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To calculate Axial Load capacity of a single pile, we should first understand how the pile behaves and what are the resistances offered by it.
Basically we have a shaft resistance Qsu and a Toe resistance Qbu. The total pile capacity is calculated by summing up these two, i.e. Pile capacity Qu is the sum of the shaft resistance Qsu and toe resistances Qbu.
The maximum load that can be sustained by shallow foundation elements due to the bearing capacity is a function of the cohesion and friction angle of bearing soils as well as the width B and shape of the foundation. The net bearing capacity per unit area, qu, of a long footing is expressed as:
where
(alpha)f= 1.0 for strip footings and 1.3 for circular and square footings
cu= Un-drained shear strength of soil
(sigma) vo = effective vertical shear stress in soil at level of bottom of footing
(beta)f = 0.5 for strip footings, 0.4 for square footings, and 0.6 for circular footings
gamma =unit weight of soil
B=width of footing for square and rectangular footings and radius of footing for circular footings
Nc, Nq, N=bearing-capacity factors, functions of angle of internal friction (phi)
Group of piles means when we have more than 1 pile in a row. Many factors influence the pile group stability. The major factors are Geometry of the group, soil conditions and direction of loads.
The efficiency factor Eg is defined as the ratio of the ultimate group capacity to the sum of the ultimate capacity of each pile in the group. It is this factor which is mostly used to express the ultimate load considerations.
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When ever we are studying about a vertical pile, we need to understand that the flexural stiffness of the shaft and stiffness of the bearing soil in the upper 4D to 6D length of shaft are the two main factors on which the resistance to lateral loads of vertical pile depends.
Nondimensional solutions of Reese and Matlock help us plot the lateral-load vs. pile-head deflection relationship but the basic assumption with this is that the soil modulus K increases linearly with depth z
The most commonly used formula to determine the allowable static load on a pile is the Engineering News formula.
Case-1 The allowable load for piles driven by a drop hammer
Pa=(2WH)/(p+1)
Case-2 The allowable load for piles driven by a steam hammer
Pa=(2WH)/(p+0.1)
where
Pa=allowable pile load, tons (kg)
W= weight of hammer, tons (kg)
H= height of drop, ft (m)
p= penetration of pile per blow, in (mm)
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As per standards, the Roof beams should have a continuous upward slope equivalent to 1/4 in/ft ( 20.8 mm/m) between a drain and the high point of a roof, in addition to minimum recommended camber to avoid ponding.
For a constant cross sectional the radial stress induced by a bending moment in a member is calculated by using this formula
fr=3M/2Rbd
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Their is always some variation in the design values calculated in timber. Therefore we need to apply the required adjustment to them.
Case- Extreme Fiber Bending
Fb‘=FbCDCMCtCLCFCVCfuCrCcCf
The members which are under the combined effect of axial as well as bending load should satisfy the following equation
Pa/P +Ma /M < 1
