Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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Soldier Rev B
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- Figure 11-1 0: Effect of axial loading on plastic moment in steel pipe piles.
- 11.5 PROCEDURES FOR STRUCTURAL COMPOSITE SECTIONS
- 11.5.1 Structural Resistance
| 11.4.8 Steel Pipe Section As for steel pipe section, the elastic bending stiffness can also be used without much error in computing the bending moment. The moment of inertia of a pipe section is computed with the following equation πΌπΌ ππ = ππ(ππ 0 4 β Equation 11-51) where d 0 and d i are the outer and inner diameters of pipe piles, respectively. Considering the distribution of stresses in the pipe section as that shown in Figure 11-8, the ultimate bending moment is computed as ππ π’π’πππ‘π‘ = Equation 11-52) Where ππ ππ = 1 6 (ππ 0 3 β ππ ππ 3 ) Equation 11-53) The influence of the axial loading on the yield moment are shown in Figure 11-10 (Horne 1971) for f y = 235 MPa (34 ksi) and ratios of diameter to wall thickness equal to 12 to 48. Note that in this figure, the diameter and wall thickness are denoted as b and t, respectively. 172 Note fy = 234 MPa equivalent to 34 ksi) Figure 11-1 0: Effect of axial loading on plastic moment in steel pipe piles. Similarly to H-sections, the relationship between the normalized load and normalized yield moment becomes nonlinear for smaller axial loads. This effect also causes a reduction in plastic moment capacity as compared to a linear relationship. 11.5 PROCEDURES FOR STRUCTURAL COMPOSITE SECTIONS Composite piles for structural applications are defined as concrete filled steel pipe piles. Guidance for other composite pile types is not provided for in AASHTO (2014) specifications, and therefore structural resistances over the length of alternative pile materials should be evaluated considering the primary section material. 11.5.1 Structural Resistance 11.5.1.1 Axial Compression The behavior of composite sections is somewhat different than non-composite members and is therefore evaluated by alternate means. AASHTO (2014) provides evaluation methods to assess the Strength Limit State of composite sections, provided the following criteria are met. 1. The cross-sectional area of steel is at least 4 percent of the total cross-sectional area. If the cross- sectional area of steel is less than this limit, the pile is considered non-composite and should be evaluated following procedures in Section 11.3 Procedures for Reinforced Concrete Sections Concrete Piles. The concrete compressive strength is between 3.0 ksi and 8.0 ksi. Commentary provided in AASHTO (2014) notes the lower limit is imposed to encourage use of good quality concrete. The yield strength of longitudinal reinforcement to determine the compressive resistance cannot exceed 60.0 ksi. 173 For axial compression loading of concrete filled steel pipes, the factored Structural Limit State is taken as ππ ππ = Equation 11-54) Where Pr = Factored compressive resistance (kips. ππ = Resistance factor. ππππ = Nominal compressive resistance (kips. Download 6.03 Mb. Share with your friends:
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