Civil Insight: A Technical Magazine Volume 3 | Page 58
Gautam A. et al.
Civil Insight (2019) 57-63
introduced to compute and compare the axial load distribution in piles with the values of axial loads
computed using the classical approach.
2) Methodology
Bridge pile foundation for a real pier of a bridge under construction, namely Kamala Bridge at Dhansari
Road section, was taken into consideration for comparison. Pile configuration of 4x4 and pile of diameter
1m and length 15m was taken as per the real design. Loads coming from the superstructure and substructure
were applied at the geometric centre of the pile cap. The scour level was taken as 2.5m below the base of
the pile cap from existing hydrological calculations. The load distribution in pile cap was then evaluated
using the Classical and Finite Element Methods. The numbering of the piles is given in Fig. 1.
Fig. 1. Pile Numbering
2.1) Load Distribution on piles using the Classical Method
In Classical Method, the axial load coming to the pile from superstructure, substructure and pile cap is
distributed using the formula, as expressed in Eqn (1).
ܯ ௬ ݔ ܯ ௫ ݕ
ܲ
ܨ ൌ േ
േ
ሺͳሻ
ܰ σ ݔ ଶ σ ݕ ଶ
where F is the load at a particular pile, P is the total axial load at the base of the pile cap coming from super
structure, substructure and pile cap, N is the number of piles, M y is the Transverse Moment calculated for
substructure and superstructure, M x is the Longitudinal Moment calculated for substructure and
superstructure, x i and y i are the distances of the piles from the center of the area of the pile cap in the direction
shown in Fig. 1.
2.2) Load Distribution on piles using the Finite Element Method (FEM)
3D-model of the pile group was represented in SAP2000 (SAP2000, 2015). The pile cap was modeled as a
thick shell of thickness 2m with mesh size 0.5m in all three directions, and the pile was modeled as a frame
element of linear mesh size 1m. The mesh size was chosen such that the nodes of the pile cap coincides
with the nodes of the pile. Soil-pile interaction was modeled as linear elastic spring elements with different
values of spring stiffness to model skin friction, end bearing and lateral soil resistance. Friction and lateral
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