Closure to “Seismic Behavior of Batter Piles: Elastic Response” by A. Giannakou, N. Gerolymos, G. Gazetas, T. Tazoh, and I. Anastasopoulos

Abstract

Significant advances have been made on this important research topic in the last few years because of Giannakou et al., who have faced, in urgent terms, the matter of whether inclined piles have a beneficial or detrimental role. The discusser agreeswith the authors on the fact that the horizontal drift of a superstructure supported on a group of batter piles is generally smaller than with the exclusively vertical pile group; however, it could not really be generalized that this reduction is appreciable only with tall structures. The discusser has carried out work in his Ph.D. thesis about the inclined piles, studying the behavior of a couple of piles supporting a tall superstructure (hstr 5 10m) and a short superstructure (hstr 5 2m), in different geometrical conditions and seismic excitations than those of the authors, reaching quite different results. Specifically, from results obtained performing FEM three-dimensional analysis with the computer program ADINA (ADINA 2010), and using the base of the model with two real acceleration time histories (El Centro component NS 1940 [amax 5 0:318g]; Bagnoli Irpino Earthquake 1980 [amax 5 0:358g]), the following can be concluded. The reduction of horizontal drift because of inclined piles with regard to vertical piles was more important in short superstructures than tall ones (Figs. 1 and 2). To explain these results, it is useful to keep in mind that under seismic excitation, the horizontal drift of the superstructure mass, um, is made of three parts: horizontal translation of the cap, horizontal translation because of rotation cap, and horizontal deflection of the column. The discusser has found out that the cap's horizontal translation founded on vertical piles tends to be higher than the one with the inclined piles. Instead, the contribution because of the cap rotation can increase or reduce the horizontal drift depending on the sign of the rotation. In the case of the short superstructure, Fig. 3 shows the horizontal displacement of the cap on the inclined piles, uc, the vertical displacement of the pile on the left, vcl, and the vertical displacement of the pile on the right, vcr . For better understanding of the figures, the time considered was limited to the first 3 s. Once the vertical displacements are confirmed, the rotation is obtained by dividing the difference in the vertical displacement at the head of the piles by the distance between the two piles. In Fig. 3, the horizontal oscillation frequency of the cap is quite lower than the one in the vertical direction; the vertical displacement, vcl, also has the opposite sign and basically the same amplitude of vcr. The difference in frequency