[Foundation Design Wayne C Teng Pdf Free Download
Rancul Ratha
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Yes, only if the minimum soil pressure on the opposite corner/end is compression. This article provides insight into the calculation of maximum soil pressure when the resultant compression force on the foundation acts outside the kern distance for rectangular, circular, octagon and ring foundations. The fluid mechanic's concept of "Hydrostatic force on plane surfaces" and "Center of Pressure" is used to compute the calculation of maximum pressure for shallow foundations.
If the rectangular footing plan dimensions ( Length and Width) are designed such that the resultant compressive force applied falls within the middle one-third, the whole footing will remain in contact with the soil.
I was curious, What procedure Teng may have used to arrive at a Graphical chart giving coefficient k to compute maximum soil pressure from two ratios ( el/L and eb/B, that is force eccentricity over dimension along that eccentricity)? One thing was sure, the reaction pressure distribution is linear ( f (x,y) = Ax+By+C; with three unknown A, B and C).
To solve three unknowns with three equilibrium equations ( Summation Fy, Summation of Moment Mx and Summation of Moment My), I used MathCAD to solve a block, Giving the maximum pressure coefficient (k) for eb/B and eL/ L ratio, as presented in Table 1
The similarity between soil pressure and hydrostatic force on the plane surface inside the fluid, both are linear. In fluid mechanics, the centre of hydrostatic force is a point where the resultant hydrostatic force acts, it is deeper than the centre of gravity of the plane surface. Figure 3 provides the application of hydrostatic force to compute a maximum soil pressure
In Industrial plants, Octagon footing is used for the vertical column or similar heavy equipment. The maximum soil pressure is calculated for bending about a diagonal axis ( Axis B-B) ( Refer to Figure 4) and reinforced concrete design is performed for soil pressure from bending about a flat axis ( Axis A-A)
Ring foundation is used for circular shaft supported elevated reservoir or Chimney Structure. Figure 5 provides parameters ( Center line radius R and ring width b ) for the circular ring foundation used for coefficient k.
The coefficient provided in Table form for the eccentrically loaded foundation can be used in Excel or a similar calculation tool/program to interpolate results for intermediate values. The Tables and Graphs provided in this article can be used for manual design. Fluid mechanics concepts ( Hydrostatic force on a plane surface) applied for soil engineering problems.
A steel pile can be a rolled section, a fabricated shape, or a piece of sheet pile. Two or more sections of sheet piles may be connected together in a box shape and driven as one pile. The most important advantage of using a steel pile is its load-carrying capacity. A steel pile can take up to 100 tons per pile. Steel piles are most commonly used for foundations of large structures with heavy loads.
H-piles are proportioned, especially, to withstand the large impact stresses during hard driving. The flanges and the web are rolled with equal thickness in order to eliminate damage on thinner parts. The flange width is made at least 85% the depth of the pile section in order to provide rigidity in the weak axis.
Pipe piles are made of seamless or welded pipes and are frequently filled with concrete. They may be driven closed-ended or open-ended. The open-end piles may be driven to the desired depth, and the soil inside the pipe is cleaned out. The closed-end piles are formed by fixing a driving point to the tip of the pile. For major columns, the pipe piles should be at least 10 inches in diameter, and the thickness should not be less than 5/16 inches.
The choice between the open-end and the closed-end types depends upon the soil conditions at the site. In some cases, an open-end pipe can be driven to a greater depth since the soil inside the pipe can be cleaned as the driving progresses. If boulders or other obstructions are encountered before reaching the desired depth, they may be removed by means of a chopping bit or in the case of large diameter pipes, by blasting. In other cases where cleaning of soil inside the pipes is difficult, closed-end pipes should be used.
H-piles are spliced in the same manner as steel columns. Welded or bolted (high tension bolts) splice may be used depending primarily on the preference of the engineer or the available equipment. If the splice is located above the ground surface, or if a large bending moment will act upon the pile, the splice should be designed to resist such stresses. In normal cases, even when the piles are not subjected to horizontal thrust or bending moment, there is a certain amount of bending stress in a pile. A pile is never perfectly straight and may get bent due to driving. This can cause bending moments in the piles. Hence it is customary to design the splice to resist a moment equal to one-third to one-half of the moment capacity of the H-section. Some building codes require the splice to develop the full strength of the H or pipe section. The pipe piles may be spliced by butt welding or by use of a sleeve.
This method, employed by most codes, requires that the pile section contains a certain extra thickness (usually about 1/16 inches) in excess of the sectional area as required by strength. This may be accomplished by either deducting 1/16 inches from the actual metal thickness while computing the pile capacity or splicing another piece of steel to the pile length where corrosive action is anticipated.
Organic soils, cinder fill, unburned carbon, or industrial waste near the ground surface may be removed and replaced by noncorrosive soils. This method is economical only when such soils are at shallow depths.
Near the ground surface where moisture and oxygen are abundant, the piles may be protected very effectively by encasing with concrete. Concrete encasement extending to a great depth is a costly method.
Since corrosion is a continuing process of removing electrons from the piles, a method of preventing such a removal would be effective. This is done by cathodic method whereby a slow current is introduced towards the steel piles, instead of away from them.
It should be pointed out here that painting or other types of coating applied prior to driving are of doubtful value since the coating in the embedded portion is likely to be damaged from abrasion or handling. Piles projecting into the atmosphere should be painted periodically. Piles projecting in polluted water should be protected with concrete encasement or coal tar paint. In fresh water, the section near the water surface should be protected.
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