end with W.E.R. reinforcement stayed intact (See Figure 3).

Following the encouraging results of the exploratory test, funds and other resources were allocated to the project.

2. Glue line test

The W.E.R. system is at optimum efficiency when all components react together. Consequently, the adhesive strength of the epoxy is a most crucial factor.

A. Wood

The adhesion between wood and epoxy was tested at the Laboratory of the Restoration Services Division. Thirty test specimens were prepared by gluing three pieces of wood together with epoxy and exerting pressure on the center piece.

In all but 17% of the tests, the wood failed but the glue line remained intact. Closer examination of the specimens disclosed that in every case when the glue line failed the epoxy had not been applied properly.

In conclusion we can say that the adhesion of the wood- epoxy glue line is stronger than the "parallel to fibre" strength of the wood (See Figure 4 and Table 1).

B. Steel

The adhesion of epoxy-to-steel was tested by the Laboratoire de Construction Inc., in Quebec (See Figure 5).

The test specimens were 1/4" 0 steel rods, embedded in epoxy, representing an epoxy-steel contact surface of 0.8 sq. in. The steel rods were loaded at room temperature in an hydraulic Compression Testing Apparatus, The adhesive bond between steel and epoxy failed at a load of 1350 lbs, This represents an ultimate bond stress of 1,688 psi.

A^F Vol. VII No. 3 1975 10



PI

1

2

Fig. 4 Wood/epoxy glue line test procedure.

Testing procedure.

A r: Vol. VII No. 3 1975 11



Load (lbs.) at moment of failure.

Test Series

A B C

900+ 3000 2000+

2800 3400 2700

3000 3000 3000

1900 3300 2500

2600 2700 3000

3300 3100+ 3200+

2400 2200 3400

3200 2400 3800

2400+ 2800 2900

3400 1800 300

Note: + denotes glueline failure.

WOOD EPOXY GLUELINE TEST

TABLE 1

AD Vol. VII No. 3 1975 12



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., w,:

--:

SPECIMEN STEEL P IN EPOXY

. ,:, .OD

TESTING PROCEDURE

,/ LOAL-

ff # .,- S.. .

.

LIM

:~ J ,,?s~. ....,,"

TEST 3 : LOAD 1350 lbs. TEMPERATURE: 70 F

DURATION -

DISPLACEMENT BOND BETWEEN EPOXY AND STEEL FAILED

Fig. 5 Testing the adhesion between epoxy and steel. 1. Specimen, and testing procedure. 2. Hydraulic testing apparatus.

No. 3 1975 13

TYPICAL

ii

IA'r Vol. VII



3. Structural Strength

The structural strength of the W.E.R. system has been extensively tested at the Department of Environment, Eastern Forest Products Laboratory. At the recommendation of the Head of the Laboratory all tests were carried out on simply supported beams in bending, with centrally positioned concentrated load. Under such conditions the system is subjected to compression, tension and shear simultaneously (See Figure 6).

All tests were conducted on beams which were uniformly made to the following specification.

Species: Douglas Fir, (Structural Grade)

Size: 2" x 4" x 96"

Reduction: 1/2" wide and 3" deep groove cut in the beam along the entire length to reduce the structural strength by approximately 20%.

Over twenty test beams were treated with the W.E.R. system, using different types of reinforcement (See Figure 7).

Four "control" beams were also made, to the same dimensions as the test beams, but without the strength reducing grooves. These control beams were also subjected to the tests.

The test results clearly indicated that beams of reduced strength, if reinforced with the W.E.R. system, are stronger in all respects than normal, sound beams (See Table 2).

4. Effect of Preservatives

Usually W.E.R. reinforced timber is also treated with a preservative to prevent further deterioration. It is most desirable to apply the preservative after the epoxy has hardened, because most preservatives have no adverse effect on cured epoxy.

If for some reason the preservative must be applied before the epoxy hardens, the preservative must be selected with great care. Certain types may retard the polymerization, or lower the epoxy's adhesive strength.

After extensive testing, the following preservatives were found suitable for application on wood, before the epoxy hardens:

A rF Vol. VII No. 3 1975 14



Fig. 6 Structural strength test. Test specimen under observation at the moment of failure.

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Fig. 7 Structural strength tests. Photographs of typical failures. 1. Steel rod reinforcement. 2. Steel plate reinforcement.

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A1. VII No. 3 1975 15

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AVERAGE VALUES OF SEVERAL TESTS

NO. TYPE OF REINFORCEMENT ULTIMATE STRENGTH MODULUS OF ELASTICITY

PSI % PSI %

1 Control Beam, no reinforcement 5,753 100 1,433,224 100

2 Fiberglass cloth 7,420 147 1,538,094 102

3 Epoxy only 8,449 129 1,455,274 107

4 Two 1/4" 0, steel rods 7,548 131 2,252,210 157

5 1/4" x 3", steel plate 8,374 146 2,956,025 206

NOTES:

Nos. 2 & 3

No. 4

No. 5

Considerable increase in Ultimate Strength while Modulus of Elasticity remains normal. Consequently, the deflection of beams may be dangerously high.

: Ultimate Strength and Modulus of Elasticity increased nearly equally. Most economical utilization of material.

: Modulus of Elasticity increased much more than Ultimate Strength. Beam may be too rigid.

TABULATED TEST RESULTS

TABLE 2

0

0

o

C-j

,-



1

2

Fig. 8 Results of "freeze-thaw" tests. Each specimen tested for 10 cycles. 1. Type "A" Epoxy; steel and wood

separated. 2. Type "B" Epoxy; no visible ill

effects.

No. 3 1975 17

^- - -

A^r Vol. VII



(in order of preference)

A. 7% "Osmose", dissolved in water

B. 7% o-phenyl-phenol dissolved in methanol

C. 7% pentachlorophenol dissolved in methanol

5. Effects of Freeze-Thaw Cycles

Extreme variations of temperature, which are a common occurrence in North America, have deleterious effects on most building materials, including the components of the W.E.R. system. Consequently it was necessary to study the behavior of the system under such conditions.

For the purpose of this test eight specimens were prepared, each made of Douglas Fir (Structural Grade), 2" x 4:' x 24", with a 1/2" wide and 3" deep groove cut along the entire length. The grooves were filled with different types of reinforcements and epoxies.

In the Laboratory of the Restoration Services Division the specimens were heated from room temperature to 1040 F and then cooled to -360 F, 10 times. To induce the greatest possible stresses the temperature changes were made very rapidly.

After the completion of 10 freeze-thaw cycles the specimens were thoroughly examined. We found that none of the specimens made with type 'A" epoxy, stood up to the repeated temperature variations. The adhesion of the components failed and the epoxy showed stress-fissures.

On those specimens which were made with type "B" epoxy, the repeated freeze-thaw cycles had no measurable ill effect (See Figure 8).

6. Heat Expansion

The crucial property of heat expansion was also tested.

The specimens for the test were made of type "B" epoxy, in the shape of 1/4" diameter rods, 15" long. The specimens were heated from 700 F to 4000 F and cooled to 700 F again with a constant rate of temperature change of 50 F per minute (See Table 3).

In this way the coefficient of linear expansion for epoxy could be determined and compared to other materials.

A rF Vol. VII No. 3 1975 18



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TABLE 3

A rF Vol. VII No. 3



Epoxy Ce - 0.00005

Wood Cw = 0.00000019

Steel Cs = 0.00000067

7. Adhesion at High Temperatures

It has been observed that the adhesive properties of epoxy diminish at high temperatures. This phenomenon was tested under controlled conditions, to determine the correlation between temperature and adhesive strength.

For these tests 1/2" diameter holes were drilled through 1" thick Douglas Fir blocks. Into the holes 1/4" diameter steel pins were inserted and the remaining space filled with an epoxy mixture. The specimens were then placed in a testing frame inside a furnace and 100 lbs. pressure was exerted on the pin (See Figure 9).

The loaded specimens were heated and the behaviour of the system observed for up to 45 minutes (See Tables 4A & 4B).

The results of the tests may be summarized as follows:

1. At high temperatures the adhesion between steel and epoxy fails, before the adhesion fails between wood and epoxy.

2. The higher the temperature, the lower is the adhesive strength.

3. The adhesion of epoxy fails after a short time, at temperatures of 2500 F and above:

Temperature Time of Failure

2500 F 25 - 30 min.

3000 F 16 - 20 min.

3500 F 5 min.

4. It has been repeatedly observed that at elevated temperatures the epoxy expands considerably. If the epoxy is confined then the pressure exerted by the expanding epoxy may substitute for the adhesive strength for a short period.

5. An additional series of tests revealed that if epoxy is heated, and then cooled to room temperature, the adhesive strength is reduced permanently (See Table 5).

AirF Vol. VII No. 3 1975 20



LABORATOIRE DE CONSTRUCTION DU QUEBEC INC.

Essai en marche a l'interieur de l'etuve

Poids : 100 lbs

r

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....* .:. "" ,\ .'//4.D S

Fig. -9 Sheet from Laboratory Report\

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Fig. 9 Sheet from Laboratory Report showing specimen (1) and specimen under load in test furnace (2) during high temperature adhesion tests.

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Vol. VII No. 3 1975 21

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TABLE 4A

RPsistance a la chaleur de ltensemble 6poxy-aciet,-bois

Poids applique sur la tige : 100 lbs

I"'1 -

? Essai No.

<

Tempe rature ?F

--4

1 150 z 0 2 150

co 3 150

-- 4 150

- 5 200 (-n

6 200 ro pr 7 200

8 200

9 250

10 250

Specimen Temps OBSERVATIONS Type Minutes Descente de la tige Rupture

en pouce

A

A

B

A,-S

A

A

B

A-S

A

A

45

45

45

45

45

45

45

45

45

45

Nil

Nil

Nil

Nil

Nil

Nil

Nil

Nil

1/64

NOTES

Aucune alteration visible








Apres 30 minutes, la tige commence A descendre alors que

l'epoxy se ramollit. Liaison entre la tige et l'epoxy cede.

AprAs 25 minutes, la tige commence A descendre alors que

l'epoxy se ramollit. Liaison entre la tige et 1'6poxy cede.

1/64

Tables 4A and 4B Laboratory test results showing the effects of high temperatures on the adhesion between epoxy, wood and steel.



TABLE 4B

Essai T emperature No. ?F

Specimen Temps OBSERVATIONS

Type Minutes Descente de la tige en pouce

11 250

12 250

1 3D 300

14 30

15 300

16 300

17 350

1 8 300

B

A-S

A

A

B

A-S

B

A-S

45

45

45

45

45

45

45

4

1/32

1/64

1/64

1/64

1/64

1/64

1/32

V

Apres 30 minutes, la tige commence a descendre alors que el'poxy se ramollit. La liaison entre la tige et l'epoxy cede

de meme que celle entre l'Apoxy et le bois. Le ramollissement

de letpoxy est plus prononce qu'eavec le melange A

Apres 30 minutes, la tige commence a descendre alors que l'epoxy se ramollit. La liaison entre la tige et l'epoxy cede

Apres 20 minutes, la tige commence a descendre alors que l'epoxy se ramollit. La liaison entre l'epoxy et la tige cede

Apres 16 minutes, la tige commence a descendre alors que l'epoxy se ramollit et semble vouloir ressortir a la base du

specimen. La liaison entre la tige et l'6poxy cede. On a

prolonge le chauffage de 1Y heure et ainsi la tige descend de

1/32" et la liaison entre l'epoxy et le bois cede aussi.

Apres 17 minutes, la tige commence a descendre alors que

l'epoxy se ramollit. Les liaisons entre l'epoxy, l'acier et

le bois cedent aussi bien au-dessus qu'en dessous du specimen,

Apres 16 minutes, la tige commence a descendre alors que

ltepoxy se ramollit. La liaison entre l'epoxy et l'acier cede ,

Apres 5 minutes, la tige commence a descendre alors cue

I'epoxy se ramollit. Les deux liaisons acier-epoxy et bois-

epoxy cedent.

Pour cet essai, nous avons applique une charge de.200 lbs.

La liaison entre ltepoxy et l'acier a cede et la tige a glisse

jusqu'au .maximum de sa course possible.

Rupture NOTES



Charge totale pour provoquer la rupture de l'ensemble : epoxy - acier - bois a la temperature de 70? F.

Essais Nos. Speci mens Type

Specimens d6ej chauffes a ... ?F pour le'preuve precedente

Charge a la rupture en lbs

I A non chauffe 1 200

2 B non chauff6 1350

3 A-S non chauff6 1350

4 A 150 1125

5 B 150 1400

6 A 200 1000

7 B 200 850

8 A 250 925

9 B 250 625

10

11

A

B

300 850

300 400

REMARQUE : On observe que qui cede et que

ctest la liaison entre Ilacier et l'epoxy la tige glisse vers le bas.

Table 5 Laboratory test results demonstrating that the adhesive strength of the epoxy is permanently impaired by exposure to high temperatures.

A)r Vol. VII No. 3 1975 24



500 mm

LONGITUDINAL SETION

40 mm 30 'mn 20 mm

square

/ / /' - /

/ .

/ ./ / * / .^ /1

TY PIC AL o h

r- a TEST BEAM

CROSS SE TION

Fig. 10 loading

Typical test beam for tests at high temperatures.

No. 3 1975 25

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ADr Vol. VII



8. Loaded Composite Beams at High Temperatures

The behaviour of W.E.R. reinforced beams, under bending load, at high temperatures, has been tested on several scaled-down beams.

The test beams were uniformly 500 mm long, but with different cross sectional dimensions.* All beams had a 10 x 10 mm cavity cut in the core, along the entire length. Into this groove a 5 mm diameter steel reinforcing rod was inserted and the remaining space was filled with epoxy (See Figure 10).

The beams were placed on a special testing frame, inside a furnace. Then a load was applied and the furnace was heated to a pre-determined temperature. This temperature was kept constant throughout each test.

With certain special arrangements the loads were applied in such a way that the stresses were first developed in the reinforcing rod, from there they transferred to the epoxy and the residual stresses transferred to the wood (See Figure 11).

Test Series "A"

For Test Series "A", 20 x 20 mm beams were used. The beams were subjected to 38 lbs. point load at the centre-span. Under this load the beams deflected by 3 mm. This corresponds roughly to a deflection of L/160, which is the allowable maximum in many Building Codes.

Each test beam was heated to a different temperature and the changes in deflection were observed. From the tests it was evident that at elevated temperatures the epoxy loses its rigidity, it becomes quite plastic and the load bearing capacity of the system decreases considerably.

Test Series "B" and "C"

For these tests 30 x 30 mm and 40 x 40 mm specimens were used, but the load on the beams was again 38 lbs.

The beams were heated and the deflection observed, as in Test Series "A". During these tests it became obvious that while the larger sections did not deflect as much as the small sections, the ratio of increase was the same.

* Editor's footnote: 500 mm m 19 11/16" 10 mm ~ 13/32"

These tests were carried out in a laboratory where the relevant equipment was calibrated in the metric system.

ADr Vol. VII No. 3 1975 26



1

2

ii;:~~

Composite test beams in apparatus.

Fig. 11 testing

No. 3 1975 27 A:) Vol. VII



Test Series "D" and "E"

For these tests 30 x 30 mm and 40 x 40 mm specimens were used, but the load was 150 lbs.

The test beams were divided into two groups. In Group 1 the loading was applied as described in the preamble. In Group 2 the procedure was changed so that a larger portion of the load was carried by the wood.

At room temperature the beams carried this heavy load without undue deflection, but at elevated temperatures the epoxy failed within a short time. The beams in Group 2 resisted failure somewhat longer than in Group 1, but the difference was insignificant.

Analysis:

The tests have proven conclusively:

At a constant load the deflection increases considerably at higher temperatures;

The longer the epoxy is subjected to the same high temperature, the larger will be the deflection.

The higher the temperature, the shorter the period that is required to arrive at the same deflection.

The test results are demonstrated on the attached graphs (See Tables 6A, B & C).

9. Fire Rating Test

One of the most important criteria for structural members is the ability to carry the design load in a building fire for sufficient time to enable the occupants to escape. In simple terms, "Fire Rating" is an expression of the amount of time which is available for escape from the fire.

The Fire Rating of the W.E.R. system has been tested according to the specification of the Building Research Division of the National Research Council. Since the epoxy's structural strength is considerably diminished above 2000 F, the main purpose of this test was to.find out when the epoxy reached this temperature.

For this test the specimen consisted of two wooden beams, each reinforced with epoxy and steel rod. In one beam the epoxy had 1/2" of wood-cover, in the other beam it had 1 1/2" of wood-cover. Two thermocouples were placed inside each beam to observe the temperature of the epoxy during the test (See Figure 12).

A:) Vol. VII No. 3 1975 28



-4 ,-, - 1

-. I;: -4 ..1'

/ - I-.

- - /

1 _: I

150 200 250 300

. ..__ T_e m p aure . a._t . r e .

_ .I 350

- i'

_ _

' ' : : ;

' i

- # . .- 4 i 1 1 ! ,,

... ~ ~?-- - -- ----- -- , .............

- -~--->- -----t------;--O--

i F

__ ,,? .....

.

__.

20.5 -1

200 250 300 350

~_ z~.au ___.T---t F

~~~~~~_

_

TD. .ms_t.u~_?

20 x 20 mm beams 40

DEFLECTION OF BEAMS EXPOSED TO HIGH TEMPERATURE

? _ - . TABLE 6A

x 40 mm beams

o 0-

0

Co

cn

_ _____.

T: k L CA D - A r IauDleS o, D aca u urapns snowing results of loading tests at high temperatures.

I I f I

. --

_ _ . - . , _ _ _ _ t _ -_ l __._.

9 _.

r e- - - __

_ w _ - _ _

I t

, _ __ ._. __

4 . _ . . . _ _ ,

_. ,_

-. , fi

:

_ _ . _

_ . . :

_ _

6 _ _

. _,

_ _ _ . _ _ .

3-



/ 101

c^ o I ; , ? ? 10 2__._0 30 40 50

. -E 1 a p se d t--i-m in . min-- o t-e s- -

20 x 20 mm beams

4-

3-

0 4) 0

-2----

4) 0

1

0

t . 7. i _

*

_ t -*

-r _*; -- --t b0 -E - -------...e. +.v._1_r.S.._

................ + ._... _ .._...._.... ~ ,0

!ii:i~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ; ^

/ * /

/Q/^

7

.. .. . . . .. ............ . . ..... -

.......... ................... -

. . . ....... Elapsed time in minut e s

30 x 30 mm beams

DEFLECTION AT HIGH TEMPERATURES WITH 38 LBS LOAD

TABLE 6B

.... . _._. ,,..

.--- 0

v 7- _ 1-

0 I-J

1-4

(.A

0i

0

0

0

41

I i i a

...._ - - . . _

, - - .

Y-



:i, S

>--4 - f 6 03

~. :i.

o

0 . 4.... .....6 "1.....C-- '

__A

* I I

- I

+ -- - - - I -

-- 1

N tS--- Load carried by the

_,, ,,,- entire section

-N..... .. ? _ _ ?

. 3.5

jIG-

5-,-,-

v __~Load "carried by the t"

.. .. ~ - -entire section --_ .

Toad carried mostly s-- . ..... by reinforcement

.T_eIm p.e_ra t_u r.e oF

250 . . 3tX30 A0 -...

Tom e_prat u r e ___o

30 x 30 mm beams 40 x 40 mm beams

Load: 150 lbs.

RUPTURE OF BEAMS AT HIGH TEMPERATURES AND LOADS

TABLE 6C

-- 10--

-.-. ... 9 -

-2-

-1 0 0

0o COl

i L4

GA)

? I . ,

< I-I4 I-I4

.. _ -f ___ -, _ : - 4

O%k^ - - 4cxju



31"

1/4" Steel rod

3" x 3/8" Epoxy filled cut

(33/4" x 1 3/4" Beam)

Fig. 12 Diagram of specimen for fire rating test, showing positions of epoxy, reinforcement and thermocouples.

THERMOCOUPLES CONNECTED TO THE SPECIMEN TIME FURNACE TEMP. ?F WIDE PEAM ?F NARROW BEAM 6F MIN. PRESCRIBED AVG. fl/ SIDE #2 BOTTOM #1/ SIDE 1/2 BOTTOM

0 68 75 75 75 75 75 5 1000 950 75 75 75 80

10 1300 1293 75 75 105 145 15 1399 1450 80 80 165 250 20 1462 1416 80 80 250 375 25 1510 1497 100 105 330 715 30 1550 1520 120 130 650 970 35 1584 1572 145 155 905 1300 40 1613 1610 175 180 1160 141o 45 1638 1638 200 210 1300 1485 50 1661 1622 220 225 1400 1510 55 1681 1696 230 230 1465 1580 60 1700 1710 230 235 1500 1615 65 1718 1720 230 240 1535 1630 70 1735 1750 230 240 1655 1750

Table 7 Fire rating test: test furnace temperatures in relation to thermocouple readings inside reinforced beams.

A^r Vol. VII No. 3 1975 32



FIRE RATING TEST

I I I I I L_ -_--__--_--__-I I - ---

TEST TEMPERATURE:

DURATION: 45 MIN. Fig. 13 Remains of specimen after fire rating test.

J A% T . ( r

A^r Vol. VII No. 3 1975 33

a

I I I L

it

)FtI(I\AL DI) 1 l\E

1600 F.

0



The specimen was placed in a test furnace and the ambient temperature was raised within 5 minutes to 10000 F. At the end of the test, 65 minutes later, the ambient temperature in the furnace reached 17350 F (See Table 7).

The temperature of the epoxy, with 1/2" of wood-cover in the small beam, reached 2000 F in about 12 minutes. In the larger beam the epoxy, having 1 1/2" of wood-cover, reached 2000 F after 45 minutes. At the end of the test the small beam, including the epoxy, was almost completely burned away, while in the larger beam the epoxy was still intact with some wood-cover remaining (See Figure 13).

CONCLUSIONS

My objective in this article has been to emphasize the importance of carefully testing all new conservation techniques. It is high time that preservationists forsake educated guesses for well researched facts. If a structure deserves to be preserved, its load bearing elements deserve to be well engineered.

Many details are omitted in this version of the text to make it as understandable for the un-initiated as for the expert.

The conclusions which may be derived from these tests may be summarized as follows:

1. Certain epoxies, especially when reinforced with high tensile inserts, can withstand much higher stresses than most species of wood. Also, if the epoxy is properly applied, the adhesion between epoxy and wood is stronger than the "parallel to fibre" strength of the wood. Consequently, in a well designed W.E.R. system the allowable working stresses of the wood are the governing factors.

2. If the wood has lost its structural strength the entire load can be transferred to the epoxy and reinforcement. In such cases the system may be designed according to the allowable stresses of the epoxy and reinforcement.

3. The great structural strength of epoxy quickly diminishes above normal room temperature. Such temperatures are not necessarily the results of fires or other calamities. They can occur in the vicinity of heating conduits, high wattage lighting fixtures or under an acute exposure to the sun.

This problem is aggravated by the phenonemon that the epoxy retains its strength for a period even at high temperatures, causing a false feeling of security.

A-r Vol. VII No. 3 1975 34



4. Once again, it has been proven that wood is an excellent insulating material with considerable resistance to fire. Therefore, it is advisable to provide a wood cover over the epoxy to protect it from heat.

In the final analysis we must reiterate that the rehabilitation of deteriorated wood with epoxy and reinforcing materials is a feasible technique. Like every other method this also has its limitations but if handled judiciously, the problems can be minimized.

I consider these series of tests crude and preliminary only. In the reorganized Conservation Laboratory of the D.I.N.A. a second and more sophisticated testing and development program is under way. The purpose is to develop an epoxy resin with a superior heat resistance and to define more accurately the engineering design parameters of the W.E.R. systems. The results are expected in about 18 months time.

In the meanwhile, the writer has begun to prepare an interim handbook for the engineering design of the W.E.R. system. Hopefully, we will be able to present it to the membership of the A.P.T. in the not so distant future.

A:) Vol. VII No. 3 1975 35



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