Capacity and Practical Implications of Driven Bearing H-Pile Design Using ASTM A572 Grade 50 Steel

Steel H-piles (HP shapes) are most commonly available as ASTM A572 Grade 50 material, having a nominal yield strength of F_y = 50 ksi (345 MPa). However, until fairly recently, HP shapes were typically available as ASTM A36 shapes, for which F_y = 36 ksi (248 MPa). Many state DOT provisions for driven piles continue to base design structural capacity calculations on the lower yield stress. In this paper, a parametric study investigating the impact of increasing the yield capacity from F_y = 36 ksi to F_y = 50 ksi on design structural capacity and driving analysis of steel H-piles is presented. Results of the parametric study indicate that the AASHTO-permitted pile capacity of 0.5 A_gF_y is not achievable without a reduction in the required overstrength factor of 2 (based on assessing driveability by wave analysis only), and even then, this capacity may only be achievable for smaller pile sections. Driving piles to the maximum permitted driving stress of 0.90 F_y = 45 ksi (310 MPa) resulted in pile capacities at refusal ranging from 0.64 to 0.76 A_gF_y, with smaller pile sections having marginally higher achievable capacities. A representative cost analysis led to the conclusion that increasing the design capacity of a pile results in a decrease in cost per driven pile capacity, although, because of the need for larger hammers and cranes, permitting design capacities greater than 16.5 ksi (114 MPa) results in only marginal additional savings.