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[For the Scientific American.] On the 2d of December last, a new malt house in Bethune street, in this city, fell, and was the cause of two men, who were working in it, losing their lives. As this accident necessarily led to an investigation as to the cause of the catastrophe, various opinions were expressed by the witnesses examined, and some of them contradicted one another. As it involves important questions in architectural engineering, the following article on the subject, will be found deeply interesting, not only to merely scientific, but to all practical men :—EDS. What was the cause of the "accident"? Were the floor beams or the posts at fault ? Upon this point the builders who testified before the Coroner did not agree. An investigation into the strength and strain may decide the question. First, of the floor beams. Experiments made to test the strength of hemlock when exposed to a cross strain, (as is the case with a floor beam,) show that 363 pounds is the weight that will break a piece one inch square and olTc foot long—the weight being at the middle. This is the average of seven experiments. From this unit of strength the resistance of beams of any size may be computed, by the well-known laws of pressure. The floor beams in question were 4 X 12 inches, and about 18 feet long ; they were placed 18 inches apart from centers. To break one of these beams it would require, upon the above data, 11,616 lbs. at the middle, or twice this amount if equally distributed over its length, which is equal to 860 lbs. upon every superficial foot of the flooring on the beams. This is the breaking weight. What was the load ? Barley weighs about 35 lbs. per cubic foot. The barley on the floor appears to have been from four to five feet deep. The weight, therefore, per foot superficial, could not have been more than about 175 lbs.—equal to about oi)e-fifth'of the weight required to break the beams. The barley might have been raised to the hight of 24 feet upon the floor before the beams would have broken. Hence it is clear that the barley, being only five feet deep, could not have broken the beams. Yet one of the builders testified "that the size and quality of the beams used in that building were positively insufficient." In regard to the comparative value of pine and hemlock, experiments show that pine will bear only. seven or eight per cent more than hemlock ; yet one of the witnesses testified that it would bear 150 (1) per cent more, and another witness subscribed to this, and these witnesses were both practical builders. The unit of strengtlderived from several experiments on the three kinds of wood, spruce, hemlock and pine, are respectively 345, 363 and 390 lbs. Yet one witness said : "I consider spruce as strong as pine, but hemlock I look upon as insufficient." This witness was correct, however, as regards the elasticity of pine, for experiment shows that pine will suffer a greater deflection without injury than either spruce or hemlock, and it requires a greater load to deflect it through an equal space. Now the posts. These were of red cedar, and of various sizes, those in the second and third stories being from five to eight inches diameter at the smallest end. They were in their natural shape, and some of them so crooked that the largest perfect straight post that could have been sawed from them would have been about 9X5 inches, or, at the most, 3! X 5! inches. This is the effective size, the length nine feet. Now what weight is required to break such a post ? Experiments have been made to test the strength of oak, chestnut and locust posts, but not of red cedar. The latter is, probably, stronger than either oak or chestnut, but not locust, although it may be nearly as strong as the latter wood. It requires to bend white oak 6,950 Ibs., chestnut, 7,720 pounds, and locust, 10,920 Ibs. In each case, this unit of strength is the average of several experiments, and is the ight required to bend a post one inch square and one foot long. There is reason to presume that the strength for red cedar is below 10,000, but let it be assumed at this. Upon this data, a post of red cedar, 3! X 5! inches, and 9 feet long, will require 29,113 lbs. to bend it from a straight line, and something more to complete the fracture. Each post in the building supported about 200 feet superficial of the floor; therefore the 29,113 lbs. is equal to about 140 Ibs. upon every foot of the floor. It has been shown above that if the barley was 5 feet deep, there was a weight of 175 lbs. upon each foot of the floor. This, together with some 25 lbs. for weight of floor timbers, &c., was quite sufficient to break a post of the size stated. From this computation, and the fact that a broken post was found in the ruins, we may safely conclude that the want of size in the posts was the cause of the failure. The posts should have been at least six inches diameter, and perfectly straight at that. R. G. HATFIELD, Architect. New York, December, 1857.
