Reinforced Concrete Railway Structures (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1914 Excerpt: ...between the earth and the back of the wall. These forces are indicated in diagram form in Fig. 70. The thickness of base cannot be exactly determined until the width has been ascertained, but it must be at least as thick as the wall at the bottom. If it is assumed to be of equal thickness to the wall at this point, namely 2 ft. 3 in., the weight per square foot will be approximately as follows: --Concrete 2'25 X 156 = 351 lbs. Earth 2"0 X 120 = 240 lbs. Total 591 lbs. If the required width of the base to prevent overturning is x feet clear of the thickness of the wall, its weight per lineal foot of wall is 591x lbs. The weight of the wall per lineal foot is 22-25 X 1-4 X 156 lbs. = 4,860 lbs. The horizontal component of the earth pressure per lineal foot of wall has already been determined, and is 6,850 lbs. while the vertical component is also the same as in the case of the wall with counterforts, namely 2,220 lbs. The resultant of this earth pressure is assumed to act at a point 6 ft. 8 in. from the top of the base, or 8 ft. 11 in. from the underside. Taking moments as before, about the third point of the base nearest to the toe, which is (-+ )"" from the back of the wall 4,860 ( 1-5 +--76) + 591 (l-5 + y-2'25--) + 2,220 (l-5 + J) = 6,850 X 8-92, which equation is satisfied when x = 10-2, say 10 ft. 8 in., making the total width of the base of the wall 12 ft. 6 in. The sum total of all the vertical forces is lbs. 4,860 591 X 10-25 = 6,060 2,220 13,140 and the average pressure on the foundation 13,140-T-12-5 = 1,050 lbs. per square foot. The distribution of this pressure is shown in Fig. 70, and varies from zero at the heel to a maximum intensity of 2,100 lbs. per square foot at the toe. The maximum stress produced in the base by this pr...