Page images
PDF
EPUB

data, the questionnaire specifically requested opinion data where actual was not available, and this bulation, therefore, to a considerable extent reflects ideas rather than tested facts. However, owing to the lack of definiteness concerning many of the more important variables, as outlined above, this tabulation probably is as accurate as is possible to secure at this time.

It is to be noted that Table I concerns untreated ties only. It is also limited to returns which indicated that the failures were more than half caused by decay, and it is, therefore, an effort to compare the decay resisting qualities of untreated timber. Mechanical Strength.

Cross-ties, as regards "design," must be considered from a somewhat different angle than most parts of a railroad. A tie could, theoretically at least, be designed of such size and strength as to carry the stresses imposed at any given location under given conditions. If the tie were to substantially retain its strength throughout its life, it would be comparable, as regards designing, with rails, bridges, etc. It does, how.ever, lose its strength throughout its life, though we have no data as to whether this loss is proportional to the time (straight line) or otherwise, and it is economy, therefore, to use ties having an initial strength considerably greater than the stresses require, or in other words the new tie has reserve strength. It is believed that the amount of this reserve strength largely determines the life.

A tie performs three principal functions :
(a) Acts as a beam to distribute the load,
(b) Acts as a block to transmit the load from rail to ballast,
(c) Holds the rails in place.

It is, therefore, required to possess beam strength, crushing strength and ability to hold fastenings. As between the three, the beam strength is fundamental, because, if deficient in any given tie, there is no remedy, whereas a deficiency in crushing strength or ability to stand compression across the grain can be remedied by suitable tie plates and the ability to hold fastenings modified by the design of the fastenings.

As between different kinds of timber, the strength can be said to vary with the specific gravity. Table II has been prepared from data contained in Bulletin 556, L'. S. Department of Agriculture (Forest Service). The modulus of rupture is used by your Committee as indicating relative beam strength for any given cross-section of tie and the compression perpendicular to the grain at elastic limit as indicative of relative bearing strengths. Diagrams A and B show graphically how the modulus of rupture and the compression at elastic limit vary with the specific gravity. It is to be noted that the modulus of rupture varies about as the first power of the specific gravity and that the compression varies, for tie timbers selected, about as the 2.6 power.

Under the assumptions that the mechanical life of a tie is proportional to its strength, which seems reasonable in view of the surplus strength when new feature, and that the strength is proportional to the specific gravity, Table III has been prepared. Another assumption made in preparing this table is that the relative resistance of various woods to decay is constant for variations in climate.

Effect of Size and Tie Plates.

The replies to the Committee's questionnaire indicated a general belief that ties 7 inches by 9 inches would outlast ones 6 inches by 8 inches when subjected to the same conditions. The replies would, perhaps, average 25 per cent.

The data given in the questionnaire relative to ties failing by decay shows an average of 30 per cent. greater life for the 7 inch ties, plated, over the 6 inch ties and 20 per cent. for the 7 inch ties, unplated, over the 6 inch ties. These check the opinions fairly well. It is also found that the value of the tie plate in the case of 6 inch ties is 12 per cent., and the case of the 7 inch ties 21 per cent. All of these percentages must be considered only approximate, due to the character of the data. The greater value of the tie plate in the case of 7 inch tie may be ascribed to the fact that the 7 inch ties are, in general, used under heavier traffic.

Annual Cost.

Diagrams C and D have been prepared from the formula recommended by this Committee for ascertaining annual cost. They are self-explanatory. Applications of Data.

The following examples will indicate how the information contained in this report may be applied:

EXAMPLE 1. In a location where white oak ties costing $1.50 in track have been in use, and where they have failed largely through mechanical wear in an average of six years, how much more or less per year will chestnut ties at $1.25 in track cost? Referring to diagram C, it is found that the white oak ties are it is found in column six that chestnut ties have a mechanical costing 30/2 cents per year (6 per cent.). Referring to Table III, per diagram C, this would result in a cost of about 36 cents per

EXAMPLE 2. In a location where white oak ties exposed to light traffic fail by decay in six years, and where the traffic is such that failures are about equally divided, decay and mehanical, cedar ties costing $1.25 in track have been in use. How much could be paid for Douglas fir ties, in order that the cost per year would be III the cedar ties should average 69 or 5.5 years. As per diagram the same as for the cedar ties? According to column 10 of Table Douglas fir, column 10,_gives an average life of 51 or 4.1 years.

per cent.) the cost per year is 28 cents, and Table III for As per diagram D, the Douglas fir ties should cost about 97 cents

in place.

year.

D(7

each, Conclusions.

be reachedo follows :

Tie life data does not exist from which satisfactory conclusions may

on the subjects assigned. Information lacking is partly as

completely enough to permit satisfactory comparisons between

Actual life data with the conditions of use recorded results on different railroads.

(0) Information as to how the "average" life reported is C) Information as to whether the relative resistance to

of various woods is independent of climate.

obtained

deca

238

(d) Information as to whether the best decay resisting tie untreated is also the best decay resisting tie when treated, whether treatment results in the addition of a uniform number of years life to all kinds of timber, or more to some kinds than others, or whether it results in giving all kinds of ties the same average life under the same conditions.

(e) How mechanical strength is related to resistance to mechanical wear.

(f) How mechanical strength varies with time in track, i. e., from the condition new to the condition when decay necessitates

removal. Recommendations.

(1) The inclusion of the standard test tie in all test installations, for the purpose of comparison, as more particularly outlined above.

(2) The adoption of white oak ties, grade 3, (6" x 8") class U, untreated, 8 feet long as standard for test purposes.

(3) Laboratory test of the mechanical properties of tie timber, which has been subjected to contact with the soil for varying periods under conditions similar to those to which ties are subjected in track. Such tests should develop the relationship between strength and time exposed to the tie destroying agencies other than traffic.

TABLE I-COMPARATIVE LIFE, FAILURES MORE THAN 50 PER CENT DECAY, All Ties UN TREATED

WHITE OAK TAKEN AT 100

Baxrd on Returns Contained in A. R. E. A. Bulletin 232

Based on Forest
Service Bulletin

118, Page 44

Independent Tabulation Made by
an Individual Railroad of the
Serviceability of Ties Used

in Studies of Economy

[blocks in formation]
[blocks in formation]

Black locust .247 Cypress. 122 Black locust 181 Cedar

145 Black locust 214

250 Cedar 200 Princess pid 115 Cedar 170 Chestnut 117 Cedar

156

138
Walnut.
148 Cedar
109 Walnut
160 Walnut
114 Walnut

141
Redwood 148 Fir

103 Cypress
133 Larch

96 Heart pine

. 130 Cypress 133 White oak 100 Redwood .117 Cypress.

94 Cypress

121

125 Heart pine 130 Larch 90 White oak 100 Cherry

90 Princess pine. . 115
Jack pine,
102 Jack pine. 90 So. yellow pine. 91 So. yellow pine. 82 Redwood. .112

150
White oak . 100 Ash

82 Chestnut
85 Fir
72 Chestnut

101

88 Fir 99 Beech. 77 Fir 85 W. Y. pine 72 White oak 100

100 Larch 93 Birch 77| Mulberry 85 Redwood 72 Jack pine

96 Spruce. 86 Hemlock 64 West.yellow pine 85 Spruce

72 Fir

90|(Douglas) 75 fo. yellow pine. 74 West.yellow pine 64 Spruce.

85 R. or B. oak 43 Larch

90
Lim
68 Spruce.
64 Larch,
80 Loblolly pine.
36 Cherry

90
Gum.
64 Tamarack 64 Gum

64

Mulberry

85
Ash.
62 So. yellow pine. 62 R. & B. oak 50

Spruce

77

75
Beech,
62 Gum.
58) Hackberry 32

So. yellow pine. 77 (LL) 88
Hemlock 62 R. & B. oak. 56 Honey locust 32

Ash

72
West.yellow pine 62 Maple.

51 Loblolly pine.
32
West.yellow pine 71

63 Tamarack 62 Loblolly pine. 38Butternut 21

Beech

701

50
Birch
58

Elm

68
Loblolly pine.
56

Birch
R. & B. osk. 54

Hemlock

63

63
Maple.
43

Tamarack

63

63
Sycamore 37

Gum

62

38
R. & B. oak 51

50
Maple

47

50 Loblolly pine.

41

38
Sycamore.

37
Hackberry

32
Honey locust 32
Butternut.

21 Hickory

[blocks in formation]

68

[blocks in formation]

TABLE II-RELATION BETWEEN SPECIFIC GRAVITY, BEAM STRENGTH

RAIL BEARING STRENGTH OF TIMBERS USED FOR CROSS-TIES

[blocks in formation]

Compression
Specific perpendicular

Modulus of
Gravity to grain,

rupture, S. G.
elastic limit static bending
Lb. per sq. in. Lb. per sq. in.

[blocks in formation]

Oak-canyon, live Quercus

chrysolepis Hickory-pignut Hicoria glabra Locust-black Robinia

pseudacacia Hickory

mockernut Hicoria alba Gum-blue Eucalyptus

globulus Oak-Spanish

(lowland) Q. pagodaefolia Locust-honey Gleditsia

triacanthos
Hickory-pecan Hicoria pecan
Oak-white Q. alba
Oak-cow Q. michauxii
Oak-post

Q. minor
Birch-sweet Betula lenta
Elm-cork Ulmus racemosa
Oak-bur

Q. macrocarpa
Oak-chestnut Q. prinus
Maple-sugar Acer saccharum
Oak-willow

Q. phellos
Oak-laurel Q. laurifolia
Oak-water Q. nigra
Oak-red

Q. rubra
Oak-scarlet Q. coccinea
Oak-yellow Q. velutina
Pine-longleaf Pinus palustris
Birch yellow Betula lutea
Beech

Fagus atropunicea
Oak-pin

Q. Palustris Ash-blue

Fraxinus

quadrangulata Oak-Spanish

(highland) Q. digitata Ash-white Fraxinus

(forest grown) americana
Walnut-black Juglans nigra
Oak-California
black

Q. californica
Pine-shortleaf Pinus echinata
Pine-loblolly Pinus taeda
Tamarack Larix laricina
Elm-slippery Ulmus pubescens
Maple-red Acer rubrum
Larch-western Larix occidentalis
Hackberry Celtis occidentalis
Birch-paper Betula papyrifera
Mulberry-red Morus rubra
Pine-pitch Pinus rigida
Cherry black Prunus serotina
Gum-black Nyssa sylvatica
Gum-cotton

(tupelo) Nyssa aquatics Sycamore Platanus

occidentalis Ash-black Fraxinus nigra Douglas fir, Peeudotsuga coast

tarifolia Elm-white Ulmus americans Gum-red Liquidambar

styraciflua

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][subsumed][merged small][merged small][merged small][merged small][merged small][subsumed][merged small][merged small][merged small][subsumed][merged small][merged small][merged small][subsumed][merged small][ocr errors][ocr errors][merged small][merged small][merged small][subsumed][merged small][merged small][merged small][merged small][merged small][subsumed][merged small][ocr errors][merged small][merged small][subsumed][merged small][merged small][merged small][merged small][merged small][subsumed][merged small][merged small][merged small][subsumed][merged small]
« PreviousContinue »