Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities



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11.3.1 Material Properties - General
Unless otherwise noted, materials and material properties should be in accordance with the provisions of the current AASHTO LRFD Specifications (2014). Structural considerations of these material properties are discussed hereafter.
11.3.2 Concrete
Concrete foundation elements are generally designed with concrete having a specified compressive strength, f’
c
, of 3.5 ksi to 5.0 ksi. Note that AASHTO (Section 5.4.2.1) prohibits the use of concrete with a specified compressive strength less than 2.4 ksi for structural applications (including foundation elements. Concrete for foundation elements shall be normal weight. The modulus of elasticity for concrete, Ec, can be approximated by Equation 11-5:
𝐸𝐸𝑐𝑐 = Equation 11-5) Refer to AASHTO (2014) Section 5.4.2 for additional requirements for concrete foundation elements concrete.


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11.3.3 Reinforcing Steel
Reinforcing steel for concrete foundation elements will generally be AASHTO M (ASTM A) Grade
60, with a minimum yield strength of 60 ksi. The use of reinforcing steel with yield strengths less than 60 ksi is not recommended. Bars with yield strengths less than 60 ksi should be used only with the approval of the owner. The use of reinforcing steel conforming to ASTM A, Low Alloy Steel Deformed Bars for Concrete Reinforcement, should be considered where improved ductility is needed or where welding is required. The modulus of elasticity, Es, for reinforcing steel can be assumed to be 29,000 ksi. Refer to AASHTO (2014) Section 5.4.3 for additional information on concrete foundation element reinforcing steel.
11.3.4 Casings
Casings are sometimes required for foundation element constructed using drilling techniques such as drilled shafts. When required, steel for permanent casings should generally conform to the values shown in Table 11-2.

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