147 Where d
f
= Depth to fixity below the ground (ft. E = Elastic modulus of the foundation element material (ksi). Es Elastic modulus of clay soils. s
u
= Undrained shear strength of clay (ksf). l
w
= Weak axis moment of inertia of foundation element (ft. n
h
= Rate of increase of soil modulus with depth (ksi/ft).
11.3 PROCEDURES FOR REINFORCED CONCRETE SECTIONS This section provides a description of the structural design considerations for foundation elements constructed from reinforced concrete. Foundation elements covered under this manual included bored piles,
drilled shafts, concrete cylinder piles, and reinforced concrete piles (both conventionally reinforced and prestressed). Although there are cases where the reinforced-column approach is unnecessary for concrete foundation elements due to zero
or very low moment effects, concrete foundation elements must always be designed with the minimum reinforcement required for compression members as stipulated in Section 5 of
AASHTO (2014) because of the potential for unforeseen loading. Detailing of the reinforcing and prestressing steel should be in accordance with the requirements of Section 5 AASHTO (2014). Numerous commercially available computer programs are also available for the design of concrete compression members.
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