A Treatise On The Principles And Practice Of Dock Engineering
Forfatter: Brysson Cunningham
År: 1904
Forlag: Charles Griffin & Company
Sted: London
Sider: 784
UDK: Vandbygningssamlingen 340.18
With 34 Folding-Plates and 468 Illustrations in the Text
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TRANSVERSE STRENGTH. 131
practice is to dissolve 1 Ib. of salt in 18 gallons of water when the temper-
ature is 32° F., and to add 3 ounces for every 3° of lower temperature.
The surface of such work, left for the night, must be protected by boards,
tarpaulins, sacking, gravel, or littered straw.
Strength of Conorete.
Compressive Strength.—The following results were obtained by Mr.
Grant.* Experiments were undertaken witli 12-inch cubes of compact
concrete made with Portland cement, weighing 110'56 Ibs. per bushel, and
having a tensile stress of 427 Ibs. per square inch after seven days’ immersion
in water. The tests took place at the end of twelve months.
TABLE VII.
Composition of Concrete. Crushing Weight in Tons.
Blocks kept in Air. Blocks kept in Water.
1 cement, 1 ballast, 107 170-5
1 2 149 160
1 3 113 115-5
1 4 103 108-5
1 5 89 99-5
1 6 80-5 91
1 7 „ 75 80-5
1 8 „ 61-5 76
1 9 54 68-5
10 „ 48-5 48
Experiments made with 9-inch cubes of the concrete (6 of gravel and
broken stone to 1 of Portland cement) used in the construction of the
Vyrnwy Dam gave 84-23 tons per square foot as the lowest resistance to
compression in the case of a block little more than three months old, and
298-6 tons per square foot as the highest resistance in the case of a block
three years old. The mean resistance to cracking, under compression, of all
the blocks tested between two and three years after moulding was 215-6
tons. Still higher results were obtained from blocks cut out of the hearting
of the actual work. The mean resistance to cracking, under compression, of
19 blocks, between one and two years old, was 263 tons per square foot.
Transverse Strength.—In an experiment by Mr. Golson t a beam of
9 to 1 concrete, 28 days old, 21 inches wide, 9 inches deep, and 3 feet
9 inches clear span, fractured with a weight of 1-044 ton applied centrally.
The coefficient derived from this, for the unit beam, 1 foot wide, 1 foot deep,
and 1 foot span, becomes 4 tons.
* Grant on “Strength of Portland Cement,” Min. Proc. Inst. G.E., vol. xxxii.
+ Min. Proc. Inst. C.E., vol. liv., p. 270.