Electronic Thesis and Dissertation Repository


Doctor of Philosophy


Civil and Environmental Engineering


Dr. M. Hesham El Naggar


Despite the wide application of the connections between slender pile types, which end with a mono steel bar at the ground level (e.g. helical piles and micro piles), and new reinforced concrete foundations with limited width (e.g. RC grade beams) in the piling industry in North America, neither a clear understanding of the connections' behaviour nor a specific design criteria for their implementation is presented.

The main goal of this research was to clearly understand the behaviour of these connections and their failure mechanism under monotonic and cyclic loadings. The research methodology involved conducting experimental tests on 33 full-scale pile-foundation connections subjected to tension, compression, and shear loadings. The experimental results were used to calibrate a three-dimensional nonlinear finite element model that accurately simulated the structural behaviour and captured the possible failure modes of these connections. Based on the findings from the experimental and numerical investigations, analytical equations were developed to determine the connection capacity.

Both the experimental and the numerical investigations confirmed that it is unsafe to ignore the connection capacity in the foundation design considering only the grade beam capacity. It was shown that the connection behaviour under tension and compression loadings can be represented by the behaviour of the reinforced concrete beams subjected to indirect shear loading, while the connection behaviour under shear loading can be represented by the behaviour of cast-in-place headed anchors subjected to shear loading. The connection behaviour was mainly affected by the concrete compressive strength, the pile embedment depth, the beam's reinforcement, the pile cap configurations, and some other variables depending on the type of loading. Cyclic compression loading had a limited effect on the connection behaviour, while alternating cyclic shear loading had a major effect on the connection behaviour.

The developed connection design equations took into consideration the main factors affecting the connection behaviour under different cases of loading including cyclic loading and they were consistent with the recorded results from the experimental and numerical investigations.

Finally, the research objectives were achieved by providing a design aid and design precautions for helical pile-RC grade beam connections design.