A distinction shall be made between a pier-type pile, with a long unsupported length and a wharf-landside-type pile with a short unsupported length between the deck and soil. The effective length, L, is the distance between the pinned deck/pile connection and in-ground fixity as shown in Figure 31F-7-15. For pier-type (long unsupported length) vertical piles, three simplified procedures to determine fixity or displacement capacity are described in UFC 4-151-10 [7.12], UFC 3-220-01A [7.13] and Chai [7.14].
In order to determine fixity in soft soils, another alternative is to use Table 31F-7-8.
The displacement capacity, Δ, for a pile pinned at the top, with effective length, L, (see Table 31F-7-8 and UFC 4-151-10 [7.12]), and moment, M, is:
where:
| E | = | Modulus of elasticity |
| I | = | Moment of inertia |
ASSUMED IN-GROUND FIXITY
DISTANCE BELOW GROUND TO POINT OF FIXITY
| PILE EIg | SOFT CLAYS | LOOSE GRANULAR & MEDIUM CLAYS |
| < 1010 lb in2 | 10 feet | 8 feet |
| > 1010 lb in2 | 12 feet | 10 feet |
Assuming linear curvature distribution along the pile, the allowable curvature, ϕa, can be established fromml:
where:
εa = allowable strain limit according to Section 3107F.3.3.3
c = distance to neutral axis which can be taken as Dp/2, where Dp is the diameter of the pile
The curvature is defined as:
The maximum allowable moment therefore becomes:
The displacement capacity is therefore given by:
