Chance Technical Design Manual

ect soils as either “fluid” (N 60 =0), “soft” (0

Section 7 is broken down by specific helical pile product fami lies. Each family sub-section lists the tension and compression strengths in various tables, in addition to specifications and available configurations. For example, the P2 (shaft) strength and P4 (geotechnical) tension capacity for Type SS175 helical piles are shown in Table C-4. The pre-qualified and verified torque correlation factor (K t ) is 10 for Type SS175. The torque rating for SS175 is 10,500 ft-lb. Therefore, per P4 [Method 2], the torque correlated capac ity limit for SS175 is 105 kip (see Section 6 TDM). The nominal strength of Type SS175 shaft (P2) is limited to 100 kip by the shear strength of the coupling bolt. Comparing the two, 105

HELICAL PILES & ANCHORS

TABLE C-4 - SS175 - P2 TENSION STRENGTH AND P4 TORQUE CORRELATED CAPACITY

TORQUE PROPERTIES Torque Correlation Factor

10 ft -1

33 m -1

P4

Torque Rating

10,500 ft-lb

14,240 N-m

STRUCTURAL CAPACITY

Nominal

LRFD Design

Tension Strength

100 kip 445 kN 75 kip 334 kN

P2

Allowable Tension Strength

50 kip

222 kN

TORQUE CORRELATED CAPACITY Capacity Limit Based on Torque Correlation, Tension/ Compression Ultimate

Allowable

P4

105 kip 467 kN 52.5 kip 234 kN

kip > 100 kip, therefore P2 tension strength controls at max torque. If the installation torque is less than 10,000 ft-lb, then P4 [Method 2] will control. The allowable geotechnical capac ity of 52.5 kip is based on a deterministic factor of safety of 2. It is convenient to tabulate axial compression strength in terms of either P2 (shaft) & P3 (helix), or P1 (bracket) & P2 (shaft). Table C-5, from Section 7 of this manual, lists the P2 (shaft) and P3 (helix) ASD allowable strengths for Type SS175 square shaft helical piles. It is used to easily determine P2 and P3, which can then be compared to P4 to see which will control the design. The table is broken down by soil type, end condition, and num ber/diameter of the helix plates. For example, a Type SS175 helical pile in firm soil & fixed end condition with multi-helix plates (3 or more plates) has ASD allowable compression strength of 98.3 kip. However, that ex ceeds the P4 geotechnical allowable capacity of 52.5 kip. But if the soil is soft with the same fixed end condition, the ASD allowable compression strength is 30.2 kip; which is less than the P4 geotechnical allowable capacity of 52.5 kip. The differ ence is the depth to fixity, which is 5’-0 in firm soils and 10’-0 in soft soils. Table C-6, reprinted from Section 7 of the TDM lists the P1 (new construction bracket) and P2 (shaft) ASD allowable strengths for Type SS175 helical piles. It is used to easily determine P1 and

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