Structural Design of Driven Piles.

Allowable stresses in piles should be limited to values described below for steel, concrete, and timber piles and will not exceed the factored structural capacity given by equation 2-1. Allowable stresses rnay be increased by 33 percent for unusual loads such as from maintenance and construction. Allowable stresses may be increased up to 75 percent for extreme loads such as accidental or natural disasters that have a vezy remote probability of occurrence and that require emergency maintenance following such disasters. Special provisions (such as field instrumentation, frequent or continuous field monitonng of peifomiance, engineering studies and analyses, constraints on operational or rehabilitation activities) are required to ensure that the structure vill not catastrophically fail during or after extreme loads. Figure 2-2 provides limiting axial driving stresses.

a. Steel piles.  Pile shoes should be used when driving in dense sand, gravel, cobble-boulder zones and when driving piles to refusal on a hard layer such as bedrock....
b. Concrete piles.  (1) Prestressed concrete piles. Allowable concrete stresses should follow the basic criteria of ACI 318-89, except the strength performance....
c. Timber piles.  Representative allowable stresses for pressure-treated round timber piles for normal load duration in hydraulie structures are given in....
d. Design example.  A 30-foot length L of A-36 unbraced H-pile, HP14 x 73, has a cross section area Ay = 21.4 in.^2, Table 1-3. This pile is made of A36 steel....

Figure 2-2.  Limits to pile driving stresses