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1 E 4374 100x 18x Isx27 137

base, vertical, wall and moment

E= =4374 _ 100X 18X ISX27 =_137,1 pounds per foot of length of wall.

The bending moment caused by this thrust upon the section at the top of the base is .1/=4371X6X12=:31•192S in.-lb.

From Table VII, for = 650 and L= 16,000, we find R=108 and p= .0078.

Then Rbd" = M becomes 108 X and (1=15.5 inches.

Assuming the steel to be embedded 1.5 inches in the concrete, total thickness of the vertical stein at the top of the base will be 17 inches.

The steel area required for a length of 12 inches of wall is From Table we find that ;-inch bars spaced 5 inches apart will anwer the purpose.

If we assume 10 inches to be the minimum allowable thickness at the top of the wall and make the faces of the Avail plane surfaces, the thickness at all intermediate points will he greater than required for strength. At a point 12 feet below the top, the bending moment.

and from Table IX, we find p=.0032. The area of steel required is 12X13X.0032=0.5 per foot of length, or about one-third of that at the base. Similarly at a section 6 feet below the top, no steel would theoretically be required.

If all of the bars be carried up 6 feet, every third bar 12 feet and every sixth bar to the top the reinforcement will be amply strong. The lower ends of these bars should be turned up in the base for anchorage.

The maximum shear in section at base is 4371 pounds, and No diagonal tension reinforcement is necessary.

Overturning 3foment--Assume the width of base at about 45 per cent of the total height, or S.5 feet. Let the inner surface

of the vertical stein be vertical, and place the stem at a distance equal to one-third the width of base (b, 3) from the toe of the wall. (See Fig. 67.) The moment of the thrust about the toe at A tends to overturn the wall, while the moments of the weights of the wall and earth resting upon it resist overturning.

The weight of the vertical stein is The moment on the toe at A is 3f =3035X3.65+ 1275 X4.25+7650X6.4-4S73X6.33=34610 ft.-lb. The point of application of the resultant on the foundation soil is equal to the moment about A divided by the vertical component of the resultant, or The factor of safety against overturning is Pressure on total vertical load on the foun dation is 3035+1275+7650=11,960 pounds. The pressure at the toe is twice the average pressure, 2 X11960, 8.5=2814 lb., ft.', which is within safe limits.

Inner Base length of the inner cantilever is 4.25 feet. It is subject to the action of three loads: (1) The weight of the earth resting upon it (1800 pounds per linear foot) ; (2) Weight of the cantilever itself (150 pounds per linear foot).

(3) Upward pressure of the foundation soil (which is 0 at the end D and 1400 pounds where the cantilever joins the vertical wall at C).

The bending moment on the section at C is l . 25 4.25 1400X 4.25 4.25