269
5.2.3 Group Multipliers Pile
group modifiers, also referred to as P-multipliers (Pm, are commonly mentioned in the investigated documents. Due to the passive D wedge used in strain wedge model, these modifiers do not apply to the strain wedge model.
5.2.4 Head Fixity Head fixity, as related to modeling
procedure in SSI software, is not discussed inmost referenced documents. When discussed some manuals recommend Supplying both free and fixed conditions Supplying full head fixity and 50 percent head fixity Calculating cap embedment for head fixity A literature review with regard to pile embedment in the pile cap and the degree of fixity is presented in the commentary to the Iowa LRFD Bridge Design Manual. A summary of that review is presented in Table E.
Table E Summary of head fixity literature review.Reference Pile Size Results for 12 in embedment into pile cap (1.2 * Diameter) Notes Castilla (1984) HP x 61 to 83% fixity Based on computer modeling
Wasserman and Walker (1996)
HP x Strong axis, full plastic moment Hughes et al. (2007) HP x 50% fixity Rollins and
Stenlund (2008) HP x Weak axis, full
moment capacity Strong axis, not full moment capacity Based on testing Rollins and
Stenlund (2008) HP x
-
5 inches embedment, 25 to 66%
ultimate moment capacity 5.2.5 Deflection Limits Head deflection for deep foundation elements were listed by 22 DOTs ranging from 0.25 to 2 inches for the Service Limit State. A chart showing the distribution is included as Figure E. Note that if the Limit State was not specifically indicated, the Service
Limit State was assumed, consistent with LRFD requirements for assessing deflection. Ina few cases, Strength and Extreme Limit States were defined as correlating with specific maximum values of deflection rather than ultimate geotechnical capacity. Five limit values were reported among the
DOTs for use as a defining criteria for strength and extreme
limits cases as follows •
1.0 inches (Strength)
•
1.5 inches (Extreme)
•
2 inches (Strength/Extreme for assessing rotation)
•
3 inches for prestressed concrete (Strength)
•
6 inches for steel (Strength)
