Rabie Farrag, winner of the DFI 2020 Paper Competition. We are so excited that the paper co-authored by Rabie and our Research Team was selected as the paper winner for 2020. Rabie will be giving a short presentation at DFI’s annual meeting, October 27-30th, 2020.
Abstract of the paper:
The determination of internal pile reactions is critical to designing and assessing the structural performance of deep foundations. Internal shear and moment profiles strongly depend on lateral pile-soil interaction, which in turn depends on pile and soil stiffnesses as well as the stiffness contrast between soft and stiff strata, such as occurs at a soil/rock interface. At zones of strong geomaterial stiffness contrast, Winkler-spring-type analyses predict abrupt changes in the internal pile reactions for laterally-loaded foundation elements. In particular, the sudden deamplification of internal moments when transitioning from a soft to stiff layer is accompanied by amplification of pile shear. This “shear spike” can result in bulky transverse reinforcement designs for drilled shaft rock sockets that pose constructability challenges due to reinforcement congestion, increasing the risk of defective concrete on the outside of the cage. This paper presents an experimental research program of three large-scale, instrumented drilled shafts with simulated rock sockets constructed from concrete. Each shaft had a different transverse reinforcement design intended to bound the amplitude of the predicted amplified shear demand, with a particular empaphasis on performance of shafts with shear resistance less than predicted demand and below code minimums. Test results suggested that the shafts experienced a flexure-dominated failure irrespective of the transverse reinforcement detailing.