244 Step 2: Obtain Preliminary Structural Design A preliminary structural design needs to be established
before calculating deflections, bending moment and shear. For this example, the following preliminary structural design is selected Close Ended Pipe Pile Diameter = 24 inches Concrete Compressive Strength = 4,000 psi No steel rebars Pile Wall Thickness = 1 inch Pile Length = 120 feet (5 feet embedment into Layer No. 6) Pile head is assumed to be fixed Steel grade = 36 ksi (A) Piles Center to Center Spacing = 6 feet Step 3: Determine p-multipliers The group effect due to closely spaced piles is typically accounted by utilizing a p-multiplier value which reduces the soil resistance pin the p-y curves by a factor equal to the p-multiplier. The selection of p- multipliers is discussed in more detail in Chapter 7. For this example, the procedure highlighted in AASHTO LRFD Paragraph 10.7.2.4 is used.
For each pile, a p-multiplier in the longitudinal and transverse direction must be calculated. Referring to Figure
B with the piles ID shown, the p-multipliers shown in Table Bare calculated.
Figure B Piles arrangement and ID. LONGITUDINAL
TRA
NS
VER
SE
