Chance Technical Design Manual

or less. The use of battered (inclined) piles can be utilized to resist lateral loads if needed and are discussed in Sec tion 5 of the TDM. 5. For tension only foundation elements, square shaft is always the logical choice. As noted above, square shaft helical anchors are more efficient in regards to load ca pacity versus installation energy (torque correlation), are better at penetrating dense soils, and have less surface area for corrosion potential. The size and strength of the square shaft section is governed by the required installa tion torque, not the tension capacity. There is more steel section available than is required to carry the rated axial tension load. The reason for this is because the steel in the shaft is subjected to more stress during installation than it will ever see while in service. Once the helical anchor is installed, the tension strength is governed by the shear strength of the coupling bolt – see Section 7 of the TDM. 6. For piles required to resist compression and tension loads, the designer must recognize that helical piles are a pre manufactured product with bolted connections. There is manufacturing tolerance in each connection. For example, most helical piles have up to 1/8” axial tolerance in each connection. The tolerance is required to ensure the con nections fit together in the field. If the load reverses, the top of the pile will displace (up or down) a distance equal ing the sum of the bolt tolerance in all of the bolted con

nections before it can resist the reversed load. This may or may not be of concern to the designer and is depen dent on the type of structure that is being supported with the piles. The grout column of Helical Pulldown Micropiles fills the connections, thereby removing the bolt tolerance as well as stiffening the axial load response. That is why grouted shafts are often utilized for piles with reversing load conditions. Grouting the ID of pipe shaft helical piles will also stiffen the coupling for reversing load conditions. Pipe shaft piles with couplings above grade should be grout filled to stiffen the connection. V. P1, P2 AND P3 – STRUCTURAL STRENGTH The axial and lateral strength of the helical pile components (shaft, helix and connection to structure) is determined per the methods detailed in AISC 360-10 Steel Construction Manual and Chapter 18 of the International Building Code (IBC). The structural strength of Chance helical piles is detailed in Section 7 of the TDM [Method 4]. The factors required for structural design are soil strength (firm, soft, fluid), the strength of the concrete, end condition (pinned, fixed, free), Application (new construction, remedial repair, tiebacks), coupling strength, and load direction (tension, compression, or both). Soil strength is an important factor because it affects buckling & bracing of helical piles. It is important to categorize the proj

HELICAL PILES & ANCHORS

TABLE C-C2.2 - APPROXIMATE VALUES OF EFFECTIVE LENGTH FACTOR K, FROM AISC 360-05

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