Cyclic load behavior of helical pile-to-pile cap connections subjected to uplift loads

Abstract

Although significant research has been conducted on helical piles, there is a lack of research and official design guidelines on how to create resilient helical pile-to-pile cap connections, especially in tall and light structures where tensile uplift loads may govern the foundation design. The objective of this study is to advance the current understanding, quantify the influence of helical pile-to-pile cap connection detailing on the global system behavior, and propose recommendations for their resilient design. For this purpose, high-fidelity nonlinear finite element models are developed, experimentally verified, and 162 response simulations of helical pile cap systems are conducted to quantify the influences of: termination bracket types, bracket embedment depths, reinforcement ratios, shear span-to-depth ratios, and loading types. The results are analyzed in terms of the load, deformation, cracking, and failure behaviors. The analysis of variance and the factorial design methods are employed to quantify the percentage contribution of each parameter, as well as multi-parameter interactions, on the system capacity. The results, which are also applicable to micropile connections, demonstrate that the helical pile-to-pile cap connection capacity may govern the system capacity for the load conditions involving tension components. The tension load capacities of the pile cap systems (all of which are doubly and symmetrically reinforced) are found to be only 54% of their compression load capacities due to connection zone failures. This result is in contrast with the results from the traditional sectional analysis methods, which are not intended for the analysis of the connection zones and thus calculate the tension and compression capacities as equal. This paper presents the studies undertaken, conclusions reached, and recommendations made to create resilient helical pile-to-pile cap connections.